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BRCA 1在细胞活动中发挥的作用以及其损伤如何导致乳腺肿瘤发生。虽然在大多数散发性乳腺癌中未发现BRCA 1突变，但其表达在20-61%的病例中下调，从而将BRCA 1缺陷与一般乳腺癌发病机制的相关性扩展。我们先前已经阐明了BRCA 1在DNA损伤反应中的作用，并通过与修复机制蛋白相互作用来保护基因组稳定性。然而，BRCA 1作为一个完整的肿瘤抑制因子，必须发挥作用，以调节细胞增殖和分化。BRCA 1如何执行这些活动尚未得到充分发展。以前，我们确定了一种新的BRCA 1相互作用蛋白，ZBRK 1，它结合到一个特定的DNA序列中发现的BRCA 1靶基因的子集，从而建立了一种方法，BRCA 1是物理和功能拴系到特定的调控位点，并作为一个共同的阻遏物。我们还证明，在乳腺上皮细胞（MEC）3-D培养物（一种体内环境的近似模拟物）中，通过RNAi消除BRCA 1、CtIP或ZBRK 1，导致MEC增殖，并通过改变包括ANG 1（血管生成素1）、HMGA 2（高迁移率族AT-钩2）等基因的表达来损害乳腺腺泡分化。这些结果强烈支持BRCA 1在调节MEC增殖和分化方面发挥关键作用。重要的是，从正常分化的MEC分泌的因子能够抑制乳腺癌细胞生长。其中，我们已经鉴定了通过半胱天冬酶介导的细胞死亡途径杀死乳腺癌细胞并在动物中以不可检测的毒性抑制致瘤性的IL 17 E（IL 25），以及也特异性抑制乳腺癌细胞生长但不抑制正常MEC的BMP 10。基于这些进展，我们提出了三个具体的目标来测试假设，BRCA 1及其相互作用的合作伙伴协调调节功能多样的基因参与增殖和分化的MEC和调制微环境如下：目的1。目的2.研究BRCA 1/ZBRK 1介导的ANG 1和HMGA 2转录抑制的方式和后果。阐明BRCA 1介导但不依赖于ZBRK 1的FGF 2、RFC 1、TIP 30和TFDP 1转录调节的调控模式;和Aim 3。鉴定分化中MEC分泌的IL-17 E和BMP 10因子对乳腺癌细胞的杀伤作用。我们期望从该提案中获得的结果将对未来乳腺癌的诊断和治疗做出重要贡献，因为这些BRCA 1调节基因本质上是致癌或肿瘤抑制基因，具有潜在的诊断和预后价值。特别是，这些特异性抑制增殖并诱导乳腺癌细胞死亡的天然因子将潜在地为治疗乳腺癌提供新的肿瘤休眠疗法。

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.