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

描述（由申请人提供）：随着上皮细胞进展为癌，增加的自分泌TGF-β信号传导通过诱导可导致上皮-间充质转化（EMT）的上皮可塑性反应在癌症进展中起重要作用。EMT导致细胞去粘附和增加的细胞运动性和侵袭性，这是癌细胞转移的先决条件。 肿瘤干细胞是肿瘤干细胞的重要组成部分。由于TGF-β信号驱动EMT，TGF-β反应有助于癌症进展，我们一直在研究TGF-β信号的调节，因为它与上皮可塑性有关。 研究充分的Smad信号通路调节基因表达以响应TGF-β，但TGF-β诱导的上皮可塑性反应不能仅仅通过基因调控的变化来解释。因此，TGF-β诱导的非Smad信号转导受到越来越多的重视。在该基金的支持下，我们一直在研究TGF-β诱导的Erk MAPK和PI 3 K-Akt-mTOR通路的激活，并开始研究它们在EMT中的作用。TGF-β诱导的任一途径在上皮可塑性反应中的激活的具体作用仍有待进一步确定。我们还发现，细胞通过调节细胞表面的TGF-β受体水平来调节其对TGF-β的反应性。增加的葡萄糖水平和胰岛素激活细胞表面TGF-β受体的上调，这似乎是由Akt激活和Rab GT3激活蛋白AS 160介导的，后者是Akt磷酸化的直接靶点。我们假设Akt激活的增加，如癌中常见的，或由葡萄糖或胰岛素刺激增加引起的，增强了细胞的TGF-β反应性，以及癌细胞对EMT的敏感性和易感性，因此可能通过增强TGF-β反应性促进癌症进展。 我们现在寻求继续我们的研究计划，旨在表征非Smad信号传导机制在控制细胞表面TGF-β受体水平、产生TGF-β反应性和TGF-β诱导的EMT中的作用。本课题的主要研究内容包括：（1）研究葡萄糖或胰岛素对TGF-β信号通路、上皮-间质转化、肿瘤干细胞生成和EMT依赖性肿瘤进展的影响;（2）阐明Akt激活后TGF-β受体在细胞表面表达的分子调控机制;（3）探讨TGF-β诱导的Erk MAPK和PI 3 K-Akt通路在上皮间质转化和肿瘤干细胞生成中的作用。 我们的研究应该为TGF-β反应性的调节和TGF-β诱导的非Smad信号在细胞TGF-β反应中的作用提供新的机制见解，特别是在EMT和癌症干细胞生成中。这些见解可能通过增加TGF-β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Akt信号传导增加的新作用，这在癌症中很常见，从而通过增强TGF-β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.