Expressions of two adenomatous polyposis coli and E-cadherin proteins on human colorectal cancers

Mutations in the adenomatous polyposis coli (APC) gene contribute to the progression of colorectal tumorigenesis. Despite the importance, few studies regarding the localization of this protein on surgically resected human colorectal cancer specimens using immunohistochemistry have been reported so far because of the unavailability of the antibodies for this use. The goal of this study has been to provide the APC protein expression and to validate the APC molecular studies. We took advantage of an immunohistochemistry procedure of applying the unique detergent-mediated antigen retrieval technique to frozen sections and examined the expressions of one amino (N)-terminal (AC4) and one carboxy (C)-terminal APC antibody (HG2). Further, we compared the stainings of APC antibodies with those of the E-cadherin antibody using a quantitative image analysis. E-cadherin is a critical morphogenetic regulator during embryogenesis and recent evidence strongly suggests that downregulation of E-cadherin expression in cancers is associated with a high rate of invasion and metastasis. The analysis indicated statistically that normal epithelia showed stronger staining than cancer cells ( P<0.05). Further, in normal epithelia, the amino (N)-terminal APC antibody (AC4) showed a positive correlation with another carboxy (C)-terminal APC antibody (HG2). E-cadherin showed no positive correlation with other APCs in either the normal epithelia or cancer cells. This study verified reduced expressions of APCs and E-cadherin proteins in colorectal cancer cells. This suggests that the normal APC and E-cadherin protein expressions in benign epithelium are progressively and independently lost in the sporadic colorectal cancers.