Involved in regulation of NF-kappa-B transcription factor complexes (PubMed:16513645, PubMed:16622025). Inhibits NF-kappa-B activity without affecting its nuclear translocation upon stimulation (PubMed:16513645). Inhibits DNA-binding of RELA and NFKB1/p50, and of the NF-kappa-B p65-p50 heterodimer and the NF-kappa-B p50-p50 homodimer (PubMed:16513645). Also seems to activate NF-kappa-B-mediated transcription (PubMed:16622025). In vitro, upon association with NFKB1/p50 has transcriptional activation activity and, together with NFKB1/p50 and RELA, is recruited to LCN2 promoters (PubMed:16622025). Promotes transcription of LCN2 and DEFB4 (PubMed:16622025). Is recruited to IL-6 promoters and activates IL-6 but decreases TNF production in response to LPS (By similarity). Seems to be involved in the induction of inflammatory genes activated through TLR/IL-1 receptor signaling (By similarity). Involved in the induction of T helper 17 cells (Th17) differentiation upon recognition of antigen by T cell antigen receptor (TCR) (By similarity). {ECO:0000250|UniProtKB:Q9EST8, ECO:0000269|PubMed:16513645, ECO:0000269|PubMed:16622025}. This is the function of NFKBIZ (NFKB inhibitor zeta, Ensembl gene identifier ENSG00000144802).