Past studies have been conducted on competitiveness and achievement orientation as two noncooperative explanations for achievement motivation and achievement behavior. But a complimentary representation of a competitive-achievement orientation has yet to be explored. This paper developed and validated the need for competing inventory (NCI), and further investigated its relations with achievement orientation, emotional assessment, self-efficacy, grit, anxiety, and flow. The results from the present study support the theoretical construct of the need for competing, in the hope that it will provide a solid foundation for a competitive-achievement orientation, which is suggested to play a significant role in competitive achievement behavior. It is anticipated that the results from the present study will open a debate for including a competitive-achievement orientation in future research with the aim for a stronger predictor for achievement behavior. Competition is a comprehensive and complex term with several definitions. Competition can be defined as a negative social interdependence, meaning that the situation is competitive if the progress or success of one party interferes with the progress or likelihood of success of other parties . Within Achievement goals are rooted in the need to experience competence, but there might also be another factor explaining achievement behavior, namely competitiveness. Previous research has faced challenges in determining the conceptualization and operationalization of competitiveness, and achievement motivation may have supplemented the focus for a discussion on the definition of competition. In previous research, The Achievement Goal Questionnaire (AGQ) and SOQ offer two different explanations for achievement motivation. This paper attempts to provide a clearer distinction and relation between the competitive factor and achievement factor and their contribution to achievement motivation, orientation and behavior. By conceptualizing and validating a need for competing measurement tool, and redefining the concept of competitiveness, it might offer a more suitable model for the motivation/orientation for achievement behavior, namely competitive-achievement orientation.A competitive-achievement orientation is posited to offer a clearer distinction between the need/desire to compete (competitive) and the need/desire for competence (achievement). This is believed to be important because of the proposed differences between the satisfaction of competing and the satisfaction of achieving; wanting to succeed, for example, is qualitatively different from wanting to work to succeed. Establishing a competitive-achievement orientation might help understand these differences as well as the relationship between the competitive-achievement orientations, how these orientations complement each other, and the distinction between individuals with high ambitions for succeeding in competition, and those competitors who are willing to make sacrifices and work to realize their aspirations. Being willing to compete for success, means wanting to compete despite the costs of effort, risk of losing and potential experience of failure. This balance between the competitive orientation (enjoyment of the competition) and achievement orientation (the importance of achieving), might be two closely related interactive dimensions of competitiveness. Thus, being able to generate competitive-achievement motivation and utilizing it for competition could lead to a redefinition of competitiveness.The purpose for challenging and reconceptualizing a more appropriate and relevant model for explaining achievement orientation and behavior is to improve the measurement and predictability for achievement behavior.The need for competing is the competitive spirit or strive in the engagement of competition, and can be defined as the desire to enter, participate and enjoy the competition itself. Evidence suggests, however, that the competitive need has a comprehensive relationship with engagement and aggression, motivation, competitive flow and performance levels. Being competitive means getting more activated/aroused  when faced with a competitive task , which cResearch to date has predominantly focused on the association between achievement behavior and grit . As demonstrated in MD = 3.06, p < 0.001), as well as a significantly higher score difference than the high school students specializing in sports . The students specializing in sports scored higher on need for competing than the general education students, although not significantly . These results seem to support previous assumptions that highly competitive individuals seek highly competitive environments.A one-way ANOVA revealed there was a significant difference in the amount of the need for competing score at the ze [F2, 32 = 15.42The purpose of this study was to further explore the need for competing and propose a more accurate representation of the competitive-achievement orientation to give a more distinct and clearer explanation for motivation and orientation for achievement behavior in the future.The first prediction, in study 1, was that the items in the NCI would all measure the same factor, named the need for competing. An exploratory factor analysis revealed that two of the items seemed to be measuring another factor and was later removed, leaving 5 remaining items as valid measures of the need for competing factor.An acceptable factorial validity and reliability do not ensure that the scale is measuring the construct it is designed to measure . It is vThe NCI and AGQ total score were positively correlated , howeverThe relation between NCI and emotional assessment (SAM) had also a positive relation, confirming the suspicion that being competitive are closely related to his/her perceived emotions and emotional response . This stFlow had the strongest positive relation with the need for competing, even stronger than achievement orientation , confirmAs expected, the prediction of a negative relation between anxiety and the NCI was confirmed. This further strengthens the theoretical and empirical explanations that a highly competitive individual will more frequently respond in an aggressive fight response, rather than in an anxious flight response . Grit waIn the final prediction, the elite prospect students were expected to score higher on the NCI than the students specializing in sports and the general high school education students. Study 2 confirmed the prediction, which further supports the assumption that highly competitive individuals are more likely to seek and participate in competitive environments. It also raises the question of the importance of the need for competing for successful achievement behavior.Although some minor weaknesses have been mentioned in this paper, four major limitations are acknowledged in the current research. First, relying exclusively on a self-report questionnaire to measure the need for competing, which is an instrument with several limitations . AlthougBased on the current study, some future directions need to be highlighted. The vast majority of the studies are basing achievement orientation as a main predictor for achievement behavior . The eviFor future studies it is also suggested a bigger set of items in the NCI for increasing its validation, as well as a further exploration of more converging and diverging relational factors. For further investigation and validation of the need for competing construct it is also suggested that the NCI should be further analyzed with both the exploratory factor analysis and confirmatory factor analysis. Including the confirmatory factor analysis for future research might help finding the factor structure of the need for competing. Finally, future research should involve larger and more varied samples to improve representativeness, generalizability, and comparability.Studies have been conducted on competitiveness and the achievement orientation as two noncooperative explanations for achievement motivation and achievement behavior. But a complimentary representation of a competitive-achievement orientation was yet to be explored, and also the objective of the current study. By developing and validating the NCI, and additionally investigate its relations with achievement orientation, emotional assessment, self-efficacy, grit, anxiety, and flow, for further validation, gave a solid foundation for a competitive orientation and its relation to the achievement orientation. This opened a possibility to include the competitive orientation with the achievement orientation. Although, the findings should be carefully interpreted due to limitations in the present data. These results encourage debate for including a competitive-achievement orientation in future research with the aim for a stronger predictor for achievement behavior.The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.The studies involving human participants were reviewed and approved by The Norwegian Centre for Research Data (NSD). The patients/participants provided their written informed consent to participate in this study.RL and KS contributed with guidance surrounding method design, data analysis, and proofreading. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Biologicals are widely used therapeutic agents for rheumatologic diseases, cancers, and other chronic inflammatory diseases. They are characterized by complex structures and content of variable amounts of foreign regions, which may lead to anti-drug antibodies (ADA) development. ADA onset may limit the clinical usage of biologicals because they may decrease their safety. In fact they are mainly associated with immediate hypersensitivity reactions (HSRs). Development of ADAs is reduced by concomitant immunosuppressive treatment, while it is increased by longer intervals between drug administrations; thus, regular infusion regimens should be preferred to reduce HSRs. Once ADAs have formed, some procedures can be implemented to reduce the risk of HSRs. ADAs may belong to different isotype; the detection of IgE ADA is advisable to be assessed when high and early ADAs are detected, in order to reduce the risk of severe HRs. In patients who need to reintroduce the biological culprit, as alternative therapies are not available, drug desensitization (DD) may be applied. Desensitization should be conceptually dedicated to patients with an IgE-mediated HSR; however, it can be performed also in patients who had developed non-IgE-mediated HSRs. Although the underlying mechanisms behind successful DD has not been fully clarified, the DD procedure is associated with the inhibition of mast cell degranulation and cytokine production. Additionally, some data are emerging about the inhibition of drug-specific immune responses during DD. Biologicals are indispensable therapeutic agents in immunological, oncological, and inflammatory diseases, and their application in clinical practice is increasing. However, despite the therapeutic benefits, biologicals may cause hypersensitivity reactions (HSRs) that represent a major safety concern and a significant challenge for clinicians. Hypersensitivity reactions may occur during the first lifetime exposure or after repeated administrations and different pathogenic mechanisms are involved. In addition, immediate and delayed HSRs have been conveniently described; immediate reactions occur during the drug administration or within 1 h after the end of infusion, whereas delayed reactions appear from 1 h to several days after .The potential risk of biologicals’ immunogenicity is an important issue in clinical practice, leading to the development of anti-drug antibodies (ADA). Immunogenicity is expected following treatment with non-human sequence proteins, but it is now well established that the immune response may be elicited also by fully human sequences. The unexpected and unpredictable unwanted immunogenicity may impact both the efficacy and the safety of the drug. The induced ADA may compromise the clinical efficacy by altering the circulating drug levels and/or neutralizing its