Up‐regulation of a BCL9‐related β‐catenin‐binding protein, B9L, in different stages of sporadic colorectal adenoma

Aberrant activation of Wnt signaling is a critical event in the development of human colorectal tumors. The aim of this study was to elucidate the role of B9L and its association with β‐catenin in each stage of the adenoma‐carcinoma sequence of human colorectal tumorigenesis. We investigated the expression levels of B9L in sporadic colorectal adenomas and carcinomas, categorized according to the Vienna classification, using real‐time quantitative polymerase chain reaction (RTQ‐PCR) and immunohistochemical analysis. B9L was expressed in the nuclei of non‐neoplastic colonic mucosa cells and was overexpressed in the nuclei of neoplasias and invasive carcinoma cells. Immunoreactivity to B9L protein was correlated with the progressive grades of colorectal neoplasias, as was the expression of B9L mRNA. A high level of immunoreactivity to nuclear B9L was present in 27% of low‐grade neoplasias and in more than 50% of high‐grade neoplasias and invasive carcinomas, whereas a high level of nuclear B9L immunoreactivity was not observed in any of the non‐neoplastic mucosa samples. The expression of B9L was dramatically increased in low‐grade neoplasias compared with that in non‐neoplastic mucosa. B9L may play an important role in tumorigenesis induced by aberrant activation of Wnt signaling and may act as a key protein in the progressive dysplasia of adenoma. (Cancer Sci 2007; 98: 83–87)