多发性骨髓瘤（MM）是难治性浆细胞恶性肿瘤，表现为多种染色体易位和癌基因异常表达，其中t(6;14)染色体易位引起细胞周期素CCND3的高表达。CCND3是细胞周期的重要调控因子，促进MM的增殖，并参与MM的耐药。最近发现CCND3可以被泛素连接酶FBXL2介导发生多聚泛素化并经蛋白酶体快速降解而使细胞周期停滞。而蛋白质的泛素化是一个涉及泛素连接酶和去泛素化酶的动态过程，但CCND3的去泛素化酶尚不清楚。我们前期通过免疫亲和纯化偶联质谱学和生化方法发现去泛素化酶USP10能与CCND3相互作用，使其泛素化水平下降而蛋白质稳定性升高，提示USP10可能是CCND3的去泛素化酶。为此，本项目拟通过体内外泛素化、基因敲除和过表达等方法阐明USP10介导CCND3发生去泛素化的分子机制，并分析USP10在MM细胞周期调控、细胞增殖、成瘤能力和治疗中的作用，为MM的精准治疗提供新的分子靶标。

Multiple myeloma (MM) is an incurable malignancy derived from plasma cells. MM is featured with clonal heterogeneicity including chromosomal translocations. Among the frequent translocations, t(6;14) leads to the overexpression of cyclin D3 (CCND3). CCND3 is a major D-type cyclin that binds to and activates cyclin-dependent kinases CDK4/6, thus leading to high phosphorylation of Rb and cell cycle progress, MM cell proliferation and drug resistance. It is reported that cyclin D3 stability is processed by the ubiquitin-proteasome pathway. Ubiquitination is a dynamic biochemical process that requires ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), as well as de-ubiquitinases (DUBs). A recent study found that FBXL2, a member of the F-box ubiquitin ligases, mediates CCND3 polyubiquitination and degradation, but the specific DUB of CCND3 has not been reported. In the preliminary study, the ubiquitination enzymes associated with CCND3 was identified by affinity-purification coupled tandem mass spectrometry, from which USP10, a typical ubiquitin-specific peptidase, was singled out as the candidate but the mechanisms are yet to know. To further elucidate USP10 as a DUB of CCND3, in the present proposal, we will apply a series of biochemical, genetic and biological methods to determine the specific mechanisms in which USP10 interacts with CCND3 and decreases its ubiquitination levels. The specific mechanism under which UPS10 modulates CCND3 de-ubiquitination will be extensively investigated. We will also evaluate the association between USP10 and CCND3 in myelomagenesis. Because CCND3 plays a key role in the cell cycle regulation, we will investigate the effect of USP10 in cell cycle regulation. Furthermore, targeting at the USP10/CCND3/CDK4/6 axle for MM treatment will also be examined. Finally we will measure the expression of USP10 in primary MM cells and evaluate whether USP10 is associated with the prognosis of patients with MM. The study will form a novel modulation network of cyclin D signaling. This study will help for understanding myelomagenesis and will provide a potential therapeutic target for MM.