hsa_circ_0006168 sponges miR-100 and regulates mTOR to promote the proliferation, migration and invasion of esophageal squamous cell carcinoma

Appraising the value of CircRNAs for the diagnosis and prognosis of esophageal squamous cell cancer: An updated meta-analysis

OBJECTIVE

The purpose of this study was to thoroughly assess the relevance of circular RNAs (circRNAs) in the diagnosis and prognosis of esophageal squamous cell carcinoma (ESCC)， and design a systematic review and meta-analysis.

METHODS

Using Stata 14.0 software, a meta-analysis was carried out by looking for pertinent studies up to February 20, 2023, in the online databases PubMed, Embase, Web of Science, and CNKI. The clinicopathologic and prognostic data were evaluated using the combined advantage ratio (OR) and combined hazard ratio (HR), respectively. The threshold effects and publication bias were quantified using Spearman's correlation and the Deeks funnel plot asymmetry tests, respectively.

RESULTS

A total of 36 pertinent studies with a literature quality score of 7 or above were included in this study. Of them, 22 papers dealt with clinicopathological characterization, 15 dealt with prognostic analysis, and 13 dealt with diagnostic analysis. The findings demonstrated that high expression of upregulated circRNAs was associated with worse clinicopathological features (tumor size: OR=3.61, 95% CI:1.45-5.78; TNM stage: OR=2.12, 95% CI:1.41-2.83; lymph node metastasis: OR=2.87, 95% CI:1.67-4.07) and worse OS (HR=1.49, 95% CI:1.26-1.77). High downregulated circRNAs expression was linked to improved clinicopathologic characteristics (TNM staging: OR=0.35, 95% CI:0.13- 0.95) and longer survival (HR=0.48, 95% CI:0.27-0.84); combined sensitivity was 0.77 (95% CI: 0.71-0.82), specificity was 0.80 (95% CI:0.74-0.86), and area under the subject operating characteristic curve (AUC) was 0.86 (95% CI:0.82- 0.88).

CONCLUSION

CircRNAs are useful for ESCC patient diagnosis and prognosis, and they are anticipated to be unique potential biomarkers for ESCC clinical diagnosis.

Exosomal circCNOT6L Regulates Astrocyte Apoptotic Signals Induced by Hypoxia Exposure Through miR99a-5p/SERPINE1 and Alleviates Ischemic Stroke Injury

Circular RNAs are involved in intervention strategies for treating ischemic stroke (IS). However, circCNOT6L (hsa_circ_0006168) has not yet been reported in IS. Thus, we aimed to explore the potential role of circCNOT6L and its molecular mechanism in IS. In this study, we first found that the expression of both exosomal circCNOT6L (P = 0.0006) and plasma circCNOT6L (P = 0.0054) was down-regulated in IS patients compared with controls. Clinically, a negative correlation was observed between the relative expression level of circCNOT6L and the National Institutes of Health Stroke Scale (NIHSS) score and infarct volume of the brain. Simultaneously, the relative expression level of circCNOT6L was negatively associated with multiple risk factors for IS, such as mean platelet volume (MPV), red cell distribution width (RDW), very low-density lipoprotein (VLDL), and serum potassium, whereas it was positively correlated with high-density lipoprotein (HDL). In vitro, circCNOT6L silencing blocked cell viability and proliferation, while it promoted cell apoptosis of astrocytes undergoing oxygen-glucose deprivation/reperfusion (OGD/R) treatment. Mechanistically, the RNA antisense purification (RAP) assay and luciferase reporter assay revealed that circCNOT6L acts as a miRNA sponge to absorb miR-99a-5p and then regulates the expression of serine proteinase inhibitor (SERPINE1). In the further rescue experiment, overexpressing SERPINE1 could rescue the cell apoptotic signals due to circCNOT6L depletion. In conclusion, CircCNOT6L attenuated the cell apoptotic signal of astrocytes via the miR99a-5p/SERPINE1 axis and then alleviated injury after hypoxia induced by ischemic stroke.

Association between circ_0004365 and cisplatin resistance in esophageal squamous cell carcinoma

Cisplatin is one of the most predominant drugs for the chemotherapy of esophageal squamous cell carcinoma (ESCC); however, the underlying resistance mechanisms are still almost unknown. The present study performed RNA sequencing of human circular RNA (circRNA) in TE11 cells and cisplatin-resistant TE11 cells (TE11R). The expression profiles determined using CIRCexplorer2 revealed that the expression of circ_0004365, mapped on the Semaphorin 3C gene, was significantly greater in TE11R compared with in TE11. In reverse transcription-quantitative PCR, circ_0004365 expression was observed in human ESCC and non-tumor tissues and was significantly upregulated in ESCC tumor tissues after chemotherapy. Circ_0004365 expression was significantly upregulated in patients with poor pathological response (P=0.02). Furthermore, patients with advanced pT stage showed an upregulation in circ_0004365 expression after chemotherapy (P=0.02). The MTT assay revealed that knockdown of circ_0003465 in TE11 significantly decreased resistance to cisplatin. In conclusion, the present study suggested that circ_0004365 was associated with cisplatin resistance in ESCC and can be used as both a novel biomarker and a therapeutic target.

The potential role and mechanism of circRNAs in foam cell formation

Atherosclerosis is a significant risk factor for coronary heart disease (CHD) and myocardial infarction (MI). Atherosclerosis develops during foam cell generation, which is caused by an imbalance in cholesterol uptake, esterification, and efflux. LOX-1, SR-A1, and CD36 all increased cholesterol uptake. ACAT1 and ACAT2 promote free cholesterol (FC) esterification to cholesteryl esters (CE). The hydrolysis of CE to FC was aided by nCEH. FC efflux was promoted by ABCA1, ABCG1, ADAM10, and apoA-I. SR-BI promotes not only cholesterol uptake but also FC efflux. Circular RNAs (circRNAs), which are single-stranded RNAs with a closed covalent circular structure, have emerged as promising biomarkers and therapeutic targets for atherosclerosis due to their highly tissue, cell, and disease state-specific expression profiles. Numerous studies have shown that circRNAs regulate foam cell formation, acting as miRNA sponges to influence atherosclerosis development by regulating the expression of SR-A1, CD36, ACAT2, ABCA1, ABCG1, ADAM10, apoA-I, SR-B1. Several circRNAs, including circ-Wdr91, circ 0004104, circRNA0044073, circRNA_0001805, circDENND1B, circRSF1, circ 0001445, and circRNA 102682, are potential biomarkers for atherosclerosis to better evaluate cardiovascular risk. It is difficult to deliver synthetic therapeutic circRNAs to the desired target tissues. Nanotechnology, such as GA-RM/GZ/PL, may be an important solution to this problem. In this review, we focus on the potential role and mechanism of circRNA/miRNA axis in foam cell formation in the hopes of discovering new targets for the diagnosis, prevention, and treatment of atherosclerosis.

Downregulation of miR-100-5p in cancer-associated fibroblast-derived exosomes facilitates lymphangiogenesis in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC), an aggressive gastrointestinal tumor, often has high early lymphatic metastatic potential. Cancer-associated fibroblasts (CAFs) are primary components in tumor microenvironment (TME), and the impact of CAFs and its derived exosomes on lymphangiogenesis remains elusive.

MATERIALS AND METHODS

CAFs and the microlymphatic vessel density (MLVD) in ESCC was examined. Exosomes were extracted from primary normal fibroblast (NFs) and CAFs. Subsequently, tumor-associated lymphatic endothelial cells (TLECs) were treated with these exosomes, and the effect on their biological behavior was examined. miR-100-5p was selected as the target miRNA, and its effect on TLECs was examined. The target of miR-100-5p was predicted and confirmed. Subsequently, IGF1R, PI3K, AKT, and p-AKT expression in TLECs and tumors treated with exosomes and miR-100-5p were examined.

RESULTS

A large number of CAFs and microlymphatic vessels were present in ESCC, leading to a poor prognosis. CAF-derived exosomes promoted proliferation, migration, invasion, and tube formation in TLECs. Further, they also enhanced lymphangiogenesis in ESCC xenografts. miR-100-5p levels were significantly lower in CAF-derived exosomes than in NF-derived exosomes. miR-100-5p inhibited proliferation, migration, invasion, and tube formation in TLECs. Further, miR-100-5p inhibited lymphangiogenesis in ESCC xenografts. Mechanistic studies revealed that this inhibition was mediated by the miR-100-5p-induced inhibition of IGF1R/PI3K/AKT axis.

CONCLUSION

Taken together, our study demonstrates that CAF-derived exosomes with decreased miR-100-5p levels exhibit pro-lymphangiogenesis capacity, suggesting a possibility of targeting IGF1R/PI3K/AKT axis as a strategy to inhibit lymphatic metastasis in ESCC.

