Identification and integrated analysis of key differentially expressed circular RNAs in ER-positive subtype breast cancer

Non-Coding RNAs in Breast Cancer: Diagnostic and Therapeutic Implications

Breast cancer (BC) is one of the most prevalent forms of cancer globally, and has recently become the leading cause of cancer-related mortality in women. BC is a heterogeneous disease comprising various histopathological and molecular subtypes with differing levels of malignancy, and each patient has an individual prognosis. Etiology and pathogenesis are complex and involve a considerable number of genetic alterations and dozens of alterations in non-coding RNA expression. Non-coding RNAs are part of an abundant family of single-stranded RNA molecules acting as key regulators in DNA replication, mRNA processing and translation, cell differentiation, growth, and overall genomic stability. In the context of breast cancer, non-coding RNAs are involved in cell cycle control and tumor cell migration and invasion, as well as treatment resistance. Alterations in non-coding RNA expression may contribute to the development and progression of breast cancer, making them promising biomarkers and targets for novel therapeutic approaches. Currently, the use of non-coding RNAs has not yet been applied to routine practice; however, their potential has been very well studied. The present review is a literature overview of current knowledge and its objective is to delineate the function of diverse classes of non-coding RNAs in breast cancer, with a particular emphasis on their potential utility as diagnostic and prognostic markers or as therapeutic targets and tools.

The Diagnostic Value of circFBXW7, circABCB10, and circ0103552 Levels in Breast Cancer

Despite advances in cancer treatment, breast cancer (BC) remains one of the most common cancers affecting women worldwide. This study aimed to determine serum circFBXW7, circABCB10, and circ0103552 levels and compare BC patients and healthy controls to investigate their roles in the molecular mechanism of BC and the significance of these circRNAs in BC diagnosis. The study group consisted of 92 patients with BC and 31 healthy controls. Total RNA was isolated from serum samples. Following total RNA, complementary DNA was synthesized from this material. Following complementary DNA analysis, the circRNA levels were analyzed by the qRT-PCR method. Expression levels were evaluated in ΔCt values. High ΔCt values of circFBXW7 and circ0103552 and low ΔCt values of circABCB10 were correlated with BC diagnosis (circFBXW7, p = 0.043, r = 0.183, circ0103552, p < 0.001, r = 0.321, circABCB10, p = 0.001, r = -0.291). According to Fold Change (FC) values, circFBXW7 (FC = 0.30) and circ0103552 (FC = 0.26) showed low expression in the patient group compared to the control group, while circABCB10 (FC = 11.09) showed high expression (p < 0.05, for all comparisons). We think that our study is one of the rare studies investigating the relationship between BC and serum circRNA levels. This study concludes that the significant downregulation of circFBXW7 and circ0103552 and the upregulation of circABCB10 are directly related to the diagnosis of BC and can be used for diagnosis, but further studies are needed to elucidate the molecular mechanism of the relationship between circRNAs and BC.

In silico analysis and comprehensive review of circular-RNA regulatory roles in breast diseases; a step-toward non-coding RNA precision

In the current comprehensive review, we first highlighted circRNAs, which are key ncRNAs. Next, we discussed the relationships among circRNAs and breast cancer subtypes via in silico databases analysis and extensive literature search. CircRNAs, that sponge miRNA axes or act as silencers of oncogenic mRNAs, have been extensively addressed in the context of this review. During BC pathogenesis, the circRNA/microRNA/messenger RNA (mRNA) axis plays a major role in disease growth, progression, and survival/resistance and could be targeted for improved treatment options. This review also aimed to address oncogenic and tumor suppressor mRNAs, which are regulated by various circRNAs in BC. Moreover, we mentioned the relation of different circRNAs with cancer hallmarks, patient survival together with drug resistance. Additionally, we discussed circRNAs as vaccines and biomarkers in BC. Finally, we studied exosomal circRNAs as a hot interesting area in the research. REVIEW SIGNIFICANCE: Via using in silico databases, bioinformatics analysis, and a thorough literature search to first highlight circRNA as a crucial ncRNA and its biogenesis, and then we explored the connection between circRNA and breast illnesses. In the framework of the review, circRNA sponged-miRNAs axis or as silencers to oncogenic mRNAs were extensively discussed. In the pathophysiology of BC, the circular RNA/microRNA/messenger RNA axis is crucial for the propagation of the disease and resistance that may be targeted for more effective treatment options, in order to confront tumor suppressor and oncogenic mRNAs that are presently regulated by circRNAs in BC. For better patient results, we advised further mechanistic research to elucidate additional ncRNA axis that may be targeted for the therapy of BC and for prognosis/ or early diagnosis.

