Shc is required for specific signal transduction pathways downstream of integrins and VEGF. (A) The role of Shc in VEGF signaling was assayed in HUVECs. Cells were treated for 5 minutes with 100 ng/mL of VEGF or vehicle. Cell lysates were separated by SDS-PAGE and immunoblotted for the indicated proteins. Quantitation values shown are means ± SEM (n = 4 independent experiments). (B) The role of Shc in integrin signaling was assayed in HUVECs. Cells were allowed to adhere and spread on FN or CL (10 μg/mL) or kept as controls. Cell lysates were separated by SDS-PAGE and immunoblotted for the indicated proteins. Quantitation values shown are means ± SEM (n = 3 independent experiments). *P < .05. (C) Schematic model of how Shc is thought to regulate angiogenesis in ECs. Shc participates in signaling from FN-binding integrins such as α_vβ₃ and α₅β₁, which is required for EC spreading and migration. Shc is simultaneously required for EC survival induced by VEGF. Loss of Shc results in attenuation of Akt activation by the integrin and VEGF pathways in ECs and therefore results in defective angiogenesis, as is seen in the zebrafish and the mouse.