Circular RNA circ-Foxo3 inhibits esophageal squamous cell cancer progression via the miR-23a/PTEN axis

Circular RNAs: Epigenetic regulators of PTEN expression and function in cancer

Epigenetic regulation of gene expression, without altering the DNA sequence, is involved in many normal cellular growth and division events, as well as diseases such as cancer. Epigenetics is no longer limited to DNA methylation, and histone modification, but regulatory non-coding RNAs (ncRNAs) also play an important role in epigenetics. Circular RNAs (circRNAs), single-stranded RNAs without 3' and 5' ends, have recently emerged as a class of ncRNAs that regulate gene expression. CircRNAs regulate phosphatase and tensin homolog (PTEN) expression at various levels of transcription, post-transcription, translation, and post-translation under their own regulation. Given the importance of PTEN as a tumor suppressor in cancer that inhibits one of the most important cancer pathways PI3K/AKT involved in tumor cell proliferation and survival, significant studies have been conducted on the regulatory role of circRNAs in relation to PTEN. These studies will be reviewed in this paper to better understand the function of this protein in cancer and explore new therapeutic approaches.

Non‑coding RNA: A promising diagnostic biomarker and therapeutic target for esophageal squamous cell carcinoma (Review)

Esophageal cancer (EC) is a common form of malignant tumor in the digestive system that is classified into two types: Esophageal squamous cell carcinomas (ESCC) and esophageal adenocarcinoma. ESCC is known for its early onset of symptoms, which can be difficult to identify, as well as its rapid progression and tendency to develop drug resistance to chemotherapy and radiotherapy. These factors contribute to the high incidence of disease and low cure rate. Therefore, a diagnostic biomarker and therapeutic target need to be identified for ESCC. Non-coding RNAs (ncRNAs) are a class of molecules that are transcribed from DNA but do not encode proteins. Initially, ncRNAs were considered to be non-functional segments generated during transcription. However, with advancements in high-throughput sequencing technologies in recent years, ncRNAs have been associated with poor prognosis, drug resistance and progression of ESCC. The present study provides a comprehensive overview of the biogenesis, characteristics and functions of ncRNAs, particularly focusing on microRNA, long ncRNAs and circular RNAs. Furthermore, the ncRNAs that could potentially be used as diagnostic biomarkers and therapeutic targets for ESCC are summarized to highlight their application value and prospects in ESCC.

Circ-FOXO3 inhibits triple-negative breast cancer growth and metastasis via regulating WHSC1-H3K36me2-Zeb2 axis

Circular RNAs (circRNAs), a subclass of non-coding RNAs characterized by covalently closed continuous loops, play a key role in tumorigenesis and aggressiveness. However, the potential molecular mechanism of circRNAs in triple-negative breast cancer (TNBC) remains largely unknown. Exploring their roles and mechanisms in TNBC progression may help identify new diagnostic markers and therapeutic targets. In this study, we found that circ-FOXO3 was dramatically downregulated in TNBC tissues and blood samples from patients with TNBC. Notably, low circ-FOXO3 expression in TNBC tissues and bloods was associated with lymph node metastasis and unfavorable outcomes in patients with TNBC. Overexpression of circ-FOXO3 significantly inhibited the growth, invasion, and metastasis of TNBC cells both in vitro and in vivo. Moreover, we demonstrated that circ-FOXO3 was predominantly expressed in the cytoplasm and directly interacted with Wolf-Hirschhorn syndrome candidate 1 (WHSC1), thereby inhibiting WHSC1 nuclear localization and activity, resulting in the inhibition of H3K36me2 modifications at the Zeb2 promoter, ultimately inhibiting Zeb2 expression and halting TNBC growth and metastasis. Taken together, these results reveal the tumor-suppressive functions of circ-FOXO3 in inhibiting WHSC1-mediated H3K36me2 modification of Zeb2, suggesting that circ-FOXO3 could serve as a potential novel predictive prognostic biomarker and therapeutic target for TNBC.

Circular RNA circCHSY1 silencing inhibits the malignant progression of esophageal squamous cell carcinoma

BACKGROUND

CircRNAs play a crucial role in the regulation of various cancers. This study aims to investigate the involvement of circCHSY1 in the development of esophageal squamous cell carcinoma (ESCC).

METHODS

RNA levels were quantified using qRT-PCR, and protein levels were measured by western blot. The stability of circCHSY1 was analyzed using RNase R. The functional effect of circCHSY1 on cell behavior was evaluated by CCK-8, EdU, flow cytometry, transwell, tube formation, and xenograft tumor model assays. The associations among circCHSY1, miR-1229-3p, and Tectonic-1 (TCTN1) were certified by bioinformatics analysis, dual-luciferase reporter assay, and RNA pull-down assay.

RESULTS

CircCHSY1 was up-regulated in both ESCC tissues and cell lines in comparison with the control groups. Knockdown of circCHSY1 inhibited the proliferation, migration, invasion, and tube formation and promoted apoptosis of ESCC cells. Mechanistically, circCHSY1 targeted miR-1229-3p, which was downregulated in ESCC tissues and cells. Inhibition of miR-1229-3p attenuated the effects mediated by circCHSY1 suppression. Besides, miR-1229-3p bound to TCTN1, and TCTN1 overexpression restored miR-1229-3p-induced effects in ESCC cells. Animal experiments revealed that circCHSY1 silencing suppressed tumor tumorigenesis in vivo.

CONCLUSION

CircCHSY1 contributed to ESCC cell malignancy, and the underlying mechanism involved the circCHSY1/miR-1229-3p/TCTN1 axis, providing potential therapeutic targets for ESCC.

MicroRNAs: A novel signature in the metastasis of esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a malignant epithelial tumor, characterized by squamous cell differentiation, it is the sixth leading cause of cancer-related deaths globally. The increased mortality rate of ESCC patients is predominantly due to the advanced stage of the disease when discovered, coupled with higher risk of metastasis, which is an exceedingly malignant characteristic of cancer, frequently leading to a high mortality rate. Unfortunately, there is currently no specific and effective marker to predict and treat metastasis in ESCC. MicroRNAs (miRNAs) are a class of small non-coding RNA molecules, approximately 22 nucleotides in length. miRNAs are vital in modulating gene expression and serve pivotal regulatory roles in the occurrence, progression, and prognosis of cancer. Here, we have examined the literature to highlight the intimate correlations between miRNAs and ESCC metastasis, and show that ESCC metastasis is predominantly regulated or regulated by genetic and epigenetic factors. This review proposes a potential role for miRNAs as diagnostic and therapeutic biomarkers for metastasis in ESCC metastasis, with the ultimate aim of reducing the mortality rate among patients with ESCC.

