Circ_0000520 contributes to triple‐negative breast cancer progression through mediating the miR‐1296/ZFX axis

BACKGROUND: Triple‐negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with a high incidence of local recurrence and metastasis. Circular RNAs (circRNAs) are implicated in the pathomechanism of TNBC. Here, we investigated the function of circ_0000520 in TNBC and its associated mechanism. METHODS: Reverse transcription quantitative polymerase chain reaction (RT‐qPCR) and Western blot assay were used to measure RNA and protein expression. Cell proliferation was analyzed by cell counting kit‐8 (CCK8) assay, flow cytometry and colony formation assay. Cell apoptosis was assessed by flow cytometry. Cell migration ability was analyzed by transwell migration and wound healing assays. Transwell invasion assay was conducted to analyze the invasion ability. Dual‐luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA‐pulldown assay were performed to verify the interaction between microRNA‐1296 (miR‐1296) and circ_0000520 or zinc finger protein X‐linked (ZFX). Xenograft mice model was established to analyze the role of circ_0000520 in xenograft tumor growth in vivo. RESULTS: Circ_0000520 expression was upregulated in TNBC tissues and cell lines. Circ_0000520 knockdown suppressed the proliferation, migration, and invasion whereas induced the apoptosis of TNBC cells. miR‐1296 was verified as a target of circ_0000520, and circ_0000520 silencing‐mediated suppressive effects on the malignant potential of TNBC cells were partly overturned by miR‐1296 knockdown. miR‐1296 interacted with the 3′ untranslated region (3′UTR) of ZFX, and ZFX overexpression partly reversed miR‐1296 overexpression‐mediated effects in TNBC cells. Circ_0000520 absence reduced ZFX expression by upregulating miR‐1296 in TNBC cells. Circ_0000520 silencing suppressed xenograft tumor growth in vivo. CONCLUSIONS: Circ_0000520 contributed to TNBC development by binding to miR‐1296 to induce ZFX expression.