Epithelial-restricted with serine box (ESX), a member of the ETS transcription factor family, is elevated and regulates EGFR in head and neck squamous cell carcinoma (HNSCC). However, the molecular mechanisms that contribute to ESX dysregulation remain to be elucidated. In this study, in silico analysis of the 3'-untranslated region (UTR) of ESX predicted two miR-124-binding sites. Delivery of miR-124 inhibited the 3'UTR ESX-driven reporter activity by 50% (P < 0.05) confirming ESX as a direct target of miR-124. Loss of miR-124 was found to be a frequent event in HNSCC. miR-124 expression was significantly depleted in the primary tumor compared with matched normal tissue in 100% (12/12) of HNSCC patients; relative mean miR-124 expression of 0.01197 and 0.00118 (P < 0.001, n = 12) in matched normal adjacent tissue and primary HNSCC tumor, respectively. Overexpression of miR-124 decreased ESX and EGFR levels in miR-124(low)/ESX(high)/EGFR(high) SCC15 HNSCC cells and reduced cell invasion, migration, proliferation, and colony formation. SCC15 cells with miR-124 restoration were less tumorigenic in vivo than miR-control SCC15 cells (70% inhibition, P < 0.01). Restoration of miR-124 in SCC15 cells enhanced the antiproliferative efficacy of the EGFR/Her2 tyrosine kinase inhibitors. Furthermore, recapitulation of EGFR in miR-124-overexpressing SCC15 cells was sufficient to completely block the antiproliferative effects of lapatinib and afatinib. Taken together, our work provides intriguing evidence that miR-124 is a novel therapeutic approach to reduce ESX/EGFR, and may be a tractable strategy to enhance the response rate of HNSCC patients to current anti-EGFR/Her2 therapies.
©2015 American Association for Cancer Research.