The receptors of Notch family play an important role in controlling the development, differentiation, and function of multiple cell types.,The aim of this study is to investigate the role of Notch1 signaling upon immune suppression induced by melanoma cells.,Melanoma cell line B16 cells were transfected by lentivirus containing mouse Notch1 gene or Notch1 shRNA to generate B16 cell line that highly or lowly expressed Notch1.,Notch1 in anti-tumor immune response was comprehensively appraised in murine B16 melanoma tumor model in immunocompetent and immunodeficient mice.,The ratios of CD3+CD8+ cytotoxic T cells, CD49b+NK cells, CD4+CD25+FoxP3+ Tregs and Gr1+CD11b+ MDSCs in tumor-DLN or spleen were examined by flow cytometry.,After the co-culture of B16 cells and CD8+ T cells, the effects of Notch1 on the proliferation and activation of T cells were assessed by CCK8 assay, CFSE dilution and Chromium-release test.,The mRNA expression and supernatant secretion of immunosuppressive cytokines, TGF-β1, VEGF, IL-10 and IFN-γ were measured by RT-PCR and ELISA, respectively.,Downregulation or overexpression of Notch1 in B16 melanoma cells inhibited or promoted tumor growth in immunocompetent mice, respectively.,Notch1 expression in B16 melanoma cells inhibited the infiltration of CD8+ cytotoxic T lymphocytes and NK cells and reduced IFN-γ release in tumor tissue.,It could also enhance B16 cell-mediated inhibition of T cell proliferation and activation, and upregulate PD-1 expression on CD4+ and CD8+ T cells.,The percentage of CD4+CD25+FoxP3+ Tregs and Gr1+CD11b+MDSCs were significantly increased in tumor microenvironment, and all these were attributed to the upregulation of TGF-β1.,These findings suggested that Notch1 signaling in B16 melanoma cells might inhibit antitumor immunity by upregulation of TGF-β1.
People with pale skin, red hair, freckles, and an inability to tan-the “redhair/fairskin” phenotype- are at highest risk of developing melanoma, compared to all other pigmentation types1.,Genetically, this phenotype is frequently the product of inactivating polymorphisms in the Melanocortin 1 receptor (MC1R) gene.,MC1R encodes a cAMP stimulating G-protein coupled receptor that controls pigment production.,Minimal receptor activity, as in redhair/fairskin polymorphisms, produces red/yellow pheomelanin pigment, while increasing MC1R activity stimulates production of black/brown eumelanin2.,Pheomelanin has weak UV shielding capacity relative to eumelanin and has been shown to amplify UVA-induced reactive oxygen species (ROS) 3-5.,Several observations, however, complicate the assumption that melanoma risk is completely UV dependent.,For example, unlike non-melanoma skin cancers, melanoma is not restricted to sun-exposed skin and UV signature mutations are infrequently oncogenic drivers6.,While linkage of melanoma risk to UV exposure is beyond doubt, UV-independent events are also likely to play a significant role1,7.,Here, we introduced into mice carrying an inactivating mutation in the Mc1r gene (who exhibit a phenotype analogous to redhair/fairskin humans), a conditional, melanocyte-targeted allele of the most commonly mutated melanoma oncogene, BRafV600E.,We observed a high incidence of invasive melanomas without providing additional gene aberrations or UV exposure.,To investigate the mechanism of UV-independent carcinogenesis, we introduced an albino allele, which ablates all pigment production on the Mc1r e/e background.,Selective absence of pheomelanin synthesis was protective against melanoma development.,In addition, normal Mc1re/e mouse skin was found to have significantly greater oxidative DNA and lipid damage than albino-Mc1re/e mouse skin.,These data suggest that the pheomelanin pigment pathway produces UV-independent carcinogenic contributions to melanomagenesis by a mechanism of oxidative damage.,While UV protection remains important, additional strategies may be required for optimal melanoma prevention.