Control of TGF-Beta/Smad Signaling by mTOR in Prostate Cancer

描述（由申请人提供）：前列腺癌中mTOR对TGF-β/Smad信号传导的控制转化生长因子-β（TGF-β）被公认为是前列腺的有效肿瘤抑制因子，据信在雄激素戒断后细胞死亡的激活中起关键作用。TGF-β的功能在前列腺癌发生过程中TGF-β受体功能丧失;然而，TGF-β受体功能丧失的潜在机制仍然研究不足。大卫Danielpour博士的实验室在过去几年进行的研究表明，胰岛素样生长因子-I（IGF-I）和雄激素受体（AR）信号通路，这似乎是组成性激活在相当大的比例的前列腺肿瘤，可以阻止TGF-β信号通路的多个步骤，从而导致TGF-β的能力丧失。发挥肿瘤抑制剂的作用IGF-I/PI 3 K/Akt信号通路通常通过PTEN功能的丧失和/或IGF-I水平的升高在前列腺癌中被激活。我们发表了第一份报告，IGF-I/PI 3 K/Akt通路通过依赖于哺乳动物雷帕霉素抑制剂（mTOR）的机制抑制Smads 2和3的磷酸化激活。然而，mTOR介导这种抑制的机制尚不清楚，将按照本提案的目标1和2进行研究。这些目标将检验我们的假设，即mTOR复合物（TORC 1）直接与TGF-β受体相互作用并拦截TGF-β信号通路。目标2将在分子水平上开发mTOR如何与TGF-β受体相互作用的实质性机制见解，并能够调节TGF-β受体信号传导。来自我们实验室的最新数据表明，雷帕霉素对mTOR的抑制通过前列腺癌细胞系中Smads 1、3、5或8的c-末端磷酸化激活Smads 1、3、5或8。目的3将验证被雷帕霉素磷酸化的磷酸-Smads的身份，并测试我们的假设，即Smads 1、3、5或8对雷帕霉素对培养的前列腺癌细胞和无胸腺小鼠中前列腺肿瘤异种移植物的生长的细胞抑制作用的介导至关重要。了解PI 3 K/Akt/mTOR如何与TGF-β和BMP信号转导进行交叉对话，可能对前列腺癌具有巨大的治疗潜力。公共卫生相关性：转化生长因子-β（TGF-β）被公认为是前列腺的有效肿瘤抑制因子。TGF-β的这种功能在前列腺中通过尚未解决的方式丢失。发生这种情况的一种方式是通过肿瘤抑制基因PTEN的丢失或功能失活，据报道在30 - 50%的前列腺癌中。PTEN的缺失通过PI 3 K/Akt/mTOR信号通路激活肿瘤生长。我们的实验室首次报道Akt和mTOR信号阻断TGF-β抑制细胞生长和诱导凋亡的能力。我们已经研究了这种情况如何发生的组成部分;然而，在我们能够清楚地了解这些分子相互作用如何发生之前，还需要更多的努力。在这项研究调查中，我们建议通过在详细的分子水平上寻求解决我们模型的更基本方面来进行重大的概念性进展，重点关注mTOR对TGF-β受体信号传导的相互作用，并研究Smads的作用，TGF-β的直接介导剂。和骨形态发生蛋白，在雷帕霉素抑制mTOR的生物活性和治疗作用中，使用无胸腺小鼠作为人类前列腺肿瘤生长的宿主。了解这种串扰背后的分子细节有望对前列腺癌治疗产生重大影响。

DESCRIPTION (provided by applicant): Control of TGF-¿/Smad Signaling by mTOR in Prostate Cancer Transforming growth factor-beta (TGF-¿) is well recognized to function as a potent tumor suppressor of the prostate, where it is believed to play a pivotal role in activation of cell death following androgen withdrawal. The function of TGF- ¿ is lost during carcinogenesis of the prostate; however, the underlying mechanisms for this loss of TGF- ¿ receptor function remain poorly studied. Studies conducted in Dr. David Danielpour's laboratory in the past several years have demonstrated that both the insulin-like growth factor-I (IGF-I) and the androgen receptor (AR) signaling pathways, which appear to be constitutively activated in a sizable proportion of prostate tumors, can block multiple steps in the TGF- ¿ signaling pathway and thus contribute to loss of the ability of TGF- ¿ to function as a tumor suppressor. The IGF-I/PI3K/Akt signaling pathway is commonly activated in prostate cancer through loss of PTEN function and/or elevation of IGF-I levels. We published the first reports that the IGF-I/PI3K/Akt pathway suppresses phospho-activation of Smads 2 and 3 through a mechanism that is dependent on the mammalian inhibitor of rapamycin (mTOR). However, the mechanism by which mTOR mediates such suppression is not known, and will be investigated as detailed in Aims 1 and 2 of this proposal. These aims will test our hypothesis that an mTOR complex (TORC1) directly interacts with TGF- ¿ receptors and intercepts the TGF- ¿ signaling pathway. Aim 2 will develop substantial mechanistic insight at the molecular level of how mTOR interacts with TGF- ¿ receptors and is able to modulate TGF- ¿ receptor signaling. Recent data from our laboratory suggests that inhibition of mTOR by rapamycin activates Smads 1, 3, 5 or 8 through their c- terminal phosphorylation in prostate cancer cell lines. Aim 3 will validate the identity of the phospho-Smads that are phosphorylated by rapamycin, and test our hypothesis that Smads 1, 3, 5 or 8 are critical to mediation of the cytostatic effects of rapamycin on prostate cancer cells in culture and in growth of prostate tumor xenographs in athymic mice. Understanding the how PI3K/Akt/mTOR cross-talks with those TGF- ¿ and BMP signaling will likely have substantial therapeutic potential in prostate cancer. PUBLIC HEALTH RELEVANCE: Transforming growth factor-beta (TGF- ¿) is well recognized to function as a potent tumor suppressor of the prostate. This function of TGF- ¿ is lost in prostate through ways that remains unresolved. One way this could occur is through loss or functional inactivation of the tumor suppressor gene PTEN, reported in 30 to 50% of prostate cancers. Loss of PTEN activates tumor growth through the PI3K/Akt/mTOR signaling pathway. Our laboratory was first to report that Akt and mTOR signals intercept the ability of TGF- ¿ to suppress cell growth and induce apoptosis. We have studied components of how this may occur; however, much more effort is necessary before we can develop of clear picture of how these molecular interactions take place. In this research investigation we propose to undertake a major conceptual advance by seeking to address the more fundamental aspects of our model at a detailed molecular level, focusing on the interaction of mTOR on TGF- ¿ receptor signaling, and study the role Smads, direct mediators of TGF- ¿ and bone morphogenic proteins, in the biological activity and therapeutic action of inhibition of mTOR by rapamycin, using athymic mice as a host for growth of human prostate tumors. Understanding the molecular details behind such cross-talk is expected to substantially impact prostate cancer therapeutics.