Glucocorticoid stimulation of amnion cell prostaglandin synthesis: suppression by protein kinase C inhibitors and independence of phorbol ester-sensitive protein kinase C

Abstract

Glucocorticoids stimulate the prostaglandin E 2 production of confluent amnion cell cultures, but have no stimulatory effect on the PGE 2 output of freshly isolated human amnion cells. Since protein phosphorylation may modify the responsiveness of target cells to steroids, and activators of protein kinase C (PKC), as well as corticosteroids, promote amnion cell PGE 2 output by stimulating the synthesis of prostaglandin endoperoxide H synthase (PGHS), we investigated the possibility that PKC is involved in the glucocorticoid-induction of PGE 2 synthesis in cultured amnion cells. The dexamethasone-induced PGE 2 output of arachidonate-stimulated cells was blocked by the protein kinase inhibitors staurosporine, K-252a, H7, HA1004, and sphinganine, in a manner consistent with their effect on PKC. However, dexamethasone increased the PGE 2 production of cultures treated with maximally effective concentrations of the PKC-activator compound TPA. Moreover, dexamethasone stimulated PGE 2 synthesis in cultures which were desensitized to TPA-stimulation by prolonged phorbol ester treatment. Concentration-dependence studies showed that staurosporine completely (> 95%) blocked glucocorticoid-provoked PGE 2 synthesis at concentrations which did not inhibit TPA-stimulated prostaglandin output, and that K-252a inhibited the effect of TPA by more than 95% at concentrations which decreased the effect of dexamethasone only moderately ≈ 40%). Dibutyryl cyclic AMP had no influence on the basal- or dexamethasone-stimulated PGE 2 production, and on the staurosporine inhibition of the steroid effect. These results show that glucocorticoids and phorbol esters control amnion PGE 2 production by separate regulatory mechanisms. It is suggested that the response of human amnion cells to glucocorticoids is modulated by protein kinase(s) other than phorbol ester-sensitive PKC and cyclic AMP-dependent protein kinase.