AR Transcriptional Activation Domains in Prostate Cancer Progression

描述(申请人提供)：雄激素耗竭，阻止雄激素的产生或作用，是局部晚期或转移性前列腺癌(PCA)的有效治疗方法。雄激素耗竭的主要局限性是PCa经常复发，表现为侵袭性和致死性雄激素耗竭非依赖性(ADI)表型。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)的活性仍然是持续生长的关键。因此，AR被认为是治疗ADI Pca的一个可行的靶点。我们一直在研究主成分分析进展模型中AR激活的机制。AR能够在ADI细胞中没有雄激素的情况下实现活动，但不能在雄激素依赖的PCa细胞中实现活动。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CTD是雄激素耗竭的最终靶点。相反，非配体依赖的AR活性需要在特征不佳的AR N末端结构域(NTD)上的反式激活单元(TAU)-5。AR TAU5映射到一个离散的WHTLF基序，该基序的功能是一个新的转录激活结构域。重要的是，只有在ADI PCA细胞中，WHTLF活性才是AR在NO/低雄激素条件下激活所必需的。在雄激素依赖的PCa细胞中，从依赖AR AF-2的转录激活转变为ADI PCA细胞中依赖WHTLF的转录激活，这为PCa对以AR CTD为靶点的治疗耐药提供了一个合理的、基于机制的解释。这种机制得到了最近发现的新的、具有结构性活性的AR剪接异构体的有力支持，这些剪接异构体缺乏完整的AR CTD，并且可以在雄激素耗竭期间支持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，使其将AR转录激活结构域依赖从AF-2转移到WHTLF，从而允许AR激活靶基因并支持PCa的持续生长。该建议的目标是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基序能够激活转录的机制。总体而言，这些研究将建立离散的AR转录激活结构域对ADI PCA生长的相对贡献，并确定介导AR WHTLF基序转录活性的分子。最终，这些研究将确定WHTLF是否代表了一个新的功能AR结构域，可以作为治疗ADI PCA的靶点。 公共卫生相关性：在美国和其他工业化国家，前列腺癌是最常见的男性癌症，是男性癌症死亡的第二大原因。雄激素受体是前列腺癌发生、生长、治疗和向雄激素耗竭非致命性表型发展的关键调节因子。这项建议的目标是确定雄激素受体支持雄激素耗竭非依赖性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.