AR Transcriptional Activation Domains in Prostate Cancer Progression

描述（由申请人提供）：雄激素耗竭可阻止雄激素的产生或作用，可作为局部晚期或转移性前列腺癌（PCa）的有效治疗方法。雄激素耗竭的主要限制是 PCa 经常复发，并具有侵袭性和致命的雄激素耗竭无关 (ADI) 表型。雄激素耗竭期间 PCa 复发的临床和实验研究表明，尽管 ADI PCa 可能不再完全依赖雄激素，但雄激素受体 (AR) 的活性对于持续生长仍然至关重要。因此，AR被认为是治疗ADI PCa的可行靶点。我们一直在研究 PCa 进展模型中 AR 激活的机制。 AR 能够在 ADI 中缺乏雄激素的情况下发挥活性，但雄激素依赖性 PCa 细胞则不能。然而，与配体诱导的 AR 激活不同，配体非依赖性 AR 激活不需要 AR C 末端结构域 (CTD) 中的 AR 配体结合/激活功能 (AF)-2 模块，而 AR C 末端结构域 (CTD) 是雄激素消耗的最终目标。相反，配体独立的 AR 活性需要在特征较差的 AR N 末端结构域 (NTD) 中存在反式激活单元 (TAU)-5。 AR TAU5 映射到一个离散的 WHTLF 基序，该基序充当新型转录激活域。重要的是，只有在 ADI PCa 细胞中，在无/低雄激素条件下，WHTLF 活性是 AR 激活所必需的。从雄激素依赖性 PCa 细胞中 AR AF-2 依赖性转录激活到 ADI PCa 细胞中 WHTLF 依赖性转录激活的转变，为 PCa 对针对 AR CTD 的治疗的耐药性提供了合理的、基于机制的解释。这种机制得到了最近发现的新型、组成型活性 AR 剪接亚型的有力支持，该剪接亚型缺乏完整的 AR CTD，并且可以在雄激素耗尽期间支持 ADI PCa 细胞的生长。因此，我们假设雄激素耗竭对 PCa 细胞施加选择性压力，将 AR 转录激活结构域依赖性从 AF-2 转变为 WHTLF，这使得 AR 能够激活靶基因并支持 PCa 的持续生长。该提案的目标是 1) 确定 AR AF-2 和 WHTLF 在支持 ADI PCa 细胞生长方面的相对作用； 2) 确定 AR WHTLF 基序激活转录的机制。总体而言，这些研究将确定离散 AR 转录激活结构域对 ADI PCa 生长的相对贡献，并鉴定介导 AR WHTLF 基序转录活性的分子。最终，这些研究将确定 WHTLF 是否可能代表一种新的功能性 AR 结构域，可用于治疗 ADI PCa。 公共健康相关性：在美国和其他工业化国家，前列腺癌是最常诊断出的男性癌症，也是男性癌症死亡的第二大原因。雄激素受体是参与前列腺癌发生、生长、治疗和进展为致命的雄激素消耗无关表型的关键调节因子。该提案的目标是确定雄激素受体支持雄激素消耗无关的前列腺癌生长的机制，并确定治疗这种疾病的新靶点。

DESCRIPTION (provided by applicant): Androgen depletion, which blocks the production or action of androgens, serves as an effective treatment for locally advanced or metastatic prostate cancer (PCa). The main limitation of androgen depletion is that PCa frequently recurs with an aggressive and lethal androgen depletion-independent (ADI) phenotype. Clinical and experimental studies of PCa recurrence during androgen depletion have revealed that although ADI PCa may no longer be fully dependent on androgens, activity of the androgen receptor (AR) remains critical for continued growth. Therefore, the AR is regarded as a viable target for treating ADI PCa. We have been studying the mechanisms of AR activation in models of PCa progression. The AR is able to achieve activity in the absence of androgens in ADI, but not androgen dependent PCa cells. However, unlike ligand-induced AR activation, ligand-independent AR activation does not require the AR ligand binding/activation function (AF)-2 module in the AR C-terminal domain (CTD), which is the ultimate target of androgen depletion. Rather, ligand- independent AR activity requires transactivation unit (TAU)-5 in the poorly-characterized AR N-terminal domain (NTD). AR TAU5 maps to a discrete WHTLF motif, which functions as a novel transcriptional activation domain. Importantly, WHTLF activity is required for AR activation under conditions of no/low androgens, only in ADI PCa cells. A shift from AR AF-2-dependent transcriptional activation in androgen-dependent PCa cells to WHTLF-dependent transcriptional activation in ADI PCa cells provides a rational, mechanism-based explanation for PCa resistance to therapies that target the AR CTD. Such a mechanism is strongly supported by the recent discovery of novel, constitutively active AR splice isoforms that lack the entire AR CTD and can support the growth of ADI PCa cells during androgen depletion. We therefore hypothesize that androgen depletion exerts a selective pressure on PCa cells to shift AR transcriptional activation domain dependence from AF-2 to WHTLF, which allows the AR to activate target genes and support continued PCa growth. The goals of this proposal are to 1) Determine the relative roles of AR AF-2 and WHTLF for supporting the growth of ADI PCa cells; and 2) Identify the mechanisms by which the AR WHTLF motif is able to activate transcription. Overall, these studies will establish the relative contributions of discrete AR transcriptional activation domains to the growth of ADI PCa, and identify molecules that mediate transcriptional activity of the AR WHTLF motif. Ultimately, these studies will determine whether WHTLF may represent a novel functional AR domain that could be targeted to treat ADI PCa. PUBLIC HEALTH RELEVANCE: In the United States and other industrialized countries, prostate cancer is the most frequently diagnosed male cancer and second leading cause of male cancer deaths. The androgen receptor is a key regulator involved in prostate cancer development, growth, treatment, and progression to a lethal androgen depletion-independent phenotype. The goal of this proposal is to define the mechanisms by which the androgen receptor supports the growth of androgen depletion-independent prostate cancer and identify novel targets to treat this disease.