Circular RNA hsa_circ_0008039 promotes breast cancer cell proliferation and migration by regulating miR-432-5p/E2F3 axis. Biochem Biophys Res Commun. 2018;502:358-363. [PMID: 29807010 DOI: 10.1016/j.bbrc.2018.05.166]

Circular RNAs in Cell Cycle Regulation of Cancers

Cancer has been one of the most problematic health issues globally. Typically, all cancers share a common characteristic or cancer hallmark, such as sustaining cell proliferation, evading growth suppressors, and enabling replicative immortality. Indeed, cell cycle regulation in cancer is often found to be dysregulated, leading to an increase in aggressiveness. These dysregulations are partly due to the aberrant cellular signaling pathway. In recent years, circular RNAs (circRNAs) have been widely studied and classified as one of the regulators in various cancers. Numerous studies have reported that circRNAs antagonize or promote cancer progression through the modulation of cell cycle regulators or their associated signaling pathways, directly or indirectly. Mostly, circRNAs are known to act as microRNA (miRNA) sponges. However, they also hold additional mechanisms for regulating cellular activity, including protein binding, RNA-binding protein (RBP) recruitment, and protein translation. This review will discuss the current knowledge of how circRNAs regulate cell cycle-related proteins through the abovementioned mechanisms in different cancers.

Circular RNA-mediated miRNA sponge & RNA binding protein in biological modulation of breast cancer

Circular RNAs (circRNAs) and small non-coding RNAs of the head-to-junction circle in the construct play critical roles in gene regulation and are significantly associated with breast cancer (BC). Numerous circRNAs are potential cancer biomarkers that may be used for diagnosis and prognosis. Widespread expression of circRNAs is regarded as a feature of gene expression in highly diverged eukaryotes. Recent studies show that circRNAs have two main biological modulation models: sponging and RNA-binding. This review explained the biogenesis of circRNAs and assessed emerging findings on their sponge function and role as RNA-binding proteins (RBPs) to better understand how their interaction alters cellular function in BC. We focused on how sponges significantly affect the phenotype and progression of BC. We described how circRNAs exercise the translation functions in ribosomes. Furthermore, we reviewed recent studies on RBPs, and post-protein modifications influencing BC and provided a perspective on future research directions for treating BC.

Optimal control strategies for SGLT2 inhibitors as a novel anti-tumor agent and their effect on human breast cancer cells with the effect of time delay and hyperglycemia

Breast cancer is the most frequent cancer in the world, and it continues to have a significant impact on the total number of cancer deaths. Recently, oncology findings hint at the role of excessive glucose in cancer progression and immune cells' suppression. Sequel to this revelation is ongoing researches on possible inhibition of glucose flow into the tumor micro-environment as therapeutics for malignant treatment. In this study, the effect of glucose blockage therapeutics such as SGLT-2 inhibitors drug on the dynamics of normal, tumors and immune cells interaction is mathematically studied. The asymptomatic nature of the breast cancer is factored into the model using time delay. We first investigate the boundedness and non-negativity of the solution. The condition for existence of critical equilibrium point is determined, and its global stability conditions are derived using Lyapunov function. This revealed that a timely administration of the SGLT-2 inhibitors drug can eliminate tumor cells. Secondly, we determine the sufficient and necessary conditions for optimal control strategy of SGLT-2 inhibitors so as to avert side effects on normal cells using a Pontryagin's Minimum Principle. The results showed that if the ingestion rate of the inhibitor drug is equal to the digestion rate, the tumor cells can be completely eliminated within 9 months without side effects. The analytical results were numerically verified and the qualitative views of interacting cells dynamics is showcased.

Hsa_circ_0007823 Overexpression Suppresses the Progression of Triple-Negative Breast Cancer via Regulating miR-182-5p-FOXO1 Axis

Background

This study aimed to analyze the specific expression of hsa_circ_0007823 in triple-negative breast cancer (TNBC) and explore the roles and related molecular mechanisms of hsa_circ_0007823 in TNBC.

Materials and Methods

Relative hsa_circ_0007823 levels in TNBC tissues and cell lines were examined by reverse transcription-quantitative polymerase chain reaction. The value of hsa_circ_0007823 levels was evaluated in patients' clinicopathological characteristics and prognostic prediction. A dual-luciferase reporter assay was used to determine the relationship between hsa_circ_0007823, miR-182-5p, and FOXO1. The effect of circ_0007823 overexpression on the growth of TNBC cells was investigated in vitro and in vivo.

Results

Lower levels of hsa_circ_0007823 were found in TNBC tissues and cell lines and were closely associated with lymph node metastasis, poorer overall and disease-free survival rates. MiR-182-5p was significantly up-regulated, whereas FOXO1 was down-regulated in TNBC cell lines. The miR-182-5p inhibition up-regulated FOXO1 in TNBC cells. Dual-luciferase reporter assays showed that hsa_circ_0007823, miR-182-5p, and FOXO1 interacted with each other. Overexpression of circ_0007823 significantly inhibited the viability, migration, and invasion of TNBC cell lines, but promoted apoptosis. In vivo experiments showed that circ_0007823 overexpression inhibited tumor growth and down-regulated miR-182-5p and up-regulated FOXO1.

Conclusion

Hsa_circ_0007823 overexpression could suppress the growth, invasion, and migration of TNBC cells, and inhibit tumor growth by regulating miR-182-5p/FOXO1.

Regulatory miRNAs, circRNAs and lncRNAs in cell cycle progression of breast cancer

Breast cancer is a complex and heterogeneous disease that poses a significant public health concern worldwide, and it remains a major challenge despite advances in treatment options. One of the main properties of cancer cells is the increased proliferative activity that has lost regulation. Dysregulation of various positive and negative modulators in the cell cycle has been identified as one of the driving factors of breast cancer. In recent years, non-coding RNAs have garnered much attention in the regulation of cell cycle progression, with microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs) being of particular interest. MiRNAs are a class of highly conserved and regulatory small non-coding RNAs that play a crucial role in the modulation of various cellular and biological processes, including cell cycle regulation. CircRNAs are a novel form of non-coding RNAs that are highly stable and capable of modulating gene expression at posttranscriptional and transcriptional levels. LncRNAs have also attracted considerable attention because of their prominent roles in tumor development, including cell cycle progression. Emerging evidence suggests that miRNAs, circRNAs and lncRNAs play important roles in the regulation of cell cycle progression in breast cancer. Herein, we summarized the latest related literatures in breast cancer that emphasize the regulatory roles of miRNAs, circRNAs and lncRNAs in cell cycle progress of breast cancer. Further understanding of the precise roles and mechanisms of non-coding RNAs in breast cancer cell cycle regulation could lead to the development of new diagnostic and therapeutic strategies for breast cancer.

Therapeutic and diagnostic applications of exosomal circRNAs in breast cancer

Circular RNAs (circRNAs) are regulatory elements that are involved in orchestrating gene expression and protein functions and are implicated in various biological processes including cancer. Notably, breast cancer has a significant mortality rate and is one of the most common malignancies in women. CircRNAs have been demonstrated to contribute to the pathogenesis of breast cancer including its initiation, progression, metastasis, and resistance to drugs. By acting as miRNA sponges, circRNAs can indirectly influence gene expression by disrupting miRNA regulation of their target genes, ultimately altering the course of cancer development and progression. Additionally, circRNAs can interact with proteins and modulate their functions including signaling pathways involved in the initiation and development of cancer. Recently, circRNAs can encode peptides that play a role in the pathophysiology of breast cancer and other diseases and their potential as diagnostic biomarkers and therapeutic targets for various cancers including breast cancer. CircRNAs possess biomarkers that differentiate, such as stability, specificity, and sensitivity, and can be detected in several biological specimens such as blood, saliva, and urine. Moreover, circRNAs play an important role in various cellular processes including cell proliferation, differentiation, and apoptosis, all of which are integral factors in the development and progression of cancer. This review synthesizes the functions of circRNAs in breast cancer, scrutinizing their contributions to the onset and evolution of the disease through their interactions with exosomes and cancer-related intracellular pathways. It also delves into the potential use of circRNA as a biomarker and therapeutic target against breast cancer. It discusses various databases and online tools that offer crucial circRNA information and regulatory networks. Lastly, the challenges and prospects of utilizing circRNAs in clinical settings associated with breast cancer are explored.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

Advances in high-throughput sequencing techniques and bioinformatic analysis have refuted the "junk" RNA hypothesis that was claimed against non-coding RNAs (ncRNAs). Circular RNAs (circRNAs); a class of single-stranded covalently closed loop RNA molecules have recently emerged as stable epigenetic regulators. Although the exact regulatory role of circRNAs is still to be clarified, it has been proven that circRNAs could exert their functions by interacting with other ncRNAs or proteins in their own physiologically authentic environment, regulating multiple cellular signaling pathways and other classes of ncRNAs. CircRNAs have also been reported to exhibit a tissue-specific expression and have been associated with the malignant transformation process of several hematological and solid malignancies. Along this line of reasoning, this review aims to highlight the importance of circRNAs in Breast Cancer (BC), which is ranked as the most prevalent malignancy among females. Notwithstanding the substantial efforts to develop a suitable anticancer therapeutic regimen against the heterogenous BC, inter- and intra-tumoral heterogeneity have resulted in an arduous challenge for drug development research, which in turn necessitates the investigation of other markers to be therapeutically targeted. Herein, the potential of circRNAs as possible diagnostic and prognostic biomarkers have been highlighted together with their possible application as novel therapeutic targets.

