Vascular endothelial growth factor-mediated activation of p38 is dependent upon Src and RAFTK/Pyk2

Vascular endothelial growth factor ( VEGF) induces activation of p38 mitogen-activated protein kinase ( MAPK) in primary endothelial cells and may be critical for VEGF-induced angiogenesis. We investigated the molecular basis for p38 activation in response to VEGF. The expression of a C-terminal splice variant of FAK, FRNK, had no affect on VEGF-induced activation of p38; however, expression of a dominant-negative RAFTK/ Pyk2 mutant led to a decrease in the activation of p38, but had no affect on extracellular signal-regulated kinase (ERK). Since calcium regulates RAFTK/ Pyk2, we investigated its role in p38 activity. Preincubation with EGTA suppressed p38 activation, while calcium ionophore induced p38 activity. Inhibition of phospholipase C ( PLC) resulted in complete inhibition of ERK, while having no affect on p38 activity. These data suggested a bifurcation in the regulation of MAPKs that occurs at the level of PLC and RAFTK/ Pyk2 activation. Src family kinases interact with RAFTK/ Pyk2. Inhibition of Src by either pharmacological or genetic means decreased p38 activity. Finally, we found that both Src and RAFTK/ Pyk2 were essential for endothelial cell migration. These data identified a novel regulatory network involving extracellular calcium, RAFTK/ Pyk2, Src and p38. This signaling network appears to be critical for VEGF-induced endothelial cell migration.