PKC-ALPHA REGULATES THROMBIN-INDUCED PDGF-B CHAIN GENE-EXPRESSION IN MESANGIAL CELLS

Thrombin is a potent mitogen for mesangial cells and stimulates PDGF B -chain gene expression in these cells, It also activates phospholipase C (PLC) resulting in an increase in cytosolic Ca2+ and diacylglycerol (DAG) that are the physiological activators of protein kinase C (PKC) , Immunoprecipitation of specific PKC isotypes from thrombin-stimulate d mesangial cells with subsequent measurement of their enzymatic activ ity shows activation of Ca2+-dependent PKC alpha and Ca2+-independent PKC zeta in a time dependent manner, Optimum activation of both of the se isozymes was obtained at 60 minutes, PKC alpha activity increased 8 3% over basal while activity of PKC zeta increased 104%, Prolonged exp osure of mesangial cells to phorbol myristate acetic acid (PMA) inhibi ted the enzymatic activity of PKC alpha but not PKC zeta. This inhibit ion of PKC alpha had no effect on thrombin-induced DNA synthesis but a bolished PDGF B-chain gene expression induced by thrombin, These data provide the first evidence that PKC alpha activation is necessary for thrombin-induced PDGF B-chain gene expression but not for thrombin-ind uced DNA synthesis.