The Tumorigenic Role of Circular RNA-MicroRNA Axis in Cancer

Circular RNAs (circRNAs) are a class of endogenous RNAs that control gene expression at the transcriptional and post-transcriptional levels. Recent studies have increasingly demonstrated that circRNAs act as novel diagnostic biomarkers and promising therapeutic targets for numerous cancer types by interacting with other non-coding RNAs such as microRNAs (miRNAs). The miRNAs are presented as crucial risk factors and regulatory elements in cancer by regulating the expression of their target genes. Some miRNAs are derived from transposable elements (MDTEs) that can transfer their location to another region of the genome. Genetic interactions between miRNAs and circular RNAs can form complex regulatory networks with various carcinogenic processes that play critical roles in tumorigenesis and cancer progression. This review focuses on the biological regulation of the correlative axis among circular RNAs, miRNAs, and their target genes in various cancer types and suggests the biological importance of MDTEs interacting with oncogenic or tumor-suppressive circRNAs in tumor progression.

Identification of a dysregulated CircRNA-associated gene signature for predicting prognosis, immune landscape, and drug candidates in bladder cancer

Increasing evidences have demonstrated that circular RNA (circRNAs) plays a an essential regulatory role in initiation, progression and immunotherapy resistance of various cancers. However, circRNAs have rarely been studied in bladder cancer (BCa). The purpose of this research is to explore new circRNAs and their potential mechanisms in BCa. A novel ceRNA-regulated network, including 87 differentially expressed circRNAs (DE-circRNAs), 126 DE-miRNAs, and 217 DE-mRNAs was constructed to better understanding the biological processes using Cytoscape 3.7.1 based on our previously high-throughput circRNA sequencing and five GEO datasets. Subsequently, five randomly selected circRNAs (upregulated circ_0001681; downregulated circ_0000643, circ_0001798, circ_0006117 and circ_0067900) in 20 pairs of BCa and paracancerous tissues were confirmed using qRT-PCR. Functional analysis results determined that 772 GO functions and 32 KEGG pathways were enriched in the ceRNA network. Ten genes (PFKFB4, EDNRA, GSN, GAS1, PAPPA, DTL, TGFBI, PRSS8, RGS1 and TCF4) were selected for signature construction among the ceRNA network. The Human Protein Atlas (HPA) expression of these genes were consistent with the above sequencing data. Notably, the model was validated in multiple external datasets (GSE13507, GSE31684, GSE48075, IMvigor210 and GSE32894). The immune-infiltration was evaluated by 7 published algorithms (i.e., TIMER, CIBERSORT, CIBERSORT-ABS, QUANTISEQ, MCPCOUNTER, XCELL and EPIC). Next, Correlations between riskscore or risk groups and clinicopathological data, overall survival, recognized immunoregulatory cells or common chemotherapeutic agents of BCa patients were performed using wilcox rank test, chi-square test, cox regression and spearman’s correlation analysis; and, these results are significant. According to R package “GSVA” and “clusterProfiler”, the most significantly enriched HALLMARK and KEGG pathway was separately the ‘Epithelial Mesenchymal Transition’ and ‘Ecm Receptor Interaction’ in the high- vs. low-risk group. Additionally, the functional experiments in vitro also revealed that the overexpression of has_circ_0067900 significantly impaired the proliferation, migration, and invasion capacities of BCa cells. Collectively, the results of the current study provide a novel landscape of circRNA-associated ceRNA-regulated network in BCa. The ceRNA-associated gene model which was constructed presented a high predictive performance for the prognosis, immunotherapeutic responsiveness, and chemotherapeutic sensitivity of BCa. And, has_circ_0067900 was originally proposed as tumor suppressor for patients with BCa.

DRAIC promotes growth of breast cancer by sponging miR-432-5p to upregulate SLBP

Mounting evidence suggests that lncRNAs can exert functions in cancer progression in multiple manners. In recent years, competing endogenous RNA (ceRNA) has been widely reported in human cancers as a lncRNA-dominant molecular pathway. The current study aimed at proving the role of lncRNA downregulated RNA in cancer (DRAIC) in breast cancer (BRCA) progression. To be specific, qRT-PCR assay was conducted to measure the expression of DRAIC and other downstream target genes. It was uncovered that DRAIC was expressed at a high level in BRCA cells. Functional analyses, including CCK-8, colony formation, and EdU assays demonstrated that DRAIC depletion suppressed BRCA cell proliferation. In addition, cell apoptosis was promoted due to DRAIC knockdown. The inhibitory effect of DRAIC reduction on BRCA cell migration and invasion was proven by transwell assays. Mechanistically, DRAIC was confirmed to predominantly distribute in the cytoplasm and could interact with miR-432-5p. In addition, stem-loop binding protein (SLBP) was verified to be a downstream target of miR-432-5p and was positively regulated by DRAIC. Taken together, DRAIC sponged miR-432-5p to enhance SLBP expression, by which malignant behaviors of BRCA cells were promoted. Our findings may help to provide a promising therapeutic target for BRCA patients.

Prospect of exosomal circular RNAs in breast Cancer: presents and future

Implementing precision oncology for breast cancer (BC) is a critical method for improving patient outcomes, which relies on the use of reliable biomarkers to be effective and safe. exosomes represent a potential alternative for the diagnosis and therapy of BC, As a "liquid biopsy" and a novel source for biomarkers. Exosomes are nanoscale phospholipid bilayer vesicles released by most cells that contain a large payload of various RNA species that can alter recipient cell activity. Circular RNAs (circRNAs) were recently revealed as a looping subclass of competing endogenous noncoding RNAs (ceRNAs) capable of microRNA sponging to regulate gene expression. They provide critical regulatory functions in carcinogenesis, proliferation, invasion, metastasis, and treatment resistance, as well as cancer prognostic. However, there is still a major gap in our understanding of the role of circRNA in the advancement of BC. CircRNAs are abundant in exosomes, according to various studies, and exosomal circRNAs (exo-circRNAs) play a significant role in cancer biology. Exo-circRNAs can be picked up by nearby or distant cells, affecting many features of the target cells' pathophysiological states, thus boosting cell communication and tumor spread. In this review, we have briefly summarized the major properties and functions of exosomes. Then, we have focused on exo-circRNAs, discussing their potential roles in both driving and inhibiting BC, as well as for cancer diagnosis, prognosis, and monitoring.

Roles and clinical application of exosomal circRNAs in the diagnosis and treatment of malignant tumors

Exosomes are microvesicles secreted by cells. They contain a variety of bioactive substances with important roles in intercellular communication. Circular RNA (circRNA), a type of nucleic acid molecule found in exosomes, forms a covalently bonded closed loop without 5′ caps or 3′ poly(A) tails. It is structurally stable, widely distributed, and tissue specific. CircRNAs mainly act as microRNA sponges and have important regulatory roles in gene expression; they are superior to other non-coding RNAs as molecular diagnostic markers and drug treatment targets. Exosomal-derived circRNAs in the body fluids of tumor patients can modulate tumor proliferation, invasion, metastasis, and drug resistance. They can be used as effective biomarkers for early non-invasive diagnosis and prognostic evaluation of tumors, and also represent ideal targets for early precision therapeutic intervention. This review provides a theoretical basis for exploring the applications of exosomal circRNAs in malignant tumor diagnosis and treatment. We describe the biological functions of exosomal circRNAs in the occurrence and development of malignant tumors, their potential utility in diagnosis and treatment, and possible mechanisms.

