Glycogen synthase kinase 3β is tyrosine phosphorylated by PYK2

Glycogen synthase kinase 3β (GSK3β) is a Ser/Thr kinase that is involved in numerous cellular activities. GSK3β is activated by tyrosine phosphorylation. However, very little is known about the tyrosine kinases that are responsible for phosphorylating GSK3β. In this report, we investigated the ability of the calcium-dependent tyrosine kinase, proline-rich tyrosine kinase 2 (PYK2) to tyrosine phosphorylate GSK3β. In transfected CHO cells, it was demonstrated that PYK2 tyrosine phosphorylates GSK3β in situ. The two kinases also coimmunoprecipitated. Furthermore, GSK3β was tyrosine phosphorylated in vitro by an active, wild type PYK2, but not by the inactive, kinase dead form of PYK2. Therefore, this study is the first to demonstrate that GSK3β is a substrate of PYK2 both in vitro and in situ.