Suppression of glutathione transferase P expression by glucocorticoid.

A strong enhancer element, GPEI, of the glutathione transferase P gene (GST-P) gene is composed of two phorbol 12-O-tetradecanoate 13-acetate (TPA) responsive element (TRE)-like sequences at opposite orientation. Unlike TRE sequences of other genes, GPEI exhibits a strong enhancer activity in F9 cells, which contains little AP-1. GPEI bound to AP-1 In vitro and GST-P expression was activated by TPA and exogenously introduced c-jun gene in a rat fibroblast cell line. Both the stimulated expression of GST-P gene by TPA and that by over-expressed c-Jun were suppressed to the basal level by dexamethasone, an inhibitor of AP-1. Basal expression of GST-P gene, however, was not inhibited by dexamethasone. Transfected chloramphenicol acetyltransferase (CAT) gene having GPEI also behaved as the endogenous GST-P gene. These results indicate that the GPEI is activated by AP-1 but constitutive activity of this enhancer in a rat fibroblast cell line 3Y1 cells is due to some unknown mechanism other than AP-1.     

Analysis of glutathione transferase P gene regulation with liver cells in primary culture.

Glutathione transferase P (GST-P) gene is specifically and highly activated during rat chemical hepatocarcinogenesis. We have previously cloned the GST-P gene and have identified putative regulatory regions. To further explore regulatory mechanisms, deletion constructs of the GST-P gene fused to the chloramphenicol acetyltransferase (CAT) structural gene were introduced into primary cultured rat hepatocytes by electroporation, and their activity was determined. The expression of the GST-P-CAT fusion gene is quite low in these cells as compared to that in both a rat fibroblast cell line, 3Y1 cells, and a rat hepatoma cell line, dRLh84. The presence of the strong enhancer GPEI did not elicit any enhancing activity at its original position, or when it was located 3' of the CAT gene, although this element does enhance CAT activity significantly when located adjacent to the promoter. Cotransfection of neither c-jun nor c-fos expression vector, nor both vectors, could enhance the CAT activity, even though GPEI consists of two phorbol ester response element-like sites. Furthermore, the expression of jun family gene was not correlated with GST-P gene expression either in primary cultured hepatocytes or in hepatoma cell lines.