Our results indicate that NF-κB is constitutively active in human breast and colorectal cancer cell lines examined and that Nar down-regulated the nuclear pool, or active form, of NF-κB and suppressed IκBα phosphorylation and the expression of the NF-κB-regulated gene products IκBα, Bcl2 and c-IAP-2. This evidence concerns the gene BIRC3 and colorectal cancer.