title: Redox regulation of methylthioadenosine phosphorylase in liver cells: molecular mechanism and functional implications.
abstract: MTAP (5'-methylthioadenosine phosphorylase) catalyses the reversible phosphorolytic cleavage of methylthioadenosine leading to the production of methylthioribose-1-phosphate and adenine. Deficient MTAP activity has been correlated with human diseases including cirrhosis and hepatocellular carcinoma. In the present study we have investigated the regulation of MTAP by ROS (reactive oxygen species). The results of the present study support the inactivation of MTAP in the liver of bacterial LPS (lipopolysaccharide)-challenged mice as well as in HepG2 cells after exposure to t-butyl hydroperoxide. Reversible inactivation of purified MTAP by hydrogen peroxide results from a reduction of V(max) and involves the specific oxidation of Cys(136) and Cys(223) thiols to sulfenic acid that may be further stabilized to sulfenyl amide intermediates. Additionally, we found that Cys(145) and Cys(211) were disulfide bonded upon hydrogen peroxide exposure. However, this modification is not relevant to the mediation of the loss of MTAP activity as assessed by site-directed mutagenesis. Regulation of MTAP by ROS might participate in the redox regulation of the methionine catabolic pathway in the liver. Reduced MTA (5'-deoxy-5'-methylthioadenosine)-degrading activity may compensate for the deficient production of the precursor S-adenosylmethionine, allowing maintenance of intracellular MTA levels that may be critical to ensure cellular adaptation to physiopathological conditions such as inflammation.
authors.affiliation: Division of Hepatology and Gene Therapy, Center for Applied Medical Research (CIMA), University of Navarra, 31008 Pamplona, Spain.
authors.forename: Joaquín
authors.initials: J
authors.lastname: Fernández-Irigoyen
authors.forename: Mónica
authors.initials: M
authors.lastname: Santamaría
authors.forename: Virginia
authors.initials: V
authors.lastname: Sánchez-Quiles
authors.forename: Maria U
authors.initials: MU
authors.lastname: Latasa
authors.forename: Enrique
authors.initials: E
authors.lastname: Santamaría
authors.forename: Javier
authors.initials: J
authors.lastname: Muñoz
authors.forename: Manuel M
authors.initials: MM
authors.lastname: Sánchez Del Pino
authors.forename: María L
authors.initials: ML
authors.lastname: Valero
authors.forename: Jesús
authors.initials: J
authors.lastname: Prieto
authors.forename: Matías A
authors.initials: MA
authors.lastname: Avila
authors.forename: Fernando J
authors.initials: FJ
authors.lastname: Corrales
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010084:Oxidation-Reduction; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry / Q000378:metabolism*; D013872:Thionucleosides / Q000378:metabolism
chemical_list: D004220:Disulfides; D008070:Lipopolysaccharides; D013872:Thionucleosides; D006861:Hydrogen Peroxide; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase