Vasoactive intestinal peptide induces tyrosine phosphorylation in PC12h cells.

Vasoactive intestinal peptide (VIP) is a neuropeptide that induces neuronal differentiation through a cAMP-dependent mechanism. We have previously shown that VIP induces tyrosine phosphorylation and activation of MAP kinases in PC12h cells [J. Biochem. 115, 304-308 (1994)]. In the present study, we showed by Western blotting with anti-phosphotyrosine antibodies that in PC12h cells VIP induced tyrosine phosphorylation of proteins of 140, 120, 110, and 70 kDa in addition to MAP kinases. The immunoprecipitates with anti-phosphotyrosine antibody from VIP-treated cells contained high activity of protein kinase phosphorylating poly(glu-tyr) and enolase; the activity from VIP-stimulated cells was 1.5-2 times higher than that from unstimulated cells. In vitro kinase reaction without extrinsic substrates resulted in tyrosine phosphorylation of doublet proteins which migrated slower than pp125FAK on SDS-PAGE. An increase in kinase activity of the immunecomplex was detected when the cells were stimulated with forskolin. These results suggest that protein tyrosine phosphorylation is involved in differentiation of neuronal cells stimulated by VIP and that it is regulated by a cAMP-dependent mechanism.