The Tumor Suppressor DACT2,Frequently Silenced By Cpg Methylation,Sensitizes Nasopharyngeal Cancer Cells To Paclitaxel And 5-FU Toxicity Via ?-catenin/Cdc25c Signaling And G2/M Arrest

Background: Nasopharyngeal carcinoma(NPC)is prevalent in South China including Hong Kong and Southeast Asia,constantly associated with Epstein-Barr virus(EBV)infection.Epigenetic etiology attributed by EBV plays a critical role in NPC pathogenesis.Through previous CpG methylome study,we identified Disheveled-associated binding antagonist of beta catenin 2(DACT2)as a methylated target in NPC.Although DACT2 was shown to regulate Wnt signaling in some carcinomas,its functions in NPC pathogenesis remain unclear.Methods: RT-PCR,q PCR,MSP and BGS were applied to measure expression levels and promoter methylation of DACT2 in NPC.Transwell,flow cytometric analysis,colony formation and BrdU-ELISA assay were used to assess different biological functions affected by DACT2.Immunofluorescence,Western blot and dual-luciferase reporter Assay were used to explore the mechanisms of DACT2 functions.Chemosensitivity assay was used to measure the impact of DACT2 on chemotherapy drugs.Results: We found that DACT2 is readily expressed in multiple normal adult tissues including upper respiratory tissues.However,it is frequently downregulated in NPC,and correlated with promoter methylation.DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine restored its expression in NPC cells.DACT2 methylation was further detected in 29/32(91%)NPC tumors,but not in any(0/8)normal nasopharyngeal tissue samples.Ectopic expression of DACT2 in NPC cells suppressed their proliferation,migration and invasion through down-regulating MMPs.DACT2 expression also induced G2/M arrest in NPC cells through directly suppressing ?-catenin/Cdc25 c signaling,which sensitized NPC cells to paclitaxel and 5-FU,but not cisplatin.Conclusion: Our results demonstrate that DACT2 is frequently inactivated epigenetically by CpG methylation in NPC,while it inhibits NPC cell proliferation and metastasis via suppressing ?-catenin/Cdc25 c signaling.Our study suggests that DACT2 promoter methylation is a potential epigenetic biomarker for the detection and chemotherapy guidance of NPC.