biological functions; furthermore, ADA development has been associated with the onset of HSR, ranging from mild to severe grade. Patients with ADA, as IgG or IgE developed during treatment with biologicals or preexisting, are more likely to have increased risk of immediate HSRs .In patients with HSR toward a biological, approaches for avoiding future adverse events differ depending on the mechanism of reactions. These strategies are very important when no alternative therapies are available. Similarly, it was shown that in some cases, reactions against the biological could be predicted by the presence of ADA.In this review we discuss the clinical and diagnostic strategies to prevent and mitigate HSR toward biologicals, especially when related to the development of immunogenicity.Taking into account the structural characteristics of biologicals, which differ from traditional drugs, and their ability to elicit ADA, the mechanisms underlying HSR to biologicals can be divided into ADA and non-ADA mediated. Additionally, ADA may belong to different isotypes, so ADA-mediated HSR may be classified as IgE- and non-IgE-mediated reactions. According to clinical manifestations, immediate HSRs are classified as mild, moderate, or severe, and in some cases even life-threatening reactions have been described . HyperseThe development of IgE ADA has been described in patients treated with different types of biologicals –9. IgE bThe IgE antibody pathway had been universally accepted as the only pathogenic explanation of anaphylaxis until more recent observations obtained in mouse models suggest the existence of a non-classical (non-IgE-mediated) pathway for anaphylaxis . Taking The identification of those patients with higher risk for ADA development and HSR onset represents an important clinical issue. Risk assessment for biologicals-related HSR requires accurate evaluation of risk factors associated with immunogenicity.Female patients seem to show a higher rate of biological-induced HSR, although this point remains a matter of debate . Atopic Finally, taking a thorough history, including the course of treatment, represents the most useful risk-assessment tools in HSR to biologicals related to immunogenicity. In fact, intermittent therapy or re-exposure after a long treatment-free interval may be associated with an enhanced immune response (or loss of tolerance) to the biological agent, and thus, re-treated patients must be considered at risk of reactions –30.Using current technology and reagents, it is possible to develop highly sensitive ADA screening assays capable of detecting the most prevalent classes of ADA ; however, a separate IgE ADA assay may be required for IgE detection, due to the low circulating levels of specific IgE. It has been shown that ADA may be present in serum before therapy as in the case of cetuximab (pre-existing ADA), or developed during the course of treatment (induced ADA). Anyway, also in the case of induced antibodies, the development of ADA precedes the onset of reactions. In a longitudinal study performed in 91 infliximab-treated patients, assayed for ADA and drug levels by enzyme-linked immunosorbent assay and for IgE by ImmunoCAP system, it has been shown that the HSR tends to be preceded by ADA development, which in turn is associated with the reduction in drug serum levels . SpecifiData from literature clearly show that the detection of pre-existing ADA IgE, in the serum of patients at baseline, is helpful to identify patients at risk of (severe) cetuximab-induced HSR . FinallyCompared to biologic monotherapy, concomitant use of immunomodulators often increases the systemic exposure of the biologicals and decreases the formation of anti-drug antibodies, consequently enhancing clinical efficacy .The use of methotrexate (MTX) may attenuate the frequency of ADA in patients suffering from rheumatoid arthritis, spondiloarthritis, and inflammatory bowel diseases. Azathioprine, also an immunosuppressive drug with a similar effect to MTX, has been observed with azathioprine usage in the management of Crohn’s disease, where it can be given in combination with infliximab or adalimumab to improve treatment and reduce immunogenicity and ADA formation. Some studies looked at concomitant therapy with leflunomide and mycophenolate that have also been shown to be associated with lower ADA prevalence, suggesting that all DMARDs may be associated with benefits against drug-induced immunogenicity . HoweverAntihistamines, corticosteroids, and acetaminophen are commonly used in premedication protocols to prevent HSR towards biologicals, with a high variability of protocols among centers . Among aHypersensitivity reactions to biologicals may be characterized by severe anaphylaxis that can be rapidly progressing and fatal, and therefore establishing its cause is pivotal to long-term risk management, but more importantly, the optimal management of reactive patients must ensure the patient the most effective therapy for the treatment of the underlying disease in a safe manner.Both skin testing and detection of serum ADA may be useful to define the pathogenic mechanisms in HSR patients. Skin testing represents the gold standard for the identification of true allergy (IgE-mediated) towards biologicals and are safe procedures also in patients who had experienced severe reactions . HoweverAlthough they are not widely used, several commercial tests are available for the assay of ADA (CE marked), able to detect non-isotype-specific ADA. On the other hand, commercially available tests for IgE ADA detection are lacking, thus representing a crucial unmet need in the diagnostic workup of immediate HSR to biologicals . Other cRe-treatment with the same biological represents an option following an HSR, and drug desensitization (DD) is a therapeutic approach to safely administer biologicals causing an HSR. It is able to provide a temporary immune tolerance to drugs, and it is highly recommended when switching to alternate products with equal efficacy is not possible. Drug desensitization is a method largely applied for chemotherapy  and moreAlthough DD is conceptually dedicated to patients in which an IgE-mediated mechanism is demonstrated by positive skin testing or serum IgE for culprit drug, patients with immediate HSR to chemotherapy (taxanes and platins) in which the IgE mechanism cannot be demonstrated have also been successfully desensitized .There is as yet no consensus in literature about the underlying mechanisms operating in DD; the majority of data focused on the role of mast cells showing that desensitization procedure is associated with the inhibition of mast cell degranulation and cytokine production . PatientBiologicals are structurally immunogenic and are able to elicit a complete adaptive immune response, which negatively impacts their safety and may limit their clinical use. Specific diagnostic workup and a modified method of drug delivery (drug desensitization) are available in the clinical setting to manage patients with HSR. The knowledge of the mechanisms underlying HSR and biologicals’ immunogenicity is useful to increase the safety profile of current and novel biologicals.AV and AM wrote the manuscript. EM, MP, FN, and EV revised the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


No statistically significant differences after intragroup analysis were found. A statistically significant difference within the Gr.1 between the screws in positions 33 and 36, equal to 15.2% , was found. The OT Bridge seems a useful system to maintain the retention of a prosthesis during mechanical stress conditions even in the absence of one screw in an “all-on-four” rehabilitation. This could represent a good solution to solve the esthetic problem of the screw buccal access hole for fixed solutions.The aim of this study was to evaluate the stability of prosthetic screws after applying cyclic loadings in an “all-on-four” rehabilitation model with the OT Bridge system. The model was tested both with and without anterior screws. Four implant analogues following the “all-on-four” concept were inserted in an edentulous mandibular resin model. An OT Bridge system with a Cr–Co prosthetic framework was fabricated. Depending on the presence or absence of one or two anterior screws on the implant analogues, three groups were created, i.e., Gr.1: three tightening screws, Gr.2: two tightening screws, Control Group: four tightening screws. Each single group underwent subsequent 400,000 cyclic loads, simulating approximately a year of chewing by using a dynamometer machine. This cycle was repeated five times for each group, and preload loss values were evaluated on each prosthetic screw after each cycle. All the data obtained were analyzed by one-way ANOVA and Student’s  One of the fixed solutions that has been commonly used for several years in implant prosthodontics for the complete-arch rehabilitation of the upper and lower jaws is the “all-on-four” protocol ,2,3. ThiIn order to connect implants with prosthetic frameworks, the most used solution is today represented by the Multi Unit Abutment (M.U.A) which has the function to change the implant connection from an internal hexagon to an external one. When titled implants are inserted to correct the implant axis and to solidarize distal implants with the anterior ones, angulated M.U.A components are necessary. In this system, the prosthetic screw is the only component that allows the binding between the prosthetic framework and the implants ,13,14,15® , has been introduced on the dental market as an alternative to M.U.A. [Recently, another screw-retained system, called OT Bridgeo M.U.A. . The OT An important clinical issue, arising with “screw-retained” rehabilitations, especially in the case of severely resorbed jaws, is the presence of a buccal screw access channel that constitutes an anesthetic problem independently of the prosthetic material use ,19,20,21A possible solution, retaining the benefits of a screw-in prosthesis, may be provided by the OT-Bridge system  in the aTherefore, the aim of this study was to evaluate, in an “all-on-four” model with an OT Bridge prosthetic system, the stability of its connecting screws after cyclic loadings, both in the presence and in the absence of the anterior screws. The null hypotheses (H0) considered for this study were the absence of removal torque difference between the model without one or two screws and the model with all four screws  and the absence of removal torque difference between the values of the screws within each aforesaid solution .A resin model, already described in a previous article , was fabA milled cobalt–chrome framework for hybrid prosthesis connecting the four implant analogues was fabricated from a digital STL file. Extragrade-titanium angulated and straight abutments  were used for the model.According to the most predicted protocols described in the literature, two monolithic zirconia crowns, whose central fossa was 7 mm distal to the last implant analogue emergences (36 and 46), were distally positioned and cemented on the cobalt–chrome framework using the dual resinous cement OT Cem  ,26. The According to the indications proposed by the manufacturer , the connection screws were tightened at 25 Ncm by means of the torque-controlled dynamometric micromotor Implant-Med-Plus ; for this study, the white acetalic Seeger  was used. After 10 min, a second screwing was performed at 25 Ncm, according to the screwing protocol proposed by Winkler et al. .Group 1 (Gr.1): Group with 3 tightening screws  inserted on 4 implant analogs without the screw in position 43.Group 2 (Gr.2): Group with 2 tightening screws  inserted on 4 implant analogs without the anterior screws 33 and 43.Control Group (Gr.CTR): Group with 4 tightening screws  on 4 implant analogs. This group was the same as that a previous study by Catapano et al. .Depending on the presence or absence of one or two anterior screws on the implant analogues, three groups of five screws for removal torque evaluation after cyclic loadings were created and compared to each other :Group 1 The MTS Acumen, which is