SUMOylation Of MCL1 Regulates Its Function

Apoptosis is important to maintain the growth and development of the body.In cancers,apoptosis evasion through dysregulation of pro?apoptotic and anti?apoptotic intracellular signals is a recurring event.Myeloid cell leukemia 1(MCL1)is an anti-apoptotic protein of the BCL-2 family,which is overexpressed in many cancers.MCL1 is essential for the survival of human malignancies,including breast cancer,non - SCLC,acute myeloid leukaemia,MYC-driven lymphomas and multiple myeloma.Studies have shown that reducing the stability of MCL1 can improve the therapeutic effects of cancer.SUMOylation is a crucial post-translational modification that can regulates substrate functions including protein activity,stability,transcriptional activity,subcellular distribution,and control of protein interactions.Sequence analysis of MCL1 reveals two potential SUMO conjugation sites.Therefore,we hypothesize that MCL1 is a target of SUMO.The main works of the paper are as follows:1.We observed that MCL1 could be modified by SUMO at K234 and K238 sites using immunoprecipitation assay in COS7 cells.In addition,the SUMOylation level of MCL1 was enhanced by Ubc9.And we found that endougenous MCL1 could also be modified by SUMO.So,we believed that MCL1 was a target of SUMO.2.We found the SUMOylation did not affect subcellular distribution between wide-type MCL1 or its mutant 2K by immunofluorescence staining.We also observed that the half-life of wild-type MCL1 was longer than the mutant 2K.It demonstrated that the SUMOylation could stabilize the protein level of MCL1.3.The direct association of TRIM11(a novel MCL1 ubiquitin E3 ligase)and MCL1 was identified using the mammalian two-hybrid system.In addition,we found that the SUMOylation of MCL1 could improve its stability by inhibiting the MCL1ubiquitin-proteasome pathway mediated by TRIM11 using immunoprecipitation assay.4.Cell growth assay,colony formation assay and apoptosis assay demonstrated that the SUMOylation of MCL1 promoted the proliferation of cancer cells by inhibiting apoptosis.Collectively,our data identified MCL1 a novel target of SUMO,and showed the specific molecular mechanism of regulating the stability and function of MCL1 by SUMO.