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

Circ_0008500 Knockdown Improves Radiosensitivity and Inhibits Tumorigenesis in Breast Cancer Through the miR-758-3p/PFN2 Axis

Breast cancer is one of the most common malignancies worldwide. Circular RNAs (CircRNAs) were revealed to be implicated in the development of breast cancer. In this research, we aimed to investigate the role and underlying mechanism of circ_0008500 in the development and radiosensitivity of breast cancer. Using real-time quantitative PCR (RT-qPCR) and western blot, we found that hsa_circ_0008500 (circ_0008500) and profilin 2 (PFN2) were increased, while microRNA-758-3p (miR-758-3p) was decreased in breast cancer tissues and cells. Cell viability, the number of colonies, proliferation and apoptosis were detected using CCK-8, colony formation, EdU assays and flow cytometry, respectively. Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays were devoted to test the interaction between miR-758-3p and circ_0008500 or PFN2. The results showed that circ_0008500 knockdown inhibited cell growth, and facilitated cell apoptosis and radiosensitivity in breast cancer cells in vitro. Moreover, circ_0008500 regulated PFN2 expression by sponging miR-758-3p. Functionally, circ_0008500 knockdown regulated cell behaviors and radiosensitivity by targeting miR-758-3p to downregulate PFN2 expression in vitro. Additionally, in vivo tumor formation assay and immunohistochemistry (IHC) assay demonstrated that circ_0008500 knockdown enhanced the radiosensitivity and repressed tumor growth in vivo. In conclusion, circ_0008500 inhibition promoted the radiosensitivity and restrained the development of breast cancer by downregulating PFN2 expression via targeting miR-758-3p.

Tumor-associated macrophages promote cholangiocarcinoma progression via exosomal Circ_0020256

This study investigated the exosomal circular RNAs (CircRNAs) produced by tumor-associated macrophages and delivered into the microenvironment of cholangiocarcinoma cells in order to use them as molecular targets for clinical therapy. Tumor-associated M2 macrophages (TAMs) were induced from THP-1 cells and identified by flow cytometry. The TAM-secreted exosomes were isolated from conditioned medium and a CircRNA microarray assay was performed to identify CircRNAs that were uniquely expressed in the isolated exosomes. Circ_0020256 was especially identified based on having the highest differential expression level among all of the CircRNA candidates. In vitro and in vivo experiments were performed to assess the effects of TAMs, exosomes, and Circ_0020256 on the growth and migration of cholangiocarcinoma (CCA) cells. The induced TAMs promoted the proliferation, migration, and invasion of CCA cells and those effects were mediated by exosomes secreted by the TAMs. In CCA cells (RBE and HCCC-9810), Circ_0020256 significantly promoted cellular activity by interacting with its intra-cellular microRNA target, miR-432-5p. In contrast, overexpression of transcription factor E2F3 in CCA cells restored the CCA cellular activities that were inhibited by miR-432-5p. On the other hand, treatment with small interference RNA (siRNA) for Circ_0020256 inhibited CCA cell proliferation, migration, and invasion both in vitro and in vivo. In conclusion, Circ_0020256 in TAM-secreted exosomes promoted the proliferation, migration, and invasion of CCA cells, and that promotional activity was regulated via a Circ_0020256/miR-432-5p/E2F3 axis.

eIF4A3-induced circWAC promotes breast cancer progression through mediating miR-599/E2F3 axis

Circular RNAs (circRNAs) are implicated in the regulation of tumor progression via the "competitive endogenous RNAs (ceRNAs)" mechanism. We intended to explore the molecular mechanism of circRNA WW domain containing adaptor with coiled-coil (circWAC) in breast cancer (BC) progression. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot assay were applied to analyze RNA and protein expression. Cell proliferation, migration, invasion, apoptosis, glycolysis, and tumorigenesis in nude mice were assessed to analyze the role of circWAC/microRNA-599 (miR-599)/E2F transcription factor 3 (E2F3) axis in BC. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA-pull down assay were performed to verify intermolecular interactions. CircWAC was up-regulated in BC tissues and cell lines. CircWAC knockdown restrained the proliferation, migration, invasion, and glycolysis and promoted the apoptosis of BC cells. CircWAC acted as miR-599 sponge, and miR-599 interference largely reversed circWAC silencing-induced effects in BC cells. MiR-599 interacted with the 3' untranslated region (3'UTR) of E2F3, and miR-599 overexpression-induced suppressive effect on cellular malignant potential was overturned by the accumulation of E2F3 in BC cells. Eukaryotic initiation factor 4A3 (eIF4A3) induced the expression of circWAC in BC cells. CircWAC knockdown suppressed xenograft tumor growth in vivo. Our results demonstrated that eIF4A3-induced circWAC promoted the proliferation, migration, invasion, and glycolysis and suppressed the apoptosis of BC cells through mediating miR-599/E2F3 axis, which provided novel potential targets for BC therapy.

Integrated Analysis of Circular RNA-Associated ceRNA Network Reveals Potential circRNA Biomarkers in Human Breast Cancer

Circular RNA (circRNA) is closely related to tumorigenesis and cancer progression. Yet, the roles of cancer-specific circRNAs in the circRNA-related ceRNA network of breast cancer (BRCA) remain unclear. The aim of this study was to construct a ceRNA network associated with circRNA and to explore new therapeutic and prognostic targets and biomarkers for breast cancer. We downloaded the circRNA expression profile of BRCA from Gene Expression Omnibus (GEO) microarray datasets and downloaded the miRNA and mRNA expression profiles of BRCA from The Cancer Genome Atlas (TCGA) database. Differentially expressed mRNAs (DEmRNAs), differentially expressed miRNAs (DEmiRNAs), and differentially expressed circRNAs (DEcircRNAs) were identified, and a competitive endogenous RNA (ceRNA) regulatory network was constructed based on circRNA-miRNA pairs and miRNA-mRNA pairs. Gene ontology and pathway enrichment analyses were performed on mRNAs regulated by circRNAs in ceRNA networks. Survival analysis and correlation analysis of all mRNAs and miRNAs in the ceRNA network were performed. A total of 72 DEcircRNAs, 158 DEmiRNAs, and 2762 DE mRNAs were identified. The constructed ceRNA network contains 60 circRNA-miRNA pairs and 140 miRNA-mRNA pairs, including 40 circRNAs, 30 miRNAs, and 100 mRNAs. Functional enrichment indicated that DEmRNAs regulated by DEcircRNAs in ceRNA networks were significantly enriched in the PI3K-Akt signaling pathway, microRNAs in cancer, and proteoglycans in cancer. Survival analysis and correlation analysis of all mRNAs and miRNAs in the ceRNA network showed that 13 mRNAs and 6 miRNAs were significantly associated with overall survival, and 48 miRNA-mRNA interaction pairs had a significant negative correlation. A PPI network was established, and 21 hub genes were determined from the network. This study provides an effective bioinformatics basis for further understanding of the molecular mechanisms and predictions of breast cancer. A better understanding of the circRNA-related ceRNA network in BRCA will help identify potential biomarkers for diagnosis and prognosis.

CircARL8B Contributes to the Development of Breast Cancer Via Regulating miR-653-5p/HMGA2 Axis

Circular RNAs (circRNAs) act as essential regulators in breast cancer (BC) progression. In this paper, we aimed to investigate the functions of circARL8B in BC. The levels of circARL8B, ADP Ribosylation Factor Like GTPase 8B (ARL8B), miR-653-5p and high-mobility group AT-hook 2 (HMGA2) mRNA were examined by qRT-PCR. The stability of circARL8B was determined by RNase R assay and Actinomycin D assay. Cell viability and metastasis were evaluated by Cell Counting Kit-8 (CCK-8) assay and transwell assay, respectively. The levels of cellular phospholipids and triglycerides were measured using relevant kits. Protein levels were measured by western blot analysis. The association between miR-653-5p and circARL8B or HMGA2 was verified by dual-luciferase reporter assay. A murine xenograft model was established to explore the function of circARL8B in vivo. CircARL8B was increased in BC tissues and cells. CircARL8B silencing inhibited cell viability, migration, invasion and fatty acid metabolism in BC cells in vitro and blocked tumor growth in vivo. MiR-653-5p was identified as the target of circARL8B and miR-653-5p was negatively modulated by circARL8B. The suppressive role of circARL8B silencing in BC cell progression was abolished by miR-653-5p downregulation. Moreover, HMGA2 was the target gene of miR-653-5p. HMGA2 overexpression abrogated the effect of miR-653-5p on BC cell development. In addition, circARL8B knockdown might block PGE2/PI3K/AKT/GSK-3β/Wnt/β-catenin pathway. Silencing of circARL8B inhibited cell viability, migration, invasion and fatty acid metabolism via miR-653-5p/HMGA2 axis in BC.

