G-CSF-induced proliferation of primary myeloid progenitors. (A) 20 000 Lin^- bone marrow cells from wild-type mice were cultured for 7 days in the presence of G-CSF and kit ligand. On day 3 of culture, the indicated amount of PP2 or vehicle alone (DMSO) was added to the culture. (B) 20 000 Lin^- bone marrow cells isolated from wild-type (WT) or HLF mice were cultured for 7 days in the presence of G-CSF and kit ligand. On day 3 of culture, 1.0 μM PP2 was added to the indicated HLF culture. Treatment of HLF cells with vehicle alone (DMSO) had no effect on cell proliferation (data not shown). Data represent the mean ± SEM of triplicate measurements and are representative of 3 independent experiments.