Regulation Of Autophagy By MiR-30d Impacts Sensitivity Of Anaplastic Thyroid Carcinoma To Cisplatin

Objective: To study the effects of miR-30d on sensitivity of Anaplastic ThyroidCarcinoma cells to cisplatin, and the involved molecular mechanism.Methods: miR-30d has been observed to be significantly down-regulated inhuman anaplastic thyroid carcinoma (ATC), and is believed to be an important event inthyroid cell transformation. In this study, we determined the regulatory role ofmiR-30d in autophagy and the effect miR-30d-mediated autophagy on cisplatinsensitivity. Cell biology, molecular biology, pharmacology and animal experimentmethods were used in this study.Results: We observed:1) A reporter gene assay demonstrated that the bindingsequences of miR-30d in the beclin1-3’ UTR was the region required for the inhibitionof beclin1expression. miR-30d could negatively regulate the expression of beclin1, akey autophagy gene, as indicated by a significant reduction of the reporter gene activity,and expressions of beclin1mRNA and protein were also inhibited in the cellstransfected with the miR-30d mimic.2) Cisplatin-induced autophagy was blunted by amiR-30d mimic in ATC cells, as evidenced by the decreases in the amount of LC3IIand the numbers of GFP-LC3puncta.3) The miR-30d mimic could sensitize ATC cellsto cisplatin, as shown by the increases in Annexin V staining and in the amounts of thecleaved caspase-3and cleaved PARP.4) Forced expression of beclin1could rescue thedown-regulation of autophagy caused by the miR-30d mimic, as evidenced by theincreases in the expression of LC3II and the decreases in the amounts of the cleavedPARP and cleaved caspase-3, and in the Annexin V staining after transfection with abeclin1expression plasmid.5) The miR-30d mimic enhanced the antitumor efficacy ofcisplatin in an ATC xenograft mouse model, as indicated by the decreases of tumor sizeand the ability of proliferation with Ki67staining and the increases of apoptosis withTUNEL staining. Conclusion: Autophagy activation induced by down-regulation of miR-30dexpression, which is mediated by beclin1, is involved in cellular resistance to cisplatinThese findings should help further understand the molecular and cellular functions ofmiR-30d in cancer, and may provide a potential target for cancer prevention andtreatment.