title: shRNA silencing of AS3MT expression minimizes arsenic methylation capacity of HepG2 cells.
abstract: Several methyltransferases have been shown to catalyze the oxidative methylation of inorganic arsenic (iAs) in mammalian species. However, the relative contributions of these enzymes to the overall capacity of cells to methylate iAs have not been characterized. Arsenic (+3 oxidation state) methyltransferase (AS3MT) that is expressed in rat and human hepatocytes catalyzes the conversion of iAs, yielding methylated metabolites that contain arsenic in +3 or +5 oxidation states. This study used short hairpin RNA (shRNA) to knock down AS3MT expression in human hepatocellular carcinoma (HepG2) cells. In a stable clonal HepG2/A cell line, AS3MT mRNA and protein levels were reduced by 83 and 88%, respectively. In comparison, the capacity to methylate iAs decreased only by 70%. These data suggest that AS3MT is the major enzyme in this pathway, although an AS3MT-independent process may contribute to iAs methylation in human hepatic cells.
authors.affiliation: Department of Nutrition, Curriculum in Toxicology, and Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina at Chapel Hill, 27599-2774, USA. drobnazu@med.unc.edu
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Drobna
authors.forename: Weibing
authors.initials: W
authors.lastname: Xing
authors.forename: David J
authors.initials: DJ
authors.lastname: Thomas
authors.forename: Miroslav
authors.initials: M
authors.lastname: Stýblo
mesh_terms: D001151:Arsenic / Q000378:metabolism* / Q000633:toxicity; D001483:Base Sequence; D045744:Cell Line, Tumor; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008745:Methylation / Q000187:drug effects; D008780:Methyltransferases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D034741:RNA, Small Interfering; D008780:Methyltransferases; C505756:AS3MT protein, human; D001151:Arsenic