Fig. 8. Src kinase inhibition does not block Rac activation by S1P. Serum-starved HUVECs were pretreated with 5 µM PP2 for 20 minutes and 0.5 µM S1P was added for the indicated times. Active, CRIB-bound Rac1 is shown in the upper panel and the total amount of proteins in the middle panel. Fold stimulation of GTP-bound Rac was determined following normalization against total Rac. Blotting of the same samples with an anti-active-Erk1/2 antibody (pErk1/2) is shown below. The results shown are representative of three independent experiments.