PLATELET-DERIVED GROWTH FACTOR-INDUCED DISRUPTION OF GAP JUNCTIONAL COMMUNICATION AND PHOSPHORYLATION OF CONNEXIN43 INVOLVES PROTEIN-KINASE-C AND MITOGEN-ACTIVATED PROTEIN-KINASE

Previously we showed a rapid and transient inhibition of gap junctiona l communication (GIC) by platelet-derived growth Factor (PDGF) in T51B rat liver epithelial cells expressing wild-type platelet-derived grow th factor beta receptors (PDCFr beta). This action of PDGF correlated with the hyperphosphorylation of the gap junction protein connexin43 ( Cx43) and required PDGFr beta tyrosine kinase activity, suggesting the participation of protein kinases and phosphatases many of which are a ctivated by PDGF treatment. In the present study, two such kinases, na mely protein kinase C (PKC) and mitogen-activated protein kinase (MAPK ), are investigated for their possible involvement in PDCF-induced clo sure of junctional channels and Cx43-phosphorylation. Down-regulation of PKC-isoforms by 12-O-tetradecanoylphorbol-13-acetate or pretreatmen t with the PKC inhibitor calphostin C, completely blocked PDGF action on GJC and Cx43. Activation of MAPK correlated with PDGF-induced Down phosphorylation, and prevention of MAPK activation by PD98059 eliminat ed the PDGF effects. Interestingly, elimination of CIC recovery by cyc loheximide was associated with a sustained activated-MAPK level. Based on these results we postulate that the activation of PKC and MAPK are required in PDCF-mediated Down phosphorylation and functional closure . (C) 1998 Wiley-Liss, Inc.