REGULATION OF GLUTATHIONE-S-TRANSFERASE GENE-EXPRESSION BY PHENOBARBITAL IN CULTURED ADULT-RAT HEPATOCYTES

Previous studies, by using Northern blotting analyses, showed that phenobarbital (PB) affects the steady-state mRNA levels of glutathione S-transferase (GST) subunits 1/2, 3/4 and 7 in both conventional cultures of adult rat hepatocytes and co-cultures, with rat liver epithelial cells [Vandenberghe et al., 1989, FEBS Lett. 251, 59-64; Morel et al., 1989, FEBS Lett. 258, 99-102]. To determine whether PB acts at the transcriptional level, nuclear 'run-on' experiments using cDNA probes hybridizing to GST subunits 1/2, 3/4 and 7 mRNA were performed on purified nuclei isolated from control and PB treated hepatocytes seeded under conventional and co-culture conditions. Data from this study demonstrate that the increase in steady-state mRNA levels observed in both conventional culture and co-culture after 4 days PB exposure results from an increased transcriptional activity of the GST genes. However, a substantial increase in steady-state mRNA levels in the absence of a commensurate increase in transcriptional activity at 12 days of co-culture, indicates that the barbiturate has also a stabilizing effect in vitro on the GST mRNAs.