REGULATORY MECHANISMS INVOLVED IN ACTIVATOR-PROTEIN-1 (AP-1)-MEDIATEDACTIVATION OF GLUTATHIONE-S-TRANSFERASE GENE-EXPRESSION BY CHEMICAL-AGENTS

Induction of murine glutathione-S-transferase (GST) Ya gene expression by a variety of chemical agents is mediated by a regulatory element, EpRE, composed of an Ets and two adjacent activator protein-1 (AP-1)-l ike sites and activated by the Fos/Jun heterodimeric complex (AP-1). T he mechanism of this induction was examined in the present study. We f ind that the regulation of EpRE-mediated GST Ya gene expression by 3-m ethylcholanthrene, tert-butylhydroquinone and beta-naphthoflavone is a ssociated with an induction of AP-1 DNA-binding activity and that the AP-1 complex induced in hepatoma cells by these chemicals contains mem bers of the Fos and Jun protein families. We show that tert-butylhydro quinone induces c-fos gene expression and indicate the formation of a transcriptionally active AP-1 complex that contains Fos/Jun heterodime r. In F9 cells, which are considered to lack AP-1 complex, a careful e xamination reveals that tert-butylhydroquinone induces a low level of an AP-1-related activity responsible for the enhanced expression of Ep RE as well as of AP-1 reporter constructs. We find that protein phosph orylations mediate the activation of the GST Ya gene by chemical agent s since okadaic acid, an inhibitor of protein phosphatases, can mimic this activation while protein kinase inhibitors abolish it. Evidence i s presented that 3-methylcholanthrene, terl-butylhydroquinone and beta -naphthoflavone use a signal transduction pathway to Fos/Jun-dependent GST Ya gene expression via Ras and protein-tyrosine kinase activity. Furthermore, we find that activation by phorbol 12-myristate 13-acetat e, which uses both protein kinase C and protein-tyrosine kinase activi ties, may share a common pathway with these chemicals downstream of Ra s.