Role of circular RNAs and gut microbiome in gastrointestinal cancers and therapeutic targets

Gastrointestinal cancers are a huge worldwide health concern, which includes a wide variety of digestive tract cancers. Circular RNAs (circRNAs), a kind of non-coding RNA (ncRNAs), are a family of single-stranded, covalently closed RNAs that have become recognized as crucial gene expression regulators, having an impact on several cellular functions in cancer biology. The gut microbiome, which consists of several different bacteria, actively contributes to the regulation of host immunity, inflammation, and metabolism. CircRNAs and the gut microbiome interact significantly to greatly affect the growth of GI cancer. Several studies focus on the complex functions of circRNAs and the gut microbiota in GI cancers, including esophageal cancer, colorectal cancer, gastric cancer, hepatocellular cancer, and pancreatic cancer. It also emphasizes how changed circRNA expression profiles and gut microbiota affect pathways connected to malignancy as well as how circRNAs affect hallmarks of gastrointestinal cancers. Furthermore, circRNAs and gut microbiota have been recommended as biological markers for therapeutic targets as well as diagnostic and prognostic purposes. Targeting circRNAs and the gut microbiota for the treatment of gastrointestinal cancers is also being continued to study. Despite significant initiatives, the connection between circRNAs and the gut microbiota and the emergence of gastrointestinal cancers remains poorly understood. In this study, we will go over the most recent studies to emphasize the key roles of circRNAs and gut microbiota in gastrointestinal cancer progression and therapeutic options. In order to create effective therapies and plan for the future gastrointestinal therapy, it is important to comprehend the functions and mechanisms of circRNAs and the gut microbiota.

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.

Curcumin modulates cell type-specific miRNA networks to induce cytotoxicity in ovarian cancer cells

AIM

To understand the epigenetic role of curcumin, a natural polyphenolic compound extracted from the spice Curcuma longa in inducing cytotoxicity in two molecularly distinct ovarian cancer cell lines: PA1 and A2780.

MATERIALS AND METHODS

An integrated mRNA-miRNA sequence analysis was performed to determine the curcumin-induced mRNA-miRNA regulatory networks in the induction of cytotoxicity. The miRNA-mRNA pathways, the miRNAs and their targets implicated in apoptosis, autophagy, DNA damage, and stemness markers were validated. Gene/miRNA expressions were validated using qPCR and protein expressions by western blotting. Curcumin-induced oncogenic /tumor-suppressor miRNAs were profiled utilising the oncomiRdb database. Similarly, the expressions of oncogenes/tumor suppressor genes were profiled and correlated with the TCGA ovarian cancer dataset. A dual luciferase assay was performed to investigate the interaction of miR-199a-5p to its direct target, DDR1.

KEY FINDINGS

The expression of several miRNAs demonstrated an inverse correlation with their respective direct targets. In curcumin-treated PA1 cells, miR-335-5p target ATG5 (autophagic), and OCT4 (pluripotent gene) were downregulated, miR-32a target PTEN (tumor suppressor) was upregulated, miR-1285 target P53 (tumor suppressor) was upregulated, and both miR-182-5p and miR-503-3p target BCL2, were down-regulated. Contrastingly, in curcumin-treated A2780 cells, miR-181a-3p target ATG5, miR-30a-5p, and miR-216a target BECN1 (autophagic) were upregulated, and miR-129a-5p target BCL2 were downregulated. The reversal of the oncomiR/TSmiR profile revealed suppression of oncogenic processes by curcumin. Curcumin treatment induced a moderate cisplatin-sensitisation effect and impaired epithelial-to-mesenchymal transition (EMT) characteristics. Curcumin also regulated the miR-199a-5p/DDR1 axis with a decrease in collagen deposition.

SIGNIFICANCE

The activity of curcumin is cell-type specific. Distinct miRNA regulatory networks were activated to induce multiple modes of cellular cytotoxicity in these ovarian cancer cells. This study further highlights the molecular mechanism of curcumin action in ovarian cancers establishing its candidacy as a promising drug candidate.

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.

Role of circ-FOXO3 and miR-23a in radiosensitivity of breast cancer

Identifying the radiosensitivity of cells before radiotherapy (RT) in breast cancer (BC) patients allows appropriate switching between routinely used treatment regimens and reduces adverse side effects in exposed patients. In this study, blood was collected from 60 women diagnosed with Invasive Ductal Carcinoma (IDC) BC and 20 healthy women. To predict cellular radiosensitivity, a standard G2-chromosomal assay was performed. From these 60 samples, 20 BC patients were found to be radiosensitive based on the G2 assay. Therefore, molecular studies were finally performed on two equal groups (20 samples each) of patients with and without cellular radiosensitivity. QPCR was performed to examine the expression levels of circ-FOXO3 and miR-23a in peripheral blood mononuclear cells (PBMCs) and RNA sensitivity and specificity were determined by plotting Receiver Operating Characteristic (ROC) curves. Binary logistic regression was performed to identify RNA involvement in BC and cellular radiosensitivity (CR) in BC patients. Meanwhile, qPCR was used to compare differential RNA expression in the radiosensitive MCF-7 and radioresistant MDA-MB-231 cell lines. An annexin -V FITC/PI binding assay was used to measure cell apoptosis 24 and 48 h after 2 Gy, 4 Gy, and 8 Gy gamma-irradiation. Results indicated that circ-FOXO3 was downregulated and miR-23a was upregulated in BC patients. RNA expression levels were directly associated with CR. Cell line results showed that circ-FOXO3 overexpression induced apoptosis in the MCF-7 cell line and miR-23a overexpression inhibited apoptosis in the MDA-MB-231 cell line. Evaluation of the ROC curves revealed that both RNAs had acceptable specificity and sensitivity in predicting CR in BC patients. Binary logistic regression showed that both RNAs were also successful in predicting breast cancer. Although only circ-FOXO3 has been shown to predict CR in BC patients, circ-FOXO3 may function as a tumor suppressor and miR-23a may function as oncomiR in BC. Circ-FOXO3 and miR-23a may be promising potential biomarkers for BC prediction. Furthermore, Circ-FOXO3 could be a potential biomarker for predicting CR in BC patients.

Bibliometric Analysis of Global Research on Circular RNA: Current Status and Future Directions

Circular RNAs (circRNAs) have gained significant attention in recent years. This bibliometric analysis aimed to provide insights into the current state and future trends of global circRNA research. The scientific output on circRNAs from 2010 to 2022 was retrieved from the Web of Science Core Collection with circRNA-related terms as the subjects. Key bibliometric indicators were calculated and evaluated using CiteSpace. A total of 7385 studies on circRNAs were identified. The output and citation number have increased rapidly after 2015. China, the USA, and Germany were top three publishing countries. Currently, circCDR1as, circHIPK3, circPVT1, circSHPRH, and circZNF609 are the most studied circRNAs; and all are related to cancer. The theme of research have shifted from transcript, exon circularization and miRNA sponge topics to the transcriptome, tumor suppressor, and biomarkers, indicating that research interests have evolved from basic to applied research. CircRNAs will continue to be a highly active research area in the near future. From the current understanding of circRNA characterization and regulatory mechanisms as miRNA sponges in cancer, future directions may examine potential diagnostic and therapeutic roles of circRNAs in cancers or the function and mechanism of circRNAs in other diseases.

IGF2BP2-induced circRUNX1 facilitates the growth and metastasis of esophageal squamous cell carcinoma through miR-449b-5p/FOXP3 axis

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the most common digestive malignancies with relatively high morbidity and mortality. Emerging evidence suggests circular RNAs (circRNAs) play critical roles in tumor cell malignancy. However, the biological function and clinical significance of many circRNAs in ESCC remain elusive.

METHODS

The expression level and clinical implication of circRUNX1 in ESCC tissues were evaluated using qRT-PCR. In vitro and in vivo functional studies were conducted to investigate the underlying biological effects of circRUNX1 on ESCC cell growth and metastasis. Moreover, bioinformatics analysis, RNA sequencing (RNA-seq), RNA immunoprecipitation (RIP) assays, dual-luciferase reporter assays, and rescue experiments were performed to explore the relationships between circRUNX1, miR-449b-5p, Forkhead box protein P3 (FOXP3), and insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2).

