Steel factor activation of c-Kit receptor, Erk, and PKB. HPCs were harvested after stimulation with SF (50 ng/mL) for various times, as indicated. c-Kit protein was immunoprecipitated and immunoprecipitates (A-B) or whole cell lysates (20 μg per lane) (C-F) analyzed by SDS-PAGE, followed by immunoblotting with the indicated antibodies. (A) Immunoblotting with antiphosphotyrosine antibody PY100. (B) Membrane from panel A was stripped and reprobed with anti–c-Kit antibody. (C) Immunoblotting with phospho-specific antibody toward Erk. (D) Membrane from panel C was stripped and reprobed with anti-Erk2 antibody. (E) Immunoblotting with phospho-specific antibody toward PKB. (F) Membrane from panel E was stripped and reprobed with antipan-PKB antibody.