Methylation Mediated Downregulation of TOB1-AS1 and TOB1 Correlates with Malignant Progression and Poor Prognosis of Esophageal Squamous Cell Carcinoma

Background TOB1, a member of the transducer of erbB-2 /B-cell translocation gene family, was detected to be down-regulated in ESCC by RNA sequencing. TOB1-AS1, a head-to-head antisense lncRNA with TOB1, was down-regulated in several cancers. However, the roles of them in esophageal squamous cell carcinoma (ESCC) remained unclarified. Aims To investigate the roles and functions of TOB1-AS1 and TOB1 in ESCC tumorigenesis. Materials and Methods The expression levels, methylation status, biological function and mechanisms of TOB1-AS1 and TOB1 in ESCC were, respectively, detected. Results Frequent down-regulation of TOB1-AS1 and TOB1 was verified in esophageal cancer cells and ESCC tissues, and there was a positive correlation between them in ESCC tissues. The CpG sites hypermethylation within proximal promoter of TOB1-AS1 and TOB1 could lead to transcriptional inhibition of both genes. Furthermore, expression and proximal promoter methylation status of TOB1-AS1 or TOB1 may be associated with ESCC patients’ prognosis. TOB1-AS1 and TOB1 may function as tumor suppressors by inhibiting growth, migration, and invasion of esophageal cancer cells. Up-regulation of TOB1-AS1 increased expression level of TOB1, and TOB1-AS1 could work as a ceRNA to modulate ATF3 expression via competitively binding with miR-103a-2-5p. Meanwhile, ATF3, as a transcription factor, could regulate transcription of TOB1; down-regulation of TOB1-AS1 in ESCC led to decreased expression of ATF3 through ceRNA mechanism, and further influenced the transcription of TOB1. Conclusion TOB1-AS1 and TOB1 may act as tumor suppressors and may serve as potential targets for antitumor therapy in ESCC.