Circular RNAs as a novel molecular mechanism in diagnosis, prognosis, therapeutic target, and inhibiting chemoresistance in breast cancer

Breast cancer (BC) is the most common cancer among women, characterized by significant heterogeneity. Diagnosis of the disease in the early stages and appropriate treatment plays a crucial role for these patients. Despite the available treatments, many patients due to drug resistance do not receive proper treatments. Recently, circular RNAs (circRNAs), a type of non-coding RNAs (ncRNAs), have been discovered to be involved in the progression and resistance to drugs in BC. CircRNAs can promote or inhibit malignant cells by their function. Numerous circRNAs have been discovered to be involved in the proliferation, invasion, and migration of tumor cells, as well as the progression, pathogenesis, tumor metastasis, and drug resistance of BC. Circular RNAs can also serve as a biomarker for diagnosing, predicting prognosis, and targeting therapy. In this review, we present an outline of the variations in circRNAs expression in various BCs, the functional pathways, their impact on the condition, and their uses in clinical applications.

Circular RNAs in Breast Cancer: An Update

Breast cancer (BC), characterized by high heterogeneity, is the most commonly reported malignancy among females across the globe. Every year, many BC patients die owing to delayed diagnosis and treatment. Increasing researches have indicated that aberrantly expressed circular RNAs (circRNAs) are implicated in the tumorigenesis and progression of various tumors, including BC. Hence, this article provides a summary of the biogenesis and functions of circRNAs, as well as an examination of how circRNAs regulate the progression of BC. Moreover, circRNAs have aroused incremental attention as potential diagnostic and prognostic biomarkers for BC. Exosomes enriched with circRNAs can be secreted into the tumor microenvironment to mediate intercellular communication, affecting the progression of BC. Detecting the expression levels of exosomal circRNAs may provide reference for BC diagnosis and prognosis prediction. Illuminating insights into the earlier diagnosis and better treatment regimens of BC will be potentially available following elucidation of deeper regulatory mechanisms of circRNAs in this malignancy.

MicroRNA Expression Profile in Early-Stage Breast Cancers

BACKGROUND

Breast cancer is one of the leading causes of cancer deaths in women. Early diagnosis offers the best hope for a cure. Ductal carcinoma in situ is considered a precursor of invasive ductal carcinoma of the breast. In this study, we carried out microRNA sequencing from 7 ductal carcinoma in situ (DCIS), 6 infiltrating ductal carcinomas (IDC Stage IIA) with paired normal, and 5 unpaired normal breast tissue samples.

METHODS

We have deployed miRge for microRNA analysis, DESeq for differential expression analysis, and Cytoscape for competing endogenous RNA network investigation.

RESULTS

Here, we identified 76 miRNAs that were differentially expressed in DCIS and IDC. Additionally, we provide preliminary evidence of miR-365b-3p and miR-7-1-3p being overexpressed, and miR-6507-5p, miR-487b-3p, and miR-654-3p being downregulated in DCIS relative to normal breast tissue. We also identified a miRNA miR-766-3p that was overexpressed in earlystage IDCs. The overexpression of miR-301a-3p in DCIS and IDC was confirmed in 32 independent breast cancer tissue samples.

CONCLUSION

Higher expression of miR-301a-3p is associated with poor overall survival in The Cancer Genome Atlas Breast Cancer (TCGA-BRCA) dataset, indicating that it may be associated with DCIS at high risk of progressing to IDC and warrants deeper investigation.

Inverse Impact of Cancer Drugs on Circular and Linear RNAs in Breast Cancer Cell Lines

Altered expression of circular RNAs (circRNAs) has previously been investigated in breast cancer. However, little is known about the effects of drugs on their regulation and relationship with the cognate linear transcript (linRNA). We analyzed the dysregulation of both 12 cancer-related circRNAs and their linRNAs in two breast cancer cell lines undergoing various treatments. We selected 14 well-known anticancer agents affecting different cellular pathways and examined their impact. Upon drug exposure circRNA/linRNA expression ratios increased, as a result of the downregulation of linRNA and upregulation of circRNA within the same gene. In this study, we highlighted the relevance of identifying the drug-regulated circ/linRNAs according to their oncogenic or anticancer role. Interestingly, VRK1 and MAN1A2 were increased by several drugs in both cell lines. However, they display opposite effects, circ/linVRK1 favors apoptosis whereas circ/linMAN1A2 stimulates cell migration, and only XL765 did not alter the ratio of other dangerous circ/linRNAs in MCF-7. In MDA-MB-231 cells, AMG511 and GSK1070916 decreased circGFRA1, as a good response to drugs. Furthermore, some circRNAs might be associated with specific mutated pathways, such as the PI3K/AKT in MCF-7 cells with circ/linHIPK3 correlating to cancer progression and drug-resistance, or NHEJ DNA repair pathway in TP-53 mutated MDA-MB-231 cells.

