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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: BACKGROUND, METHODS, RESULTS. Meshes: Blotting, Western, Breast Neoplasms, Cyclin E, Cyclin-Dependent Kinase 2, Cyclin-Dependent Kinase Inhibitor p21, Cyclin-Dependent Kinase Inhibitor p27, E2F1 Transcription Factor, Female, Fluorescent Antibody Technique, G1 Phase, Humans, Immunoprecipitation, Ligases, Oncogene Proteins, Phosphorylation, RNA, Messenger, RNA, Small Interfering, Real-Time Polymerase Chain Reaction, Retinoblastoma Protein, Reverse Transcriptase Polymerase Chain Reaction, S Phase, Signal Transduction, Tumor Cells, Cultured.
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Does depletion of SUMO ligase hMMS21 impair G1 to S transition in MCF-7 breast cancer cells? Context: hMMS21 is a human SUMO ligase required for DNA damage repair and mitotic progression in HeLa cervical cancer cells. Owing to the diversity of cancer, we further investigated the effect of hMMS21-depletion on MCF-7 breast cancer cells. hMMS21-depletion was achieved by RNA interference. Cellular hMMS21 and E2F1 mRNA levels were estimated by RT-PCR and real-time PCR. Cell cycle profile was assessed by flow cytometry. Western blot and co-immunoprecipitation were used to determine the protein levels of various factors involved in G1-S transition and CDK2- or CDK4-associated p21 and p27. Kinase activity of cyclin E/CDK2 was measured in anti-cyclin E immunoprecipitate. hMMS21-depletion induced slower cell growth and G1-S transition. While it had no effect on cyclin D1 or phospho-Rb (S807/811) levels, hMMS21-depletion provoked lower E2F1 levels and cyclin E/CDK2 activity. The decreased cyclin E/CDK2 activity correlated with increased cellular p21(CIP1) levels and CDK2-p21 association. Moreover, ectopic expression of Flag-hMMS21 but not its ligase-inactive mutant rescued the decreased growth rates of hMMS21-depletd cells. Thus, depletion of hMMS21 seems to impair G1-S transition due to lowered E2F1 protein levels and cyclin E/CDK2 activity. The decreased cyclin E/CDK2 activity is probably attributable to its greater association with p21 as a result of increased p21 levels. In addition, hMMS21-mediated sumoylation appears to be involved.
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This study demonstrates that hMMS21 is required for G1-S transition in breast cancer cells and implies that manipulation of hMMS21-mediated sumoylation may alter the growth rates of breast cancer cells. Final Decision: yes