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Ou X, Yang H, Ramani K, Ara A, Chen H, Mato J, Lu S. Inhibition of human betaine-homocysteine methyltransferase expression by S-adenosylmethionine and methylthioadenosine. Biochem J 2007; 401:87-96. [PMID: 16953798 PMCID: PMC1698693 DOI: 10.1042/bj20061119] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BHMT (betaine-homocysteine methyltransferase) remethylates homocysteine to form methionine. SAM (S-adenosylmethionine) inhibits BHMT activity, but whether SAM modulates BHMT gene expression is unknown. Transcriptional regulation of the human BHMT is also unknown. The present study examined regulation of the human BHMT gene by SAM and its metabolite, MTA (5'-methylthioadenosine). To facilitate these studies, we cloned the 2.7 kb 5'-flanking region of the human BHMT gene (GenBank accession number AY325901). Both SAM and MTA treatment of HepG2 cells resulted in a dose- and time-dependent decrease in BHMT mRNA levels, which paralleled their effects on the BHMT promoter activity. Maximal suppression was observed with the BHMT promoter construct -347/+33, which contains a number of NF-kappaB (nuclear factor kappaB) binding sites. SAM and MTA treatment increased NF-kappaB nuclear binding and NF-kappaB-driven luciferase activities, and increased nuclear binding activity of multiple histone deacetylase co-repressors to the NF-kappaB sites. Overexpression of p50 and p65 decreased BHMT promoter activity, while blocking NF-kappaB activation increased BHMT expression and promoter activity, and prevented SAM but not MTA's ability to inhibit BHMT expression. The NF-kappaB binding site at -301 is responsible, at least in part, for this effect. Lower BHMT expression can impair homocysteine metabolism, which can induce ER (endoplasmic reticulum) stress. Indeed, MTA treatment resulted in increased expression ER stress markers. In conclusion, SAM and MTA down-regulate BHMT expression in HepG2 cells in part by inducing NF-kappaB, which acts as a repressor for the human BHMT gene. While SAM's mechanism is NF-kappaB-dependent, MTA has both NF-kappaB-dependent and -independent mechanisms.
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Affiliation(s)
- Xiaopeng Ou
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
| | - Heping Yang
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
| | - Komal Ramani
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
| | - Ainhoa Iglesias Ara
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
| | - Hui Chen
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
| | - José M. Mato
- †CIC Biogune (Centro de Investigación Cooperativa en Biociencias), Parque Tecnológico de Bizkaia, 48160 Derio, Bizkaia, Spain
| | - Shelly C. Lu
- *Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, USC–UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, U.S.A
- To whom correspondence should be addressed at, Division of Gastrointestinal and Liver Diseases, Department of Medicine, USC School of Medicine, HMR Bldg, 415, 2011 Zonal Ave., Los Angeles, CA 90033, U.S.A. (email )
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Rodríguez JL, Boukaba A, Sandoval J, Georgieva EI, Latasa MU, García-Trevijano ER, Serviddio G, Nakamura T, Avila MA, Sastre J, Torres L, Mato JM, López-Rodas G. Transcription of the MAT2A gene, coding for methionine adenosyltransferase, is up-regulated by E2F and Sp1 at a chromatin level during proliferation of liver cells. Int J Biochem Cell Biol 2007; 39:842-50. [PMID: 17317269 DOI: 10.1016/j.biocel.2007.01.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Revised: 12/28/2006] [Accepted: 01/08/2007] [Indexed: 12/15/2022]
Abstract
Methionine adenosyltransferase (MAT) is an essential enzyme because it catalyzes the formation of S-adenosylmethionine, the main methyl donor. Two MAT-encoding genes (MAT1A, MAT2A) are found in mammals. The latter is expressed in proliferating liver, dedifferentiation and cancer, whereas MAT1A is expressed in adult quiescent hepatocytes. Here, we report studies on the molecular mechanisms controlling the induction of MAT2A in regenerating rat liver and in proliferating hepatocytes. The MAT2A is up-regulated at two discrete moments during liver regeneration, as confirmed by RNApol-ChIP analysis. The first one coincides with hepatocyte priming (i.e. G0-G1 transition), while the second one takes place at the G1-S interface. Electrophoretic mobility shift assays showed that a putative E2F sequence present in MAT2A promoter binds this factor and ChIP assays confirmed that E2F1, E2F3 and E2F4, as well as the pocket protein p130, are bound to the promoter in quiescent liver. MAT2A activation is accompanied by changes in the binding of histone-modifying enzymes to the promoter. Interestingly, p130 is not displaced from MAT2A promoter during hepatocyte priming, but it is in the late expression of the gene at the G1-S transition. Finally, the transcription factor Sp1 seems to play a decisive role in MAT2A induction, as it binds the promoter when the gene is being actively transcribed. In summary, the present work shows that the molecular mechanism of MAT2A expression is different during G0-G1 or G1-S transition and this may be related to the distinct requirements of S-adenosylmethionine during liver regeneration.
