Technical Abstract: Cellular methylation processes enable expression of gluconeogenic enzymes and metabolism of the nutrient selenium (Se). Se status may relate to type-II diabetes and plasma levels of selenoprotein P (SEPP1) are positively correlated with insulin resistance. Increased expression of gluconeogenic enzymes glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase 1 (PCK1) has negative consequences for blood-sugar management in type-II diabetics. Transcriptional regulation of SEPP1 is directed by the same factors as those controlling the expression of G6PC and PCK1, and those transcription factors are methylated on arginine residues to increase activity. Here we sought to determine whether expression of SEPP1 and the aforementioned glucoconeogenic enzymes is regulated by relative concentrations of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). A human hepatocyte cell line, HepG2, was treated with periodate-oxidized adenosine (POA) and other mechanistically distinct inhibitors of SAH hydrolase (AHCY) known to reduce methylation capacity, or was induced to form SAH prior to analysis of G6PC, PCK1 and SEPP1 mRNA. Inhibiting AHCY or increasing SAH decreased SAM/SAH ratio, protein-arginine methylation and the expression of SEPP1, G6PC and PCK1 transcripts. Further, hormonal induction of gluconeogenic enzymes was reduced by inhibition of methylation capacity. When protein-arginine methyltransferase 1 expression was reduced by siRNA-treatment, G6PC expression was inhibited. This work demonstrates that hepatocellular SAM-dependent methylation regulates both SEPP1 and gluconeogenic enzyme expression, and that inhibition of protein arginine methylation might provide a route to therapeutic interventions in Type-II diabetes.