The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Jose M Mato - One of the best experts on this subject based on the ideXlab platform.

  • deregulated Methionine Adenosyltransferase α1 c myc and maf proteins together promote cholangiocarcinoma growth in mice and humans
    Hepatology, 2016
    Co-Authors: Heping Yang, Hui Peng, Jiaohong Wang, Wei Fan, Ting Liu, Anuradha Krishnan, Gregory J Gores, Jose M Mato
    Abstract:

    c-Myc induction drives cholestatic liver injury and cholangiocarcinoma (CCA) in mice, and induction of Maf proteins (MafG and c-Maf) contributes to cholestatic liver injury, whereas S-adenosylMethionine (SAMe) administration is protective. Here, we determined whether there is interplay between c-Myc, Maf proteins, and Methionine Adenosyltransferase α1 (MATα1), which is responsible for SAMe biosynthesis in the liver. We used bile duct ligation (BDL) and lithocholic acid (LCA) treatment in mice as chronic cholestasis models, a murine CCA model, human CCA cell lines KMCH and Huh-28, human liver cancer HepG2, and human CCA specimens to study gene and protein expression, protein-protein interactions, molecular mechanisms, and functional outcomes. We found that c-Myc, MATα1 (encoded by MAT1A), MafG, and c-Maf interact with one another directly. MAT1A expression fell in hepatocytes and bile duct epithelial cells during chronic cholestasis and in murine and human CCA. The opposite occurred with c-Myc, MafG, and c-Maf expression. MATα1 interacts mainly with Mnt in normal liver, but this switches to c-Maf, MafG, and c-Myc in cholestatic livers and CCA. Promoter regions of these genes have E-boxes that are bound by MATα1 and Mnt in normal liver and benign bile duct epithelial cells that switched to c-Myc, c-Maf, and MafG in cholestasis and CCA cells. E-box positively regulates c-Myc, MafG, and c-Maf, but it negatively regulates MAT1A. MATα1 represses, whereas c-Myc, MafG, and c-Maf enhance, E-box-driven promoter activity. Knocking down MAT1A or overexpressing MafG or c-Maf enhanced CCA growth and invasion in vivo. Conclusion: There is a novel interplay between MATα1, c-Myc, and Maf proteins, and their deregulation during chronic cholestasis may facilitate CCA oncogenesis. (Hepatology 2016;64:439-455)

  • Methionine Adenosyltransferase α2 sumoylation positively regulate bcl 2 expression in human colon and liver cancer cells
    Oncotarget, 2015
    Co-Authors: Maria Lauda Tomasi, Komal Ramani, Minjung Ryoo, Ivan Tomasi, Pasquale Giordano, Jose M Mato
    Abstract:

    Ubiquitin-conjugating enzyme 9 (Ubc9) is required for sumoylation and inhibits apoptosis via Bcl-2 by unknown mechanism. Methionine Adenosyltransferase 2A (MAT2A) encodes for MATα2, the catalytic subunit of the MATII isoenzyme that synthesizes S-adenosylMethionine (SAMe). Ubc9, Bcl-2 and MAT2A expression are up-regulated in several malignancies. Exogenous SAMe decreases Ubc9 and MAT2A expression and is pro-apoptotic in liver and colon cancer cells. Here we investigated whether there is interplay between Ubc9, MAT2A and Bcl-2. We used human colon and liver cancer cell lines RKO and HepG2, respectively, and confirmed key finding in colon cancer specimens. We found MATα2 can regulate Bcl-2 expression at multiple levels. MATα2 binds to Bcl-2 promoter to activate its transcription. This effect is independent of SAMe as MATα2 catalytic mutant was also effective. MATα2 also directly interacts with Bcl-2 to enhance its protein stability. MATα2's effect on Bcl-2 requires Ubc9 as MATα2's stability is influenced by sumoylation at K340, K372 and K394. Overexpressing wild type (but not less stable MATα2 sumoylation mutants) protected from 5-fluorouracil-induced apoptosis in both colon and liver cancer cells. Colon cancer have higher levels of sumoylated MATα2, total MATα2, Ubc9 and Bcl-2 and higher MATα2 binding to the Bcl-2 P2 promoter. Taken together, Ubc9's protective effect on apoptosis may be mediated at least in part by sumoylating and stabilizing MATα2 protein, which in turn positively maintains Bcl-2 expression. These interactions feed forward to further enhance growth and survival of the cancer cell.

  • polyamine and Methionine Adenosyltransferase 2a crosstalk in human colon and liver cancer
    Experimental Cell Research, 2013
    Co-Authors: Maria Lauda Tomasi, Minjung Ryoo, Anna Skay, Ivan Tomasi, Pasquale Giordano, Jose M Mato
    Abstract:

    Methionine Adenosyltransferase (MAT) is an essential enzyme that is responsible for the biosynthesis of S-adenosylMethionine (SAMe), the principal methyl donor and precursor of polyamines. MAT1A is expressed in normal liver and MAT2A is expressed in all extrahepatic tissues. MAT2A expression is increased in human colon cancer and in colon cancer cells treated with mitogens, whereas silencing MAT2A resulted in apoptosis. The aim of the current work was to examine the mechanism responsible for MAT2A-dependent growth and apoptosis. We found that in RKO (human adenocarcinoma cell line) cells, MAT2A siRNA treatment lowered cellular SAMe and putrescine levels by 70-75%, increased apoptosis and inhibited growth. Putrescine supplementation blunted significantly MAT2A siRNA-induced apoptosis and growth suppression. Putrescine treatment (100pmol/L) raised MAT2A mRNA level to 4.3-fold of control, increased the expression of c-Jun and c-Fos and binding to an AP-1 site in the human MAT2A promoter and the promoter activity. In human colon cancer specimens, the expression levels of MAT2A, ornithine decarboxylase (ODC), c-Jun and c-Fos are all elevated as compared to adjacent non-tumorous tissues. Overexpression of ODC in RKO cells also raised MAT2A mRNA level and MAT2A promoter activity. ODC and MAT2A are also overexpressed in liver cancer and consistently, similar MAT2A-ODC-putrescine interactions and effects on growth and apoptosis were observed in HepG2 cells. In conclusion, there is a crosstalk between polyamines and MAT2A. Increased MAT2A expression provides more SAMe for polyamines biosynthesis; increased polyamine (putrescine in this case) can activate MAT2A at the transcriptional level. This along with increased ODC expression in cancer all feed forward to further enhance the proliferative capacity of the cancer cell.