RESULTS

CircRUNX1 was found to be significantly up-regulated in ESCC tissues and associated with TNM stage and differentiation grade. Functionally, circRUNX1 promoted ESCC cell proliferation and metastasis in vitro and in vivo. CircRUNX1 enhanced FOXP3 expression by competitively sponging miR-449b-5p. Notably, both miR-449b-5p mimics and FOXP3 knockdown restored the effects of circRUNX1 overexpression on cell proliferation and metastasis. Furthermore, IGF2BP2 binding to circRUNX1 prevented its degradation.

CONCLUSIONS

IGF2BP2 mediated circRUNX1 functions as an oncogenic factor to facilitate ESCC progression through the miR-449b-5p/FOXP3 axis, implying that circRUNX1 has the potential to be a promising diagnostic marker and therapeutic target for ESCC patients.

Functions and clinical significance of circular RNAs in acute myeloid leukemia

Circular RNAs (circRNAs) are a class of covalently closed single-stranded RNA molecules. Four types of circRNAs have been reported in animal cells, and they have typical characteristics in their biogenesis, nuclear export and degradation. Advances in our understanding of the molecular functions of circRNAs in sponging microRNAs, modulating transcription, regulating RNA-binding proteins, as well as encoding proteins have been made very recently. Dysregulated circRNAs are associated with human diseases such as acute myeloid leukemia (AML). In this review, we focus on the recently described mechanisms, role and clinical significance of circRNAs in AML. Although great progress of circRNAs in AML has been achieved, substantial efforts are still required to explore whether circRNAs exert their biological function by other mechanisms such as regulation of gene transcription or serving as translation template in AML. It is also urgent that researchers study the machineries regulating circRNAs fate, the downstream effectors of circRNAs modulatory networks, and the clinical application of circRNAs in AML.

CircRNA has_circ_0017109 promotes lung tumor progression via activation of Wnt/β-catenin signaling due to modulating miR-671-5p/FZD4 axis

INTRODUCTION

Accumulating evidence highlights the critical roles of circular RNAs (circRNAs) in the malignant progression of cancers. In this study, we investigated the expression pattern of a newly identified circRNA (hsa_circ_0017109) in non-small cell lung cancer (NSCLC), and examined its downstream molecular targets.

METHODS

Quantitative real-time PCR (qRT-PCR) and Western blotting (WB) were conducted to quantify gene and protein expression. In vitro functional assays such as colony formation assay, cell counting kit-8 (CCK-8) and flow cytometry were used to study cell proliferation and apoptosis. RNA pull-down assay, luciferase reporter assay and RNA immunoprecipitation were performed to validate molecular interaction. Mouse xenograft model of NSCLC cells was used to assess the role of circ_0017109 in tumorigenesis.

RESULTS

Circ_0017109 was upregulated in NSCLC tumor samples and cells. Silencing circ_0017109 impaired cell proliferation and promoted apoptosis in NSCLC cells, and circ_0017109 knockdown suppressed in vivo tumorigenesis of NSCLC cells in mouse xenograft model. MiR-671-5p was identified as a target of circ_0017109, and circ_0017109 negatively impacted on miR-671-5p expression. MiR-671-5p downregulated FZD4 and dampened the activity of Wnt/β-catenin signaling pathway. Circ_0017109 modulated FZD4 expression by suppressing miR-671-5p activity.

CONCLUSIONS

Elevated circ_0017109 expression promotes tumor progression of NSCLC by modulating miR-671-5p/FZD4/β-catenin axis.

Morphine-mediated release of astrocyte-derived extracellular vesicle miR-23a induces loss of pericyte coverage at the blood-brain barrier: Implications for neuroinflammation

Opioids such as morphine are the most potent and efficacious drugs currently available for pain management. Paradoxically, opioids have also been implicated in inducing neuroinflammation and associated neurocognitive decline. Pericytes, a critical component of the neurovascular unit (NVU), are centrally positioned between endothelial cells and astrocytes, maintaining function of the blood-brain barrier (BBB) nd regulating neuroinflammation by controlling monocyte influx under various pathological conditions. The role of pericytes in morphine-mediated neuroinflammation however, has received less attention, especially in the context of how pericytes crosstalk with other central nervous system (CNS) cells. The current study was undertaken to examine the effect of miRNAs released from morphine-stimulated human primary astrocyte-derived extracellular vesicles (morphine-ADEVs) in mediating pericyte loss at the blood-brain barrier, leading, in turn, to increased influx of peripheral monocytes. Our findings suggest that the heterogeneous nuclear ribonucleoprotein complex A2/B1 (hnRNP A2/B1) plays role in morphine-mediated upregulation and release of miR-23a in ADEVs, and through action of morphine via mu opioid receptor.We further demonstrated that miR-23a in morphine-ADEVs could be taken up by pericytes, resulting in downregulation of PTEN expression, ultimately leading to increased pericyte migration. Furthermore, both overexpression of PTEN and blocking the miR-23a target site at PTEN 3UTR (by transfecting miR-23a-PTEN target protector), attenuated morphine-ADEV-mediated pericyte migration. We also demonstrated that in the microvessels isolated from morphine-administered mice, there were fewer PDGFβR + pericytes co-localizing with CD31+ brain endothelial cells compared with those from saline mice. In line with these findings, we also observed increased loss of pericytes and a concomitantly increased influx of monocytes in the brains of morphine-administered pericyte-labeled NG2-DsRed mice compared with saline mice. In conclusion, our findings indicate morphine-ADEVs mediated loss of pericyte coverage at the brain endothelium, thereby increasing the influx of peripheral monocytes in the central nervous system, leading to neuroinflammation.

The regulatory roles of circular RNAs via autophagy in ischemic stroke

Ischemic stroke (IS) is a severe disease with a high disability, recurrence, and mortality rates. Autophagy, a highly conserved process that degrades damaged or aging organelles and excess cellular components to maintain homeostasis, is activated during IS. It influences the blood–brain barrier integrity and regulates apoptosis. Circular RNAs (circRNAs) are novel non-coding RNAs involved in IS-induced autophagy and participate in various pathological processes following IS. In addition, they play a role in autophagy regulation. This review summarizes current evidence on the roles of autophagy and circRNA in IS and the potential mechanisms by which circRNAs regulate autophagy to influence IS injury. This review serves as a basis for the clinical application of circRNAs as novel biomarkers and therapeutic targets in the future.

Circular RNAs play roles in regulatory networks of cell signaling pathways in human cancers

AIMS

Circular RNAs (circRNAs) are endogenous covalently closed non-coding RNAs produced by reverse splicing of linear RNA. These molecules are highly expressed in mammalian cells and show cell/tissue-specific expression patterns. They are also significantly dysregulated in various cancers and function as oncogenes or tumor suppressors. Emerging evidence reveals that circRNAs contribute to cancer progression via modulating different cell signaling pathways. Nevertheless, the functional significance of circRNAs in cell signaling pathways regulation is still largely elusive. Considering this, shedding light on the multi-pathway effects of circRNAs may improve our understanding of targeted cancer therapy. Here, we discuss how circRNAs regulate the major cell signaling pathways in human cancers.

