Circular RNA CDR1as sponges miR-7-5p to enhance E2F3 stability and promote the growth of nasopharyngeal carcinoma

Association study of hsa_circ_0001946, hsa-miR-7-5p and PARP1 in coronary atherosclerotic heart disease

BACKGROUND

Our previous work identified an aberrant expression of hsa_circ_0001946 in coronary atherosclerotic heart disease (CHD). Here we aimed to verify the role of hsa_circ_0001946 as a biomarker for CHD, and explore the clues of its downstream regulation.

METHODS

The hsa_circ_0001946 expression in CHD patients (n = 120) and controls (n = 120) were confirmed with qRT-PCR. CircBank and miRDB were used for target analysis in silico. Spearman correlation test was performed to infer potential interrelationships among the nucleic acid molecular biomarkers, and their predictive abilities were examined using receiver operating characteristic (ROC) curves.

RESULTS

Hsa_circ_0001946 was validated to be significantly up-regulated in the peripheral blood mononuclear cells of CHD patients, and revealed as an independent indicator of increased CHD risk (odds ratio: 2.364; 95% confidence interval [CI]: 1.765-3.165) after adjusting for confounding factors. Hsa-miR-7-5p was found to own the largest number of binding sites in has_circ_0001946 sequence, and among its targets predicted, the poly ADP-ribose polymerase 1 (PARP1) has been implicated in the pathophysiology of CHD. Spearman analysis indicated negative correlations of hsa-miR-7-5p with hsa_circ_0001946 and PARP1, respectively; while hsa_circ_0001946 was positively correlated with PARP1. The prediction accuracy of hsa_circ_0001946 in CHD was evaluated, showing an area under the ROC curve of 0.897 (95% CI: 0.791-0.961), which could further increase to 0.957 (95% CI: 0.870-0.992) upon a combination of hsa-miR-7-5p and PARP1.

CONCLUSION

The present work demonstrated the predictive power of hsa_circ_0001946, hsa-miR-7-5p and PARP1 as combined biomarkers for CHD, and suggests a regulatory axis they consisted might contribute to the CHD development.

The Emerging Picture of the Roles of CircRNA-CDR1as in Cancer

Circular RNAs (circRNAs) are covalently closed circular structures without 5′ caps and 3′ tails, which are mainly formed from precursor mRNAs (pre-mRNAs) via back-splicing of exons. With the development of RNA sequencing and bioinformatic analysis, circRNAs were recently rediscovered and found to be widely expressed in the tree of life. Cerebellar degeneration-related protein 1 antisense RNA (CDR1as) is recognized as one of the most well-identified circRNAs. It contains over 70 miR-7 binding sites and can regulate gene activity by sponging miR-7. Increasing numbers of studies have recently demonstrated that CDR1as is abnormally expressed in many types of tumors, such as colorectal cancer, cholangiocarcinoma and osteosarcoma, and plays a vital role in the development of cancer. However, there are few reviews focusing on CDR1as and cancer. Hence, it is important to review and discuss the role of CDR1as in cancer. Here, we first review the main biological features of CDR1as. We then focus on the expression and roles of CDR1as in cancer. Finally, we summarize what is known on the role of CDR1as in cancer and discuss future prospects in this area of research.

Circ_0016760 Acts as a Sponge of MicroRNA-4295 to Enhance E2F Transcription Factor 3 Expression and Facilitates Cell Proliferation and Glycolysis in Nonsmall Cell Lung Cancer

Background: Circular RNAs (circRNAs) have been validated as important regulators of nonsmall cell lung cancer (NSCLC), but the role and potential mechanism of circ_0016760 in NSCLC remain largely unclear. Materials and Methods: Quantitative real-time polymerase chain reaction was performed to detect the levels of circ_0016760, microRNA-4295 (miR-4295), and E2F transcription factor 3 (E2F3). The cell proliferation was measured by methyl-thiazolyl diphenyl-tetrazolium bromide assay. The protein levels of proliferating cell nuclear antigen and E2F3 were examined by Western blot. Xenograft mice model was constructed to explore the effect of circ_0016760 on tumor growth in vivo. The relationship among circ_0016760, miR-4295, and E2F3 was evaluated using dual-luciferase reporter assay. Glucose consumption of NSCLC cells was assessed by the glucose assay kit. Results: Circ_0016760 and E2F3 expression levels were upregulated in NSCLC tissues and cells, while miR-4295 was downregulated. Circ_0016760 could bind to miR-4295, and negatively modulate its expression in NSCLC cells. Besides, miR-4295 directly targeted E2F3 and inversely regulated E2F3 expression. More importantly, Circ_0016760 facilitated proliferation and glycolysis of NSCLC cells by increasing E2F3 by sponging miR-4295 as well as promoted the tumor growth in vivo. Conclusion: Circ_0016760 served as a growth-promoting circRNA in NSCLC by facilitating cell proliferation and glycolysis by regulating the miR-4295/E2F3 axis, providing a novel potential target for NSCLC treatment.

Circular RNAs in Cardiac Regeneration: Cardiac Cell Proliferation, Differentiation, Survival, and Reprogramming

Circular RNAs (circRNAs) are classified as long non-coding RNAs (lncRNAs) that are characterized by a covalent closed-loop structure. This closed-loop shape is the result of a backsplicing event in which the 3' and 5' splice sites are ligated. Through the lack of 3' poly(A) tails and 5' cap structures, circRNAs are more stable than linear RNAs because these adjustments make the circular loop less susceptible to exonucleases. The majority of identified circRNAs possess cell- and tissue-specific expression patterns. In addition, high-throughput RNA-sequencing combined with novel bioinformatics algorithms revealed that circRNA sequences are often conserved across different species suggesting a positive evolutionary pressure. Implicated as regulators of protein turnover, micro RNA (miRNA) sponges, or broad effectors in cell differentiation, proliferation, and senescence, research of circRNA has increased in recent years. Particularly in cardiovascular research, circRNA-related discoveries have opened the door for the development of potential diagnostic and therapeutic tools. Increasing evidence links deviating circRNA expression patterns to various cardiovascular diseases including ischemic heart failure. In this mini-review, we summarize the current state of knowledge on circRNAs in cardiac regeneration with a focus on cardiac cell proliferation, differentiation, cardiomyocyte survival, and cardiac reprogramming.

CircRNA CDR1as/miR-1287/Raf1 Axis Modulates Hepatocellular Carcinoma Progression Through MEK/ERK Pathway

Background

Hepatocellular carcinoma (HCC) is a common lethal malignant tumor worldwide. Circular RNAs (circRNAs) have been reported to affect the development of human cancers, including HCC. In this project, we aim to clarify the functional effect of circular CDR1as (circ_CDR1as) on HCC progression.

Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot is implemented to detect the expression of circ_CDR1as, microRNA (miR)-1287 and Raf-1 proto-oncogene, serine/threonine kinase (Raf1). Cell proliferation is assessed via colony formation and 3-(4, 5)-dimethylthiazole-2-y1)-2, 5-biphenyl tetrazolium bromide (MTT) assays. Cell migration and invasion are measured by Transwell assay. The target relationship between miR-1287 and circ_CDR1as or Raf1 is validated through dual-luciferase reporter assay. The levels of epithelia–mesenchymal transition (EMT) markers and the MEK/ERK signal pathway-related proteins are examined by Western blot. Model in nude mice is constructed to determine the role of circ_CDR1as in vivo.

Results

Expression of circ_CDR1as and Raf1 is elevated, while miR-1287 expression is decreased in HCC. Depletion of circ_CDR1as or Raf1 could inhibit proliferation and metastasis of HCC cells. Besides, circ_CDR1as regulates Raf1 expression by targeting miR-1287. MiR-1287 upregulation or Raf1 depletion could partially counterbalance circ_CDR1as depletion-mediated inhibitory effects on HCC cell behaviors. Moreover, circ_CDR1as depletion represses HCC progression through inactivating MEK/ERK pathway. In addition, circ_CDR1as depletion suppresses tumor growth in vivo via regulating miR-1287/Raf1 pathway.

