DESCRIPTION (provided by applicant): Liver cancer (Hepatocellular Carcinoma, HCC) is one of the leading causes of cancer mortality worldwide and unfortunately no curative therapy exists for most patients with this devastating disease because HCC is notoriously resistant to conventional chemotherapy. Thus understanding how cell growth regulation is controlled is paramount to cancer biology and the knowledge gained will facilitate rational drug design to treat HCC. Escape from cell death is a cardinal feature of the cancer cell and aversion from cell death and growth control is achieved by aberrant expression of growth and survival factors like Hepatocyte Growth Factor (HGF)-MET system. In fact overexpression or activating mutations of HGF-MET occur in a variety of human cancers including breast, colon and liver. The survival or death of cells is normally controlled by an intricate web of regulated signaling pathways intimately governed by pro-survival and pro-death ligand receptor systems. Recently it has become apparent that cell death can occur by two major disticnt programs - one called `apoptosis' which is caspase-dependent and one that is caspase-independent dubbed `programmed necrosis' or `necroptosis' (hereafter referred to as `necrosis'). RIPK1 (commonly known as Receptor Interacting Protein Kinase 1) has emerged as an important activator and executioner of necrosis. Dysregulation of cell death has dire consequences ranging from tissue degeneration to cancer. While molecular regulation of apoptosis is fairly well known, the molecular mechanisms that govern necrosis are not understood. We have recently made the novel discovery that activation of MET (a.k.a. HGFR) by its ligand HGF results in rapid recruitment of RIPK1 to the plasma membrane, RIPK1 tyrosine phosphorylation and polyubiquitination leading to inhibition of RIPK1 enzymatic activity and its degradation culminating in promotion of cell survival against necrosis. We have also discovered that RIPK1 is down regulated in human cancers including breast, colon and liver cancer (HCC). Conversely, we have discovered that blocking HGF/MET by MET inhibitors in HCC tu mor cell lines results in massive upregulation of RIPK1 and cell death. Thus, the overall goal of this proposal is to test the hypotheses that, in HCC, MET directly tyrosine phosphorylates RIPK1 inhibiting RIPK1 enzymatic activity (which is required for necrosis) and marking it for degradation thus inhibiting RIPK1- dependent HCC cell death, and that blocking the HGF-MET axis (for example, by administration of HGF-MET inhibitors) will lead to an increase in RIPK1 thus sensitizing liver cancer cells to death- inducing drugs like cisplatin. In Aim 1, we will utilize a hepatocytic cell culture system and manipulate MET and RIPK1 by genetic approaches to test our hypothesis that HGF-MET axis promotes cell survival by inhibiting RIPK1- mediated necrosis. We are the first to show that activation of MET by HGF results in rapid ty...