MATERIALS AND METHODS

We adopted a systematic search in PubMed using the following MeSH terms: circRNAs, non-coding RNAs, lncRNAs, exosomal circRNAs, cancer, and cell signaling.

KEY FINDINGS

We discussed different roles of circRNAs during tumorigenesis in which circRNAs affect tumor development through activating or inactivating certain cell signaling pathways via molecular interactions using various signaling pathways. We also discussed how crosstalk between circRNAs and lncRNAs modulate tumorigenesis and provides a resource for the identification of cancer therapeutic targets.

SIGNIFICANCE

We here elucidated how circRNAs can modulate different cell signaling pathways and play roles in cancer. This can broaden our horizons toward introducing promising prognostic, diagnostic, and therapeutic targets.

Promising Biomarkers in Head and Neck Cancer: The Most Clinically Important miRNAs

Head and neck cancers (HNCs) comprise a heterogeneous group of tumors that extend from the oral cavity to the upper gastrointestinal tract. The principal etiologic factors for oral tumors include tobacco smoking and alcohol consumption, while human papillomavirus (HPV) infections have been accused of a high incidence of pharyngeal tumors. Accordingly, HPV detection has been extensively used to categorize carcinomas of the head and neck. The diverse nature of HNC highlights the necessity for novel, sensitive, and precise biomarkers for the prompt diagnosis of the disease, its successful monitoring, and the timely prognosis of patient clinical outcomes. In this context, the identification of certain microRNAs (miRNAs) and/or the detection of alterations in their expression patterns, in a variety of somatic fluids and tissues, could serve as valuable biomarkers for precision oncology. In the present review, we summarize some of the most frequently studied miRNAs (including miR-21, -375, -99, -34a, -200, -31, -125a/b, -196a/b, -9, -181a, -155, -146a, -23a, -16, -29, and let-7), their role as biomarkers, and their implication in HNC pathogenesis. Moreover, we designate the potential of given miRNAs and miRNA signatures as novel diagnostic and prognostic tools for successful patient stratification. Finally, we discuss the currently ongoing clinical trials that aim to identify the diagnostic, prognostic, or therapeutic utility of miRNAs in HNC.

Effects of circFOXO3 on the Proliferation and Invasion of Liver Cancer Cells by Regulating PI3K/Akt Pathway

Objective

Hepatocellular carcinoma is a malignant disease occurring in the liver and is one of the main causes of death in cancer patients. Tumor cells are the main components of tumors and have a strong proliferative capacity. They are easily transferred to other parts of the body and can produce harmful substances that destroy the normal organ structure and endanger human life and health. In this study, we investigate the effect of circFOXO3 on the proliferation and invasion of hepatocellular carcinoma cells and its possible mechanism.

Methods

Human hepatocellular carcinoma cells BEL-7404, Hep G2, Hep 3B2.1–7, HuH-7, Li-7, and human normal hepatocytes HHL-5 were selected, and the expression level of circFOXO3 in the cell lines was determined by qRT-PCR. The cell line with low circFOXO3 expression level (HuH-7 cells) was used for follow-up experiments. HuH-7 liver cancer cells were divided into the control group (normal cultured), circFOXO3-NC group (transfected with circFOXO3 negative control), circFOXO3 mimic group (transfected with circFOXO3 mimic), PI3K activator group (20 μmol/L PI3K activator 740Y-P), and circFOXO3 mimic + PI3K activator group (transfected with circFOXO3 mimic + treated with PI3K activator 740Y-P). The qRT-PCR method was used to determine the expression level of circFOXO3 in HuH-7 liver cancer cells in each group, WB was used to detect the expression of apoptosis, invasion, and phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway related proteins in HuH-7 liver cancer cells in each group, the CCK-8 method was used to determine the viability of HuH-7 liver cancer cells in each group, flow cytometry was used to determine the apoptotic ability of HuH-7 liver cancer cells in each group, the transwell chamber experiment was used to determine the invasion ability of HuH-7 liver cancer cells in each group, and the scratch test was used to determine the migration ability of HuH-7 liver cancer cells in each group.

Results

circFOXO3 showed low expression in liver cancer cells; compared with the control group, the circFOXO3 expression and apoptosis rate of HuH-7 liver cancer cells in the circFOXO3 mimic group were significantly increased (P < 0.05) and the PI3K/Akt pathway-related protein expression, cell viability, invasion, and migration abilities were significantly reduced (P < 0.05); the apoptosis rate of HuH-7 liver cancer cells in the PI3K activator group was significantly reduced (P < 0.05) and the PI3K/Akt pathway related protein expression, cell viability, invasion and migration abilities were significantly increased (P < 0.05). Compared with the circFOXO3 mimic group, the apoptosis rate of HuH-7 liver cancer cells in the circFOXO3 mimic + PI3K activator group was significantly reduced (P < 0.05) and the PI3K/Akt pathway-related protein expression, cell viability, invasion and migration abilities were significantly increased (P < 0.05).

Conclusion

Highly expressed circFOXO3 can inhibit the proliferation and invasion of HuH-7 liver cancer cells, which may be achieved by inhibiting the PI3K/Akt pathway.

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.

Circular RNAs With Efficacy in Preclinical In Vitro and In Vivo Models of Esophageal Squamous Cell Carcinoma

Esophageal cancer is associated with a dismal prognosis. The armamentarium of approved drugs is focused on chemotherapy with modest therapeutic benefit. Recently, checkpoint inhibitory monoclonal antibody Pembrolizumab was approved. In order to identify new targets and modalities for the treatment of esophagus squamous cell carcinoma (ESCC) we searched the literature for circRNAs involved in the pathogenesis of ESCC. We identified two down-regulated and 17 up-regulated circRNAs as well as a synthetic circRNA with efficacy in preclinical in vivo systems. Down-regulated circRNAs sponge microRNAs directed against tumor suppressor genes. Up-regulated circRNAs sponge microRNAs directed against mRNAs, which encode proteins with pro-tumoral functions. We discuss issues such as reconstitution of down-regulated circRNAs and inhibition of up-regulated circRNAs with short interfering RNA (siRNA)- related entities. Also, we address druggability issues of the identified targets.

Identification of a novel circ_0001946/miR-1290/SOX6 ceRNA network in esophageal squamous cell cancer

Background

Circular RNAs (circRNAs) can function as competing endogenous RNAs (ceRNAs) to impact the development of esophageal squamous cell cancer (ESCC). Human circ_0001946 has been identified as a potential anticancer factor in ESCC, yet our understanding of its molecular basis remains limited.

Methods

Circ_0001946, microRNA (miR)‐1290 and SRY‐box transcription factor 6 (SOX6) were quantified by quantitative reasl‐time PCR (qRT‐PCR) or immunoblotting. Cell proliferation was assessed by CCK‐8 and EDU assays. Cell apoptosis and invasion were evaluated by flow cytometry and transwell assays, respectively. Cell migration was detected by transwell and wound‐healing assays. The direct relationship between miR‐1290 and circ_0001946 or SOX6 was determined by dual‐luciferase reporter and RNA immunoprecipitation (RIP) assays. Xenograft model assays were used to assess the role of circ_0001946 in tumor growth.

