Protein kinase C-dependent protein kinase D activation modulates ERK signal pathway and endothelial cell proliferation by vascular endothelial growth factor

Vascular endothelial growth factor ( VEGF) is essential for many angiogenic processes both in normal conditions and in pathological conditions. However, the signaling pathways involved in VEGF-induced angiogenesis are not well defined. Protein kinase D (PKD), a newly described serine/threonine protein kinase, has been implicated in many signal transduction pathways and in cell proliferation. We hypothesized that PKD would mediate VEGF signaling and function in endothelial cells. Here we found that VEGF rapidly and strongly stimulated PKD phosphorylation and activation in endothelial cells via VEGF receptor 2 (VEGFR2). The pharmacological inhibitors for phospholipase C gamma (PLC gamma) and protein kinase C(PKC) significantly inhibited VEGF-induced PKD activation, suggesting the involvement of the PLC gamma/PKC pathway. In particular, PKC alpha was critical for VEGF-induced PKD activation since both overexpression of adenovirus PKC alpha dominant negative mutant and reduction of PKC alpha expression by small interfering RNA markedly inhibited VEGF-induced PKD activation. Importantly, we found that small interfering RNA knockdown of PKD and PKC alpha expression significantly attenuated ERK activation and DNA synthesis in endothelial cells by VEGF. Taken together, our results demonstrated for the first time that VEGF activates PKD via the VEGFR2/PLC gamma/ PKC alpha pathway and revealed a critical role of PKD in VEGF-induced ERK signaling and endothelial cell proliferation.