Significance of the wingless-type/beta-catenin signaling cascade for cancer risk in inflammatory bowel disease: Association of genetic polymorphism in human dishevelled 1 with dysplasia in ulcerative colitis

Ulcerative colitis (UC) and Crohn's disease are inflammatory bowel diseases (IBD) associated with an increased risk of colorectal cancer. The objective of this dissertation is the identification of candidate genes in UC and Crohn's disease that convey predictive power for oncogenic conversion in IBD. We hypothesize that human dishevelled 1 (DVL1) is involved in the pathogenesis of UC based on physical mapping and functional plausibility. We present evidence that selective polymorphism of the human DVL1 gene is associated with dysplasia in UC. To determine gene expression levels, we prepared poly(A+) mRNA from inflamed intestinal mucosa of patients with a longstanding history of UC and Crohn's disease and hybridized radioactively labeled cDNA populations to Atlas(TM) Human Cancer Expression Arrays. Secreted apoptosis-related protein 1 (SARP-1), frizzled genes, and dishevelled homologues were differentially expressed, being elevated in UC as compared to Crohn's disease mucosa. We further generated biotinylated copy RNA derived from dysplastic and benign UC specimens and hybridized it to Affymetrix RTM Human Genome oligonucleotide arrays. Glycogen synthase kinase 3 beta (GSK3beta) and dishevelled 3 (DVL3) were differentially expressed. These genes encode proteins that are crucially involved in the wingless-type/beta-catenin signaling cascade. Genomic DNA was then obtained from patients with Crohn's disease, dysplastic or benign UC, and sporadic colon cancer. Intron 1 of DVL1 was amplified and targeted for single nucleotide polymorphism (SNP) analysis. Temperature-modulated heteroduplex chromatography was performed using partially denaturing high performance liquid chromatography (dHPLC). Resolution of the corresponding homoduplexes by ion-pair reversed phase liquid chromatography was followed by dye-terminator sequencing. Heterozygous polymorphisms within intron 1 of DVL1 were significantly over-represented among UC (66/101, 65.3%), when compared with Crohn's disease (62/125, 49.6%), or population controls (36/89, 40.4%) (p-value = .025 and .001, respectively). Stratification by the presence or absence of dysplasia showed a stronger association of DVL1 mutator genotypes with dysplastic UC (12/17, 70.6%) than benign UC (31/57, 54.4%). The frequency of DVL1 mutator genotypes in colorectal cancer was lower than in dysplastic UC (18/53, 34.0%, p < .000) and concurred with that of the control population. Our findings suggest that polymorphic genotypes within regulatory intronic regions of the DVL1 gene may impact on individual susceptibility to colorectal cancer among UC patients.