miR-122-5p suppresses the oncogenesis of PTC by inhibiting DUSP4 expression

MicroRNAs (miRNAs or miRs) play an important role in regulating the occurrence and development of papillary thyroid carcinoma (PTC). miR-122-5p is widely considered a tumour inhibitor, which has not been fully explored in PTC. Bioinformatics analysis identified dual specificity phosphatase 4 (DUSP4), a tumour promoter gene for PTC, as a downstream target of miR-122-5p. The aim of the present study was to investigate the role and molecular mechanism of miR-122-5p in PTC oncogenesis. In this study, the expression pattern of miR-122-5p in PTC cancer tissues and PTC cell lines was investigated via reverse transcription-quantitative PCR. Furthermore, the roles of miR-122-5p in PTC were explored using gain-of-function and loss-of-function assays. The results revealed that the expression of miR-122-5p was significantly lower in PTC cancer tissues, especially in cancer tissues with significant invasion or metastasis. Overexpression of miR-122-5p caused by miR-122-5p mimics inhibited the proliferation, invasion, and migration of the PTC cell line K1, while knockdown of miR-122-5p by miR-122-5p inhibitors exhibited the opposite effect. Furthermore, in vivo assays revealed that miR-122-5p overexpression inhibited tumour growth. In addition, miR-122-5p was negatively correlated with DUSP4 expression in PTC cancer tissues. miR-122-5p overexpression inhibited DUSP4 expression in K1 cells, while miR-122-5p downregulation produced the inverse effect. Specifically, a luciferase reporter assay confirmed the binding sites of miR-122-5p on the 3′-UTR of DUSP4, demonstrating the targeting effect of miR-122-5p on DUSP4. miR-122-5p inhibited the oncogenesis of PTC by targeting DUSP4, revealing the potential application value of miR-122-5p in the diagnosis and treatment of PTC.