The siRNA-mediated knockdown of Hsp90 or treatment with 17-DMAG induces apoptosis also in IL-6–independent MM.1s cells. (A) Western blot analysis of Hsp90α and Hsp90β protein expression in MM.1s cells that were transiently transfected either with siRNAs against Hsp90α, Hsp90β, or both. Staining of β-actin served as a loading control. (B-C) Viability of MM.1s cells was assayed with annexin V–FITC/PI staining either 96 hours after siRNA-mediated knockdown of Hsp90 (B) or 72 hours after treatment with different concentrations of 17-DMAG. Error bars denote the range of values derived from at least 3 independent experiments.