Prostaglandin metabolism and nonsteroidal anti-inflammatory drugs (NSAIDS) represent a promising pathway for chemoprevention of colon cancer. NSAIDs inhibit prostaglandin H synthase (PTGS) enzymes. Therefore, one hypothesis is that naturally occurring genetic variants in a prostaglandin pathway may mimic the effect of NSAIDs and shed light on biochemical mechanisms. The pathway proposed is a nuclear prostaglandin pathway defined by cytosolic phospholipase A2 (cPLA2), prostaglandin H synthase 2 (PTGS2, or COX-2), hematopoietic prostaglandin D synthase (PGDS),and peroxisome proliferator-activated receptor gamma (PPARG). Previous work has focused on PTGS2, including a novel mutation among African Americans and a case-control study. The proposed project develops the hypothesis further by analyzing PGDS, a key enzyme that has received little attention.
Specific aims are to: (1) develop efficient expression assays for PGDS variants that have already been identified; (2) develop a knockout mouse model to quantitate colon adenomas in relation to variants in PGDS; and (3) develop pilot case-control data on prevalence of colorectal adenomas in relation to PGDS variants. Methods: In vitro translation, bacterial, and/or baculovirus assays will be used for expression of PGDS variants. Dr. Osamu Hayaishi (Osaka Bioscience Institute) will provide the Pgds knockout mouse for use in the proposed work. A mouse carrying the Pgds knockout will be bred with a commercially available polyposis-prone strain, and the effect of the knockout on number and size of adenomas will be determined. Subjects for the pilot case-control analysis will come from two existing studies: a Kaiser sigmoidoscopy study (1,700 subjects) and a University of North Carolina colonoscopy study (800 subjects). Molecular genotyping will be used to assess the effect of PGDS variants in combination with PTGS2 variants. The proposed study should improve understanding of the mechanism of prevention by NSAIDs and may lead to new targets for chemopreventive agents.
