Hsa_circ_0007534/miR-761/ZIC5 regulatory loop modulates the proliferation and migration of glioma cells

The regulatory role and clinical application prospects of circRNA in the occurrence and development of CNS tumors

BACKGROUND

Central nervous system (CNS) tumors originate from the spinal cord or brain. The study showed that even with aggressive treatment, malignant CNS tumors have high mortality rates. However, CNS tumor risk factors and molecular mechanisms have not been verified. Due to the reasons mentioned above, diagnosis and treatment of CNS tumors in clinical practice are currently fraught with difficulties. Circular RNAs (circRNAs), single-stranded ncRNAs with covalently closed continuous structures, are essential to CNS tumor development. Growing evidence has proved the numeral critical biological functions of circRNAs for disease progression: sponging to miRNAs, regulating gene transcription and splicing, interacting with proteins, encoding proteins/peptides, and expressing in exosomes.

AIMS

This review aims to summarize current progress regarding the molecular mechanism of circRNA in CNS tumors and to explore the possibilities of clinical application based on circRNA in CNS tumors.

METHODS

We have summarized studies of circRNA in CNS tumors in Pubmed.

RESULTS

This review summarized their connection with CNS tumors and their functions, biogenesis, and biological properties. Furthermore, we introduced current advances in clinical RNA-related technologies. Then we discussed the diagnostic and therapeutic potential (especially for immunotherapy, chemotherapy, and radiotherapy) of circRNA in CNS tumors in the context of the recent advanced research and application of RNA in clinics.

CONCLUSIONS

CircRNA are increasingly proven to participate in decveloping CNS tumors. An in-depth study of the causal mechanisms of circRNAs in CNS tomor progression will ultimately advance their implementation in the clinic and developing new strategies for preventing and treating CNS tumors.

The "LINC" between Δ40p53-miRNA Axis in the Regulation of Cellular Homeostasis

Previous research has shown that Δ40p53, the translational isoform of p53, can inhibit cell growth independently of p53 by regulating microRNAs. Here, we explored the role of Δ40p53 in regulating the long noncoding RNA-micro-RNA-cellular process axis, specifically focusing on LINC00176. Interestingly, LINC00176 levels were predominantly affected by the overexpression/stress-mediated induction and knockdown of Δ40p53 rather than p53 levels. Additional assays revealed that Δ40p53 transactivates LINC00176 transcriptionally and could also regulate its stability. RNA immunoprecipitation experiments revealed that LINC00176 sequesters several putative microRNA targets, which could further titrate several mRNA targets involved in different cellular processes. To understand the downstream effects of this regulation, we ectopically overexpressed and knocked down LINC00176 in HCT116 p53-/- (harboring only Δ40p53) cells, which affected their proliferation, cell viability, and expression of epithelial markers. Our results provide essential insights into the pivotal role of Δ40p53 in regulating the novel LINC00176 RNA-microRNA-mRNA axis independent of FL-p53 and in maintaining cellular homeostasis.

Circ-SHPRH in human cancers: a systematic review and meta-analysis

Circular RNA (circRNA) molecules are noncoding RNAs with ring-like structures formed by covalent bonds and are characterized by no 5'caps or 3'polyadenylated tails. Increasing evidence shows that circRNAs may play an important role in tumorigenesis and cancer metastasis. Circ-SHPRH originates from exons 26-29 of the SHPRH gene, and it is closely associated with human cancers. We searched PubMed, Web of Science, and Embase databases for relevant literatures until 24 December 2022. Eighteen research papers were included in this review, and 11 papers were selected for meta-analysis after screening. Three eligible published studies about circ-SHPRH were enrolled based on their tumor diagnosis aspect, 7 eligible published studies were related to overall survival (OS), and 3 eligible published studies were related to tumor grade. Many studies have shown that circ-SHPRH acts as a miRNA sponge or encodes a protein to regulate downstream genes or signal pathways, and exerts specific biological functions that affect the proliferation, invasion, and apoptosis of cancer cells. Meta-analysis showed that patients with high expression of circ-SHPRH had better OS (HR = 0.53, 95% CI 0.38-0.74, p-value <0.05) and lower TNM stage (HR = 0.33, 95% CI 0.18-0.62, p-value = 0.001). In addition, circ-SHPRH has potential diagnostic value (AUC = 0.8357). This review will help enrich our understanding of the role and mechanism of circ-SHPRH in human cancers. Circ-SHPRH has the potential to be a novel diagnostic and prognostic biomarker for various solid cancers.

