INDUCTION OF O-6-ALKYLGUANINE-DNA-ALKYLTRANSFERASE IN THE HEPATOCYTESOF RATS FOLLOWING TREATMENT WITH 2-ACETYLAMINOFLUORENE

Molecular and immunohistological techniques have been used to study th e induction in rat liver of the DNA repair protein O-6-alkylguanine-DN A-alkyltransferase (ATase), following an acute dose (60 mg/kg) of the hepatocarcinogen, 2-acetylaminofluorene (2-AAF), An increase in ATase activity was specific to the liver, with a five- to six-fold induction being observed 72 hr after administration of 2-AAF. A similar tempora l increase of both activity and ATase protein (detected by immunoblott ing) was observed up to 1 week following treatment, but after 2 weeks the activity had returned to control levels. Although maximal inductio n of hepatic ATase mRNA was observed as early as 24 hr, the levels rem ained elevated at least 1 week after 2-AAF treatment. Using a rabbit a ntiserum raised against purified recombinant rat ATase, ATase-specific staining was observed in the nuclei of both nonhepatocytes and hepato cytes in control liver sections. There was, however, a significant dif ferential staining of hepatocytes across the liver lobule, with ATase staining being most intense in the periportal region. In the livers of 2-AAF-treated rats, an increased intensity of staining was observed i n hepatocytes throughout the liver lobule, whereas the nonparenchymal cells showed much less, or no, increase in staining. The increased exp ression of ATase in hepatocytes and its differential distribution acro ss the lobule were confirmed by image analysis. Thus, ATase induction in response to 2-AAF treatment was an hepatocyte-specific response and not confined to any particular region of the liver lobule.