RAPID DISRUPTION OF GAP JUNCTIONAL COMMUNICATION AND PHOSPHORYLATION OF CONNEXIN43 BY PLATELET-DERIVED GROWTH-FACTOR IN T51B RAT-LIVER EPITHELIAL-CELLS EXPRESSING PLATELET-DERIVED GROWTH-FACTOR RECEPTOR

Gap junctional communication (GJC) between contacting cells has been p ostulated to be involved in the regulation of cell proliferation. This suggestion stems from numerous studies showing modulation of GJC by a gents that influence cellular proliferation. Platelet-derived growth f actor (PDGF), a strong mitogen, inhibits GJC in many cell types. To un derstand the molecular nature of the signal transduction pathway respo nsible for the GJC blockade, T51B rat liver epithelial cells, which la ck endogenous PDGF receptor (PDGFr), were infected with a retrovirus c ontaining either wild-type full-length cDNA of human PDGFr beta (Kin()) or a mutant PDGFr beta lacking receptor tyrosine kinase activity (K in(-)). PDGF caused a complete but transient interruption of cell comm unication in Kin(+) cells within 15-20 min of addition. This interrupt ion of GJC was not associated with a gross destabilization of gap junc tion plaques but with the phosphorylation of connexin43 (Cx43), the on ly known gap junction protein expressed in these cells. These effects were not exhibited in either control T51B cells or in Kin(-) cells, in dicating a requirement of the receptor tyrosine kinase activity. Furth er examination revealed that the newly phosphorylated Cx43 then underg oes a rapid degradation utilizing the lysosomal pathway resulting in a decreased total Cx43 protein level. The re-establishment of GJC follo wing PDGF treatment was dependent on protein synthesis. This report de scribes a suitable cell system which is currently being utilized for t he characterization of the PDGF signaling pathway responsible for the inhibition of GJC. (C) 1998 Wiley-Liss, Inc.