Paracrine cyclooxygenase-2 activity by macrophages drives colorectal adenoma progression in the ApcMin/+ mouse model of intestinal tumorigenesis

Genetic deletion or pharmacological inhibition of cyclooxygenase (COX)-2 abrogates intestinal adenoma development at early stages of colorectal carcinogenesis. COX-2 is localised to stromal cells (predominantly macrophages) in human and mouse intestinal adenomas. Therefore, we tested the hypothesis that paracrine Cox-2-mediated signalling from macrophages drives adenoma growth and progression in vivo in the Apc(Min/+) mouse model of intestinal tumorigenesis. Using a transgenic C57Bl/6 mouse model of Cox-2 over-expression driven by the chicken lysozyme locus (cLys-Cox-2), which directs integration site-independent, copy number-dependent transgene expression restricted to macrophages, we demonstrated that stromal macrophage Cox-2 in colorectal (but not small intestinal) adenomas from cLys-Cox-2 x Apc(Min/+) mice was associated with significantly increased tumour size (P = 0.025) and multiplicity (P = 0.025), compared with control Apc(Min/+) mice. Transgenic macrophage Cox-2 expression was associated with increased dysplasia, epithelial cell Cox-2 expression and submucosal tumour invasion, as well as increased nuclear beta-catenin translocation in dysplastic epithelial cells. In vitro studies confirmed that paracrine macrophage Cox-2 signalling drives cateninrelated transcription in intestinal epithelial cells. Paracrine macrophage Cox-2 activity drives growth and progression of Apc(Min/+) mouse colonic adenomas, linked to increased epithelial cell beta-catenin dysregulation. Stromal cell (macrophage) gene regulation and signalling represent valid targets for chemoprevention of colorectal cancer.