title: S-adenosylmethionine-dependent protein methylation is required for expression of selenoprotein P and gluconeogenic enzymes in HepG2 human hepatocytes.
abstract: Cellular methylation processes enable expression of gluconeogenic enzymes and metabolism of the nutrient selenium. Selenium status has been proposed to relate to type II diabetes risk, and plasma levels of selenoprotein P (SEPP1) have been positively correlated with insulin resistance. Increased expression of gluconeogenic enzymes glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase 1 (PCK1) has negative consequences for blood glucose management in type II diabetics. Transcriptional regulation of SEPP1 is directed by the same transcription factors that control the expression of G6PC and PCK1, and these factors are activated by methylation of arginine residues. We sought to determine whether expression of SEPP1 and the aforementioned glucoconeogenic enzymes are regulated by protein methylation, the levels of which are reliant upon adequate S-adenosylmethionine (SAM) and inhibited by S-adenosylhomocysteine (SAH). We treated a human hepatocyte cell line, HepG2, with inhibitors of adenosylhomocysteine hydrolase (AHCY) known to increase concentration of SAH before analysis of G6PC, PCK1, and SEPP1 expression. Increasing SAH decreased 1) the SAM/SAH ratio, 2) protein-arginine methylation, and 3) expression of SEPP1, G6PC, and PCK1 transcripts. Furthermore, hormone-dependent induction of gluconeogenic enzymes was reduced by inhibition of protein methylation. When protein-arginine methyltransferase 1 expression was reduced by siRNA treatment, G6PC expression was inhibited. These findings demonstrate that hepatocellular SAM-dependent protein methylation is required for both SEPP1 and gluconeogenic enzyme expression and that inhibition of protein arginine methylation might provide a route to therapeutic interventions in type II diabetes.
authors.affiliation: Grand Forks Human Nutrition Research Center, Agricultural Research Service, United States Department of Agriculture, Grand Forks, North Dakota 58203, USA. matthew.jackson@ars.usda.gov
authors.forename: Matthew I
authors.initials: MI
authors.lastname: Jackson
authors.forename: Jay
authors.initials: J
authors.lastname: Cao
authors.forename: Huawei
authors.initials: H
authors.lastname: Zeng
authors.forename: Eric
authors.initials: E
authors.lastname: Uthus
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Combs
mesh_terms: D043383:Adenosylhomocysteinase / Q000096:biosynthesis / Q000235:genetics; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics / Q000378:metabolism / Q000628:therapy; D005786:Gene Expression Regulation; D005943:Gluconeogenesis; D019298:Glucose-6-Phosphate / Q000235:genetics / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics; D008745:Methylation; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000096:biosynthesis / Q000235:genetics; D011484:Protein-Arginine N-Methyltransferases / Q000096:biosynthesis / Q000235:genetics; D012436:S-Adenosylmethionine / Q000235:genetics / Q000378:metabolism*; D051149:Selenoprotein P / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D051149:Selenoprotein P; D019298:Glucose-6-Phosphate; D012436:S-Adenosylmethionine; D011484:Protein-Arginine N-Methyltransferases; D043383:Adenosylhomocysteinase; C521898:PCK1 protein, human; D010729:Phosphoenolpyruvate Carboxykinase (GTP)