AR Transcriptional Activation Domains in Prostate Cancer Progression

描述（由申请人提供）：雄激素耗竭可阻断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。雄激素耗竭的主要限制是PCa经常复发，具有侵袭性和致死性雄激素耗竭非依赖性（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可能不再完全依赖于雄激素，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。我们一直在研究前列腺癌进展模型中AR激活的机制。AR能够在ADI中不存在雄激素的情况下实现活性，但不能在雄激素依赖性PCa细胞中实现活性。然而，与配体诱导的AR活化不同，配体非依赖性AR活化不需要AR C末端结构域（CTD）中的AR配体结合/活化功能（AF）-2模块，其是雄激素耗竭的最终靶标。相反，配体非依赖性AR活性需要在表征不佳的AR N-末端结构域（NTD）中的反式激活单元（TAU）-5。AR TAU 5映射到一个离散的WHTLF基序，其功能是一个新的转录激活结构域。重要的是，WHTLF活性是在无/低雄激素条件下AR激活所必需的，仅在ADI PCa细胞中。从雄激素依赖性PCa细胞中的AR AF-2依赖性转录激活到ADI PCa细胞中的WHTLF依赖性转录激活的转变为PCa对靶向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的组成型活性AR剪接异构体的有力支持，这些异构体缺乏整个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，将AR转录激活结构域依赖性从AF-2转移到WHTLF，这使得AR能够激活靶基因并支持PCa的持续生长。本提案的目标是1）确定AR AF-2和WHTLF支持ADI PCa细胞生长的相对作用;和2）鉴定AR WHTLF基序能够激活转录的机制。总之，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，可以靶向治疗ADI PCa。 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，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展、生长、治疗和进展为致死性雄激素耗竭非依赖性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.