Clinicopathological implications of glutathione peroxidase 3 downregulation through DNA hypermethylation in oral squamous cell carcinoma

Abstract

Reactive oxygen species (ROS) have been shown to be involved in tumor initiation and progression via structural changes in cancer-related genes. Glutathione peroxidase 3 (GPX3), a member of the glutathione peroxidase family, is a major scavenger of ROS produced by normal metabolism or after oxidative damage to host cells. A possible tumor suppressor function of GPX3 and its downregulation caused by promotor hypermethylation have been investigated in various cancers. In this study, we investigated the association between methylation status and GPX3 expression in oral squamous cell carcinoma (OSCC) and further investigated the clinicopathological significance of GPX3 expression in patients with OSCC who underwent long-term follow-up. Promoter hypermethylation of GPX3 was frequently detected in both OSCC cell lines (100%) and tissue samples (75%). In contrast, only 33.3% of normal oral mucosa samples showed hypermethylation of GPX3. In OSCC cell lines, GPX3 expression was restored after 5-aza-2’-deoxycytidine treatment at both the mRNA and protein levels. GPX3 protein expression was significantly decreased in OSCC tissues (56.1%) compared to normal oral mucosa (100%). In patients with OSCC, GPX3 downregulation was significantly associated with histological grade (P=0.005), lymph node metastasis (P=0.001), vascular invasion (P=0.016), and poor prognosis (P=0.007). We concluded that promoter hypermethylation-induced GPX3 downregulation is significantly related to poor prognostic indicators and decreased overall survival in OSCC, and these findings provide further evidence for GPX3 as a novel diagnostic and prognostic biomarker in patients with OSCC.

활성산소는 암유전자의 구조적 변화를 일으켜 암의 발생과 진행에 관련이 되어있다. glutathione peroxidase 3(GPX3)는 glutathione family중 하나이며 활성산소를 제거하는 주요 항 산화 효소이다. 다양한 암에서 promoter hypermethylation에 의한 GPX3의downregulation GPX3의 tumor suppressor로서의 가능성에 관한 많은 연구들이 있었다. 본 연구의 목적은 구강편평세포암종에서 methylation정도와 GPX3발현에 관한 상관관계를 보고, 구강편평세포암종 환자에서 GPX3발현정도가 임상병리학적 예후에 미치는 영향을 보고자 하였다. GPX3 promoter hypermethylation은 구강편평세포암종 세포주와 조직에서 모두 높은 빈도(100%, 75%)로 관찰되었으나 정상 구강 점막조직에서는 낮은 빈도(33.3%)로 관찰되었다. 구강편평세포암종 세포주에서 demethylation agent인 5-Aza처리 후 GPX3 발현이 복원되었고, GPX3 downregulation과 methylation은 연관성을 가지고 있음을 확인하였다. 모든 정상 구강점막조직에서 GPX3 protein발현이 관찰되었다. 반면에 구강편평세포암종 조직에서는 정상 구강점막조직에 비하여GPX3 protein발현이 통계학적으로 유의한 감소를 보였다. 구강편평세포암종 환자 군에서 GPX3 발현은 세포 분화도, 림프절 전이, 혈관침습 및 누적 생존률에서 각각 통계학적 유의성을 보였다. 결론적으로 promoter hypermethylation에 의한GPX3 downregulation은 구강편평세포암종 환자의 진단 및 예후를 보는 생체표지자로의 의미가 있다고 할 수 있겠다.