Circ-ATIC regulates esophageal squamous cell carcinoma growth and metastasis through miR-1294/PBX3 pathway

Esophageal squamous cell carcinoma (ESCC) is a digestive tract malignancy associated with poor clinical outcome. Growing evidence have elucidated that circular RNAs (circRNAs) play important roles in the pathological process of ESCC. However, the detailed mechanisms how circRNAs modulate the development of ESCC remain largely unknown. Our study aimed to decipher the role and mechanism of circ-ATIC (also termed as circRNA_0058063) in regulating the progression of ESCC. We found that circ-ATIC and its host gene ATIC were significantly increased in ESCC tissues and cells compared with the adjacent noncancerous tissues or normal esophagus epithelial cell. Circ-ATIC knockdown substantially reduced proliferation and the number of invaded ESCC cells and retarded EMT process, reflecting by the decreased N-cadherin and elevated E-cadherin. However, the level of host gene ATIC was not changed under circ-ATIC suppression. It was predicted that circ-ATIC could bind to miR-1294 and serve as a sponge RNA. The luciferase reporter assay and RNA immunoprecipitation (RIP) assay confirmed their relations. MiR-1294 was decreased in ESCC tissues and cells, which was reversely correlated with circ-ATIC level. Furthermore, PBX3 was predicted and proved to be a downstream direct target of miR-1294. PBX3 mRNA and protein were obviously upregulated in ESCC tumor tissues and cells. PBX3 overexpression could reverse the suppressive roles of miR-1294 mimics on ESCC proliferation and invasion. In an xenograft nude mice model, stable transfection of sh-circ-ATIC significantly retarded the growth of tumor and suppressed VEGF and Ki67. Collectively, circ-ATIC promoted ESCC proliferation and invasion by regulating miR-1294/PBX3 axis.

Comprehensive Analysis of circRNA Expression Profiles in Human Brown Adipose Tissue

PURPOSE

Brown adipose tissue (BAT) can rapidly generate heat and improve energy metabolism. Circular RNAs (circRNAs) are cellular endogenous non-coding RNAs, which can regulate the development and progress of different diseases. However, the role of circRNAs in human BAT is not fully understood. Here, we analyzed the differentially expressed circRNAs (DECs) in human BAT, as well as in white adipose tissue (WAT), and identified new biomarkers of BAT.

PATIENTS AND METHODS

Three human BAT and three human subcutaneous WAT samples were selected, and circRNA microarray was performed. Additionally, quantitative real-time polymerase chain reaction (qRT-PCR) was applied to determine the expression of six circRNAs. Finally, the functional analysis was performed by bioinformatics.

RESULTS

Compared to WAT, 152 upregulated circRNAs and 201 downregulated circRNAs were identified in BAT. The DECs were further subjected to GO and KEGG enrichment analysis. Several circRNAs, for example, hsa_circ_0006168, hsa_circ_26337 and hsa_circ_0007507 were found upregulated and hsa_circ_0030162 was found downregulated in human BAT compared to WAT.

CONCLUSION

This study profiles the circRNA expression in human BAT and WAT, and suggests hsa_circ_0006168, hsa_circ_26337, hsa_circ_0007507, and hsa_circ_0030162 as novel biomarkers for human BAT.

MSC-Derived exosomes suppress colorectal cancer cell proliferation and metastasis via miR-100/mTOR/miR-143 pathway

Exosomes derived from mesenchymal stem cells (MSCs) are mostly responsible for the therapeutic effects of MSCs. To show the therapeutic effects of the human bone marrow MSC-derived exosomes (MSC-Exos) on colorectal cancer (CRC) and explore the molecular cross-talks between them, CRC cells were treated with the MSC-Exos. We found that MSC-Exos were enriched with miR-100 and miR-143, which effectively downregulated mTOR, Cyclin D1, K-RAS, HK2 while upregulated p-27 expression. All these effects were reversed by concurrent treatment with MSC-Exos and antagomiR-100, confirming that they were caused by exosomal transfer of miR-100 into recipient CRC cells. Moreover, exosomal miR-100 promoted endogenous miR-143 expression. The flow cytometry, MTT and trypan blue assays revealed that MSC-Exos could efficiently suppress proliferation and induce apoptosis of the CRC cells. Furthermore, wound healing, transwell migration and invasion assays confirmed their inhibitory effects on the migration and invasiveness of SW480 cells. We further confirmed these effects by analyzing the expression levels of epithelial to mesenchymal transition (EMT) factors and metastasis-related genes. Results showed that MSC-Exos significantly suppressed the expression of MMP2 and MMP9 (metastasis-related genes), SNAIL and TWIST (EMT-inducing transcription factors), Vimentin and N-cadherin (mesenchymal cell markers), whereas E-cadherin (epithelial cell marker) was remarkably up-regulated. Collectively, our data indicated that MSC-Exos could suppress proliferation, migration, invasion and metastasis while inducing the apoptosis of the CRC cells via miR-100/mTOR/miR-143 axis. Our findings highlight that MSC-Exo treatment as well as miR-100 restoration might be considered as potential therapeutic strategies for CRC.

circRNA: A New Biomarker and Therapeutic Target for Esophageal Cancer

Circular RNAs (circRNAs) comprise a large class of endogenous non-coding RNA with covalently closed loops and have independent functions as linear transcripts transcribed from identical genes. circRNAs are generated by a “back-splicing” process regulated by regulatory elements in cis and associating proteins in trans. Many studies have shown that circRNAs play important roles in multiple processes, including splicing, transcription, chromatin modification, miRNA sponges, and protein decoys. circRNAs are highly stable because of their closed ring structure, which prevents them from degradation by exonucleases, and are more abundant in terminally differentiated cells, such as brains. Recently, it was demonstrated that numerous circRNAs are differentially expressed in cancer cells, and their dysfunction is involved in tumorigenesis and metastasis. However, the crucial functions of these circRNAs and the dysregulation of circRNAs in cancer are still unknown. In this review, we summarize the recent reports on the biogenesis and biology of circRNAs and then catalog the advances in using circRNAs as biomarkers and therapeutic targets for cancer therapy, particularly esophageal cancer.

A novel circ_0000654/miR-375/E2F3 ceRNA network in esophageal squamous cell carcinoma

Background

The competing endogenous RNA (ceRNA) activity of circular RNAs (circRNAs) has been implicated in the pathogenesis of cancers, including esophageal squamous cell carcinoma (ESCC). Here, we identified the ceRNA mechanism of circ_0000654 regulation in ESCC.

Methods

The levels of circ_0000654, E2F transcription factor 3 (E2F3), and microRNA (miR)‐375 were gauged by quantitative real‐time PCR (qRT‐PCR) and western blot. Cell proliferation was assessed by 3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H‐tetrazolium (MTS) and 5‐ethynyl‐2′‐deoxyuridine (EdU) assays. Cell apoptosis was detected by flow cytometry. Cell colony formation was tested by colony formation assay. Dual‐luciferase reporter, RNA pull‐down and RNA immunoprecipitation (RIP) assays were performed to confirm the direct relationship between miR‐375 and circ_0000654 or E2F3. Xenograft model assays were used to evaluate the effect of circ_0000654 in vivo.

Results

Circ_0000654 and E2F3 were upregulated in ESCC. Circ_0000654 depletion enhanced cell apoptosis and hindered cell proliferation and glycolysis in vitro, as well as weakened tumor growth in vivo. Increased expression of E2F3 counteracted the effects of circ_0000654 depletion. Mechanistically, E2F3 was a target of miR‐375, and circ_0000654 modulated E2F3 expression through sequestering miR‐375. Furthermore, miR‐375 upregulation phenocopied circ_0000654 knockdown in inhibiting ESCC progression.

Conclusion

Our findings identify a new circ_0000654/miR‐375/E2F3 ceRNA crosstalk for the oncogenic role of circ_0000654 in ESCC and establish a notion that targeting circ_0000654 and its pathways may have the potential to improve ESCC outcome.

CircLONP2 Accelerates Esophageal Squamous Cell Carcinoma Progression via Direct MiR-27b-3p-ZEB1 Axis

Circular RNAs (circRNAs) are important mediators in esophageal squamous cell carcinoma (ESCC) carcinogenesis. We aim to explore the functions and mechanisms of circLONP2 in ESCC progression. The circLONP2 level was evaluated in ESCC samples and cell lines. The role and mechanisms of circLONP2 in ESCC proliferation and migration were demonstrated in vitro. We found that circLONP2 was upregulated in human ESCC and predicts poor overall survival (OS) and disease-free survival (DFS). CircLONP2 promotes ESCC aggressiveness by directly interacting with miR-27b-3p, thus upregulating the expression levels of its target gene ZEB1 by suppressing miR-27b-3p activity. Therefore, we demonstrated that circLONP2/miR-27b-3p/ZEB1 axis promotes ESCC metastasis via regulating epithelial-to-mesenchymal transition (EMT)-related proteins. CircLONP2 may serve as an oncogenic circRNA and as a prognostic biomarker in ESCC progression.

Current advances and future perspectives on the functional roles and clinical implications of circular RNAs in esophageal squamous cell carcinoma: more influential than expected

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive gastrointestinal cancers with high incidence and mortality. Therefore, it is necessary to identify novel sensitive and specific biomarkers for ESCC detection and treatment. Circular RNAs (circRNAs) are a type of noncoding RNAs featured by their covalently closed circular structure. This special structure makes circRNAs more stable in mammalian cells, coupled with their great abundance and tissue specificity, suggesting circRNAs may present enormous potential to be explored as valuable prognostic and diagnostic biomarkers for tumor. Mounting studies verified the critical roles of circRNAs in regulating ESCC cells malignant behaviors. Here, we summarized the current progresses in a handful of aberrantly expressed circRNAs, and elucidated their biological function and clinical significance in ESCC, and introduced a series of databases for circRNA research. With the improved advancement in high-throughput sequencing and bioinformatics technique, new frontiers of circRNAs will pave the path for the development of precision treatment in ESCC.