The role of circular RNA hsa_circ_0001789 as a diagnostic biomarker in gastric carcinoma

BACKGROUND

Circular RNA (circRNA) is a kind of endogenous non-coding RNAs and has shown diagnostic values in various cancers. This study aimed to explore whether hsa_circ_0001789 could be a novel biomarker for gastric cancer (GC).

METHODS

Quantitative reverse transcriptase PCR was used to detect the expression of hsa_circ_0001789 in 108 paired GC and paracancerous tissues as well as in 24 paired plasma specimens. Possible associations between hsa_circ_0001789 expression and clinicopathologic factors of GC patients were examined using one-way ANOVA. A receiver operating characteristic (ROC) curve was established to investigate the diagnostic value of hsa_circ_0001789 in GC.

RESULTS

GC tissues and plasma samples showed down-regulated hsa_circ_0001789 levels than their counterparts, which were closely correlated with the malignant characteristics of GC. The area under the ROC curve (AUC) of hsa_circ_0001789 in GC tissues was 0.82, while the cut-off value was 9.5, indicating a favorable diagnostic value. Compared with the traditional tumor biomarkers, hsa_circ_0001789 had preferred AUCs that reached 0.786 for predicting the stage of invasion, 0.603 for predicting the stage of lymphatic metastasis, 0.722 for predicting the stage of distant metastasis, and 0.786 for predicting TNM stage.

CONCLUSIONS

Hsa_circ_0001789 may be a novel biomarker for the diagnosis of gastric carcinoma.

circRNA-MSR regulates the expression of FBXO21 to inhibit chondrocyte autophagy by targeting miR-761 in osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease and is the most prevalent and disabling form of arthritis worldwide. Autophagy plays a vital role in OA. This study aimed to explore whether covalently closed circular RNA MSR (circRNA-MSR) could affect the F-box Only Protein 21 (FBXO21) expression by targeting microRNA-761 (miR-761), thereby affecting the autophagy in OA chondrocytes. Clinical OA tissues were collected, and circRNA-MSR, miR-761, and FBXO21 expressions were detected via quantitative real-time polymerase chain reaction (qRT-PCR). An in vitro OA model was constructed by treating C28/I2 cells with LPS and treating them with overexpression or knockdown vector of circRNA-MSR, miR-761, and FBXO21, and autophagy inhibitor 3-MA. Fluorescence in situ hybridization (FISH) determined the location of circRNA-MSR and miR-761. Dual-luciferase assay assessed circRNA-MSR and miR-761, along with the bindings of miR-761 and FBXO21. Cell viability was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. LC3 II/I, p62 and beclin 1 expressions were detected via the western blot. circRNA-MSR and FBXO21 levels were elevated in OA, but miR-761 level was inhibited. Suppressing circRNA-MSR promoted the autophagy of LPS-treated cells. circRNA-MSR could bind to miR-761 and inhibit its expression. MiR-761 inhibition reversed the promoted autophagy caused by circRNA-MSR knockdown in LPS-treated C28/I2 cells. Moreover, miR-761 could target FBXO21 and inhibit its expression. FBXO21 overexpression reversed the increased autophagy caused by miR-761 overexpression in LPS-treated C28/I2 cells. circRNA-MSR could affect FBXO21 level via targeting miR-761, thereby repressing autophagy in OA chondrocytes, providing a new target and strategy for OA treatment.

Circ_0007534 as new emerging target in cancer: Biological functions and molecular interactions

Circular RNA (circRNAs), an important member of the non-coding RNA (ncRNA) family, are widely expressed in a variety of biological cells. Owing to their stable structures, sequence conservations, and cell- or tissue-specific expressions, these RNA have become a popular subject of scientific research. With the development of sequencing methods, it has been revealed that circRNAs exert their biological function by sponging microRNAs (miRNAs), regulating transcription, or binding to proteins. Humans have historically been significantly impacted by various types of cancer. Studies have shown that circRNAs are abnormally expressed in various cancers and are involved in the occurrence and development of malignant tumors, such as tumor cell proliferation, migration, and invasion. As one of its star molecules, circ_0007534 is upregulated in colorectal, cervical, and pancreatic cancers; is closely related to the occurrence, development, and prognosis of tumors; and is expected to become a novel tumor marker and therapeutic target. This article briefly reviews the expression and mechanism of circ_0007534 in malignant tumors based on the domestic and foreign literature.

