MicroRNA-3666 Regulates Thyroid Carcinoma Cell Proliferation via MET.

BACKGROUND/AIMS Thyroid carcinoma (TC) is a highly lethal malignant cancer and its carcinogenesis remains undetermined. Dysregulation of microRNAs (miRNAs) is well known to be involved in the development of various cancers, including TC, whereas a role of miR-3666 in the pathogenesis of TC has not been appreciated. METHODS We analyzed the levels of MET and miR-3666 in TC tissue and the relationship of miR-3666 levels with patients' prognosis. We then overexpressed miR-3666 by miRNA mimics transfection and inhibited miR-3666 by miRNA antisense transfection in TC cells. Cell survival and growth were analyzed by CCK-8 assay and MTT assay, respectively. Cell apoptosis and proliferation were analyzed by flow cytometry. Bioinformatics analyses were applied to predict miR-3666 targets, which was then confirmed using luciferase reporter assay. RESULTS We detected significantly higher levels of MET, and significantly lower levels of miR-3666 in TC tissue, compared to the adjacent non-tumor tissue. Moreover, the low miR-3666 levels were associated with poor survival of the patients. Overexpression of miR-3666 significantly inhibited cell growth, while depletion of miR-3666 increased cell growth in TC cells. Moreover, the effects of miR-3666 on cell growth appeared to result from alteration in cell proliferation, rather than changes in cell apoptosis. MiR-3666 was found to bind to the 3'-UTR of MET mRNA to inhibit its translation in TC cells. CONCLUSION Reduced miR-3666 levels in TC tissue may promotes TC growth, possibly through MET-mediated cell proliferation.