Protein kinase C is not involved in Ah receptor transformation and DNA binding

Induction of cytochrome P4501A1 by 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD) is mediated by the Ah receptor (AhR) complex, a ligand-dependent DNA-binding transactivator. Recently a role for protein kinase C (PKC) in the induction response has been reported in which PKC or a related kinase positively modulates AhR activity. We have examined the role of PKC by determining the effect of two nonspecific PKC inhibitors, H7 and staurosporine, and one specific PKC inhibitor, calphostin c, on AhR functionality. Although no kinase activity was detectable in cytosol, under the conditions used for our assays, AhR transformation and DNA binding still occurred. Addition of relatively high concentrations of the kinase inhibitors also had no significant effect on TCDD:AhR:DRE complex formation. Thus, our results indicate that protein kinase activity does not appear to be necessary for TCDD-dependent AhR transformation and DNA binding and they imply that protein kinases must play a role in another step(s) in the AhR-dependent mechanism of P4501A1 induction.