Conclusion

Circ_CDR1as depletion inhibits HCC cell proliferation and metastasis by miR-1287/Raf1 and MEK/ERK pathways, highlighting a promising molecular target for HCC treatment.

CircZNF609 promotes cell proliferation, migration, invasion, and glycolysis in nasopharyngeal carcinoma through regulating HRAS via miR-338-3p

Circular RNA zinc finger protein 609 (circZNF609) has been reported to involve in nasopharyngeal carcinoma (NPC) tumorigenesis regulation. However, the role and the molecular mechanism of circZNF609 in NPC remain unclear. Levels of circZNF609, microRNA (miR)-338-3p, and GTPase HRas (HRAS) were detected by quantitative real-time polymerase chain reaction or Western blot. Cell proliferation, migration, and invasion were analyzed using cell counting kit-8 assay, colony formation assay, and transwell assay, respectively. Glucose metabolism was calculated by measuring glucose consumption, lactate production, adenosine triphosphate (ATP) levels, and HK2 activity. The interaction between miR-338-3p and circZNF609 or HRAS was analyzed by the dual-luciferase reporter assay. In vivo experiment was conducted using the murine xenograft model. CircZNF609 was elevated in NPC tissues and cell lines, and high circZNF609 expression had a poor prognosis. CircZNF609 knockdown suppressed NPC progression in vitro by inhibiting cell proliferation, migration, invasion, and glycolysis and hindered tumor growth in vivo. MiR-338-3p directly bound to circZNF609 and HRAS, and circZNF609 knockdown repressed NPC cell malignant properties by binding to miR-338-3p. MiR-338-3p was low in NPC, and miR-338-3p restoration performed anti-tumor effects in cells of NPC by targeting HRAS. Importantly, circZNF609 acted as a competing endogenous RNA of miR-338-3p to regulate HRAS. CircZNF609 knockdown suppressed cell tumorigenesis in NPC via regulating miR-338-3p/HRAS axis, suggesting a novel therapeutic strategy for NPC.

Downregulation of miR-7-5p Inhibits the Tumorigenesis of Esophagus Cancer via Targeting KLF4

Background

Esophageal cancer (EC) is one of the aggressive gastrointestinal malignancies. It has been reported that microRNAs (miRNAs) play key roles during the tumorigenesis of EC. To identify novel potential targets for EC, differential expressed miRNAs (DEG) between EC and adjacent normal tissues were analyzed with bioinformatics tool.

Methods

The differential expression of miRNAs between EC and adjacent normal tissues was analyzed. CCK-8 and Ki67 staining were used to detect the cell proliferation. Flow cytometry was performed to test the cell apoptosis. The correlation between miR-7-5p and KLF4 was detected by dual-luciferase report assay. Gene and protein expression in EC cells or in tissues were measured by qRT-PCR and Western blot, respectively. Cell migration and invasion were detected with transwell assay. Xenograft mice model was established to investigate the role of miR-7-5p in EC tumorigenesis in vivo.

Results

MiR-7-5p was found to be negatively correlated with the survival rate of patient with EC. In addition, downregulation of miR-7-5p significantly inhibited the growth and invasion of EC cells. Meanwhile, miR-7-5p directly targeted KLF4 in EC cells. Moreover, downregulation of miR-7-5p inhibited the tumorigenesis of EC via inactivating MAPK signaling pathway in vivo.

Conclusion

Downregulation of miR-7-5p notably suppressed the progression of EC via targeting KLF4. Thus, miR-7-5p might serve as a new target for the treatment of EC.

CircRNA Circ_0001721 Promotes the Progression of Osteosarcoma Through miR-372-3p/MAPK7 Axis

Background

Osteosarcoma (OS) is the most common bone tumor. Many studies have reported that circular RNAs (circRNAs) play an important role in the development of a variety of human cancers. However, the underlying mechanism of circ_0001721 in regulating osteosarcoma progression remains unknown.

Materials and Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the levels of circ_0001721, miR-372-3p, and mitogen-activated protein kinase 7 (MAPK7) in osteosarcoma tissues and cells. Besides, glycolysis was investigated by glucose consumption, lactate production and hexokinase II (HK2) protein level. Cell proliferation and apoptosis were determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and flow cytometry, separately. Cell migration and invasion were determined by transwell assay. Moreover, the protein levels of HK2 and epithelial-to-mesenchymal transition (EMT) markers were determined by Western blot analysis. The relationship between miR-372-3p and circ_0001721 or MAPK7 was predicated by starbase v3.0 and confirmed by dual-luciferase reporter assay or RNA binding protein immunoprecipitation (RIP) assay. Murine xenograft model was established to investigate the role of circ_0001721 in vivo.

Results

The levels of circ_0001721 and MAPK7 were upregulated in osteosarcoma tissues and cells, while miR-372-3p was downregulated. Knockdown of circ_0001721 inhibited glycolysis, cell proliferation, cell migration, invasion and epithelial-to-mesenchymal transition (EMT), and promoted apoptosis. Circ_0001721 was validated as a sponge of miR-372-3p and mediated glycolysis, cell proliferation, apoptosis, migration, invasion, and EMT of osteosarcoma cells through miR-372-3p. MAPK7 was a target of miR-372-3p and overexpression of MAPK7 attenuated anti-cancer role of miR-372-3p in OS cells. Further studies revealed that circ_0001721 regulates MAPK7 expression via sponging miR-372-3-p. Finally, knockdown of circ_0001721 inhibited tumor progression in vivo.

Conclusion

Circ_0001721 promoted osteosarcoma development through the miR-372-3p/MAPK7 axis.

Spatial expression analyses of the putative oncogene ciRS-7 in cancer reshape the microRNA sponge theory

Circular RNAs (circRNAs) have recently gained substantial attention in the cancer research field where most, including the putative oncogene ciRS-7 (CDR1as), have been proposed to function as competitive endogenous RNAs (ceRNAs) by sponging specific microRNAs. Here, we report the first spatially resolved cellular expression patterns of ciRS-7 in colon cancer and show that ciRS-7 is completely absent in the cancer cells, but highly expressed in stromal cells within the tumor microenvironment. Additionally, our data suggest that this generally apply to classical oncogene-driven adenocarcinomas, but not to other cancers, including malignant melanoma. Moreover, we find that correlations between circRNA and mRNA expression, which are commonly interpreted as evidence of a ceRNA function, can be explained by different cancer-to-stromal cell ratios among the studied tumor specimens. Together, these results have wide implications for future circRNA studies and highlight the importance of spatially resolving expression patterns of circRNAs proposed to function as ceRNAs.

Association between Circular RNA CDR1as and Post-Infarction Cardiac Function in Pig Ischemic Heart Failure: Influence of the Anti-Fibrotic Natural Compounds Bufalin and Lycorine

Anti-fibrotic therapies are of increasing interest to combat cardiac remodeling and heart failure progression. Recently, anti-fibrotic circular RNAs (circRNAs) have been identified in human and rodent cardiac tissue. In vivo (rodent) experiments proved cardiac anti-fibrotic effects of the natural compounds bufalin and lycorine by downregulating miRNA-671-5p, associated with a theoretic increase in the tissue level of circRNA CDR1as. Accordingly, we hypothesized that both anti-fibrotic drugs may inhibit focal myocardial fibrosis of the remodeled left ventricle (LV) also in a translational large animal model of heart failure (HF). Domestic pigs were repeatedly treated with subcutaneous injections of either bufalin, lycorine, or saline, (n = 5/group) between days 7-21 post acute myocardial infarction (AMI). At the 2-month follow-up, both bufalin and lycorine led to significantly reduced cardiac fibrosis. Bufalin treatment additionally led to smaller end-diastolic volumes, higher LV ejection fraction (EF), and increased expression of CDR1as of the AMI region. Elevated tissue levels of the circRNA CDR1as in the AMI region of the pig heart correlated significantly with LV and right ventricular EF, LV stroke volume, and negatively with infarct size. In conclusion, we successfully identified the circRNA CDR1as in pig hearts and show a significant association with improved LV and RV function by anti-fibrotic therapies in a translational animal model of HF.