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Affiliation(s)
- José L Rodríguez
- Department of Biochemistry and Molecular Biology, University of Valencia, Spain
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Lu SC, Mato JM. Role of methionine adenosyltransferase and S-adenosylmethionine in alcohol-associated liver cancer. Alcohol 2005; 35:227-34. [PMID: 16054984 DOI: 10.1016/j.alcohol.2005.03.011] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Accepted: 03/27/2005] [Indexed: 12/22/2022]
Abstract
Two genes (MAT1A and MAT2A) encode for the essential enzyme methionine adenosyltransferase (MAT), which catalyzes the biosynthesis of S-adenosylmethionine (SAMe), the principal methyl donor and, in the liver, a precursor of glutathione. MAT1A is expressed mostly in the liver, whereas MAT2A is widely distributed. MAT2A is induced in the liver during periods of rapid growth and dedifferentiation. In human hepatocellular carcinoma (HCC) MAT1A is replaced by MAT2A. This is important pathogenetically because MAT2A expression is associated with lower SAMe levels and faster growth, whereas exogenous SAMe treatment inhibits growth. Rats fed ethanol intragastrically for 9 weeks also exhibit a relative switch in hepatic MAT expression, decreased SAMe levels, hypomethylation of c-myc, increased c-myc expression, and increased DNA strand break accumulation. Patients with alcoholic liver disease have decreased hepatic MAT activity owing to both decreased MAT1A expression and inactivation of the MAT1A-encoded isoenzymes, culminating in decreased SAMe biosynthesis. Consequences of chronic hepatic SAMe depletion have been examined in the MAT1A knockout mouse model. In this model, the liver is more susceptible to injury. In addition, spontaneous steatohepatitis develops by 8 months, and HCC develops by 18 months. Accumulating evidence shows that, in addition to being a methyl donor, SAMe controls hepatocyte growth response and death response. Whereas transient SAMe depletion is necessary for the liver to regenerate, chronic hepatic SAMe depletion may lead to malignant transformation. It is interesting that SAMe is antiapoptotic in normal hepatocytes, but proapoptotic in liver cancer cells. This should make SAMe an attractive agent for both chemoprevention and treatment of HCC.
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Affiliation(s)
- Shelly C Lu
- USC Research Center for Liver Diseases, USC-UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, USA.