a dynamometer machine, was used to approximately simulate the developed effort of a year of chewing loads ,30. Each® on each tightening screw. After each single unscrewing session, the implant–prosthetic connection screws and the acetalic Seegers inserted in the cobalt–chrome framework were changed.To simulate the oral cavity environment during cyclic load, the model was placed in a thermostatic water bath at a constant temperature of 37 °C. . To eval® 9.2.0 and through statistical tests for variance, i.e., one-way ANOVA and Student’s t-test.All the data obtained in this in vitro study were analyzed by statistical evaluations, which were carried out through the GraphPad Prism data analysis programp-value < 0.05).For both tests, the statistical significance was set at 0.05 ;absence of removal torque difference between the values of the screws within each group .The null hypotheses considered were:The raw data of unscrewing for each connecting screw after cyclic loading were used to extrapolate the individual percentage values of preload loss used for statistical analysis. The results are shown in p-value = 0.2670).There were no significant statistical differences in torque mean values between Gr.1, Gr.2, and Gr.CTR .There were no significant statistical differences between the percentages of preload loss for the screw in position 36 between the three different groups .There were no significant statistical differences between the percentages in preload loss for the screw in position 46 between the three different groups   .p-value = 0.4184) and between screws in positions 36 and 46  in Gr.1.There was no statistical significant difference between the percentages of torque loss between screws in positions 33 and 46 .There were no statistically significant differences between Gr.1 and Gr.CTR for the screw in position 33  was accepted. On the other hand, the null hypothesis for the intra-groups evaluation (H0 nr.2) was not accepted because of the statistically significant difference within Gr.1 between the prosthetic screws in positions 33 and 36.The absence of statistically significant differences between Gr.1, Gr.2, and Gr.CTR seems to indicate that the OT bridge system could passivate the cyclic loading forces without compromising the entire implant–prosthetic connection even in case of higher mechanical stress than in the normal configuration, such as that occurring in the absence of one tightening screw. Similar results were obtained by Cervino et al.  who confFrom the comparison of the values of Gr.1 (three screws inserted), a statistically significant difference could be noted between the screws in positions 33 and 36 but not between the screws in positions 33 and 46 and 36 and 46 .For the distal 36 and 46 screws, where the loading cycle forces were vertically dissipated (in compression), the OT Bridge system appeared to guarantee stability, because a significant preload loss was not observed even when one or two anterior prosthetic screws were removed. There were also no differences between the two distal screws in the same model with or without the mesial homolateral screw.In the model with three screws (Gr.1), the screw in position 33 was more stressed by the loading cycles. Probably, the tensile force, exerted by the lever arm of the distal cantilever in positions 36 and 46, acting in the opposite direction to that of the preloading force of the screw, induced more stress on screw 33. This fact could not be appreciated in the Control Group because of the presence of the second anterior screw (43) that divided the lever arm into additional parts compared to Gr.1. Considering these values, the OT Bridge system seems to be able to dissipate the force even in situations where the mechanical stress should result in a greater overload (model with three screws instead of four).In this way, it seemed that the Seeger maintained the prosthesis stable and fixed through its retentive action even in the absence of its anterior connection screws , as observed for a system with all four screws in place (Gr.CTR).Theoretically, the removal of one or two connecting screws should lead to an overload on the remaining screws and therefore a loss of preload which, from the analysis conducted, did not occur. This could probably depend on the “Seeger action” which was kept in place, thus being able to carry out its retentive action on the abutment even in the absence of the connection screw.In support of this thesis, the system was forced beyond the recommended limits by removing the two front screws  in Gr.2. This is not a recommended clinical condition, but through the tests we performed, no statistically significant differences for the preload loss between Gr.2 and Gr.CTR were found. In this way, by keeping in place the acetalic Seeger also in the absence of one or two screws, the OT Bridge retentive capacity seems to hinder the loss of preload forces.The limits of this study are principally related to its in vitro nature because the resin model tested did not allow us to understand and determine the effect on soft and hard peri-implant tissues and the number of five unscrewing sessions per group resulted in a limited amount of data. The model used for this study was based on an edentulous lower arch, but for the upper jaws the results could be different because of the different circle arch described and the different implant angulations ,31. On tIn conclusion, from the results of this in vitro study, the OT Bridge seems to be a stable system when using three screws in the “all-on-four” technique applied to a mandibular model. This in vitro finding could suggest a good way to solve the esthetic problem of the screw buccal access hole for “screw-retained” fixed solutions, maintaining the advantages of these types of rehabilitations. The mean torque loss values were not statistically different for the groups tested.The retentive function mediated by the Seeger is useful to maintain the retention of a prosthesis even in mechanical stress conditions. However, different loading conditions, number of cyclic loads, frequency and positions of the applied loads have to be evaluated in the future in order to better understand the OT Bridge system stability.


Signaling cascades provide integrative and interactive frameworks that allow the cell to respond to signals from its environment and/or from within the cell itself. The dynamic regulation of mammalian cell signaling pathways is often modulated by cascades of protein post-translational modifications (PTMs). ADP-ribosylation is a PTM that is catalyzed by ADP-ribosyltransferases and manifests as mono- (MARylation) or poly- (PARylation) ADP-ribosylation depending on the addition of one or multiple ADP-ribose units to protein substrates. ADP-ribosylation has recently emerged as an important cell regulator that impacts a plethora of cellular processes, including many intracellular signaling events. Here, we provide an overview of the interplay between the intracellular diphtheria toxin-like ADP-ribosyltransferase (ARTD) family members and five selected signaling pathways , which are frequently described to control or to be controlled by ADP-ribosyltransferases and how these interactions impact the cellular responses. In multicellular organisms, communication between cells is mainly mediated by extracellular signaling molecules. Binding of the signal molecule, or ligand, to the corresponding receptor activates one or more intracellular signaling pathways2. These pathways often comprise a cascade of specific proteins that transduce or amplify the incoming signal, ultimately regulating the activity of effector proteins which modulate various cellular functions and behaviors3. Enzymes play a critical role in this process since they can transmit the upstream signal by generating second messengers or modifying and activating a downstream protein component of the pathway. Many of these enzymes behave like molecular switches whose activation state is regulated by post-translational modifications (PTMs)4.Communication via signals is a dynamic ability innate to every living organism. It enables cells to receive and process signals, not only from the external environment but also from discrete regions  within the cell7. ADP-ribosyltransferases (ARTs) catalyze the transfer of ADP-ribose moieties from nicotinamide adenine dinucleotide (NAD+) to a diverse range of target molecules including proteins, nucleic acids and small molecules11. While the transfer of only one ADP-ribose unit is called mono-ADP-ribosylation , the already bound unit can be elongated by the incorporation of additional ADP-ribose units, called poly-ADP-ribosylation 14. Mammalian ARTs have classically been divided into three families: (i) clostridium toxin-like ARTs (ARTCs) are mainly described to catalyze extracellular ADP-ribosylation, while (ii) diphtheria toxin-like ARTs (ARTDs) and (iii) selected members of the Sirtuins family  catalyze ADP-ribosylation in different intracellular compartments16. Here, we will focus on intracellular ARTD family members, that comprises 17 enzymes in humans17. According to a recently agreed consensus, we use “PARP” as a name on its own to describe the different ARTD family members.In recent years, ADP-ribosylation has emerged as a complex, dynamic, and reversible PTM that impacts the regulation and maintenance of many cellular processes, including intracellular signaling events+, the only known co-substrate for ADP-ribosylation, as well as its reduced form NADH, are essential molecules involved in regulating a plethora of cellular processes including cellular energy metabolism, gene expression, inflammation, aging, carcinogenesis, and cell death, thus linking ADP-ribosylation to these processes18. Moreover, NAD+ availability is tightly linked to the subcellular distribution of NAD+ pools. Due to the fact that NAD+ is cell membrane impermeable, NAD+ is compartmentalized in separate pools/organelles that differ in their NAD+ concentration and it is regulated by NAD+ transporters22. The concentration of free NAD+ in different subcellular compartments ranges from 87 to 136 μM for the nucleus and cytoplasm to 191–300 μM in the mitochondria25. While the majority of intracellular NAD+/NADH is protein bound, the unbound proportion of NAD+ exceeds free NADH by ~600–1000 times in the cytosol and 7–8 times in the mitochondria19. The concentration of cellular NAD+ not only depends on the consuming enzymes, but also on the rate of its synthesis. NAD+ can be synthesized de novo from tryptophan, from nicotinic acid (NA) in the Preiss-Handler pathway or from nicotinamide (NAM) in the salvage pathway25. Since the ARTD family members belong to the major consumers of free NAD+ in the cell this, ultimately, implies that the localization of ARTD family members, their Km NAD+ and expression levels as well as potential activators  influence the ADP-ribosylation levels17. Most ARTD family members localize either to the nucleus or the cytoplasm, except for PARP12 (ARTD12) and PARP16 (ARTD15), which localize to the endomembrane system  signaling pathway is a central element of multiple physiological and pathological processesone Fig. 30.Fig. 130. In the inactive state, IκBα sequesters and retains NF-κB in the cytoplasm. NF-κB is composed of five structurally related members, including NF-κB1 (p50), NF-κB2 (p52), RelA (p65), RelB, and c-Rel29. These subunits form diverse homo- and heterodimers which convey different transcriptional outputs upon activation. Signaling through the canonical pathway, initiated by ligand binding, results in the site-specific phosphorylation and proteasomal degradation of IκBα induced by the multi-subunit IκB-kinase (IKK) complex, resulting in the release of NF-κB32. The IKK complex is composed of two kinase subunits, IKK1 (IKKα) and IKK2 (IKKβ), and a structural subunit NEMO (IKKγ)31. The release of NF-κB is followed by nuclear translocation of NF-κB dimers. Resulting in a rapid and transient transcriptional activation of target genes32.The canonical NF-κB pathway is activated in response to diverse stimuli, including ligands of