  • micrornas regulate Methionine Adenosyltransferase 1a expression in hepatocellular carcinoma
    Journal of Clinical Investigation, 2013
    Co-Authors: Heping Yang, Michele E Cho, Hui Peng, Jose M Mato
    Abstract:

    MicroRNAs (miRNAs) and Methionine Adenosyltransferase 1A (MAT1A) are dysregulated in hepatocellular carcinoma (HCC), and reduced MAT1A expression correlates with worse HCC prognosis. Expression of miR-664, miR-485-3p, and miR-495, potential regulatory miRNAs of MAT1A, is increased in HCC. Knockdown of these miRNAs individually in Hep3B and HepG2 cells induced MAT1A expression, reduced growth, and increased apoptosis, while combined knockdown exerted additional effects on all parameters. Subcutaneous and intraparenchymal injection of Hep3B cells stably overexpressing each of this trio of miRNAs promoted tumorigenesis and metastasis in mice. Treatment with miRNA-664 (miR-664), miR-485-3p, and miR-495 siRNAs reduced tumor growth, invasion, and metastasis in an orthotopic liver cancer model. Blocking MAT1A induction significantly reduced the antitumorigenic effect of miR-495 siRNA, whereas maintaining MAT1A expression prevented miRNA-mediated enhancement of growth and metastasis. Knockdown of these miRNAs increased total and nuclear level of MAT1A protein, global CpG methylation, lin-28 homolog B (Caenorhabditis elegans) (LIN28B) promoter methylation, and reduced LIN28B expression. The opposite occurred with forced expression of these miRNAs. In conclusion, upregulation of miR-664, miR-485-3p, and miR-495 contributes to lower MAT1A expression in HCC, and enhanced tumorigenesis may provide potential targets for HCC therapy.

  • proteomic analysis of human hepatoma cells expressing Methionine Adenosyltransferase i iii characterization of ddx3x as a target of s adenosylMethionine
    Journal of Proteomics, 2012
    Co-Authors: Paul C Schroder, Jose M Mato, Joaquin Fernandezirigoyen, Emilie Bigaud, Antonio Serna, Ruben Renandezalcoceba, Jesus Prieto, Fernando J Corrales
    Abstract:

    Methionine Adenosyltransferase I/III (MATI/III) synthesizes S-adenosylMethionine (SAM) in quiescent hepatocytes. Its activity is compromised in most liver diseases including liver cancer. Since SAM is a driver of hepatocytes fate we have studied the effect of re-expressing MAT1A in hepatoma Huh7 cells using proteomics. MAT1A expression leads to SAM levels close to those found in quiescent hepatocytes and induced apoptosis. Normalization of intracellular SAM induced alteration of 128 proteins identified by 2D-DIGE and gel-free methods, accounting for deregulation of central cellular functions including apoptosis, cell proliferation and survival. Human Dead-box protein 3 (DDX3X), a RNA helicase regulating RNA splicing, export, transcription and translation was down-regulated upon MAT1A expression. Our data support the regulation of DDX3X levels by SAM in a concentration and time dependent manner. Consistently, DDX3X arises as a primary target of SAM and a principal intermediate of its antitumoral effect. Based on the parallelism between SAM and DDX3X along the progression of liver disorders, and the results reported here, it is tempting to suggest that reduced SAM in the liver may lead to DDX3X up-regulation contributing to the pathogenic process and that replenishment of SAM might prove to have beneficial effects, at least in part by reducing DDX3X levels. This article is part of a Special Issue entitled: Proteomics: The clinical link.

Maria A Pajares - One of the best experts on this subject based on the ideXlab platform.

  • nadp binding to the regulatory subunit of Methionine Adenosyltransferase ii increases intersubunit binding affinity in the hetero trimer
    PLOS ONE, 2012
    Co-Authors: Beatriz Gonzalez, Francisco Garrido, Yolanda Perezpertejo, Rebeca Ortega, Marta Martinezjulvez, Ainhoa Revillaguarinos, Adrian Velazquezcampoy, Julia Sanzaparicio, Maria A Pajares
    Abstract:

    Mammalian Methionine Adenosyltransferase II (MAT II) is the only hetero-oligomer in this family of enzymes that synthesize S-adenosylMethionine using Methionine and ATP as substrates. Binding of regulatory β subunits and catalytic α2 dimers is known to increase the affinity for Methionine, although scarce additional information about this interaction is available. This work reports the use of recombinant α2 and β subunits to produce oligomers showing kinetic parameters comparable to MAT II purified from several tissues. According to isothermal titration calorimetry data and densitometric scanning of the stained hetero-oligomer bands on denatured gels, the composition of these oligomers is that of a hetero-trimer with α2 dimers associated to single β subunits. Additionally, the regulatory subunit is able to bind NADP(+) with a 1:1 stoichiometry, the cofactor enhancing β to α2-dimer binding affinity. Mutants lacking residues involved in NADP(+) binding and N-terminal truncations of the β subunit were able to oligomerize with α2-dimers, although the kinetic properties appeared altered. These data together suggest a role for both parts of the sequence in the regulatory role exerted by the β subunit on catalysis. Moreover, preparation of a structural model for the hetero-oligomer, using the available crystal data, allowed prediction of the regions involved in β to α2-dimer interaction. Finally, the implications that the presence of different N-terminals in the β subunit could have on MAT II behavior are discussed in light of the recent identification of several splicing forms of this subunit in hepatoma cells.

