PROTEIN-KINASE-C PLAYS A KEY ROLE IN THE CROSS-TALK BETWEEN INTRACELLULAR SIGNALINGS VIA PROSTANOID RECEPTORS IN A MEGAKARYOBLASTIC CELL-LINE - MEG-01S

In a previous study, we characterized prostanoid and thrombin receptor s expressed on a megakaryoblastic cell line, MEG-01s (Blood 78, 2328-2 336, 1991). In this study, we examines the mechanism of cross-talk bet ween intracellular Ca2+ ([Ca2+](i)) and cAMP signalings through prosta noid and thrombin receptors. Addition of a thromboxane (TX)A(2) mimeti c (U46619 or STA(2)) or thrombin stimulated the formation of inositol phosphates and dose-dependently augmented a prostaglandin (PG)I-2 mime tic (iloprost)- or forskolin-induced cAMP formation. 12-O-tetradecanoy lphorbol-13-acetate (TPA) and ionomycin, to lesser extent, also augmen ted iloprost-induced cAMP formation. The enhancing effect of U46619 or TPA on cAMP formation was inhibited by prolonged pretreatment of the cells with TPA (2.5 mu M, 24 h), but not with calmodulin-antagonists; W-7, W-5, or KN-62. The elevation of [Ca2+](i) induced by thrombin, ST A(2) or PGE(2) was significantly suppressed by pretreatment of the cel ls with TPA (100 nM) as well as cAMP mimetics such as dibutyryl cAMP ( 5 mM), forskolin (5 mu M) and iloprost (1 mu M). These results suggest the key role of PKC on the cross-talk between [Ca2+](i) and cAMP sign alings through prostanoid and thrombin receptors; PKC, which is activa ted with TXA(2), or thrombin, concomitantly suppress further [Ca2+](i) elevation and enhances the PGI(2) receptor-mediated cAMP formation, w hich, in turn, suppress [Ca2+](i) elevation.