various cytokine receptors, pathogen recognition receptor (PRRs), TNF receptor (TNFR) superfamily members, as well as T-cell receptor (TCR) and B-cell receptor33. NIK activates IKK1, which induces processing of p100, a RelB-specific inhibitor and the precursor of NF-κB2 (p52). Ultimately, this results in the nuclear translocation of NF-κB2-RelB dimers and induces a slow but persistent transcriptional re-programming33.In contrast, the non-canonical pathway integrates signals from a subset of TNF receptor family members and results in the activation of NF-κB-inducing kinase (NIK)PARP10 (ARTD10) promoter leading to its transcriptional repression in hepatocellular carcinoma34. In accordance with these results, inhibition of the IKK complex, which inactivates NF-κB signaling, strongly increased PARP10 mRNA and protein levels. The p65-dependent repression of the PARP10 promoter was confirmed by the overexpression of p65, which resulted in reduced PARP10 expression34.NF-κB was described to bind to and inhibit the 35. Downregulation of PARP14 by siRNA decreases NF-κB activation in gemcitabine-resistant prostate carcinoma cells and consequently promotes apoptosis, suggesting that PARP14 is important for cell viability and required for constitutive NF-κB signaling. Mechanistically, decreased NF-κB signaling was explained by a reduced phosphorylation of IκBα35. However, the detailed molecular mechanism has not yet been elucidated.Gemcitabine-resistant prostate carcinoma depends on constitutively active NF-κB signaling and expresses high levels of PARP14 (ARTD8), which in turn correlates with poor patient survival30. Mechanistically, binding of 5′-triphosphate-modified RNA to RIG-I complexes enhances its association with MAVS, which ultimately induces IKK complex activation, leading to the degradation of IκBα and the release of NF-κB dimers36. Interestingly, the catalytically inactive RNA binding protein PARP13 (ARTD13)37 is able to restrict oncogenic virus replication by stabilizing the binding of activated RIG-I complex to MAVS, leading to increased NF-κB signaling36. This suggests that PARP13 might protect cells against malignant transformation and cancer development38. However, the exact molecular mechanism of PARP13’s mode of action remains elusive. Although PARP13 was reported to be catalytically inactive, its antiviral function is depended on trans-ADP-ribosylation of PARP13 itself, which is controlled by a so far unknown ART member38.The canonical NF-κB signaling pathway is activated in response to viral infection39. Interestingly, PARP12 localizes to p62/SQSTM1 foci and PARP12 activity is required for the activation of the NF-κB signaling cascade40. This observation was further strengthened by the co-localization of PARP12 and TRIF, a downstream component of the TLR4 receptor, required for TLR4 dependent NF-κB activation40. However, a molecular mechanism of NF-κB signaling activation by PARP12 remains to be defined. The capacity of PARP12 to promote NF-κB-dependent gene transcription requires the presence of an active catalytic domain. However, as the Km NAD+ of PARP12 is ~300 µM, this would suggest that the NAD+ concentration is higher in p62/SQSTM1 foci compared to the rest of the cytoplasm. Conversely, it might also be possible that the binding of PARP12 to its substrate decreases its Km NAD+, thereby allowing PARP12 activity.NF-κB signaling upon LPS stimulation of a murine macrophage-like cell line is positively regulated by p62/SQSTM1, whereby the scaffolding protein p62 enhances the TLR4-induced NF-κB signaling41. Mechanistically, activated IRE-1α recruits TRAF2, which in turn results in the activation of the canonical pathway through IKK and the release of NF-κB dimers. In parallel, PERK leads to an eIF2α-dependent attenuation of translation and thereby reduces overall IκB levels, shifting the balance from complexed inactive NF-κB toward a free and transiently active NF-κB42. Upon ER stress, PARP16, a tail-anchored ER protein, modifies itself as well as two ER stress sensors, IRE-1α, and PERK43. Interestingly, the third sensor of ER stress, ATF6, seems not to be regulated by PARP16. PARP16 activation is sufficient to promote IRE-1α and PERK signaling even in the absence of ER stress and is strictly required for their activity during UPR43. Since these data suggest a strong correlation between UPR functionality and PARP16 activity, it would be tempting to propose a role for PARP16 in ER-stress-induced inflammation via NF-κB signaling in cancer. In support of this observation, inhibition of PARP16 results in the suppression of ER-stress-induced PERK phosphorylation and increases cancer cell apoptosis under untreated and ER-stress-induced conditions44. However, it remains elusive whether the inhibition of PARP16 also interferes with NF-κB activation upon ER-stress and thereby induces apoptosis by inhibition of NF-κB signaling. Intriguingly, the remarkably high Km NAD+ of PARP16 (582 µM) suggests that PARP16 is not active under basal conditions. It is, however, possible that ER-stress increases the local ER NAD+ concentrations to a level that would allow PARP16 activity.ER-stress-induced inflammation and activation of the unfolded protein response (UPR) is relayed via ER-associated sensors of ER stress. These sensors are described to substantially contribute to tumor progression and metastasis in a NF-κB-dependent manner45. Furthermore, treatment of wild-type or PARP1-deficient mice with lipopolysaccharide (LPS) further supports the notion that PARP1 is involved in the transcriptional activity of NF-κB45. Mechanistically, LPS dependent NF-κB activation in primary murine fibroblasts is mediated by the interaction of PARP1 and two transcriptional coactivators, CREB-binding protein (CBP) and p30046. The formation of this complex results in PARP1 acetylation, which in turn allows the PARP1-CBP-p300 complex to interact with the p50 subunit of NF-κB. NF-κB signaling is consequently activated and the transcription of proinflammatory cytokines, chemokines, transcription factors, and other inflammatory mediators is initiated47. Besides, the PARP1 enzymatic activity has also been suggested to be important for NF-κB signaling48. Poly-ADP-ribosylation of p65 was found to be critical for its nuclear retention in TLR4-stimulated smooth muscle cells48. PARP1-dependent poly-ADP-ribosylation of p65 reduced the interaction with nuclear exporter Crm1, increasing p65 nuclear retention and ultimately enhancing NF-κB target gene expression48. Interestingly, irradiation-induced DNA damage in mice and consequential activation of PARP1 enzymatic activity results in the dynamic assembly of a complex comprising NEMO and likewise induces NF-κB activation49. This suggests that PARP1 can activate NF-κB even by endogenous signals to avert programmed cell death and emphasizes the potential beneficial effect of PARP inhibitors in combination with ionizing radiation as a tumor therapy50. Variation in nuclear NAD+ concentration governs NF-κB expression levels and transcriptional activity25. In this regard, the NAD+-dependent deacetylase SIRT1 negatively regulates PARP1 by inhibiting the expression of PARP1 and possibly through deacetylation of PARP1, reducing its enzymatic activity25. In contrast, since the Km NAD+ value of PARP1 is lower compared to the one of SIRT1, constitutive active PARP1 inhibits SIRT1 by consuming nuclear NAD+, which ultimately represses SIRT151. Therefore, lower local NAD+ concentrations favor PARP1’s role as a transcriptional co-activator of NF-κB, while a high NAD+ availability promotes SIRT1 inhibition of NF-κB activity through the deacetylation of p65 and reduction of PARP1 levels25. Hence, the competition between PARP1 and SIRT1 for NAD+ directly links the NF-κB pathway to the metabolic state of a cell.Both the PARP1 (ARTD1) protein as well as its enzymatic activity are associated with increased NF-κB signaling. NF-κB target gene expression in TNFα-stimulated NIH3T3 fibroblasts lacking PARP1 was repressed even though NF-κB was localized to the nucleus53. In a NF-κB-independent context, TBK1 is described as an activator of IRF3 in response to viral infection54. Of note, TBK1 kinase activity and thus the efficacy of the antiviral response is negatively regulated by PARP7 (ARTD14/TIPARP) mediated ADP-ribosylation55. However, whether there is a direct link between PARP7 and the downstream activation of NF-κB, through the inhibition of TBK1, remains elusive.During non-canonical NF-κB signaling, NF-κB2 processing is regulated by NIK, which in turn is downregulated by the non-canonical IKK TBK156. Mechanistically, PARP10 decreases K63-linked polyubiquitination on NEMO, which represses IKK assembly and activation56. Although NEMO is found to be ADP-ribosylated by PARP10 in vitro, neither the overexpression of a catalytic mutant or a ubiquitin-binding deficient mutant represses the inhibitory effect of PARP10 toward NF-κB in cells56. This suggests that an unknown protein property of PARP10 is involved in NEMO inhibition. Furthermore, in hepatocellular carcinoma, the inhibition of NEMO ubiquitination by PARP10 is negatively regulated by PLK1-mediated phosphorylation of PARP10. In this regard, PARP10 inhibition increases NF-κB signaling by releasing PARP10’s repression of NEMO34. Interestingly, PLK1 is mono-ADP-ribosylated by PARP10, which significantly inhibits its kinase activity and oncogenic function34. In addition, PARP10 dependent mono-ADP-ribosylation of GSK3β, a kinase that promotes NEMO stability and enhances NF-κB signaling57, represses its kinase activity in vitro58. In an active state, GSK3β positively regulates SCFFbw7 activity and thereby promotes the degradation of the p100, ultimately releasing the repression of NF-κB1 and promoting canonical NF-κB signaling59. Together, these findings support the notion of PARP10 as a negative regulator of NF-κB via inhibition of GSK3β activity. However, the influence of PARP10 on GSK3β and thus on NF-κB activation requires further evaluation, since mono-ADP-ribosylation of GSK3β only mildly reduced its kinase activity in vitro58. Nevertheless, this proposed mode of action is strengthened by the fact that removal of PARP10-mediated mono-ADP-ribosylation on GSK3β enhances its kinase activity60.In HeLa and U2OS cells, activation of the IKK complex and thus NF-κB signaling is inhibited by PARP1061. The expression of a subset of NF-κB target genes in murine macrophages is repressed by PARP1 under basal conditions and enhanced upon activation of the NLRP3 inflammasome and caspases 1/762. Caspase-dependent cleavage of PARP1 results in its release from chromatin, which promotes local chromatin de-condensation and allows enhanced gene expression63.In NF-κB signaling, PARP1 is not only described as a transcriptional co-factor but, for some genes, also as a transcriptional repressor64. On the molecular level, the pathway consists of the cytoplasmatic kinase JAK, which directly interacts with a variety of transmembrane receptors and the transcription factor STAT  cell lineage-specific susceptibility toward STAT activation, (ii) qualitative differences in the duration and/or intensity of the downstream STAT signaling, and (iii) quantitative expression differences between co-activated STATs67. Although the canonical JAK/STAT pathway is simple and direct, pathway components regulate and/or are regulated by members of other signaling pathways, including signaling cascades involving the kinases ERK and PI3K68.The Janus kinase/signal transducer and activator of transcription proteins (JAK/STAT) signaling pathway, known to operate in response to over 50 cytokines and growth factors, is a central communication node for the immune systemTAT Fig. . In mamm68. This hyperactivity, which typically involves STAT3 and/or STAT5, is now considered a defining characteristic of most solid and blood cancers69.Over the past 20 years, the link between JAK/STAT signaling and oncogenesis has become a major subject in cancer biology. It has long been known that STAT hyperactivity can drive cellular transformation downstream of classic oncogenes70. Interestingly, in