miR-635 targets KIFC1 to inhibit the progression of gastric cancer

Accumulating studies have shown that the dysregulation of microRNAs is related to the carcinogenesis and development of gastric cancer (GC), and the role of miR-635 in GC remains largely unknown. miR-635 and Kinesin Family Member C1 (KIFC1) mRNA expression in GC tissues and paracancerous tissues and cells were detected by quantitative real-time PCR. KIFC1 protein expression in GC tissues and paracancerous normal tissues and cells was detected by immunohistochemistry and western blot. Cell proliferation was monitored by Cell Counting Kit-8 assay and 5-bromo-2′-deoxyuridine assay. Transwell assay was employed to detect the migration and invasion of GC cells. The dual-luciferase reporter gene assay was adopted to detect the targeting relationship between miR-635 and KIFC1. Compared with paracancerous tissues, miR-635 expression was remarkably decreased in GC tissues; conversely, KIFC1 expression was significantly increased. Compared with human normal gastric epithelial cell GSE-1, miR-635 expression was markedly decreased in GC cell lines. Meanwhile, KIFC1 expression was significantly increased, and the Kaplan-Meier Plotter database showed that its high expression was remarkably associated with poor prognosis. Additionally, miR-635 can negatively regulate KIFC1. miR-635 can target KIFC1 to inhibit proliferation, migration and invasion of GC cells. Collectively, miR-635 is lowly expressed in GC, and it inhibits proliferation, migration and invasion of GC cells via regulating KIFC1.

Circular RNAs: Regulatory functions in respiratory tract cancers

Circular RNAs (circRNAs) are a class of single-stranded RNAs having a covalently closed loop structure generated from back-splicing of pre-mRNA. These novel RNAs are characterized by high stability, abundance and conservation. Accumulating evidence has revealed that circRNAs are intimately associated with the pathogenesis, development and progression of multiple human diseases, including respiratory tract cancers. CircRNAs may serve as oncogenes or tumor suppressors to influence cell proliferation, differentiation, apoptosis, invasion and metastasis. CircRNAs may act as microRNA (miRNA) sponges, interact with RNA-binding proteins (RBPs), regulate gene transcription and/or translate into mini-peptides or proteins. In this review, we discuss recent progress in understanding the pathologic roles of circRNAs in respiratory tract cancers, such as nasopharyngeal carcinoma, laryngeal squamous cell carcinoma, and especially lung adenocarcinoma. We further discuss the diagnostic, therapeutic and prognostic roles as potential biomarkers in respiratory tract cancers, providing insight into the possibilities of applying circRNAs as therapeutic targets and biomarkers in precision oncology.

Hsa_circ_0046263 functions as a ceRNA to promote nasopharyngeal carcinoma progression by upregulating IGFBP3

