BET inhibition–mediated upregulation of HDAC6 expression limits its efficacy against MM cells. (A) JQ1 treatment increases HDAC6 protein expression. LP-1 and RPMI-8226 MM cells were treated with the indicated concentrations of JQ1 for 24 hours. Protein expression was determined by immunoblotting. (B) JQ1 increases HDAC6 expression in a time-dependent manner. LP-1 and RPMI-8226 MM cells were treated with 500 nM JQ1 for the indicated times. Protein expression was determined by immunoblotting. (C) Silencing HDAC6 decreases c-MYC and BCL-2 expression. LP-1 cells were infected with nontarget (NT) control or HDAC6 lentiviral shRNA, and positively infected cells were selected with puromycin. Immunoblotting confirmed knockdown of HDAC6 and decreased levels of c-MYC and BCL-2. (D) Knockdown of HDAC6 augments the antimyeloma activity of JQ1. LP-1 and RPMI-8226 MM cells were infected with NT control or HDAC6 lentiviral shRNA. Cells transfected with NT control or HDAC6 shRNA were treated with the indicated concentrations of JQ1 for 72 hours, and cell viability was determined by MTT assay. Data are shown as mean ± SD; n = 3. *Indicates a significant difference compared with NT transfected cells treated with the same concentration. P < .05.