IL-6 does not protect against Dex-induced apoptosis in AS-Hsp27-transfected cells. (A) MM.1R cells were transfected with GFP vector alone or GFP-AS-Hsp27. Following transfections, GFP⁺ cells were selected by flow cytometry, treated with Dex (5 μM) in the presence or absence of IL-6 (100 ng/mL) for 48 hours, and analyzed for apoptosis by dual-fluorescence staining with DNA-binding fluorochrome Hoechst 33342 (HO) and propidium iodide (PI). PI^-- and HO+-stained cells represent apoptotic cells. Median percent apoptotic cells: Dex plus vector = 6.4%; Dex plus AS-Hsp27 = 78.6% ± 5.6%; AS-Hsp27 = 9.3%; and Dex plus AS-Hsp27 plus IL-6 = 76.3% ± 2.1%. Results are mean ± SD from 3 independent experiments; P < .003. (B) MM.1S cells were transfected with GFP vector alone or GFP-AS-Hsp27. Following transfections, GFP⁺ cells were selected by flow cytometry; treated with Dex (5 μM) in the presence or absence of IL-6 (100 ng/mL) for 48 hours, and analyzed for apoptosis, as described. Median percent apoptotic cells: Dex plus vector = 76.2% ± 3.5%; Dex plus AS-Hsp27 = 84.6% ± 5.6%; Dex plus vector plus IL-6 = 20.4% ± 1.2%; Dex plus AS-Hsp27 plus IL-6 = 73.4%. Results are mean ± SD from 3 independent experiments; P < .003. (C) Schema showing the mechanism whereby inhibition of Hsp27 enables Dex to trigger apoptosis via Smac release in Dex-resistant cells. Dex-induced apoptotic signaling in AS-Hsp27-transfected cells is not blocked by IL-6.