Fig. 1. Abl regulates PDGF-induced Rac activation. (A) Activation of PDGFRß in Abl/Arg^+/+3T3 and Abl/Arg^–/–3T3 cells. In vitro kinase assay of the immunoprecipitated PDGFRß from indicated cell lysates as described in Materials and Methods. Autophosphorylated PDGFR (³²P-PDGFR) is shown. The level of the immunoprecipitated receptor is also shown and was assessed by western blotting with the PRC antibody. (B) PDGF-induced Rac activation is impaired in Abl/Arg^–/–3T3 cells. (C) Abl-NLS^– expression restored PDGF-induced Rac activation in Abl/Arg^–/–3T3 cells (left panel). Cells were stimulated with PDGF for 0-240 minutes. GTP-bound Ras, Rho Rac and Cdc42 (shown as GTPase-GTP) were precipitated as described in Materials and Methods and detected with specific antibody. Total GTPase level is also shown. (C, right panel) Western blotting of immunoprecipitated Abl from indicated cell-lysates using Ab-3 antibody. The level of Abl-NLS^– expressed in Abl/Arg^–/–3T3 was comparable with the endogenous level of Abl in Abl/Arg^+/+3T3 cells.