Vascular endothelial growth factor (VEGF)-driven actin-based motility is mediated by VEGFR2 and requires concerted activation of stress-activated protein kinase 2 (SAPK2/p38) and geldanamycin-sensitive phosphorylation of focal adhesion kinase

In endothelial cells, vascular endothelial growth factor (VEGF) induces an accumulation of stress fibers associated with new actin polymerization and rapid formation of focal adhesions at the ventral surface of the cells. Thi s cytoskeletal reorganization results in an intense motogenic activity. Usi ng porcine endothelial cells expressing one or the other type of the VEGF r eceptors, VEGFR1 or VEGFR2, or human umbilical vein endothelial cells pretr eated with a VEGFR2 neutralizing antibody, we show that VEGFR2 is responsib le for VEGF-induced activation of the stress-activated protein kinase-2/p38 (SAPK2/p38), phosphorylation of focal adhesion kinase (FAK), and enhanced migratory activity. Activation of SAPK2/p38 triggered actin polymerization whereas FAX, which was phosphorylated independently of SAPK2/p38, initiated assembly of focal adhesions. Both processes contributed to the formation o f stress fibers. Geldanamycin, an inhibitor of HSP90 blocked tyrosine phosp horylation of FAK, assembly of focal adhesions, actin reorganization, and c ell, migration, all of which were reversed by overexpressing HSP90. We conc lude that VEGFR2 mediates the physiological effect of VEGF on cell migratio n and that two independent pathways downstream of VEGFR2 regulate actin-bas ed motility. One pathway involves SAPK2/p38 and leads to enhanced actin pol ymerization activity. The other involves HSP90 as a permissive signal trans duction factor implicated in FAK phosphorylation and assembly of focal adhe sions.