DNA Damage Response Genes Differentiate Colitis From Neoplasia in Colitis-Associated Colon Cancer
*Robert A. Malizia1, *Stephen P. Sharp1, *Travis Walrath2, *Shanti D'Souza3, *Carmen J. Booth4, *Brittany J. Kartchner2, *Edward C. Lee1, *Steven C. Stain1, *William O'Connor, Jr.2
1Department of Surgery, Albany Medical Center, Albany, NY; 2Department of Immunology and Microbial Disease, Albany Medical College, Albany, NY; 3Albany Medical College, Albany, NY; 4Department of Comparative Medicine, Yale University, New Haven, CT
Objective: To determine if altered regulation of DNA Damage response genes (DDR) occurs early in the transition from chronic colitis to Colitis-Associated Cancer (CAC) in a pre-clinical model of disease.
Design: We utilized the best characterized murine model of CAC, Azoxymethane/Dextran Sodium Sulfate (AOM/DSS), to study tumorigenesis in C57BL/6 mice. Mice were separated into four groups; control, DSS only, AOM only, and AOM/DSS. Murine colonic tumors were graded through bi-weekly high-resolution colonoscopy. Upon sacrifice, colons were opened, assessed for macroscopic tumor, and segmented. Representative colons were evaluated by histopathology. Critical DDR genes were evaluated by semi-quantitative RT-PCR.
Main Outcome Measures: N/A
Results: Tumors were observed by 5 weeks in the AOM/DSS cohort only. Administration of AOM only resulted in up-regulation of DDR genes at 35 days. Upon colonic resection, half of the AOM/DSS cohort displayed macroscopically visible tumor (MVT). In the remaining mice in the AOM/DSS group we observed barely detectable (Grade 1) tumor by colonoscopy only or no observable tumor, therefore, these mice were denoted the non-macroscopically visible tumor group (NMVT). Interestingly, both MVT and NMVT tumor-developing groups showed reduced mRNA expression of mlh1, anapc1, and ercc4 relative to DSS or mutagen alone. Moreover, colitis alone was able to reduce mRNA expression of gene ercc4.
Conclusions: For the first time, ercc4 has been shown to be down-regulated in colitis and may mark early transition to CAC in a pre-clinical model. Additionally, DDR gene expression is specific and not universal in neoplastic progression. This phenomenon has not been previously illustrated in CAC. Finally, these data highlight the AOM/DSS model as a means to further investigate potential markers of early malignant transformation.