Accumulating evidences indicate that circular RNAs (circRNAs), a subclass of noncoding RNAs, play important role in regulating gene expression in eukaryotes. Hsa_circ_0046263 (circ-0046263) was found aberrantly expressed in nasopharyngeal carcinoma (NPC), but its role in tumor growth and metastasis remains largely unclear. Sanger sequencing, RNase R assay, and nucleic acid electrophoresis were conducted to verify the identification of circ-0046263. Nuclear separation and fluorescence in situ hybridization (FISH) assays were used to determine the localization of circ-004263. Dual luciferase reporter and RNA immunoprecipitation (RIP) were employed to confirm the binding of circ-0046263 with miR-133a-5p. Colony formation, proliferation, wound healing, transwell, western blot, and in vivo tumor growth and metastasis assays were performed to assess the roles of circ-0046263, miR-133a-5p, IGFBP3 and their interactions in NPC cells. Circ-0046263 was upregulated in both NPC cell lines and tissues. The in vitro functional studies revealed that knockdown of circ-0046263 inhibited the proliferation, invasion, and migration of NPC cells, whereas its overexpression produced the opposite result. In vivo experiments indicated that knockdown or overexpression of circ-0046263 attenuated or promoted tumor growth and metastasis, respectively. Mechanistically, circ-0046263 could act as a miRNA sponge to absorb miR-133a-5p and upregulate the expression of miRNA downstream target IGFBP3. In addition, miR-133a-5p inhibition or IGFBP3 overexpression could rescue the malignant behavior induced by circ-0046263 silencing. Finally, circ-0046263 plays a tumor-promoting role in NPC to enhance malignant behavior through the miR-133a-5p/IGFBP3 axis, which could be a potential target for NPC therapy.

Downregulation of circular RNA hsa_circ_0000735 boosts prostate cancer sensitivity to docetaxel via sponging miR-7

Background

One of the main reasons for the failure of prostate cancer (PCa) treatment is the generation of chemoresistance. Circular RNA hsa_circ_0000735 (hsa_circ_0000735) is connected with the progression of cancer. Nevertheless, the role and regulatory mechanism of hsa_circ_0000735 in the resistance of PCa to docetaxel (DTX) are unclear.

Methods

Expression levels of hsa_circ_0000735 and miR-7-5p (miR-7) in tissue samples and cells were examined via quantitative real-time polymerase chain reaction (qRT-PCR). The DTX sensitivity, viability, colony formation, cell cycle progression, and apoptosis of DTX-resistant PCa cells were determined via Cell Counting Kit-8 (CCK-8), cell colony formation, or flow cytometry assays. The levels of multidrug resistance protein 1 (MDR1) protein, cyclinD1, and B cell lymphoma 2 (bcl-2) were detected by western blotting. The interaction between hsa_circ_0000735 and miR-7 was verified via dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays. The role of hsa_circ_0000735 in vivo was validated through tumor formation experiments.

Results

Hsa_circ_0000735 was upregulated and miR-7 was downregulated in DTX-resistant PCa tissues and cells. High hsa_circ_0000735 expression had a shorter overall survival. Both hsa_circ_0000735 knockdown and miR-7 mimic boosted DTX sensitivity, constrained viability, colony formation, cell cycle progression, and fostered apoptosis of DTX-resistant PCa cells. Also, hsa_circ_0000735 silencing elevated DTX sensitivity and repressed tumor growth in PCa in vivo. Mechanistically, hsa_circ_0000735 served as a sponge for miR-7. MiR-7 inhibition overturned hsa_circ_0000735 silencing-mediated impacts on DTX sensitivity and the malignant behaviors of DTX-resistant PCa cells.

Conclusion

Hsa_circ_0000735 downregulation boosted PCa sensitivity to DTX and reduced tumor growth via sponging miR-7, providing a promising prognostic biomarker and therapeutic target for PCa.

Circular RNAs in Embryogenesis and Cell Differentiation With a Focus on Cancer Development

In the recent years thousands of non-coding RNAs have been identified, also thanks to highthroughput sequencing technologies. Among them, circular RNAs (circRNAs) are a well-represented class characterized by the high sequence conservation and cell type specific expression in eukaryotes. They are covalently closed loops formed through back-splicing. Recently, circRNAs were shown to regulate a variety of cellular processes functioning as miRNA sponges, RBP binding molecules, transcriptional regulators, scaffold for protein translation, as well as immune regulators. A growing number of studies are showing that deregulated expression of circRNAs plays important and decisive actions during the development of several human diseases, including cancer. The research on their biogenesis and on the various molecular mechanisms in which they are involved is going very fast, however, there are still few studies that address their involvement in embryogenesis and eukaryotic development. This review has the intent to describe the most recent progress in the study of the biogenesis and molecular activities of circRNAs providing insightful information in the field of embryogenesis and cell differentiation. In addition, we describe the latest research on circRNAs as novel promising biomarkers in diverse types of tumors.