Hsa_circRNA_103124 Upregulation in Crohn's Disease Promotes Cell Proliferation and Inhibits Autophagy by Regulating the Hsa-miR-650/AKT2 Signaling Pathway

Circular RNAs (circRNAs) play important roles in the pathogenesis of Crohn's disease (CD). We discovered that hsa_circRNA_103124 was upregulated in CD patients in our previous study. Nonetheless, the function of hsa_circRNA_103124 is unclear. In this study, hsa_circRNA_103124 was predicted to interact with hsa-miR-650. Gene Ontology (GO) and pathway analyses identified AKT serine/threonine kinase 2 (AKT2) as the downstream target protein of hsa-miR-650. Activated AKT2 inhibits autophagy, but promotes cell proliferation. Recent studies suggest that the inhibition of autophagy is one of the mechanisms of CD pathogenesis. Therefore, we inferred that hsa_circRNA_103124 might regulate autophagy and proliferation by targeting AKT2 as a sponge for hsa-miR-650. Here, quantitative reverse transcription PCR (RT-QPCR) results revealed that upregulated hsa_circRNA_103124 expression in patients with CD was negatively correlated with hsa-miR-650 expression but positively correlated with the white blood cell count and calprotectin levels. TSC complex subunit 1 (TSC1), one of the proteins upstream of autophagy was downregulated in patients with CD. Consisting with the bioinformatics prediction, it was verified that hsa_circRNA_103124 targeted to hsa-miR650 by fluorescence in situ hybridization (FISH) and luciferase reporter assays. A hsa-miR-650 inhibitor reversed the promotion of rapamycin-induced autophagy and the inhibition of cell proliferation by the hsa_circRNA_103124 siRNA. However, hsa-miR-650 mimics reversed the inhibition of rapamycin-induced autophagy and the promotion of cell proliferation through hsa_circRNA_103124 overexpression. These results indicate that hsa_circRNA_103124 upregulation in patients with CD promotes cell proliferation and inhibits autophagy by regulating the hsa-miR-650/AKT2 signaling pathway.

The Dual Role of Circular RNAs as miRNA Sponges in Breast Cancer and Colon Cancer

Breast cancer (BC) and colon cancer (CRC) are the two most deadly cancers in the world. These cancers partly share the same genetic background and are partially regulated by the same genes. The outcomes of traditional chemoradiotherapy and surgery remain suboptimal, with high postoperative recurrence and a low survival rate. It is, therefore, urgent to innovate and improve the existing treatment measures. Many studies primarily reported that the microRNA (miRNA) sponge functions of circular RNA (circRNA) in BC and CRC have an indirect relationship between the circRNA–miRNA axis and malignant behaviors. With a covalent ring structure, circRNAs can regulate the expression of target genes in multiple ways, especially by acting as miRNA sponges. Therefore, this review mainly focuses on the roles of circRNAs as miRNA sponges in BC and CRC based on studies over the last three years, thus providing a theoretical reference for finding new therapeutic targets in the future.

EIF4A3-induced circular RNA PRKAR1B promotes osteosarcoma progression by miR-361-3p-mediated induction of FZD4 expression

Emerging evidence indicates that circRNAs are broadly expressed in osteosarcoma (OS) cells and play a crucial role in OS progression. Recently, cancer-specific circRNA circPRKAR1B has been identified by high-throughput sequencing and is recorded in publicly available databases. Nevertheless, the detailed functions and underlying mechanisms of circPRKAR1B in OS remains poorly understood. By functional experiments, we found that circPRKAR1B enhanced OS cell proliferation, migration, and promotes OS epithelial–mesenchymal transition (EMT). Mechanistic investigations suggested that circPRKAR1B promotes OS progression through sponging miR-361-3p to modulate the expression of FZD4. Subsequently, we identified that EIF4A3 promoted cirPRKAR1B formation through binding to the downstream target of circPRKAR1B on PRKAR1B mRNA. Further rescue study revealed that overexpression of the Wnt signalling could impair the onco-suppressor activities of the silencing of circPRKAR1B. Interestingly, further experiments indicated that circPRKAR1B is involved in the sensitivity of chemoresistance in OS. On the whole, our results demonstrated that circPRKAR1B exerted oncogenic roles in OS and suggested the circPRKAR1B/miR-361-3p/FZD4 axis plays an important role in OS progression and might be a potential therapeutic target.

Circular RNAs in cell cycle regulation: Mechanisms to clinical significance

Circular RNAs (circRNAs), a type of non‐coding RNA, are single‐stranded circularized molecules characterized by high abundance, evolutionary conservation and cell development‐ and tissue‐specific expression. A large body of studies has found that circRNAs exert a wide variety of functions in diverse biological processes, including cell cycle. The cell cycle is controlled by the coordinated activation and deactivation of cell cycle regulators. CircRNAs exert mutifunctional roles by regulating gene expression via various mechanisms. However, the functional relevance of circRNAs and cell cycle regulation largely remains to be elucidated. Herein, we briefly describe the biogenesis and mechanistic models of circRNAs and summarize their functions and mechanisms in the regulation of critical cell cycle modulators, including cyclins, cyclin‐dependent kinases and cyclin‐dependent kinase inhibitors. Moreover, we highlight the participation of circRNAs in cell cycle‐related signalling pathways and the clinical value of circRNAs as promising biomarkers or therapeutic targets in diseases related to cell cycle disorder.

The effects of hsa_circ_0000517/miR-326 axis on the progression of breast cancer cells and the prediction of miR-326 downstream targets in breast cancer

It has been proposed that circular RNAs (circRNAs) play crucial roles in the initiation and progression of various cancers including breast cancer. Our study aimed to determine the function and regulatory mechanism of hsa_circ_0000517 in breast cancer. qRT-PCR was applied to determine hsa_circ_0000517 expression in breast cancer cells. The circular structure of hsa_circ_0000517 was confirmed using RNase R digestion assay. The subcellular distribution of hsa_circ_0000517 was analyzed using nuclear mass separation assay. Effects of hsa_circ_0000517 on the malignant behaviors of breast cancer cells were determined using CCK-8, colony formation assay, flow cytometry analysis, caspase-3 activity assay, and Transwell invasion assay. Bioinformatics analysis, luciferase reporter assay, and RIP were used to predict and confirm the interaction between hsa_circ_0000517 and miR-326. Bioinformatics analysis was used to search the possible targets of miR-326. Hsa_circ_0000517 was upregulated in breast cancer tissues and cells. Hsa_circ_0000517 was a stable circularized transcript that was preferentially distributed in the cytoplasm. Hsa_circ_0000517 knockdown inhibited cell proliferation, colony formation ability, and invasion and triggered apoptosis in breast cancer cells. Hsa_circ_0000517 acted as a sponge of miR-326 to suppress its expression. miR-326 inhibition abolished the effects of hsa_circ_0000517 knockdown on the malignant behaviors of breast cancer cells. Totally 17 genes were identified as the potential targets of miR-326 in breast cancer. In conclusion, hsa_circ_0000517 silencing repressed breast cancer progression by upregulating miR-326 expression.

Tanshinone I restrains osteosarcoma progression by regulating circ_0000376/miR-432-5p/BCL2 axis

Circular RNAs (circRNAs) have been identified as important regulators in cancer progression. Nevertheless, little is known about the biological function of circ_0000376 in the progression of osteosarcoma (OS). Cell viability, colony formation ability, apoptosis, and motility were analyzed by Cell Counting Kit-8 assay, colony formation assay, flow cytometry, and transwell assays. Cellular glycolytic metabolism was analyzed using commercial kits. RT-qPCR and Western blot assay were performed to analyze RNA and protein expression in OS tissues and cells. Starbase software was used to establish circRNA-microRNA (miRNA)-messenger RNA linkage, and intermolecular interaction was verified by dual-luciferase reporter assay. Xenograft tumor assay was conducted to analyze the effects of Tanshinone I (Tan I) and circ_0000376 on xenograft tumor growth in vivo. Tan I treatment suppressed the viability, migration, invasion, and glycolysis and triggered the apoptosis of OS cells. Tan I treatment markedly down-regulated circ_0000376 expression in OS cells. The addition of circ_0000376 plasmid largely rescued the malignant behaviors of OS cells upon Tan I exposure. Circ_0000376 interacted with miR-432-5p in OS cells. Circ_0000376 overexpression-mediated protective effects in Tan I-induced OS cells were partly attenuated by the accumulation of miR-432-5p. miR-432-5p bound to the 3' untranslated region (3'UTR) of B-cell leukemia/lymphoma 2 (BCL2) in OS cells. miR-432-5p interference-induced effects in Tan I-treated OS cells were partly overturned by the silence of BCL2. Circ_0000376 can act as miR-432-5p sponge to up-regulate BCL2 expression in OS cells. Circ_0000376 silencing contributed to the anti-tumor effect of Tan I on the growth of xenograft tumors in vivo. Tan I exerted an anti-tumor role in OS progression by targeting circ_0000376/miR-432-5p/BCL2 axis.

