Effect of expression of dominant-negative Rac (RacN17) in mast cells. Expression of dominant-negative Rac (RacN17) in mast cells impairs integrin- and c-Kit–induced haptotaxis. Mast cells from wild-type mice were generated as described in “Materials and methods.” These cells were transduced with either the empty MIEG3-EGFP or the MIEG3-RacN17-EGFP retrovirus and sorted to homogeneity. (A) Demonstrated are the expression of HA-RacN17 (lane 2) as determined by Western blotting using an anti-HA antibody (top panel), and the expression of endogenous Rac protein as well as of HA-tagged RacN17 detected with an anti-Rac antibody (bottom panel). The positions of endogenous Rac (lanes 1-2) and the slow-migrating HA-RacN17 (lane 2) are indicated. (B) Migration assay was performed with the use of mast cells transduced with either the empty vector (MIEG3) or HA-RacN17 in the presence or absence of SCF. Data are the means ± SEMs of 3 independent experiments. *P < .05 for MIEG3 versus RacN17.