Role of Androgen Receptor Phosphorylation in Prostate Cancer

描述(申请人提供)：雄激素受体(AR)对前列腺癌的正常发育以及前列腺癌的生长和存活是必不可少的。大多数雄激素非依赖性前列腺肿瘤继续表达AR和雄激素反应基因，尽管这些患者几乎没有循环雄激素。虽然在功能上不依赖雄激素，但晚期前列腺癌仍然依赖AR。一些研究表明：1)抑制AR的表达可以减少雄激素非依赖性前列腺癌的生长，2)AR的表达水平随着前列腺癌进展到雄激素非依赖性而增加，3)AR积累突变从而扩大激活配体的范围。因此，AR是前列腺癌进展的关键调节因子。此外，越来越清楚的是，AR不仅受到其同源类固醇激素的调节，还受到与一系列协同调节和信号分子的相互作用的影响，其中许多分子随着前列腺癌的进展而升高。AR在缺乏雄激素生理水平的情况下发挥作用的能力显然是这些替代调节事件的结果。我们的指导性假说是，AR的磷酸化在调节AR功能中起着关键作用。我们进一步假设，这些磷酸化中的一个或多个在前列腺癌中发挥作用，影响基因表达、细胞生长和/或生存。虽然人们对AR的哪些部位发生翻译后修饰知之甚少，但对这些翻译后修饰如何调节AR功能却知之甚少。通过确定AR的磷酸化如何编排AR的功能，我们可能会发现开发新的前列腺癌治疗方法的关键信息。在此之前，我们确定了AR上的主要丝氨酸磷酸化位点，并观察到多种激动剂对AR磷酸化的调节。最近，我们确定应激蛋白激酶信号调节Ser650的磷酸化，并且这种磷酸化是最佳核输出所必需的。自从我们上次提交以来，我们已经确定了两个新的候选AR激酶，并发现了这些激酶和AR磷酸化可能调节AR转录活性的证据。这些数据使我们能够加强这一修订应用的重点，并为研究AR磷酸化的功能后果和调节因素提供了坚实的基础。因此，这项工作将为了解AR的功能提供重要的见解，AR是前列腺癌进展的主要调节因素。提出了以下特异性目标：1)特异性靶1：检测CDK9对AR转录活性的影响；2)特异性靶2：确定细胞周期对AR磷酸化和转录的影响；3)特异性靶3：确定AR磷酸化在前列腺癌基因表达、生长和生存中的作用。与公共卫生相关：目前还没有有效的治疗方法来治疗耐去势转移性前列腺癌。为了开发这些疗法，我们必须了解导致前列腺癌进展的分子事件，这种疾病在功能上是“雄激素非依赖性”的，但仍需要雄激素受体(AR)。这项建议的重点是确定AR磷酸化的功能后果和调节因素。这项工作将对AR功能如何与其他细胞调节活动相结合产生重要的见解，以及在晚期雄激素非依赖性前列腺癌中更有效地针对AR和AR活性调节器的方法。

DESCRIPTION (provided by applicant): The Androgen Receptor (AR) is essential for the normal development of the prostate gland as well as for the growth and survival of prostate cancers. Most androgen-independent prostate tumors continue to express the AR as well as androgen responsive genes, despite the near absence of circulating androgen in these patients. Although functionally androgen-independent, late-stage prostate cancer is still dependent on the AR. Several studies have demonstrated that 1) inhibiting AR expression reduced the growth of androgen-independent prostate cancer, 2) AR expression levels increase with prostate cancer progression to androgen independence and 3) the AR accumulates mutations that broaden the range of activating ligands. Thus, the AR is a critical regulator of prostate cancer progression. Moreover, it is increasingly clear that the AR is regulated not only by its cognate steroid hormone, but also by interactions with a constellation of co-regulatory and signaling molecules, many of which are elevated as prostate cancer progresses. The ability of the AR to function in the absence of physiologic levels of androgen is clearly a consequence of these alternative regulatory events. Our guiding hypothesis is that AR phosphorylation plays a critical role in regulating AR function. We further hypothesize that one or more of these phosphorylations play a role in prostate cancer, affecting gene expression, cell growth, and/or survival. While much is known about which sites of the AR undergo post-translational modification, little is known about how these post-translational modifications regulate AR function. By determining how AR phosphorylation choreographs AR function, we may uncover critical information for the development of novel prostate cancer therapeutics. Previously, we identified the major serine phosphorylation sites on the AR and observed regulation of AR phosphorylation by multiple agonists. Most recently, we have determined that stress kinase signaling regulates Ser650 phosphorylation and that this phosphorylation is required for optimal nuclear export. Since our last submission, we have determined two new candidate AR kinases and uncovered evidence that these kinases and AR phosphorylations may regulate AR transcriptional activity. These data have allowed us to enhance the focus of this revised application, and provide a solid foundation for examining the functional consequences and regulators of AR phosphorylation. Thus, this work will provide important insights into the function of the AR, a major regulator of prostate cancer progression. The following specific aims are proposed: 1) Specific Aim 1: Examine the effect of AR Ser81 phosphorylation by CDK9 on AR transcriptional activity; 2) Specific Aim 2: Determine the effect of the cell cycle on AR phosphorylation and transcription; 3) Specific Aim 3: Determine the role of AR phosphorylation in gene expression, growth and survival in prostate cancer. PUBLIC HEALTH RELEVANCE: There are no effective treatments for castration-resistant metastatic prostate cancer. In order to develop these therapies we must understand the molecular events that contribute to the progression of prostate cancer to a disease that is functionally "androgen independent" but that still requires the androgen receptor (AR). This proposal focuses on identifying the functional consequences and regulators of AR phosphorylation. This work should yield significant insights into how AR function is integrated with other cell regulatory activities, and ways to more effectively target the AR and regulators of AR activity in advanced and androgen independent prostate cancer.