C/EBPβ regulates IRF4-dependent transcription factors such as XBP1 and BLIMP1. MM cells were transfected with EV, (A) DN-C/EBPβ, or (B) WT-C/EBPβ. Transfected cells were selected for 10 days by G418 (500 μg/mL). The selected cells were analyzed for expression of XBP1 by Western blotting with the anti-XBP1 antibody. (C) EV- and WT-C/EBPβ–transfected and selected cells were analyzed for the protein expression of BLIMP1. β-Actin was used as a loading control. Vertical lines have been inserted to indicate a repositioned gel lane.