Knockdown of HDAC6 enhances bortezomib-induced apoptosis. (A) HDAC6 expression correlates with Myc expression in MM cell lines. HDAC6 expression was determined in MM cell lines and EBV-immortalized B cells by immunoblotting. (B,C) Knockdown of HDAC6 by siRNA sensitizes NCI-H929 cells to BZ-induced apoptosis. Cells were transfected with siRNA and knockdown was confirmed by immunoblotting. After exposure to siRNA, cells were treated with 5 nM BZ for 24 hours and apoptosis was measured by PI-FACS. Mean (n = 3), SD. * indicates a significant difference from nontarget siRNA–transfected cells treated with bortezomib, P < .05.