Circ_0006948 Contributes to Cell Growth, Migration, Invasion and Epithelial-Mesenchymal Transition in Esophageal Carcinoma

BACKGROUND

Circular RNAs (circRNAs) can act as promoters or inhibitors in cancer progression. Has_circ_0006948 (circ_0006948) was reported to aggravate the malignant behaviors of esophageal carcinoma (EC).

AIMS

This study focused on investigating the molecular mechanism of circ_0006948 in EC progression.

METHODS

The quantitative real-time polymerase chain reaction was performed to detect the expression of circ_0006948, microRNA-4262 (miR-4262) and fibronectin type III domain containing 3B (FNDC3B). Cell growth analysis was conducted by Cell Counting Kit-8 and colony formation assays. Cell migration and invasion were assessed by transwell assay. Epithelial-mesenchymal transition (EMT)-associated proteins and FNDC3B protein expression were assayed using western blot. Dual-luciferase reporter and RNA pull-down assays were performed to validate the target combination. Xenograft tumor assay was used for investigating the role of circ_0006948 in vivo.

RESULTS

Circ_0006948 was upregulated in EC tissues and cells. Downregulating the expression of circ_0006948 or FNDC3B repressed cell growth, migration, invasion and EMT in EC cells. Target analysis indicated that miR-4262 was a target for circ_0006948 and FNDC3B was a downstream gene for miR-4262. Moreover, circ_0006948 could affect the expression of FNDC3B via sponging miR-4262. The effects of si-circ_0006948#1 on EC cells were partly restored by miR-4262 inhibition or FNDC3B overexpression. In addition, circ_0006948 also facilitated EC tumorigenesis in vivo by targeting the miR-4262/FNDC3B axis.

CONCLUSION

Taken together, circ_0006948 functioned as an oncogenic factor in EC by the miR-4262-mediated FNDC3B expression regulation.

SNHG8 promotes cell proliferation, migration, and invasion of nasopharyngeal carcinoma cells as an oncogene through miR-588/HMGA2 axis

Nasopharyngeal carcinoma (NC) poses a threat to the life of patients. Long non-coding RNA (LncRNA) is a novel kind of non-coding RNA, which plays a pivotal role through sponge microRNA (miRNA). Abnormal expression of small nucleolar RNA host gene 8 (SNHG8) is involved in various tumors; however, the role of SNHG8 in NC remains unknown. Quantitative real-time PCR (qRT-PCR) and Western blotting was employed to detect the expression levels of SNHG8, miR-588, and high mobility group A2 (HMGA2). Cell proliferation, migration, and invasion were analyzed by CCK-8 and transwell assays. miR-588 binding sites in SNHG8 were predicted by LncBase analysis. Luciferase reporter and RNA pull-down assay were used to confirm the interaction of SNHG8 and miR-588. SNHG8 was highly expressed in NC cells. The prognosis of the patients with NC in the high expression levels of SNHG8 was poorer than that in the low expression levels. The expression of SNHG8 was closely related to tumor size, TNM stage, and distal metastasis. Knockdown of SNHG8 inhibited cell proliferation, migration, and invasion of NC. SNHG8 targeted miR-588. Inhibition of miR-588 could partially reverse the knockdown of SNHG8 in NC cells, and miR-588 targeted HMGA2. In conclusion, SNHG8 promotes proliferation, migration, and invasion of NC cells through miR-588/HMGA2 in NC as an oncogene.

Identification of an Immune-Related Biomarker Model Based on the CircRNA-Associated Regulatory Network for Esophageal Carcinoma

Esophageal carcinoma (ESCA) is one of the most frequent types of malignant tumor that has a dismal prognosis. This research applied datasets aimed from the GEO and TCGA to create a prognostic signature for forecasting the clinical outcome of ESCA patients on the basis of a circRNA-associated regulatory network. Methods. A regulatory network associated with ESCA was established based on transcriptome data of circRNAs, miRNAs, and mRNAs. Functional annotations were implemented to further explore the mechanism of ESCA. Cox relative regression method was applied to create a risk signature. Besides, the immune microenvironment of the signature was investigated by utilizing the CIBERSORT algorithm. Results. Based on 27 DEcircRNAs, 65 DEmiRNAs, and 780 DEmRNAs, the circRNA-miRNA-mRNA network was finally set up. Functional enrichment unearthed that the regulatory network might participate in phosphorylation negative regulation, MAPK pathway, and PI3K/AKT pathway. This study established a risk scoring signature based on the seven immune-related genes (IRGs) (MARP14, RASGR1, PTK2, HMGB1, DKK1, RARB, and IGF1R), which was validated for its reliability. A stable and accurate nomogram combining immune-related risk scores with clinical features was constructed. Furthermore, we observed that the risk model was also related to the immunocyte infiltration. Conclusion. Our study successfully created a circRNA-associated regulatory network and further developed an immune-related model to forecast the clinical outcome of ESCA patients as well as to assess their immune status.

Biological and clinical implications of metastasis-associated circular RNAs in oesophageal squamous cell carcinoma

Oesophageal squamous cell carcinoma (OSCC) is a prevalent malignancy with high morbidity and mortality as a result of early metastasis and poor prognosis. Metastasis is a multistep process, involving various signalling pathways. Circular RNAs (circRNAs) are a class of covalently closed noncoding RNAs, the aberrant expression of which is reported to be involved in several biological events, including cell transformation, proliferation, migration, invasion, apoptosis and metastasis. Several studies have reported interactions between circRNAs and metastasis-associated signalling pathways. The abundance, stability and highly specific expression of candidate circRNAs make them potential biomarkers and therapeutic targets in OSCC. In this review article, we comprehensively describe metastasis-related circRNAs and their interactions with epithelial-mesenchymal transition-associated molecules. We also describe the molecular mechanisms and clinical relevance of circRNAs in OSCC progression and metastasis.

Dysregulated circular RNAs as novel biomarkers in esophageal squamous cell carcinoma: a meta-analysis

Introduction

Circular RNAs (circRNAs) play critical roles in tumorigenesis, but their clinical efficacy in esophageal squamous cell carcinoma (ESCC) still retains controversial. This meta‐analysis aims at evaluating the associations between circRNA expressions and clinicopathologic features as well as the diagnostic and prognostic values of circRNAs in ESCC.

Materials & Methods

PubMed, EMBASE, and other online databases were systematically searched to collect studies on circRNAs and clinicopathological features, diagnostic, and/or prognostic assessments of ESCC. The quality of included studies was evaluated using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS‐2) and Newcastle‐Ottawa Scale (NOS) scales. The included studies were quantitatively weighted and merged, and diagnostic indicators, hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) were calculated. P values were merged by Fisher᾽s method. Sources of heterogeneity were traced using subgroup, sensitivity, and meta‐regression analyses.

Results

As a result, 12 studies were included, representing 769 ESCC patients. The meta‐analysis showed that abnormal expressions of circRNAs were associated to TNM stage as well as lymph node and distant metastases in ESCC cases. CircRNA was used to distinguish ESCC patients from healthy controls, and the merged sensitivity, specificity, and the area under the curve (AUC) of ESCC were 0.78 (95% CI: 0.74–0.81), 0.79 (95% CI: 0.75–0.83), and 0.86, respectively. The survival analysis showed that upregulated oncogenic circRNA levels in ESCC tissues was associated with the shorter overall survival (OS) of the patients (univariate analysis: HR = 2.25, 95% CI: 1.71–2.95, p = 0.000, I² = 0.0%; multivariate analysis: HR = 2.50, 95% CI: 1.61–3.89, p = 0.000, I² = 0.0%), while the OS of ESCC patients presenting overexpressions of tumor‐suppressive circRNAs was significantly ameliorated (HR = 0.29, 95% CI: 0.20–0.42, p = 0.000, I² = 0.0%). The subgroup analyses based on circRNA biofunctions, sample size, and reference gene also revealed robust results.

Conclusion

CircRNAs can be used as promising molecular biomarkers for the early diagnosis and prognosis monitoring of ESCC.

Comparative analysis of circRNA expression profile and circRNA-miRNA-mRNA regulatory network between palmitic and stearic acid-induced lipotoxicity to pancreatic β cells

Chronic exposure to high concentrations of circulating palmitic acid and stearic acid leads to impaired β cell function, which accelerates the development of type 2 diabetes. However, differences in the mechanisms underlying this process between these two saturated fatty acids remain largely unknown. In this study, we screened for potential circular RNAs (circRNAs) and their associated regulatory pathways in palmitic acid- and stearic acid-induced mouse β-TC6 cell dysfunction. CircRNA high-throughput sequencing, gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes analysis were performed and co-expression and competing endogenous RNAs (ceRNA) networks were constructed. We identified that four circRNAs that were differentially expressed specifically in β cells exposed to palmitic acid, whereas four circRNAs were differentially expressed specifically in β cells exposed to stearic acid. Seven circRNAs were differentially co-expressed in palmitic acid- and stearic acid-treated β cells. In pathway exploration, we identified the core protein Solute carrier family 2 member 2 (SLc2a2), which is mainly involved in insulin resistance, maturity onset diabetes of the young and type 2 diabetes. The expressions of key circRNAs in β-TC6 cells were validated by Real time quantitative PCR, with a consistent result in high-throughput sequencing. The findings aid our understanding of the mechanisms governing the difference between palmitic acid- and stearic acid-induced β cell dysfunction and provide potential therapeutic targets for developing treatments against long-term high fat diet-induced β cell injury.

