Transcriptional‐ and post‐transcriptional‐dependent regulation of glutathione S‐transferase expression in rat hepatocytes as a function of culture conditions

Abstract
Transcriptional activity of the glutathione S-transferase (GST) α (subunits 1 and 2), μ (subunits 3 and 4) and π (subunit 7) gene families has been analyzed using the nuclear ‘run-on’ technique on adult rat hepatocytes maintained for 4 days in conventional culture and for 4 and 12 days in co-culture with rat liver epithelial cells. Several medium conditions are included in this study, namely with or without fetal calf serum and with nicotinamide or dimethylsulphoxide. Hepatocytes co-cultured for 4 days maintain approximately 30–70% of the α gene family transcriptional activity, whatever the medium conditions, when compared to freshly isolated hepatocytes. A marked decrease is observed after 12 days of co-culture or when hepatocytes are maintained in conventional culture. The transcriptional activity of the μ gene family is maintained at 40–160% when hepatocytes are cultured with or without fetal calf serum, and is inducible by nicotinamide (approximately 4-fold) and dimethylsulphoxide (approximately 2-fold) in conventional culture and/or in co-culture. In contrast to freshly isolated hepatocytes, GST π gene transcriptional activity is observed in conventional and co-cultured hepatocytes, irrespective of the medium conditions. Dimethylsulphoxide treatment however, represses the expression of GST 7 in vitro. These results demonstrate that the expression of GST α, μ and π genes in conventional and co-cultured rat hepatocytes is controlled primarily at the level of transcription. It cannot be excluded, however, that dimethylsulphoxide stabilizes the GST mRNA levels in vitro.