BRCA1 MODULATES ESTROGEN RECEPTOR RESPONSE IN BREAST CAN

乳腺癌易感基因BRCA 1（17 q21）的突变增加了患乳腺癌、卵巢癌和前列腺癌的风险。 先前的研究已经确定了BRCA 1在细胞周期调控、细胞凋亡和DNA损伤反应途径中的假定作用。然而，BRCA 1突变导致这些特定肿瘤类型而不是广谱癌症的原因仍不清楚。我们的初步研究表明：1）BRCA 1选择性抑制人前列腺癌、乳腺癌和宫颈癌细胞中的雌激素受体（ER）信号传导; 2）在前列腺癌细胞系DU-145中，下调p300（一种作为BR共激活剂的转录衔接子）有助于BRCA 1介导的ER信号传导抑制。我们假设BRCA 1抑制乳腺上皮细胞中的BR活性，并且这种抑制部分是由于调节关键辅因子（如p300）的表达。ER活性的这种抑制可以作为反馈机制来限制哺乳动物上皮细胞增殖的雌激素刺激的程度，从而抑制癌发生。为了验证这一假设，我们提出了三个具体目标。在SA 1中，我们将扩展我们的初步研究，以检查BRCA 1在各种人类乳腺癌和卵巢癌细胞系中调节ER信号传导的能力;剖析BRCA 1靶向ER-α激活途径的哪个阶段;并通过确定BRCA 1是否抑制其他转录途径（包括ER信号传导的非经典途径）来研究结果的特异性。在SA 2中，我们将通过遗传操纵p3 O 0表达和活性来研究p3 O 0在BRCA 1介导的ER信号传导抑制中的作用;我们将评估其他核受体辅激活因子和辅抑制因子作为BRCA 1调节雌激素信号传导的中介体的潜在作用。在SA 3中，我们将利用一系列编码截短突变体、位点特异性突变体或两者的BRCA 1表达质粒来鉴定参与ER信号通路调节的BRCA 1区域。这些研究将建立一种机制来解释为什么BRCA 1突变易患乳腺癌。他们还将确定BRCA 1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靶点。

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.