Fig. 3. RacV12 also restores mitogenesis in cells with loss of Abl kinase activity. (A) RacV12 rescues the mitogenic defect in Abl/Arg^–/–3T3 cells. Quiescent cells that were infected with wild-type (mock) or retrovirus as shown, were stimulated or not with indicated mitogen for 16 hours in the presence of BrdU. (Top panels) The PDGF responses; (bottom panels) the serum (10% fetal calf serum) responses. (B) RacV12 rescues the mitogenic inhibition induced by the Abl kinase inhibitor STI 571. NIH3T3 quiescent cells that were infected with wild-type (mock) or RacV12-expressing retrovirus were treated or not with various concentrations of STI 571 1 hour before stimulating cells with serum for 18 hours in the presence of BrdU as indicated. The mean±s.d. of the percentage of BrdU-positive cells under the specified conditions is shown.