Combined knockdown of Hsp90α and Hsp90β is required to induce apoptosis in INA-6 cells. (A-C) Western blot analysis of Hsp90α, Hsp90β, or pan-Hsp90 protein expression in INA-6 cells that were transiently transfected either with siRNAs against Hsp90α, Hsp90β, or both and cultured in the presence of BMSCs. Staining of β-actin served as a loading control. (D) Viability of the transfected INA-6 cells measured by annexin V–FITC/PI staining. INA-6 cells were transiently transfected either with siRNAs against Hsp90α, Hsp90β, or both and cultured either in the absence or presence of BMSCs for 96 hours. Error bars denote the range of values derived from at least 3 independent experiments.