Results

Circ_0001946 expression was attenuated in human ESCC, and circ_0001946 increase impeded cell proliferation, invasion, migration and enhanced apoptosis in vitro. Moreover, circ_0001946 increase diminished xenograft growth in vivo. Mechanistically, circ_0001946 bound to miR‐1290, and re‐expression of miR‐1290 reversed circ_0001946‐dependent cell properties. SOX6 was a miR‐1290 target and it was responsible for the regulation of miR‐1290 in cell properties. Furthermore, circ_0001946 functioned as a ceRNA to regulate SOX6 expression via miR‐1290.

Conclusion

Our findings uncover an undescribed molecular mechanism, the circ_0001946/miR‐1290/SOX6 ceRNA crosstalk, for the anti‐ESCC activity of circ_0001946.

Non-coding RNAs and glioblastoma: Insight into their roles in metastasis

Glioma, also known as glioblastoma multiforme (GBM), is the most prevalent and most lethal primary brain tumor in adults. Gliomas are highly invasive tumors with the highest death rate among all primary brain malignancies. Metastasis occurs as the tumor cells spread from the site of origin to another site in the brain. Metastasis is a multifactorial process, which depends on alterations in metabolism, genetic mutations, and the cancer microenvironment. During recent years, the scientific study of non-coding RNAs (ncRNAs) has led to new insight into the molecular mechanisms involved in glioma. Many studies have reported that ncRNAs play major roles in many biological procedures connected with the development and progression of glioma. Long ncRNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are all types of ncRNAs, which are commonly dysregulated in GBM. Dysregulation of ncRNAs can facilitate the invasion and metastasis of glioma. The present review highlights some ncRNAs that have been associated with metastasis in GBM. miRNAs, circRNAs, and lncRNAs are discussed in detail with respect to their relevant signaling pathways involved in metastasis.

Roles of PTEN inactivation and PD-1/PD-L1 activation in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the most common type of esophageal cancer in China and developing countries. The purpose of this review is to summarize the roles of inactivation of the tumor suppressor gene, phosphatase and tensin homolog (PTEN), and activation of the programmed cell death protein 1 (PD-1) upon binding to its ligand (PD-L1) in the promotion of ESCC. Studies of ESCC performed in vitro and in vivo indicated that PTEN and PD-L1 function in the regulation of cell proliferation, invasion, and migration; the epithelial-mesenchymal transition; resistance to chemotherapy and radiotherapy; and the PI3K/AKT signaling pathway. Certain genetic variants of PTEN are related to susceptibility to ESCC, and PTEN and PD-L1 also function in ESCC progression and affect the prognosis of patients with ESCC. There is also evidence that the expression of PD-L1 and PTEN are associated with the progression of certain other cancers. Future studies should further examine the relationship of PD-L1 and PTEN and their possible interactions in ESCC.

Circular RNA circ-FoxO3 attenuates blood-brain barrier damage by inducing autophagy during ischemia/reperfusion

Blood-brain barrier (BBB) damage can be a result of central nervous system (CNS) diseases and may be a cause of CNS deterioration. However, there are still many unknowns regarding effective and targeted therapies for maintaining BBB integrity during ischemia/reperfusion (I/R) injury. In this study, we demonstrate that the circular RNA of FoxO3 (circ-FoxO3) promotes autophagy via mTORC1 inhibition to attenuate BBB collapse under I/R. Upregulation of circ-FoxO3 and autophagic flux were detected in brain microvessel endothelial cells in patients with hemorrhagic transformation and in mice models with middle cerebral artery occlusion/reperfusion. In vivo and in vitro studies indicated that circ-FoxO3 alleviated BBB damage principally by autophagy activation. Mechanistically, we found that circ-FoxO3 inhibited mTORC1 activity mainly by sequestering mTOR and E2F1, thus promoting autophagy to clear cytotoxic aggregates for improving BBB integrity. These results demonstrate that circ-FoxO3 plays a novel role in protecting against BBB damage, and that circ-FoxO3 may be a promising therapeutic target for neurological disorders associated with BBB damage.

Effect of circRNA_FOXO3 rs12196996 polymorphism and FOXO3 rs2232365 polymorphism on survival rate and severity of intensive care unit-acquired sepsis

The expression of circRNA_FOXO3 was found to be positively associated with the expression of Forkhead Box O3 (FOXO3), which is targeted and regulated by miR-23a. Polymorphisms in rs12196996 and rs2232365 have been reported in various diseases. In this study, we recruited intensive care unit (ICU)-acquired sepsis patients and grouped them according to their genotypes of rs12196996 and rs2232365. Quantitative real-time PCR was performed to analyze the expression of circRNA_FOXO3, FOXO3 mRNA, and miR-23a. ELISA was carried out to evaluate the abundance of cytokines and luciferase assay was used to explore the inhibitory role of miR-23a on circRNA_FOXO3 and FOXO3. Accordingly, we found that rs12196996 GG and rs2232365 AA were significantly correlated with prolonged survival of ICU-acquired sepsis patients. Rs12196996 GG and rs2232365 AA were also correlated with increased level of miR-23a, IL-10 and decreased level of TNF, IL-2, IFN, IL-6 and IL-1β in the peripheral blood cell samples of patients with ICU-acquired sepsis. The luciferase activity of wild-type (WT) circRNA_FOXO3 and FOXO3 were severely reduced by miR-23a. MiR-23a precursors could effectively suppress the expression of circRNA_FOXO3 and FOXO3 in the cells. Moreover, LPS-induced cell viability loss and dysregulation of cytokines were effectively restored by the knockdown of FOXO3 or circRNA_FOXO3 siRNA in the cells. This study revealed that the minor allele of rs12196996 polymorphism and rs2232365 polymorphism collaboratively contributed to the increased survival and suppressed severity of ICU-acquired sepsis.

Circ_0120175 promotes laryngeal squamous cell carcinoma development through up-regulating SLC7A11 by sponging miR-330-3p

The aim of our study was to illustrate the role of circular RNA 0120175 (circ_0120175) and its associated mechanism in laryngeal squamous cell carcinoma (LSCC) development. The abundance of circ_0120175, microRNA-330-3p (miR-330-3p) and solute carrier family 7, membrane 11 (SLC7A11) messenger RNA and protein was measured by quantitative real time polymerase chain reaction and Western blot assay. Cell proliferation, apoptosis, migration and invasion were assessed by cell counting kit-8 assay, flow cytometry and transwell migration and invasion assays, respectively. The interaction between miR-330-3p and circ_0120175 or SLC7A11 was confirmed by dual-luciferase reporter assay. Murine xenograft model was established to test the function of circ_0120175 in tumor growth in vivo. Circ_0120175 abundance was aberrantly increased in LSCC tissues and cell lines, and LSCC patients with high level of circ_0120175 were associated with advanced tumor staging, lymph node metastasis and short survival time. Circ_0120175 interference suppressed cell proliferation, migration and invasion and induced cell apoptosis of LSCC cells. Circ_0120175 could sponge and negatively regulate miR-330-3p expression in LSCC cells. The addition of anti-miR-330-3p partly reversed circ_0120175 knockdown-induced effects in LSCC cells. SLC7A11 bound to miR-330-3p. Circ_0120175 enhanced the abundance of SLC7A11 through sponging miR-330-3p in LSCC cells. Circ_0120175 silencing-mediated influences in LSCC cells were partly counteracted by the overexpression of SLC7A11. Circ_0120175 interference notably suppressed xenograft tumor growth in vivo. Circ_0120175 promoted proliferation, migration and invasion while impeded cell apoptosis of LSCC cells through miR-330-3p/SLC7A11 axis, which provided novel therapeutic targets for LSCC.

