The Pirc Rat Model of Human Colon Cancer: From the Epigenetics of Tumor Initiation to the Study of Human Gender Disparities

Presented by:

Dr. James M Amos-Landgraf, Assistant Scientist, University of Wisconsin


Colorectal cancer is the third most common cancer in both men and women with over 100,000 new cases found each year (ACS facts and Figures 2008). Over 80% of tumors in sporadic cases and nearly all cases of Familial Adenomatous Polyposis (FAP) result from mutations in a single gene, the Adenomatous Polyposis Coli gene (APC). We have developed a rat model of colon cancer that harbors a premature stop codon at position 1137 in Apc. We have named the rat kindred Pirc for polyposis in the rat colon.

We are investigating genetic and epigenetic events that lead to colon cancer progression in the Pirc rat. We have used optical colonoscopy in the rat to follow tumor growth over several months, obtaining biopsies of tumor material and normal epithelium at periodic intervals. We are utilizing both RNA and DNA to identify allele maintenance and loss of heterozygosity of the Apc gene in DNA. Several tumors have been identified that maintain DNA heterozygosity of Apc but show monoallelic transcription of the mutant Pirc allele, revealing an epigenetic pathway of tumor progression in the rat that may be undiscovered in humans. Expression array analysis on four sets of tumor biopsies from two time points we identified 10 genes showing significant changes in their expression pattern from the 90 day biopsies to the 120 day samples. Interestingly, one gene that is often deleted in human colon cancer (DCC), and has not been previously seen to change in mouse or rat tumors, is significantly down regulated in the Pirc rat colon tumors.

To enhance the Pirc rat phenotype we have made congenic derivatives on several inbred strains. The inbred ACI-Pirc congenic is highly sensitive to tumor initiation and growth with male ACI-Pirc animals (N7) developing 38 (SD 13.1) colonic tumors that become visible by colonoscopy beginning at 45 days of age and becoming moribund by 6 months of age. Females are significantly protected against tumor growth and initiation with female ACI congenics developing only 7 (SD 0.8) tumors at 6 months of age.

We explored the likely possibility that sex specific hormones are playing roles in tumor intiation by examining tumor counts of gonadectomized animals. Female ACI-Pirc congenic animals ovarectomized at weaning developed significantly more tumors than control animals (Wilcoxon rank sum test p=0.03). Interestingly, gonadectomized males developed a significantly lower number of tumors than control ACI-Pirc male (p=0.049) and female (p=0.019) controls but not significantly different than ovariectomized females (P=0.47). This suggests that male hormones are initiators and female hormones suppressors of tumor initiation.

We are seeking additional methods to enhance the progression of colonic adenomas. With the administration of the inflammatory agent DSS we have seen dramatic increases in distal colonic adenomas and carcinomas with local invasion. In combination with optical colonoscopy we have tested several potential chemopreventive compounds through longitudinal monitoring of tumor initiation and growth.

More about Dr. James M. Amos-Landgraf, PhD

Dr. Amos-Landgraf is originally from Milwaukee, WI, later moving to St. Louis, MO where he received his undergraduate degrees from Washington University in St. Louis in Sociology and Biology. He went on to work as a research technician for Eric Green, MD, PhD, (now head of the NHGRI) who was a post-doctoral fellow at Washington University working on genomic mapping strategies for the early human genome project under Maynard Olsen. He later worked for Robert Nichols, D.Phil. at Case Western Reserve University in Cleveland, OH. There he worked on understanding the mechanism of chromosomal rearrangements and found early evidence of the importance of low copy repeat polymorphisms (CNVs) in chromosomal deletions and was introduced to epigenetics and imprinting. He continued his interest in epigenetics with his graduate work in the laboratory of Huntington Willard, PhD at Case Western examining the human genetic inheritance of X-inactivation patterns, receiving his PhD in 2004. Jim's graduate work in epigenetics and complex traits led to his current postdoctoral work with William Dove, PhD at the University of Wisconsin, Madison. After working with the Min mouse and realizing the biological and genetic limitations in the mouse he collaborated with Michael Gould in the McArdle Laboratory for Cancer Research to develop the Pirc rat model of human colon cancer. He was an American Cancer Society fellow seeking to identify markers of tumor progression using the Pirc rat model of colon cancer using a CGH expression array, and assays of epigenetic silencing in the Pirc rat. Dr. Amos-Landgraf has a continued interest in epigenetics related to cancer development and is exploring the recently recognized gender disparity in human colon cancer.