The Clinical Significance And Functional Mechanism Of EMX2 Gene In Colorectal Cancer

·BackgroundEMX2 gene,as a member of the homeobox gene family,plays critical role in embryonic development of central nerve system and urogenital system.Low EMX2 expression is reported in several cancers and is associated with worse prognosis or resistance to chemotherapy.Its low expression is mainly due to promoter methylation rather than genetic mutation.EMX2 inhibits cell proliferation and invasion by regulating Wnt signaling pathway.Our study aims to explore the clinical relevance of EMX2 promoter methylation in colorectal cancer,and verify the gene function and signaling pathway it acts upon.·Methods170 colorectal cancer patients who underwent surgery at Cancer Hospital,Chinese Academy of Medical Sciences in 2012 were included in the study.We used methylation specific PCR(MSP)to detect promoter methylation and analyzed its association with clinical factors,survival and treatment outcome.We also detected EMX2 expression in colorectal cancer cell lines and the change in expression after adding DNA demethylation agent(DAC)to clarify its regulation mechanism.We transfected EMX2 and its shRNA to colorectal cancer cells,and measured the change in cell proliferation,migration and Wnt pathway activity,in order to test gene function and molecular pathway involved.·ResultsAccording to immunohistochemical staining result for three colorectal cancer samples and one sample of normal tissue,EMX2 had lower expression in tumors.The MSP result of 18 cancer samples and matching normal tissues showed that the gene had higher promoter methylation rate in tumors,though not significant.61 out of 170 patients(35.99%)had EMX2 promoter methylation,and hypermethylation was significantly associated with age≥65 years old(P =0.029)and KRAS mutation(P=0.045).In terms of prognosis,hypermethylated patients trended towards shorter overall survival and higher long-term progression rate.Subgroup analysis for stage II patients showed similar trend.For patients without promoter methylation,targeted therapy was associated with longer overall survival,while hypermethylated patients didn’ t seem to benefit from targeted therapy.EMX2 had lower expression in colorectal cancer cell lines compared with normal epithelial cells,and its expression could be restored by DAC treatment.Overexpression of EMX2 inhibited cell proliferation,while downregulation of EMX2 promoted cell migration.Besides,the Wnt signaling pathway was suppressed in cells with EMX2 overexpression and activated in cells with EMX2 downregulation.·ConclusionEMX2 gene is down regulated in colorectal cancer,mainly as a result of promoter methylation.Its hypermethylation trends towards shorter overall survival and higher long-term progression rate.In StageⅡcolorectal cancer,EMX2 methylation status is a possible prognostic factor.EMX2 can inhibit the proliferation and migration of colorectal cancer cells through suppression of Wnt signaling pathway.