Circ_0000514 promotes breast cancer progression by regulating the miR-296-5p/CXCL10 axis

The biological function of circular RNA 0000514 (circ_0000514) in breast cancer (BC) is still unknown. In this study, we downloaded the microarray dataset GSE101123 from Gene Expression Omnibus (GEO) database and then analyzed the differentially expressed circular RNAs in BC tissues compared with adjacent tissues, and demonstrated that circ_0000514 was up-regulated in BC tissues. Circ_0000514, miR-296-5p, and CXC chemokine ligand10 (CXCL10) expressions in BC tissues and cell lines were probed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Cell counting kit-8 (CCK-8), 5-bromo-2'-deoxyuridine (BrdU), and Transwell assays were adopted to determine the cell viability, proliferation, migration, and invasion. The targeting relationship between miR-296-5p and circ_0000514 or CXCL10 3'-UTR was predicted by bioinformatics and validated by dual-luciferase reporter assay. We demonstrated that, circ_0000514 and CXCL10 expressions were raised in BC tissues and cell lines while miR-296-5p expression was declined. Circ_0000514 knockdown could inhibit the proliferation, migration, and invasion of BC cells, and miR-296-5p overexpression also suppressed the malignant phenotypes of BC cells. Mechanistically, miR-296-5p was identified as the downstream target of circ_0000514 and could be inhibited by circ_0000514. Moreover, CXCL10 was the target of miR-296-5p, whose expression could be indirectly and positively regulated by circ_0000514. In conclusion, circ_0000514 is involved in BC progression via regulating miR-296-5p/CXCL10 axis.

circRNA-miRNA-mRNA in breast cancer

Among cancers, breast cancer has the highest incidence rate among women and poses a tremendous threat to women's health. Messenger RNA (mRNA), microRNA (miRNA) and circular RNA (circRNA) play vital roles in the progression of breast cancer through a variety of biological effects and mechanisms. Recently, the regulatory network formed by circRNAs, miRNAs and mRNAs has piqued attention and garnered interest. CircRNAs bind to miRNAs through a regulatory mechanism in which endogenous RNAs compete to indirectly regulate the expression of mRNA corresponding to downstream target genes of miRNAs, contributing to the progression of breast cancer. The circRNA-miRNA-mRNA axis may be a marker for the early diagnosis and prognosis of breast cancer and a potential breast cancer treatment target, providing unlimited possibilities for the development of breast cancer biomarkers and therapeutic strategies. This article reviews recent research progress on the circRNA-miRNA-mRNA axis as a regulatory network of competing endogenous RNAs in breast cancer. Herein, we focus on the mechanism and function of the circRNA-miRNA-mRNA axis in the occurrence and metastasis of breast cancer, and resistance to chemotherapy.

CircRNA SEPT9 contributes to malignant behaviors of glioma cells via miR-432-5p-mediated regulation of LASP1

BACKGROUND

Circular RNA (circRNA) septin 9 (circSEPT9; hsa_circ_0005320) has been reported to be abnormally up-regulated in glioma. However, the exact role and working mechanism of circSEPT9 in glioma progression are barely known.

METHODS

RNA and protein levels were measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot assay, respectively. Cell proliferation was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony formation assay and flow cytometry. Cell apoptosis was evaluated by flow cytometry. Cell motility was analyzed by transwell assays. Cell glycolytic metabolism was analyzed using commercial kits. Dual-luciferase reporter assay, RNA-pull down assay and RNA immunoprecipitation (RIP) assay were conducted to verify the intermolecular interactions. Xenograft mice model was utilized to assess the role of circSEPT9 in vivo.

RESULTS

CircSEPT9 was highly expressed in glioma tissues and cell lines. CircSEPT9 interference inhibited the proliferation, migration, invasion and glycolytic metabolism and triggered the apoptosis of glioma cells. MicroRNA-432-5p (miR-432-5p) was a target of circSEPT9, and circSEPT9 silencing-mediated effects in glioma cells were largely alleviated by the addition of anti-miR-432-5p. MiR-432-5p bound to the 3' untranslated region (3'UTR) of LIM and SH3 protein 1 (LASP1), and LASP1 overexpression largely overturned miR-432-5p-induced effects in glioma cells. CircSEPT9 up-regulated LASP1 expression by acting as miR-432-5p sponge. CircSEPT9 silencing suppressed xenograft tumor growth in vivo.

CONCLUSION

CircSEPT9 exerted an oncogenic role to enhance the malignant behaviors of glioma cells by binding to miR-432-5p to induce LASP1 expression.

CircRNA DUSP16 Knockdown Suppresses Colorectal Cancer Progression by Regulating the miR-432-5p/E2F6 Axis

Background

Circular RNAs (circRNAs) play critical roles in various types of cancer. The aim of the present study was to investigate the function and underlying mechanism of CircRNA DUSP16 (circDUSP16) in colorectal cancer (CRC) development.

Materials and Methods

The expression levels of circDUSP16, microRNA-432-5p (miR-432-5p), and E2F transcription factor 6 (E2F6) were measured by RT-qPCR. Cell proliferation, migration, invasion, and apoptosis were investigated by CCK-8, Transwell, and flow cytometry assays. Western blot analysis was used to evaluate the levels of the pro-apoptotic protein (Bax and cleaved-caspase 3) and the anti-apoptotic protein (Bcl-2). Luciferase reporter assay and RIP assay were used to analyze the association between miR-432-5p and circDUSP16 or E2F6. A xenograft tumor model was employed to explore the effect of circDUSP16 on CRC tumor growth in vivo.

Results

CircDUSP16 expression was upregulated in CRC tissues and cell lines. High circDUSP16 expression was correlated with low survival rate. Furthermore, circDUSP16 knockdown repressed cell proliferation, migration, and invasion and induced apoptosis in CRC. CircDUSP16 caused a negative regulation in miR-432-5p expression. In addition, E2F6 expression was elevated in CRC tissues. Inhibition of miR-432-5p promoted the proliferative and metastatic activity of CRC cells and inhibited the induction of apoptosis. Inhibition of E2F6 expression partially abolished the effects caused by miR-432-5p depletion. Moreover, circDUSP16 upregulated E2F6 expression by reducing miR-432-5p expression. Furthermore, circDUSP16 silencing repressed CRC tumor growth in vivo.

Conclusion

The results supported the hypothesis that circDUSP16 knockdown suppressed CRC progression by regulating the miR-432-5p/E2F6 axis, suggesting that the circDUSP16/miR-432-5p/E2F6 network may be a potential therapeutic target for CRC.

Circular RNAs Interaction with MiRNAs: Emerging Roles in Breast Cancer

Despite significant advances in cancer therapy strategies, breast cancer is one of the most common and lethal malignancies worldwide. Characterization of a new class of RNAs using next-generation sequencing opened new doors toward uncovering etiopathogenesis mechanisms of breast cancer as well as prognostic and diagnostic biomarkers. Circular RNAs (circRNAs) are a novel class of RNA with covalently closed and highly stable structures generated primarily from the back-splicing of precursor mRNAs. Although circRNAs exert their function through various mechanisms, acting as a sponge for miRNAs is their primary mechanism of function. Furthermore, growing evidence has shown that aberrant expression of circRNAs is involved in the various hallmarks of cancers. This paper reviews the biogenesis, characteristics, and mechanism of functions of circRNAs and their deregulation in various cancers. Finally, we focused on the circRNAs roles as a sponge for miRNAs in the development, metastasis, angiogenesis, drug resistance, apoptosis, and immune responses of breast cancer.

The Regulation Network and Clinical Significance of Circular RNAs in Breast Cancer

Breast cancer is one of the most common malignant tumors in women worldwide. Circular RNA (circRNA) is a class of structurally stable non-coding RNA with a covalently closed circular structure. In recent years, with the development of high-throughput RNA sequencing, many circRNAs have been discovered and have proven to be clinically significant in the development and progression of breast cancer. Importantly, several regulators of circRNA biogenesis have been discovered. Here, we systematically summarize recent progress regarding the network of regulation governing the biogenesis, degradation, and distribution of circRNAs, and we comprehensively analyze the functions, mechanisms, and clinical significance of circRNA in breast cancer.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

Emerging role of circular RNAs in breast cancer

Circular RNAs (cirRNAs) are generally considered as non-coding RNAs which can act as molecular sponges for miRNAs, exert regulatory roles in transcription or splicing, and interplay with RNA binding proteins. These single-stranded transcripts can affect tumor growth, the metastatic ability of cancer cells, stemness properties, and resistance to therapeutic options. Recent investigations have shown the crucial effects of circrNAs in the evolution of breast cancer. Signature of circRNAs in breast cancer samples has been mostly assessed through microarray-based methods revealing up-regulation of some circRNAs such as circ-TFF1, circACAP2, circ-TFCP2L1, hsa_circ_0000519, circDENND4C, circPLK1 and circRNA_069718, while down-regulation of other circRNAs such as hsa_circ_0000375, circYap, hsa_circ_0025202, circTADA2A-E6, circASS1 and circRNA_BARD1 in breast cancer samples. Mechanistically, these transcripts mainly affect breast cancer tumorigenesis via serving as sponges for miRNAs. In the current manuscript, we explore the results of researches that appraised the role of circRNAs in breast cancer.

