Downregulation of estrogen-metabolizing 17 beta-hydroxysteroid dehydrogenase type 2 expression correlates inversely with Ki67 proliferation marker in colon-cancer development.

The 17HSDs are a group of isozymes that catalyze the interconversion between high-activity 17 beta-hydroxysteroids and low-activity 17-ketosteroids. In the present study, we characterized the expression of 17HSD types 1 and 2 in normal and malignant gastrointestinal tissues and cells. Using the colon as a model for cancer of the gastrointestinal tract, expression of the 17HSD enzymes in cancer development was studied and correlated with proliferation and differentiation markers as assessed by Ki67 and mucin staining, respectively. In normal colon and small intestine, 17HSD type 2 mRNA was expressed in the surface epithelial cells and, to a lesser extent, in the cryptal epithelial cells. In colon-cancer specimens, 17HSD type 2 expression was downregulated both in the tissues and in the cell lines and correlated inversely with the proliferation marker. No expression for the 17HSD type 1 enzyme was observed in normal or cancerous gastrointestinal tract tissues. In line with the expression studies, 17HSD activity measurements with colon cells showed that only the oxidative conversion of E2 to E1 was present, and Northern blot analysis showed the signal only for 17HSD type 2. Localization of the ERs alpha and beta, assessed by immunohistochemistry and in situ hybridization, showed the presence of ER beta in the lamina propria of the colon. Our study shows that 17HSD type 2 expression is associated with the functional integrity of the gastrointestinal tract. The decrease in expression of the type 2 enzyme may increase estrogen influence in colon cancer.