Hypoxia-Induced FUS-circTBC1D14 Stress Granules Promote Autophagy in TNBC

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer that is suggested to be associated with hypoxia. This study is the first to identify a novel circular RNA (circRNA), circTBC1D14, whose expression is significantly upregulated in TNBC. The authors confirm that high circTBC1D14 expression is associated with a poor prognosis in patients with breast cancer. circTBC1D14-associated mass spectrometry and RNA-binding protein-related bioinformatics strategies indicate that FUS can interact with circTBC1D14, which can bind to the downstream flanking sequence of circTBC1D14 to induce cyclization. FUS is an essential biomarker associated with stress granules (SGs), and the authors find that hypoxic conditions can induce FUS-circTBC1D14-associated SG formation in the cytoplasm after modification by protein PRMT1. Subsequently, circTBC1D14 increases the stability of PRMT1 by inhibiting its K48-regulated polyubiquitination, leading to the upregulation of PRMT1 expression. In addition, FUS-circTBC1D14 SGs can initiate a cascade of SG-linked proteins to recognize and control the elimination of SGs by recruiting LAMP1 and enhancing lysosome-associated autophagy flux, thus contributing to the maintenance of cellular homeostasis and promoting tumor progression in TNBC. Overall, these findings reveal that circTBC1D14 is a potential prognostic indicator that can serve as a therapeutic target for TNBC treatment.

Circular RNAs: biology and clinical significance of breast cancer

Circular RNAs (circRNAs) are novel noncoding RNAs with covalently closed-loop structures that can regulate eukaryotic gene expression. Due to their stable structure, circRNAs are widely distributed in the cytoplasm and have important biological functions, including as microRNA sponges, RNA-binding protein conjugates, transcription regulators, and translation templates. Breast cancer is among the most common malignant cancers diagnosed in women worldwide. Despite the development of comprehensive treatments, breast cancer still has high mortality rates. Recent studies have unmasked critical roles for circRNAs in breast cancer as regulators of tumour initiation, progression, and metastasis. Further, research has revealed that some circRNAs have the potential for use as diagnostic and prognostic biomarkers in clinical practice. Herein, we review the biogenesis and biological functions of circRNAs, as well as their roles in different breast cancer subtypes. Moreover, we provide a comprehensive summary of the clinical significance of circRNAs in breast cancer. CircRNAs are believed to be a hot focus in basic and clinical research of breast cancer, and innovative future research directions of circRNAs could be used as biomarkers, therapeutic targets, or novel drugs.Abbreviations: CeRNA: Competitive endogenous RNA; ciRNA: Circular intronic RNA; circRNA: Circular RNA; EIciRNA: Exon-intron circRNA; EMT: Epithelial-mesenchymal transition; IRES: Internal ribosome entry site; lncRNA: Long non-coding RNA; miRNA: MicroRNA; MRE: MiRNA response element; ncRNA: Non-coding RNA; RBP: RNA-binding protein; RNA-seq: RNA sequencing; RT-PCR: Reverse transcription-polymerase chain reaction.

CircCDK1 knockdown reduces CDK1 expression by targeting miR-489-3p to suppress the development of breast cancer and strengthen the sensitivity of Tamoxifen

