Inside-out signaling induces paxillin association with high-affinity α4 integrins. (A) Formyl peptide receptor-transfected U937 cells were stimulated with fMLP (100 nM) for the indicated time prior to lysis and precipitation of cell lysates with VCAM-1/Fc (7 mg/lane). A representative Western blot probed for paxillin (1 of 4 experiments) is shown. (B) Blots from all 4 experiments were analyzed by densitometry and normalized to the 0 time point. The mean ± SEM is shown.