RelB and p52 transcriptionally regulate IRF4. (A) The IκB kinase inhibitor BMS-34554 (“BMS”) decreased IRF4 promoter activity 3 hours postadministration (P = .0086; Karpas 299). (B) Individual and concurrent knockdown of NFKB2 (p52) and RELB attenuated IRF4 promoter activity (P = .014; Karpas 299). (C) Knockdown of RELA (p65) alone or in combination with NFKB1 (p50) had no effect on IRF4 promoter activity (P = .25; Karpas 299). (D) Knockdown of REL (c-Rel) did not significantly inhibit IRF4 promoter activity (P = .063; Karpas 299). (E) ChIP demonstrated that all NF-κB subunits interacted with NF-κB REs 1 and 2 in the IRF4 promoter, located 1166 bp and 103 bp upstream of the IRF4 transcription start site, respectively (Karpas 299). These interactions were diminished to varying degrees by BMS-345541 3 hours postadministration. (F) Concurrent knockdown of NFKB2 and RELB resulted in decreased IRF4 protein expression in Karpas 299 and FE-PD cell lines. Densitometry values for IRF4 bands normalized to β-actin are shown. (G) Simultaneous overexpression of p52 and RelB increased nuclear IRF4 protein abundance in Karpas 299.