Contribution of microRNA-30d to the prevention of the thyroid cancer progression: mechanism and implications

Abstract Background Thyroid cancer is a major endocrine tumor and represents an emerging health problem worldwide. MicroRNAs (miRNAs) have been addressed to be associated with the pathogenesis and progression of thyroid cancer. However, it remains largely unknown what functions miR-30d may exert on thyroid cancer. This study herein aimed to identify the functional significance and mechanism of miR-30d in the progression of thyroid cancer. Methods The expression of miR-30d and ubiquitin-specific protease 22 (USP22) in cancerous tissues of patients with thyroid cancer was measured using RT-qPCR and Western blot analysis. In response to the gain- or loss-of-function of miR-30d and USP22, cell apoptosis was evaluated by flow cytometry and TUNEL staining in combination with the measurement of apoptosis-related proteins. The interactions among miR-30d, USP22, SIRT1, FOXO3a and PUMA were explored using a series of assays, including dual-luciferase reporter gene assay, Co-IP and ChIP assay. The effects of miR-30d and USP22 on thyroid tumorigenesis were finally validated in vivo. Results MiR-30b presented aberrant low expression in thyroid cancer tissues and this low expression correlated with poor prognosis of thyroid cancer patients. miR-30d promoted apoptosis of thyroid cancer cells through targeting USP22, an up-regulated gene in thyroid cancer. USP22 could enhance the stability of SIRT1 by inducing deubiquitination which consequently contributed to FOXO3a deacetylation-induced PUMA repression. It was verified that this regulatory mechanism was responsible for the pro-apoptotic effect of miR-30d by the in vivo tumorigenicity assay. Conclusion To conclude, the progression of thyroid cancer can be suppressed by miR-30d-mediated inhibition of USP22, provides a promising therapeutic target for thyroid cancer treatment.