No abstract

In earlier experiments, adrenocorticotropic hormone (ACTH) was shown to decrease the level of glutathione transferase M1 (murine glutathione transferase mu-1) (mGSTM1), as well as of the corresponding mRNA, in a murine adrenocortical cell line. In the present study, the effect of ACTH on mGSTM1 gene transcription was examined using two techniques. First, a cDNA that coded for the mGSTM1 subunit but lacked the corresponding promoter sequences was transfected into the adrenocortical cell line, and the effect of ACTH on the level of the corresponding transcript was compared to that of endogenous mGSTM1 mRNA. The other technique used was nuclear run-on transcription, where the rate of transcription of endogenous mGSTM1 mRNA in ACTH-treated cells was compared to that in untreated control cells. These experimental approaches indicated that the rate of transcription of the mGSTM1 gene is regulated by ACTH in adrenocortical cells.

Analysis by reverse-phase HPLC revealed that these cells express four isoenzymes of GST, i.e., A1, A2, P1, and M4, as well as another unidentified protein that was retained by our affinity column (elution time of 32 min) and, thus, presumably binds glutathione. Among these forms, A1 was present at the highest level. Upon addition of forskolin (an activator of adenylate cyclase which has been shown previously to mimic the effect of ACTH on adrenal cells) to the culture medium, the level of A1 decreased approximately 70% by forskolin, whereas the levels of the other isoenzymes were slightly increased, and that of the unknown form doubled. Thus, the influence of ACTH on expression of GST isoenzymes in this human adrenal cell line differs from that in rat and mouse adrenal cells.