LAUSR

An increasing number of findings have verified the critical roles of circular RNAs (circRNAs) in human cancers, and chemotherapy resistance is a poor prognostic factor for breast cancer (BC). This study is designed to explore the function of hsa_circ_0097922 in the tamoxifen resistance of breast cancer. Hsa_circ_0097922, microRNA‐876‐3p (miR‐876‐3p), and alpha‐actinin 4 (ACTN4) level were detected by real‐time quantitative polymerase chain reaction (RT‐qPCR). Cell survival, proliferation, apoptosis, migration and invasion were detected by Cell Counting Kit‐8 (CCK‐8), 5‐ethynyl‐2′‐deoxyuridine (EdU), and flow cytometry, wound healing and Transwell assays. Protein levels of proliferating cell nuclear antigen (PCNA), B‐cell lymphoma‐2 (Bcl‐2), cleaved caspase 3, matrix metalloproteinase 9 (MMP9), and ACTN4 were determined using western blot assay. Using bioinformatics software, the binding between miR‐876‐3p and hsa_circ_0097922 or ACTN4 was predicted, followed by confirmation by RNA immunoprecipitation (RIP) and RNA pull‐down assays. A xenograft tumour model in vivo analysed the biological role of hsa_circ_0097922 on BC tumour growth and drug resistance. Hsa_circ_0097922 and ACTN4 were increased, and miR‐876‐3p was decreased in tamoxifen resistance BC cells. Moreover, hsa_circ_0097922 knockdown can block BC cell malignant behaviour and tamoxifen resistance in vitro. Mechanically, hsa_circ_0097922 acted as a sponge of miR‐876‐3p to regulate ACTN4 expression. Hsa_circ_0097922 silencing increased the drug sensitivity of BC in vivo. Hsa_circ_0097922 might regulate BC cell malignant behaviour and tamoxifen resistance partly by regulating the miR‐876‐3p/ACTN4 axis, hinting at a promising therapeutic target for the BC treatment.