Reduced expression of the IL-3/GM-CSF receptor β-chain subunit in bcr-abl–expressing/Stat-5–activated cells.

(A, top) The β-chain of IL-3/GM-CSF receptor was immunoprecipitated from equal-protein extracts (200 μg) of Mo7e or MBA cells (experiment 1) or from these cell extracts and K562 cells (experiment 2). Immunoprecipitates were immunoblotted with β-chain antibody. The migration of the 130-kd β-chain band is shown. (bottom) Equal-protein lysates (400 μg) from bcr-abl⁺ (K562, MBA, KBM5) and bcr-abl⁻ (KG-1, TF₁, Mo7e) cells were subjected to receptor β-chain immunoprecipitation and immunoblotting with anti–β-chain. Arrows depict the 130-kd β-chain band and the immunoglobulin heavy-chain band. (B) Stat-5 activation in leukemic cells. Leukemic cell lines were examined for activated Stat-5 by immunoblotting equal-protein cell lysates (30 μg) with anti–phospho–Stat-5. All cells were cultured in the absence of exogenous cytokines for 8 hours before extracts were prepared. As a control (last lane), Mo7e cells were treated with 30 ng/mL IL-3 for 15 minutes before harvesting. The relative migrations of p210^bcr-abl and 95 kd Stat-5 are depicted.