  • structural basis for the stability of a thermophilic Methionine Adenosyltransferase against guanidinium chloride
    Amino Acids, 2012
    Co-Authors: Francisco Garrido, John C Taylor, Carlos Alfonso, George D Markham, Maria A Pajares
    Abstract:

    The Methionine Adenosyltransferase from the thermophile Methanococcus jannaschii is fully and irreversibly unfolded in the presence of guanidinium chloride. Unfolding of this dimeric protein is a three-state process in which a dimeric intermediate could be identified. The less stable secondary structural elements of the protein are the C-terminal ends of β-strands E2 and E6, as deduced from the behavior of tyrosine to tryptophan mutants at residues 72 and 170, which are located in the subunit interface. Unraveling of these elements at the monomer interface may soften intersubunit interactions, leading to the observed 85% activity loss. Accumulation of the intermediate was associated with maintenance of residual activity, an increase in the elution volume of the protein upon gel filtration and a decrease in the sedimentation coefficient. Elimination of the remaining enzymatic activity occurred in conjunction with a 50% reduction in helicity and fluorescence alterations illustrating a transient burial of tryptophans at β-strands E2, E3 and E9. The available 3D-model predicted that these β-strands are involved in the central and N-terminal domains of the monomer structure. Severe perturbation of this area of the monomer–monomer interface may destroy the remaining intermolecular interactions, thus leading to dissociation and aggregation. Finally, transition to the denatured state includes completion of the changes detected in the microenvironments around tryptophans included at α-helixes H5 and H6, the loops connecting H5–E8 and E9, β-strands E3 and E12.

  • refolding and characterization of Methionine Adenosyltransferase from euglena gracilis
    Protein Expression and Purification, 2011
    Co-Authors: Francisco Garrido, Sylvie Estrela, Claudia Alves, Gabino F Sanchezperez, Antonio Sillero, Maria A Pajares
    Abstract:

    Abstract Methionine Adenosyltransferase from Euglena gracilis (MATX) is a recently discovered member of the MAT family of proteins that synthesize S-adenosylMethionine. Heterologous overexpression of MATX in Escherichia coli rendered the protein mostly in inclusion bodies under all conditions tested. Therefore, a refolding and purification procedure from these aggregates was developed to characterize the enzyme. Maximal recovery was obtained using inclusion bodies devoid of extraneous proteins by washing under mild urea (2 M) and detergent (5%) concentrations. Refolding was achieved in two steps following solubilization in the presence of Mg2+; chaotrope dilution to

  • conformational signals in the c terminal domain of Methionine Adenosyltransferase i iii determine its nucleocytoplasmic distribution
    The FASEB Journal, 2009
    Co-Authors: Edel Reytor, Juliana Perezmiguelsanz, Luis Alvarez, Dolores Perezsala, Maria A Pajares
    Abstract:

    The methyl donor S-adenosylMethionine is synthesized in mammalian cytosol by three isoenzymes. Methionine Adenosyltransferase II is ubiquitously expressed, whereas isoenzymes I (homotetramer) and III (homodimer) are considered the hepatic enzymes. In this work, we identified Methionine Adenosyltransferase I/III in most rat tissues, both in the cytoplasm and the nucleus. Nuclear localization was the preferred distribution observed in extrahepatic tissues, where the protein colocalizes with nuclear matrix markers. A battery of mutants used in several cell lines to decipher the determinants involved in Methionine Adenosyltransferase subcellular localization demonstrated, by confocal microscopy and subcellular fractionation, the presence of two partially overlapping areas at the C-terminal end of the protein involved both in cytoplasmic retention and nuclear localization. Immunoprecipitation of coexpressed FLAG and EGFP fusions and gel-filtration chromatography allowed detection of tetramers and monomers in n...

  • Methionine Adenosyltransferase α helix structure unfolds at lower temperatures than β sheet a 2d ir study
    Biophysical Journal, 2004
    Co-Authors: Ibon Iloro, Maria A Pajares, Rosana Chehin, Felix M Goni, Jose Luis R Arrondo
    Abstract:

    Two-dimensional infrared spectroscopy has been used to characterize rat liver Methionine Adenosyltransferase and the events taking place during its thermal unfolding. Secondary structure data have been obtained for the native recombinant enzyme by fitting the amide I band of infrared spectra. Thermal denaturation studies allow the identification of events associated with individual secondary-structure elements during temperature-induced unfolding. They are correlated to the changes observed in enzyme activity and intrinsic fluorescence. In all cases, thermal denaturation proved to be an irreversible process, with a Tm of 47–51°C. Thermal profiles and two-dimensional infrared spectroscopy show that unfolding starts with α-helical segments and turns, located in the outer part of the protein, whereas extended structure, associated with subunit contacts, unfolds at higher temperatures. The data indicate a good correlation between the denaturation profiles obtained from activity measurements, fluorescence spectroscopy, and the behavior of the infrared bands. A study of the sequence of events that takes place is discussed in light of the previous knowledge on Methionine Adenosyltransferase structure and oligomerization pathway.

