PHORBOL ESTER-LIKE ACTION OF STAUROSPORINE ON THE CAMP RESPONSE TO PROSTAGLANDIN-E2 IN 2 MACROPHAGE-LIKE CELL-LINES AT DISTINCT DIFFERENTIATION STAGES

The purpose of this study is to investigate the involvement of protein kinase C (PKC) in prostaglandin E2 (PGE2)-stimulated cAMP production of two macrophage-like cell lines (G3 and XC). XC cells are thought to be placed at a more differentiated stage than G3 cells [Orikasa et al. (1991) Cell Immunol. 132, 350-365]. In RPMI 1640 containing 10% (v/v) heat-inactivated foetal calf serum (FCS), in which the cAMP response of both cells to PGE, increased with duration of culture, XC cells showed greater response than G3 cells at 2 days of culture. In alpha-minimum essential medium (alpha-MEM) containing 20% (v/v) heat-inactivated horse serum (HS), the cAMP response of both cells was apparently greater than that in RPMI 1640 containing 10% (v/v) FCS. These cells increased cAMP production also in response to PGE, and PGF2alpha, and the order of potency in increase was PGE1 > PGE2 much greater than PGF2alpha. Interestingly, a short-term (20 min) treatment with phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC or staurosporine, a relatively specific inhibitor of PKC, augmented the PGE2-stimulated cAMP production in these cells cultured in alpha-MEM containing 20% (v/v) HS. However, a long-term (24 h) treatment with these compounds did not alter the cAMP response. In G3 cells, PMA appeared more potent than staurosporine in terms of augmentation, whereas in XC cells, the former appeared less potent than the latter. Although the mechanism of this augmentation seems complex and is still unclear, our findings suggest that PKC modulates the regulation of the PGE2-cAMP signalling system, and that the macrophage differentiation may decrease the involvement of PMA-sensitive PKC, but not that of staurosporine-sensitive PKC, in this cAMP system.