Overexpression of C/EBPβ induces resistance to IMiD compounds. (A) MM.1S cells (2 × 10⁶) were transfected by electroporation with either empty vector pcDNA3.1 or WT-C/EBPβ plasmids. After selection, cells were treated with pomalidomide (10μM) for 2 days. Cells were then lysed, and whole cell lysates were analyzed for C/EBPβ expression by Western blotting. β-actin expression was probed for loading control. (B) MM.1S cells overexpressing WT-C/EBPβ were treated with pomalidomide (10μM) for 2 days, and DNA synthesis was measured by ³H-thymidine incorporation. The amount of DNA synthesis in treated cells relative to the amount in control cells (as a percentage) was graphed. Results are shown as triplicates of mean ± SD.