Circ_0001667 knockdown blocks cancer progression and attenuates adriamycin resistance by depleting NCOA3 via releasing miR‐4458 in breast cancer.

Accumulating evidence suggests that developmental chemoresistance in cancers is closely associated with the dysregulation of circular RNA transcriptions. The objective of this study is to disclose the role of circ_0001667 and provide a potential functional mechanism in breast cancer. Quantitative real‐time PCR was applied for the analysis of circ_0001667, microRNA‐4458 (miR‐4458) and nuclear receptor coactivator 3 (NCOA3) expression. In adriamycin (ADM)‐resistant cell lines, we investigated cell proliferation using 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5 diphenyl tetrazolium bromide (MTT) assay and colony formation assay. Cell migration and cell invasion were determined by transwell assay. The protein levels of multi‐drug resistance‐1, matrix metalloproteinases‐9, cleaved‐caspase3, cleaved‐caspase9 and NCOA3 were detected by western blot. ADM resistance was ascertained by IC50 value using MTT assay. Cell apoptosis was checked by flow cytometry assay. The putative relationship between miR‐4458 and circ_0001667 and NCOA3 was validated by pull‐down assay, dual‐luciferase reporter assay or RNA Immunoprecipitation assay. Circ_0001667 knockdown inhibited MCF‐7/ADM and MDA‐MB‐231/ADM cell proliferation, migration, invasion and ADM resistance. MiR‐4458 was a target of circ_0001667, and its expression was decreased in ADM‐resistant tumor tissues and cells. MiR‐4458 inhibition reversed the effects of circ_0001667 knockdown. In depth, NCOA3 was a target of circ_0001667, and circ_0001667 knockdown weakened NCOA3 expression by releasing miR‐4458. MCF‐7/ADM and MDA‐MB‐231/ADM cell proliferation, migration, invasion, and ADM resistance inhibited by miR‐4458 restoration were recovered by NCOA3 overexpression. Circ_0001667 knockdown also repressed tumor growth and ADM resistance in vivo. Circ_0001667 knockdown blocks cancer progression and attenuates ADM resistance by depleting NCOA3 via releasing miR‐4458 in breast cancer. [ABSTRACT FROM AUTHOR]