The deleted in colon cancer (DCC) gene is consistently expressed in colorectal cancers and metastases

Abstract

The DCC (deleted in colorectal cancer) gene was originally identified as a candidate tumour suppressor gene in colon carcinogenesis on the basis of allelic losses in chromosome 18q.21 in 70% of colon cancers. Reverse transcriptase polymerase chain reaction (RT-PCR) of DCC mRNA suggests that DCC expression may also be reduced in colon cancers. We have used monoclonal antibodies generated against the DCC immunoglobulin-like domain to investigate DCC isoforms and DCC protein expression during colon cancer progression. Normal mucosa and colonic tumour specimens representative of the range of colonic tumour progression from benign adenomatous polyps to metastases were compared by Western blot analyses. We show that while M(r) 194 000 DCC is present in normal colonic mucosa and adenomatous polyps, it is also similarly expressed in colorectal carcinomas and colonic metastases in the liver. The presence of DCC protein is consistent with the presence of DCC mRNA transcripts in the same tissue specimens. Notably DCC was not completely lost in any colonic tumour specimens examined, even those that had progressed to metastatic cancers. Quantitation of DCC protein expression in tissue specimens by densitometry demonstrated that both normal and malignant specimens exhibit a wide range of DCC protein levels and there was no significant correlation between diminished DCC protein expression and colon cancer progression. These results demonstrate the pattern of expression of the DCC gene product in colonic tumour progression and show that absence of DCC expression is not associated with colonic tumour progression.