Abbreviations: Acvr1c: Activin A receptor, type 1C; CeRNA, Competing endogenous RNAs; circRNA, circular RNA; DEcircRNA: Differentially Expressed circular RNA; DEmiRNA: Differentially Expressed microRNA; DEmRNA: Differentially Expressed mRNA; GO: Gene Ontology; HPDHigh Palmitic acid Diet; HSD: High Stearic acid Diet; KEGG: Kyoto Encyclopedia of Genes and Genomes; miRNA: microRNA; ncRNAs: non-coding RNAs; qPCR: Real time quantitative PCRS; FAs: Saturated Fatty Acids; SLc2a2: Solute carrier family 2 member 2; T2D: Type 2 Diabetes

Circular RNA hsa_circ_0026552 inhibits the proliferation, migration and invasion of trophoblast cells via the miR‑331‑3p/TGF‑βR1 axis in pre‑eclampsia

Globally, pre-eclampsia (PE) is a gestational disorder that causes increased morbidity of the fetus and mortality induced by pregnancy. Despite various studies, the understanding of the causes or mechanism of the development of PE remains elusive. Thus, the present study aimed to investigate the role of circular (circ)RNA hsa_circ_0026552 (hsa_circ_0026552) in the development of PE and its mechanism of regulation. hsa_circ_0026552 differential expression in PE tissue data and clinical samples were analyzed and it was observed that hsa_circ_0026552 is highly upregulated in PE samples. Furthermore, miR-331-3p was detected as an hsa_circ_0026552 target miRNA and TGF-βR1 gene as a target of miR-331-3p. These results were confirmed using various assays, including dual-luciferase reporter, reverse transcription-quantitative PCR and RNA pull-down assay. It was observed that miR-331-3p expression was negatively correlated to hsa_circ_0026552 relative expression, while TGF-βR1 expression was positively correlated to hsa_circ_0026552 expression evaluated by Pearson's correlation test. The functional experiments, including Cell Counting Kit-8, colony formation and Transwell assay, showed that silencing hsa_circ_0026552 could significantly strengthen the proliferation, migration and invasion of the trophoblastic HTR-8/SVneo cells, but the subsequent overexpression of hsa_circ_0026552 reversed this. Mechanistically, it was concluded that hsa_circ_0026552 acts as a miR-331-3p sponge to upregulate TGF-βR1 expression in trophoblasts and is involved significantly in PE development and progression in pregnant women. The circRNA hsa_circ_0026552 could be a novel therapeutic target and prognostic biomarker for PE.

Circular RNA BMI1 Serves as a Potential Target for Diagnosis and Treatment in Esophageal Cancer

AIMS

Previous studies have confirmed that BMI1 is elevated in esophageal cancer, which is a potential therapeutic target for esophageal cancer. However, the clinical significance of circular RNA BMI1 (circ-BMI1) in esophageal cancer is not yet clear. Herein, we revealed the clinical implication of circ-BMI1 in esophageal cancer, and provided a theoretical basis for molecular diagnosis and potential targeted therapy of esophageal cancer.

METHODS

Firstly, 10 fresh paired esophageal cancer tissues and paracancer tissues, 49 esophageal cancer serum samples and 28 healthy control serum samples were involved in our study. Differential expression and clinical significance of circ-BMI1 in esophageal cancer patients and healthy controls were evaluated by quantitative Real-time RT-PCR (RT-qPCR). Secondly, effects of circ-BMI1 differential expression on biological function of esophageal cancer cell line Eca109 were analyzed. Effects of circ-BMI1 on cell proliferation, migration and colony forming ability were evaluated by CCK-8, wound healing, and colony-forming assay. Cell apoptosis, drug sensitivity tests were also be conducted. Finally, influence of Eca109 cells differentially expressed by circ-BMI1 on tumorigenicity in nude mice was studied.

RESULTS

Expression of circ-BMI1 in serum and tissues of esophageal cancer patients was significantly decreased compared to controls (P < 0.001 and P = 0.003, respectively). Area under the receiver operating characteristic curve (ROC) was 0.726. Cell proliferation, migration and colony forming ability of circBMI1-Eca109 cells were obviously decreased than that of NC-Eca109 cells (P < 0.05). circBMI1-Eca109 cells were more sensitive to 5-fluorouracil and cisplatin, and tumor volume of nude mice in circBMI1-Eca109 group was smaller (P < 0.05).

CONCLUSIONS

The study indicated that expression of circ-BMI1 was significantly down-regulated in esophageal cancer. Overexpression of circ-BMI1 inhibited proliferation, migration, colony formation of Eca109 cells, and tumor growth of Eca109 cells in nude mice. circ-BMI1 may be a potential target for diagnosis and treatment in esophageal cancer.

Blocking hsa_circ_0006168 suppresses cell proliferation and motility of human glioblastoma cells by regulating hsa_circ_0006168/miR-628-5p/IGF1R ceRNA axis

BACKGROUND

hsa_circ_0006168 is an oncogenic circular RNA in esophageal cancer. However, its role remains unclarified in tumor progression of gliomas, especially in glioblastoma (GBM).

METHODS

Cell counting kit-8 assay, transwell assays, western blotting, and xenograft experiment, as well as colony formation assay and flow cytometry were performed to measure cell proliferation and motility. Expression of hsa_circ_0006168, microRNA (miR)-628-3p, insulin‑like growth factor 1 receptor (IGF1R), and Ras/extracellular signal regulated kinases (Erk)-related proteins were determined by quantitative real-time polymerase chain reaction and western blotting. The physical interaction was confirmed by dual-luciferase reporter assay and RNA pull-down assay.

RESULTS

hsa_circ_0006168 and IGF1R were upregulated, and miR-628-5p was downregulated in human GBM tissues and cells. Functionally, blocking hsa_circ_0006168 and overexpressing miR-628-5p suppressed cell proliferation, migration, invasion, and expression of Vimentin and Snail (mesenchymal markers) in A172 and LN229 cells, accompanied with increased E-cadherin (epithelial marker), decreased colony formation, and promoted apoptosis rate. Silencing miR-628-5p counteracted the suppression of hsa_circ_0006168 deficiency on these behaviors, and restoring IGF1R blocked miR-628-5p-mediated inhibition as well. More importantly, hsa_circ_0006168 knockdown could delay xenograft tumor growth in vivo and lower Ras and phosphorylated Erk1/2 expression in vitro and in vivo. Mechanically, hsa_circ_0006168 targeted and sponged miR-628-5p, and IFG1R was a novel target for miR-628-5p. Inhibiting miR-628-5p could abrogate in vitro role of hsa_circ_0006168 knockdown, and similarly IGF1R upregulation counteracted miR-628-5p role.

CONCLUSION

Silencing hsa_circ_0006168 might suppress GBM proliferation and motility via serving as competitive endogenous RNA for miR-628-5p and regulating IGF1R/Ras/Erk pathway.

Circular RNA circ_0006168 enhances Taxol resistance in esophageal squamous cell carcinoma by regulating miR-194-5p/JMJD1C axis

Background

Chemoresistance is one of the major obstacles for cancer therapy in the clinic. Circular RNAs (circRNAs) are involved in the pathogenesis of esophageal squamous cell carcinoma (ESCC) and chemoresistance. This study aimed to explore the role and molecular mechanism of circ_0006168 in Taxol resistance of ESCC.

Methods

The expression levels of circ_0006168, microRNA-194-5p (miR-194-5p) and jumonji domain containing 1C (JMJD1C) were measured by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. The half-inhibition concentration (IC₅₀) value of Taxol was evaluated by Cell Counting Kit-8 (CCK-8) assay. Cell proliferation was evaluated by CCK-8 and colony formation assays. Cell migration and invasion were detected by transwell assay. Cell apoptosis was determined by flow cytometry. The interaction between miR-194-5p and circ_0006168 or JMJD1C was predicted by bioinformatics analysis (Circinteractome and TargetScan) and verified by dual-luciferase reporter and RNA Immunoprecipitation (RIP) and RNA pull-down assays. The mice xenograft model was established to investigate the roles of circ_0006168 in vivo.

Results

Circ_0006168 and JMJD1C were upregulated and miR-194-5p was downregulated in ESCC tissues, ESCC cells, and Taxol-resistant cells. Functionally, knockdown of circ_0006168 or JMJD1C increased Taxol sensitivity of ESCC in vitro via inhibiting cell proliferation, migration and invasion, and promoting apoptosis. Moreover, circ_0006168 could directly bind to miR-194-5p and JMJD1C was verified as a direct target of miR-194-5p. Mechanically, circ_0006168 was a sponge of miR-194-5p to regulate JMJD1C expression in ESCC cells. Furthermore, JMJD1C overexpression reversed the promotive effect of circ_0006168 knockdown on Taxol sensitivity. Besides, circ_0006168 silence suppressed tumor growth in vivo.

