ADRENOCORTICOTROPIC-HORMONE-DEPENDENT REGULATION OF A MU-CLASS GLUTATHIONE TRANSFERASE IN MOUSE ADRENOCORTICAL-CELLS

Three different forms of glutathione transferase (GST) have been resolved in the two mouse adrenal tumour cell lines Y1 and Kin 8. Two of these belong to the mu and pi classes respectively. The third form is so far unidentified. In the Y1 cells, the levels of the mu form (mGTmul) and the unidentified form, are both downregulated in the presence of adrenocorticotrophic hormone (ACTH) while the pi form is unaffected. The Kin 8 cell line is derived from Y1 cells and harbours a defect in the cyclic AMP (cAMP)-dependent protein kinase, making it refractory to cAMP-dependent regulation of several enzymes. The GST levels in this cell line were unaffected by ACTH. Also, the steady-state levels of mGTmul mRNA were much lower in Y1 cells treated with forskolin (which activates adenylate cyclase) compared with control cells, but there was no difference in mGTmul mRNA levels between control and forskolin-treated Kin 8 cells. This indicates that the ACTH-dependent regulation of the LL class GST is pre-translational and that a functional cAMP-dependent protein kinase is required for the regulation. We have further shown that the difference in mRNA steady-state levels between control and forskolin-treated Y1 cells is abolished when transcription is inhibited by actinomycin D. In light of the stability of mGTmul mRNA, it would appear most likely that actinomycin D inhibits the transcription of short-lived factors which regulate the turn-over of mGTmul transcripts in response to changes in intracellular cAMP levels.