BRCA1 and Transcriptional Control in DNA Damage Response

我们的主要目标是了解人类乳腺癌易感基因(BRCA1)的失活如何导致乳腺肿瘤的发生。BRCA1通过双重参与DNA双链断裂修复和DNA损伤诱导基因的转录调控，确保全球基因组的稳定性。这项建议旨在了解BRCA1的看守功能是如何通过其在转录控制中的作用来实现的。BRCA1及其相关的辅阻遏子CtIP已被证明抑制GADD45基因的转录，GADD45基因在G2/M细胞周期检查点控制中发挥作用。最近，我们发现了一种新的蛋白质ZBRK1，它与存在于DNA损伤诱导的BRCA1靶基因子集中的特定DNA序列元件结合，并通过其同源结合部位以BRCA1依赖的方式抑制转录。基于这些初步观察，我们假设在没有遗传毒性应激的情况下，ZBRK1、BRCA1和CtIP协同抑制一组功能不同的DNA损伤反应基因。为了支持我们的假设，我们提出了以下目的：在分子细节上定义和表征ZBRK1作为聚合在BRCA1和CtIP上的DNA损伤诱导信号与其下游效应器转录控制之间的直接联系的生物学作用。目的1.确定ZBRK1和BRCA1在包括GADD45和MnSOD基因在内的多种DNA损伤反应基因的转录调控中的作用。目的2阐明电离辐射(IR)诱导的位点特异性磷酸化在体内ZBRK1与其相关的共抑制物BRCA1和CtIP功能相互作用网络中的作用。目的3是通过相应基因的种系失活，确定CTiP和Zbrk1在小鼠IR反应中的生物学作用。这些研究可能会揭示BRCA1，可能还有ZBRK1和CtIP在维持基因组稳定性方面的潜在基础，并为未来乳腺癌的干预提供明确的分子靶点。

Our major goal is to understand how inactivation of the human breast cancer susceptibility gene (BRCA1) leads to breast tumorigenesis. BRCA1 ensures global genome stability through its dual participation in DNA double-strand break repair and transcriptional regulation of DNA damage-inducible genes. This proposal aims to understand how the caretaker function of BRCA1 is subserved by its role in transcription control. BRCA1 and its associated corepressor CtIP have been shown to repress transcription of the GADD45 gene that functions in G2/M cell cycle checkpoint control. Recently, we discovered ZBRK1, a novel protein, that binds to a specific DNA sequence element present in a subset of DNA damage-inducible BRCA1 target genes and represses transcription through its cognate binding site in a BRCA1- dependent manner. Based upon these preliminary observations, we hypothesize that ZBRK1, BRCA1, and CtIP coordinately repress a functionally diverse group of DNA damage-response genes in the absence of genotoxic stress. To provide support for our hypothesis, we propose the following Aims to define and characterize in molecular detail the biological role ZBRK1 as a direct link between DNA damage induced signals that converge on BRCA1 and CtIP and transcriptional control of their downstream effectors. Aim 1. is to establish the role of ZBRK1 and BRCA1 in the coordinate transcriptional regulation of functionally diverse DNA damage-response genes including GADD45 and MnSOD genes. Aim 2 is to elucidate the role of ionizing radiation (IR)-induced site-specific phosphorylation on the network of functional interactions between ZBRK1 and its associated co-repressors BRCA1 and CtIP in vivo. And Aim 3 is to establish the biological role of Ctip and Zbrk1 in response to IR in mice by germline inactivation of each corresponding gene. These studies will likely reveal novel insight into the underlying basis for the caretaker properties of BRCA1, and possibly ZBRK1 and CtIP, in preserving genomic stability and provide defined molecular targets for future intervention of breast cancer.