Emerging landscape of circular RNAs as biomarkers and pivotal regulators in osteosarcoma

Osteosarcoma represents the most prevailing primary bone tumor and the third most common cancer in children and adolescents worldwide. Among noncoding RNAs, circular RNAs (circRNAs) refer to a unique class in the shape of a covalently closed continuous loop with neither 5' caps nor 3'-polyadenylated tails, which are generated through back-splicing. Recently, with the development of whole-genome and transcriptome sequencing technologies, a growing number of circRNAs have been found aberrantly expressed in multiple diseases, including osteosarcoma. circRNA are capable of various biological functions including miRNA sponge, mediating alternatives, regulating genes at posttranscriptional levels, and interacting with proteins, indicating a pivotal role of circRNA in cancer initiation, progression, chemoresistance, and immune response. Moreover, circRNAs have been thrust into the spotlight as potential biomarkers and therapeutic targets in osteosarcoma. Herein, we briefly summarize the origin and biogenesis of circRNA with current knowledge of circRNA in tumorigenesis of osteosarcoma, aiming to elucidate the specific role and clinical implication of circRNAs in osteosarcoma.

CircEIF4G2 Promotes Tumorigenesis and Progression of Osteosarcoma by Sponging miR-218

Circular RNAs (circRNAs) play a key role in regulating the tumorigenesis and development of human cancers, including osteosarcoma (OS). Of note, the molecular mechanism underlying the progression of OS has remained largely unclear. The present study identified that a novel circRNA circEIF4G2 was upregulated in OS tissues and cells. Moreover, we constructed a circEIF4G2-mediated ceRNA network and revealed that circEIF4G2 was involved in regulating multiple cancer pathways, such as the EGFR signaling pathway, the PI3K-Akt signaling pathway, and the ErbB signaling pathway. Loss-of-function assays showed that circEIF4G2 knockdown significantly suppressed OS cell proliferation, migration, and invasion. Mechanically, we found that circEIF4G2 could directly bind to miR-218, and miR-218 mediated the effect of circEIF4G2 knockdown on OS progression. In conclusion, the present study showed that circEIF4G2 could be a potential biomarker for OS.

Emerging Role of Circular RNAs in Cancer

Circular RNAs (circRNAs), which are generated mainly from back-splicing of exons in precursor mRNAs (pre-mRNAs), are a novel class of endogenous covalently closed RNA molecules. Their functions as microRNA sponges, protein scaffolds, and modulators of transcription and splicing, as well as occasional templates for polypeptide production, are beginning to be recognized, though the investigation of circRNAs is in its infancy. circRNAs play critical roles in diverse cellular processes. Aberrant expression of circRNAs in malignancies sustains cellular growth and proliferation, promotes cellular invasiveness, and circumvents cellular senescence and death, suggesting their potential for exploitation as clinical biomarkers and therapeutic targets. In this review, we highlight recent progress in research on circRNAs in cancer, emphasizing the molecular mechanisms and potential clinical value of circRNAs.

Circular RNAs in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a geographical distributed epithelial tumor of head and neck, which is prevalent in east Africa and Asia, especially southern China. Moreover, NPC has an unfavorable clinical effect and is prone to metastasis at an advanced stage. Although the recovery rate of patients has been improved due to concurrent chemoradiotherapy, poor curative effects and low overall survival remain key issues. The precise mechanisms and pivotal regulators of NPC remain still unclear. To improve the therapeutic efficacy, we focused on related-NPC circular RNAs (circRNAs). CircRNAs are a unique type of endogenous non-coding RNAs (ncRNAs) with a covalent closed-loop structure. Their expression is rich, stable and conservative. Different circRNA have specific tissue and developmental stages and can be detected in body fluids. In addition, circRNAs are involved in multiple pathological processes, especially in cancers. In recent years, using high-throughput indicator technology and bioinformatics technology, a large number of circRNAs have been identified in NPC cells and verified to have biological functions and mechanisms of action. This article aims to provide a retrospective review of the latest research on the proliferation and migration of related-NPC circRNA. Specifically, we focused on the roles and mechanisms of circRNAs in the development and progression of NPC.

