MECHANISMS ON THE REGULATION OF PTEN

描述(由申请人提供)： PI的目的是阐明转化生长因子-β对PTEN表达的调节作用机制，这对于理解胰腺恶性肿瘤的发病机制至关重要。我们的初步数据表明，转化生长因子-β通过SMAD依赖和非依赖途径影响PTEN的激活、稳定性和转录。我们的总体假设是，转化生长因子-β调节胰腺癌中PTEN的表达，并将转化生长因子-β从肿瘤抑制因子转化为肿瘤促进剂。我们的具体目标集中在这一假说上，该假说旨在确定转化生长因子-β双重功能作用的机制。我们的第一个目标是研究K-RAS如何调节转化生长因子-β诱导的、依赖SMAD的PTEN表达，因为K-RAS在90%的胰腺癌中被激活。初步数据表明，抑制致癌的K-RAS可以改善SMAD的核转位，并逆转转化生长因子-β诱导的PTEN抑制。我们认为这种PTEN上调是SMAD依赖的信号抑制肿瘤的关键。我们的第二个目标是研究转化生长因子-β诱导的PTEN在翻译后水平的调节。根据我们的数据，转化生长因子-β在降低胰腺癌中的PTEN方面至少有两个作用--抑制PTEN转录和减少胞浆PTEN池。等电点将决定酪蛋白激酶是否调节PTEN的稳定性，以及转化生长因子-β诱导的酪蛋白激酶下调是否会影响PTEN的C末端磷酸化。我们的第三个目标是研究转化生长因子-β诱导的不依赖于SMAD的PTEN表达，特别是关注作为中介的核因子-kB。在我们的胰腺细胞模型中，转化生长因子-β诱导的PTEN抑制发生在(A)Smad4缺失细胞和(B)致癌K-RAS细胞中，基本上完全抑制了SMAD依赖的信号转导。我们从我们的数据中推断，NF-kB是这一SMAD非依赖途径的一个很好的候选者。这些研究的策略将结合药理学、分子和生化方法来表征胰腺癌中调节PTEN表达的途径。这些研究将为调控转化生长因子-β对PTEN表达的调控作用的精确机制提供新的见解。本研究将探索对胰腺癌患者的基本认识和治疗方法，为该院的癌症研究发展提供优秀的指导性项目。

DESCRIPTION (provided by applicant): The goal of the PI is to elucidate the mechanisms of the modulatory action of TGF-beta on PTEN expression that is critical to understand the pathogenesis of malignant pancreatic tumors. Our preliminary data show that TGF-beta functionally affects activation, stability, and transcription of PTEN via SMAD-dependent and - independent pathways. Our overall hypothesis is that TGF-beta modulates PTEN expression in pancreatic cancer, and this modulation converts TGF-beta from a tumor suppressor to a tumor promoter. Our Specific Aims center on this hypothesis, which are designed to determine the mechansims for the dual functional roles of TGF-beta. Our first aim studies how K-RAS modulates TGF-beta-induced, SMAD-dependent PTEN expression, as K-RAS is activated in >90% of pancreatic cancers. Preliminary data indicate that inhibition of oncogenic K-RAS improves SMAD nuclear translocation and reverses TGF-beta-induced PTEN suppression. We suggest that this PTEN upregulation is key to SMAD-dependent signaling being tumor suppressive. Our second aim studies TGF-beta-induced regulation of PTEN at post-translational levels. Based on our data, TGF-beta has at least two effects on reducing PTEN in pancreatic cancer - suppression of PTEN transcription and reduction of the cytoplasmic PTEN pool. The PI will determine if casein kinase regulates PTEN stability, and whether C-terminus phosphorylation of PTEN can be affected by TGF-beta- induced downregulation of casein kinase. Our third aim examines TGF-beta-induced PTEN expression that is SMAD-independent, and particularly focuses on NF-kB as the mediator. TGF-beta-induced PTEN suppression in our pancreatic cell models occurred in (a) SMAD4-null cells, and (b) with oncogenic K-RAS, essentially completely inhibiting SMAD-dependent signaling. We infer from our data that NF-kB is an excellent candidate for this SMAD-independent pathway. The strategy for these studies will combine pharmacological, molecular, and biochemical approaches to characterize pathways that regulate PTEN expression in pancreatic cancer. These studies should provide novel insights into the precise mechanisms that regulate the modulatory effect of the TGF-beta on PTEN expression. The research proposed here will explore basic understanding and treatment to patients with pancreatic cancer, and serve as an outstanding mentored project for the Pi's cancer research development.