In vitro analysis of the role of DCC in mucus-secreting intestinal differentiation

The deleted in colorectal cancer (DCC) gene was initially described as a colon cancer-associated tumor suppressor gene and subsequently proposed to be involved in goblet cell differentiation, but its precise role in normal intestine physiology and in cancer remains to be established. We have analyzed DCC mRNA expression in a panel of human colorectal cancer cell lines with a variety of differentiation phenotypes by reverse transcription-polymerase chain reaction (RT-PCR) and have shown that (1) most cell lines showed lower levels of DCC mRNA than normal colonic tissue; (2) only 1 cell line lacked detectable levels of DCC mRNA expression; (3) a discrepancy was found between the detectability of RT-PCR products corresponding to the extracellular and intracellular domains of DCC; and (4) there was no association between the presence of DCC transcripts and the differentiation phenotype. Specifically, DCC was not exclusively associated with the mucus-secreting phenotype, as determined by Alcian blue staining and Northern blotting with mucin gene probes. This was further supported by immunohistochemical results on DCC product and mucins in normal colon: DCC was detected in both goblet and absorptive cells. The introduction of full-length DCC cDNA in undifferentiated HT-29 cells did not have any effect on their differentiation phenotype, as shown by morphological studies and analysis of markers for this process in colon, such as mucins, dipeptidylpeptidase IV, villin and sucrase-isomaltase. There were no effects on cell proliferation in vitro. Our results indicate that DCC is not selectively involved in the mucosecretory differentiation pathway and that it is neither sufficient nor essential for normal intestinal differentiation.