SELECTIVITY OF PHOSPHOLIPASE-C ISOZYMES IN GROWTH-FACTOR SIGNALING

Xenopus laevis oocytes were injected with mRNA extracted from growth f actor-responsive CCL39, Chinese hamster lung fibroblasts. The expressi on of functional growth factor receptors on the oocytes was demonstrat ed by growth factor-induced Ca-45(2+) efflux. To determine the isozyme (s) of phospholipase C (PLC) coupled to growth factor receptors, growt h factor-induced Ca-45(2+) efflux were measured following coinjection of mRNA from CCL39 cells with PLC antibodies. PLC-gamma1 antibody did not lead to loss of Ca-45(2+) efflux induced by thrombin but resulted in loss of that induced by platelet-derived growth factor (PDGF). In c ontrast, PLC-delta1 antibody did not block PDGF-induced Ca-45(2+) effl ux but led to inhibition of thrombin-induced Ca-45(2+) efflux. PLC-bet a1 antibody did not affect Ca2+ efflux by the treatment of either thro mbin or PDGF. These results suggest that these growth factor receptors are coupled to specific effectors, i.e. thrombin receptor to PLC-delt a1 and PDGF receptor to PLC-gamma1.