Depolarization-Induced Tyrosine Phosphorylation of pl30cas.

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KCl-treatment of PC12 cells induces depolarization of the plasma membrane and Ca2+ influx into the cells. We have previously shown that KCl induced tyrosine phosphorylation of cellular proteins of 120, 110, 68, 44, and 42 k, and that the 68 k protein was paxillin. In the present study, we found that the 120 k protein was a Crk-associated Src substrate, p130cas. KCl-induced tyrosine phosphorylation of p130cas was not observed in EGTA-containing medium, suggesting that it was due to Ca2+ influx into the cells. Time course experiments showed that tyrosine phosphorylation of p130cas peaked at 5min after stimulation and returned to the basal level at 60min, while mobility shift of p130cas was observed within 2 min and lasted over 60min, indicating that serine or threonine residues, in addition to tyrosine, were phosphorylated on KCl stimulation. In vitro kinase assay of immunoprecipitates with anti-p130cas antibody suggested that some protein-tyrosine kinases were associated with p130cas. Using the substrate region of p130cas as the substrate, we found that Fyn and Src were activated on stimulation with KCl. These results indicate that tyrosine phosphorylation of p130cas may be involved in Ca2+-dependent events in neuronal and neuroendocrine cells.
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