CaM kinase II-dependent activation of tyrosine kinases and ERK1/2 in vascular smooth muscle

In vascular smooth muscle (VSM) and many other cells, G protein receptor-coupled activation of mitogen-activated protein kinases has been linked, in part, to increases in free intracellular Ca2+. Previously, we demonstrated that ionomycin-, angiotensin II-, and thrombin-induced activation of extracellular signal-regulated kinase (ERK)1/2 in VSM cells was attenuated by pretreatment with KN-93, a selective inhibitor of the multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase II). In the present study, we show that the Ca2+ dependent pathway leading to activation of ERK1/2 is preceded by nonreceptor proline-rich tyrosine kinase (PYK2) activation and epidermal growth factor (EGF) receptor tyrosine phosphorylation and is attenuated by inhibitors of src family kinases or the EGF receptor tyrosine kinase. Furthermore, we demonstrate that pretreatment with KN-93 or a CaM kinase II inhibitor peptide inhibits Ca2+-dependent PYK2 activation and EGF receptor tyrosine phosphorylation in response to ionomycin, ATP, and platelet-derived growth factor but has no effect on phorbol 12,13-dibutyrate- or EGF-induced responses. The results implicate CaM kinase II as an intermediate in the Ca2+/calmodulin-dependent activation of PYK2.