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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.

The cancer stem cell (CSC) hypothesis suggests that a subset of cancer cells possesses stem cell properties and is crucial in tumor initiation, metastasis, and drug resistance. To determine the mechanism of CSCs in breast cancer, we focused on LGR5, a marker of adult stem cells that potentially serves as a functional factor in CSCs.LGR5 overexpression was detected in breast cancer and significantly associated with breast cancer recurrence and poor outcome.LGR5 promoted cell mobility, tumor formation, and epithelial-mesenchymal transition in breast cancer cells by activating Wnt/b-catenin signaling. In addition, LGR5 was more highly expressed in tumorspheres and increased the stemness of breast cancer cells. Compared with LGR5 lowexpression (LGR5 low ) cells, LGR5 high cells exhibited CSC/tumor-initiating cell-like properties, including the formation of self-renewing spheres and high tumorigenicity. Importantly, our studies indicate that LGR5 activation of Wnt/b-catenin signaling is a possible mechanism to regulate breast CSC/tumor-initiating cell renewal. These findings indicate that LGR5 not only participates in carcinogenesis but also maintained stemness by activating Wnt/b-catenin signaling in breast cancer. STEM CELLS 2015;33:2913-2924 SIGNIFICANCE STATEMENTThe cancer stem cell hypothesis suggests that a subset of cancer cells possess stem cell properties and are crucial in tumor initiation, metastasis and drug resistance. To determine the mechanism of cancer stem cell in breast cancer, we focused our sight on LGR5, a marker for adult stem cells.LGR5 is overexpressed in breast cancer and is associated with poor outcomes. LGR5 promotes cell mobility, tumor formation and Epithelial-Mesenchymal Transition in breast cancer cells by activating Wnt/b-catenin signaling. Importantly, LGR5 activation of Wnt/b-catenin signaling is a possible mechanism to regulate breast cancer stem cell renewal. These findings indicate that LGR5 not only participates in carcinogenesis but also maintained stemness by activating Wnt/b-catenin signaling in breast cancer.

Purpose: The purpose of this study was to investigate the clinicopathologic significance and potential role of miR-200b and miR-200c

BackgroundIncreasing studies has found that circular RNAs (circRNAs) play vital roles in cancer progression. But the expression profile and function of circRNAs in triple-negative breast cancer (TNBC) are unclear.MethodsWe used a circRNA microarray to explore the circRNA expression profile of TNBC. The expression of the top upregulated circRNA, circKIF4A, was confirmed by qRT-PCR in breast cancer cell lines and tissues. Kaplan-Meier survival analysis was conducted to analyze the clinical impact of circKIF4A on TNBC. A series of experiments was performed to explore the functions of circKIF4A in TNBC progression, such as cell proliferation and migration. We investigated the regulatory effect of circKIF4A on miRNA and its target genes to explore the potential regulatory mechanisms of circKIF4A in TNBC.ResultsqRT-PCR analyses verified that circKIF4A was significantly upregulated and positively associated with poorer survival of TNBC. The inhibition of circKIF4A suppressed cell proliferation and migration in TNBC. Luciferase reporter assay and RNA immunoprecipitation assay revealed that circKIF4A and KIF4A could bind to miR-375 and that circKIF4A regulated the expression of KIF4A via sponging miR-375.ConclusionsThe circKIF4A-miR-375-KIF4A axis regulates TNBC progression via the competitive endogenous RNA (ceRNA) mechanism. circKIF4A may therefore serve as a prognostic biomarker and therapeutic target for TNBC.Electronic supplementary materialThe online version of this article (10.1186/s12943-019-0946-x) contains supplementary material, which is available to authorized users.

BackgroundMicroRNAs (miRNAs) have been documented as playing important roles in cancer development. In this study, we investigated the role of miR-124 in breast cancer and clarified the regulation of flotillin-1 (FLOT1) by miR-124.MethodsThe expression levels of miR-124 were examined in breast cancer cell lines and patient specimens using quantitative reverse transcription-PCR. The clinicopathological significance of the resultant data was later analyzed. Next, we explored the function of miR-124 to determine its potential roles on cancer cell growth and migration in vitro. A luciferase reporter assay was conducted to confirm the target gene of miR-124, and the results were validated in cell lines and patient specimens.ResultsWe found that miR-124 expression was significantly downregulated in breast cancer cell lines and patient specimen compared with normal cell lines and paired adjacent normal tissues (P < 0.0001), respectively. MiR-124 was also associated with tumor node metastasis (TNM) stage (P = 0.0007) and lymph node metastasis (P = 0.0004). In breast cancer cell lines, the ectopic expression of miR-124 inhibited cell growth and migration in vitro. Moreover, we identified the FLOT1 gene as a novel direct target of miR-124, and miR-124 ectopic expression significantly inhibited FLOT1. Luciferase assays confirmed that miR-124 could directly bind to the 3′ untranslated region of FLOT1 and suppress translation. Moreover, FLOT1 was widely upregulated, and inversely correlated with miR-124 in breast cancer tissues. Consistent with the effect of miR-124, the knockdown of FLOT1 significantly inhibited breast cancer cell growth and migration. We also observed that the rescue expression of FLOT1 partially restored the effects of miR-124.ConclusionsOur study demonstrated that miR-124 might be a tumor suppressor in breast cancer via the regulation of FLOT1. This microRNA could serve as a potential diagnostic marker and therapeutic target for breast cancer.

Recurrence and metastasis result in a poor prognosis for breast cancer patients. Recent studies have demonstrated that microRNAs (miRNAs) play vital roles in the development and metastasis of breast cancer. In this study, we investigated the therapeutic potential of miR-34a in breast cancer. We found that miR-34a is downregulated in breast cancer cell lines and tissues, compared with normal cell lines and the adjacent nontumor tissues, respectively. To explore the therapeutic potential of miR-34a, we designed a targeted miR-34a expression plasmid (T-VISA-miR-34a) using the T-VISA system, and evaluated its antitumor effects, efficacy, mechanism of action, and systemic toxicity. T-VISA-miR-34a induced robust, persistent expression of miR-34a, and dramatically suppressed breast cancer cell growth, migration, and invasion in vitro by downregulating the protein expression levels of the miR-34a target genes E2F3, CD44, and SIRT1. In an orthotopic mouse model of breast cancer, intravenous injection of T-VISA-miR-34a:liposomal complex nanoparticles significantly inhibited tumor growth, prolonged survival, and did not induce systemic toxicity. In conclusion, T-VISA-miR-34a lead to robust, specific overexpression of miR-34a in breast cancer cells and induced potent antitumor effects in vitro and in vivo. T-VISA-miR-34a may provide a potentially useful, specific, and safe-targeted therapeutic approach for breast cancer.

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