Circular RNAs and Drug Resistance in Genitourinary Cancers: A Literature Review

Simple Summary

Drug resistance to systematic treatment in genitourinary tumors severely aggravated the burden on patients and society. Multiple mechanisms were involved in drug resistance. As typical non-coding RNAs, circRNAs play a critical role in the onset and development of cancers and several studies implied their function in the regulation of drug resistance. Here, we reviewed the investigations of circRNAs’ behavior in drug resistance of genitourinary cancers and summarized the underlying mechanisms. This review emphasized the essential role of circRNAs in drug resistance development and also pointed out the potential topics that need further investigations in the future.

Abstract

In recent years, systematic treatment has made great progress in genitourinary tumors. However, some patients develop resistance to the treatments, resulting in an increase in mortality. Circular RNAs (circRNAs) form a class of non-coding RNAs with high stability and significant clinical relevance. Accumulating evidence indicates that circRNAs play a vital role in cancer development and tumor chemotherapy resistance. This review summarizes the molecular and cellular mechanisms of drug resistance mediated by circRNAs to common drugs used in the treatment of genitourinary tumors. Several circRNAs were identified to regulate the responsiveness to systemic treatments in genitourinary tumors, including chemotherapies such as cisplatin and targeted therapies such as enzalutamide. Canonically, cicrRNAs participate in the competing endogenous RNA (ceRNA) network, or in some cases directly interact with proteins, regulate downstream pathways, and even some circRNAs have the potential to produce proteins or polypeptides. Several cellular mechanisms were involved in circRNA-dependent drug resistance, including autophagy, cancer stem cells, epithelial-mesenchymal transition, and exosomes. The potential clinical prospect of circRNAs in regulating tumor drug resistance was also discussed.

Role of circular RNAs in gastrointestinal tumors and drug resistance

The incidence of gastrointestinal cancers has increased significantly over the past decade and gastrointestinal malignancies now rank among the leading causes of mortality globally. Although newer therapeutic strategies such as targeted therapies have greatly improved patient outcomes, their clinical success is limited by drug resistance, treatment failure and recurrence of metastatic disease. Therefore, there is an urgent need for further research identifying accurate and reliable biomarkers for precise treatment strategies. Circular RNAs (circRNAs) exhibit a covalently closed structure, high stability and biological conservation, and their expression is associated with the occurrence and development of gastrointestinal tumors. Moreover, circRNAs may significantly influence drug resistance of gastrointestinal cancers. In this article, we review the role of circRNAs in the occurrence and development of gastrointestinal cancer, their association with drug resistance, and potential application for early diagnosis, treatment and prognosis in gastrointestinal malignancies. Furthermore, we summarize characteristics of circRNA, including mechanism of formation and biological effects via mRNA sponging, chromatin replication, gene regulation, translational modification, signal transduction, and damage repair. Finally, we discuss whether circRNA-related noninvasive testing may be clinically provided in the future. This review provides new insights for the future development of diagnostics and therapeutics based on circRNAs in gastrointestinal tumors.

A novel protein AXIN1-295aa encoded by circAXIN1 activates the Wnt/β-catenin signaling pathway to promote gastric cancer progression

BACKGROUND

Circular RNA (circRNA), a subclass of non-coding RNA, plays a critical role in cancer tumorigenesis and metastasis. It has been suggested that circRNA acts as a microRNA sponge or a scaffold to interact with protein complexes; however, its full range of functions remains elusive. Recently, some circRNAs have been found to have coding potential.

METHODS

To investigate the role of circRNAs in gastric cancer (GC), parallel sequencing was performed using five paired GC samples. Differentially expressed circAXIN1 was proposed to encode a novel protein. FLAG-tagged circRNA overexpression plasmid construction, immunoblotting, mass spectrometry, and luciferase reporter analyses were applied to confirm the coding potential of circAXIN1. Gain- and loss-of-function studies were conducted to study the oncogenic role of circAXIN1 and AXIN1-295aa on the proliferation, migration, invasion, and metastasis of GC cells in vitro and in vivo. The competitive interaction between AXIN1-295aa and adenomatous polyposis coli (APC) was investigated by immunoprecipitation analyses. Wnt signaling activity was observed using a Top/Fopflash assay, real-time quantitative RT-PCR, immunoblotting, immunofluorescence staining, and chromatin immunoprecipitation.

RESULTS

CircAXIN1 is highly expressed in GC tissues compared with its expression in paired adjacent normal gastric tissues. CircAXIN1 encodes a 295 amino acid (aa) novel protein, which was named AXIN1-295aa. CircAXIN1 overexpression enhances the cell proliferation, migration, and invasion of GC cells, while the knockdown of circAXIN1 inhibits the malignant behaviors of GC cells in vitro and in vivo. Mechanistically, AXIN1-295aa competitively interacts with APC, leading to dysfunction of the "destruction complex" of the Wnt pathway. Released β-catenin translocates to the nucleus and binds to the TCF consensus site on the promoter, inducing downstream gene expression.

CONCLUSION

CircAXIN1 encodes a novel protein, AXIN1-295aa. AXIN1-295aa functions as an oncogenic protein, activating the Wnt signaling pathway to promote GC tumorigenesis and progression, suggesting a potential therapeutic target for GC.

From circRNAs to fusion circRNAs in hematological malignancies

Circular RNAs (circRNAs) represent a type of endogenous noncoding RNA generated by back-splicing events. Unlike the majority of RNAs, circRNAs are covalently closed, without a 5' end or a 3' poly(A) tail. A few circRNAs can be associated with polysomes, suggesting a protein-coding potential. CircRNAs are not degraded by RNA exonucleases or ribonuclease R and are enriched in exosomes. Recent developments in experimental methods coupled with evolving bioinformatic approaches have accelerated functional investigation of circRNAs, which exhibit a stable structure, a long half-life, and tumor specificity and can be extracted from body fluids and used as potential biological markers for tumors. Moreover, circRNAs may regulate the occurrence and development of cancers and contribute to drug resistance through a variety of molecular mechanisms. Despite the identification of a growing number of circRNAs, their effects in hematological cancers remain largely unknown. Recent studies indicate that circRNAs could also originate from fusion genes (fusion circRNAs, f-circRNAs) next to chromosomal translocations, which are considered the primary cause of various cancers, notably hematological malignancies. This Review will focus on circRNAs and f-circRNAs in hematological cancers.

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.

Status of diagnosis and treatment of esophageal cancer and non-coding RNA correlation research: a narrative review

OBJECTIVE

To describe and discuss the progression of the non-coding RNA as biomarkers in early esophageal cancer.

BACKGROUND

Esophageal cancer without obvious symptoms during early stages is one of the most common cancers, the current clinical treatments offer possibilities of a cure, but the survival rates and the prognoses remain poor, it is a serious threat to human life and health. Most patients are usually diagnosed during terminal stages due to low sensitivity of esophageal cancer's early detection techniques. With the development of molecular biology, an increasing number of non-coding RNAs are found to be associated with the occurrence, development, and prognosis of esophageal cancer. Some of these have begun to be used in clinics and laboratories for diagnosis, treatment, and prognosis, with the goal of reducing mortality.

