p38 was phosphorylated by Epo and IL-3 stimulation. p38 was immunoprecipitated at various time points (0 to 60 minutes) in Epo-stimulated FD-EPO cell lysates (A) or IL-3–stimulated FDC-P2 cell lysates (B). The immunoprecipitates were immunoblotted with antiphosphotyrosine antibody 4G10 (left panels) or with p38 antibody (right panels). Arrows indicate the phosphorylated p38 (left panels) and total p38 (right panels).