Noxa is induced in Myc-expressing cells after bortezomib or BZ + SAHA treatment. (A) Myc activation promotes BZ- and BZ + SAHA–induced Noxa expression. HFFs expressing the MSCV-IRES-puro or MSCV-Myc-ER^TAM-IRES-puro retroviruses were pretreated with 1 μM 4-HT for 24 hours and then treated with 100 nM BZ, 2 μM SAHA, or both for 24 hours. Cells were collected and immunoblotting was performed as described in “Immunoblot analyses.” (B) Knockdown of Noxa blocks caspase-4 activation by BZ + SAHA. Cells were exposed to Noxa or nontarget (NT) siRNA and then pretreated with 1 μM 4-HT for 24 hours followed by treatment with 100 nM BZ, 2 μM SAHA, or both for 24 hours. Inhibition of Noxa induction and caspase-4 cleavage were determined by immunoblotting. (C) Knockdown of Noxa reduces BZ- and BZ + SAHA–induced apoptosis. Knockdown of Noxa and treatment of cells were performed as described in panel B. Apoptosis was measured by PI-FACS analysis. Mean (n = 3), SD. * indicates a significant difference from nontarget siRNA–treated cells, P < .05. (D) Noxa expression is induced by bortezomib and BZ + SAHA in NCI-H929 MM cells but not in EBV-immortalized B cells. Cells were treated with 5 nM BZ, 2 μM SAHA, or both agents for 24 hours. Noxa expression was determined by immunoblotting. (E,F) Noxa expression was knocked down in NCI-H929 cells using siRNA and the Nucleofector system. Cells were then treated with 5 nM BZ, 2 μM SAHA, or both agents for 24 hours. Inhibition of Noxa expression was confirmed by immunoblotting and apoptosis was measured by PI-FACS analysis. Mean (n = 3), SD. * indicates a significant difference from nontarget siRNA–treated cells, P < .05.