METHODS

The information for this paper was collected from a variety of sources, including a search of the keynote's references, a search for texts in college libraries, and discussions with experts in the field of esophageal cancer clinical treatment.

CONCLUSIONS

Non-coding RNA does play a regulatory role in the development of esophageal cancer, which can predict the occurrence or prognosis of tumors, and become a new class of tumor markers and therapeutic targets in clinical applications. In this review, we survey the recent developments in the incidence, diagnosis, and treatment of esophageal cancer, especially with new research progresses on non-coding RNA biomarkers in detail, and discuss its potential clinical applications.

Circular RNA Foxo3 enhances progression of ovarian carcinoma cells

Background: Ovarian carcinoma (OC) is the deadliest gynecologic malignancy in females worldwide. Circular RNA Foxo3 (Foxo3) plays essential roles in various cancers. However, the detailed function of Foxo3 in OC remains unclear. This study aimed to investigate the role of Foxo3 in OC and the underlying molecular mechanism.

Methods: The abundance of Foxo3 was detected in OC cell lines by qPCR. Lentivirus transduction, CCK-8, wound healing assays, transwell migration and invasion assays, luciferase reporter assay, western blotting, fluorescence in situ hybridization (FISH), transmission electron microscopy, nanoparticle tracking analysis, and bioinformatics analysis were performed to investigate the underlying mechanism.

Results: The results demonstrated that Foxo3 was significantly upregulated in OC cell lines. Overexpression and knockdown of Foxo3 promoted and inhibited the proliferation, migration, and invasion of OC cells, respectively. Foxo3 could bind to miR-422a to negatively regulate miR-422a expression. Also, proteolipid protein 2 (PLP2) was a targeting gene of miR-422a. Additionally, Foxo3 was highly expressed in exosomes derived from OC cells. Furthermore, Foxo3 could be shuttled to OC cells by exosomes and promoted OC progression.

Conclusions: Foxo3 promoted OC progression through exosome-mediated intercellular interaction to target miR-422a/PLP2 axis. Foxo3 may serve as a potential biomarker for OC.

Identification of the tumor‑suppressive role of circular RNA‑FOXO3 in colorectal cancer via regulation of miR‑543/LATS1 axis

Colorectal cancer (CRC) is a common malignancy with significant prevalence and mortality rates. Circular RNA FOXO3 (circ-FOXO3; hsa_circ_0006404) has been reported to be involved in cancer regulation; however, its role in CRC is yet to be fully elucidated. Therefore, the aim of the present study was to investigate the effect of circ-FOXO3 on CRC progression and identify its underlying mechanism. In the present study, the expression of circ-FOXO3 was investigated in CRC tissues and cells via reverse transcription-quantitative PCR. A Cell Counting Kit-8 and colony formation assays were used to assess cell proliferation. The cell migratory and invasive abilities were detected using the Transwell migration and invasion assays. The luciferase assay and RNA pull-down assay were conducted to verify the relationship of circ-FOXO3, microRNA (miR)-543 and Large tumor suppressor kinase 1 (LATS1). The results demonstrated that circ-FOXO3 expression was downregulated in CRC tissues and cells, and was associated with poor overall survival of patients with CRC. Moreover, circ-FOXO3 was associated with tumor size, distant metastasis, differentiation, lymph node metastasis and TMN stages of patients with CRC. circ-FOXO3 overexpression suppressed CRC cell proliferation, migration and invasion. Luciferase assay and RNA pull-down assay results indicated that circ-FOXO3 functioned as a sponge for miR-543. In addition, circ-FOXO3 increased the expression of LATS1 via sponging miR-543, thus inhibiting CRC cell aggressive features. Collectively, the present results suggested that circ-FOXO3 inhibited CRC metastasis and progression via elevated LATS1 expression by sponging miR-543. Therefore, circ-FOXO3 may be a promising target for CRC therapy.

Circular RNA: A novel type of biomarker for glioma (Review)

With the rapid development of sequencing technologies, the characteristics and functions of circular RNAs (circRNAs) in different tissues, and their underlying pathophysiological mechanisms, have been identified. circRNAs are significantly enriched in the brain and are continually expressed from the embryonic stage to the adult stage in rats. Previous studies have reported that certain circRNAs are differentially expressed in glioma and regulate a number of biological processes, such as cell proliferation, metastasis and oncogenesis of glioma. Furthermore, certain circRNAs have been associated with tumor size, World Health Organization tumor grade and poor prognosis in patients with glioma. It has been hypothesized that circRNAs may be involved in the onset and progression of glioma through transcriptional regulation, protein translation and binding to microRNAs. These properties and functions suggest the potential of circRNAs as prognostic biomarkers and therapeutic targets for glioma. For the present review, published studies were examined from PubMed, Embase, Cochrane Central and the reference lists of the retrieved articles. The aim of the present review was to summarize the progress of circRNA research in glioma, discuss the potential diagnostic and prognostic values, and the roles of circRNAs in glioma, and provide a novel theoretical basis and research concepts for the prediction, diagnosis and treatment of glioma.

The Emerging Roles of circFOXO3 in Cancer

Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs which are mainly formed by reverse splicing of precursor mRNAs. They are relatively stable and resistant to RNase R because of their covalently closed structure without 5' caps or 3' poly-adenylated tails. CircRNAs are widely expressed in eukaryotic cells and show tissue, timing, and disease specificity. Recent studies have found that circRNAs play an important role in many diseases. In particular, they affect the proliferation, invasion and prognosis of cancer by regulating gene expression. CircRNA Forkhead box O3 (circFOXO3) is a circRNA confirmed to be abnormally expressed in a variety of cancers, including prostate cancer, hepatocellular carcinoma, glioblastoma, bladder cancer, and breast cancer, etc. At present, the feature of circFOXO3 as a molecular sponge is widely studied to promote or inhibit the development of cancers. However, the diverse functions of circFOXO3 have not been fully understood. Hence, it is important to review the roles of circFOXO3 in cancers. This review has summarized and discussed the roles and molecular mechanism of circFOXO3 and its target genes in these cancers, which can help to enrich our understanding to the functions of circRNAs and carry out subsequent researches on circFOXO3.

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.

Roles of noncoding RNAs in the initiation and progression of myocardial ischemia-reperfusion injury

The morbidity and mortality of myocardial ischemia-reperfusion injury (MIRI) have increased in modern society. Noncoding RNAs (ncRNAs), including lncRNAs, circRNAs, piRNAs and miRNAs, have been reported in a variety of studies to be involved in pathological initiation and developments of MIRI. Hence this review focuses on the current research regarding these ncRNAs in MIRI. We comprehensively introduce the important features of lncRNAs, circRNAs, piRNA and miRNAs and then summarize the published studies of ncRNAs in MIRI. A clarification of lncRNA-miRNA-mRNA, lncRNA-transcription factor-mRNA and circRNA-miRNA-mRNA axes in MIRI follows, to further elucidate the crucial roles of ncRNAs in MIRI. Bioinformatics analysis has revealed the biological correlation of mRNAs with MIRI. We provide a comprehensive perspective for the roles of these ncRNAs and their related networks in MIRI, providing a theoretical basis for preclinical and clinical studies on ncRNA-based gene therapy for MIRI treatment.