Circular RNAs (circRNAs) are implicated with the progression of multiple cancers, including breast cancer. Besides, circRNA dysregulation is involved in the chemoresistance of cancer development. This study aimed to investigate the role of circRNA-cyclin dependent kinase 1 (circCDK1) in breast cancer. Quantitative real-time PCR (qPCR) and western blot were applied for expression analysis. Cell viability was determined by the cell counting kit-8 (CCK-8). Cell proliferation was evaluated by CCK-8, colony formation and 5-ethynyl-2'-deoxyuridine assays. Cell apoptosis was assessed by flow cytometry and the activities of caspase3 and caspase9. The potential binding between miR-489-3p and circCDK1 or CDK1 was verified by RNA immunoprecipitation assay, dual-luciferase reporter assay and pull-down assay. Animal models were constructed to explore the role of circCDK1 in vivo. CircCDK1 was overexpressed in Tamoxifen-resistant breast cancer cells, LCC2 and LCC9. The expression of circCDK1 in tumor tissues with Tamoxifen resistance was higher than that in tissues without Tamoxifen resistance. CircCDK1 knockdown strengthened the sensitivity of Tamoxifen in LCC2 and LCC9 cells and reduced Tamoxifen IC50. The downregulation of circCDK1 inhibited LCC2 andLCC9 cell proliferation and promoted cell apoptosis. CDK1 was the parent gene of circCDK1 and circCDK1 positively regulated CDK1 expression by targeting miR- 489-3p. CDK1 overexpression reversed the effects of circCDK1 knockdown. MiR-489-3p inhibition also reversed the effects of circCDK1 knockdown. CircCDK1 knockdown was verified to enhance Tamoxifen sensitivity in animal models. CircCDK1 knockdown enhanced the sensitivity of Tamoxifen in breast cancer cells and suppressed cell growth and survival by depleting CDK1 expression via releasing miR- 489-3p.

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.

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.

Estrogen-decreased hsa_circ_0001649 promotes stromal cell invasion in endometriosis

Endometriosis (EMs) is an estrogen (E2)-dependent inflammatory disorder. Although EMs is considered a benign disease, it presents with malignant characteristics, such as migration and invasion. An increasing number of studies have shown that aberrantly expressed circular RNAs (circRNAs) play an essential role in disease development and progression. However, the mechanisms by which circRNAs exert their pathological effects in EMs remain unclear. Hsa_circ_0001649, a novel cancer-associated circRNA, has been previously reported to be downregulated in several cancer types and related to cell migration and invasion. In the present study, real-time PCR (qRT-PCR) was carried out to measure hsa_circ_0001649 levels in human tissues, human primary endometrial stromal cells (ESCs) and a human endometrial stromal cell line (ThESCs). Matrix metalloproteinase 9 (MMP9) levels in ESCs and ThESCs were assessed by qRT-PCR and Western blotting, and the migration and invasion capacities of ThESCs were evaluated by transwell assay. As a result, hsa_circ_0001649 expression was significantly decreased in ectopic and eutopic endometrial samples compared with that in normal endometrial samples. E2 decreased hsa_circ_0001649 expression but increased MMP9 expression in ESCs and ThESCs. Furthermore, ThESCs were more invasive under E2 stimulation. However, these effects disappeared when ICI or hsa_circ_0001649 transfection was used. Collectively, our findings reveal that decreased hsa_circ_0001649 expression plays a role in E2-increased MMP9 expression through E2 receptors (ERs), which have critical functions in EMs.

Circ_0040039 May Aggravate Intervertebral Disk Degeneration by Regulating the MiR-874-3p-ESR1 Pathway

The functional alteration of nucleus pulposus cells (NPCs) exerts a crucial role in the occurrence and progression of intervertebral disk degeneration (IDD). Circular RNAs and microRNAs (miRs) are critical regulators of NPC metabolic processes such as growth and apoptosis. In this study, bioinformatics tools, encompassing Gene Ontology pathway and Venn diagrams analysis, and protein–protein interaction (PPI) network construction were used to identify functional molecules related to IDD. PPI network unveiled that ESR1 was one of the most critical genes in IDD. Then, a key IDD-related circ_0040039-miR-874-3p-ESR1 interaction network was predicted and constructed. Circ_0040039 promoted miR-874-3p and repressed ESR1 expression, and miR-874-3p repressed ESR1 expression in NPCs, suggesting ESR1 might be a direct target of miR-874-3p. Functionally, circ_0040039 could enhance NPC apoptosis and inhibit NPC growth, revealing that circ_0040039 might aggravate IDD by stabilizing miR-874-3p and further upregulating the miR-874-3p-ESR1 pathway. This signaling pathway might provide a novel therapeutic strategy and targets for the diagnosis and therapy of IDD-related diseases.

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.

