Decreased Expression of Retinoid X Receptors During Human and Azoxymethane-induced Colorectal Carcinogenesis in the Rat

Background/Aim: The family of retinoid X receptors (RXRs) including RXR alpha, beta and gamma, is involved in regulating cell proliferation, differentiation, apoptosis and development. Materials and Methods: In order to characterize the role of RXRs during colorectal carcinogenesis, the expression of RXRs in human and azoxymethane (AOM)-induced rat colorectal tumors was profiled by immunohistochemistry. Results: Both human and rat normal colorectal epithelia and hyperplasia exhibited strong nuclear, but weak cytoplasmic staining for all three proteins. Expression of RXR alpha, beta and gamma was significantly reduced in rat carcinomas compared to high-grade dysplasia whether in aberrant crypt foci or in adenomas. All three proteins displayed dramatically reduced nuclear expression in both human adenomas and carcinomas. Reduced expression of RXR alpha and RXR gamma seems more significant than RXR beta in both human and rat carcinomas. Conclusion: Reduced expression of RXRs is associated with colorectal carcinogenesis in both humans and AOM-treated rats.