Mcl-1 induction does not sufficiently explain the IL-6–dependent survival of INA-6. (A) Cells were deprived of IL-6 for 12 hours and were restimulated for the times indicated. INA-6 cells permanently cultured in the presence of IL-6 were taken as a reference. Cell lysates were prepared, and equal amounts of protein were subjected to immunoblot analysis. (B) Mcl-1 and EGFP were coexpressed in INA-6 cells by lentiviral infection (INA-6–Mcl-1).As a control, infection was performed with a corresponding vector carrying EGFP cDNA only (INA-6). Infection efficiency was about 75% as measured by green fluorescence. The infected cells were cultured in the presence of IL-6 (+) or were withdrawn from IL-6 for 12 hours (–). Mcl-1 expression was analyzed by immunoblotting. (C) Control, Mcl-1–, and Bcl-xL–expressing INA-6 cells were grown with or without IL-6 for the times indicated and were subjected to an annexin V apoptosis assay. Viable cells are referred to as annexin V–negative cells. INA-6 cells grown in the presence of IL-6 were set 100%. Data for control and INA-6–Mcl-1 cells represent mean values ± SD of 3 independent experiments.