macrophages PARP9 and PARP14 exert anti- and proinflammatory effects respectively, and thereby regulate macrophage activation71. However, whether these findings are dependent on their enzymatic activity is currently under debate and will be discussed in greater detail in the section “Positive regulation of JAK/STAT signaling by ARTD family members”. In addition, the expression of PARP9 is regulated by the IFNγ-JAK2/STAT1-IRF1 signaling axis that is required for cancer cell survival in diffuse large B-cell lymphoma (DLBCL) with an active host inflammatory response72.A proteomic study conducted in IFNγ-stimulated THP-1 cells revealed that PARP9 (ARTD9) and PARP14 were highly expressed and increasingly ADP-ribosylated73. This finding is based on the assumption that the proposed STAT6 ADP-ribosylation site lies in close proximity to a potentially functional relevant STAT6 phosphorylation site (Tyr629) and that PARP14-mediated ADP-ribosylation would promote phosphorylation-dependent activation of STAT6. However, this interpretation was called into question, since the proposed STAT6 phosphorylation site (Tyr629) was so far not described. In this regard, a large body of research agreed on Tyr641 as the functionally critical and possibly sole phosphorylated tyrosine of human STAT674. Nonetheless, phosphorylation and ADP-ribosylation sites, specifically for Ser and Tyr residues, significantly overlap, suggesting a site-specific regulatory interplay between the two modifications76. Interestingly, Ser phosphorylation and ADP-ribosylation seem to be mutually exclusive77. The emerging crosstalk between ADP-ribosylation and phosphorylation might represent an additional layer of regulation which requires further functional validation. Although direct ADP-ribosylation of STAT6 by PARP14 remains elusive74, it was reported for the mouse lymphoma cell line M12 B that the catalytic activity of PARP14 functions as a molecular switch for IL-4-induced and STAT6-dependent gene expression of IL-4 responsive promotors79. In presence of IL-4, PARP14 promotes the mono-ADP-ribosylation of HDAC2 and HDAC3 which leads to their dissociation from the IL-4 responsive promotors and facilitates promotor-binding of STAT6 as well as transcriptional co-factors such as p300, subsequently resulting in active gene transcription80. Furthermore, IL-4 and STAT6-dependent Th2 responses and immunoglobulin class switching to IgE are collectively linked to the development of asthmatic conditions81. Consequently, the functional relevance of PARP14-mediated ADP-ribosylation for STAT6-dependent gene activation might be a potential therapeutic target in order to reduce the progression of allergic airway diseases.In macrophages, IL-4-induced STAT6 phosphorylation and the subsequent expression of anti-inflammatory genes are dependent on PARP14 activation and seem to include PARP14-mediated STAT6 ADP-ribosylation82. PARP1 downregulation results in decreased STAT6 protein stability, which in turn is reflected by a reduction in IL-5 expression in murine splenocytes82. Furthermore, depletion of NAD+ via excessive PARP1 activation, is considered to contribute to the pathogenesis of various cardiovascular diseases, including atherosclerosis and cardiac hypertrophy83. In a phenylephrine-induced cardiac hypertrophy model, PARP1 and its enzymatic activity retain phosphorylated STAT3 in the nucleus. This prolongs STAT3 transcriptional activity independent of JAK2 activity and contributes to the hypertrophy phenotype84. A detailed molecular mechanism of how PARP1 affects the phosphorylation status of STAT3 was not described. Moreover, either PARP1 protein or its enzymatic function regulates the expression of multiple pro- and anti-inflammatory cytokines, which in turn modulate the activity of the JAK/STAT signaling cascade in a para- or autocrine fashion. The role of PARP1 in cytokine expression was already extensively discussed elsewhere85.Interestingly, PARP1 positively regulates STAT6-dependent transcriptional activation86. Noteworthy, the PARP9/DTX3L complex acts as the rate limiting factor for STAT1 transcriptional activity and is able to enhance the host defense response following viral infection86. In support of this observation, PARP9 activates proinflammatory genes and STAT1 phosphorylation in response to IFNγ in monocytes73. Although PARP9 was thought to be enzymatically inactive, PARP9 as a heterodimer with DTX3L seems to possess mono-ADP-ribosylation activity87. Therefore, in the presence of high NAD+ concentrations PARP9 modifies ubiquitin and thereby restrains DTX3L’s E3 activity. Remarkably, in DLBCL PARP9 stimulates the phosphorylation of both STAT1 isoforms. However, it especially promotes the nuclear accumulation of the transcriptionally repressive isoform STAT1β88. In this regard, PARP9 directly inhibits, together with STAT1β, the expression of tumor suppressor IRF1. Conversely, PARP9 enhances the expression of the proto-oncogenes IRF2 and BCL6. Overall, PARP9 represses the anti-proliferative and pro-apoptotic IFNγ-STAT1-IRF1-p53 axis and mediates proliferation and survival in DLBCL88.PARP9 and its binding partner DTX3L are associated with STAT1 and are important for interferon signal transduction89.Type 1 interferon receptor (IFNAR1) protein stability is an essential determinant of the IFN1 antiviral response. Strikingly, viral infection promotes the expression of PARP11 (ARTD11), which in turn mono-ADP-ribosylates the ubiquitin E3 ligase β-TrCP. This ultimately results in IFNAR1 ubiquitination and degradation, and finally in the suppression of the IFN antiviral signaling90. However, the molecular mechanism underlying the PARP1-dependent IFNAR1 degradation has yet to be investigated.Similarly, influenza A viral infection results in the transient cytoplasmic co-localization of HA and PARP1, which in turn mediates IFNAR1 degradation in an ADP-ribosylation-dependent manner73. However, it was called into question whether this finding is dependent on the catalytic activity of PARP14. This is mostly because a previously described SUMO conjugation site of STAT1, which is a critical regulator of IFNγ signaling and in close proximity to the proposed ADP-ribosylation site of STAT1, was not further considered74.In IFNγ-stimulated monocytes, PARP14 suppresses proinflammatory genes and STAT1 phosphorylation91. This contrasts with the positive regulation of STAT3 discussed in the “Positive regulation of JAK/STAT signaling by ARTD family members” section and emphasizes the context-specific regulation of STAT3 by PARP1.In ovarian, lung, and colon cancer cell lines, PARP1 downregulates PD-L1 expression by ADP-ribosylating STAT3 and, thus, decreasing its phosphorylation92. In the absence of Wnt ligands the plakoglobin β-catenin, also critical for cell–cell adhesion, is sequestered in the cytoplasm by the Axin complex that comprises the scaffolding protein Axin, the tumor suppressor APC and the two kinases CK1 and GSK393. In this steady-state, CK1 and GSK3 sequentially phosphorylate β-catenin, resulting in β-catenin ubiquitination mediated proteasomal degradation by SCFβ-TRCP, thus preventing its nuclear translocation  regulate telomere length105. However, the degree to which the basal level of Axin increased following Tankyrase 1/2 inhibition was not sufficient to disrupt Wnt signaling in Drosophila melanogaster105. Therefore, it was suggested that the Drosophila melanogaster Tankyrase 1/2 homolog promotes the interaction of Axin with phospho-LRP6. It was suggested that the Tankyrase 1/2 homolog in Drosophila melanogaster acts in a biphasic manner: (i) at the basal level it promotes the degradation of Axin, which alone is not sufficient to induce Wnt signaling; (ii) upon binding of Wnt ligands to the receptor, Tankyrase 1/2 activity is enhanced and induces Axin binding to phosphor-LRP6, which shifts the balance toward stable β-catenin105. The mechanism of Wnt ligand-dependent activation of Tankyrase 1/2 has yet to be defined.Tankyrase inhibitors were previously thought to disrupt Wnt signaling solely by increasing the basal levels of Axin and subsequently increasing β-catenin degradation109. Colon cancers often harbor tumor suppressor APC inactivating mutations that lead to constitutive activation of Wnt signaling110. Surprisingly, even under these conditions, Tankyrase 1/2 inhibition reduces the cellular β-catenin levels, which could be explained by Tankyrase 1/2 modifying and inhibiting APC2 and thus decreasing the activity of the degradome111. However, the mechanisms of APC2 regulation by Tankyrase 1/2 appears to be different compared to Axin, as Tankyrase 1/2 inhibition did not result in global changes of APC2 protein levels. This suggests that Tankyrase 1/2 promote Wnt/β-catenin signaling by an additional mechanism that has not yet been characterized.The promotion of apoptosis or tumor regression in colon and lung cancer after treatment with Tankyrases inhibitors, suggests a role of Tankyrase 1/2 as oncogenic factorsDrosophila melanogaster lacking Tankyrase 1/2 homolog are viable and fertile, and mice lacking both Tankyrase 1 and Tankyrase 2 proteins, although embryonic lethal, survive to E10 without obvious defects in Wnt signaling. Thus, while Tankyrase 1/2 can fine-tune the Wnt signaling pathway it seems not to be an essential regulator112.Since Axin is still degraded after extended Wnt signaling in a Tankyrase 1/2-independent fashion, Tankyrase 1/2 are not solely responsible for the Axin degradation. In support of this notion, 58. This proposed mode of action was further strengthened by the discovery that the hydrolase MacroD2 is able to counteract PARP10-mediated mono-ADP-ribosylation of GSK3, which restores its kinase activity60. Noteworthy, MacroD2 knockdown in HCC cells markedly enhanced proliferation and invasiveness in vitro, tumor progression in vivo, and promoted epithelial–mesenchymal transition113. Furthermore, PLK1 induces the destabilization of β-catenin115 and is mono-ADP-ribosylated by PARP1034. The modification of PLK1 significantly reduces its enzymatic activity34, suggesting a potential secondary mechanism by which PARP10 might positively regulate β-catenin stability.The kinase activity of GSK3 is a crucial repressor of the β-catenin stability and is negatively regulated by PARP10-mediated mono-ADP-ribosylation, which leads to increased β-catenin levels61. Conversely, Ku70 has been observed to associate with TCF-4/β-catenin and to repress TCF/LEF function116. Noteworthy, Ku70 competes with PARP1 for binding to the complex, suggesting that this mutually exclusive behavior is a determinant for Wnt target gene expression. In colon cancer, PARP1 is often overexpressed, which indicates its beneficial functional role for β-catenin transcriptional activity116.Wnt target gene expression in APC deficient family and sporadic colorectal cancer (CRC) is enhanced by PARP1 as a co-factor of TCF-4/β-catenin96. This transition results in the increase of cytoplasmic NAD+ levels117. In this context, the expression of LDH is increased and thus favors NADH oxidation and increases cytoplasmic NAD+ levels118. Therefore, it would be interesting to elucidate whether increased Wnt/β-catenin signaling promotes a positive feedback loop involving increased free cytosolic NAD+ and enhanced ADP-ribosylation.As mentioned above, constitutive Wnt/β-catenin signaling in cancer cells can promote the metabolic switch from oxidative phosphorylation to aerobic glycolysisSo far, no negative regulation of the Wnt signaling by ARTD family members was reported.121. The phosphorylation cascade comprises three sequentially activated protein kinases starting with the MAPK kinase kinases (MKKKs) that are followed by the MAPK kinases (MKK) and the MAPKs , c-Jun N-terminal kinase (JNK), and the p38 kinases121.The mitogen-activated protein kinases (MAPK) pathway is a cascade of cytoplasmic phosphorylation events, initiated by the binding of different ligands  to their respective receptorsPKs Fig. 119–121. 