Abstract: Background and purpose: Circular RNA (circRNA), as a newly discovered non-coding RNA with important regulatory potential, is closely related to the occurrence and development of various tumors, but it is rarely reported in triple-negative breast cancer (TNBC). The aim of the present study was to investigate the expression of circRNA hsa_circ_0005320 in TNBC and its effect on the proliferation of TNBC. Methods: RNA sequencing (RNA-seq) was adopted to analyze 4 pairs of TNBC tissues and adjacent non-cancerous tissues who received surgical resection in the First Affiliated Hospital of Chongqing Medical University. Using real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR), we detected the relative expression levels of circRNA hsa_circ_0005320 in 20 pairs of TNBC tissues and adjacent non-cancerous tissues, normal breast epithelial cell MCF-10A and TNBC cell MDA-MB-231 and BT-549, and further tested the expression by fluorescence in situ hybridization (FISH) assay. After silencing hsa_circ_0005320, the relative expression level of hsa_circ_0005320 was detected by RTFQ-PCR. The proliferation of TNBC cells was determined by cell counting kit-8 (CCK-8) and EdU assays. Flow cytometry, Hoechst 33342 and TUNEL assay were employed to detect cell apoptosis, respectively. Cell cycle distribution was analyzed by flow cytometry. Western blot was used to detect the expression levels of proteins related to the LIF-STAT3 pathway. Results: circRNA hsa_circ_0005320 was highly expressed in TNBC tissues and cells. After silencing hsa_circ_0005320 in TNBC cells, its expression was significantly reduced, the ability of cell proliferation was decreased, cell apoptosis was promoted, leading to cell cycle arrest in G₁ phase, and lower protein levels BTof LIF and p-STAT3 were observed clearly. Conclusion: CircRNA hsa_circ_0005320 is highly expressed in TNBC, and silencing hsa_circ_0005320 can significantly inhibit the proliferation of TNBC cells and induce apoptosis.

Key words: Circular RNA, Triple-negative breast cancer, hsa_circ_0005320, Proliferation