Induction of Human Methionine Adenosyltransferase 2A Expression by Tumor Necrosis Factor α

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-B and AP-1 elements, and the present study examined whether they regulate MAT2A promoter activity. We Methionine adenosyltransferase (MAT)1 is an essential cellular enzyme that catalyzes the formation of S-adenosylmethionine (SAMe), the principal biological methyl donor and the ultimate source of the propylamine moiety used in polyamine biosynthesis (1, 2). In mammals, two different genes, MAT1A and MAT2A, encode for two homologous MAT catalytic subunits, ␣1 and ␣2 (3-5). MAT1A is expressed mostly in liver, and it encodes the ␣1 subunit found in two native MAT isozymes, which are either a dimer (MAT III) or tetramer (MAT I) of this single subunit (5). MAT2A encodes for a catalytic subunit (␣2) found in a native MAT isozyme (MAT II), which is associated with a catalytically inactive regulatory subunit (␤) in lymphocytes encoded by yet a third gene (5, 6). MAT2A is widely distributed (3-5). MAT2A also predominates in the fetal liver and is progressively replaced by MAT1A during liver development (7,8). In adult liver, increased expression of MAT2A is associated with rapid growth or de-differentiation of the liver (9 -11). Using a cell line model that differs only in the type of MAT expressed, we demonstrated that a switch in MAT expression in liver cancer (from MAT1A to MAT2A) plays an important pathogenetic role by facilitating liver cancer growth (12). The influence of MAT expression on liver growth and injury was further demonstrated using a MAT1A knockout mouse model (13,14). In this model, absence of hepatic MAT1A is compensated by induction of MAT2A. These animals exhibit chronic hepatic SAMe deficiency, are prone to liver injury and develop spontaneous hepatocellular carcinoma (HCC) (13,14).Given the importance of MAT expression in liver disease and cancer, we have been interested in understanding transcriptional regulation of MAT genes. We characterized the promoter region of both human MAT genes (15, 16) and showed previously that in human HCC, both promoter hypomethylation (17) and increased expression of c-Myb and Sp1 with subsequent trans-activation of the MAT2A promoter contribute to transcriptional up-regulation of MAT2A in HCC (18). In the latter work we described increased protein binding to the MAT2A promoter region (Ϫ354 to Ϫ312) in HCC as compared with normal liver (18). Two other consensus elements in this DNase I protected region are nuclear factor kappa B (NF-B) and activator protein 1 (AP-1). We had previously observed that nuclear binding of NF-B and AP-1 to the promoter of huma...

Acute Liver Injury Induces Nucleocytoplasmic Redistribution of Hepatic Methionine Metabolism Enzymes

“…Many liver diseases associated with impairment of methionine metabolism proceed with changes in the MAT isoenzymes that are expressed (MAT1A to MAT2A switch) (7,12,14,31,33,56,61). By this expression switch, the cell changes from high-to-low V max MAT isoenzymes with the corresponding reductions in MAT activity, AdoMet levels, and the methylation index.…”

Nrf1 and Nrf2 Regulate Rat Glutamate-Cysteine Ligase Catalytic Subunit Transcription Indirectly via NF-κB and AP-1

“…Gels were dried and subjected to autoradiography. Further confirmation of the identity of the binding proteins was done by antibody supershift assays for c-Jun, c-Fos, p50, p65, Nrf1, and Nrf2 (Biotechnology, Lake Placid, NY, or Santa Cruz Biotechnology) as we described previously (36,38). To see whether Nrf1 or Nrf2 binds to the AP-1 and NF-B sites of the rat GCLC promoter, EMSA with supershift was done using DNA fragment 5Ј-CCCCTG ACGGCCCCGCCCACGAC-3Ј for the AP-1 site (Ϫ358 to Ϫ336 of rat GCLC, with the AP-1 site underlined) and 5Ј-CCGGGAACACCCACGGCCTCAAC-3Ј for the NF-B site (Ϫ380 to Ϫ358 of the rat GCLC, with the NF-B site underlined).…”

“…Electrophoretic mobility shift assays (EMSAs) for AP-1, NF-B, and ARE were done as described previously (36,38). Five to 15 g of nuclear protein from WT, F1, or F2 cells treated with TBH (60 M for 6 h) or vehicle control (dimethyl sulfoxide [DMSO]) were preincubated with 2 g of poly(dI-dC) in a buffer containing 10 mM HEPES (pH 7.6), 50 mM KCl, 0.1 mM EDTA, 1 mM dithiothreitol, 5 mM MgCl 2 , and 10% glycerol for 10 min on ice.…”

SUMOylation and phosphorylation cross-talk in hepatocellular carcinoma

“…MAT1A is a marker of normal differentiated liver, whereas MAT2A is widely distributed, and it is down-regulated in chronic liver disease and often silenced in HCC. Several studies showed a switch from MAT1A to MAT2A expression in human HCC, which facilitates cancer cell growth (23). We previously demonstrated that the expression level of UBC9 is higher in HCC and when hepatic SAMe level falls.…”