Downregulation of MicroRNA-644a Promotes Esophageal Squamous Cell Carcinoma Aggressiveness and Stem Cell-like Phenotype via Dysregulation of PITX2

Purpose: We previously reported the oncogenic role of paired-like homeodomain 2 (PITX2) in esophageal squamous cell carcinoma (ESCC). In this study, we aimed to identify the miRNA regulators of PITX2 and the mechanism underlying the pathogenesis of ESCC. Experimental Design: Using miRNA profiling and bioinformatics analyses, we identified miR-644a as a negative mediator of PITX2 in ESCC. A series of in vivo and in vitro assays were performed to confirm the effect of miR-644a on PITX2-mediated ESCC malignancy. Results: ESCC cells and tissues expressed less miR-644a than normal epithelial controls. In patient samples, lower expression of miR-644a in ESCC tissues was significantly correlated with tumor recurrence and/or metastasis, such that miR-644a, PITX2, and the combination of the two were independent prognostic indicators for ESCC patient's survival (P < 0.05). Gain-and loss-of-function studies demonstrated that miR-644a inhibited ESCC cell growth, migration, and invasion in vitro and suppressed tumor growth and metastasis in vivo. In addition, miR-644a dramatically suppressed self-renewal and stem cell-like traits in ESCC cells. Furthermore, the effect of upregulation of miR-644a was similar to that of PITX2 knockdown in ESCC cells. Mechanistic studies revealed that miR-644a attenuates ESCC cells' malignancy and stem cell-associated phenotype, at least partially, by inactivation of the Akt/GSK-3 beta/beta-catenin signaling pathway through PITX2. Furthermore, promoter hypermethylation caused downregulation of miR-644a in ESCC. Conclusions: Downregulation of miR-644a plays an important role in promoting both aggressiveness and stem-like traits of ESCC cells, suggesting that miR-644a may be useful as a novel prognostic biomarker or therapeutic target for the disease. (C) 2016 AACR.