A functional SH2 domain of Lnk is required for inhibition of Kit-dependent proliferation and MAPK activation. (A,B) BMMCs expressing different Lnk forms were cultured with the indicated concentrations of SCF (A) or IL-3 (B) for 24 hours, and proliferation was measured as [³H]thymidine incorporation. The values are the mean counts per minute plus or minus SD (error bars) of triplicate determinations and are representative of at least 2 independent experiments. (C) Total BMMC lysates were stimulated with SCF for the indicated times and then subjected to immunoblot analysis with anti–phospho-Erk1/2 (p-Erk) and anti-Erk1/2 antibodies.