Patulin and LL‐Z1640 ‐2 induce apoptosis of cancer cells by decreasing endogenous protein levels of Zic family member 5

Zic family member 5 (ZIC5) is a transcription factor that promotes the survival of several cancer cell types. As ZIC5 is expressed at minimal levels in normal human adult tissues, it is a potential therapeutic target. In this study, we screened a chemical library containing 3398 compounds that includes pre‐existing drugs and compounds with known effects to identify ZIC5 inhibitors. In the first screening, 18 hit compounds decreased GFP intensity in melanoma A375 cells overexpressing GFP‐tagged ZIC5. In the second screening, five compounds that attenuated ZIC5 protein levels in A375 cells were identified. Among them, LL‐Z1640‐2 and patulin selectively induced apoptosis in melanoma cells expressing ZIC5, while only inducing very low levels of apoptosis in normal human melanocytes, which have no detectable ZIC5 expression. LL‐Z1640‐2 and patulin also induced apoptosis in BRAF inhibitor‐resistant melanoma, pancreatic cancer, cholangiocarcinoma and colorectal cancer cells. LL‐Z1640‐2‐ and patulin‐mediated suppression of melanoma proliferation were rescued by ZIC5 overexpression. These results suggest that LL‐Z1640‐2 and patulin are promising compounds that decrease ZIC5 expression to induce apoptosis in cancer cells.

Downregulation of miR-761 ameliorates radiation-induced pulmonary fibrosis by regulating PGC-1α

Background: Radiation-induced pulmonary fibrosis (RIPF) is a serious complication in patients treated with transthoracic irradiation. To date, there are no effective drugs for RIPF treatment. In this study, we attempted to explore the function of miR-761 in RIPF, further investigate its potential mechanism and evaluate its effectiveness in the treatment of RIPF. Methods: qRT-PCR analysis was used to detect miR-761 and peroxisome proliferator-activated receptor gamma (PPARg) coactivator-1 (PGC-1α) expression. Western Blot (WB) assay was applied to verify the regulation of PGC-1α by miR-761 and the expression of fibrosis-related proteins. Gel contraction assay was performed to demonstrate the level of fibroblast activation in vitro. A mouse RIPF model was used to validate the anti-fibrotic effect of Antagomir761. Bioinformatics analysis and dual-luciferase reporter assays were utilized to confirm the regulation relationship between miR-761 and PGC-1α. Results: The results showed that miR-761 was significantly elevated in irradiated mice lungs and fibroblasts. Overexpression of miR-761 in vitro promoted fibroblast activation. Whereas inhibition of miR-761 attenuated the degree of RIPF and inhibited fibroblast activation. Mechanistically, PGC-1α was a direct and functional target of miR-761, overexpression of PGC-1α inhibited irradiation-induced fibroblast activation, and knockdown of PGC-1α caused miR-761 inhibitor loses its anti-activation ability in irradiated cells. Conclusion: Our findings demonstrated that miR-761 regulated RIPF by targeting PGC-1α. Inhibition of miR-761 restored PGC-1α expression and attenuated RIPF damage, and miR-761 was a potential target for preventing the development of RIPF.

Zic family member 5 promotes survival in human pancreatic cancer and cholangiocarcinoma cells

Pancreatic ductal adenocarcinoma (PDAC) and cholangiocarcinoma (CCA) are malignant tumors with poor prognosis because of the limited effectiveness of traditional chemotherapy and few effective molecular therapeutic agents. Here, we determined the essential roles of Zic family member 5 (ZIC5) in the survival of PDAC and CCA cells. The results showed that ZIC5 is strongly expressed in PDAC and CCA tissues, while ZIC5 expression is barely observed in most normal human adult tissues. Furthermore, ZIC5 expression is related to poor prognosis of patients with PDAC. ZIC5 knockdown via small interfering RNA decreased the phosphorylation of signal transducer and activator of transcription 3 (STAT3), a protein that is associated with PDAC and CCA aggressiveness. However, ZIC5 knockdown induced cell death regardless of STAT3 activation, which is promoted by interleukin (IL) −6, a factor associated with inflammation. Furthermore, knockdown of ZIC5 in PDAC and CCA cells additively or synergistically induced apoptosis with the anti-cancer drug gemcitabine. Thus, ZIC5 constitutes a potential therapeutic target for the treatment of PDAC and CCA.

