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Background: Breast cancer (BC) is a common malignant tumor in women worldwide. Circular RNA (circRNA) has been proven to play a critical role in BC progression. However, the exact biological functions and underlying mechanisms of circRNAs in BC remain largely unknown. Methods: Here, we first screened for differentially expressed circRNAs in 4 pairs of BC tissues and adjacent non-tumor tissues using a circRNA microarray. Functionally, gain- and loss-of-function experiments in vitro and in vivo showed that circDNAJC11 promoted BC cell proliferation, migration, invasion, and tumor growth. Mechanistically, RNA pull-down, mass spectrum, RNA immunoprecipitation, fluorescence in situ hybridization assays, and rescue experiments were executed. Results: We found that circDNAJC11 was significantly upregulated in triple-negative breast cancer tissues and cells. Clinical data revealed that the high expression of circDNAJC11 was closely correlated with a poor prognosis of BC patients and could be an independent risk factor for BC prognosis. Functionally, gain- and loss-of-function experiments in vitro and in vivo showed that circDNAJC11 promoted BC cell proliferation, migration, invasion, and tumor growth. Mechanistically, RNA pull-down, mass spectrum, RNA immunoprecipitation, fluorescence in situ hybridization assays, and rescue experiments were executed. We demonstrated that circDNAJC11 combined with TAF15 to promote BC progression via stabilizing MAPK6 mRNA and activating the MAPK signaling pathway. Conclusions: The circDNAJC11/TAF15/MAPK6 axis played a crucial role in the progression and development of BC, suggesting that circDNAJC11 might be a novel biomarker and therapeutical target for BC. [ABSTRACT FROM AUTHOR]

Background: Hypoxia has long been considered as a hallmark of solid tumors and is closely associated with tumor progression. Circular RNAs (circRNAs) have been identified as a critical modulator in various cancers. However, the connections between hypoxia and circRNAs are largely unknown. Methods: Here, we investigated the expression profile of circRNAs in breast cancer (BC) MCF-7 cells under hypoxia and normoxia using microarray. We identified a novel hypoxia-responsive circRNA named circWSB1, whose expression pattern, potential diagnostic value and prognostic significance were assessed by qRT-PCR and in situ hybridization. Loss- and gain-of-function investigations in vivo and in vitro were performed to determine the biological functions of circWSB1. Mechanistically, chromatin immunoprecipitation and dual luciferase reporter assays were carried out to analyze the biogenesis of circWSB1. Furthermore, biotin-labeled RNA pull-down, mass spectrometry, RNA immunoprecipitation, fluorescent in situ hybridization, RNA electrophoretic mobility shift, deletion-mapping, co-immunoprecipitation assays and rescue experiments were applied to investigate the interaction between circWSB1 and Ubiquitin-specific peptidase 10 (USP10) as well as the relationship between USP10 and p53. Results: We found that the expression of circWSB1 was significantly upregulated in BC tissues and correlated with poor clinical outcomes, which might serve as an independent prognostic factor for BC patients. Ectopic expression of circWSB1 promoted the proliferation of BC cell in vitro and in vivo. Mechanistically, circWSB1 was transcriptionally upregulated by HIF1α in response to hypoxia and could competitively bind to deubiquitinase USP10 to prevent the access of p53 to USP10 in BC cells, leading to degradation of p53 and tumor progression of BC. Conclusions: Taken together, our findings disclose a novel mechanism that hypoxia-inducible circWSB1 could interact with USP10 to attenuate USP10 mediated p53 stabilization and promote the progression of BC, providing an alternative prognostic biomarker and therapeutic target for BC. [ABSTRACT FROM AUTHOR]

Background: Recent studies have revealed that circular RNAs (circRNAs) play significant roles in the occurrence and development of many kinds of cancers including breast cancer (BC). However, the potential functions of most circRNAs and the molecular mechanisms underlying progression of BC remain elusive. Method: Here, Circular RNA microarray was executed in 4 pairs of breast cancer tissues and para-cancer tissues. The expression and prognostic significance of circACTN4 in BC cells and tissues were determined by qRT-PCR and in situ hybridization. Gain-and loss-of-function experiments were implemented to observe the impacts of circACTN4 on the growth, invasion, and metastasis of BC cells in vitro and in vivo. Mechanistically, chromatin immunoprecipitation, luciferase reporter, RNA pulldown, mass spectrum, RNA immunoprecipitation, fluorescence in situ hybridization and co-immunoprecipitation assays were executed. Results: CircACTN4 was significantly upregulated in breast cancer tissues and cells, its expression was correlated with clinical stage and poor prognosis of patients with BC. Ectopic expression of circACTN4 strikingly facilitated the growth, invasion, and metastasis of breast cancer cells in vitro and in vivo. Whereas knockdown of circACTN4 revealed opposite roles. CircACTN4 was mainly distributed in the nucleus. Further mechanistic research proved that circACTN4 could competitively bind to far upstream element binding protein 1 (FUBP1) to prevent the combination between FUBP1 and FIR, thereby activating MYC transcription and facilitating tumor progression of breast cancer. Furthermore, we found that upstream transcription factor 2 (USF2) might promote the biogenesis of circACTN4. Conclusion: Our findings uncover a pivotal mechanism that circACTN4 mediated by USF2 might interact with FUBP1 to promote the occurrence and development of breast cancer via enhancing the expression of MYC. CircACTN4 could be a novel potential target for diagnosis and treatment of breast cancer. [ABSTRACT FROM AUTHOR]

Background: Increasing studies have shown that circRNA is closely related to the carcinogenesis and development of many cancers. However, biological functions and the underlying molecular mechanism of circRNAs in triple-negative breast cancer (TNBC) remain largely unclear so far. Methods: Here, we investigated the expression pattern of circRNAs in four pairs of TNBC tissues and paracancerous normal tissues using RNA-sequencing. The expression and prognostic significance of circSEPT9 were evaluated with qRT-PCR and in situ hybridization in two TNBC cohorts. The survival curves were drawn by the Kaplan-Meier method, and statistical significance was estimated with the log-rank test. A series of in vitro and in vivo functional experiments were executed to investigate the role of circSEPT9 in the carcinogenesis and development of TNBC. Mechanistically, we explored the potential regulatory effects of E2F1 and EIF4A3 on biogenesis of circSEPT9 with chromatin immunoprecipitation (ChIP), luciferase reporter and RNA immunoprecipitation (RIP) assays. Furthermore, fluorescent in situ hybridization (FISH), luciferase reporter and biotin-coupled RNA pull-down assays were implemented to verify the relationship between the circSEPT9 and miR-637 in TNBC. Results: Increased expression of circSEPT9 was found in TNBC tissues, which was positively correlated with advanced clinical stage and poor prognosis. Knockdown of circSEPT9 significantly suppressed the proliferation, migration and invasion of TNBC cells, induced apoptosis and autophagy in TNBC cells as well as inhibited tumor growth and metastasis in vivo. Whereas up-regulation of circSEPT9 exerted opposite effects. Further mechanism research demonstrated that circSEPT9 could regulate the expression of Leukemia Inhibitory Factor (LIF) via sponging miR-637 and activate LIF/Stat3 signaling pathway involved in progression of TNBC. More importantly, we discovered that E2F1 and EIF4A3 might promote the biogenesis of circSEPT9. Conclusions: Our data reveal that the circSEPT9 mediated by E2F1 and EIF4A3 facilitates the carcinogenesis and development of triple-negative breast cancer through circSEPT9/miR-637/LIF axis. Therefore, circSEPT9 could be used as a potential prognostic marker and therapeutical target for TNBC. [ABSTRACT FROM AUTHOR]