Down-regulation Of GPx-3 By MiR-146b-5p Leads To Disturbance Of Peroxide Clearance In Thyroid Cancer Cells

Background: Glutathione peroxidase(GPx)is an antioxidant enzyme whose main function is to remove intracellular hydrogen peroxide(H2O2).It is divided into eight subtypes of GPx1-GPx8.The thyroid releases a large amount of H2O2 in the process of thyroid hormone synthesis.In order to maintain the redox balance in thyroid cells,the antioxidant system is needed to remove excess peroxide.GPx is an important antioxidant enzyme in thyroid follicular cells.The decrease in GPx-3 expression in papillary thyroid carcinoma(PTC)is related to metastasis,but the reason for the decrease in GPx-3 expression is not clear.Therefore,the main purpose of this study is to explore the reasons for the decreased expression of GPx-3 in PTC and its effect on peroxide clearance in PTC.Methods: The expression of GPx-3 in thyroid cancer and thyroid tissues was obtained from the Cancer Genome Atlas(TCGA)database and verified by Western Blotting(n=18).Bioinformatics tools was used to predict the relationship between the expression of GPx-3 and gender,age,stage,lymph node metastasis,BRAFV600 E,and recurrence-free survival(RFS)of patients.The possible upstream micro RNAs of GPx-3 were analyzed.We verified the relationship between GPx-3 and upstream micro RNA by Enzyme-linked immunosorbent assay(ELISA)and dual luciferase reporter gene experiments.Results: The level of GPx-3 decreased in papillary thyroid cancer and its expression is lower in the elderly,thyroid patients with lymph node metastasis,later stage,or BRAF mutation(p < 0.05).The low expression of GPx-3 indicates poor prognosis,which is characterized by low RFS.miR-146b-5p was significantly overexpressed in PTC.Knockdown of miR-146b-5p in thyroid cancer cell lines TPC-1 and BCPAP caused an increase in GPx-3 expression levels,accompanied by an increase in the conversion of GSH to GSSG.The dual luciferase reporter assay verified the binding of miR-146b-5p with 3’-UTR of GPx-3 m RNA.Conclusions: In conclusion,miR-146b-5p,which is highly expressed in thyroid cancer,interferes with intracellular peroxide clearance by directly targeting GPx-3 m RNA.the accumulation of intracellular peroxides due to low GPx-3 levels may contribute to the poor prognosis of thyroid cancer.