Familial adenomatous polyposis (FAP) is a rare autosomal-inherited disease that highly predisposes to colorectal cancer, characterized by a diffuse duodenal and colorectal polyposis associated with various extradigestive tumors and linked to germline mutations within the APC gene.
However, thus far few studies have analyzed the impact of numerical abnormalities of chromosomes 17 and 18, which carry the p53 and DCC plus SHAD4/DPC4 genes involved in colorectal cancer, on the clinical and biological behaviors of the disease.
Protein expression of the putative tumour-suppressor gene DCC on chromosome 18q was evaluated in a panel of 16 matched colorectal cancer and normal colonic tissue samples together with DCC mRNA expression and allelic deletions (loss of heterozygosity, LOH).
However, the remaining 13 (37%) hypermutated CRCs lacked MLH1 silencing, contained tumours with the highest mutation rates ('ultramutated' CRCs), and exhibited higher incidences of APC and KRAS mutations, but infrequent BRAF mutations.
In addition, we have partially transformed the HCEC 1CT line by introducing stable knockdown of wild type APC and TP53, and ectopically introducing a mutant Krasv12 and a mutant version of APC (A1309), all commonly found mutations in colorectal cancer (CRC).
We found that BCL9 is required for efficient beta-catenin-mediated transcription in Wnt-stimulated HEK 293 cells, and in the SW480 colorectal cancer cell line whose Wnt pathway is active due to APC mutation.
A low-penetrance susceptibility allele that is common in Jews from Eastern Europe, APC 11307K, confers a two-fold increased risk of colorectal cancer without the full expression of familial adenomatous polyposis.