EPO and IL-3 activate tyrosine phosphorylation of Cbl. Ba/F3 (lanes 1-3), DA-3-EPO-R (lanes 4-6), and HCD-57 (lanes 7-10) cells were depleted of cytokine for 4 hours and stimulated with no factor (lanes 1, 4, 7, and 9), 50 U of murine IL-3 (lanes 2 and 5) or 50 U/mL of human EPO (lanes 3, 6, 8, and 10) for 15 minutes. Following cell lysis, an immunoprecipitation was performed with an anti-Cbl polyclonal antibody. Lysate controls are shown in lanes 9 and 10. Immune complexes were resolved by SDS-PAGE and blotted to nitrocellulose. The immunoblot was probed with an anti-phosphotyrosine (pTyr) monoclonal antibody 4G10. Molecular mass standards are indicated.