PROTEIN-KINASE-C REGULATION OF THE ADENYLYL-CYCLASE SYSTEM IN RAT PROSTATIC EPITHELIUM

In the context of the crosstalk between transmembrane signalling pathw ays, we studied the loci within the stimulatory receptor/Gs protein/ad enylyl cyclase system at which protein kinase C (PKC) exerts regulator y effects in rat prostatic epithelial cells. The treatment of cells wi th the PKC activator phorbol 12-myristate 13-acetate (PMA) resulted in an impairment of the stimulation of adenylyl cyclase activity in term s of both potency, as seen with both vasoactive intestinal peptide (VI P) and pituitary adenylyl cyclase-activating peptide (PACAP-27), and e fficacy, as seen with the P-adrenergic agonist isoproterenol. This inh ibitory effect of PMA could be prevented by cell incubation with pertu ssis toxin but not with cholera toxin, pointing to a Gi- but not Gs-de pendent mechanism. This hypothesis was reinforced by ADP-ribosylation experiments that showed a low extent of ai with pertussis toxin but no change of a, with cholera toxin, as well as by the observation of the loss of the ability of low Gpp[NH]p doses to inhibit forskolin-stimul ated adenylyl cyclase activity (a measure of Gi function) after cell t reatment with PMA. However, the phorbol ester did not modify the adeny lyl cyclase catalytic subunit, as shown by experiments on direct stimu lation of the enzyme by forskolin. Whatever the exact mechanisms, the results support a crosstalk between the PKC and the adenylyl cyclase s ystems in rat prostatic epithelial cells in terms of an impairment of adenylyl cyclase stimulation, due presumably to phosphorylation of bot h membrane receptors (coupled to Gs) and Gi protein, but not of Gs pro tein or the adenylyl cyclase itself. (C) 1995 Wiley-Liss, Inc.