A, Activation of Arf6 and tyrosine phosphorylation of VEGFR2 upon VEGF stimulation of HUVECs. B, Coprecipitation of GEP100 with VEGFR2 upon VEGF stimulation of HUVECs, analysed by anti-GEP100 immunoprecipitation (IP) and anti-VEGFR2 immunoblot. PI, pre-immune serum. C–D, Activities of Arf6 (C), and Erk and Akt (D) in HUVECs transfected with siRNAs for GEP100 or irrelevant sequences (Irr) upon VEGF stimulation. E, Coprecipitation of VEGFR2-V5 and its tyrosine phosphorylation-deficient mutants (951F, 1175F and 1214F) with HA-GEP100 expressed in Cos-7 cells, analysed by anti-HA (GEP100) immunoprecipitation and anti-V5 (VEGFR2) immunoblot. F, Activation of Arf6-HA by VEGFR2-V5 or its mutants (951F, 1175F and 1214F) upon VEGF stimulation in Cos-7 cells, in which non-tagged GEP100 cDNA was simultaneously transfected. In A–F, 10 ng ml−1 VEGF was used for stimulation for 1 min (+) or for the indicated times, while controls included cells without stimulation (0 min or −). Arf6 activities were assessed by the GST-GGA pulldown method (A, C, F). Total, total cell lysates (20 µg). In A–D, HUVECs were cultured in low serum (0.5% FCS) medium for 16 h before stimulation. These assays were performed at least twice and representative figures are shown.