122. While growth factor and mitogen-activated ERK signaling is mainly involved in promoting cell growth, proliferation, and survival123, prolonged retention of activated ERK1/2 in the nucleus in neuronal cells resulted in cell death124. The stress-activated JNK can be activated as a consequence of inflammatory cytokine signaling or environmental stress and is important for a proper immune response and cytokine production as well as stress-induced apoptosis and cell proliferation123. In cancer cells, JNK regulates opposing cell fates ranging from inducing apoptosis to facilitating proliferation and survival125. Finally, the p38 kinase pathway can be activated by cytokines, TLR ligands, growth factors, and environmental stress and is involved in the production of inflammatory mediators123. Besides its involvement in inflammation, p38 was described to be associated with various phenotypes ranging from cell growth and cell differentiation to cell death123. In cancer cells active ERK1/2 signaling promotes the expression of transcriptional regulators that in turn drive the expression of glycolytic enzymes126. Moreover, JNK2, but not JNK1, promotes aerobic glycolysis by reducing the phosphorylation of PKM2 126.In general, differences in signal-duration and ERK1/2 organelle localization modulate the outcome of ERK signaling128. Inhibition of MEK, the MAPK kinase upstream of ERK, in conditioned medium-stimulated endothelial cells led to downregulation of PARP1 expression127, while overexpression of p-ERK2 in neurons led to an increased PARP1 activity129. In turn, the p-ERK2-induced PARP1 activation correlated with enhanced phosphorylation of ERK targets129. A positive correlation between ERK signaling and PARP1 activity was also observed in astrocytes, where both ERK1 and ERK2 phosphorylated PARP1130. However, only ERK2 was essential for PARP1 activation130. In addition, following prolonged seizure in rats the enzymatic activity of PARP1 in astrocytes was reduced after ERK inhibition131, indicating that ERK might be a positive upstream regulator of PARP1 signaling. Moreover, MEK inhibitors markedly decreased MNNG-induced PARP1 activation and consequential astrocyte cell death130. A positive regulatory loop between PARP1 and ERK was proposed, whereby p-ERK-induced PARP1 auto-PARylation promoted PARP1-dependent retention of p-ERK in the nucleus, and ultimately facilitated phosphorylation of nuclear targets by p-ERK132. The interaction between p-ERK and activated PARP1 was reviewed in greater detail elsewhere132. Of note, MNNG-induced PARylation in HeLa cells was not affected by MEK inhibitor treatment133, suggesting that ERK affects the activity of ARTDs in a cell-type-specific manner.ERK signaling positively regulates both PARP1 expression and activity134. In insulin, PDGF and EGF-stimulated 3T3-L1 fibroblasts and adipocytes ERK phosphorylated Tankyrase 1134. ERK-dependent phosphorylation increased Tankyrase 1 auto-modification and ADP-ribosylation of its binding partner IRAP (an abundant protein in GLUT4 storage vesicles) in vitro. Conversely, after insulin stimulation, endogenous Tankyrase 1 was not ADP-ribosylated134. Intriguingly, the enzymatic activity of Tankyrase 1 seems to be essential for GLUT4 storage vesicle trafficking and thus insulin-stimulated glucose uptake135. Of note, ERK-dependent Tankyrase 1 phosphorylation was also found in a different context, namely upon herpes simplex virus (HSV) infection of Hep-2 cells136. Moreover, Tankyrase 1 depletion or inhibition by Tankyrase inhibitor impaired HSV growth, suggesting that the enzymatic activity, potentially enhanced by phosphorylation, of Tankyrase 1 may be essential for HSV infection136.Besides PARP1, Tankyrase 1 activity was also found to be modulated by ERK signaling2O2-mediated cell death in mouse embryonic fibroblasts (MEFs)137. JNK1 sustained PARP1 activation only upon prolonged H2O2 stimulation by directly phosphorylating PARP1, but it did not affect ADP-ribosylation during early timepoints137. Similarly, in the context of multiple myeloma, JNK2 positively regulated PARP14 protein levels through an unknown mechanism138.In addition, JNK1 was postulated to be a positive upstream regulator of PARP1 activation in H139. This ultimately induces the phosphorylation of downstream substrates that promote cell growth, survival, and migration139. Interestingly, PARP1-mediated ADP-ribosylation was found to promote cell survival by enhancing ERK phosphorylation (p-ERK) in different cellular contexts142. Knockdown and/or inhibition of PARP1 in lung cancer and osteosarcoma cells decreased ERK phosphorylation, which reduced cell proliferation and migration, and increased apoptosis142. In lung cancer cells, not only ERK phosphorylation but also total ERK protein levels were decreased upon inhibition of ADP-ribosylation or PARP1-siRNA treatment141. Interestingly, PARP1 inhibition or knockdown also reduced the expression and phosphorylation of EGFR, an upstream activator of ERK141. This suggests that PARP1-mediated ADP-ribosylation not only reinforces ERK1/2 signaling but also the expression of its pathway components. Conversely, siRNA-mediated knockdown of PARP1 in osteosarcoma cells did not affect the abundance of total ERK142. In addition, the positive effect of ADP-ribosylation on ERK signaling and survival was also observed in a non-cancer cell context140. Inhibition of ADP-ribosylation (PJ-34) in primary epithelial cells stimulated by conditioned medium not only reduced ERK phosphorylation, but also phosphorylation of its downstream target Elk-1127. Consequently, cell viability and migration were reduced127. A reduction in ERK activation in response to inhibition of ADP-ribosylation was also observed in macrophages140. LPS-induced ERK phosphorylation was reduced by the treatment with PARP inhibitors 140. Together, these findings indicate an involvement of PARP1 and ADP-ribosylation in survival, proliferation, and growth by increasing ERK phosphorylation, which modulates ERK pathway activity. While most studies did not investigate the mechanism of PARP1-dependent modulation of ERK activity, one proposed that auto-PARylated, nuclear PARP1 acts as a scaffold protein that retains p-ERK in the nucleus and allows enhanced downstream phosphorylation127.The MAPK signaling pathways were described to be positively regulated by PARP1 and Tankyrase 1/2. Under normal conditions, MEK1/2 (MAPKK)-mediated phosphorylation of ERK1/2 (p-ERK1/2) induces conformational changes in ERK1/2 that result in ERK1/2 activation145. Perfusion of rat hearts with a cytostatic agent led to an increase in cardiotoxicity and ERK, JNK, and p38 phosphorylation143. MAPK phosphorylation was significantly reduced when inhibiting (presumably) PARP1-dependent ADP-ribosylation with BGP-15143. Similarly, in LPS-treated mice, ADP-ribosylation inhibition with 4-HQN significantly decreased LPS-induced mortality145. Interestingly, the decrease in mortality was partly attributed to tissue-specific reduction of ERK1/2 and p38 phosphorylation145. While it is possible that reducing extended ERK phosphorylation has beneficial effects for the cells, it seems more likely that the protective effect observed upon PARP inhibition is associated with the reduction in JNK and p38 activity, both widely described to induce cell death. Even though no mechanism was defined, such a protective role of ADP-ribosylation inhibitors has been observed in a rat model of retinal degeneration, where phosphorylation of JNK and p38 was significantly reduced by PARP inhibitor HO3089146. Nonetheless, whether changes in one, two, or all three MAP kinases are the cause of the observed cytoprotective effects of PARP inhibitors and to which extent the cell type and the kind of stimulation play a role remains to be further explored. One could, however, speculate that while moderate activation of PARP1 allows the formation of PAR chains that act as scaffold for p-ERK and enhance downstream signaling127, the excessive activation of PARP1 leads to NAD+ depletion which in turn might prompt energy sensors to activate JNK or p38 and induce cell death147. It is also possible that direct PARylation of a kinase modulates protein-protein interactions and thereby enhances signaling or prompts cell death.In the above-mentioned findings, PARP1 activity correlated with enhanced ERK signaling and improved survival. However, under certain circumstances, the inhibition/absence of ADP-ribosylation and the associated reduction in MAPK signaling conveys a protective effect to the cells145. Moreover, PARP inhibitor-induced AKT signaling has been speculated to mediate the inhibition of MAP kinases145, highlighting the possibility of crosstalk between different signaling pathways. The importance of crosstalk and their highly context-specific outcomes can be appreciated by taking into consideration a model of H2O2-induced cell death in MEFs144, another example where inhibition of PARP1 conveys a protective effect to cells. H2O2 treatment of MEFs resulted in decreased cell survival and rapid ERK phosphorylation compared to the same treatment in PARP1 knockout cells144. Survival of WT cells could not be rescued with MEK inhibitors144, suggesting that ERK phosphorylation, especially at early timepoints, depends on PARP1 but that ERK signaling does not regulate cell death in this context. On the other hand, AKT phosphorylation kinetics were comparable to the observed ERK activation, and treatment with a PI3K inhibitor not only reduced AKT and ERK phosphorylation, but also increased cell survival, in WT but not PARP1 knockout cells144. This suggests that within this context, AKT signaling is the essential pathway for cell survival and ERK activation might merely be a downstream byproduct of AKT signaling. Overall, while PARP1 and ADP-ribosylation correlate with ERK signaling in diverse biological systems, the consequence of PARP1 and ADP-ribosylation-induced ERK phosphorylation is highly cell type and context-specific; under certain circumstances, PARP1-dependent ERK signaling was demonstrated to be beneficial for cell growth, survival and migration. In contrast, in systems where PARP1-dependent cell death was inhibited or PARP1 was absent, the concomitant decline in ERK signaling was shown to be cytoprotective. It is, however, likely that reduced ERK phosphorylation is not the driving force for cell survival in these systems.Intriguingly, besides its effect on the MAPK pathway, 4-HQN also decreased the LPS-induced activation of nuclear transcription factor NF-κB, which is presumably activated by members of the MAPK pathway149. H2O2-induced ADP-ribosylation, cell death, and mitochondrial dysfunction in human WRL-68 cells promoted JNK1/2 and p38 phosphorylation and activation in a PARP1-dependent manner149. Similarly, cell death during osteo-differentiation depended on ROS-activated PARP1, which in turn promoted p38 phosphorylation resulting in a metabolic collapse and cell death150. Furthermore, ROS produced upon hypoxia/reoxygenation of the eye of rats led to PARP1 activation151. Inhibition of ADP-ribosylation reversed the induced histological changes in the eye and reduced JNK and p38 phosphorylation151. Mechanistically, H2O2- or ROS-activated PARP1 indirectly upregulated JNK and p38 MAP kinase activities by ADP-ribosylating the activating transcription factor 4 (ATF4) in rats and human cells. Therefore, the binding of ATF4 to its DNA response element was reduced. As a result, the expression of MKP-1, a negative regulator of JNK and p38152, was decreased, ultimately leading to increased JNK and p38 kinase activity151.Besides its effect on ERK phosphorylation, PARP1 activation also correlates with JNK and p38 signaling in various cell types. This is primarily the case in the context of reactive oxygen species (ROS) dependent PARP1 activation and cell death which depends on JNK and/or p38 signaling147. PARP1-dependent cell death upon MNNG treatment of MEFs required JNK1 activity147. Moreover, JNK1 activation was dependent on TRAF2 and RIP1, two proteins involved in tumor necrosis factor receptor 1 (TNFR1)-mediated signal transduction153. It is possible that NAD+ depletion upon PARP1 activation, rather than direct ADP-ribosylation of