New developments in oestrogen signalling in colonic epithelium

Epidemiological studies show that oestrogen reduces the risk of colorectal cancer in postmenopausal women and ERβ (oestrogen receptor β)-selective ligands have been reported to be very effective treatment in animal models of inflammatory bowel disease. Several studies have shown that ERβ is the predominant ER in the colonic epithelium, but it is not clear whether the benefit of ERβ agonists in inflammatory bowel disease are due to their action on the colon epithelium itself, or on the immune system. In order to address this issue, we have compared colons of ERβ^−/− and wild-type mice with regard to morphology, histology, proliferation and differentiation. We found that the number of proliferating cells was higher in ERβ^−/− mice, and the migration of labelled cells from base to lumen of the crypts was faster. Additionally, immunohistochemical staining revealed fewer apoptotic cells (cleaved caspase 3-positive), a significant decrease in expression of the epithelial differentiation marker, cytokeratin CK20, the adherens junction protein, α-catenin, and the hemidesmosomal protein, plectin, in ERβ^−/− mice. These findings suggest a role for ERβ in growth, organization and maintenance of the normal colonic crypt–villus architecture. The next step is to elucidate the molecular mechanisms that underlie the signalling of ERβ in normal cell growth and assess whether or not ERβ agonists will be useful drugs in the prevention or treatment of colorectal cancer. Dietary phyto-oestrogens are believed to play a role in protection against colorectal cancer. Lignans, such as enterolactone, an ER agonist, prevent cancer development in animal models. Since ERβ is the only ER in the colon, there is enough reason to speculate that phyto-oestrogens are acting through ERβ.