Malak Kotb - One of the best experts on this subject based on the ideXlab platform.

  • regulation of the human mat2b gene encoding the regulatory β subunit of Methionine Adenosyltransferase mat ii
    Journal of Biological Chemistry, 2001
    Co-Authors: Leighton Legros, Margaret E Chamberlin, Arthur M Geller, Abdelbaset Halim, Malak Kotb
    Abstract:

    Methionine Adenosyltransferase (MAT) catalyzes the biosynthesis of S-adenosylMethionine (AdoMet), a key molecule in transmethylation reactions and polyamine biosynthesis. The MAT II isozyme consists of a catalytic alpha2 and a regulatory beta subunit. Down-regulation of the MAT II beta subunit expression causes a 6-10-fold increase in intracellular AdoMet levels. To understand the mechanism by which the beta subunit expression is regulated, we cloned the MAT2B gene, determined its organization, characterized its 5'-flanking sequences, and elucidated the in vitro and in vivo regulation of its promoter. Transcription of the MAT2B gene initiates at position -203 relative to the translation start site. Promoter deletion analysis defined a minimal promoter between positions +52 and +93 base pairs, a GC-rich region. Inclusion of the sequences between -4 and +52 enhanced promoter activity; this was primarily because of an Sp1 recognition site at +9/+15. The inclusion of sequences up to position -115 provided full activity; this was attributed to a TATA at -32. The Sp1 site at position +9 was key for the formation of protein.DNA complexes. Mutation of both the Sp1 site at +9 and the TATA at -32 reduced promoter activity to its minimal level. Supershift assays showed no effect of the anti-Sp1 antibody on complex formation, whereas the anti-Sp3 antibody had a strong effect on protein.DNA complex formation, suggesting that Sp3 is one of the main factors binding to this Sp1 site. Chromatin immunoprecipitation assays supported the involvement of both Sp1 and Sp3 in complexes formed on the MAT2B promoter. The data show that the 5'-untranslated sequences play an important role in regulating the MAT2B gene and identifies the Sp1 site at +9 as a potential target for modulating MAT2B expression, a process that can have a major effect on intracellular AdoMet levels.

  • cloning expression and functional characterization of the β regulatory subunit of human Methionine Adenosyltransferase mat ii
    Journal of Biological Chemistry, 2000
    Co-Authors: Malak Kotb, Arthur M Geller, Leighton H Legros, Abdelbaset Halim
    Abstract:

    MAT II, the extrahepatic form of Methionine Adenosyltransferase (MAT), consists of catalytic alpha(2)/alpha(2') subunits and a noncatalytic beta subunit, believed to have a regulatory function. The full-length cDNA that encodes the beta subunit of human MAT II was cloned and found to encode for a 334-amino acid protein with a calculated molecular weight of 37,552. Analysis of sequence homology showed similarity with bacterial enzymes that catalyze the reduction of TDP-linked sugars. The beta subunit cDNA was cloned into the pQE-30 expression vector, and the recombinant His tagged protein, which was expressed in Escherichia coli, was recognized by antibodies to the human MAT II, to synthetic peptides copying the sequence of native beta subunit protein, and to the rbeta protein. There is no cross-reactivity between the MAT II alpha(2) or beta subunits. None of the anti-beta subunit antibodies reacted with protein extracts of E. coli host cells, suggesting that these bacteria have no beta subunit protein. Interestingly, the rbeta subunit associated with E. coli as well as human MAT alpha subunits. This association changed the kinetic properties of both enzymes and lowered the K(m) of MAT for L-Methionine. Together, the data show that we have cloned and expressed the human MAT II beta subunit and confirmed its long suspected regulatory function. This knowledge affords a molecular means by which MAT activity and consequently the levels of AdoMet may be modulated in mammalian cells.

  • differential regulation of Methionine Adenosyltransferase in superantigen and mitogen stimulated human t lymphocytes
    Journal of Biological Chemistry, 1997
    Co-Authors: Leighton H Legros, Arthur M Geller, Malak Kotb
    Abstract:

    Abstract Superantigens interact with the T cell receptor for antigen (TCR) and are, therefore, more physiological stimulators of T lymphocytes than nonspecific polyclonal T cell mitogens. The effects of these two classes of T cell stimulators on Methionine Adenosyltransferase (MAT) andS-adenosylMethionine (AdoMet) levels were investigated. Activation of resting human peripheral blood T lymphocytes by the mitogen phytohemagglutinin (PHA) or the superantigen staphylococcal enterotoxin B (SEB) caused a 3- to 6-fold increase in MAT II specific activity. Although the proliferative response was higher in cultures stimulated with PHA compared with SEB, MAT II activity was comparable in both cultures. Both stimuli caused down-regulation of the MAT 68-kDa λ subunit expression and induced a comparable increase in the expression of the catalytic α2/α2′ subunit mRNA and protein. However, in superantigen-stimulated cells, the expression of the noncatalytic β subunit was down-regulated and virtually disappeared by 72 h post-stimulation; whereas, no change in the expression of this subunit was noted in PHA-stimulated cells. Thus, at 72 h following stimulation, PHA-stimulated cells expressed MAT II α2/α2′ and β subunits while SEB-stimulated cells expressed the α2/α2′ subunits only; the β subunit was no longer expressed in superantigen-stimulated cells. Kinetic analysis of MAT II in extracts of PHA- and SEB-stimulated cells using reciprocal kinetic plots revealed that in the absence of the β subunit theK m of the enzyme for l-Methionine (l-Met) was 3-fold higher than in the presence of the β subunit. Furthermore, AdoMet levels were 5-fold higher in cell extracts lacking the β subunit (SEB-stimulated cell extracts) compared with extracts containing MAT II α2/α2′ and β subunits. We propose that the increased levels of AdoMet in superantigen-stimulated cells may be attributed to the absence of the β subunit, which seems to have rendered MAT II less sensitive to product feedback inhibition by (−)AdoMet. The data suggest that the β subunit of MAT II, which has no catalytic activity, may be a regulatory subunit that imparts a lowerK m for l-Met but increases the sensitivity to feedback inhibition by AdoMet. The down-regulation of the β subunit, which occurred when T cells were stimulated via the TCR, may be an important mechanism to regulate AdoMet levels at different stages of T cell differentiation under physiological conditions.

