The BRCA1-GADD45 Pathway and Genomic Stability

乳腺癌易感基因BRCA1与维持基因组完整性有关。然而，BRCA1在维持基因组保真度中起作用的分子机制(S)仍有待确定。有趣的是，我们小组和其他人最近的研究表明，BRCA1可以调节GADD45，这是一个由p53调节的应激诱导基因，在细胞对DNA损伤的反应中发挥重要作用。这些结果明显地将GADD45与BRCA1联系在一起，并提出了GADD45可能是BRCA1下游的效应因子，并介导了BRCA1‘S在维持基因组稳定性中的作用。因此，本研究试图明确BRCA1反式激活GADD45基因的生化机制(S)，以及BRCA1-GADD45通路在遗传毒性应激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)。目的：研究Gadd45基因是否为BRCA1‘S下游效应基因。我们将定义GADD45启动子中的BRCA1调节元件，并确定调节GADD45启动子BRCA1反式激活的蛋白质。(2)。以确定GADD45是否在BRCA1诱导的细胞凋亡中起重要作用。我们将分析GADD45和BRCA1表达对细胞凋亡的诱导作用。我们还将研究BRCA1激活的细胞凋亡和BRCA1诱导的生长抑制在GADD45缺陷细胞中的变化。(3)。我们最近的研究表明，在DNA损伤诱导的细胞凋亡过程中，BRCA1被caspase-3切割。这种DNA损伤激活的切割导致BRCA1 C末端积累了90 kDa的条带。因此，我们将首先确定在DNA损伤剂作用下BRCA1激活的细胞凋亡是否需要BRCA1的切割。我们还将确定BRCA1 C末端切割的90 kDa条带在激活细胞凋亡中的功能作用。最后，我们将分析该切割产物在GADD45启动子BRCA1反式激活中的作用。本申请中提出的研究将定义一条控制DNA损伤后细胞凋亡的新途径(BRCA1-GADD45)，并提供有关BRCA1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，前瞻性的结果也将为治疗药物的发展提供洞察力。

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.