JNK, modulates the activation status of the TRAF2/RIP1-JNK signaling cascade147. Furthermore, PARP1-dependent JNK1 activation was essential for TNFα/ATRA-induced apoptosis in NF-κB repressed human leukemia cells, further highlighting the interplay between TNFR and PARP1/JNK1-mediated cell death154. Of note, the involvement of RIP1 in PARP1/JNK-induced cell death is controversial, as not all studies could confirm the indispensable role of RIP1 in this process156. Overall, PARP1-dependent JNK and p38 phosphorylation is essential for PARP1-induced cell death in different cell types.In addition to ROS, MNNG-induced DNA damage can also activate PARP1 and consequently JNKDrosophila melanogaster and not mammalian cells158. Strong activation of JNK caused defective eye and wing development158. Overexpression of the Drosophila melanogaster Tankyrase 1/2 homolog in the wing not only impaired wing formation but also resulted in high activity of caspase 3, suggesting that the apoptotic cell death is induced by JNK signaling158. Inhibiting JNK signaling in wings that overexpressed Tankyrase 1/2 decreased the apoptotic cell death, suggesting that JNK is a mediator of Drosophila melanogaster Tankyrase 1/2-induced cell death158. Tankyrase 1/2-induced JNK activation was dependent on ADP-ribosylation of Drosophila melanogaster JNK which induces K63-linked ubiquitination, ultimately enhancing JNK kinase activity157.Last, Tankyrase 1/2 have been described in JNK activation, albeit in 159, suggesting that ADP-ribosylation prevents ERK signaling, downstream NF-κB activity, and IL-6 expression at an early timepoint of infection159.In contrast to the positive correlation between ARTD activation and MAP kinase signaling discussed previously, PARP1- and PARP14-dependent ADP-ribosylation have also been associated with decreased MAPK signaling in different cellular systems. In the context of Salmonella infection of human colonic epithelial cells, increased ERK phosphorylation, NF-κB signaling, and IL-6 production/secretion was observed in PARP inhibitor (PJ-34) treated cells already at early timepoints. In untreated cells, both phosphorylation of ERK and nuclear NF-κB were detectable only at later timepoints133. A similar effect was observed in H2O2-induced ADP-ribosylation and apoptosis in cardiomyoblasts, which correlated with a reduction in both ERK and p38 phosphorylation160. PARP inhibitor administration (INH2BP) increased phosphorylation of ERK and p38 and cell viability, led to a downregulation of ROS and pro-apoptotic factors and increased levels of anti-apoptotic proteins160. Specific ERK and p38 inhibitors individually and in combination counteracted the pro-survival effect of INH2BP160, suggesting that the pro-survival effect of this PARP inhibitor could be ascribed to both MAP kinases. Of note, the ERK pathway had already been implicated in cardiac protection, while the pro-apoptotic or protective consequences of p38 signaling for the heart continue to be controversially discussed161. In addition, in cells and tissues other than heart an opposing effect of PARP inhibitor administration on the different MAP kinases can be observed. Inhibition of PARP1 increased ERK activation and counteracted cell death in the context of H2O2-induced apoptosis of human WRL-68 cells, while simultaneously decreasing p-JNK and p-p38 148. Similarly, a protective role of ADP-ribosylation inhibition has also been described in a model of retinal degeneration, where phosphorylation of ERK was increased, while p-JNK and p-p38 were decreased  upon PARP inhibitor administration (HO3089)146. The mechanism for simultaneous upregulation of ERK and downregulation of JNK and p38 was not discussed in detail in these models of H2O2-induced cell death and retinal degradation. However, one could speculate that the protective effect of PARP inhibitors arises from increased pro-survival ERK signaling and simultaneous dampening of stress-induced JNK and p38 signaling.In HeLa cells, extensive activation of PARylation by MNNG specifically decreased phosphorylation of ERK1/2, which ultimately induced cell death in an ERK-dependent manner2O2-treated PARP1 knockout MEFs survival correlated with enhanced JNK and p38 phosphorylation, while p-ERK decreased in absence of PARP1 144. However, it is worth mentioning that the inhibition of JNK and p38 did not affect cell survival of H2O2-treated PARP1 knockout MEFs144. In addition, cell survival of H2O2-treated WT cells could not be rescued by MEK inhibitors144, indicating that cell viability is not affected by JNK and p38 nor by ERK signaling, respectively.From this point of view, it seems controversial that in H162. Similarly, L-2286 was also found to be protective in isoproterenol-induced myocardial injury162. However, in this case, PARP inhibitor administration correlated with increased p-ERK and p-p38 but decreased p-JNK162. Intriguingly, AKT phosphorylation was found to be elevated in both cases of myocardial injury162, which further suggests that AKT signaling might be an upstream ERK activator. Unfortunately, despite the wealth of correlative data collected, for most of the above discussed findings, the molecular mechanism(s) remain elusive. While the protective effect of PARP inhibitors seems to be applicable to a variety of different biological systems, in most studies they have not been further investigated to determine whether these protective effects are dependent on the observed changes in MAPK activity. Therefore, it is possible that changes in MAP kinase phosphorylation are merely a secondary consequence and not the cause of the observed phenotype.In contrast, in Langendorff perfused rat hearts, PARP inhibitor (L-2286) administration resulted in an increased activation in all three MAP kinases and protected from myocardial injury163. PARP14 was found to interact with and probably ADP-ribosylate JNK1, thereby inhibiting its kinase activity and suppressing JNK1-dependent apoptosis138. Similarly, PARP14 depletion or inhibition by PJ-34 resulted in increased JNK1 activity and cell death138. Moreover, in hepatocellular carcinoma cells, PARP14 promoted aerobic glycolysis by inhibiting JNK1-dependent phosphorylation of PKM2163. Since the unphosphorylated form of PKM2 is a positive regulator of the transition from oxidative phosphorylation to glycolysis, PARP14 might be a crucial mediator of the Warburg effect in hepatocellular carcinoma163. Albeit not in the context of JNK, the importance of PARP14 as an anti-apoptotic factor and regulator of glycolysis has also been discussed under different conditions164. Interestingly, by promoting aerobic glycolysis, PARP14 also increases the levels of the reducing equivalent NADPH163 and shifts the cellular redox state. On the other hand, aerobic glycolysis in cancer cells generally increases the cytoplasmic NAD+ pool, a phenomenon that might also be found in hepatocellular carcinoma. However, due to an extremely low Km NAD+ PARP14 activity is possible under normal conditions and does not depend on an increase in NAD+.ADP-ribosylation mediated inhibition of JNK1 signaling in multiple myeloma and hepatocellular carcinoma induced a pro-survival effect166. Moreover, activated AKT participates in control of altered glucose metabolism in cancer cells  and is sufficient to promote aerobic glycolysis165 which usually results in increased cytoplasmic NAD+ levels117. AKT is activated downstream of different receptor tyrosine kinases, cytokine receptors, and G protein-coupled receptors , which binds with its SH2 domain to the phosphorylated tyrosine residues of the cytosolic receptor domains or to adaptor molecules167. This retains PI3K at the plasma membrane and, thus, allows phosphorylation of membrane-bound phosphoinositides167. AKT binds to the phosphorylated phosphoinositide and is phosphorylated by PDK1 at threonine residue T308167. AKT then becomes fully activated by mTORC2 via a second phosphorylation event at a distinct serine residue Ser473167. Fully activated AKT is involved in regulating diverse cellular processes by specifically phosphorylating multiple cytoplasmic substrates167. For instance, phosphorylation of the pro-apoptotic proteins BAD and FOXO counteracts apoptosis, while AKT-dependent phosphorylation of GSK3 changes the cellular metabolism by increasing glycogen synthesis166. Interestingly, AKT targets are implicated in the regulation of the MAPK pathway167 and AKT itself has been shown to suppresses the JNK and p38 pathway166. Moreover, AKT phosphorylates NAD kinase (NADK), which activates NADK and promotes the conversion of NAD+ to NADP+ and aerobic glycolysis165. Thus, AKT is directly involved in regulating the cellular metabolic homeostasis, modulating the availability of free NAD+ levels which in turn might reduce ADP-ribosylation activity.The serine-threonine kinase AKT  is a signaling molecule involved in regulating diverse biological processes including glucose metabolism, cell cycle, cell growth, and survival131. Inhibition of AKT signaling dampened PARP1 protein abundance and activity in both cases131. AKT might, thus, be involved in enhancing PARP1 expression and signaling.Only a few and opposing results are known about the regulation of ARTD family members by AKT signaling. While seizure induction increased PARP1 abundance and enzymatic activity in a certain type of astrocyte, in another type of astrocyte seizure led to a decrease in PARP1 and its enzymatic activity168. The increase in PARP2 led to enhanced cell proliferation, as well as increased phosphorylation of components of the AKT signaling cascade, including PI3K, AKT, and mTOR168, suggesting that PARP2 mediates cell survival and proliferation via AKT signaling. Interestingly, in HeLa cells, knockdown of PARP2 led to a decrease in total protein levels of PI3K, AKT, and mTOR, however the phosphorylation status was not analyzed169. Of note, tissue biopsies of cervical cancer patients displayed increased expression of PARP2 and components of the AKT cascade compared to non-tumor tissue169, illustrating the potential importance of this signaling network in vivo. Whether the observed effects depend on the ADP-ribosylation capacity of PARP2 or simply rely on the protein itself was not further elucidated. However, due to the comparatively high Km NAD+ value of PARP2, it is more likely that it is the protein itself and not its enzymatic activity that contributes to the observed phenotype. Nevertheless, PARP2 ADP-ribosylation activity contributions cannot be completely excluded.PARP2 (ARTD2) expression in synovial cells from a rat rheumatoid arthritis model was found to be increased compared to control cells170. It was suggested that the activity of GSK3β, a negative regulator of the mTORC2 component RICTOR, was inhibited by PARP3-dependent ADP-ribosylation170. This resulted in enhanced expression of RICTOR and ultimately in increased phosphorylation of AKT by mTORC2170.In BRCA1-deficient triple-negative breast cancer cell lines, the enzymatic activity of PARP3 (ARTD3) was involved in promoting cell survival and proliferation and correlated with increased AKT phosphorylation171. However, more recent evidence suggested that PARP inhibitor treatment could be applicable to a wide range of malignancies, including tumors with high replication stress and homologous recombination deficient cancers173. Prolonged inhibition of ADP-ribosylation in different human cancer cells either decreased phosphorylated AKT only175 or reduced both total and phosphorylated AKT protein141, which in turn reduced proliferation or induced cell cycle arrest. Although it was assumed that the observed cytotoxic effect was independent of the DNA repair capacity of the cell174, others emphasized increase in DNA damage as one of the primary causes of cell death175. Phosphorylation of FOXO3A by AKT, was reduced upon PARP inhibitor administration, allowing nuclear translocation and transcriptional activation of pro-apoptotic target genes174. Mechanistically, PARP inhibitors enhanced the phosphatase activity of the negative AKT regulator PHLPP1, which is responsible for the reduction