  • chromosomal localization and catalytic properties of the recombinant alpha subunit of human lymphocyte Methionine Adenosyltransferase
    Journal of Biological Chemistry, 1995
    Co-Authors: James De La Rosa, Malak Kotb, Jacek Ostrowski, M M Hryniewicz, Nicholas M Kredich, Leighton H Legros, Marc Valentine, Arthur M Geller
    Abstract:

    Human lymphocyte Methionine Adenosyltransferase (HuLy MAT) consists of heterologous subunits alpha and beta. The cDNA sequence of the alpha subunit of HuLy MAT from Jurkat leukemic T cells was identical to that of the human kidney alpha subunit and highly homologous to the sequence of the extrahepatic MAT from other sources. The 3'-untranslated sequence was found to be highly conserved, suggesting that it may be important in regulating the expression of MAT. The extrahepatic alpha subunit unit of MAT was found to be expressed also in human liver, and no differences were found in the sequence of the alpha subunit from normal and malignant T cells. The sequence of two unspliced introns found in the cDNA clones from the Jurkat library enabled us to isolate genomic clones harboring the human extrahepatic alpha subunit gene and to localize it to the centromere on chromosome arm 2p, an area that corresponds to band 2p11.2. Expression of the alpha subunit cDNA in Escherichia coli yielded two peptides with the immunoreactivity and mobilities of authentic alpha/alpha' subunits from HuLy. The Km of the recombinant alpha subunit was 80 microM, which is 20-fold higher than found for the (alpha alpha')x beta y holoenzyme purified from leukemic lymphocytes and 4-10-fold higher than found for the normal lymphocyte enzyme. The data suggest that the alpha/alpha' subunits mediate the enzyme catalytic activity and that the beta subunit may be a regulatory subunit of extrahepatic MAT.

  • Methionine Adenosyltransferase structure and function
    Pharmacology & Therapeutics, 1993
    Co-Authors: Malak Kotb, Arthur M Geller
    Abstract:

    Methionine Adenosyltransferase (MAT), a key enzyme in metabolism, catalyzes the synthesis of one of the most important and pivotal biological molecules, S-adenosyl-Methionine. In every organism studied thus far, MAT exists in multiple forms; most are encoded by related, but distinct genes. Molecular and immunological studies revealed the presence of considerable conservation in the structure of MAT from different species; however, the various MAT isozymes differ in their physical and kinetic properties in ways that allow them to be regulated differently. Recent studies suggest that human MAT is composed of nonidentical subunits that can assume multiple states of aggregation, each with different kinetic characteristics. The tissue distribution of MAT isozymes and the ability of cells within the same tissue to switch between the different forms of MAT suggest that this mode of regulation is important for cellular function and differentiation. Therefore, understanding the regulation and structure-function relationship of this fascinating enzyme should help us clarify its role in biology and may provide us with tools to effectively manipulate its activity in clinical situations such as cancer, autoimmunity and organ transplantation.

Heping Yang - One of the best experts on this subject based on the ideXlab platform.

  • deregulated Methionine Adenosyltransferase α1 c myc and maf proteins together promote cholangiocarcinoma growth in mice and humans
    Hepatology, 2016
    Co-Authors: Heping Yang, Hui Peng, Jiaohong Wang, Wei Fan, Ting Liu, Anuradha Krishnan, Gregory J Gores, Jose M Mato
    Abstract:

    c-Myc induction drives cholestatic liver injury and cholangiocarcinoma (CCA) in mice, and induction of Maf proteins (MafG and c-Maf) contributes to cholestatic liver injury, whereas S-adenosylMethionine (SAMe) administration is protective. Here, we determined whether there is interplay between c-Myc, Maf proteins, and Methionine Adenosyltransferase α1 (MATα1), which is responsible for SAMe biosynthesis in the liver. We used bile duct ligation (BDL) and lithocholic acid (LCA) treatment in mice as chronic cholestasis models, a murine CCA model, human CCA cell lines KMCH and Huh-28, human liver cancer HepG2, and human CCA specimens to study gene and protein expression, protein-protein interactions, molecular mechanisms, and functional outcomes. We found that c-Myc, MATα1 (encoded by MAT1A), MafG, and c-Maf interact with one another directly. MAT1A expression fell in hepatocytes and bile duct epithelial cells during chronic cholestasis and in murine and human CCA. The opposite occurred with c-Myc, MafG, and c-Maf expression. MATα1 interacts mainly with Mnt in normal liver, but this switches to c-Maf, MafG, and c-Myc in cholestatic livers and CCA. Promoter regions of these genes have E-boxes that are bound by MATα1 and Mnt in normal liver and benign bile duct epithelial cells that switched to c-Myc, c-Maf, and MafG in cholestasis and CCA cells. E-box positively regulates c-Myc, MafG, and c-Maf, but it negatively regulates MAT1A. MATα1 represses, whereas c-Myc, MafG, and c-Maf enhance, E-box-driven promoter activity. Knocking down MAT1A or overexpressing MafG or c-Maf enhanced CCA growth and invasion in vivo. Conclusion: There is a novel interplay between MATα1, c-Myc, and Maf proteins, and their deregulation during chronic cholestasis may facilitate CCA oncogenesis. (Hepatology 2016;64:439-455)

