Cancer Biology and Signal Transduction miR-124 Regulates the Epithelial-Restricted with Serine Box/Epidermal Growth Factor Receptor Signaling Axis in Head and Neck Squamous Cell Carcinoma

Epithelial-restrictedwith serine box (ESX), amember 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 30-untranslated region (UTR) of ESX predicted two miR-124– binding sites. Delivery of miR-124 inhibited the 30UTR 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 fre-quent event in HNSCC. miR-124 expression was significantly depleted in the primary tumor compared with matched normal tissue in 100%(12/12)ofHNSCCpatients; relativemeanmiR-124 expression of 0.01197 and0.00118 (P < 0.001, n 12) inmatched normal adjacent tissue and primary HNSCC tumor, respectively. Overexpression ofmiR-124decreased ESX andEGFR levels inmiR-124low/ESXhigh/EGFRhigh 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, reca-pitulation 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 intrigu-ing 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. Mol Cancer Ther; 14(10); 2313–20. 2015 AACR