Modulation of VEGF activity by the p110 and p85 subunits of PI 3-kinase in Ha-ras–transformed cells (NIH3T3R). (A) Stimulation of VEGF expression by cotransfection of increasing concentrations of the wt p110 subunit (0.1, 1, and 10 μg) of PI 3-kinase and 5 μg of wt HIF-1 expression vector. (B) Inhibition of VEGF expression under low-oxygen conditions by a mutant p85 subunit of PI 3-kinase (Δp85). NIH3T3R cells were cotransfected with the mutant p85 (2.5 μg) subunit of PI 3-kinase and a constant amount of reporter plasmid (5 μg; 385 bp; HIF-1 wt [×4]; HIF-1 mut [×5]; Fos-luc) and exposed to hypoxia (except Fos-luciferase) before assaying for luciferase activity. The relative fold induction refers to the ratio of luciferase activity measured in treated cells relative to the activity observed in the untreated controls. Values represent the means of at least three independent transfections. Error bars represent 1 SD of the mean. (C) Thin-layer chromatogram of PI 3-kinase activity from lysates of NIH3T3 and NIH3T3R cells treated with hypoxia and PDGF BB.