Profiling of circular RNAs and circTPCN/miR-634/mTOR regulatory pathway in cervical cancer

Circular RNAs (circRNAs) are highly stable forms of endogenous non-coding RNA molecules with diverse biological functions. Some of them have been demonstrated to play crucial roles in the initiation or development of cancers through regulation of gene expression. However, the profiles and the roles of circRNAs in tumorigenesis of cervical cancer remain largely unknown. In the current study, we investigated the expression profiles of circRNAs and their potential oncogenic mechanisms in cervical cancer. The expression patterns, obtained using a microarray assay, revealed a total of 192 differentially expressed circRNAs, of which 106 were upregulated and 86 were downregulated, in cervical cancer samples compared with normal cervical samples. The differential expression of circRNAs was validated using quantitative real-time polymerase chain reaction. Two circRNAs (circTPCN and circFAM185A) were confirmed to be significantly upregulated in cervical cancer samples, indicating that they represent potential biomarkers of cervical cancer. The role and the potential molecular mechanism of circTPCN in cervical cancer tumorigenesis were further investigated. Knockdown of circTPCN significantly suppressed proliferation, migration, and invasion and increased apoptosis of cervical cancer cells in vitro. Molecular analysis revealed that circTPCN acted as a sponge of miR-634 to enhance mTOR expression. Thus, the circTPCN/miR-634/mTOR regulatory pathway might be involved in cervical cancer tumorigenesis, and circTPCN is a potential therapeutic target in cervical cancer.

Current research on circular RNAs and their potential clinical implications in breast cancer

Breast cancer (BC) is one of the most common cancers and the leading causes of death among women worldwide, and its morbidity rate is growing. Discovery of novel biomarkers is necessary for early BC detection, treatment, and prognostication. Circular RNAs (circRNAs), a novel type of endogenous non-coding RNAs with covalently closed continuous loops, have been found to have a crucial role in tumorigenesis. Studies have demonstrated that circRNAs are aberrantly expressed in the tumor tissues and plasma of patients with BC, and they modulate gene expression affecting the proliferation, metastasis, and chemoresistance of BC by specifically binding and regulating the expression of microRNAs (miRNAs). Therefore, circRNAs can be used as novel potential diagnostic and prognostic markers, and therapeutic targets for BC. This article summarizes the properties, functions, and regulatory mechanisms of circRNAs, particularly current research on their association with BC proliferation, metastasis, and chemoresistance.

Circ_0132817 facilitates cell proliferation, migration, invasion and glycolysis by regulating the miR-432-5p/NOL4L axis in neuroblastoma

Neuroblastoma (NB) is one of the most common extracranial solid tumors in children. Circular RNAs (circRNAs) have been shown to be involved in the development of NB. However, the function of circ_0132817 in NB is currently unclear. In this paper, the levels of circ_0132817 and NOL4L were induced in NB tissues and cells, and miR-432-5p expression was on the contrary. MiR-432-5p was verified as a target of circ_0132817 and miR-432-5p could bind to NOL4L. The inhibitory effects of miR-432-5p overexpression on cell proliferation, migration, invasion and glycolysis could be reversed by circ_0132817 facilitation. The suppression of NOL4L knockdown on NB cells progression could be rescued by miR-432-5p inhibition. Besides, knockdown of circ_0132817 repressed tumor growth in vivo. Thus, we came to a conclusion that circ_0132817 promoted the tumorigenesis of NB cells by up-regulating NOL4L and acting as a sponge for miR-432-5p.

Circular RNAs: Their Role in the Pathogenesis and Orchestration of Breast Cancer

As one of the most frequently occurring malignancies in women, breast cancer (BC) is still an enormous threat to women all over the world. The high mortality rates in BC patients are associated with BC recurrence, metastatic progression to distant organs, and therapeutic resistance. Circular RNAs (circRNAs), belonging to the non-coding RNAs (ncRNAs), are connected end to end to form covalently closed single-chain circular molecules. CircRNAs are widely found in different species and a variety of human cells, with the features of diversity, evolutionary conservation, stability, and specificity. CircRNAs are emerging important participators in multiple diseases, including cardiovascular disease, inflammation, and cancer. Recent studies have shown that circRNAs are involved in BC progress by regulating gene expression at the transcriptional or post-transcriptional level via binding to miRNAs then inhibiting their function, suggesting that circRNAs may be potential targets for early diagnosis, treatment, and prognosis of BC. Herein, in this article, we have reviewed and summarized the current studies about the biogenesis, features, and functions of circRNAs. More importantly, we emphatically elucidate the pivotal functions and mechanisms of circRNAs in BC growth, metastasis, diagnosis, and drug resistance. Deciphering the complex networks, especially the circRNA-miRNA target gene axis, will endow huge potentials in developing therapeutic strategies for combating BC.

Circular RNA circ_0021093 regulates miR-432/Annexin A2 pathway to promote hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is a major histological subtype of liver cancer cases. Previous studies showed that circular RNA (circRNA) circ_0021093 was upregulated in HCC, but the regulatory mechanism of circ_0021093 is still rare. The expression levels of circ_0021093, miR-432 and Annexin A2 (ANXA2) were analyzed by real-time quantitative PCR. The relationship between the overall survival time of HCC patients and circ_0021093 level was analyzed with Kaplan-Meier analysis. Cell proliferation, migration and invasion were examined with cell counting kit-8 and transwell assays. Western blot was used to assess the protein expression of epithelial-mesenchymal transition markers and ANXA2. In addition, loss- or gain-of-function experiments and dual-luciferase reporter assay were performed to probe the relationship between miR-432 and circ_0021093 or ANXA2. The influences of circ_0021093 silencing in vivo were measured by using xenograft models. Circ_0021093 was highly expressed in HCC tissues and cells, and its level was associated with poor prognosis of HCC patients. Functional experiments showed that knockdown of circ_0021093 repressed proliferation, migration and invasion in vitro and tumor growth in vivo by regulating miR-432, while upregulation of circ_0021093 reversed these results. Moreover, miR-432 negatively regulated ANXA2 expression in HCC, and introduction of ANXA2 could abolish overexpression of miR-432-induced effects on HCC cells. Collectively, circ_0021093 boosted HCC progression via regulating proliferation, migration and invasion of HCC cells by acting as competing endogenous RNA to sponge miR-432.

Circular RNA CDR1as promotes tumor progression by regulating miR-432-5p/E2F3 axis in pancreatic cancer

BACKGROUND

Pancreatic cancer (PC), characterized with high growth rate and metastatic rate. It's urgently necessary to explore new mechanism of PC. Circular RNA/miRNA/mRNA network was widely reported to participate in the cancer progression.

METHODS

In this research, circular RNA CDR1as (circCDR1as) was identified by microarray analysis and detected in pancreatic cancer (PC) tissues and cells. Transwell, colony-forming assay, nude mouse tumorigenicity assay were used to determine the function of circCDR1as in PC. Western blot, dual luciferase reporting test were applied to investigate the mechanism.

RESULTS

We found that circCDR1as was highly expressed in PC tissues. The levels of circCDR1as in PC tissues and cells were higher than those in controls. CircCDR1as promoted the migration, invasion and proliferation of PC cells in vitro and tumor growth in vivo via mediating E2F3 expression by sponging miR-432-5p.

CONCLUSIONS

In conclusion, circCDR1as could promote the development of PC and might be a novel diagnostic target for PC.

Coronary artery disease: differential expression of ceRNAs and interaction analyses

Background

Previous studies have demonstrated associations between cardiovascular disease and the expression of various messenger RNAs (mRNAs), microRNAs (miRNAs), and long non-coding RNAs (lncRNAs). This study aimed to investigate the differential expression of mRNAs, lncRNAs, and miRNAs between tissues from patients with coronary artery disease (CAD) and healthy controls, and to determine the interactions between these molecules in CAD.

Methods

We investigated the differential expression of competitive endogenous RNAs (ceRNAs) between patients with CAD and healthy controls by collecting data from Gene Expression Omnibus (GEO) microarrays. We also investigated the biological function of these differentially expressed ceRNAs by performing Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. We then created a protein-protein interaction (PPI) network to identify the hub genes. Biosystems and literature searches were also carried out to identify relevant signaling pathways and the potential function of the differentially expressed ceRNAs.

Results

We identified 456 expression profiles for miRNAs, 16,325 mRNA expression profiles, and 2,869 lncRNA expression profiles. With regards to connectivity, GO and KEGG analyses (count ≥9) identified the top 11 PPI network nodes in rank order. We also identified the top 15 significant nodes for the ceRNAs identified according to degree centrality (DC) (P<0.05). Collectively, our analyses confirmed that the differential expression of certain ceRNAs, and their respective signaling pathways were associated with CAD.

