Bortezomib inhibits Sp1 protein expression and function. (A) Reduced Sp1 protein expression in Kasumi-1 and MV4-11 cells treated with indicated dosage of bortezomib for 24 hours. (B) Reduced Sp1 protein level in MV4-11 xenografts following 48-hour exposure to a single dose (2 mg/kg) of bortezomib (intravenous bolus). Error bars represent SD. (C) Bortezomib abolished Sp1 and NF-κB binding to DNMT1 promoter. EMSA was performed with nuclear extracts prepared from MV4-11 cells untreated or treated with bortezomib or decitabine. The DNMT1/Sp1 probes used are shown on the top of each panel. C indicates untreated; D: decitabine (2.5 μM); and B: bortezomib (60 nM).