Association between activation of atypical NF‐κB1 p105 signaling pathway and nuclear β‐catenin accumulation in colorectal carcinoma

Recent studies have demonstrated that increased expression of coding region determinant‐binding protein (CRD‐BP) in response to β‐catenin signaling leads to the stabilization of β‐TrCP1, a substrate‐specific component of SCF E3 ubiquitin ligase complex, resulting in an accelerated degradation of IκBα and activation of canonical nuclear factor‐κB (NF‐κB) pathway. Here, we show that the noncanonical NF‐κB1 p105 pathway is constitutively activated in colorectal carcinoma specimens, being particularly associated with β‐catenin‐mediated increased expression of CRD‐BP and β‐TrCP1. In the carcinoma tissues exhibiting high levels of nuclear β‐catenin the phospho‐p105 levels were increased and total p105 amounts were decreased in comparison to that of normal tissue indicating an activation of this NF‐κB pathway. Knockdown of CRD‐BP in colorectal cancer cell line SW620 resulted in significantly higher basal levels of both NF‐κB inhibitory proteins, p105 and IκBα. Furthermore decreased NF‐κB binding activity was observed in CRD‐BP siRNA‐transfected SW620 cells as compared with those transfected with control siRNA. Altogether, our findings suggest that activation of NF‐κB1 p105 signaling in colorectal carcinoma might be attributed to β‐catenin‐mediated induction of CRD‐BP and β‐TrCP1. © 2009 Wiley‐Liss, Inc.