Activation of insulin-like growth factor type-1 receptor is required for H2O2-induced PKB phosphorylation in vascular smooth muscle cells

Evidence accumulated in recent years has revealed a potential role for reactive oxygen species (ROS) in the pathophysiology of cardiovascular diseases. However, the precise mechanisms by which ROS contribute to the development of these diseases are not fully established. Previous work from our laboratory has indicated that exogenous hydrogen peroxide (H2O2) activates several signaling protein kinases, such as extracellular signal-regulated kinase 1 and 2 (ERK1/2) and protein kinase B (PKB) in A10 vascular smooth muscle cells (VSMC). However, the upstream elements responsible for this activation remain unclear. Although a role for epidermal growth factor receptor (EGFR) protein tyrosine kinase (PTK) in H2O2-induced ERK1/2 signaling has been suggested, the contribution of this PTK or other receptor or nonreceptor PTKs to PKB activation is not well defined in VSMC. In this study, we used pharmacological inhibitors to investigate the role of receptor and Src-family-PTKs in H2O2-induced PKB phosphorylation. AG1478, a specific inhibitor of EGFR, failed to attenuate the H2O2-induced increase in PKB Ser473 phosphorylation, whereas AG1024, an inhibitor of insulin-like growth factor type1 receptor (IGF-1R)-PTK, almost completely blocked this response. H2O2 treatment also enhanced tyrosine phosphorylation of the IGF-1Rbeta subunit, which was significantly inhibited by AG1024 pretreatment of cells. Furthermore, pharmacological inhibition of Src by PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazole(3,4-d) pyrimidine) decreased PKB phosphorylation. Moreover, H2O2-induced PKB phosphorylation was associated with increased tyrosine phosphorylation of c-Src and Pyk2 in an AG1024- and PP2-inhibitable manner. In conclusion, these data provide evidence of the contribution of IGF-1R-PTK in initiating H2O2-evoked PKB phosphorylation in A10 VSMC, with an intermediary role for c-Src and Pyk2 in this process.