p110β inactivation does not inhibit VEGF-stimulated Akt phosphorylation. ECs were serum-starved overnight, then (A) pretreated with TGX-221 (100 nM; gray bar) for 60 minutes or (B) treated with Siβ siRNA (gray bar) as in supplemental Figure 3 to decrease p110β expression, before stimulation with VEGF (20 ng/mL). Control cells were treated with carrier or nonspecific siRNA (black bars). Lysates were immunoblotted for phospho-S473 Akt or phospho-T24 FoxO1/3, a target for Akt-mediated phosphorylation. PI3Kβ inactivation did not significantly affect Akt phosphorylation (mean ± SEM; n ≥ 3 independent experiments; P = nonsignificant by ANOVA).