The BRCA1-GADD45 Pathway and Genomic Stability

乳腺癌易感基因BRCA 1与维持基因组完整性有关。然而，BRCA 1在维持基因组保真度中发挥作用的分子机制仍有待确定。有趣的是，我们小组和其他人最近的研究表明，BRCA 1可以调节GADD 45，这是一种p53调节的应激诱导基因，在细胞对DNA损伤的反应中起着重要作用。 这些结果明显地将GADD 45与BRCA 1联系起来，并提出了GADD 45可能是BRCA 1下游效应子并介导BRCA 1在维持基因组稳定性中的作用的可能性。 因此，本提案旨在确定BRCA 1反式激活GADD 45基因的生化机制，并确定BRCA 1-GADD 45途径在遗传毒性应激后诱导细胞凋亡中的作用。本申请中描述的长期目标将具体集中在三个关键问题上：（1）。GADD 45基因作为BRCA 1的下游效应子。 我们将定义GADD 45启动子中的BRCA 1调控元件，并鉴定调节GADD 45启动子的BRCA 1反式激活的蛋白质。 （二）、确定GADD 45是否在BRCA 1诱导的细胞凋亡中起重要作用。 我们将分析GADD 45和BRCA 1表达后细胞凋亡的诱导。我们还将研究GADD 45缺陷细胞中BRCA 1激活的凋亡和BRCA 1诱导的生长抑制的改变。 （三）、我们最近的研究表明，BRCA 1在DNA损伤诱导的细胞凋亡过程中被caspase-3切割。 这种DNA损伤激活的切割导致BRCA 1 C-末端积累90 kDa条带。 因此，我们将首先确定BRCA 1裂解是否是DNA损伤剂后BRCA 1激活的细胞凋亡所必需的。 我们还将确定BRCA 1 C-末端切割的90-kDa条带在细胞凋亡激活中的功能作用。 最后，我们将分析这种切割产物在GADD 45启动子的BRCA 1反式激活中的作用。本申请中提出的研究将定义一种控制DNA损伤后细胞凋亡的新途径（BRCA 1-GADD 45），并提供有关BRCA 1调节其靶基因的生化机制的信息。 由于细胞凋亡与治疗敏感性密切相关，因此，前瞻性结果也将为治疗药物的开发提供见解。

Breast cancer susceptibility gene, BRCA1, has been implicated in the maintenance of genomic integrity. However, the molecular mechanism(s) by which BRCA1 plays a role in maintenance of genomic fidelity remains to be defined. Interestingly, recent studies in our group and others have demonstrated that BRCA1 can regulate the GADD45, a p53-regulated stress inducible gene that plays an important role in cellular response to DNA damage. These results have evidently linked GADD45 to BRCA1 and raised the possibility that GADD45 might be a BRCA1-downstream effector and mediate BRCA1's role in maintenance of genomic stability. Therefore, this proposal seeks to define the biochemical mechanism(s) by which BRCA1 transactivates the GADD45 gene, and to define the role of the BRCA1-GADD45 pathway in the induction of apoptosis following genotoxic stress. The long-term objective described in this application will specifically focus on three key issues: (1). To characterize the GADD45 gene as a BRCA1's downstream effector. We will define the BRCA1-regulatory elements in the GADD45 promoter and identify the proteins that modulate the BRCA1 transactivation of the GADD45 promoter. (2). To define whether the GADD45 is an essential player in the BRCA1-induced apoptosis. We will analyze the induction of apoptosis following expression of GADD45 and BRCA1. We will also examine the alterations of the BRCA1-activated apoptosis and BRCA1-induced growth suppression in GADD45- deficient cells. (3). Our most recent studies demonstrated that BRCA1 is cleaved by caspase-3 during apoptosis induced by DNA damage. This DNA damage-activated cleavage results in an accumulated 90-kDa band of the BRCA1 C-terminus. Therefore, we will first determine whether the BRCA1 cleavage is required for BRCA1-activated apoptosis following DNA damaging agents. We will also determine the functional role of the cleaved 90-kDa band of the BRCA1 C-terminus in activation of apoptosis. Finally, we will analyze the role of this cleaved product in the BRCA1 transactivation of the GADD45 promoter. The studies proposed in this application would define a novel pathway (BRCA1-GADD45) controlling apoptosis following DNA damage and provide information regarding the biochemical mechanism by which BRCA1 regulates its targeted genes. Since apoptosis is closely associated with the therapeutic sensitivity, the perspective outcome will also provide insight into the development of therapeutic agents.