PMA INHIBITS THE GROWTH OF HUMAN FIBROBLASTS AFTER THE INDUCTION OF IMMEDIATE-EARLY GENES

WS-1 cells, human fibroblasts derived from embryonic skill, become qui escent in serum-free medium. Addition of serum or thrombin stimulates incorporation of H-3-labeled thymidine 16-40 h later. The tumor promot er phorbol 12-myristate 13-acetate (PMA) inhibited this response in qu iescent cells stimulated with serum or thrombin. PMA also inhibited th ymidine incorporation in rapidly growing WS-1 cells. Since the inhibit ion caused by PMA could result from activation of protein kinase C (PK C) or the down-regulation of PKC, the effect of the PKC inhibitor, GF 109203X, was tested. GF 109203X did not affect thymidine incorporation induced by serum. GF 109203X prevented the inhibition caused by PMA, suggesting that the activation of PKC is required for the inhibition o f DNA synthesis. A prolonged activation of PKC is probably required, s ince a single treatment of a synthetic diacylglycerol does not inhibit and addition of GF 109203X 2 to 8 h after PMA reverses the inhibition . One possible target for PMA activity is the induction of immediate-e arly response genes. Thrombin or serum treatment of quiescent WS-l cel ls induced protooncogenes c-fos and c-jun. PMA also induced c-fos and c-jun with a time course similar to that of serum or thrombin. The ind uction of c-fos by PMA was sensitive to staurosporine or GF 109203X. A time course of PMA addition indicated that maximal inhibition of DNA synthesis occurred when PMA was added 4 h after stimulation with serum . These results suggest that the PMA-induced inhibition of DNA synthes is occurs through an activation of PKC that inhibits DNA synthesis at a point after the induction of c-fos and c-jun. (C) 1994 Academic Pres s, Inc.