Circular RNAs: Novel potential regulators in embryogenesis, female infertility, and pregnancy-related diseases

Circular RNAs (circRNAs) are endogenous noncoding RNAs with unique cyclic structures. Although they were previously considered as nonfunctional transcription byproducts, numerous studies have demonstrated that circRNAs regulate gene transcription and expression via different mechanisms. Reproductive health influences the quality of life and affects offspring propagation in women. CircRNAs have been found to modify pregnancy-related diseases, gynecologic cancers, polycystic ovary syndrome, aging, gamete, and embryo development. It's promising for circRNAs to be the novel diagnostic and therapeutic targets for multiple reproductive diseases. With the widespread application of assisted reproduction technology (ART), it has been revealed that circRNA identification contributes to estimating the quality of gametes and embryos, reflecting the success rate of ART. CRISPR-Cas9 gene editing technology has enabled the discovery of new roles of circRNAs. So far, the roles of circRNAs in the reproductive system remain poorly defined. In this review, we describe the classification and functions of circRNAs in embryogenesis and the female reproductive system diseases, revealing potential roles of circRNAs physiologically and pathologically. In so-doing, we provide ideas for developing circRNA-based therapeutic treatment and clinical application of various female reproductive system diseases.

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.

Regulatory mechanisms, functions, and clinical significance of CircRNAs in triple-negative breast cancer

Circular RNAs (circRNAs) are a new class of endogenous regulatory RNAs characterized by covalently closed cyclic structure lacking poly-adenylated tails, and are capable of regulating gene expression at transcription or post-transcription levels. Recently, plentiful circRNAs have been discovered in breast cancer and some circRNAs expression profiles are specifically involved in the triple-negative breast cancer (TNBC). TNBC is a type of malignant tumor defined by the lack of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expression. Considering its clinical characteristics of high invasion, metastasis, poor prognosis, and lack of effective response to conventional chemotherapies or targeted therapies, it could be a promosing option to discover specific circRNAs as new targets for TNBC treatment. Meanwhile, accumulating evidence has demonstrated that circRNAs are dysregulated in TNBC tissues and are correlated with clinicopathological features and prognosis of TNBC patients. Furthermore, looking for circRNAs with high specificity and sensitivity will provide a new opportunity for the early diagnosis, clinical treatment, and prognosis monitoring of TNBC. Herein, we reviewed the biogenesis, regulatory mechanisms, and biological functions of circRNAs in TNBC and summarized the relationship between circRNAs expression and the clinicopathology, diagnosis, and prognosis of patients with TNBC.

Knockdown of circRNA circ_0087378 Represses the Tumorigenesis and Progression of Esophageal Squamous Cell Carcinoma Through Modulating the miR-140-3p/E2F3 Axis

BACKGROUND

We aimed to investigate the function and underlying mechanisms of circ_0087378 in esophageal squamous cell carcinoma (ESCC).

METHODS

We verified higher circ_0087378 expression in ESCC tissues by performing qRT-PCR assays. We further confirmed the oncogenic roles of circ_0087378 in ESCC cells through a series of biological function assays. Then, we used an RNA pull-down assay and luciferase reporter assay to identify miR-140-3p that directly interacts with circ_0087378. Subsequent studies were performed to demonstrate that the circ_0087378/miR-140-3p/E2F3 axis promotes ESCC development.

RESULTS

We demonstrated that upregulated circ_0087378 expression was positively associated with tumor size, histological grade, tumor stage, the presence of metastasis, and worse survival in patients with ESCC. Our results further revealed that knockdown of circ_0087378 suppressed the proliferation, migration, and invasion of ESCC cells and reduced tumor growth in vivo. Mechanistically, we showed that circ_0087378 could directly bind to miR-miR-140-3p and relieve the suppression for target E2F3, which accelerated cell proliferation, migration, and invasion. Correlation analysis in ESCC specimens supported the involvement of the circ_0087378/miR-140-3p/E2F3 axis in ESCC progression.

CONCLUSIONS

This study demonstrated that circ_0087378 might act as a competing endogenous RNA for miR-140-3p, which could inhibit the tumorigenesis and progression of ESCC through upregulating E2F3 expression.