Conclusion

Circ_0006168 facilitated Taxol resistance in ESCC by regulating miR-194-5p/JMJD1C axis, providing a promising therapeutic target for ESCC chemotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-01984-y.

Circ_0006168 Promotes the Migration, Invasion and Proliferation of Esophageal Squamous Cell Carcinoma Cells via miR-516b-5p-Dependent Regulation of XBP1

Background

Circular RNAs (circRNAs) exert important roles in carcinogenesis. Here, we aimed to uncover the working mechanism of circ_0006168 in esophageal squamous cell carcinoma (ESCC) development.

Methods

Western blot assay and real-time quantitative polymerase chain reaction (RT-qPCR) were used to determine protein and RNA expression, respectively. Wound healing assay and transwell migration assay were performed to assess cell migration ability, whereas cell invasion ability was evaluated by transwell invasion assay. 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and colony formation assay were utilized to analyze cell proliferation ability. Xenograft tumor model was utilized to assess the role of X-box binding protein 1 (XBP1) in xenograft tumor growth in vivo. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay and RNA pull down assay were used to verify intermolecular interactions.

Results

XBP1 silencing suppressed the migration, invasion and proliferation of ESCC cells in vitro and restrained the xenograft tumor growth in vivo. MicroRNA-516b-5p (miR-516b-5p) interacted with the 3ʹ untranslated region (3ʹUTR) of XBP1 in ESCC cells. MiR-516b-5p overexpression inhibited the proliferation and motility of ESCC cells. MiR-516b-5p was a molecular target of circ_0006168 in ESCC cells. The interference of circ_0006168 restrained the motility and proliferation of ESCC cells. Circ_0006168 acted as miR-516b-5p sponge to up-regulate XBP1 expression in ESCC cells. MiR-516b-5p silencing or the accumulation of XBP1 largely rescued the proliferation ability and motility in circ_0006168-silenced ESCC cells.

Conclusion

In conclusion, circ_0006168 contributed to ESCC development through promoting the proliferation and motility of ESCC cells via mediating miR-516b-5p/XBP1 axis.

CircDUSP16 Contributes to Cell Development in Esophageal Squamous Cell Carcinoma by Regulating miR-497-5p/TKTL1 Axis

BACKGROUND

The vital roles of circular RNAs in human cancers have been demonstrated. In this study, we aimed to investigate the functions of circDUSP16 in esophageal squamous cell carcinoma (ESCC) development.

METHODS

Quantitative real-time polymerase chain reaction was executed for the expression levels of circDUSP16, DUSP16, miR-497-5p, and transketolase-like-1 (TKTL1) messenger RNA. Actinomycin D assay and RNase R digestion assay were used to determine the characteristics of circDUSP16. Cell Counting Kit-8 assay and colony formation assay were applied for cell proliferation. Transwell assay was performed to assess cell migration and invasion. The glycolysis level was evaluated using specific kits. Protein levels were measured by Western blot assay. RNA pull-down assay and dual-luciferase reporter assay were adopted to explore the relationships among circDUSP16, miR-497-5p, and TKTL1. Murine xenograft model was used to determine the role of circDUSP16 in ESCC in vivo.

RESULTS

CircDUSP16 level was elevated in ESCC tissues, cells, and hypoxia-stimulated ESCC cells. Knockdown of circDUSP16 suppressed hypoxia-induced ESCC cell viability, colony formation, migration, invasion, and glycolysis. For mechanism analysis, circDUSP16 could positively regulate TKTL1 expression by sponging miR-497-5p in ESCC cells. Moreover, miR-497-5p inhibition restored the effects of circDUSP16 knockdown on the malignant behaviors of ESCC cells under hypoxia condition. MiR-497-5p overexpression suppressed hypoxia-induced ESCC cell progression by targeting TKTL1. In addition, circDUSP16 knockdown repressed the tumorigenesis of ESCC in vivo.

CONCLUSIONS

CircDUSP16 knockdown suppressed hypoxia-induced ESCC cell growth, invasion, and glycolysis by regulating TKTL1 expression through sponging miR-497-5p.

Biological roles and potential clinical values of circular RNAs in gastrointestinal malignancies

Circular RNAs (circRNAs), a class of endogenous RNA molecules, are produced by alternative splicing of precursor RNA and are covalently linked at the 5' and 3' ends. Recent studies have revealed that dysregulated circRNAs are closely related to the occurrence and progression of gastrointestinal malignancies. Accumulating evidence indicates that circRNAs, including circPVT1, circLARP4, circ-SFMBT2, cir-ITCH, circRNA_100782, circ_100395, circ-DONSON, hsa_circ_0001368, circNRIP1, circFAT1(e2), circCCDC66, circSMARCA5, circ-ZNF652, and circ_0030235 play important roles in the proliferation, differentiation, invasion, and metastasis of cancer cells through a variety of mechanisms, such as acting as microRNA sponges, interacting with RNA-binding proteins, regulating gene transcription and alternative splicing, and being translated into proteins. With the characteristics of high abundance, high stability, extensive functions, and certain tissue-, time- and disease-specific expressions, circRNAs are expected to provide novel perspectives for the diagnoses and treatments of gastrointestinal malignancies.

Circular RNA hsa_circ_0000700 promotes cell proliferation and migration in Esophageal Squamous Cell Carcinoma by sponging miR-1229

Accumulating evidence has demonstrated that circular RNAs (circRNAs) are involved in the pathogenesis of cancer, including that of esophageal squamous cell carcinoma (ESCC). The current study aimed to investigate the role of hsa_circ_0000700 in ESCC. hsa_circ_0000700, miR-1229, and related functional gene expression was measured by RT-qPCR. To characterize the functions of hsa_circ_0000700 and miR-1229, ESCC cells were infected with hsa_circ_0000700-specific siRNA, miR-1229 mimics, and an inhibitor alone or in combination. Cell Counting Kit-8 (CCK8), colony formation, EdU, flow cytometry, and Transwell assays were employed to evaluate cell proliferation, apoptosis, and migration. Luciferase reporter and RNA immunoprecipitation assays were used to confirm the targeting relationship between hsa_circ_0000700 and miR-1229. Finally, a competing endogenous RNAs (ceRNA) network was built for hsa_circ_0000700, and miR-1229 targets were analyzed by bioinformatics. circ_0000700 expression was significantly upregulated in ESCC cell lines. Actinomycin D and RNase R treatment confirmed that circ_0000700 was more stable than its linear CDH9 mRNA form. Moreover, a cytoplasmic and nuclear fractionation assay suggested that circ_0000700 was mainly distributed in the cytoplasm of ECA-109 and TE-1 cells. In vitro, the proliferative and migratory capacities of ECA-109 and TE-1 cells were inhibited by knocking down circ_0000700 expression. Additionally, miR-1229 silencing reversed the circ_0000700-specific siRNA-induced attenuation of malignant phenotypes. Mechanistically, circ_0000700 was identified as a sponge of miR-1229 and could activate PRRG4, REEP5, and PSMB5 indirectly to promote ESCC progression. In summary, our results suggest that hsa_circ_0000700 functions as an oncogenic factor by sponging miR-1229 in ESCC.

RNA sequencing reveals the expression profiles of circRNA and identifies a four-circRNA signature acts as a prognostic marker in esophageal squamous cell carcinoma

Background

CircRNAs with tissue-specific expression and stable structure may be good tumor prognostic markers. However, the expression of circRNAs in esophageal squamous cell carcinoma (ESCC) remain unknown. We aim to identify prognostic circRNAs and construct a circRNA-related signature in ESCC.

Methods

RNA sequencing was used to test the circRNA expression profiles of 73 paired ESCC tumor and normal tissues after RNase R enrichment. Bioinformatics methods, such as principal component analysis (PCA), t-distributed Stochastic Neighbor Embedding (t-SNE) algorithm, unsupervised clustering and hierarchical clustering were performed to analyze the circRNA expression characteristics. Univariate cox regression analysis, random survival forests-variable hunting (RSFVH), Kaplan–Meier analysis, multivariable Cox regression and ROC (receiver operating characteristic) curve analysis were used to screen the prognostic circRNA signature. Real-time quantitative PCR (qPCR) and fluorescence in situ hybridization(FISH) in 125 ESCC tissues were performed.

Results

Compared with normal tissues, there were 11651 differentially expressed circRNAs in cancer tissues. A total of 1202 circRNAs associated with ESCC prognosis (P < 0.05) were identified. Through bioinformatics analysis, we screened a circRNA signature including four circRNAs (hsa_circ_0000005, hsa_circ_0007541, hsa_circ_0008199, hsa_circ_0077536) which can classify the ESCC patients into two groups with significantly different survival (log rank P < 0.001), and found its predictive performance was better than that of the TNM stage(0.84 vs. 0.66; 0.65 vs. 0.62). Through qPCR and FISH experiment, we validated the existence of the screened circRNAs and the predictive power of the circRNA signature.

