Abstract: Background and purpose: Circular RNA (circRNA) is a class of non-coding RNAs with important regulatory potential. It is involved in the development and progression of various cancers, but has not been reported in triple-negative breast cancer. The aim of the present study was to investigate the effects of circRNA hsa_circ_0058514 on the development and progression of triple-negative breast cancer. Methods: RNA sequencing (RNA-seq) was performed on 4 pairs of triple-negative breast cancer tissues and adjacent non-cancerous tissues. The relative expression levels of hsa_circ_0058514 in 20 pairs of triplenegative breast cancer tissues and adjacent non-cancerous tissues, normal breast epithelial cell MCF-10A and triple-negative breast cancer MDA-MB-231 and BT-549 cells were detected by real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR). The interference vector pLL3.7-sh-circ was transfected into triple-negative breast cancer MDA-MB-231 and BT-549 cells, and the expression level of hsa_circ_0058514 was determined by RTFQ-PCR. The proliferations of MDA-MB-231 and BT-549 cells were detected by cell counting kit-8 (CCK-8) and EdU assays. The abilities of migration and invasion of MDA-MB-231 and BT-549 cells were examined by wound healing assay and Transwell assay, respectively. The cell apoptosis and cell cycle distribution were analyzed by flow cytometry. Western blot was employed to observe the protein expression levels of CCNE1 and CDK2. Results: The expression levels of circRNA hsa_circ_0058514 in triple-negative breast cancer tissues and cells were significantly up- regulated (P<0.001, P<0.01). The expression of hsa_circ_0058514 in the group transfected with interference vector was much lower than that in the control group. Downregulation of hsa_circ_0058514 decreased the abilities of proliferation, migration and invasion of triple-negative breast cancer cells, leading to cell apoptosis and cell cycle arrest. And lower protein expression levels of CCNE1 and CDK2 were observed by Western blot after transfection of hsa_circ_0058514 (P<0.05). Conclusion: The expression of circRNA hsa_circ_0058514 is significantly upregulated in triple-negative breast cancer tissues and MDA-MB-231 and BT-549 cells. It may serve as an oncogene in the development and progression of triple-negative breast cancer, and it is expected to become a new target for the treatment of triple-negative breast cancer.

Key words: Circular RNA, Triple-negative breast cancer, hsa_circ_0058514, Proliferation, Apoptosis, Cell cycle