title: Induction of human methionine adenosyltransferase 2A expression by tumor necrosis factor alpha. Role of NF-kappa B and AP-1.
abstract: Two genes (MAT1A and MAT2A) encode for methionine adenosyltransferase (MAT), an essential cellular enzyme responsible for S-adenosylmethionine biosynthesis. MAT1A is expressed mostly in the liver, whereas MAT2A is widely distributed. We showed a switch from MAT1A to MAT2A expression in human hepatocellular carcinoma (HCC), which facilitates cancer cell growth. Using DNase I footprinting analysis, we previously identified a region in the MAT2A promoter protected from DNase I digestion in HCC. This region contains NF-kappa B and AP-1 elements, and the present study examined whether they regulate MAT2A promoter activity. We found nuclear binding of NF-kappa B and AP-1 to the MAT2A promoter increased in HCC. Tumor necrosis factor alpha (TNFalpha), which activates both NF-kappa B and AP-1, increased MAT2A expression in a dose- and time-dependent manner, binding of both NF-kappa B and AP-1 to the MAT2A promoter and MAT2A promoter activity, with the latter effect blocked by site-directed mutagenesis of the NF-kappa B and AP-1 binding sites. Blocking NF-kappa B with I kappa B super-repressor or AP-1 with dominant-negative c-Jun led to decreased basal MAT2A expression and prevented the TNF alpha-induced increase in MAT2A expression. Although blocking NF-kappa B had no influence on the ability of TNF alpha to increase AP-1 nuclear binding, blocking AP-1 with dominant-negative c-Jun prevented the TNF alpha-mediated increase in NF-kappa B binding. In conclusion, both NF-kappa B and AP-1 are required for basal MAT2A expression in HepG2 cells and mediate the increase in MAT2A expression in response to TNF alpha treatment. Increased trans-activation of these two sites also contributes to MAT2A up-regulation in HCC.
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Liver Disease Research Center, USC-UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Heping
authors.initials: H
authors.lastname: Yang
authors.forename: Mamatha R
authors.initials: MR
authors.lastname: Sadda
authors.forename: Victor
authors.initials: V
authors.lastname: Yu
authors.forename: Ying
authors.initials: Y
authors.lastname: Zeng
authors.forename: Taunia D
authors.initials: TD
authors.lastname: Lee
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Ou
authors.forename: Lixin
authors.initials: L
authors.lastname: Chen
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
mesh_terms: D001665:Binding Sites / Q000235:genetics; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000473:pathology; D005786:Gene Expression Regulation; D006801:Humans; D008099:Liver / Q000166:cytology / Q000201:enzymology / Q000473:pathology; D008716:Methionine Adenosyltransferase / Q000096:biosynthesis* / Q000235:genetics; D016328:NF-kappa B / Q000502:physiology*; D011401:Promoter Regions, Genetic; D016755:Proto-Oncogene Proteins c-jun / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D016328:NF-kappa B; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D014409:Tumor Necrosis Factor-alpha; D008716:Methionine Adenosyltransferase