CircRNA circ-OGDH (hsa_circ_0003340) Acts as a ceRNA to Regulate Glutamine Metabolism and Esophageal Squamous Cell Carcinoma Progression by the miR-615-5p/PDX1 Axis

Background

Circular RNA hsa_circ_0003340 (circ-OGDH) has been uncovered to be involved in esophageal squamous cell carcinoma (ESCC) progression. However, the mechanism by which circ-OGDH regulates ESCC progression is unclear.

Methods

Expression levels of circ-OGDH, microRNA (miR)-615-5p, and PDX1 (pancreatic and duodenal homeobox 1) mRNA were evaluated with quantitative real-time polymerase chain reaction (qRT-PCR). The proliferation, apoptosis, migration, invasion, and cell cycle progression of ESCC cells were analyzed by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide), colony formation, flow cytometry, and transwell assays. Measurement of glutamine consumption, α-KG (α-ketoglutarate) production, and ATP (Adenosine Triphosphate) content using corresponding kits. Protein levels were analyzed by Western blotting. The targeting relationship between circ-OGDH or PDX1 and miR-615-5p was verified by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The function of circ-OGDH in ESCC was confirmed by animal experiments.

Results

Circ-OGDH was upregulated in ESCC. Circ-OGDH inhibition reduced ESCC growth in vivo and accelerated cell apoptosis, cell cycle arrest, repressed cell proliferation, migration, invasion, and reduced cell glutamine metabolism in ESCC cells in vitro. MiR-615-5p was downregulated in ESCC, while PDX1 had an opposite result. Circ-OGDH sponged miR-615-5p to regulate PDX1 expression. MiR-615-5p inhibitor neutralized the repressive effect of circ-OGDH knockdown on malignancy and glutamine metabolism of ESCC cells. PDX1 overexpression counteracted the inhibitory impact of miR-615-5p mimic on malignancy and glutamine metabolism of ESCC cells.

Conclusion

Circ-OGDH sponged miR-615-5p to elevate PDX1 expression, thus elevating glutamine metabolism and promoting tumor growth in ESCC. The study offered evidence to support circ-OGDH as a promising target for ESCC therapy.

c-Myc-induced circ-NOTCH1 promotes aggressive phenotypes of nasopharyngeal carcinoma cells by regulating the miR-34c-5p/c-Myc axis

Nasopharyngeal carcinoma (NPC) is the subclass of head and neck cancer with the highest incidence among otolaryngology malignancies. A growing amount of evidence has proven that circular RNAs (circRNAs) play key roles in the progression of multiple cancers. It has been reported that circ-NOTCH1 is a novel circRNA and functions as an oncogene in gastric cancer, while the regulatory mechanism of circ-NOTCH1 in NPC remains unknown. In the present research, our findings revealed that circ-NOTCH1 was overexpressed in NPC tissues and cells. Circ-NOTCH1 knockdown suppressed NPC cell proliferation, invasion, and migration. Subsequently, we discovered that c-Myc can activate circ-NOTCH1 by binding to the NOTCH1 promoter. c-Myc functioned as a tumor promoter in NPC cells. Mechanistically, circ-NOTCH1 served as a competitive endogenous RNA to modulate c-Myc expression by sponging miR-34c-5p. Additionally, overexpression of c-Myc reversed the circ-NOTCH1 knockdown-mediated inhibition of NPC cellular progression. Overall, this study suggested that c-Myc-induced circ-NOTCH1 promoted malignant phenotypes of NPC cells by regulating the miR-34c-5p/c-Myc 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.

Circular RNA Foxo3: A Promising Cancer-Associated Biomarker

Circular RNAs (circRNAs) are a class of novel non-coding RNAs (ncRNAs). Emerging evidence demonstrates that circRNAs play crucial roles in many biological processes by regulating linear RNA transcription, downstream gene expression and protein or peptide translation. Meanwhile, recent studies have suggested that circRNAs have the potential to be oncogenic or anti-oncogenic and play vital regulatory roles in the initiation and progression of tumors. Circular RNA Forkhead box O3 (circ-Foxo3, hsa_circ_0006404) is encoded by the human FOXO3 gene and is one of the most studied circular RNAs acting as a sponge for potential microRNAs (miRNAs) (Du et al., 2016). Previous studies have reported that circ-Foxo3 is involved in the development and tumorigenesis of a variety of cancers (bladder, gastric, acute lymphocytic leukemia, glioma, etc.). In this review, we summarize the current studies concerning circ-Foxo3 deregulation and the correlative mechanism in various human cancers. We also point out the potential clinical applications of this circRNA as a biomarker for cancer diagnosis and prognosis.

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.

Systematic Identification of circRNA-miRNA-mRNA Regulatory Network in Esophageal Squamous Cell Carcinoma

Background

Circular RNAs (circRNAs) are described as endogenous non-coding RNAs that have been reported to play important roles in the development and progression of cancers. This study aimed to reveal the circRNA-related regulatory mechanism in esophageal squamous cell carcinoma (ESCC).

Methods

A genome-wide circRNA microarray assay was performed to profile the expression of circRNAs in the blood of preoperative ESCC patients and healthy controls. A systematic method of data mining was performed to identify the differentially expressed miRNAs (DEmiRs) and differentially expressed genes (DEGs) based on the metaMA and RankProd analysis. Bioinformatics analyses and multiple tools were employed to construct the potential circRNA–miRNA–mRNA regulatory network.

Results

Thirty-three differentially expressed circRNAs were identified in the ESCC blood, including 31 downregulated and two upregulated circRNAs in the blood of ESCC patients compared with the healthy controls. Twenty-three DEmiRs and 2,220 DEGs were obtained by the integration of microarray datasets. An ESCC-associated circRNA–miRNA–mRNA network was constructed based on 31 circRNAs, 3 DEmiRs, and 190 DEGs. Enrichment analyses indicated that the DEGs were associated with a series of biological processes and cancer-related pathways. The protein–protein interaction (PPI) network was generated by the 190 DEGs, with 10 hub genes verified in the network. Subsequently, a sub-network was established for ESCC, which included 29 circRNAs, 2 miRNAs, and 10 hub genes.

Conclusion

Our study provided a novel clue to help understand the circRNA–miRNA–mRNA regulatory mechanism, highlighting the potential roles of circRNAs in the pathogenesis and development of ESCC.

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.

Role of circular RNAs in colorectal tumor microenvironment

Circular RNAs (circRNAs) are a class of endogenous noncoding RNA, which were previously considered as a byproduct of RNA splicing error. Numerous studies have demonstrated the altered expression of circRNAs in organ tissues during pathological conditions and their involvements in disease pathogenesis and progression, including cancers. In colorectal cancer (CRC), multiple circRNAs have been identified and characterized as "oncogenic", given their involvements in the downregulation of tumor suppressor genes and induction of tumor initiation, progression, invasion, and metastasis. Additionally, other circRNAs have been identified in CRC and characterized as "tumor suppressive" based on their ability of inhibiting the expression of oncogenic genes and suppressing tumor growth and proliferation. circRNAs could serve as potential diagnostic and prognostic biomarkers, and therapeutic targets or vectors to be utilized in cancer therapies. This review briefly describes the dynamic changes of the tumor microenvironment inducing immunosuppression and tumorigenesis, and outlines the biogenesis and characteristics of circRNAs and recent findings indicating their roles and functions in the CRC tumor microenvironment. It also discusses strategies and technologies, which could be employed in the future to overcome current cancer therapy challenges associated with circRNAs.