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

描述(申请人提供)：在前列腺癌中通过mTOR控制转化生长因子-β(TGF-β)对转化生长因子-β/Smad信号的控制被公认为是一种有效的前列腺癌肿瘤抑制因子，在雄激素停用后激活细胞死亡中起着关键作用。转化生长因子受体的功能在前列腺癌发生过程中丢失；然而，这种转化生长因子受体功能丧失的潜在机制仍未得到很好的研究。戴维·丹尼尔普尔博士的实验室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)信号通路在相当大比例的前列腺癌中似乎被结构性激活，可以阻断转化生长因子-β信号通路的多个步骤，从而导致转化生长因子-β作为肿瘤抑制因子的功能丧失。在前列腺癌中，IGF-I/PI3K/Akt信号通路通常通过PTEN功能丧失和/或IGF-I水平升高而被激活。我们首次报道了IGF-I/PI3K/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。然而，mTOR调节这种抑制的机制尚不清楚，将按照本提案的目标1和2进行详细调查。这些目的将检验我们的假设，即mTOR复合体(TORC1)直接与转化生长因子-β受体相互作用，并拦截转化生长因子-β信号通路。目标2将在分子水平上对mTOR如何与转化生长因子受体相互作用并能够调节转化生长因子受体信号进行实质性的机械性洞察。我们实验室的最新数据表明，雷帕霉素抑制mTOR通过其C端磷酸化激活前列腺癌细胞系中的Smads 1、3、5或8。目的3将验证被雷帕霉素磷酸化的Smads的身份，并验证我们的假设，即Smads 1、3、5或8在介导雷帕霉素对培养的前列腺癌细胞和裸鼠前列腺癌异种移植瘤生长的细胞抑制作用中起关键作用。了解PI3K/Akt/mTOR与这些转化生长因子-β和骨形态发生蛋白信号的相互作用可能会对前列腺癌有很大的治疗潜力。公共卫生相关性：转化生长因子-β(转化生长因子-β)被公认为是一种有效的前列腺癌抑制因子。转化生长因子-β的这一功能通过尚未解决的途径在前列腺中丧失。发生这种情况的一种方式是通过肿瘤抑制基因PTEN的缺失或功能失活，据报道，在30%到50%的前列腺癌中。PTEN的缺失通过PI3K/Akt/mTOR信号通路激活肿瘤生长。本实验室首次报道Akt和mTOR信号阻断了转化生长因子β抑制细胞生长和诱导细胞凋亡的能力。我们已经研究了如何发生这种情况的组成部分；然而，在我们能够清楚地了解这些分子相互作用是如何发生的之前，还需要付出更多的努力。在这项研究调查中，我们建议进行一项重大的概念性进展，试图在详细的分子水平上解决我们模型的更基本的方面，重点关注mTOR对转化生长因子-β受体信号的相互作用，并使用裸鼠作为人类前列腺癌生长的宿主，研究转化生长因子-β和骨形态发生蛋白的直接介导物Smads在雷帕霉素抑制mTOR的生物学活性和治疗作用中的作用。了解这种串扰背后的分子细节预计将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.