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.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA095782-10
Application #
8469000
Study Section
Tumor Cell Biology Study Section (TCB)
Program Officer
Salnikow, Konstantin
Project Start
2002-02-15
Project End
2014-05-31
Budget Start
2013-06-01
Budget End
2014-05-31
Support Year
10
Fiscal Year
2013
Total Cost
$309,137
Indirect Cost
$105,086
Name
University of Pittsburgh
Department
Pathology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Ma, Jihong; Zou, Chunbin; Guo, Lida et al. (2014) Novel Death Defying Domain in Met entraps the active site of caspase-3 and blocks apoptosis in hepatocytes. Hepatology 59:2010-21
Dai, James Y; DeFrances, Marie C; Zou, Chunbin et al. (2009) The Met protooncogene is a transcriptional target of NF kappaB: implications for cell survival. J Cell Biochem 107:1222-36
Zou, Chunbin; Ma, Jihong; Wang, Xue et al. (2007) Lack of Fas antagonism by Met in human fatty liver disease. Nat Med 13:1078-85
Wang, Xue; DeFrances, Marie C; Dai, Yu et al. (2002) A mechanism of cell survival: sequestration of Fas by the HGF receptor Met. Mol Cell 9:411-21