DNMT1–MicroRNA126 Epigenetic Circuit Contributes to Esophageal Squamous Cell Carcinoma Growth via ADAM9–EGFR–AKT Signaling

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Abstract
Purpose: MicroRNAs (miRNA) are involved in and are controlled by epigenetic regulation, and thereby form a reciprocal regulatory circuit. Using next-generation sequencing (NGS)–based miRNA profiling, this study aimed to discover esophageal squamous cell carcinoma (ESCC)–specific miRNAs and miRNA-related epigenetic modulations. Experimental Design: NGS-based miRNA profiles were generated for four pairs of ESCC tissues and adjacent normal tissues. In situ hybridization was used to assess miRNA expression and its correlation with prognosis. miRNA-related DNA methylations were identified using bisulfite genomic sequencing, and the role of DNA methyltransferase 1 (DNMT1) was investigated using RNA interference. miRNA targets were screened by mRNA sequencing, and functional validation was performed in vitro and in vivo. Results: NGS-based miRNA profiling identified 78 differentially expressed miRNAs in ESCC. Among them, microRNA126-3p (miR-126) was significantly downregulated, and its downregulation correlated with poor ESCC prognosis. Downregulation of miR-126 was due to promoter hypermethylation of its host gene, Egfl7. DNMT1 was aberrantly upregulated in ESCC and responsible for the hypermethylation of Egfl7. Intriguingly, DNMT1 was suppressed by overexpression of miR-126, indicating the existence of a regulatory feedback circuit. ADAM9 was identified as a key target of miR-126. Ectopic expression of miR-126 or silencing of ADAM9 reduced ESCC cell proliferation and migration by inhibiting epidermal growth factor receptor–AKT signaling. Conclusions: Our results indicate that miR-126 is a potential prognostic indicator for ESCC and suggest that a novel “DNMT1–miR-126 epigenetic circuit” is involved in ESCC progression. Consequently, miR-126–based epigenetic modulations may provide a basic rationale for new approaches to antitumor therapeutics. Clin Cancer Res; 21(4); 854–63. ©2014 AACR.

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