Corepressor Function of Steroid Receptor Coactivator-3 in Breast Cancer

 描述(申请人提供)：类固醇受体辅活化子-3(SRC-3)是第二高表达的癌基因，在乳腺癌的发展中起重要作用。尽管SRC-3作为一种癌基因很重要，但它是否以及如何促进癌症干细胞(CSCs)活性以推动侵袭性癌症的发展仍不清楚。在这项应用中，我们解决了理解SRC-3如何推动乳腺癌侵袭性发展的挑战，并揭示了SRC-3在CSCs中发挥作用的新的和意想不到的机制。有趣的是，SRC-3作为辅助抑制因子而不是辅助激活因子来抑制miR-34a的表达，miR-34a是CSCs活性的关键抑制因子。乳腺癌组织中SRC-3的表达与肿瘤分级、分期呈正相关，而与miR-34a的表达呈负相关，提示SRC-3和miR-34a的表达与疾病状态之间存在因果关系。我们的研究确定了SRC-3的第一个辅阻遏子活性，SRC-3是第一个 肿瘤干细胞中miR-34a表达的抑制子。我们的假设是，SRC-3以上下文和信号依赖的方式发挥辅助抑制因子的作用，促进CSCs的活性。本应用的目的是确定SRC-3的辅抑制子功能的机制，并阐明这种辅抑制子功能在乳腺癌进展中的意义。我们提出三个目标来实现我们的目标。目的1.阐明SRC-3非预期辅抑制子功能的机制。为了了解miR-34a是如何被抑制的，转录抑制因子X1(RFX1)和S505上SRC-3的去磷酸化被确定为CSCs中抑制miR-34a的潜在决定因素。我们的目标是阐明S505的去磷酸化是如何决定SRC-3和RFX1在CSCs中抑制miR-34a的。目的2.确定SRC-3 S505去磷酸化在肿瘤干细胞中的功能。SRC-3和RFX1被确定为miR-34a的新抑制因子，重要的是，抑制miR-34a需要SRC-3 S505的去磷酸化。本研究的目的是证明S505的去磷酸化在SRC-3/RFX1促进CSCs功能的能力中起重要作用。目的3.阐明HSP70K246去乙酰化的功能重要性。CSCs在治疗耐药中发挥重要作用。阐明SRC-3-miR-34a CSCs通路的耐药机制具有重要意义。我们确定HDAC1和HDAC7是miR-34a的新靶点，并表明HDACs1和7在K246处对HSP70进行去乙酰化。我们的目的是证明HDACs1和7通过去乙酰化HSP70 K246来促进SRC-3-miR-34a CSCs通路的耐药活性，并确定K246去乙酰化的耐药机制。我们的研究具有创新性。它发现了一个新的辅阻遏子活性，它调控了CSCs中致癌辅活化子SRC-3的功能，并揭示了转录抑制子RFX1和S505的去磷酸化的重要作用。我们的研究有望对靶向癌症治疗的诊断和发展产生重大影响，以治疗侵袭性和治疗耐药的乳腺癌。

 DESCRIPTION (provided by applicant): Steroid receptor coactivator-3 (SRC-3) is the second most overexpressed oncogene that plays a significant role in the development of breast cancer. Despite its importance as an oncogene, whether and how SRC-3 promotes cancer stem cells (CSCs) activity to drive aggressive cancer development remains unknown. In this application, we address the challenge of understanding how SRC-3 drives aggressive breast cancer development, and uncover a novel and unexpected mechanism for the function of SRC-3 in CSCs. Interestingly, SRC-3 functions as a corepressor and not a coactivator to suppress expression of miR-34a, a critical suppressor of CSCs' activity. Expression of SRC-3 is positively correlated with tumor grades and stages, but inversely correlated with expression of miR-34a in breast cancer, suggesting a causal relationship between SRC-3 and miR-34a expression and disease state. Our study identifies the first corepressor activity of SRC-3, and SRC-3 as the first suppressor of miR-34a expression in CSCs. Our hypothesis is that SRC-3 functions as a corepressor in a context- and signaling-dependent manner to promote CSCs activity. The objective of this application is to identify the mechanism which dictates the corepressor function of SRC-3, and to elucidate the significance of this corepressor function in the progression of breast cancer. We propose three aims to achieve our objective. Aim 1. Elucidate the mechanism for the unexpected corepressor function of SRC-3. To understand how miR-34a is suppressed, transcription repressor regulatory factor X1 (RFX1) and de-phosphorylation of SRC-3 at S505 were identified as potential determinants for the suppression of miR-34a in CSCs. Our objective is to elucidate how de-phosphorylation of S505 dictates the suppression of miR-34a by SRC-3 and RFX1 in CSCs. Aim 2. Determine the function of SRC-3 S505 de-phosphorylation in cancer stem cells. SRC-3 and RFX1 are identified to be novel suppressors of miR-34a, and importantly, suppression of miR-34a requires de-phosphorylation of SRC-3 S505. The objective of this aim is to demonstrate that de-phosphorylation of S505 plays an important role in the ability of SRC-3/RFX1 to promote CSCs function. Aim 3. Elucidate the functional importance of HSP70 K246 deacetylation. CSCs play an important role in therapy resistance. Elucidating the therapy resistant mechanism of SRC-3-miR-34a CSCs pathway is clearly important. We identified HDAC1 and HDAC7 as novel targets of miR-34a, and showed that HDACs1 and 7 deacetylate HSP70 at K246. Our objective is to demonstrate that HDACs1 and 7 promote the therapy resistant activity of SRC-3-miR-34a CSCs pathway by deacetylating HSP70 K246, and to identify the resistant mechanism of K246 deacetylation. Our study is innovative. It uncovers a novel corepressor activity that governs the function of oncogenic coactivator SRC-3 in CSCs, and reveals an important role of transcriptional repressor RFX1 and de-phosphorylation of S505. Our study is expected to have a significant impact on the diagnosis and development of targeted cancer therapy to treat aggressive and therapy resistant breast cancer.