Conclusion

The prognostic four-circRNA signature could be a new prognostic biomarker for ESCC, which has high clinical application value.

CircRNAs: a new target for the diagnosis and treatment of digestive system neoplasms

A circRNA is a type of endogenous noncoding RNA that consists of a closed circular RNA molecule formed by reverse splicing; these RNAs are widely distributed in a variety of biological cells. In contrast to linear RNAs, circRNAs have no 5′ cap or 3′ poly(A) tail. They have a stable structure, a high degree of conservation, and high stability, and they are richly and specifically expressed in certain tissues and developmental stages. CircRNAs play a very important role in the occurrence and progression of malignant tumors. According to their origins, circRNAs can be divided into four types: exon-derived circRNAs (ecRNAs), intron-derived circRNAs (ciRNAs), circRNAs containing both exons and introns (EIciRNAs) and intergenic circRNAs. A large number of studies have shown that circRNAs have a variety of biological functions, participate in the regulation of gene expression and play an important role in the occurrence and progression of tumors. In this paper, the structure and function of circRNAs are reviewed, along with their biological role in malignant tumors of the digestive tract, in order to provide a reference for the diagnosis and treatment of digestive system neoplasms.

Cancer-related circular RNA: diverse biological functions

Noncoding RNAs, including long noncoding RNAs (lncRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs), are involved in regulating biological functions. In recent decades, miRNAs and lncRNAs have both inspired a wave of research, but the study of circRNA functions is still in its infancy. Studies have found that circRNAs actively participate in the occurrence and development of various diseases, which emphasizes the importance of circRNAs. Here, we review the features and classification of circRNAs and summarize their functions. Then, we briefly describe how to analyze circRNAs by bioinformatics procedures. In addition, the relationship between circRNAs and cancers is discussed with an emphasis on proving whether circRNAs can be potential biomarkers for the prognosis and diagnosis of cancer.

circRNA hsa_circ_0018414 inhibits the progression of LUAD by sponging miR-6807-3p and upregulating DKK1

Lung adenocarcinoma (LUAD) is a subtype of lung cancer with a high incidence and mortality all over the world. In recent years, circular RNAs (circRNAs) have been verified to be a novel subtype of noncoding RNAs that exert vital functions in various cancers. Our research was designed to investigate the role of circ_0018414 in LUAD. We first observed that circ_0018414 was downregulated in LUAD tissues and cells. Also, low expression of circ_0018414 predicted unfavorable prognosis of LUAD patients. Then, upregulation of circ_0018414 repressed cell proliferation and stemness, while promoting cell apoptosis, in LUAD. Moreover, circ_0018414 overexpression enhanced the expression of its host gene, dickkopf WNT signaling pathway inhibitor 1 (DKK1), therefore inactivating the Wnt/β-catenin pathway. Additionally, circ_0018414 could sponge miR-6807-3p to protect DKK1 mRNA from miR-6807-3p-induced silencing, leading to DKK1 upregulation in LUAD cells. Finally, rescue assays proved that circ_0018414 inhibited the progression of LUAD via the miR-6807-3p/DKK1 axis-inactivated Wnt/β-catenin pathway. The findings in our work indicated circ_0018414 as a tumor inhibitor in LUAD, which might provide a new perspective for LUAD treatment.

Circ-ZDHHC5 Accelerates Esophageal Squamous Cell Carcinoma Progression in vitro via miR-217/ZEB1 Axis

Circular RNA (circRNA) exhibits a covalently closed circular conformation and is structurally stable. Nevertheless, the precise effects exerted by circRNA in esophageal squamous cell carcinoma (ESCC) remains uncertain. circRNA was ascertained by a human circRNA array study and was confirmed by the quantification of reverse transcriptase polymerase reactions. A luciferase reporter, fluorescence in situ hybridization experiment was exploited to explore the interaction between circ-ZDHHC5 and miR-217. The function of circ-ZDHHC5 was determined by siRNA-mediated knockout of circ-ZDHHC5 in in vitro proliferation, migration, and invasion. circ-ZDHHC5, rather than linear ZDHHC5 mRNA, rose in the tissues of patients with ESCC, plasma, and ESCC cell lines in comparison with normal controls. Knockdown of circ-ZDHHC5 inhibited tumorigenesis in ESCC cells, and the co-transfection of si-circ-ZDHHC5 and miR-217 mimics further enhanced the above effect. Noticeably, the present study showed that circ-ZDHHC5 was an miR-217 sponge that modulated the expression of zinc finger E-box binding homeobox 1 (ZEB1), further facilitating ESCC tumorigenesis. As revealed by this study, circ-ZDHHC5 can act as a new potential circular biomarker for detecting ESCC. It provides a novel perceptivity for the treatment of ESCC suggesting that circ-ZDHHC5 could impact on ESCC progression by sponging miR-217 with ZEB1.

Hsa_circ_0004831 serves as a blood-based prognostic biomarker for colorectal cancer and its potentially circRNA-miRNA-mRNA regulatory network construction

Background

Colorectal cancer (CRC) is a common malignant tumor with unsatisfactory overall prognosis. CircRNAs could be promising prognostic biomarkers in cancers, and play important role in the process of tumorigenesis and progression. Here, we explored the role of hsa_circ_0004831 in blood extracellular vesicles and its prognostic value in CRC.

Methods

The circRNA and mRNA expression level matrix in extracellular vesicles of CRC and normal samples were obtained from the exoRBase database. The corresponding miRNA expression level matrix in extracellular vesicles was downloaded from the BBCancer database. Differentially expressed circRNAs, miRNAs and mRNAs were identified using the limma package of R software at the cut-off criteria of fold change (FC) > 2 and adj. p < 0.05. RT-qPCR assay was conducted to measure hsa_circ_0004831 expression level in CRC blood samples. A circRNA-miRNA-mRNA regulatory network of hsa_circ_0004831 was constructed based on competitive endogenous RNA mechanism and differentially expressed genes. The mRNAs co-expressed with hsa_circ_0004831 were screened at the cut-off criteria of pearson |r| > 0.3 and p < 0.05. Gene set enrichment analysis (GSEA) based on co-expressed mRNAs was used to explore the potential molecular function of hsa_circ_0004831.

Results

Differentially expressed circRNAs, miRNAs and mRNAs were identified and hsa_circ_0004831 had a FC value of 3.92 in CRC blood extracellular vesicles. The RT-qPCR assay showed that the hsa_circ_0004831 was up-regulated in CRC blood samples. The overall survival analysis found that high expression of hsa_circ_0004831 was linked with poorer prognosis. Finally, a circRNA-miRNA-mRNA regulatory network of hsa_circ_0004831 was constructed based on down-regulated miR-4326 and 12 up-regulated mRNAs. GSEA indicated that mRNAs co-expressed with hsa_circ_0004831 were involved in EMT, WNT and p53 signaling pathways.

Conclusions

The study confirmed the up-regulation of hsa_circ_0004831 in CRC, and it may act as a vital prognostic biomarker. The circRNA-miRNA-mRNA regulatory network of hsa_circ_0004831 could be used to uncover the tumorigenesis and progression of CRC.

Circular RNAs in gastrointestinal cancer: Current knowledge, biomarkers and targeted therapy (Review)

Circular RNAs (circRNAs) are a type of endogenous non‑coding RNAs that are connected at the 3' and 5' ends by exon or intron cyclization, which forms a covalently closed loop. They are stable, well conserved, exhibit specific expression in mammalian cells and can function as microRNA (miRNA or miR) sponges to regulate the target genes of miRNAs, which influences biological processes. Such as tumor proliferation, invasion, metastasis, apoptosis and tumor stage. circRNAs represent promising candidates for clinical diagnosis and treatment. In the present review, the biogenesis, classification and functions of circRNAs in tumors are briefly summarized and discussed. In addition, the participation of circRNAs in signal transduction pathways regulating gastrointestinal cancer cellular functions is highlighted.

Circ_0072088 Promotes Proliferation, Migration, and Invasion of Esophageal Squamous Cell Cancer by Absorbing miR-377

Circular RNA (circRNA) is an endogenous noncoding RNA. Accumulative investigations have confirmed that circRNAs play a vital role in carcinogenesis and tumor progression. Herein, we examined the expression and mechanism of circ_0072088 in esophageal squamous cell carcinoma (ESCC). As a result, circ_0072088 was significantly overexpressed in ESCC tissues and cells, which was closely associated with tumor size, invasion depth, clinical stage, and lymph node metastasis of esophageal cancer. Nuclear and cytoplasmic separation as well as FISH assays showed that circ_0072088 was mainly localized in the cytoplasm of ESCC cells. RNase R treatment assay revealed that circ_0072088 was steadier than linear ZFR mRNA. circ_0072088 promoted ESCC cell proliferation, migration and invasion in vitro, and cell proliferation in vivo. Mechanistically, circ_0072088 upregulated VEGF gene expression by acting as the sponge of miRNA-377. In conclusion, circ_0072088 might be used as a diagnostic biomarker and therapeutic target for ESCC.

circPTCH1 promotes invasion and metastasis in renal cell carcinoma via regulating miR-485-5p/MMP14 axis

Background: Circular RNAs (circRNAs) are a new class of non-coding RNAs (ncRNAs) that are derived from exons or introns by special selective shearing. circRNAs have been shown to play critical roles in various human cancers. However, their roles in renal cell carcinoma (RCC) and the underlying mechanisms remain largely unknown.

