The new 6q27 tumor suppressor DACT2, frequently silenced by CpG methylation, sensitizes nasopharyngeal cancer cells to paclitaxel and 5-FU toxicity via β-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 to 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, qPCR, 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 downregulating matrix metalloproteinases. DACT2 expression also induced G2/M arrest in NPC cells through directly suppressing β-catenin/Cdc25c 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 β-catenin/Cdc25c signaling. Our study suggests that DACT2 promoter methylation is a potential epigenetic biomarker for the detection and chemotherapy guidance of NPC.