Several effects of bile acids (BA) on colonic epithelial cells (CEC) have been described including induction of proliferation and apoptosis. Some of these effects are mediated through activation of the NFB transcriptional system. In this study, we investigated the molecular mechanisms underlying the BA-induced gene expression in CEC. Methods: The human CEC line HT29 and primary human CEC were treated with dilutions of salts of deoxycholic acid (DCA) and taurodeoxycholic acid (TDCA). NFB binding activity was analyzed with EMSA, RelA translocation with immunofluorescence, and IB- and RelA-phosphorylation with western-blotting. IL-8 mRNA and protein expression were assessed by quantitative PCR and ELISA. Functional impact of NFB-activation was determined by blocking the proteasome activity with MG132 or by preventing IKK activity with a dominant negative IKK delivered by an adenoviral vector (Ad5dnIKK). Results: DCA and TDCA induced IL-8 expression in a dose and time dependent manner. Interestingly, DCA but not TDCA induced IB-phophorylation, RelA translocation and NFB binding activity. In accordance, the proteasome inhibitor MG132 blocked DCA- but not TDCA-induced IL-8 gene expression. In contrast, TDCA induced IL-8 gene expression correlated with enhanced RelA phosphorylation, which was blocked by Ad5dnIKK. Discussion: Our data suggest that DCA induced signal transduction mainly utilized the IB degradation and RelA nuclear translocation pathway whereas TDCA primarily induced IL-8 gene expression through RelA phosphorylation. These differences may have implications for the understanding of the pathophysiology of inflammation and carcinogenesis in the gut.