An alternative cyclin-D1 splice site is not linked to inflammatory bowel disease-associated neoplasia

Inflammatory bowel diseases (IBD) encompass inflammatory disorders affecting the gastrointestinal tract, primarily ulcerative colitis (UC) and Crohn's disease (CD). The risk of developing colorectal cancer (CRC) is increased in patients with IBD. The CCND1 protein is the regulatory subunit of an enzyme that inactivates the retinoblastoma protein, a tumor suppressor protein, and promotes progression through the G1-S phase of the cell cycle. The CCND1 870G-A gene polymorphism influences susceptibility to colorectal cancer. The mutant allele of CCND1 in IBD-associated neoplasia leads to a greater frequency of alternate splicing during transcription, resulting in a more stable CCND1 protein. This creates a higher concentration of CCND1, facilitating easier passage through the G1/S checkpoint, abnormal cell cycle progression, and possibly carcinogenesis.

We conducted a case-control study involving 396 individuals with IBD. IBD subgroups included CD, UC, and indeterminate colitis (IC). We studied patients with sporadic colorectal cancer (n=75) and patients without gastrointestinal disease as a control group (n=93). We extracted DNA from blood and performed polymerase chain reaction followed by high-performance liquid chromatography to screen for mutations. We confirmed the polymorphism at nucleotide A870G in exon 4. For statistical analysis, we used exact analyses of two-way contingency tables. Power calculations were done and correction for multiple testing was performed by computing the false discovery rate (FDR).

Our study had a power of 75% at a 0.05 significance level. A870G SNP allele frequency in the IBD group was 44.8%, compared to 51.6% in the control population. Only the IC group showed a significant association with CCND1 splice site after correction for multiple testing (FDR=0.042). There were no differences between the other IBD groups and controls.

We found an association between CCND1 A870G SNP and IC group only (p=0.014, FDR=0.042). However, our data do not show an association between CCND1 A870G SNP and CD-associated or UC-associated neoplasia.