  • micrornas regulate Methionine Adenosyltransferase 1a expression in hepatocellular carcinoma
    Journal of Clinical Investigation, 2013
    Co-Authors: Heping Yang, Michele E Cho, Hui Peng, Jose M Mato
    Abstract:

    MicroRNAs (miRNAs) and Methionine Adenosyltransferase 1A (MAT1A) are dysregulated in hepatocellular carcinoma (HCC), and reduced MAT1A expression correlates with worse HCC prognosis. Expression of miR-664, miR-485-3p, and miR-495, potential regulatory miRNAs of MAT1A, is increased in HCC. Knockdown of these miRNAs individually in Hep3B and HepG2 cells induced MAT1A expression, reduced growth, and increased apoptosis, while combined knockdown exerted additional effects on all parameters. Subcutaneous and intraparenchymal injection of Hep3B cells stably overexpressing each of this trio of miRNAs promoted tumorigenesis and metastasis in mice. Treatment with miRNA-664 (miR-664), miR-485-3p, and miR-495 siRNAs reduced tumor growth, invasion, and metastasis in an orthotopic liver cancer model. Blocking MAT1A induction significantly reduced the antitumorigenic effect of miR-495 siRNA, whereas maintaining MAT1A expression prevented miRNA-mediated enhancement of growth and metastasis. Knockdown of these miRNAs increased total and nuclear level of MAT1A protein, global CpG methylation, lin-28 homolog B (Caenorhabditis elegans) (LIN28B) promoter methylation, and reduced LIN28B expression. The opposite occurred with forced expression of these miRNAs. In conclusion, upregulation of miR-664, miR-485-3p, and miR-495 contributes to lower MAT1A expression in HCC, and enhanced tumorigenesis may provide potential targets for HCC therapy.

  • insulin like growth factor 1 activates Methionine Adenosyltransferase 2a transcription by multiple pathways in human colon cancer cells
    Biochemical Journal, 2011
    Co-Authors: Heping Yang, Jian Peng, Jose M Mato
    Abstract:

    We have previously reported that the expression of MAT2A (Methionine Adenosyltransferase 2A) is increased in human colon cancer and in colon cancer cells treated with IGF-1 (insulin-like growth factor-1), which was required for its mitogenic effect. The aim of the present study was to elucidate the molecular mechanisms of IGF-1-mediated MAT2A induction. Nuclear run-on analysis confirmed that the increase in MAT2A expression lies at the transcriptional level. DNase I footprinting of the MAT2A promoter region revealed a similar protein-binding pattern in colon cancer and IGF-1-treated RKO cells. IGF-1 induced MAT2A promoter activity and increased nuclear protein binding to USF (upstream stimulatory factor)/c-Myb, YY1 (Yin and Yang 1), E2F, AP-1 (activator protein 1) and NF-κB (nuclear factor κB) consensus elements. IGF-1 increased the expression of c-Jun, FosB, MafG, p65, c-Myb, E2F-1 and YY1 at the pre-translational level. Knockdown of p65, MafG, c-Myb or E2F-1 lowered basal MAT2A expression and blunted the inductive effect of IGF-1 on MAT2A, whereas knockdown of YY1 increased basal MAT2A expression and had no effect on IGF-1-mediated MAT2A induction. Consistently, mutation of AP-1, NF-κB, E2F and USF/c-Myb elements individually blunted the IGF-1-mediated increase in MAT2A promoter activity, and combined mutations completely prevented the increase. In conclusion, IGF-1 activates MAT2A transcription by both known and novel pathways. YY1 represses MAT2A expression.

  • novel function and intracellular localization of Methionine Adenosyltransferase 2β splicing variants
    Journal of Biological Chemistry, 2010
    Co-Authors: Meng Xia, Luz M Martinezchantar, Heping Yang, Yongheng Chen, Lingchi Wang, Ebrahim Zandi, Sean Bemanian, Jose M Mato
    Abstract:

    Human Methionine Adenosyltransferase 2β (MAT2β) encodes for two major splicing variants, V1 and V2, which are differentially expressed in normal tissues. Both variants are induced in human liver cancer and positively regulate growth. The aim of this work was to identify interacting proteins of V1 and V2. His-tagged V1 and V2 were overexpressed in Rosetta pLysS cells, purified, and used in a pulldown assay to identify interacting proteins from human colon cancer cell line RKO cell lysates. The eluted lysates were subjected to Western blot and in solution proteomic analyses. HuR, an mRNA-binding protein known to stabilize the mRNA of several cyclins, was identified to interact with V1 and V2. Immunoprecipitation and Western blotting confirmed their interaction in both liver and colon cancer cells. These variant proteins are located in both nucleus and cytoplasm in liver and colon cancer cells and, when overexpressed, increased the cytoplasmic HuR content. This led to increased expression of cyclin D1 and cyclin A, known targets of HuR. When endogenous expression of V1 or V2 is reduced by small interference RNA, cytoplasmic HuR content fell and the expression of these HuR target genes also decreased. Knockdown of cyclin D1 or cyclin A blunted, whereas knockdown of HuR largely prevented, the ability of V1 or V2 overexpression to induce growth. In conclusion, MAT2β variants reside mostly in the nucleus and regulate HuR subcellular content to affect cell proliferation.