in AKT Ser473 phosphorylation and subsequent inactivation174. Overall, these findings suggest that ADP-ribosylation-dependent enhancement of AKT signaling benefits cell survival and proliferation, thus confirming that PARP inhibitor administration in tumors might be beneficial even in BRCA-proficient tumors. Of note, there is yet another mechanism that adds complexity to the treatment with PARP inhibitors: independently of its effect on the cellular DNA repair capacity, PARP inhibitors have also been shown to promote cell surface PD-L1 levels177. Besides STAT3 , GSK3β was proposed to be involved in regulating cell surface PD-L1 levels downstream of PARP1176. These data suggest that a combined treatment of PARP inhibitor and PD-1/PD-L1 blockade might be beneficial in cancer patients. Moreover, normalization of characteristics such as heart size and cardiac function in the hearts of diabetic rats was observed after inhibition of ADP-ribosylation by 1,25(OH)2D3178. Interestingly, in diabetic rats, PARP1 inhibition not only dampened PARP1 expression but also mTOR phosphorylation, which correlated with increased phosphorylation of TSC2 (a negative regulator of mTORC1), and enhanced expression of SIRT1178. Therefore a regulatory circuit was proposed that involves the positive regulation of TSC2 by SIRT1, which in turn is inhibited by PARP1 178. Since prolonged mTOR activation can be detrimental179, it is possible that in the context of diabetic cardiomyopathy, inhibition of mTOR can confer a protective effect. Of note, the PARP inhibitor 1,25(OH)2D3 is an active form of vitamin D180 and diabetic patients often display vitamin D insufficiency178.Inhibition of ADP-ribosylation by PARP inhibitors such as Olaparib, Rucaparib, and Niraparib was originally approved by the FDA for the treatment of BRCA-deficient tumors187. In cardiomyocytes, high glucose treatment-induced oxidative stress, and DNA damage increased the expression and activity of PARP1183. Silencing of PARP1 reduced the observed inflammatory response induced by high glucose treatment and protected cardiomyocytes against high glucose-induced apoptosis by activating the pro-survival AKT pathway through insulin-like growth factor 1 receptor183. In a diabetic cardiomyopathy mouse model, PARP1 knockout improved cardiac function as well as diabetic cardiomyopathy-induced structural changes183. In line with the high glucose treated cardiomyocytes in vitro, PARP1 deletion in mice reduced the concentration of proinflammatory cytokines, decreased apoptosis, and enhanced activation of IGF-1R and AKT in the diabetic cardiomyopathy model183. Similarly, in pathologies involving heart cells (different perfusion models in rat hearts), the cytoprotective effect of different PARP inhibitor treatments correlated with a significant increase in AKT phosphorylation162, suggesting that under these conditions ADP-ribosylation negatively regulates the PI3K/AKT signaling pathway. Of note, in models of heart pathologies, changes in MAP kinases were evident upon PARP inhibitor administration. However, there is no consensus on whether MAP kinases were decreased143 or increased162. Knockdown of PARP1 in hypoxia-stimulated rat cardiomyocytes and rat myoblasts resulted in decreased apoptosis and increased viability and phosphorylation of AKT187. The protective effect of PARP inhibitors also holds true for seizure in the hippocampus of rats that led to a considerable amount of ADP-ribosylation186. Inhibition of ADP-ribosylation by 3-aminobenzamide (3-AB) attenuated neuronal apoptosis in this model of epilepsy and correlated with increased activation of the pro-survival AKT signaling186.In contrast to the evidence presented above, PARP1-dependent ADP-ribosylation was also reported to inhibit the AKT signaling cascade and PARP inhibitor administration exerted a protective role in this context151. Of note, in both pathologies the observed increase in AKT phosphorylation correlated with a decrease in JNK and p38 phosphorylation151. Furthermore, PARP inhibitor (3-AB or DPQ and PJ-34) administration after NMDA-elicited cell death in primary hippocampal neurons, and in a model for bladder dysfunction, counteracted cell death and correlated with enhanced AKT phosphorylation182.In ocular pathologies, inhibition of ADP-ribosylation upon hypoxia/reoxygenation of rat eye or hypoperfusion-induced retinal degradation not only increased phosphorylation of AKT but also resulted in phosphorylation of downstream targets such as GSK3β. Furthermore, reversal of the induced histological changes was observed in both ocular pathologies2O2-induced PARP1 in WRL-69 human liver cells185. An explanation as to how nuclear PARP1 could negatively influence the cytoplasmic AKT has been proposed: PARP1-dependent ADP-ribosylation counteracts the formation of a signalosome in the nucleus185. In contrast, inhibition of PARP1 activity allowed the formation of the signalosome, translocation to the cytoplasm, association with additional factors, and ultimately AKT phosphorylation and activation185. Moreover, PARP1 bound to and ADP-ribosylated FOXO1, thereby inhibiting FOXO1-induced transcription of p27Kip188. The latter examples highlight the fact that PARP1 influences PI3K/AKT signaling not just at one point, but at various levels throughout the cascade.Increased AKT phosphorylation and higher cell viability were also observed upon inhibition or silencing of H189. In addition, PARP inhibitor  administration decreased activity and expression of the stress sensor LKB1, as well as the phosphorylation states of LKB1 downstream targets AMPK and TSC2189. As both AMPK and TSC2 are negative regulators of mTORC1, this suggests that PARP inhibition drives PI3K/AKT signaling at least partly by increasing ATP availability which reduces stress response signaling via LKB1189. Interestingly, the sensitivity of different small cell lung cancer (SCLC) cell lines to the ADP-ribosylation inhibitor BMN 673 negatively correlated with the activity of the pro-survival pathway AKT. This suggests that cells with higher AKT activation were less sensitive to PARP inhibition190 and the increase of AKT pathway signaling could potentially depict an attempt of SCLC cells to escape PARP inhibition189. Similarly, the combination of a cytotoxic drug and inhibition or knockdown of PARP1 rendered human bladder carcinoma cells more resistant to apoptosis compared to treatment with a cytotoxic drug only191. Moreover, inhibition or knockdown of PARP1 correlated with increased phosphorylation of AKT and AKT’s downstream target GSK191. Of note, inhibition of the AKT pathway reversed the beneficial cytoprotective effects observed in PARP inhibitor-treated cells, confirming that PARP inhibition-induced AKT pathway activation could be responsible for the increased viability observed in these cancer cells191. In this case, a combination of both PARP inhibitors and PI3K/AKT pathway inhibitors might be beneficial in anti-tumor therapy191. Based on the data discussed above, it is evident that AKT activity correlates with survival. Controversially, the opposite was found in malignant pleural mesothelioma192. Inhibition of ADP-ribosylation decreased cell viability while simultaneously correlating with increased phosphorylation of pro-survival protein AKT192. The phosphorylation of a downstream effector of AKT, mTOR, was decreased192. It was speculated that inhibition of ADP-ribosylation increased the nuclear NAD+ concentration, allowing SIRT1 to de-acetylate AKT, which is then phosphorylated192. However, a second role of SIRT1 was discussed; by interacting with TSC1/2 (negative regulator of mTORC1) the phosphorylation of mTOR was inhibited192. This dual role of SIRT1 could explain why high AKT phosphorylation cannot necessarily be translated into mTOR activity.Inhibition of ADP-ribosylation or knockdown of PARP1 in lung cancer cell lines increased PI3K/AKT signaling, as well as global ATP levels73. Their induction suggests that they play a role in the antiviral defense. Indeed, several ARTD family members are found to restrict viral replication73. On the other hand, viruses encode both ARTs as well as ADP-ribosylhydrolases193. For example, viral macrodomains have been described to interfere with the innate immune response193. This provides evidence for an ancient and central role of ADP-ribosylation in host-pathogen interactions and suggests a co-evolution of ARTs.The importance of signaling events as a hallmark for a plethora of cellular processes in health and disease has become apparent in the last decades. However, the influence of intracellular ARTD family members mediated ADP-ribosylation on signaling has only recently emerged. Importantly, beyond the regulation of signaling pathways by ADP-ribosylation, the non-enzymatic properties of ARTD family members can also impact signaling as described in multiple examples throughout this review. So far, PARP1 is the most studied member of the ARTD family, due to its abundance and involvement in genomic integrity. Nonetheless, a growing body of evidence is supporting the importance of the other ARTDs for intracellular signaling. As discussed here, the effect of a single ARTD member on a signaling cascade can be both inhibitory and/or activating. Despite the abundance of studies showing a correlation between ARTD family members and signaling events, the precise mechanism of regulation as well as the contribution of the enzymatic activity often remains elusive or is under debate. Acquiring more detailed insights into the context-specific mechanism of action will help us to gain an understanding of this post-translational modification in intracellular signaling. While many studies focus on elucidating the impact of ARTDs on cellular function, little is known about the transcriptional regulation of ARTD family member. Additional efforts are thus required to understand these cross-talks and regulations. One prominent exception for this aspect are the ARTD family members induced in response to a viral infection85.Furthermore, ADP-ribosylation and ARTDs can promote immune signaling as well as the inflammatory response and subsequently promote or suppress chronic inflammatory diseases and oncogenic phenotypes. Besides the well-established use of PARP inhibitors in anti-tumor therapy, beneficial effects of PARP inhibitor administration were demonstrated in various inflammatory disease models including myocardial infarction and different auto-immune diseases+-bioavailability is the most basic requirement for the regulation of signaling cascades by ADP-ribosylation. Therefore, synthesis as well as spatial compartmentalization and temporal changes in cellular NAD+ concentration might strongly influence the enzymatic activity of ARTD family members and subsequently their signaling output. Since the affinities of the known ARTD family members for NAD+ are quite different , very likely contribute to their activity. In addition, co-factors might influence NAD+ and substrate affinity and, thus, alter the ADP-ribosylation profiles of a particular cell198. Since the unbound NAD+ exceeds free NADH by 600–1000 times in the cytoplasm but only 7–8 times in the mitochondria, metabolic changes affecting NAD+/NADH ratio might have a much bigger effect on NAD+ availability in the mitochondria. This suggests that the recently described mitochondrial ADP-ribosylation197 is likely more tightly coupled to metabolic changes  compared to nuclear and cytosolic ADP-ribosylation. The roles of various ARTs are not only dependent on their catalytic activities, but also on non-catalytic activities . Whether the latter ultimately impacts NAD+-bioavailability is currently not clear. The generation of biosensors capable of measuring free NAD+ in cells has enabled studies examining compartmentalized NAD+ concentration in all cellular compartments. In future studies, it will be interesting to determine cellular NAD+ levels under specific physiological and pathophysiological conditions to understand whether NAD+ availability does indeed provide a framework for enzymatic activity of ARTD members.NADnt Table , local N