title: Inhibition of DNA methylation by S-adenosylethionine with the production of methyl-deficient DNA in regenerating rat liver.
abstract: Ethionine, a liver carcinogen, was administered p.o. (300 mg/kg) to rats 17 hr after partial hepatectomy. At 6 hr after administration of the ethionine, hepatic S-adenosylethionine levels were 30- to 40-fold greater than the hepatic level of S-adenosylmethionine. A 10-fold ratio of S-adenosylethionine to S-adenosylmethionine still persited at 24 hr after ethionine administration. When given at 17 hr after partial hepatectomy, ethionine produced a 30% inhibition of DNA synthesis, measured by the incorporation of [methyl-3H]thymidine at 23 to 24 hr after partial hepatectomy (6 to 7 hr after ethionine administration). DNA synthesized during this interval was methyl deficient as judged by the reduced incorporation of radioactivity from L-[methyl-3H]methionine into 5-methylcytosine residues of DNA. In an assay for DNA methylation in vitro using whole nuclei, the methyl-deficient DNA was methylated by S-adenosylmethionine 8 times more than was control DNA; the DNA methylation was competitively inhibited by S-adenosylethionine. These data suggest that S-adenosylethionine, formed in vivo from ethionine, competitively inhibits the methylation of DNA in vivo by S-adenosylmethionine, resulting in the production of methyl-deficient DNA.
mesh_terms: D000818:Animals; D002273:Carcinogens; D004247:DNA / Q000096:biosynthesis / Q000378:metabolism*; D005001:Ethionine / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism*; D008115:Liver Regeneration; D008297:Male; D008745:Methylation; D051381:Rats; D012436:S-Adenosylmethionine / Q000378:metabolism*
chemical_list: D002273:Carcinogens; D012436:S-Adenosylmethionine; D004247:DNA; D005001:Ethionine