  • forced expression of Methionine Adenosyltransferase 1a in human hepatoma cells suppresses in vivo tumorigenicity in mice
    American Journal of Pathology, 2010
    Co-Authors: Komal Ramani, Heping Yang, Meng Xia, Zhanfeng Sun, Chishing Zee, Edward Grant, Jose M Mato
    Abstract:

    Methionine Adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylMethionine, the principal methyl donor, and is encoded by MAT1A and MAT2A in mammals. Normal liver expresses MAT1A, which is silenced in hepatocellular carcinoma. We have shown that hepatoma cells overexpressing MAT1A grew slower, but whether this is also true in vivo remains unknown. To investigate the effect of overexpressing MAT1A on in vivo tumorigenesis, we generated stable transfectants of Huh7 cells overexpressing either MAT1A or empty vector. Real-time PCR and Western blotting were used to measure expression, and BALB/c nude mice were injected subcutaneously with untransfected or Huh7 cells transfected with empty or MAT1A expression vector to establish tumors. Tumor properties such as proliferation, angiogenesis, and apoptosis were compared, and microarray analysis was performed. Huh7 cells overexpressing MAT1A had higher S-adenosylMethionine levels but lower bromodeoxyuridine incorporation than control cells. Tumor growth rates and weights were lower in MAT1A transfected tumors. In addition, microvessel density and CD31 and Ki-67 staining were lower in MAT1A transfected tumors than control tumors, whereas the apoptosis index was higher in MAT1A-transfected tumors. Forced expression of MAT1A induced genes related to apoptosis and tumor suppression and lowered expression of cell growth and angiogenesis proteins. Our data demonstrate in vivo overexpression of MAT1A in liver cancer cells can suppress tumor growth. They also suggest inducing MAT1A expression might be a strategy to treat hepatocellular carcinoma.

Fernando J Corrales - One of the best experts on this subject based on the ideXlab platform.

  • proteomic analysis of human hepatoma cells expressing Methionine Adenosyltransferase i iii characterization of ddx3x as a target of s adenosylMethionine
    Journal of Proteomics, 2012
    Co-Authors: Paul C Schroder, Jose M Mato, Joaquin Fernandezirigoyen, Emilie Bigaud, Antonio Serna, Ruben Renandezalcoceba, Jesus Prieto, Fernando J Corrales
    Abstract:

    Methionine Adenosyltransferase I/III (MATI/III) synthesizes S-adenosylMethionine (SAM) in quiescent hepatocytes. Its activity is compromised in most liver diseases including liver cancer. Since SAM is a driver of hepatocytes fate we have studied the effect of re-expressing MAT1A in hepatoma Huh7 cells using proteomics. MAT1A expression leads to SAM levels close to those found in quiescent hepatocytes and induced apoptosis. Normalization of intracellular SAM induced alteration of 128 proteins identified by 2D-DIGE and gel-free methods, accounting for deregulation of central cellular functions including apoptosis, cell proliferation and survival. Human Dead-box protein 3 (DDX3X), a RNA helicase regulating RNA splicing, export, transcription and translation was down-regulated upon MAT1A expression. Our data support the regulation of DDX3X levels by SAM in a concentration and time dependent manner. Consistently, DDX3X arises as a primary target of SAM and a principal intermediate of its antitumoral effect. Based on the parallelism between SAM and DDX3X along the progression of liver disorders, and the results reported here, it is tempting to suggest that reduced SAM in the liver may lead to DDX3X up-regulation contributing to the pathogenic process and that replenishment of SAM might prove to have beneficial effects, at least in part by reducing DDX3X levels. This article is part of a Special Issue entitled: Proteomics: The clinical link.

  • hypermethioninaemia due to Methionine Adenosyltransferase i iii mat i iii deficiency diagnosis in an expanded neonatal screening programme
    Journal of Inherited Metabolic Disease, 2008
    Co-Authors: Maria L Couce, Fernando J Corrales, M D Boveda, Daisy E Castineiras, M I Mora, Jose M Fraga, S H Mudd
    Abstract:

    The Expanded Newborn Screening Program (MS/MS) in the region of Galicia (NW Spain) was initiated in 2000 and includes the measurement of Methionine levels in dried blood spots. Between June 2000 and June 2007, 140 818 newborns were analysed, and six cases of persistent hypermethioninaemia were detected: one homocystinuria due to cystathionine β-synthase (CβS) deficiency, and five Methionine Adenosyltransferase I/III (MAT I/III) deficiencies. The five cases of MAT I/III deficiency represent an incidence of 1/28 163 newborns. In these five patients, Methionine levels in dried blood spots ranged from 50 to 147 μmol/L. At confirmation of the persistence of the hypermethioninaemia in a subsequent plasma sample, plasma Methionine concentrations were moderately elevated in 4 of the 5 patients (mean 256 μmol/L), while total homocysteine (tHcy) was normal; the remaining patient showed plasma Methionine of 573 μmol/L and tHcy of 22.8 μmol/L. All five patients were heterozygous for the same dominant mutation, R264H in the MAT1A gene. With a diet not exceeding recommended protein requirements for their age, all patients maintained Methionine levels below 300 μmol/L. Currently, with a mean of 2.5 years since diagnosis, the patients are asymptomatic and show developmental quotients within the normal range. Our results show a rather high frequency of hypermethioninaemia due to MAT I/III deficiency in the Galician neonatal population, indicating a need for further studies to evaluate the impact of persistent isolated hypermethioninaemia in neonatal screening programmes.

