Proliferation synergism of SCF correlates with Mcl-1 inducibility.

(A) Requirement of SCF costimulation for optimal proliferation of TF-1 cell line. Stationary TF-1 and JYTF-1 cells were transferred into fresh culture media containing IL-5 (⋄), SCF (▵), IL-5 plus SCF (○), or no cytokine (■) and the viable cell numbers were measured every 24 hours by trypan blue dye exclusion assay. Left panel is for TF-1 cells and right panel is for JYTF-1 cells. Each number is the average of 3 independent measurements and SDs are shown as error bars. (B) SCF costimulation induced Mcl-1 expression in TF-1 cells. TF-1 (lanes 1-4) and JYTF-1 (lanes 5-8) cells were starved in cytokine-free medium for 24 hours (lanes 1 and 5) and then treated with IL-5 (lanes 2 and 6), SCF (lanes 4 and 8), or IL-5 plus SCF (lanes 3 and 7) for 1 hour before harvesting for lysate preparation. Western blot analysis was performed for the expression of Mcl-1, Bcl-2, Bax, and α-tubulin as described in Figure 1B. Experiments were repeated twice and a representative result is shown in this figure.