Methods: A novel circRNA-circPTCH1, was identified from a microarray analysis of five paired RCC tissues. Then, we validated its expression and characterization through qRT-PCR, gel electrophoresis, RNase R digestion assays and Sanger sequencing. Functional experiments were performed to determine the effect of circPTCH1 on RCC progression both in vitro and in vivo. The interactions between circPTCH1 and miR-485-5p were clarified by RNA pull-down, luciferase reporter and RNA immunoprecipitation (RIP) assays.

Results: We observed that circPTCH1 was up-regulated in RCC cell lines and tumor samples, and higher levels of circPTCH1 were significantly correlated with worse patient survival, advanced Fuhrman grade and greater risk of metastases. Elevated circPTCH1 expression led to increased migration and invasion of RCC cells both in vitro and in vivo whereas silencing circPTCH1 decreased migration and invasion and impeded the epithelial-mesenchymal transition (EMT) of RCC cells. Mechanistically, we elucidated that circPTCH1 could directly bind miR-485-5p and subsequently suppress expression of the target gene MMP14.

Conclusion: circPTCH1 promotes RCC metastasis via the miR-485-5p/MMP14 axis and activation of the EMT process. Targeting circPTCH1 may represent a promising therapeutic strategy for metastatic RCC.

Circular RNA circLPAR3 Facilitates Esophageal Squamous Cell Carcinoma Progression Through Upregulating HMGB1 via Sponging miR-375/miR-433

Background

Circular RNAs (circRNAs) are critical regulators of many diseases, including esophageal squamous cell carcinoma (ESCC). A recent study has shown that circLPAR3 is highly expressed in ESCC, but its role and mechanism in ESCC are still unclear.

Methods

The expression levels of circLPAR3, microRNA-375 (miR-375), miR-433, and high-mobility group box 1 (HMGB1) were measured by quantitative real-time polymerase chain reaction (qRT-PCR). The circular characteristic and localization of circLPAR3 were identified by Ribonuclease R (RNase R) and nuclear-cytoplasmic separation assay. Also, cell proliferation was detected by cell counting kit-8 (CCK-8) and colony formation assays. Cell migration and invasion were tested by transwell assay. Moreover, Western blot (WB) analysis was used to test the levels of proliferation and metastasis-related protein, as well as the HMGB1 protein. Besides, mice xenograft models were constructed to assess the effect of circLPAR3 on ESCC tumor growth in vivo. In addition, dual-luciferase reporter and RNA pull-down assays were used to identify the mechanism of circLPAR3.

Results

CircLPAR3 was upregulated in ESCC tissues and cells, and its high expression was related to the poor prognosis of ESCC patients. CircLPAR3 was a stable cyclic transcript, mainly located in the cytoplasm, and its knockdown hindered the proliferation, migration and invasion of ESCC cells and inhibited ESCC tumor growth in vivo. MiR-375/miR-433 could be sponged by circLPAR3, and their inhibitors could reverse the suppression effect of silenced circLPAR3 on ESCC progression. HMGB1 could be targeted by miR-375/miR-433, and its overexpression also could invert the inhibition effect of circLPAR3 knockdown on ESCC progression.

Conclusion

CircLPAR3 might play an oncogenic role in ESCC through sponging miR-375/miR-433 to promote HMGB1 expression, which might provide a theoretical basis for circLPAR3 to become a biomarker for ESCC therapy.

Circular RNAs and esophageal cancer

As a new kind of RNA, circular RNA (circRNA) is a endogenous non-coding RNA with circular structure, which has the characteristics of universality, stability, conservatism and specificity. CircRNA can specifically bind to microRNAs (miRNAs) in the form of competitive endogenous RNA, thus directly or indirectly regulating the expression of related genes. In addition to the role of sponge, circRNA also regulates parental gene expression, transcriptional translation and protein modification; and it can be used as a biomarker to develop potential diagnosis and treatment methods and evaluate prognosis. Due to changes in dietary habits and genetic factors, the morbidity and mortality of esophageal cancer (EC) in the world are still high, and are prone to early metastasis. Although the diagnosis and treatment techniques have been improved in recent years, the early diagnosis of EC is not common, and the 5-year survival rate of patients is still very low. This article reviews the function and significance of circRNA and discusses the research progress of circRNA as biomarkers in EC.

circ_KIAA1429 accelerates hepatocellular carcinoma advancement through the mechanism of m6A-YTHDF3-Zeb1

AIMS

Hepatocellular carcinoma (HCC), one of the most common cancer, causes the fourth cancer-related deaths around the world. N6-methyladenosine (m⁶A) has been reported to mediate circRNA translation in cancer biology. However, the mechanisms by which m⁶A and circRNA in post-transcriptional in HCC progression remain poorly understood. This study aimed to explore the mechanisms by which m⁶A and circRNA in post-transcriptional in HCC progression.

MAIN METHODS

circ_KIAA1429 (hsa_circ_0084922) expression profiles in matched normal and HCC tissues were detected using microarray analysis. The biological roles of circ_KIAA1429 in progression of HCCC were measured both in vitro and in vivo.

KEY FINDINGS

In this study, we found hsa_circ_0084922, which came from KIAA1429, named circ_KIAA1429, was upregulated in HCC cells and tumor tissues. Overexpression of circ_KIAA1429 can facilitate HCC migration, invasion, and EMT process. However, knockdown of circ_KIAA1429 lead to the opposite results. Furthermore, it was demonstrated that Zeb1 was the downstream target of circ_KIAA1429. Up-regulation of Zeb1 led to HCC cells metastasis induced by circ_KIAA1429. In addition, YTHDF3 enhanced Zeb1 mRNA stability via an m⁶A dependent manner.

SIGNIFICANCE

This study revealed that circ_KIAA1429 could accelerate HCC advancement, maintained the expression of Zeb1 through the mechanism of m⁶A-YTHDF3-Zeb1 in HCC. What's more, it might represent a potential therapeutic target in HCC.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

Role of non-coding RNAs in esophageal carcinoma

In recent years, the research on the role of non-coding RNAs (ncRNAs) in tumors has received more and more attention. Although research on the role of ncRNAs in the early diagnosis, disease monitoring, treatment guidance, and prognosis prediction of esophageal carcinoma has been gradually carried out, there are still many problems that need to be addressed. In the current paper, I review the progress in the research of ncRNAs in esophageal carcinoma, with an aim to help provide new strategies for the prevention and treatment of esophageal carcinoma.

Knockdown of circ_0003340 induces cell apoptosis, inhibits invasion and proliferation through miR-564/TPX2 in esophageal cancer cells

Circular RNA (circRNA) is a promising biomarker of cancer occurrence and development. The different expression levels of circRNAs in various cancers also make them possible therapeutic targets. In this work, we researched the function and underlying mechanisms of circ_0003340 (circ3340) in esophageal cancer EC1 and EC9706 cells. Firstly, we found the expression levels of circ3340 are higher in ESCC and two esophageal cancer cells than in adjacent normal tissues and Het-1a cells. Bioinformatics analysis showed circ3340 has a binding site with miR-564. This was verified by luciferase assay, which revealed that miR-564 can be sponged by circ3340, and that the TPX2 3'UTR is a direct target of miR-564. Upregulation of miR-564 decreased TPX2 protein levels, as shown by Western blot. Moreover, knockdown of circ3340 or enhancement of miR-564 expression had similar effects in EC1 and EC9706 cells, i.e., inducing cell apoptosis, inhibiting cell proliferation, and arresting cell invasion. Downregulation of circ3340 had a negative influence on EC1 and EC9706 cells by affecting the miR-564/TPX2 pathway. Additionally, animal experiments revealed that downregulation of circ3340 inhibited tumor growth in vivo, making circ3340 a potential therapeutic target for patients with esophageal squamous cell cancer.

The function and mechanism of circular RNAs in gastrointestinal tumours

Gastrointestinal tumours are tumours that originate in the digestive tract and have extremely high morbidity and mortality. The main categories include: oesophageal, gastric, and colorectal cancers. Circular RNAs are a new class of non‐coding RNAs with a covalent closed‐loop structure without a 5’ cap or a 3’ poly A tail, which can encode a small amount of polypeptide. Recent studies have shown that circRNAs are involved in multiple biological processes during the development of gastrointestinal tumours including proliferation, invasion and metastasis, radio‐ and chemoresistance, and inflammatory responses. Also, the clinical and pathological characteristics of the patient, such as staging and lymph node metastasis, are closely associated with the expression level of circRNAs. Further investigation of the function and the role of circRNAs in the development of gastrointestinal tumours will provide new directions for its clinical diagnosis and treatment.