CONCLUSION

CircRNA can act as an oncogene or tumor suppressor gene and participate in NPC progression (e.g., proliferation, apoptosis, migration, and invasion). In short, circRNAs have potential as biomarkers for the diagnosis, prognosis and treatment of NPC.

Circular RNA: A novel potential biomarker for skin diseases

Circular RNA (circRNA) has been classified as noncoding RNA with a covalent closed continuous loop, the 3'and 5' ends of which are normally joined together to increase its own stability. More recently, circRNA has been shown to encode proteins and may be involved in the regulation of gene transcription. This provides more evidence for the involvement of circRNA in disease progression. Accumulating investigations have found that the expression of many circRNAs is abnormal in plenty of skin diseases such as malignant melanoma, psoriasis, and abnormal wound healing. Herein, in addition to the summary of recent studies on the nuclear export, N⁶-methyladenosine (m⁶A) modification, degradation, and other biogenesis and properties of circRNA, we highlight the importance of circRNAin skin diseases. Although their exact roles and mechanisms in most skin disease remain preliminary, circRNAs have potential applications as diagnostic biomarkers and novel therapeutic targets for skin diseases due to its structural and functional properties (stability, specificity and sensitivity), which is worthy of deeper exploration and greater research efforts.

Vitamin D3 mediates miR-15a-5p inhibition of liver cancer cell proliferation via targeting E2F3

Vitamin D3 has been demonstrated to suppress the development and progression of liver cancer, but the mechanism is unclear. The effects of vitamin D3 and microRNA (miR)-15a-5p on liver cancer cells were investigated in the present study using MTT and colony formation assays, flow cytometry, western blotting and reverse transcription-quantitative PCR. A dual-luciferase reporter assay was performed to determine whether E2F transcription factor 3 (E2F3) was a target of miR-15a-5p. The effects of silencing the E2F3 gene expression in liver cancer cells were investigated using a small interfering RNA. Vitamin D3 suppressed liver cancer cell proliferation, induced apoptosis and increased miR-15a-5p expression. Treatment with the miR-15a-5p mimics significantly suppressed liver cancer cell proliferation compared with that of the controls. Bioinformatics analysis and a dual-luciferase reporter assay demonstrated that E2F3 was a target of miR-15a-5p and that silencing E2F3 inhibited liver cancer cell proliferation. Therefore, Vitamin D3 suppressed cell proliferation by miR-15a-5p-mediated silencing of E2F3 gene expression. These findings suggested a role for vitamin D3 and E2F3 targeting as potential novel liver cancer therapies.

Cell proliferation and invasion is promoted by circSERPINA3 in nasopharyngeal carcinoma by regulating miR-944/MDM2 axis

Growing evidence has demonstrated that in tumor progression, circular RNAs (circRNAs) play important roles. However, the roles of circRNAs in nasopharyngeal carcinoma (NPC) have not been fully elucidated. In this study, it was demonstrated that that hsa_circ_0033074 (circSERPINA3) expression was found to be significantly upregulated in NPC tissues and cell lines. CircSERPINA3 inhibition significantly attenuated the invasion and proliferation abilities of NPC cells. The mechanism by which circSERPINA3 interacted with miR-944 was identified and MDM2 was demonstrated to function as a target gene of miR-944. Rescue experiments showed that miR-944 inhibitors or MDM2 overexpression reserved the effects of circSERPINA3 knockdown on NPC progression. Therefore, our study uncovered the circSERPINA3/miR-944/MDM2 axis in NPC, which may be a potential NPC therapeutic target.