BRCA1 Modulates Estrogen Receptor Response in Cancer

简介(申请人提供)：背景。乳腺癌易感基因-1(BRCA1)的遗传突变会增加特定肿瘤类型的风险，包括乳腺癌和卵巢癌。BRCA1在DNA修复、细胞周期进程、细胞凋亡和基因转录等方面发挥着重要的调节作用。但这些通用的作用并不能解释为什么BRCA1突变会导致特定的肿瘤类型，比如乳腺癌。我们一直在研究BRCA1的乳腺组织特异性作用，即它抑制雌激素受体(ER-α信号)的能力，这可能部分解释了BRCA1突变与雌激素(E2)依赖的肿瘤类型(如乳腺癌、子宫内膜癌和宫颈癌)相关的原因。 初步研究。在最初的资助期间，我们在理解BRCA1调节雌激素作用的机制方面已经完成并超越了最初提出的目标。在新的初步研究中，我们以高分辨率绘制了BRCA1和ER-α蛋白之间的相互作用位点。我们列举了BRCA1的ER-α调节功能失活的两种不同机制的证据：1)通过致癌信号通路(例如，细胞周期蛋白D1、c-Myc和c-Akt激酶的过度表达)；2)通过ER-α铰链区域内的乙酰化位点的肿瘤相关突变。最后，我们获得了外源性E2诱导BRCA1基因缺陷小鼠乳腺增生和乳癌发生的初步证据。 假设。BRCA1预防乳腺癌，部分是通过抑制ER-α的活性，部分是通过雌激素(E2)非依赖的作用(即，通过其作为“看守”基因的功能，以防止基因组不稳定)。BRCA1的E2依赖功能和E2非依赖功能是不同的，在结构上是可以分离的。最后，BRCA1抑制ER-α的能力可以被癌蛋白和生长因子信号通路功能失活。 研究目的。该项目的主要目标是：SA1。为了准确确定BRCA1：ER-α相互作用的分子决定因素；SA2。目的：探讨癌基因信号转导解救BRCA1对ER-α抑制的机制。SA3.确定乙酰化在调节ER-α抵抗BRCA1和SA4抑制中的作用。目的：探讨雌激素与BRCA1在体内乳腺肿瘤发生中的相互作用。 意义重大。这些研究解决了BRCA1失活导致乳腺癌的一个主要机制：即ER-α信号的解除调控。它们与遗传性和散发性乳腺癌的发病机制有关。因此，散发性乳腺癌经常表现出BRCA1的表达缺失或降低；我们发现，通过RNA干扰抑制内源性BRCA1会导致ER-α的配体无关激活。除了它们对乳腺癌发病机制的影响外，这些研究还具有实际意义，因为它们可能为乳腺癌的预防和治疗提供新的方法。

DESCRIPTION (provided by applicant): Background. Inherited mutations of the breast cancer susceptibility gene-1 (BRCA1) confer a high risk for specific tumor types, including breast and ovarian cancers. BRCA1 plays roles in the regulation of DNA repair, cell cycle progression, apoptosis, and gene transcription. But these generic actions do not explain why BRCA1 mutations lead to specific tumor types, such as breast cancer. We have been studying a mammary tissue-specific action of BRCA1 [ie., its ability to repress estrogen receptor (ER-alpha signaling) that may, in part, explain why BRCA1 mutations are associated with estrogen (E2)-dependent tumor types (eg., breast, endometrial, and cervical cancers). Preliminary Studies. During the initial funding period, we have completed and gone beyond the original proposed objectives in understanding the mechanisms by which the BRCA1 regulates estrogen action. In new preliminary studies, we mapped the interacting sites between the BRCA1 and ER-alpha proteins at a high resolution. And we adduced evidence for two distinct mechanisms by which the ER-alpha regulatory function of BRCA1 can be inactivated: 1) through oncogenic signaling pathways (eg., over-expression of cyclin D1, c-Myc, and the c-Akt kinase); and 2) via a tumor-associated mutation of an acetylation site within the hinge region of ER-alpha. Finally, we generated preliminary evidence that exogenous E2 induces mammary hyperplasia and preneoplasia in Brca1-deficient mice. Hypothesis. BRCA1 prevents breast cancer, in part, by inhibition of ER-alpha activity and, in part, by estrogen (E2)-independent actions (ie., by its function as a "caretaker" gene, to prevent genomic instability). The E2-dependent and E2-independent functions of BRCA1 are distinct and can be structurally dissociated. Finally, the ability of BRCA1 to repress ER-alpha can be functionally inactivated by oncoproteins and growth factor signaling pathways. Research Aims. The major goals of this project are: SA1. To precisely identify the molecular determinants of the BRCA1:ER-alpha interaction; SA2. To determine the mechanisms by which oncogene signaling rescues BRCA1 inhibition of ER-alpha. SA3. To determine the role of acetylation in regulating ER-alpha resistance to inhibition by BRCA1; and SA4. To examine the interaction between estrogen and Brca1 in mammary tumorigenesis in vivo. Significance. These studies address a major mechanism by which BRCA1 inactivation leads to breast cancer: namely, deregulation of ER-alpha signaling. They are relevant to the pathogenesis of both hereditary and sporadic breast cancers. Thus, sporadic breast cancers frequently exhibit absent or reduced expression of BRCA1; and we found that knockdown of endogenous BRCA1 by RNA interference causes ligand-independent activation of ER-alpha. In addition to their implications for breast cancer pathogenesis, these studies are of practical importance, since they may suggest novel approaches for breast cancer prevention and treatment.