TRANSCRIPTIONAL INDUCTION OF CHOLESTEROL 7-ALPHA-HYDROXYLASE BY DEXAMETHASONE IN L35 HEPATOMA-CELLS REQUIRES SULFHYDRYL REDUCING AGENTS

It is known that hepatic levels of reduced glutathione correlate with the activity of the liver-specific enzyme cholesterol-7 alpha-hydroxyl ase. We examined the possibility that sulfhydryl reducing agents activ ate transcription of cholesterol 7 alpha-hydroxylase. Adding dithiothr eitol (DTT, 1 mM) and dexamethasone to L35 hepatoma cells increased th e content of 7 alpha-hydroxylase mRNA 3-fold above the levels observed with dexamethasone alone. Without dexamethasone, DTT had no affect. T he addition of reduced glutathione to L35 cells demonstrated a similar potentiation of expression dependent on dexamethasone. Nuclear run-on assays showed that in the presence of both dexamethasone and DTT, the transcription of the 7 alpha-hydroxylase gene was clearly increased. In contrast, by itself, dexamethasone did not cause a detectable incre ase in the transcription of the 7 alpha-hydroxylase gene. Dexamethason e and DTT did not affect the transcription of p-actin, suggesting a se lective induction of the 7 alpha-hydroxylase gene. DTT reversed repres sion of 7 alpha-hydroxylase expression by insulin but not the repressi on by phorbol ester. Our data show for the first time that the sulfhyd ryl redox potential of the hepatocyte (i.e. level of reduced glutathio ne) has a marked influence on the transcription and expression of the liver-specific gene 7 alpha-hydroxylase.