Importance of guanine exchange factor Vav2 for C. jejuni -induced Cdc42 activation. INT-407 cells were transfected for 48 hours with siRNA for Vav2 (A), Tiam-1 (B) or DOCK180 (C) as well as a scrambled siRNA as control. Immunoblotting with the indicated antibodies confirmed knockdown of the respective proteins. GAPDH expression levels were determined as control. Quantification of Cdc42 GTPase activity after infection with wt C. jejuni 81-176 for 6 hours. The presence of bound, active Cdc42-GTP was analyzed in CRIB-GST pulldown assays followed by Western blotting using α-Cdc42 antibody. One hundred % of activity corresponds to the highest amount of detected Cdc42-GTP level (lane 1).