Role of circular RNAs in digestive system malignancies

Gastrointestinal malignancies have very high morbidity and mortality worldwide, seriously endangering human life and health. However, there are still many challenges in their early diagnosis and effective treatment. Circular RNAs (circRNAs) are a new class of endogenous long non-coding RNAs characterized by covalently closed loops. Because they do not have a 5' cap structure and a 3' poly(A) tail, circRNAs have higher stability, abundance, and evolutionary conservation than linear RNAs. CircRNAs are expressed in a tissue- or developmental stage-specific manner. These features produce various potential biological functions of circRNAs, such as acting as sponges of microRNAs (miRNAs; circRNAs bind to miRNAs to eliminate the inhibitory effect of miRNAs on their target genes and play a role of competing endogenous RNAs) or forming RNA protein complexes through RNA binding proteins, participating in the regulation of protein functions. In recent years, more and more studies have shown that circRNAs play a vital role in the occurrence and development of digestive system tumors. At the same time, their enormous potential as a biomarker and therapeutic target is also evolving. In this review, we summarize the latest research progress of circRNAs in digestive system malignancies.

Dysregulation of CircRNA_0001946 Contributes to the Proliferation and Metastasis of Colorectal Cancer Cells by Targeting MicroRNA-135a-5p

This study was aimed to evaluate the potential function of circ-0001946 in the progression of colorectal cancer (CRC) and the related regulatory mechanism. First, the expression levels of circRNA_0001946 and microRNA-135a-5p (miR-135a-5p) in normal and CRC tissues were measured by quantitative real-time polymerase chain reaction (RT-qPCR). In addition, cell proliferation was assessed by the Cell Counting Kit-8 (CCK-8) assay, cell migration and invasion were evaluated by Transwell assays, and the cell cycle patterns were determined by flow cytometry. The relationship between the expression levels of circ_0001946 and miR-135a-5p was determined by dual-luciferase reporter assays. Our data showed that the expression of circ_0001946 was upregulated in CRC tissues, which was negatively correlated with tumor size, histologic grade, lymphatic metastasis, and TMN stage, and patients with circ_0001946 overexpression were more likely to have a poor prognosis. In addition, in vitro experiments showed that silencing circ_0001946 inhibited the epithelial–mesenchymal transition (EMT) pathway and markedly suppressed CRC cell growth, migration, and invasion. Furthermore, we discovered that the transfection of miR-135a-5p mimics could reverse the antitumor effects of circRNA_0001946 downregulation. To summarize, this study revealed that circRNA_0001946 might act as a tumor promoter by activating the miR-135a-5p/EMT axis and may be a promising treatment target for CRC.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

Circular RNA (circRNA) is an intriguing class of RNA with covalently closed-loop structure and is highly stable and conservative. As new members of the ncRNAs, the function, mechanism, potential diagnostic biomarker, and therapeutic target have raised increased attention. Most circRNAs are presented with characteristics of abundance, stability, conservatism, and often exhibiting tissue/developmental-stage-specific manner. Over 30,000 circRNAs have been identified with their unique structures to maintain stability more easily than linear RNAs. An increased numbers of circRNAs are dysregulated and involved in several biological processes of malignance, such as tumorigenesis, growth, invasion, metastasis, apoptosis, and vascularization. Emerging evidence suggests that circRNAs play important roles by acting as miRNA sponge or protein scaffolding, autophagy regulators, and interacting with RNA-binding protein (RBP), which may potentially serve as a novel promising biomarker for prevention, diagnosis and therapeutic target for treatment of human cancer with great significance either in scientific research or clinic arena. This review introduces concept, major features of circRNAs, and mainly describes the major biological functions and clinical relevance of circRNAs, as well as expressions and regulatory mechanisms in various types of human cancer, including pathogenesis, mode of action, potential target, signaling regulatory pathways, drug resistance, and therapeutic biomarkers. All of which provide evidence for the potential utilities of circRNAs in the diagnosis and treatment of cancer.

Circular RNA circ_0001105 Inhibits Progression and Metastasis of Osteosarcoma by Sponging miR-766 and Activating YTHDF2 Expression

Background

Circular RNAs (circRNAs) play vital roles in the modulation of tumor progression. This study explored the biological functions of circ_0001105 in the progression of osteosarcoma (OS).

Methods

qRT-PCR and in situ hybridization (ISH) were performed to detect the expression status of circ_0001105 in cells and tissues. Bioinformatics analysis, dual-luciferase reporter gene assay, Western blot and qRT-PCR were performed to determine the relationships among RNAs. The CCK-8, colony formation, EdU, transwell and wound healing assays were conducted to evaluate the cell growth, invasion and migration of OS cells. Tumor xenografts were established to investigate the effects of circ_0001105 on tumor growth in vivo. Lastly, the protein expression of YTHDF2 in OS tissues was measured using immunohistochemical staining.

Results

Data showed that circ_0001105 and YTHDF2 were significantly lower, while miR-766 was higher in OS tissues compared to adjacent tissues. Low expression of circ_0001105 or YTHDF2 was associated with poor survival of OS patients as demonstrated by the Kaplan-Meier analysis. In addition, miR-766 was identified as a direct binding target of circ_0001105 and YTHDF2. Ectopic overexpression of circ_0001105 or YTHDF2 significantly suppressed OS cell viability and invasion through regulating miR-766. Last, overexpression of circ_0001105 significantly attenuated in vivo tumor growth.

Conclusion

Our findings suggest that circ_0001105 inhibits OS progression, at least partially, by regulating miR-766/YTHDF2 signaling pathway.

circRNA circFUT8 Upregulates Krüpple-like Factor 10 to Inhibit the Metastasis of Bladder Cancer via Sponging miR-570-3p

Circular RNAs (circRNAs) are broad and diverse endogenous non-coding RNAs. Emerging evidence has revealed that circRNAs play pivotal roles in cancers, regulating the gene expression by acting as a microRNA (miRNA) sponge. However, the biological functions of circRNAs in bladder cancer (BCa) remain largely unknown. In this study, we identified an altered circRNA, termed circFUT8, by screening RNA sequencing data generated from three BCa tissues and matched adjacent normal bladder tissues. Quantitative real-time PCR analysis demonstrated that circFUT8 was downregulated in BCa tissues and correlated with patients’ prognosis, histological grade, and lymph node (LN) metastasis. Functionally, gain- and loss-of-function assays indicated that circFUT8 inhibited the migration and invasion of BCa cell lines in vitro and LN metastasis in vivo. Mechanistically, circFUT8 directly bound to miR-570-3p and partially abrogated its oncogenic role, and miR-570-3p could suppress the expression of tumor suppressor gene Krüpple-like factor 10 (KLF10) by binding its 3′ untranslated region (3′ UTR). Moreover, we found that circFUT8 promoted the expression of KLF10 by competitively sponging miR-570-3p. In conclusion, circFUT8 functions as a tumor suppressor in BCa cells by targeting the miR-570-3p/KLF10 axis and may serve as a potential biomarker and therapeutic target for the management of BCa patients with LN metastasis.

Prognostic and Diagnostic Significance of circRNA Expression in Esophageal Cancer: A Meta-analysis

BACKGROUND AND AIMS

Circular RNA (circRNA) demonstrates potential biological application in various solid tumors. We intended to evaluate the diagnostic, prognostic, and clinicopathological value of circRNA for esophageal cancer (EC).

METHODS

We screened relative studies from Pubmed, Embase, Web of Science, and Cochrane Library. The diagnostic role of circRNAs was testified by pooled sensitivity and specificity. Pooled odds ratio (OR) and pooled hazard ratio (HR) were computed to appraise the clinicopathological and prognostic value, respectively.

RESULTS

There were total 15 articles suitable with our included criteria, in which 7 for diagnosis, 8 for prognosis, and 9 for clinicopathological features. The pooled sensitivity and specificity were 0.77 and 0.80, respectively, while the AUC was 0.85. Patients with aberrant expression of circRNAs had a 2.92-fold increased risk of developing EC. The proportion of EC patients with normal circRNA expression only accounted for 29%. Upregulated expression of oncogenic circRNA was correlated with poor clinicopathological features, including lymph node metastasis, tumor size, and T classification, while downregulation of tumor-suppressor circRNA was contributed to worse TNM stage. As for prognosis, upregulated expression of circRNA carried out a diverse survival outcome, with a pooled HR of 2.76 for tumor promoter and that of 0.21 for tumor suppressor. High expression of oncogenic circRNA in both plasma and tumor tissue would lead to a shorter survival duration.

CONCLUSION

circRNAs might be a promising biomarker for diagnosis, prognosis, and clinicopathological features of EC.

Circular RNAs and gastrointestinal cancers: Epigenetic regulators with a prognostic and therapeutic role

Both environmental and genetic factors are involved in the initiation and development of gastrointestinal cancer. Covalent closed circular RNAs (circRNAs) are produced by a mechanism called "back-splicing" from mRNAs. They are highly stable and show cell and tissue specific expression patterns. Although some functions such as "microRNA sponge" and "RNA binding protein sponge" have been reported for a small number of circRNAs, the function of thousands of other circRNAs is still unknown. Dysregulation of circRNAs has been reported in many GI cancers and are involved in metastasis and invasion. CircRNAs have been reported to be useful as prognostic markers and targets for developing new treatments. We first describe the properties and biogenesis of circRNAs. We then summarize recent reports about circRNA functions, expression status, and their potential to be used as biomarkers in GI cancers including, gastric cancer, colorectal cancer, esophageal cancer, hepatocellular carcinoma, gallbladder cancer and pancreatic cancer.