Deleted in Colorectal Cancer - Background

Background

Early studies of colorectal tumours found that allelic deletions of segments of chromosome 18q occur in a very high percentage of colorectal cancers. DCC was initially cloned out of the region and put forth as a putative tumour suppressor gene, though nothing was known about its function at the time. The DCC gene was examined for the genetic changes found with most other tumour suppressor genes, but it was found to have a comparatively low frequency of somatic mutation. Several years later DCC was shown to encode a transmembrane receptor protein that mediated the effects of netrin-1 on axon outgrowth.

Soon after the protein product was confirmed, DCC knockout mice were created. As DCC-/- mutations are rapidly fatal due to a lack of nervous system development, DCC+/- mice were assessed for increased tumour development over two years, and no increase in tumour predisposition was detected.

The discovery of a specific function for DCC that seemed to have little to do with cell cycle control, the low somatic mutation rate and the absence of cancer predisposition in DCC heterozygotes were fairly discouraging evidence for DCC's putative tumour suppressor status. This caused focus to shift to DCC's role in axon guidance for a time, until one study implicated DCC in regulation of cell death. As the 18q chromosomal deletions were never resolved to be related solely to another gene, DCC was rapidly reaccepted as a candidate. Recent research into the mechanisms of DCC signaling and in-vitro studies of DCC modifications have solidified DCC's tumour suppressor position, and have begun to integrate DCCs divergent functions as both an axon guidance molecule and a tumour suppressor into a single concept.