S-adenosylmethionine (SAMe) is the principal biological methyl donor, precursor of polyamines and GSH. SAMe is made in all mammalian cells via the enzyme methionine adenosyltransferase (MAT). In liver, SAMe biosynthesis is carried out by MATI/III isoenzymes (tetramer and dimer of a1 encoded by MAT1A). Patients with chronic liver disease have reduced hepatic MAT activity and SAMe levels. We showed that mice lacking MAT1A exhibit increased oxidative stress and develop hepatocellular carcinoma (HCC) spontaneously. SAMe is widely available in the United States as a health supplement and is used therapeutically in Europe and Asia. Despite its wide usage, the molecular mechanisms of its actions are largely unclear. We have reported that many of SAMe's actions are mimicked by its metabolite methylthioadenosine (MTA). In particular, both are selectively pro-apoptotic in liver and colon cancer cells and inhibit the expression of pro-inflammatory cytokines. SAMe is a methyl donor but MTA inhibits methylation. Our accumulated results show three key post- translational protein modifications, methylation, sumoylation and phosphorylation, are dysregulated in the setting of chronic hepatic SAMe depletion that can be corrected by SAMe. There is interesting crosstalk and interplay between these pathways, which are frequently dysregulated in HCC, and are targeted by pharmacologic administration of SAMe and MTA. This application is designed to examine how hepatic SAMe deficiency impacts on these protein posttranslational modifications (PTMs) and how pharmacologic SAMe/MTA work on these pathways.
Four specific aims are proposed: 1. Define the effect of SAMe depletion on sumoylation machinery and protein PTMs. We will elucidate the effect of hepatic SAMe deficiency on sumoylation machinery and changes in the SUMO-, Ser/Thr-phospho- and methyl-proteomes. 2. Examine how SAMe depletion affects activity of MAPKs, receptor tyrosine kinases (RTKs) and Tyr-phospho- proteome. Our preliminary data indicate the activity of several MAPKs and RTKs are affected by SAMe level. We will elucidate the mechanisms involved and how SAMe level impacts on the Tyr-phosphoproteome. 3. Examine pharmacologic SAMe and MTA actions on protein PTMs. Pharmacologic SAMe and MTA reduce ubiquitin-conjugating enzyme 9 (Ubc9), the sole E2 enzyme for sumoylation, and inhibit ERK and Akt signaling. We will determine the molecule responsible, mechanisms involved, and examine their effects on protein PTMs in liver cancer cell lines and normal human intestinal epithelial cells. 4. Examine effectiveness of SAMe/MTA or sorafenib alone or in combination in HCC treatment. We will examine the efficacy of oral SAMe or MTA sorafenib versus sorafenib alone in the treatment of HCC growth and recurrence. The effect of these treatments on protein PTMs will also be examined in tumor tissues. Successful completion of these aims should enhance our knowledge of the complex interplay between the protein PTMs that is regulated by SAMe and assess SAMe/MTA efficacy in HCC treatment, topics that are highly relevant to public health.
S-adenosylmethionine (SAMe) is made in all cells and is involved in many critical reactions including control of growth and death. Patients with chronic liver disease have reduced liver SAMe level, which may predispose to them to liver injury and cancer. SAMe is widely available as a health supplement. However, its mechanisms of action and guide for therapy remain ill defined. The ultimate goal of this project is to understand how SAMe works in pathways that can lead to cancer and whether it can be useful in prevention and treatment of liver cancer.
