Inhibition of prostaglandin E2-responsive adenylyl cyclase in embryonal human kidney 293 cells by phorbol esters.

A clonal primary embryonal human kidney cell line, 293, increased cAMP production in response to prostaglandin E2 (PGE2) (0.02-2 microM). The purpose of this study was to show the effects of tumor-promoting phorbol esters (e.g., 4 beta-phorbol 12-myristate 13-acetate, PMA) on PGE2-stimulated cAMP production. Pretreatment with PMA (0.2-200 nM) for 30 min markedly reduced PGE2-stimulated cAMP production in the presence of 0.5 mM isobutylmethylxanthine. The reduction by PMA was dose- and time-dependent. PMA seems to attenuate the increase in cAMP accumulation elicited by PGE2 primarily, if not entirely, by inhibiting adenylyl cyclase activity, since we were unable to demonstrate an effect of PMA on the degradation half-life of cAMP in intact 293 cells. The action of PMA had some specificity for the agonist used; thus, PMA inhibited PGE2-activated adenylyl cyclase but had no effect on the forskolin-activated enzyme. Co-pretreatment with PMA and H-7, an inhibitor of protein kinase C (PKC), partially prevented the PMA-induced attenuation of the PGE2-stimulated cAMP accumulation, and 1-oleoyl-2-acetylglycerol, a synthetic diacylglycerol analog, partially mimicked the PMA action. Thus, PMA appeared to decrease cAMP production by a PKC-mediated mechanism, inhibiting adenylyl cyclase activity at a point other than the catalytic subunit of the enzyme in the kidney 293 cell line.