Transcriptional Role of BRCA1 in Breast Cancer

描述(申请人提供)：我们的长期目标是了解BRCA1在细胞活动中扮演的角色，以及它的损伤如何导致乳腺肿瘤的发生。虽然在大多数散发性乳腺癌中没有发现BRCA1突变，但它的表达在20%-61%的病例中下调，这扩大了BRCA1缺陷与一般乳腺癌发病机制的相关性。我们之前已经阐明了BRCA1通过与修复机制蛋白相互作用而在DNA损伤反应和保护基因组稳定性中的作用。然而，BRCA1作为一个完整的肿瘤抑制因子，必须调节细胞的增殖和分化。BRCA1如何执行此类活动尚未得到充分开发。在此之前，我们发现了一种新的BRCA1相互作用蛋白ZBRK1，它与BRCA1靶基因子集中发现的特定DNA序列结合，从而建立了一种BRCA1在物理和功能上与特定调控基因位点挂钩并作为共抑制因子的手段。我们还证明了乳腺上皮细胞(MECs)3-D培养中BRCA1、CtIP或ZBRK1的RNAi缺失，导致MEC增殖，并通过改变Ang1(Angiopoietin1)、HMGA2(High Mobility Group AT-Hook 2)等基因的表达而损害乳腺腺泡分化。这些结果有力地支持了BRCA1在MEC的增殖和分化中起关键作用。重要的是，正常分化的MEC分泌的因子能够抑制乳腺癌细胞的生长。其中，IL17E(IL25)通过caspase介导的细胞死亡途径杀死乳腺癌细胞，并在动物体内以不可检测的毒性抑制致瘤性；BMP10也特异性地抑制乳腺癌细胞的生长，但不能抑制正常的MEC。目的1.研究BRCA1/ZBRK1介导的Ang1和HMGA2转录抑制的方式和结果；目的2.阐明BRCA1介导但ZBRK1不依赖于ZBRK1的调控方式，对FGF2、Rfc1、TIP30和TFDP1的转录调控；以及3.研究分化中的MEC分泌的IL-17E和BMP10因子对乳腺癌细胞的杀伤作用。我们期望从这项建议中获得的结果将对未来乳腺癌的诊断和治疗做出重大贡献，因为这些BRCA1调节的基因本质上是致癌或抑瘤的，具有潜在的诊断和预后价值。特别是，这些特异性抑制增殖和诱导乳腺癌细胞死亡的自然因素将有可能为乳腺癌的治疗提供一种新的肿瘤休眠疗法。

DESCRIPTION (provided by applicant): Our long-term goal is to understand which roles BRCA1 plays in cellular activities and how its impairment leads to breast tumorigenesis. Although no BRCA1 mutation is found in the majority of sporadic breast cancers, its expression is down-regulated in 20-61% of the cases, extending the relevance of BRCA1 deficiency to the general breast cancer pathogenesis. We have previously elucidated the role of BRCA1 in DNA damage response and guarding genome stability through interacting with repair machinery proteins. However, BRCA1 as a full tumor suppressor must act to modulate cellular proliferation and differentiation. How BRCA1 executes such activities has not been fully developed. Previously, we identified a novel BRCA1-interacting protein, ZBRK1, which binds to a specific DNA sequence found in a subset of BRCA1 target genes, thus establishing a means by which BRCA1 is physically and functionally tethered to particular regulatory loci and serves as a co-repressor. We have also demonstrated that depletion of BRCA1, CtIP or ZBRK1 by RNAi in mammary epithelial cells (MECs) 3-D culture, a close mimicry of an in vivo environment, leads to MEC proliferation and impairs mammary acinus differentiation by altering the expression of genes including ANG1 (Angiopoietin1), HMGA2 (High Mobility Group AT-hook 2) and others. These results strongly support that BRCA1 has a critical role in governing MEC proliferation and differentiation. Importantly, factors secreted from normal differentiating MEC are able to inhibit breast cancer cell growth. Among these, we have identified IL17E (IL25) that kills breast cancer cells through caspase-mediated cell death pathway and inhibits tumorigenicity with non-detectable toxicity in animals, and BMP10 that also specifically inhibits breast cancer cell growth but not normal MEC. Based on these advances, we propose three specific aims to test the hypothesize that BRCA1 and its interacting partners coordinately regulate functionally diverse genes involved in proliferation and differentiation of MECs and modulating the microenvironment as follows: Aim 1. To study the mode and consequence of transcriptional repression of ANG1 and HMGA2 mediated by BRCA1/ZBRK1; Aim 2. To elucidate regulatory modes of BRCA1-mediated, but ZBRK1 independent, transcriptional modulation of FGF2, RFC1, TIP30 and TFDP1; and Aim 3. To characterize factors of IL-17E and BMP10 secreted from differentiating MEC that kill breast cancer cells. We expect that the results obtained from this proposal will contribute significant to the future diagnosis and treatment of breast cancer because these BRCA1-modulated genes are oncogenic or tumor-suppressive in nature and have potential diagnostic and prognostic values. Especially, these natural factors that specifically suppress proliferation and induce breast cancer cell death will potentially provide a novel tumor dormancy therapy for treating breast cancer.