Transcriptional Role of BRCA1 in Breast Cancer

描述（由申请人提供）：我们的长期目标是了解BRCA1在细胞活动中的作用以及它的损伤如何导致乳腺肿瘤发生。尽管在大多数散发性乳腺癌中未发现BRCA1突变，但在20-61%的病例中，其表达下调，这扩大了BRCA1缺陷与乳腺癌一般发病机制的相关性。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增殖和分化。BRCA1如何执行这些活动尚未得到充分研究。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BRCA1在物理和功能上与特定调控位点结合并作为共同抑制因子的方法。我们还证明，在模拟体内环境的乳腺上皮细胞（MECs） 3d培养中，RNAi对BRCA1、CtIP或ZBRK1的消耗会导致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BRCA1在MEC增殖和分化中起关键作用。重要的是，正常分化MEC分泌的因子能够抑制乳腺癌细胞的生长。其中，我们发现IL17E （IL25）通过caspase介导的细胞死亡途径杀死乳腺癌细胞，并在动物中抑制致瘤性，但毒性检测不到；BMP10也特异性抑制乳腺癌细胞生长，但不抑制正常的MEC。基于这些进展，我们提出了三个具体目标来验证BRCA1及其相互作用伙伴协调调节mec增殖和分化以及调节微环境的功能多样基因的假设：研究BRCA1/ZBRK1介导的ANG1和HMGA2转录抑制的模式和后果；目标2。阐明brca1介导但不依赖ZBRK1的FGF2、RFC1、TIP30和TFDP1的转录调节模式；和Aim 3。鉴定分化MEC分泌的IL-17E和BMP10杀死乳腺癌细胞的因子。我们期望从该提案中获得的结果将对乳腺癌的未来诊断和治疗做出重大贡献，因为这些brca1调节基因在本质上是致癌的或肿瘤抑制的，具有潜在的诊断和预后价值。特别是这些特异性抑制乳腺癌细胞增殖和诱导乳腺癌细胞死亡的自然因子，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.