STAT3 knockdown partially reverses the protective effect of IL-6. RNA (A) and protein lysates (B) were prepared from cells 72 hours after nucleoporation with either control siRNA or STAT3 siRNA and after 24 hours IL-6 treatment. RNA expression of Mcl-1 and SOCS3 was determined by qRT-PCR and is graphed as fold change relative to untreated control siRNA cells. Protein was subjected to SDS-PAGE and western blotting for phospho-STAT3, total STAT3, Mcl-1, and actin. (C) Forty-eight hours after siRNA nucleoporation, cells were treated with 1.5 μM of ABT-737 with or without 1 ng/mL IL-6 for 24 hours and cell death measured by annexin V-FITC and PI staining. Data are presented as the mean ± SE of 3 independent experiments (**P < .01; ****P < .0001).