Cooperative regulation of IRF4 by the cell cycle and bortezomib. Quantitative RT-PCR analysis and immunoblotting of IRF4 expression in MM1.S cells (A) cultured as in Figure 1B, and (B) at 7 hours from pulsing with BTZ (1 hour, 120nM) in pG1 (PD, 24 hours) or in pG1-S (4 hours after PD withdrawal). (C) IRF4 protein level, MT⁻ and live cells were determined in MM1.S cells at 72 hours after infection with IRF4 or the control GFP shRNA lentivirus. (D) MM1.S cells were treated with PD and pulsed with BTZ (60nM) after lentivirus infection as indicated. Percentage of live cells was determined using cells infected with the GFP shRNA lentivirus as a control. (E) KMS12PE cells infected with a retrovirus expressing human IRF4 (ToIRF4) or the control virus (Vxy) were treated with doxycycline (Dox, 20 ng/mL), PD (0.3μM), or BTZ (250nM) as indicated. The IRF4 protein level was determined by immunoblotting and cell death by ToPro-3 staining. Data are representative of 3 independent experiments.