Activates CDC42, a member of the Ras-like family of Rho- and Rac proteins, by exchanging bound GDP for free GTP. Mediates VEGF-induced CDC42 activation. May regulate proangiogenic action of VEGF in vascular endothelial cells, including network formation, directional movement and proliferation. May play a role in regulating the actin cytoskeleton and cell shape. In peripheral membrane ruffles, colocolizes with F-actin. In confluent HUVECs, detected at cell-cell-contact sites where it colocalizes with vascular endothelial cadherin/CDH5. Expressed in endothelial cells (at protein level). Truncated N-terminus. Truncated N-terminus. Truncated C-terminus.