circEPSTI1 as a Prognostic Marker and Mediator of Triple-Negative Breast Cancer Progression

Circular RNAs (circRNAs) represent a class of non-coding RNAs that play a vital role in modulating gene expression and several pathological responses. However, the expression profile and function of circRNAs in triple-negative breast cancer (TNBC) remain unknown. In the current study, we investigated the expression profile of human circRNAs in TNBC tissues and identified circEPSTI1 (hsa_circRNA_000479) as a significantly upregulated circRNA. Methods: We performed circular RNA microarray assays to screen circular RNA expression profiles of TNBC and further investigated circEPSTI1. We observed the effect of circEPSTI1 on proliferation, clonal formation and apoptosis in TNBC by knocking downcircEPSTI1 in three TNBC cell lines. Based on the MRE analysis and luciferase reporter assay, we found that circEPSTI1 binds to miRNAs as a miRNA sponge and the co-target genes of miRNAs. We performed xenograft experiments in mice to confirm our findings. We evaluated circEPSTI1 levels in 240 TNBC patients by ISH. Results: Knockdown of circEPSTI1 inhibits TNBC cell proliferation and induces apoptosis. In vitro and in vivo experiments indicated that circEPSTI1 binds to miR-4753 and miR-6809 as a miRNA sponge to regulate BCL11A expression and affect TNBC proliferation and apoptosis. High levels of circEPSTI1 correlate with reduced survival in TNBC patients. Conclusions: The circEPSTI1-miR-4753/6809-BCL11A axis affect the proliferation and apoptosis of triple-negative breast cancer through the mechanism of competing endogenous RNAs (ceRNA). In addition, our results identify circEPSTI1 as an independent prognostic marker for survival in patients with TNBC.