Requirement of Ca2+ and PKCδ for janus kinase 2 activation by angiotensin II:: Involvement of PYK2

In vascular smooth muscle cells, angiotensin II (AngII) stimulates association of its G protein-coupled AngII type I (AT(1)) receptor with Janus kinase 2 (JAK2), resulting in the activation of signal transducer and activator of transcription proteins. Although the association and activation of subsequent signal transducer and activator of transcription proteins appear to prerequire JAK2 activation, the signaling mechanism by which the AT(1) receptor activates JAK2 remains uncertain. Here, we have examined the signaling mechanism required for JAK2 activation by AngII in vascular smooth muscle cells. We found that AngII, through the AT(1) receptor, rapidly stimulated JAK2 phosphorylation at Tyr(1007/1008), the critical sites for the kinase activation. By using selective agonists and inhibitors, we demonstrated that PLO and its derived signaling molecules, phosphatidylinositol triphosphate/ Ca2+ and diacylglycerol/PKC, were essential for AngII-induced JAK2 phosphorylation. The PKC isoform required for JAK2 activation appears to be PKCdelta since a selective PKCdelta but not PKCalpha/beta inhibitor and dominant-negative PKCdelta overexpression inhibited JAK2 activation. We further examined a link between JAK2 and a Ca2+/PKC-sensitive tyrosine kinase, PYK2. We found that PYK2 activation by AngII requires PKCdelta, and that PYK2 associates with JAK2 constitutively. Moreover, transfection of two distinct PYK2 dominant-negative mutants markedly inhibited AngII-induced JAK2 activation. From these data we conclude that AT(1)-derived signaling molecules, specifically Ca2+ and PKCdelta, participate in AngII-induced JAK2 activation through PYK2. These data provide a new mechanistic insight by which the hormone AngII exerts its cytokine-like actions in mediating vascular remodeling.