Jiangsu Key Laboratory for Translational Research and Therapeutics of Neuro-Psycho- Diseases, Department of Pharmacology, College of Pharmaceutical Sciences, Soochow University, Suzhou, Jiangsu 215123, China.
Program in Molecular Structure and Function, The Hospital for Sick Children, Department of Molecular Genetics, University of Toronto, Toronto M5G 0A4, Canada.
Cell Death Dis. 2017 Sep 21;8(9):e3058. doi: 10.1038/cddis.2017.450.
The deubiquitinase USP5 stabilizes c-Maf, a key transcription factor in multiple myeloma (MM), but the mechanisms and significance are unclear. In the present study, USP5 was found to interact with c-Maf and prevented it from degradation by decreasing its polyubiquitination level. Specifically, the 308th and 347th lysine residues in c-Maf were critical for USP5-mediated deubiquitination and stability. There are five key domains in the USP5 protein and subsequent studies revealed that the cryptic ZnF domain and the C-box domain interacted with c-Maf but the UBA1/UBA2 domain partly increased its stability. Notably, MafA and MafB are also members of the c-Maf family, however, USP5 failed to deubiquitinate MafA, suggesting its substrate specificity. In the functional studies, USP5 was found to promoted the transcriptional activity of c-Maf. Consistent with the high level of c-Maf protein in MM cells, USP5 was also highly expressed. When USP5 was knocked down, c-Maf underwent degradation. Interestingly, USP5 silence led to apoptosis of MM cells expressing c-Maf but not MM cells lacking c-Maf, indicating c-Maf is a key factor in USP5-mediated MM cell proliferation and survival. Consistent with this finding, WP1130, an inhibitor of several Dubs including USP5, suppressed the transcriptional activity of c-Maf and induced MM cell apoptosis. When c-Maf was overexpressed, WP1130-induced MM cell apoptosis was abolished. Taken together, these findings suggest that USP5 regulates c-Maf stability and MM cell survival. Targeting the USP5/c-Maf axis could be a potential strategy for MM treatment.
去泛素化酶 USP5 稳定 c-Maf，c-Maf 是多发性骨髓瘤（MM）中的关键转录因子，但作用机制和意义尚不清楚。本研究发现 USP5 与 c-Maf 相互作用，并通过降低其多泛素化水平来防止其降解。具体而言，c-Maf 的第 308 位和第 347 位赖氨酸残基对于 USP5 介导的去泛素化和稳定性至关重要。USP5 蛋白有五个关键结构域，后续研究表明，隐藏的 ZnF 结构域和 C 盒结构域与 c-Maf 相互作用，但 UBA1/UBA2 结构域部分增加了其稳定性。值得注意的是，MafA 和 MafB 也是 c-Maf 家族的成员，然而，USP5 未能去泛素化 MafA，表明其具有底物特异性。在功能研究中，USP5 被发现促进了 c-Maf 的转录活性。与 MM 细胞中 c-Maf 蛋白水平较高一致，USP5 的表达也很高。当 USP5 被敲低时，c-Maf 发生降解。有趣的是，USP5 沉默导致表达 c-Maf 的 MM 细胞凋亡，但不表达 c-Maf 的 MM 细胞则不会，表明 c-Maf 是 USP5 介导的 MM 细胞增殖和存活的关键因素。与这一发现一致，WP1130 是包括 USP5 在内的几种 Dub 的抑制剂，抑制了 c-Maf 的转录活性并诱导 MM 细胞凋亡。当 c-Maf 过表达时，WP1130 诱导的 MM 细胞凋亡被消除。总之，这些发现表明 USP5 调节 c-Maf 的稳定性和 MM 细胞的存活。靶向 USP5/c-Maf 轴可能是 MM 治疗的一种潜在策略。
