Mechanisms of Met Induced Hepatocytes Survival

描述(申请人提供)：逃脱凋亡是来自肝脏肿瘤和其他恶性肿瘤的癌细胞的基本特征。肝细胞生长因子受体(HGFR)又称Met，是一种跨膜受体酪氨酸激酶(RTK)，在促进肝细胞存活和增殖中发挥重要作用，在包括肝细胞癌在内的多种人类肿瘤组织和细胞系中过表达。了解肝癌发生的分子机制是NIDDK的一项关键倡议(即，肝病研究行动计划)。通过结构-功能研究，我们发现人Met胞内区的C末端含有一个新的串联Caspase-3裂解位点，我们称之为Met Caspase诱骗位点(MCDS)。其序列如下：DNAD(DEVD(TRPASFWETS((表示caspase裂解位点)。我们在A2续订申请中要检验的中心假设是，通过含有一个独特的caspase底物诱骗基序(MCDs)，人Met的细胞质尾巴作为一个‘诱饵’发挥作用，并通过在切割过程中形成一个稳定的过渡态中间产物来捕获Caspase-3的活性部位。从而抑制Caspase-3活性，抵抗细胞凋亡，促进肝细胞癌的发生。计划采用最先进的分子生化和生物学方法来测试这一有趣的假说。在目标1中，我们将通过功能丧失和功能获得的方法，研究Met Caspase诱骗位点(MCDS)在抑制和促进Caspase-3的肝细胞存活和肝癌发生中的功能作用。在目标2中，我们将评估MCDS-Caspase-3相互作用和Caspase-3抑制的分子机制。在目标3中，我们将确定MCDS的功能是否取决于Met的激活状态。从这些研究中，我们应该对一种以前从未描述过的支持生存的新机制有了实质性的见解。 公共卫生相关性：肝细胞癌是最致命的癌症之一(仅次于胰腺癌)。目前还没有有效的治疗方法，因为这些肿瘤对化疗药物具有耐药性，化疗药物主要通过诱导细胞凋亡(或程序性细胞死亡)来杀死细胞。我们已经发现，Met是一种致癌蛋白质，它劫持了导致细胞死亡的细胞凋亡机制(称为caspase的专门酶)，从而有助于癌细胞的存活和长寿。我们将探讨Met抑制半胱氨酸氨基转移酶的分子机制。总之，我们提出的研究将对肝癌生长和细胞存活的分子机制建立新的见解。它们可能为合理的药物设计(即模拟Met caspase诱骗位点的药物)开辟道路，以治疗从肝炎到肝细胞癌的各种肝病。

DESCRIPTION (provided by applicant): Escape from apoptosis is a cardinal feature of cancer cells derived from liver tumors and other malignancies. The Hepatocyte Growth Factor Receptor (HGFR) known as Met is a transmembrane receptor tyrosine kinase (RTK) that plays an important role in promoting hepatocyte survival and proliferation, and it is overexpressed in various human carcinoma tissues and cell lines including hepatocellular carcinoma (HCC). Understanding the molecular mechanisms of HCC development is a key NIDDK initiative (i.e., the Action Plan for Liver Disease Research). Using structure-function studies, we discovered that the C-terminal end of human Met's intracellular domain harbors a novel tandem Caspase-3 cleavage site which we named the Met Caspase Decoy Site (MCDS). It has the following sequence: DNAD(DEVD(TRPASFWETS ((denotes the caspase cleavage site). Our central hypothesis to be tested in this A2 Renewal Application is that, by virtue of harboring a unique caspase substrate decoy motif (MCDS), the cytoplasmic tail of human Met functions as a 'bait' and traps the active site of Caspase-3 by forming a stable transition state intermediate during the cleavage process. This results in inhibition of Caspase-3 activity, apoptosis resistance and promotion of HCC. State-of-the-art molecular biochemical and biological approaches are planned to test this intriguing hypothesis. In Aim 1, we will investigate the functional role of the Met Caspase Decoy Site (MCDS) in Caspase-3 inhibition and promotion of hepatocyte survival and hepatocarcinogenesis using loss-of-function and gain-of-function approaches. In Aim 2, we will assess the molecular mechanisms involved in MCDS-Caspase-3 interaction and Caspase-3 inhibition. In Aim 3, we will determine whether MCDS function depends on the activation status of Met. From these studies, we should gather substantial insight into a novel pro-survival mechanism never before described. PUBLIC HEALTH RELEVANCE: Hepatocellular carcinoma (HCC) is the one of most lethal forms of cancer (only second to pancreatic adenocarcinoma). No effective treatment for HCC exists as these tumors are notorious for being resistant to chemotherapeutic agents which kill cells mainly via induction of apoptosis (or programmed cell death). We have discovered that Met, a cancer-causing protein, highjacks the cellular apoptotic machinery (specialized enzymes called caspases) that causes cell death hence contributing to survival and longevity of cancer cells. We will look at the molecular mechanisms of caspase inhibition by Met. Collectively our proposed studies will establish novel insights into the molecular mechanisms of HCC growth and cell survival. They may open avenues for rational drug design (i.e. drugs that mimic Met caspase decoy site) to treat liver diseases ranging from hepatitis to HCC.