Epidermal growth factor-induced activation and translocation of phospholipase C-gamma 1 to the cytoskeleton in rat hepatocytes.

In this study, we have examined the relationship between epidermal growth factor (EGF)-induced tyrosine phosphorylation of phospholipase C-gamma 1 (PLC-gamma 1) and its translocation from the cytosol to the Triton X-100-insoluble cytoskeleton fraction in rat hepatocytes. The translocation of PLC-gamma 1 was specific for EGF stimulation, because a similar effect was not observed with insulin or vasopressin. EGF caused a transient increase of PLC activity in the cytoskeleton fraction which could be abolished by immunoprecipitating PLC-gamma 1. Tyrosine phosphorylated PLC-gamma 1 was seen only in the cytoskeleton fraction, suggesting that tyrosine phosphorylation is required for PLC-gamma 1 translocation to the cytoskeleton. This process may involve binding of PLC-gamma 1 to actin filaments, since actin was immunoprecipitated together with PLC-gamma 1 in the cytoskeleton after EGF treatment. EGF-induced translocation of PLC-gamma 1 to the cytoskeleton was not inhibited by pertussis toxin, but Gi alpha was translocated in an EGF-dependent manner, suggesting that the interaction of PLC-gamma 1 with its activated Gi-protein is downstream from both PLC-gamma 1 tyrosine phosphorylation and its translocation to the cytoskeleton. Taken together, the present studies indicate that EGF-induced tyrosine phosphorylation of PLC-gamma 1, its association with the cytoskeleton, and its interaction with activated Gi alpha protein are all obligatory for PLC-gamma 1 activation in hepatocytes.