Induction of rat liver O6-alkylguanine-DNA alkyltransferase following whole body X-irradiation.
The promutagenic DNA lesion O6-alkylguanine can be enzymically removed from cellular DNA by an O6-alkylguanine-DNA alkyltransferase (O6-AT) which transfers the alkyl group from the O6-position of guanine to a cysteine residue contained within its sequence. We report that whole body X-irradiation induces the O6-AT activity in the liver of adult Wistar rats. In vivo repair activity was assessed by radiochromatographic determination of the persistence of O6-methylguanine in hepatic DNA of irradiated rats following a single i.p. injection of N-nitroso-[14C]dimethylamine (2 mg/kg). In addition, the O6-alkylguanine repair capacity was assayed in vitro by incubation of extracts from whole liver, hepatocytes, or hepatic cell nuclei with 3H-methylated DNA and high performance liquid chromatography analysis of this DNA substrate. We found that whole body X-irradiation increased in a dose-dependent manner the O6-AT activity over a range of 100-800 R. The repair induction was first detectable 12 h after X-ray exposure, reached a maximum level at 72 h, and declined to control values within 12 days. Deoxythymidine incorporation into hepatic DNA was significantly reduced during the initial 72 h following application of 500 R. In a split dose irradiation schedule with daily doses of 15 R, a delayed enzyme induction occurred after a 30-day treatment period. Pretreatment of rats with the translational inhibitor cycloheximide completely suppressed the O6-AT stimulation. This indicates that the induction of hepatic O6-alkylguanine repair is due to de novo synthesis of alkyltransferase molecules.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004790:Enzyme Induction / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000528:radiation effects; D008780:Methyltransferases / Q000096:biosynthesis*; D019853:O(6)-Methylguanine-DNA Methyltransferase; D051381:Rats; D014916:Whole-Body Irradiation
D006147:Guanine; D003513:Cycloheximide; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase