Androgen Control of TGF-beta signaling

描述(申请人提供)：转化生长因子-β(转化生长因子-β)是一种25 kDa的多功能自分泌/旁分泌多肽，对上皮细胞的生长抑制和凋亡具有很强的活性。在前列腺中，雄激素去势诱导了转化生长因子-β蛋白及其受体的表达，这与前列腺组织中伴随发生的细胞凋亡相一致。前列腺细胞在癌变过程中失去对雄激素的依赖，并对转化生长因子-β反应产生抵抗力，其机制仍有待确定。进一步支持转化生长因子-β在前列腺癌中的肿瘤抑制作用的研究来自我们通过逆转录病毒转导显性阴性的TbetaRII来阻断两个非致瘤细胞系(NRP-152和DP-153)中的转化生长因子-β信号，并显示了随后对转化生长因子-β触发恶性转化的反应丧失。转化生长因子-β受体表达缺失是转化生长因子-β耐药的多种潜在机制之一。其他途径可能涉及某些癌基因的激活，这些癌基因在不同水平上拦截转化生长因子-β信号。我们最近报道，DHT可以通过AR和Smad3之间的联系直接阻断转化生长因子-β信号转导，导致LNCaP和NRP-154前列腺上皮细胞Smad3的转录失活。我们用EMSA提供了证据，证明AR的抑制作用是通过阻断Smad3与靶基因的Smad结合元件(SBE)的结合来实现的。在此，我们拟研究：1)DHT/AR对转化生长因子-β(或活性Smad3)诱导的生长停滞和细胞凋亡的影响；2)DHT/AR诱导的转化生长因子-β基因的表达；3)AR与Smad3结合的结构/功能基础；4)AR共激活子作为共调节因子或Smad3通过AR可能发挥的作用；5)AR与Smad3在不同的非致瘤和致瘤细胞系中相互作用的差异。我们相信，这些研究肯定会对前列腺癌的治疗干预产生影响。

DESCRIPTION (provided by applicant): Transforming growth factor-betas (TGF-betas) are 25 kDa multifunctional autocrine/paracrine peptides with potent activity on growth suppression and apoptosis of epithelial cells. In the prostate, expression of TGF-beta protein and their receptors are induced upon androgen ablation, coincident with apoptotic cell death that occurs concomitantly in this tissue. Prostatic cells lose dependence on androgens and become resistant to TGF-beta responses during carcinogenesis, through mechanisms that remain to be defined. Further support for a tumor suppressor role of TGF-beta in the prostate comes from studies where we ablated TGF-beta signaling in two non-tumorigenic cell lines (NRP-152 and DP-153) by retroviral transduction of a dominant-negative TbetaRII, and showed the consequent loss of response to TGF-beta triggers malignant transformation. Loss of TGF-beta receptor expression is one of many potential mechanisms of TGF-beta resistance. Other pathways may involve activation of certain oncogenes that intercept TGF-beta signals at various levels. We have recently reported that DHT can directly block TGF-beta signaling through an association between AR and Smad3, leading to the transcriptional inactivation of Smad3 in LNCaP and NRP-154 prostatic epithelial cells. We provide evidence using EMSAs that AR's inhibitory effect is through blocking the binding of Smad3 to Smad Binding Elements (SBE) of target genes. Here we propose to investigate:1) the effects of DHT/AR on growth arrest and apoptosis induced by TGF-beta (or active Smad3), 2) expression of TGF-beta inducible genes by DHT/AR, 3) the structure/functional basis behind the binding of AR to Smad3, 4) possible function of AR co-activators as co-regulators or Smad3 through AR, and 5) differences in the interaction of AR with Smad3 in various nontumorigenic and tumorigenic cell lines. We believe these studies will most certainly impact on the therapeutic intervention of prostate cancer.