The role of c-Myb and Sp1 in the up-regulation of methionine adenosyltransferase 2A gene expression in human hepatocellular carcinoma

Liver-specific and non-liver-specific methionine adenosyltransferase (MAT) are products of two genes, MAT1A and MAT2A, respectively, that catalyze the formation of S-adenosylmethionine. We showed a switch from MAT1A to MAT2A expression at the transcriptional level in human hepatocellular carcinoma ( HCC) that facilitates cancer cell growth. The purpose of the present study was to better understand the molecular mechanism of increased MAT2A express ion in HCC. In vitro DNase I footprinting analysis revealed two protected s ites (-354 to -312 and -73 to -28) using nuclear proteins from HCC and HepG 2 cells, but not normal liver. These sites are also protected in HepG2 cell s on in vivo DNase I footprinting analysis. These protected sites contain c onsensus binding sites for c-Myb and Sp1. In HCC, the mRNA levels of c-myb and Sp1 and binding to their respective sites increased. Mutation of the c- Myb or Sp1 site reduced MAT2A promoter activity by 67% and 50%, respectivel y. The importance of these cis-acting elements and trans-activating factors was confirmed using heterologous promoter and expression vectors. Increase d expression of c-Myb and Sp1 and binding to the MAT2A promoter contribute to transcriptional up-regulation of MAT2A in HCC.