Conclusions

Data arising from 11 GO and KEGG pathways, the top 15 PPI network nodes with the best connectivity rank, and the top 15 ceRNA network nodes, as determined by DC rank in CAD population, indicated that the differential expression of these ceRNAs plays a key role in the CAD. Our findings highlight new molecular mechanisms for CAD and provide new options for the development of therapeutic targets.

A risk progression breast epithelial 3D culture model reveals Cx43/hsa_circ_0077755/miR-182 as a biomarker axis for heightened risk of breast cancer initiation

mRNA-circRNA-miRNAs axes have been characterized in breast cancer, but not as risk-assessment axes for tumor initiation in early-onset breast cancer that is increasing drastically worldwide. To address this gap, we performed circular RNA (circRNA) microarrays and microRNA (miRNA) sequencing on acini of HMT-3522 S1 (S1) breast epithelial risk-progression culture model in 3D and chose an early-stage population miRNome for a validation cohort. Nontumorigenic S1 cells form fully polarized epithelium while pretumorigenic counterparts silenced for gap junction Cx43 (Cx43-KO-S1) lose epithelial polarity, multilayer and mimic premalignant in vivo mammary epithelial morphology. Here, 121 circRNAs and 65 miRNAs were significantly dysregulated in response to Cx43 silencing in cultured epithelia and 15 miRNAs from the patient cohort were involved in epithelial polarity disruption. Focusing on the possible sponging activity of the validated circRNAs to their target miRNAs, we found all miRNAs to be highly enriched in cancer-related pathways and cross-compared their dysregulation to actual miRNA datasets from the cultured epithelia and the patient validation cohort. We present the involvement of gap junction in post-transcriptional axes and reveal Cx43/hsa_circ_0077755/miR-182 as a potential biomarker signature axis for heightened-risk of breast cancer initiation, and that its dysregulation patterns might predict prognosis along breast cancer initiation and progression.

MicroRNA-432 Acts as a Prognostic Biomarker and an Inhibitor of Cell Proliferation, Migration, and Invasion in Breast Cancer

BACKGROUND

Accumulating studies have demonstrated that microRNAs (miRNAs) are involved in the progression of various cancers. This study aimed to investigate the potential clinical and functional role of miR-432 in breast cancer.

MATERIALS AND METHODS

We evaluated the expression of miR-432 in 117 breast cancer samples and paired nontumor tissue samples, as well as 4 breast cancer cell lines using RT-qPCR analysis. Kaplan-Meier survival curve and multivariate Cox regression analysis were used to evaluate the prognostic significance of miR-432 in breast cancer patients. CCK-8 assay and Transwell assays were used to evaluate the biological function of miR-432 in the progression of breast cancer.

RESULTS

miR-432 was downregulated in breast cancer tissues and cell lines, and its exotic expression was associated with tumor size, lymph node metastasis, and TNM stage. In addition, breast cancer patients with low miR-432 expression exhibited a shorter overall survival outcome. Further experiments revealed that overexpression of miR-432 inhibited the cell proliferation, migration, and invasion of breast cancer cells, while knockdown of miR-432 promoted these cellular activities. AXL was a direct target of miR-432 in breast cancer cells.

CONCLUSION

The present study suggested that miR-432 may be a tumor suppressor in the progression of breast cancer through inhibiting cell proliferation, migration, and invasion by targeting AXL. And miR-432 might be a prognostic biomarker and therapeutic target for the treatment of breast cancer. This study provided a novel insight into breast cancer prognosis and treatment.

Circular RNA circNINL promotes breast cancer progression through activating β-catenin signaling via miR-921/ADAM9 axis

We investigated the expression and functions of circular RNA (circRNA) circNINL and miR-921 in breast cancer (BC) in this study. We found that the expression of circNINL increased while the expression of miR-921 decreased in BC tissues and cell lines, and their anomalous expressions were associated with malignant features and poor prognostic of BC. Then, we demonstrated that circNINL could interact with miR-921 and facilitate BC cells malignant process including proliferation acceleration, migration enhancement and apoptosis evasion via sponging miR-921 in vitro. Further investigations revealed that circNINL/miR-921 axis could mediate the expression of ADAM9 which was a direct target of miR-921. In addition, we exhibited that ADAM9 may activate β-catenin signaling by interacting with E-cadherin. We presented the vital roles of circNINL/miR-921/ADAM9/β-catenin signaling in the progression of BC.

Negative Correlation Between Circular RNA SMARC5 and MicroRNA 432, and Their Clinical Implications in Bladder Cancer Patients

Objective: Our study aimed to evaluate the correlation of circular RNA SMARCA5 (circ-SMARCA5) and microRNA 432 (miR-432) with clinical characteristics and survival in bladder cancer patients. Methods: Preoperative clinicopathologic features and survival data of 156 bladder cancer patients were retrospectively reviewed. A total of 156 cases of tumor tissues, whereas 71 cases out of 156 available adjacent tissues were obtained from the Pathology Department for circ-SMARCA5 and miR-432 detections using real-time quantitative polymerase chain reaction. Results: Circ-SMARCA5 was upregulated but miR-432 was downregulated in tumor tissues compared with adjacent tissues; meanwhile, circ-SMARCA5 expression was negatively correlated with miR-432 in bladder cancer tissues. Circ-SMARCA5 high expression was correlated with larger tumor size, higher tumor stage, and lymph node (LYN) metastasis. However, miR-432 high expression was correlated with single multiplicity, smaller tumor size, lower tumor stage, less LYN metastasis in bladder cancer patients. Regarding survival, circ-SMARCA5 high expression was correlated with shorter disease-free survival (DFS) and overall survival (OS); whereas, miR-432 high expression was correlated with longer DFS and OS in bladder cancer patients. Further multivariate Cox's regression analysis displayed that circ-SMARCA5 high expression was an independent predictive factor for both worse DFS and OS in bladder cancer patients. Conclusion: Circ-SMARCA5 high expression but miR-432 low expression is correlated with advanced tumor features and poor survival of bladder cancer patients, which present as potential prognostic markers in bladder cancer.

Circular RNA circPLK1 promotes breast cancer cell proliferation, migration and invasion by regulating miR-4500/IGF1 axis

Background

Circular RNAs (circRNAs) can regulate gene expression in different malignancies. However, the biological functions of circRNA polo-like kinase-1 (circPLK1) in the tumorigenesis of breast cancer (BC) and its potential mechanisms have not been well elucidated yet.

Methods

The expression levels of circPLK1, microRNA-4500 (miR-4500), insulin-like growth factor 1 (IGF1) were measured by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Cell viability, cell cycle distribution, cell migration and invasion were determined by Cell Counting Kit-8 (CCK-8) assay, flow cytometry and transwell assay, respectively. Western blot assay was used to analyze the protein levels of cyclin-dependent kinase (CDK) 4 and CDK-6. The relationship between miR-4500 and circPLK1 or IGF1 was predicted by starBase v3.0 and verified by dual-luciferase reporter assay and RNA pull-down assay. The mice xenograft model was established to investigate the roles of circPLK1 in vivo.

Results

CircPLK1 and IGF1 were upregulated and miR-4500 was downregulated in BC tissues and cells. Interference of circPLK1 inhibited BC cell growth, migration and invasion, which was reversed by overexpression of IGF1. Moreover, circPLK1 could directly bind to miR-4500 and IGF1 was verified as a direct target of miR-4500. Furthermore, IGF1 overexpression abated the inhibitory effects of miR-4500 upregulation on proliferation, migration and invasion of BC cells. Mechanically, circPLK1 was a sponge of miR-4500 to regulate IGF1 expression in BC cells. Besides, circPLK1 knockdown suppressed tumor growth via upregulating miR-4500 and downregulating IGF1.

Conclusions

CircPLK1 silence inhibited BC cell growth, migration and invasion by regulating miR-4500/IGF1 axis, suggesting circPLK1/miR-4500/IGF axis might be a potential therapeutic target.

circSLC8A1 sponges miR-671 to regulate breast cancer tumorigenesis via PTEN/PI3k/Akt pathway

Breast cancer is the most frequently diagnosed and the leading cause of cancer-related deaths in women worldwide. However, the role of circSLC8A1 in breast cancer remains elusive. Herein, a cohort of 77 breast tumors and paired adjacent normal mammary tissues were collected. We demonstrated that circSLC8A1 was significantly down-regulated in breast cancer tissues and cell lines, of which expression was negatively correlated with clinical severity and dismal prognosis. Overexpression of circSLC8A1 suppressed cell proliferation, migration and invasion in vitro, and inhibited tumor growth in vivo. CircSLC8A1 directly targeted miR-671 to execute tumor suppressive activities via regulating PI3k/Akt signaling. Krüppel-like factor 16 (KLF16), a transcriptional activator of PTEN, was identified as a target of miR-671. Furthermore, circSLC8A1 could sponge miR-671 to suppress breast tumor growth via PTEN/PI3k/Akt signaling in vivo. In summary, circSLC8A1/miR-671 regulates breast cancer progression through PTEN/PI3k/Akt signaling, which may provide efficient therapeutic target for this devastating cancer.

