Knockdown of IκB-ζ is toxic to ABC DLBCL. (A) IκB-ζ shRNA 1 and 2 downregulate IκB-ζ mRNA and protein in HBL-1 and OCI-Ly3, measured by quantitative PCR and western blotting. Error bars indicate the standard deviation. (B) IκB-ζ knockdown by 2 independent shRNAs is toxic to IκB-ζ-positive ABC DLBCL cell lines. In contrast, IκB-ζ-negative DLBCLs are not affected by IκB-ζ downregulation. Positive control shRNAs directed against CARD11 (for ABC DLBCL cell lines) or MYC (for GCB DLBCL cell lines) were toxic to all DLBCLs, whereas a negative control shRNA against MSMO1 is not toxic to any cell line. Representative results from at least 3 independent replicates are shown. Baseline expression of IκB-ζ in the investigated cell lines is indicated, based on western blotting (Figure 1C). (C) Exogenous expression of IκB-ζ cDNA rescues HBL-1 cells from IκB-ζ shRNA-mediated toxicity. Representative results from 3 independent replicates are shown. *P < .05; **P < .01; ***P < .001.