Expression of Phosphatidylethanolamine N-Methyltransferase in Human Hepatocellular Carcinomas

Abstract

Objective: Hepatic phosphatidylethanolamine is converted into phosphatidylcholine by the enzyme phosphatidylethanolamine N-methyltransferase (PEMT) when the dietary choline supply is inadequate. Our previous reports implicated PEMT in the regulation of hepatocyte growth and transformation. In the present study, we analyzed PEMT activity, Pempt gene status and its mRNA expression in 29 human hepatocellular carcinomas (HCC). Methods: The status of the Pempt gene and PEMT2 mRNA expression were evaluated with Southern and Northern blotting, respectively, in HCC and the noninvolved liver. PEMT activity was assessed by biochemical assay. Cell proliferation markers were defined by immunohistochemical or histoautoradiographic methods. Results: PEMT activity was lower in HCC than in the noninvolved liver and it was negligible in 62% of the tumors. No deletions or mutations of the Pempt gene were found and PEMT2 mRNA expression was absent or reduced in HCC compared with peritumoral liver tissue. PEMT2 mRNA expression was inversely related to tumor proliferation and to histologic grade. Patients whose HCC did not express PEMT2 mRNA showed poorer outcomes for cancer-related survival than those with PEMT2-positive HCC. Conclusions: The present findings suggest that (1) clones lacking PEMT2 expression may have been selected during liver tumorigenesis and progression, and (2) PEMT2 expression seems to be associated with clinical progression.