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Yang H, Sadda MR, Li M, Zeng Y, Chen L, Bae W, Ou X, Runnegar MT, Mato JM, Lu SC. S-adenosylmethionine and its metabolite induce apoptosis in HepG2 cells: Role of protein phosphatase 1 and Bcl-x(S). Hepatology 2004; 40:221-31. [PMID: 15239106 DOI: 10.1002/hep.20274] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
S-adenosylmethionine (SAMe) and its metabolite 5'-methylthioadenosine (MTA) are proapoptotic in HepG2 cells. In microarray studies, we found SAMe treatment induced Bcl-x expression. Bcl-x is alternatively spliced to produce two distinct mRNAs and proteins, Bcl-x(L) and Bcl-x(S). Bcl-x(L) is antiapoptotic, while Bcl-x(S) is proapoptotic. In this study we showed that SAMe and MTA selectively induced Bcl-x(S) in a time- and dose-dependent manner in HepG2 cells. There are three transcription start sites in the human Bcl-x gene which yield only Bcl-x(L) in control HepG2 cells. SAMe and MTA treatment did not affect promoter usage, but while one promoter yielded only Bcl-x(L), the other two yielded both Bcl-x(L) and Bcl-x(S), with Bcl-x(S) as the predominant messenger RNA (mRNA) species. Trichostatin A, 3-deaza-adenosine, cycloleucine, and okadaic acid had no effect on Bcl-x(S) induction by SAMe or MTA. Calyculin A and tautomycin, on the other hand, blocked SAMe and MTA-mediated Bcl-x(S) induction and apoptosis in a dose-dependent manner. SAMe and MTA increased protein phosphatase 1 (PP1) catalytic subunit mRNA and protein levels and dephosphorylation of serine-arginine proteins, with the latter blocked by calyculin A. The effects of SAMe and MTA on Bcl-x(S), PP1 expression, and apoptosis were also seen in 293 cells, but not in primary hepatocytes. Induction of Bcl-x(S) by ceramide in HepG2 cells also resulted in apoptosis. In conclusion, we have uncovered a highly novel action of SAMe and MTA, namely the ability to affect the cellular phosphorylation state and alternative splicing of genes, in this case resulting in the induction of Bcl-x(S) leading to apoptosis.
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Affiliation(s)
- Heping Yang
- Division of Gastroenterology and Liver Diseases, University of Southern California Research Center for Liver Diseases, USC-UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine, Los Angeles, 90033, USA
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Yang H, Sadda MR, Yu V, Zeng Y, Lee TD, Ou X, Chen L, Lu SC. Induction of human methionine adenosyltransferase 2A expression by tumor necrosis factor alpha. Role of NF-kappa B and AP-1. J Biol Chem 2003; 278:50887-96. [PMID: 14530285 DOI: 10.1074/jbc.m307600200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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.
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Affiliation(s)
- Heping Yang
- 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
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Mato JM, Corrales FJ, Lu SC, Avila MA. S-Adenosylmethionine: a control switch that regulates liver function. FASEB J 2002; 16:15-26. [PMID: 11772932 DOI: 10.1096/fj.01-0401rev] [Citation(s) in RCA: 311] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Genome sequence analysis reveals that all organisms synthesize S-adenosylmethionine (AdoMet) and that a large fraction of all genes is AdoMet-dependent methyltransferases. AdoMet-dependent methylation has been shown to be central to many biological processes. Up to 85% of all methylation reactions and as much as 48% of methionine metabolism occur in the liver, which indicates the crucial importance of this organ in the regulation of blood methionine. Of the two mammalian genes (MAT1A, MAT2A) that encode methionine adenosyltransferase (MAT, the enzyme that makes AdoMet), MAT1A is specifically expressed in adult liver. It now appears that growth factors, cytokines, and hormones regulate liver MAT mRNA levels and enzyme activity and that AdoMet should not be viewed only as an intermediate metabolite in methionine catabolism, but also as an intracellular control switch that regulates essential hepatic functions such as regeneration, differentiation, and the sensitivity of this organ to injury. The aim of this review is to integrate these recent findings linking AdoMet with liver growth, differentiation, and injury into a comprehensive model. With the availability of AdoMet as a nutritional supplement and evidence of its beneficial role in various liver diseases, this review offers insight into its mechanism of action.
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Affiliation(s)
- Jose M Mato
- Division of Hepatology and Gene Therapy, School of Medicine, University of Navarra, 31008 Pamplona, Spain.
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