Phorbol esters inhibit adenylate cyclase activity in cultured collecting tubular cells

Abstract

Activators of protein kinase C, a calcium- and phospholipid-dependent protein kinase, inhibit vasopressin-stimulated water flow in toad bladder. To determine the biochemical mechanisms of this inhibition, we examined the effects of activators of protein kinase C on arginine vasopressin (AVP)-stimulated adenylate cyclase activity in cultured rabbit cortical collecting tubular cells. The phorbol ester, 4 beta-phorbol 12-myristate 13-acetate (PMA), the diacylglycerol, 1-oleyl-2-acetyl glycerol (OAG), and the diacylglycerol kinase inhibitor, R59022, all rapidly activate protein kinase C in collecting tubular cells. Pretreatment with PMA produces a delayed inhibition (greater than or equal to 4 h) of AVP-stimulated adenylate cyclase activity. The 4-h time lag suggests that the effects of protein kinase C are mediated indirectly, possibly as a consequence of stimulating cell proliferation. PMA does not inhibit cholera toxin- or forskolin-stimulated adenylate cyclase activity, suggesting an effect on the vasopressin receptor or coupling of the receptor to the stimulatory guanine nucleotide regulatory protein. Neither prostaglandins nor the inhibitory guanine nucleotide regulatory protein appear to mediate this effect. In contrast, treatment with either OAG or R59022 produces a rapid inhibition of both AVP- and forskolin-stimulated adenylate cyclase activity suggesting a prominent distal site of action, presumably at the catalytic subunit of adenylate cyclase. The results demonstrate that different activators of protein kinase C inhibit AVP-stimulated adenylate cyclase activity by distinctly different mechanisms possibly by altering the substrate specificity or activating multiple forms of the kinase. These results have important implications when using different activators to study the biological effects of protein kinase C.