NF-κB inhibition attenuates IRF4 expression and proliferation in PTCL cells. (A) The proteasome and NF-κB inhibitor bortezomib inhibited IRF4 protein expression in Karpas 299 cells in a time-dependent manner. (B) Bortezomib inhibited cell proliferation in a dose-dependent manner in Karpas 299 cells. (C) The IκB kinase inhibitor BMS-34554 (dissolved in dimethylsulfoxide [DMSO]) inhibited IκBα Ser32 phosphorylation 10 minutes postadministration compared with vehicle alone (0.5% DMSO) or no treatment in Karpas 299 cells. (D) BMS-345541 decreased IRF4 mRNA expression 4 hours postadministration (P < .0001, Karpas 299). (E) BMS-345541 inhibited protein expression of IRF4 and the NF-κB target, X-linked inhibitor of apoptosis (XIAP), 24 hours postadministration in 4 IRF4-positive PTCL cell lines.