NF-kappaB Regulation by Androgen Receptor

描述(由申请人提供)： 雄激素受体(AR)是类固醇受体超家族转录因子的一员。与该家族的其他成员一样，AR主要通过与特定配体的相互作用来调节。因此，雄激素与AR结合，导致核转位，与转录共激活因子相互作用，并通过与相关基因启动子中的雄激素受体反应元件(ARs)结合来刺激特定基因的表达，从而控制基因表达。有趣的是，雄激素已经被证明可以抑制基因的表达，但与这一过程相关的机制却知之甚少。虽然有越来越多的证据表明AR功能的复杂调控不依赖于雄激素，但对AR影响可能影响生长或肿瘤发生的不同调控途径的能力知之甚少。在这方面，前列腺癌发展为一种雄激素依赖型癌症。由于标准形式的癌症治疗无效，雄激素消融仍然是晚期前列腺癌患者唯一有效的系统治疗形式。不幸的是，雄激素非依赖性癌症的进展发生在雄激素停用后的几年内，这与极差的治疗选择和负面预后有关。由于AR介导的基因激活似乎在雄激素依赖和雄激素非依赖性肿瘤中都存在，因此推测AR反应的异常有助于雄激素非依赖性肿瘤的复发。 转录因子NF-kappaB通过控制细胞因子、细胞因子受体和趋化因子基因的表达，被认为是免疫和炎症反应的关键调节因子。此外，核因子-kappaB是一种强有力的细胞凋亡抑制因子，可通过上调细胞周期蛋白D1等基因促进细胞增殖。与这些观点一致的是，核因子-kappaB被认为是关节炎和炎症性肠病等炎症性疾病的关键效应因子。重要的是，核因子-kappaB现在被认为在包括鳞状细胞癌、乳腺癌和多发性骨髓瘤在内的许多癌症中都是重要的。核因子-kappaB的活性在两个水平上被控制。一种机制涉及与一种称为IkappaB的抑制蛋白的相互作用，另一种机制涉及控制反式激活潜能的核因子-kappaB的p65亚单位的直接磷酸化。在每种情况下，IkappaB激酶(IKK)通过其磷酸化IkappaB的能力，导致其泛素化和降解，以及通过其磷酸化丝氨酸536上的p65，来控制NF-kappaB的活性。 我们的初步数据表明，雄激素通过抑制IkappaBalpha的降解来有效地抑制核因子-KB的激活。此外，我们提供的证据表明，丝氨酸536上p65的磷酸化，这一过程与IKK相关，并伴随着增强的反式激活潜力，在雄激素受体缺失的细胞和雄激素非依赖性前列腺癌样本中上调。这一设想的基本假设是，雄激素激活的AR通常通过控制IkappaB-α的降解和抑制p65的磷酸化来抑制NF-kappaB的激活。基于这些发现，我们还假设，向雄激素非依赖性前列腺癌的转变与这种对核因子-kappaB功能的控制的丧失有关，从而使与核因子-kappaB相关的致癌机制得以体现。该应用程序的目标是确定雄激素激活的AR如何阻断核因子-kappaB，重点是对IKK的直接调节和上游信号成分，并确定核因子-kappaB在雄激素非依赖性前列腺癌中是否功能上调。这些实验有可能在与雄激素/AR信号相关的调节级联中识别新的靶点，并可能确定治疗雄激素非依赖性癌症的新靶点。

DESCRIPTION (provided by applicant): The androgen receptor (AR) is a member of the steroid receptor superfamily of transcription factors. Like other members of the family, AR is regulated primarily through interactions with a specific ligand. Thus androgens bind to AR leading to nuclear translocation, interaction with transcriptional coactivators, and control of gene expression through binding to androgen receptor response elements (AREs) in the promoters of relevant genes to stimulate specific gene expression. Interestingly, androgens have been shown to inhibit gene expression but the mechanisms associated with this process are poorly understood. While there is growing evidence of complex regulation of AR function which occurs independent of androgens, less is known about the ability of AR to affect distinct regulatory pathways that may impact growth or oncogenesis. In this regard, prostate cancer develops as an androgen-dependent cancer. Androgen ablation remains the only effective form of systemic therapy for patients with advanced prostate cancer due to the ineffectiveness of standard forms of cancer therapy. Unfortunately, progression to androgen-independent cancer occurs within a few years of androgen withdrawal and this is associated with extremely poor therapeutic options and with negative prognosis. Because AR-mediated gene activation appears to occur in both androgen-dependent and androgen-independent cancer, it is assumed that aberrant AR responses contribute to the recurrent, androgen-independent tumor. The transcription factor NF-kappaB is considered a key modulator of the immune and inflammatory response through its ability to control expression of genes encoding cytokines, cytokine receptors, and chemokines. Additionally NF-kappaB is a potent inhibitor of apoptosis and can promote cell proliferation through the upregulation of genes such as cyclin D1. Consistent with these points, NF-kappaB is considered a key effector of inflammatory diseases such as arthritis and inflammatory bowel disease. Importantly, NF-kappaB is now recognized as important in a number of cancers including squamous cell carcinoma, breast cancer, and multiple myeloma. The activity of NF-kappaB is controlled at two levels. One mechanism involves interactions with an inhibitory protein known as IkappaB and another mechanism involves direct phosphorylation of the p65 subunit of NF-kappaB which controls transactivation potential. In each case, the IkappaB kinase (IKK) controls the activity of NF-kappaB through its ability to phosphorylate IkappaB, leading to its ubiquitination and degradation, and through its ability to phosphorylate p65 on serine 536. Our preliminary data indicate that androgens potently suppress NF-KB activation through a mechanism which involves inhibition of IkappaBalpha degradation. Additionally, we provide evidence that the phosphorylation of p65 on serine 536, a process associated with IKK and with enhanced transactivation potential, is upregulated in androgen-receptor null cells and in androgen-independent prostate cancer samples. The underlying hypothesis of this proposal is that androgen-activated AR normally functions to suppress NF-kappaB activation through control of IkappaB-alpha degradation and inhibition of phosphorylation of p65. Based on the findings, we also hypothesize that the transition to androgen-independent prostate cancer is associated with a loss of this control on NF-kappaB function, allowing the oncogenic mechanisms associated with NF-kappaB to be manifested. The goals of the application are to determine how androgen activated AR blocks NF-kappaB, with a focus on direct regulation of IKK and on upstream signaling components, and to determine if NF-kappaB is functionally upregulated in androgen-independent prostate cancer. The experiments have the potential to identify a new target in the regulatory cascade associated with androgen/AR signaling and to possibly identify a new target for treatment of androgen-independent cancer.