Regulatory non-Smad signaling in TGF-b-induced epithelial-mesenchymal transition

描述(申请人提供)：随着上皮细胞进展为癌症，增加的自分泌转化生长因子-β信号在癌症进展中获得显著作用，通过诱导可导致上皮细胞-间充质转化(EMT)的上皮可塑性反应。EMT导致细胞去黏附，增加细胞的运动性和侵袭性，这是癌细胞的先决条件 扩散，并越来越多地被视为癌症干细胞的一个不可或缺的属性。由于转化生长因子-β信号驱动EMT，转化生长因子-β反应促进肿瘤进展，我们一直在研究转化生长因子-β信号的调节，因为它与上皮的可塑性有关。 Smad信号通路调节基因表达以响应转化生长因子β，但转化生长因子β诱导的上皮可塑性反应不能仅仅用基因调控的变化来解释。因此，转化生长因子β诱导的非Smad信号转导受到越来越多的重视。在这笔赠款的支持下，我们一直在研究转化生长因子β诱导的Erk MAPK和PI3K-Akt-mTor通路的激活，并开始研究它们在EMT中的作用。转化生长因子-β诱导的这两条通路中任一条通路在上皮可塑性反应中的具体作用仍有待进一步研究。我们还发现，细胞通过调节细胞内储存的细胞表面的转化生长因子受体水平来调节其对转化生长因子-β的反应。葡萄糖水平和胰岛素水平的增加激活了细胞表面转化生长因子受体的上调，这似乎是由Akt激活和Akt磷酸化的直接靶点Rab GTPase激活蛋白AS160介导的。我们推测，在癌症中常见的Akt激活增加，或由于葡萄糖或胰岛素刺激增加而导致的Akt激活，增强了细胞的转化生长因子-β反应，以及癌细胞对EMT的敏感性和易感性，从而可能通过增强转化生长因子-β反应促进癌症进展。 我们现在寻求继续我们的研究计划，旨在表征非Smad信号机制在控制细胞表面转化生长因子受体水平和由此产生的转化生长因子受体反应性中的作用，以及在转化生长因子β诱导的内皮细胞转化中的作用。我们将当前和未来的研究安排在三个目标上：(1)研究葡萄糖或胰岛素对转化生长因子-β信号转导、上皮-间充质转化、肿瘤干细胞生成和EMT依赖的癌症进展的影响；(2)确定Akt激活后调节细胞表面转化生长因子-β受体的分子机制；(3)确定转化生长因子β诱导的ERK MAPK和PI3K-Akt通路激活在上皮-间充质转化和肿瘤干细胞生成中的作用。 我们的研究将为调节转化生长因子β的反应性以及转化生长因子β诱导的非Smad信号在细胞转化生长因子β反应中的作用，特别是在EMT和肿瘤干细胞生成中的作用提供新的机制见解。这些见解可能通过增加转化生长因子-β的反应性，将高血糖或胰岛素治疗与癌症进展联系起来，并揭示了癌症中常见的Akt信号增加的新作用，从而通过增强转化生长因子-β的反应性促进癌症进展。

DESCRIPTION (provided by applicant): As epithelial cells progress to carcinomas, increased autocrine TGF-¿ signaling acquires a prominent role in cancer progression, by inducing an epithelial plasticity response that can lead to epithelial-mesenchymal transition (EMT). EMT results in cell de-adhesion and increased cell motility and invasion, a prerequisite of cancer cell dissemination, and is increasingly seen as an integral property of carcinoma stem cells. As TGF-¿ signaling drives EMT, and TGF-¿ responsiveness contributes to cancer progression, we have been studying the regulation of TGF-¿ signaling, as it pertains to epithelial plasticity. The well-studied Smad signaling pathway regulates gene expression in response to TGF-¿, but the TGF-¿- induced epithelial plasticity response cannot be explained merely by changes in gene regulation. Accordingly, TGF-¿-induced non-Smad signaling has received increasing appreciation. Supported by this grant, we have been studying the TGF-¿-induced activation of the Erk MAPK and PI3K-Akt-mTOR pathways, and have started addressing their roles in EMT. The specific roles of TGF-¿-induced activation of either pathway in the epithelial plasticity response remain to be further defined. We also found that cells regulate their responsiveness to TGF-¿, by regulating the TGF-¿ receptor levels at the cell surface from intracellular stores. Increased glucose levels and insulin activate this upregulation of cell surfae TGF-¿ receptors, which appears to be mediated by Akt activation and the Rab GTPase activating protein AS160, a direct target of Akt phosphorylation. We hypothesize that increased Akt activation, as commonly seen in carcinomas, or resulting from increased glucose or insulin stimulation, enhances the cell's TGF-¿ responsiveness, and the sensitivity and susceptibility of cancer cells to EMT, and thus may promote cancer progression by enhancing TGF-¿ responsiveness. We now seek to continue our research program aimed at characterizing the roles of non-Smad signaling mechanisms in the control of the cell surface TGF-¿ receptor levels, and resulting TGF-¿ responsiveness, and in TGF-¿-induced EMT. We organized our current and future research in three Aims: (1) To study the effects of glucose or insulin on TGF-¿ signaling, epithelial-mesenchymal transition, cancer stem cell generation and EMT-dependent cancer progression; (2) To define the molecular mechanisms regulating the cell surface presentation of the TGF-¿ receptors in response to Akt activation; (3) To define the roles of TGF-¿-induced Erk MAPK and PI3K-Akt pathway activation in epithelial-mesenchymal transition, and cancer stem cell generation. Our studies should provide novel mechanistic insights into the regulation of TGF-¿ responsiveness and the roles of TGF-¿-induced non-Smad signaling in the cellular TGF-¿ response, in particular in EMT and cancer stem cell generation. These insights may link hyperglycemia or insulin treatment with cancer progression, through increased TGF-¿ responsiveness, and reveal a new role for the increased Akt signaling that is commonly seen in carcinomas, thus contributing to cancer progression by enhancing TGF-¿ responsiveness.