Circular RNA circTP63 enhances estrogen receptor-positive breast cancer progression and malignant behaviors through the miR-873-3p/FOXM1 axis

Circular RNAs (circRNAs) have been shown to play a functional role in a variety of cancers. However, few studies on circRNAs in estrogen receptor-positive breast cancer have been conducted. Here, we investigated the role of circRNA circTP63 in estrogen receptor-positive breast cancer progression and malignant behaviors. First, we observed increased expression of circTP63 in MCF7 cells relative to normal human mammary epithelial cell lines, such as DU4475 and MCF-10A, and the changed oncogenicity of MCF7 cells correlated with circTP63 overexpression and downregulation. Interestingly, a series of gain- and loss-of-function assays revealed that a higher level of FOXM1 was closely associated with MCF7 malignant behaviors induced by circTP63 overexpression. Further investigations showed that circTP63 sponged to miR-873-3p, which targeted FOXM1 mRNA and inhibited its expression. Mechanistically, circTP63 binds to miR-873-3p and prevents the targeting of FOXM1, thus inducing the progression and malignant behaviors of estrogen receptor-positive breast cancer, such as cell proliferation, cell cycle dysregulation, invasion, migration and even tumor growth. CircTP63 might be a potential biomarker or target to treat estrogen receptor-positive breast cancer patients in the future.

Perspectives on the Role of Non-Coding RNAs in the Regulation of Expression and Function of the Estrogen Receptor

Estrogen receptors (ERs) comprise several nuclear and membrane-bound receptors with different tissue-specific functions. ERα and ERβ are two nuclear members of this family, whereas G protein-coupled estrogen receptor (GPER), ER-X, and Gq-coupled membrane estrogen receptor (Gq-mER) are membrane-bound G protein-coupled proteins. ERα participates in the development and function of several body organs such as the reproductive system, brain, heart and musculoskeletal systems. ERβ has a highly tissue-specific expression pattern, particularly in the female reproductive system, and exerts tumor-suppressive roles in some tissues. Recent studies have revealed functional links between both nuclear and membrane-bound ERs and non-coding RNAs. Several oncogenic lncRNAs and miRNAs have been shown to exert their effects through the modulation of the expression of ERs. Moreover, treatment with estradiol has been shown to alter the malignant behavior of cancer cells through functional axes composed of non-coding RNAs and ERs. The interaction between ERs and non-coding RNAs has functional relevance in several human pathologies associated with estrogen regulation, such as cancers, intervertebral disc degeneration, coronary heart disease and diabetes. In the current review, we summarize scientific literature on the role of miRNAs and lncRNAs on ER-associated signaling and related disorders.

Circular RNAs serve as miRNA sponges in breast cancer

Circular RNAs are a large group of non-coding RNAs with a closed-loop structure. circRNAs play significant roles in many biological processes as miRNA sponges, regulators for gene transcription, combining with RNA-binding proteins and translation of protein. Nowadays, circRNAs have become a research hotspot in the field of cancer and molecular biology. Accumulating evidences have indicated that circRNAs participate in the initiation and development of various cancers such as breast cancer. Breast cancer is a heterogeneous disease, which is the most common malignancy in women. The incidence and mortality rates of breast cancer indicate that it is the leading cause of cancer-related deaths. The goal of the present review is to introduce biogenesis, function characteristics and types of circRNAs, and also their biological functions on breast cancer, especially as miRNA sponges. Additionally, we discuss their use as a new therapeutic target for the treatment of breast cancer.

Circular RNA expression profile and m6A modification analysis in poorly differentiated adenocarcinoma of the stomach

Aims: To profile and characterize the circular RNA (circRNA) expression pattern in poorly differentiated gastric adenocarcinoma (PDGA). Methods & materials: CircRNA expression profiles in PDGA and adjacent nontumor tissues were analyzed by microarray. Five randomly selected differentiated expressed circRNAs (DECs) were validated by real-time quantitative PCR. m6A qualification of the top 20 DECs was conducted by m6A-immunoprecipitation and real-time quantitative PCR. Results: A total of 65 DECs were found in PDGA compared with the control. Hsa_circRNA_0077837 had the largest area under the curve. Most DECs had m6A modifications, the trend of m6A modification alteration was mainly consistent with the circRNA expression level. Conclusion: Our study revealed a set of DECs and their m6A modification alterations, which may provide new insight for their potential function in PDGA.

Circular RNA circNTRK2 facilitates the progression of esophageal squamous cell carcinoma through up-regulating NRIP1 expression via miR-140-3p

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most prevalent gastrointestinal malignancies with high mortality. Circular RNAs (CircRNAs) have become a research hotspot in recent years for their vital roles in cancer development and progression. This study aims to clarify the roles of circNTRK2 and its underlying molecular mechanisms in ESCC.