  • impaired liver regeneration in mice lacking Methionine Adenosyltransferase 1a
    The FASEB Journal, 2004
    Co-Authors: Lixin Chen, Fernando J Corrales, Matias A Avila, Elena R Garciatrevijano, Heping Yang, Ying Zeng, Taunia D Lee, Samuel W French, Jose M Mato
    Abstract:

    Methionine Adenosyltransferase (MAT) is an essential enzyme because it catalyzes the formation of S-adenosylMethionine (SAMe), the principal biological methyl donor. Of the two genes that encode MAT, MAT1A is mainly expressed in adult liver and MAT2A is expressed in all extrahepatic tissues. Mice lacking MAT1A have reduced hepatic SAMe content and spontaneously develop hepatocellular carcinoma. The current study examined the influence of chronic hepatic SAMe deficiency on liver regeneration. Despite having higher baseline hepatic staining for proliferating cell nuclear antigen, MAT1A knockout mice had impaired liver regeneration after partial hepatectomy (PH) as determined by bromodeoxyuridine incorporation. This can be explained by an inability to up-regulate cyclin D1 after PH in the knockout mice. Upstream signaling pathways involved in cyclin D1 activation include nuclear factor kappaB (NFkappaB), the c-Jun-N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and signal transducer and activator of transcription-3 (STAT-3). At baseline, JNK and ERK are more activated in the knockouts whereas NFkappaB and STAT-3 are similar to wild-type mice. Following PH, early activation of these pathways occurred, but although they remained increased in wild-type mice, c-jun and ERK phosphorylation fell progressively in the knockouts. Hepatic SAMe levels fell progressively following PH in wild-type mice but remained unchanged in the knockouts. In culture, MAT1A knockout hepatocytes have higher baseline DNA synthesis but failed to respond to the mitogenic effect of hepatocyte growth factor. Taken together, our findings define a critical role for SAMe in ERK signaling and cyclin D1 regulation during regeneration and suggest chronic hepatic SAMe depletion results in loss of responsiveness to mitogenic signals.

  • Methionine Adenosyltransferase i iii deficiency two korean compound heterozygous siblings with a novel mutation
    Journal of Inherited Metabolic Disease, 2003
    Co-Authors: Sook Kim, Fernando J Corrales, Jose M Mato, Harvey L Levy, Enrique Santamaria, T E Jeong, S H Mudd
    Abstract:

    Two Korean sisters, one detected during neonatal screening, the other ascertained at age 3 years during family screening, have persistent hypermethioninaemia without elevation of plasma tyrosine or severe liver disease. Plasma total homocysteine (tHcy) is mildly elevated, but not so markedly as to establish a diagnosis of homocystinuria due to cystathionine beta-synthase (CBS) deficiency. CBS deficiency was ruled out by the presence of slightly elevated concentrations of plasma cystathionine. Although the plasma concentrations of Methionine were markedly elevated, plasma S-adenosylMethionine (AdoMet) was not. This pattern of metabolic abnormalities suggested that the patients have deficient activity of Methionine Adenosyltransferase (MAT) in their livers (MAT I/III deficiency). Molecular genetic studies demonstrate that each patient is a compound heterozygote for two mutations in MAT1A, the gene that encodes the catalytic subunit that composes MAT I and MAT III: a previously known inactivating G378S point mutation, and a novel W387X truncating mutation. W387X mutant protein, expressed in E. coli and purified, has about 75% of wild-type activity. Negative subunit interaction between the mutant subunits is suggested to explain the hypermethioninaemia of these sisters. They have had normal growth and development and have no mental retardation, neurological abnormalities, or other clinical problems. They are the first individuals of Korean descent proven to have MAT I/III deficiency.

  • spontaneous oxidative stress and liver tumors in mice lacking Methionine Adenosyltransferase 1a
    The FASEB Journal, 2002
    Co-Authors: Maria L Martinezchantar, Fernando J Corrales, Matias A Avila, Elena R Garciatrevijano, Alfonso L Martinezcruz, Zongzhi Huang, Lixin Chen, Gary Kanel, Jose M Mato
    Abstract:

    In mammals, Methionine metabolism occurs mainly in the liver via Methionine Adenosyltransferase-catalyzed conversion to S-adenosylMethionine. Of the two genes that encode Methionine Adenosyltransferase(MAT1Aand MAT2A), MAT1A is mainly expressed in adult liver whereas MAT2A is expressed in all extrahepatic tissues. Mice lacking MAT1A have reduced hepatic S-adenosylMethionine content and hyperplasia and spontaneously develop nonalcoholic steatohepatitis. In this study, we examined whether chronic hepatic S-adenosylMethionine deficiency generates oxidative stress and predisposes to injury and malignant transformation. Differential gene expression in MAT1A knockout mice was analyzed following the criteria of the Gene Ontology Consortium. Susceptibility of MAT1A knockout mice to CCl4-induced hepatotoxicity and malignant transformation was determined in 3- and 18-month-old mice, respectively. Analysis of gene expression profiles revealed an abnormal expression of genes involved in the metabolism of lipids and carbohydrates in MAT1A knockout mice, a situation that is reminiscent of that found in diabetes, obesity, and other conditions associated with nonalcoholic steatohepatitis. This aberrant expression of metabolic genes in the knockout mice was associated with hyperglycemia, increased hepatic CYP2E1 and UCP2 expression and triglyceride levels, and reduced hepatic glutathione content. The knockout animals have increased lipid peroxidation and enhanced sensitivity to CCl4-induced liver damage, which was largely due to increased CYP2E1 expression because diallyl sulfide, an inhibitor of CYP2E1, prevented CCl4-induced liver injury. Hepatocellular carcinoma developed in more than half of the knockout mice by 18 months of age. Taken together, our findings define a critical role for S-adenosylMethionine in maintaining normal hepatic function and tumorigenesis of the liver.