(A and B) Overexpression of miR-548m induces HDAC6 downregulation and lymphoma cell apoptosis and enhances mitoxantrone-induced cell apoptosis. Jeko-1 and SUDHL-4 cells transfected with pre–miR-548m or pre-miR control were treated with vehicle control or mitoxantrone (0.2 μM) for 24 hours with or without HK cell adhesion. *P < 0.05; **P > 0.05. (A) The relative level of HDAC6 protein was measured by quantitative densitometry and is indicated below each lane. (C) HDAC6 knockdown after 48 hours of transfection with HDAC6 shRNA constructs 1 or 2 or nonsilencing control. (D) Knockdown of HDAC6 induces cell apoptosis and enhances mitoxantrone-induced cell apoptosis with and without HK cell adhesion. Jeko-1 or SUDHL-4 cells transfected with HDAC6 shRNA-2 (shHDAC6) or control shRNA (shCtrl) were incubated for 48 hours and then treated with vehicle control or mitoxantrone (0.2 μM) for 24 hours. Apoptosis was analyzed by Annexin V. (E and F) Overexpression of HDAC6 inhibits mitoxantrone-induced lymphoma cell apoptosis in Jeko-1 cells in the presence of HK cell adhesion. Jeko-1 cells were transfected with pCDNA3 control (pLCtrl) or pCDNA3-HDAC6 (pLHDAC6) for 24 hours. Cells, collected and washed in suspension versus in adhesion with HK, were treated with mitoxantrone (0.2 μM) for 12 hours. (E) HDAC6 protein levels were then analyzed by Western blot and (F) apoptosis was analyzed by Annexin V. Data are representative of at least 3 independent experiments (mean ± SD).