Methods

The levels of circNTRK2, miR-140-3p, and nuclear receptor-interacting protein 1 (NRIP1) mRNA were examined by qRT-PCR. The cell proliferation ability was detected via CCK-8, EdU and colony formation assays. The invasion capacity was tested by using transwell assay. The apoptotic rate was evaluated through flow cytometry. The protein levels of cleaved PARP, cleaved caspase-3, E-cadherin, vimentin, and NRIP1 were measured by western blot assay. The validation of circular structure was performed by Sanger sequencing, divergent primer PCR, and RNase R treatments. The ceRNA regulatory mechanism of circNTRK2 was observed via dual-luciferase reporter, RIP and RNA pull-down assays. The mice xenograft models were constructed to confirm the oncogenicity of circNTRK2 in ESCC in vivo.

Results

CircNTRK2 was highly expressed in ESCC tissues and cells. High expression of circNTRK2 was correlated with advanced TNM stage, lymph node metastasis and short survival. Knockdown of circNTRK2 inhibited ESCC cell proliferation, invasion and epithelial-mesenchymal transition (EMT), and accelerated apoptosis in vitro. Mechanistic assays disclosed that circNTRK2 could act as a sponge for miR-140-3p to abate its suppression on target NRIP1 expression. Moreover, miR-140-3p-induced inhibitory effects on ESCC cell malignant phenotypes were attenuated by the overexpression of circNTRK2. In addition, depletion of NRIP1 impeded cell proliferation, invasion and EMT, while enhanced apoptosis. Furthermore, silencing of circNTRK2 suppressed cell proliferation and invasion through regulating NRIP1 expression. Also, knockdown of circNTRK2 slowed ESCC tumor growth in vivo.

Conclusion

CircNTRK2 promoted ESCC progression by regulating miR-140-3p/NRIP1 pathway. Our findings contribute to a better understanding of circRNAs as miRNA sponges and highlight a promising therapy target in ESCC.

Circular RNAs: from biogenesis and function to diseases

OBJECTIVE

Evidence suggests that various diseases may contribute to the circular RNAs (circRNAs) expression disorder. This review was aimed at looking for appropriate biomarkers for the treatment of diseases.

DATA SOURCES

The comprehensive search used online literature databases including PubMed of National Center for Biotechnology Information and Web of Science.

STUDY SELECTION

The study selection was based on the following keywords: circRNAs, biogenesis, biologic function, and disease. The time limit for literature retrieval was from the year 1976 to 2019, with language restriction in English. Relevant articles were carefully reviewed, with no exclusions applied to study design and publication type.

RESULTS

CircRNAs are one of the critical non-coding RNAs (ncRNAs), which are covalently closed continuous loops that do not possess 5' and 3' ends. This makes them resistant to exoribonuclease activity and potentially more stable than their cognate linear transcripts, thus making them ideal candidates for biomarker development. Due to the stable and extensive tissue-specific expression of circRNAs, they can function as microRNA sponges and bind to RNA-binding proteins, regulate transcription and splicing, and translate into proteins to participate in the regulation of physiologic and pathologic processes. Moreover, the expression disorders of circRNAs in diseases, such as neurodegenerative disease, cardiovascular disease, and cancer, make them have potential applications for the diagnosis and treatment of diseases.

CONCLUSIONS

Changes in circRNA expression profiles related to various diseases, and circRNAs often exhibit low expression in cancer tissues. In addition, circRNAs can be detected in patient's body fluids to indicate that circRNAs are effective biomarkers for disease diagnosis. These characteristics make circRNAs have potential applications as novel therapeutic targets for diseases.

Profiling and integrated analysis of differentially expressed circRNAs as novel biomarkers for breast cancer

Breast cancer (BC) is a globally common cancer with the highest and increasing morbidity and mortality among females. Novel biomarkers are warranted to be discovered for the early detection, treatment, and prognosis of BC. In this study, we investigated the profiles of differentially expressed (DE) circular RNAs (circRNAs) by competing endogenous RNAs (ceRNA) microarray to construct a genome-wide circRNA profile. Then, we performed Gene Ontology (GO) analysis and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway analysis of the host genes (HGs) of circRNAs. A total of 4,370 DE circRNAs were detected and GO and KEGG analysis showed that they were significantly associated with cell cycle, DNA replication, BC, and familial BC. We validated the differential circRNAs and relevant HGs through quantitative real-time polymerase chain reaction and constructed a putative circRNA-microRNA-messenger RNA regulatory network. Eight circRNAs, including hsa_circ_0069094, hsa_circ_0062558, hsa_circ_0074026, hsa_circ_0079876, hsa_circ_0017536, hsa_circ_0023302, hsa_circ_0017650, and hsa_circ_0017545, were validated significantly DE in BC tissue and associated with TNM staging, lymph node infiltration, and Ki67. Hsa_circ_0069094, hsa_circ_0079876, hsa_circ_0017650, and hsa_circ_0017526 were upregulated in plasma. This study revealed the general expression characteristics of specific DE circRNAs in BC and hsa_circ_0069094, hsa_circ_0079876, hsa_circ_0017650, and hsa_circ_0017526 might be promising candidate targets.

