BRCA1 MODULATES ESTROGEN RECEPTOR RESPONSE IN BREAST CAN

乳腺癌易感基因BRCA1(17q21)的突变增加了乳腺癌、卵巢癌和前列腺癌的风险。先前的研究已经确定了BRCA1在细胞周期调节、细胞凋亡和DNA损伤反应通路中的假定作用。然而，BRCA1突变导致这些特定肿瘤类型而不是广泛的癌症的原因尚不清楚。我们的初步研究表明：L)BRCA1选择性地抑制人前列腺、乳腺和宫颈癌细胞中的雌激素受体(ER)信号；以及2)在前列腺癌DU-145细胞中，p300的下调有助于BRCA1介导的ER信号的抑制。我们假设BRCA1抑制乳腺上皮中BR的活性，部分原因是调节了关键辅助因子的表达，如p300。这种对ER活性的抑制可以作为一种反馈机制，以限制雌激素刺激哺乳动物上皮细胞增殖的程度，从而抑制癌症的发生。为了检验这一假设，我们提出了三个具体目标。在SA1中，我们将扩展我们的初步研究，以检查BRCA1在不同的人类乳腺和卵巢癌细胞系中调节ER信号的能力；剖析BRCA1针对ER-α激活通路的哪个阶段(S)；并通过确定BRCA1是否抑制其他转录途径，包括非经典的ER信号通路，来研究发现的特异性。在SA2中，我们将通过基因操作p3O0的表达和活性来研究p3O0在BRCA1介导的ER信号抑制中的作用；我们还将评估其他核受体共激活因子和共抑制因子作为BRCA1调节雌激素样信号的媒介的潜在作用。在SA3中，我们将利用一系列编码截断突变和/或定点突变的BRCA1表达质粒来确定BRCA1参与ER信号通路调控的区域(S)。这些研究将建立一种机制来解释为什么BRCA1突变与乳腺癌的发生有关。他们还将确定BRCA1的下游中间体，这些中间体是乳腺癌预防和控制的潜在治疗目标。

Mutations of breast cancer susceptibility gene BRCA1 (17q21) confer an increased risk for breast, ovarian, and, possibly, prostate cancer. Prior studies have established putative roles for BRCA1 in cell cycle regulation, apoptosis, and DNA-damage response pathways. However, the reason that BRCA1 mutations result in these specific tumor types rather than a broad spectrum of cancers remains unclear. Our preliminary studies indicate that: l) BRCA1 selectively inhibits estrogen receptor (ER) signalling in human prostate, breast, and cervical cancer cells; and 2) in prostate cancer cell line DU-145, down-regulation of the p300, a transcriptional adaptor that functions as a co-activator for BR, contributes to BRCA1-mediated inhibition of ER signalling. We hypothesize that BRCA1 inhibits BR activity in mammary epithelium and that inhibition is due, in part, to modulation of expression of key co-factors, such as p300. This inhibition of ER activity could serve as a feedback mechanism to limit the extent Of estrogenic stimulation of mammal epithelial cell proliferation and, thereby, to suppress carcinogenesis. To test this hypothesis, we propose to carry out three specific aims. In SA1, we will extend our preliminary studies to examine the ability of BRCA1 to modulate ER signalling in various human breast and ovarian cancer cell lines; dissect which phase(s) of the ER-alpha activation pathway is targeted by BRCA1; and investigate the specificity of the findings by determining if BRCA1 represses other transcriptional pathways, including non-classical pathways of ER signalling. In SA2, we will examine the role of p3O0 in BRCA1-mediated inhibition of ER signalling by genetically manipulating p3O0 expression and activity; and we will assess the potential roles of other nuclear receptor coactivators and co-repressors as intermediaries through which BRCA1 regulates estrogenic signalling. In SA3, we will utilize a series of BRCA1 expression plasmids encoding truncation mutants, site-specific mutants, or both, to identify the region(s) of BRCA1 involved in modulation of ER signalling pathways. These studies will establish a mechanism to explain why BRCA1 mutations pre-dispose to breast cancer development. They will also identify down-stream intermediaries of BRCA1 that are potential therapeutic targets for breast cancer prevention and control.