Circ_0008039 supports breast cancer cell proliferation, migration, invasion, and glycolysis by regulating the miR-140-3p/SKA2 axis

Circular RNAs (circRNAs) have been shown to modulate gene expression and participate in the development of multiple malignancies. The purpose of this study was to investigate the role of circ_0008039 in breast cancer (BC). The expression of circ_0008039, miR-140-3p, and spindle and kinetochore-associated protein 2 (SKA2) was detected by qRT-PCR. Cell viability, colony formation, migration, and invasion were evaluated using methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, colony formation assay, and transwell assay, respectively. Glucose consumption and lactate production were measured using commercial kits. Protein levels of hexokinase II (HK2) and SKA2 were determined by western blot. The interaction between miR-140-3p and circ_0008039 or SKA2 was verified by dual-luciferase reporter assay. Finally, a mouse xenograft model was established to investigate the roles of circ_0008039 in BC in vivo. We found that circ_0008039 and SKA2 were upregulated in BC tissues and cells, while miR-140-3p was downregulated. Knockdown of circ_0008039 suppressed BC cell proliferation, migration, invasion, and glycolysis. Moreover, miR-140-3p could bind to circ_0008039 and its inhibition reversed the inhibitory effect of circ_0008039 interference on proliferation, migration, invasion, and glycolysis in BC cells. SKA2 was verified as a direct target of miR-140-3p and its overexpression partially inhibited the suppressive effect of miR-140-3p restoration in BC cells. Additionally, circ_0008039 positively regulated SKA2 expression by sponging miR-140-3p. Consistently, silencing circ_0008039 restrained tumor growth via increasing miR-140-3p and decreasing SKA2. In conclusion, circ_0008039 downregulation suppressed BC cell proliferation, migration, invasion, and glycolysis partially through regulating the miR-140-3p/SKA2 axis, providing an important theoretical basis for treatment of BC.

miRNA biomarkers for predicting overall survival outcomes for head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a malignant tumor of the upper aerodigestive tract. The loss and gain of miRNA function promote cancer development through various mechanisms. RNA sequencing (RNA-seq) and miRNAs sequencing data from the Cancer Genome Atlas (TCGA) was used to show the dysfunctional miRNAs microenvironment and to provide useful biomarkers for miRNAs therapy. Seven miRNAs were found to be independent prognostic factors of HNSCC patients in the training cohort. A total of 60 target genes for these miRNAs were predicted. Nine target genes (CDCA4, CXCL14, FLNC, KLF7, NBEAL2, P4HA1, PFKM, PFN2 and SEPPINE1) were correlated with patient's overall survival (OS) outcomes. We identified novel miRNAs markers for the prognosis of head and neck squamous cell carcinoma.

Tumor promoting effects of circRNA_001287 on renal cell carcinoma through miR-144-targeted CEP55

Background

Renal cell carcinoma (RCC) is a common urological cancer. circular RNAs (circRNAs) is involved in the development of various types of cancers. However, the roles and underlying mechanisms of circRNAs in RCC are not fully elucidated. Herein, we aimed to examine the potential effect of circ_001287 on RCC progression.

Materials and Methods

Microarray-based gene expression profiling of RCC was initially employed in order to identify differentially expressed genes. Next, the expression of circ_001287 was examined, and the cell line with the highest circ_001287 expression was selected for subsequent investigation. The interaction among circ_001287, miR-144, and CEP55 was identified by conducting luciferase reporter assay, RNA-pull down, RIP, RT-qPCR and FISH. The effect of circ_001287 on proliferative, invasive and migratory capacities as well as tumorigenicity of transfected cells in mice was examined using gain- and loss-of-function experiments.

Results

circ_001287 and CEP55 were highly expressed while miR-144 was decreased in RCC tissues and cell lines. circ_001287 can up-regulate CEP55 by binding to miR-144, which resulted in increased proliferative, invasive and migratory capacities and tumor growth in vivo. In addition, down-regulation of miR-144 was also observed to promote these biological activities.

Conclusions

Overall, these results elucidate a new mechanism for circ_001287 in RCC development and provide a potential therapeutic target for RCC patients.

Circ_0061825 Acts as a miR-593-3p Sponge to Promote Breast Cancer Progression by Regulating FGFR3 Expression

Background

Breast cancer (BC) remains the most common malignancy among women. Circular RNAs (circRNAs) have been demonstrated to play important roles in human cancers, including BC. In this study, we sought to identify the precise parts of circ_0061825 (circRNA trefoil factor 1, circ_TFF1) in BC pathogenesis.

Methods

The expression levels of circ_0061825, miR-593-3p and fibroblast growth factor receptor 3 (FGFR3) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot. Circ_0061825 was characterized using ribonuclease (RNase) R digestion, actinomycin D and subcellular fractionation assays. Cell viability, colony formation, migration, invasion, cell cycle progression and apoptosis were evaluated using Cell Counting Kit-8 (CCK-8), colony formation, wound-healing, transwell and flow cytometry assays, respectively. Targeted relationships among circ_0061825, miR-593-3p and FGFR3 were determined by a dual-luciferase reporter assay. Animal studies were used to assess the impact of circ_0061825 in tumor growth in vivo.

Results

Our data indicated that circ_0061825 was overexpressed in BC tissues and cells, and it was mainly localized in the cytoplasm of BC cells. Circ_0061825 knockdown hampered BC cell viability, colony formation, migration, invasion, cell cycle progression and enhanced cell apoptosis in vitro and weakened tumor growth in vivo. Mechanistically, circ_0061825 functioned as a molecular sponge of miR-593-3p, and circ_0061825 knockdown repressed BC cell malignant progression in vitro by miR-593-3p. FGFR3 was a direct target of miR-593-3p, and circ_0061825 modulated FGFR3 expression through sponging miR-593-3p. Moreover, miR-593-3p overexpression hindered BC cell malignant progression in vitro by down-regulating FGFR3.

Conclusion

Our current work provided evidence that circ_0061825, an up-regulated circRNA in BC, regulated BC malignant progression at least in part through targeting the miR-593-3p/FGFR3 axis, illuminating a novel therapeutic target for BC management.

Overexpression of hsa_circ_0001715 is a Potential Diagnostic and Prognostic Biomarker in Lung Adenocarcinoma

Background

Circular RNAs (circRNAs) play important roles in tumorigenesis, including lung cancer. However, the expression profile and clinical value of circRNAs in lung adenocarcinoma remain unclear. The purpose of this study was to establish the circRNAs expression profile of lung adenocarcinoma and determine its potential diagnostic and prognostic value.

Materials and Methods

The global expression profile of circRNAs in lung adenocarcinoma tissue was determined from five paired lung adenocarcinoma tissues and adjacent normal tissues. The expression levels of selected candidate circRNA were validated by qRT-PCR. Sequence analysis was used to confirm the specificity of amplified circRNA. The candidate circRNA level was further detected in plasma samples from lung adenocarcinoma patients and healthy controls. The relationships between their levels and clinicopathological factors were explored. Receiver operating characteristic (ROC) curve was constructed to differentiate lung adenocarcinoma from healthy controls. Kaplan–Meier was performed to show survival curves and survival characteristics. The significance of different prognostic factors for overall survival (OS) was analyzed using Cox proportional hazards model.

Results

CircRNA microarray showed 394 circRNAs were differentially expressed, including 215 up-regulated and 179 down-regulated circRNAs. Hsa_circ_0001715 was the most up-regulated circRNA in lung adenocarcinoma tissues. Plasma hsa_circ_0001715 levels were significantly higher in lung adenocarcinoma patients versus healthy controls (P < 0.001). We further found that high plasma hsa_circ_0001715 was significantly correlated with TNM stage (P = 0.039) and distant metastasis (P = 0.030). Furthermore, ROC curve analysis showed that hsa_circ_0001715 had high diagnostic value, and the area under the curve (AUC) was 0.871. Lung adenocarcinoma patients with plasma hsa_circ_0001715 levels over 0.417 had significantly shorter OS than those with lower levels (P = 0.004). Univariate and multivariate survival analysis showed that plasma hsa_circ_0001715 level was an independent prognostic factor for the OS.

Conclusion

Our study revealed an aberrant circRNA expression profile in lung adenocarcinoma, and hsa_circ_0001715 is up-regulated and could act as a novel diagnostic and prognostic biomarker for lung adenocarcinoma.