Selectivity of phospholipase C isozymes in growth factor signaling

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Abstract
Xenopus laevis oocytes were injected with mRNA extracted from growth factor‐responsive CCL39, Chinese hamster lung fibroblasts. The expression of functional growth factor receptors on the oocytes was demonstrated by growth factor‐induced 45Ca2+ efflux. To determine the isozyme(s) of phospholipase C (PLC) coupled to growth factor receptors, growth factor‐induced 45Ca2+ efflux were measured following coinjection of mRNA from CCL39 cells with PLC antibodies. PLC‐γ1 antibody did not lead to loss of 45Ca2+ efflux induced by thrombin but resulted in loss of that induced by platelet‐derived growth factor (PDGF). In contrast, PLC‐δ1 antibody did not block PDGF‐induced 45Ca2+ efflux but led to inhibition of thrombin‐induced 45Ca2+ efflux. PLC‐β1 antibody did not affect Ca2+ efflux by the treatment of either thrombin or PDGF. These results suggest that these growth factor receptors are coupled to specific effectors, i.e. thrombin receptor to PLC‐δ1 and PDGF receptor to PLC‐γ1.