Analysis of circular RNA-associated competing endogenous RNA network in breast cancer

As the most common type of cancer in female patients, the morbidity and mortality rates of breast cancer (BC) are high, and its incidence is gradually increasing worldwide. However, the underlying molecular and genetic mechanisms involved in the etiopathogenesis of BC remain unclear. Circular RNAs (circRNAs) are a novel type of non-coding RNAs that have been verified to serve a crucial role in tumorigenesis. However, the majority of functions and mechanisms of circRNAs remain unknown. The present study identified 47 differentially expressed circRNAs in a dataset from Gene Expression Omnibus. Using the cancer-specific circRNA database, the potential microRNA (miRNA) response elements, RNA-binding proteins and open reading frames of the candidate circRNAs were predicted. Combing the predictions of miRNAs and target mRNAs, a competing endogenous RNA network was constructed, which may serve as the theoretical basis for further research. Furthermore, the analyses conducted using Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways indicated that candidate circRNAs may serve a role in transcriptional regulation. Moreover, 20 BC tissue specimens and their paired adjacent normal tissue specimens were used to evaluate the expression levels of the screened circRNAs. Thus, the analyses of the raw microarray data conducted in the present study offer perspectives on the exploration of mechanisms associated with BC tumorigenesis with regard to the circRNA-miRNA-mRNA network.

Comprehensive circRNA/miRNA/mRNA analysis reveals circRNAs protect against toxicity induced by BPA in GC-2 cells

Aim: To identify the circRNAs expression pattern and roles in bisphenol A (BPA) induced germ cell apoptosis. Materials & methods: We performed circRNA/miRNA/mRNA-Seq in 120 μM BPA treated and nontreated GC-2 cells. Bioinformatic analysis, qPCR, apoptosis assays, luciferase report were done in the function analysis. Results: A large number of apoptosis related circRNAs/miRNAs/mRNAs were differentially expressed with competing endogenous RNA network constructed. Interestingly, most investigated upregulated circRNAs, including circDcbld2, circMapk1, circMpp6 and circTbc1d20 showed protective effects in antagonizing BPA toxicity, with the effects individually and synergistically observed. CircMapk1 may take its role by sponging miR-214-3p. Conclusion: circRNAs can play protective roles via sponging miRNAs in toxicity. Some circRNAs may serve as novel targets for BPA toxicity intervention or as biomarkers.

Upregulation of hsa_circ_0136666 contributes to breast cancer progression by sponging miR-1299 and targeting CDK6

Circular RNAs (circRNAs) can participate in multiple cancers, including breast cancer. Increasing circRNAs are recognized in various cancers because of the high-throughput sequencing. However, the potential physiological effect of hsa_circ_0136666 in breast cancer progression is unknown. In our study, the biological role of hsa_circ_0136666 in breast cancer development was studied. It was displayed that hsa_circ_0136666 was greatly increased in breast cancer. In addition, overexpression of hsa_circ_0136666 was able to promote Michigan Cancer Foundation-7 (MCF7) and BT474 cell proliferation and triggered cell cycle in G2/M phase. microRNA plays critical role in tumor development and they can act as direct targets of circRNAs. miR-1299 has been implicated as a famous tumor suppressor in many cancers. Here, miR-1299 was predicted as the target of hsa_circ_0136666. Meanwhile, its Upregulation repressed breast cancer proliferation, migration and invasion capacity, which could be reversed by the increase of hsa_circ_0136666. Furthermore, Cyclin-dependent kinase 6 (CDK6) was speculated as the downstream target of miR-1299. In MCF7 and BT474 cells, CDK6 was greatly overexpressed and it was shown that CDK6 contributed a lot to breast cancer progression. Subsequently, it was implied that hsa_circ_0136666 could modulate CDK6 levels positively in vitro. In conclusion, it was revealed that Upregulation of hsa_circ_0136666 promoted breast cancer progression by sponging miR-1299 and targeting CDK6.