BRCA1负调控因子-E3连接酶的分离及其功能研究

BRCA1 is a key tumor suppressor, mutation of which or loss of function strongly predisposes women to breast and ovarian cancer. BRCA1 participates in various cellular processes including DNA damage repair, cell cycle and checkpoint control as well as mitosis, playing important roles in the maintenance of genome integrity and tumor suppression. As a key tumor suppressor, the protein level of BRCA1 is tightly regulated and turnover of BRCA1 directly affects the execution of its various functions and antitumor activities. One of the main pathways for the regulation of BRCA1 protein levels is ubiquitin-proteasome system, in which many E3 ligases may directly target BRCA1 for ubiquitination and subsequent proteasomal degradation, playing critical roles in the regulation and equilibrium of BRCA1, and therefore could be potential breast tumor-related genes. However, the identities and functions of these molecules remain undetermined. In this proposal, we will aim to isolate and characterize these potential E3 ligases and to investigate their roles in the regulation of BRCA1 protein level as well as its function. This study will also promote the identification of novel members in the BRCA1 tumor suppression network, providing new insight on the mechanisms underlying tumorigenesis of breast cancer, and has important implications in the prevention, treatment of breast cancer as well as in the development of novel antitumor drugs.

BRCA1是一个重要的抑癌分子，BRCA1突变、缺失或功能异常是乳腺癌和卵巢癌发病的重要原因。BRCA1参与DNA损伤修复、细胞周期和检验点调控以及有丝分裂等多种细胞生理生化过程，在维护细胞基因组稳定性和抑制乳腺癌的发生中起重要作用。作为一个关键的抑癌分子，BRCA1蛋白质水平在细胞内受到精密调控。BRCA1的蛋白质水平和维持及其转换对于其功能的行使和抑癌功能的实现至关重要。泛素-蛋白酶体途径是调控BRCA1水平的一种重要方式。许多泛素E3连接酶可能参与对BRCA1分子的修饰和降解，在调控和平衡细胞中BRCA1的水平中发挥重要作用，因而也是潜在的乳腺癌相关基因。目前对于这些分子的身份及其功能并不清楚。本研究拟分离和鉴定这些BRCA1负性调控因子，揭示其调控BRCA1的分子机制。这项研究对于阐明BRCA1的功能和抑癌机理、分离新的乳腺癌相关基因，以及乳腺癌的防治和抗癌药物研发等都具有重要意义

BRCA1是一个重要的抑癌分子，参与DNA损伤修复、细胞周期和检验点调控等诸多重要过程，在维护细胞基因组稳定性和抑制乳腺癌的发生中起重要作用。作为一个重要的肿瘤抑制因子，BRCA1蛋白质水平受严格的调控，其蛋白质水平的异常直接影响其在细胞中的功能。的确，BRCA1突变或其蛋白质水平异常与乳腺癌发生高度相关。揭示细胞内BRCA1蛋白质水平的调控机制，对于解析BRCA1的调控机制和阐明乳腺癌发病机理具有重要意义。本项目通过一系列方法分离和鉴定了BRCA1的负性调控因子，即负责其降解的E3连接酶HUWE1，揭示了其可以与BRCA1相互作用，并通过对BRCA1泛素化介导其蛋白酶体降解的机制。进一步研究发现，BARD1可以抑制HUWE1泛素E3酶活性，从而保护BRCA1免受HUWE1的降解，从而达到稳定BRCA1的作用。重要的是BARD1 Q564H突变体不具备上述功能。上述研究揭示了BRCA1稳定性调控的新机制，也为进一步阐明BARD1 Q564H致癌机理提供了依据。本项目还发现，泛素化酶CUL4B在DNA损伤条件下可以被nedd8修饰活化，介导对HUWE1的泛素化及其蛋白酶体降解。抑制Cul4B可以稳定HUWE1,在一定水平影响 BRCA1的介导的细胞对DNA损伤试剂的敏感性，以及促进HUWE1对MCL-1的降解，促进细胞凋亡。有意思的是，我们最新研究发现，CUL4复合物可以直接作用于BRCA1/BARD1，参与对其蛋白质水平进行调控。上述研究表明，BRCA1水平的维持和调控受包括 HUWE1 、CUL4和BARD1等多种蛋白E3酶的严密的调控，而这些酶之间也存在着彼此的相互作用。因此进一步解析CUL4-HUWE1-BRCA1-BARD1这个轴心的调控机制，对于阐明BRCA1蛋白质水平的调控和乳腺癌的发生机制具有深远的意义。

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