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ZIC5 is expressed in PDAC and CCA, while barely observed in normal adult tissues.

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ZIC5 expression is related to poor prognosis of patients with PDAC.

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ZIC5 knockdown induces apoptosis in several PDAC and CCA cell lines.

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Knockdown of ZIC5 additively or synergistically induces apoptosis with gemcitabine.

The function and regulation network mechanism of circRNA in liver diseases

Circular RNA (circRNA), a new type of endogenous non-coding RNA, is abundantly present in eukaryotic cells, and characterized as stable high conservation and tissue specific expression. It has been generated increasing attention because of their close association with the progress of diseases. The liver is the vital organ of humans, while it is prone to acute and chronic diseases due to the influence of multiple pathogenic factors. Moreover, hepatocellular carcinoma (HCC) is the one of most common cancer and the leading cause of cancer death worldwide. Overwhelming evidences indicate that some circRNAs are differentially expressed in liver diseases, such as, HCC, chronic hepatitis B, hepatic steatosis and hepatoblastoma tissues, etc. Additionally, these circRNAs are related to proliferation, invasion, migration, angiogenesis, apoptosis, and metastasis of cell in liver diseases and act as oncogenic agents or suppressors, and linked to clinical manifestations. In this review, we briefly summarize the biogenesis, characterization and biological functions, recent detection and identification technologies of circRNA, and regulation network mechanism of circRNA in liver diseases, and discuss their potential values as biomarkers or therapeutic targets for liver diseases, especially on HCC.

Identification of circRNA Biomarker for Gastric Cancer through Integrated Analysis

Gastric cancer (GC) is one of the most common malignant tumors and ranks third in cancer mortality globally. Although, a lot of advancements have been made in diagnosis and treatment of gastric cancer, there is still lack of ideal biomarker for the diagnosis and treatment of gastric cancer. Due to the poor prognosis, the survival rate is not improved much. Circular RNAs (circRNAs) are single-stranded RNAs with a covalently closed loop structure that don't have the 5'-3' polarity and a 3' polyA tail. Because of their circular structure, circRNAs are more stable than linear RNAs. Previous studies have found that circRNAs are involved in several biological processes like cell cycle, proliferation, apoptosis, autophagy, migration and invasion in different cancers, and participate in some molecular mechanisms including sponging microRNAs (miRNAs), protein translation and binding to RNA-binding proteins. Several studies have reported that circRNAs play crucial role in the occurrence and development of different types of cancers. Although, some studies have reported several circRNAs in gastric cancer, more studies are needed in searching new biomarkers for gastric cancer diagnosis and treatment. Here, we investigated potential circRNA biomarkers for GC using next-generation sequencing (NGS) data collected from 5 paired GC samples. A total of 45,783 circRNAs were identified in all samples and among them 478 were differentially expressed (DE). The gene ontology (GO) analysis of the host genes of the DE circRNAs showed that some genes were enriched in several important biological processes, molecular functions and cellular components. The Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis revealed that some host genes were enriched in several GC related pathways. The circRNA-miRNA-gene interaction network analysis showed that two circRNAs circCEACAM5 and circCOL1A1 were interacted with gastric cancer related miRNAs, and their host genes were also the important therapeutic and prognostic biomarkers for GC. The experimental results also validated that these two circRNAs were DE in GC compared to adjacent normal tissues. Overall, our findings suggest that these two circRNAs circCEACAM5 and circCOL1A1 might be the potential biomarkers for the diagnosis and treatment of GC.

Potential roles of hsa_circ_000839 and hsa_circ_0005986 in breast cancer

Background

Breast cancer (BC) is one of the leading causes of death among women around the world. Circular RNAs (circRNAs) are a newly discovered group of non‐coding RNAs that their roles are being investigated in BC and other cancer types. In this study, we evaluated the association of hsa_circ_0005986 and hsa_circ_000839 in tumor and adjacent normal tissues of BC patients with their clinicopathological characteristics.

Materials and methods

Total RNA was extracted from tumors and adjacent non‐tumor tissues by the Trizol isolation reagent, and cDNA was synthesized using First Strand cDNA Synthesis Kit (Thermo Scientific). The expression level of hsa_circ_0005986 and hsa_circ_000839 was quantified using RT‐qPCR. Online in silico tools were used for identifying potentially important competing endogenous RNA (ceRNA) networks of these two circRNAs.

Results

The expression level of hsa_circ_0005986 and hsa_circ_000839 was lower in the tumor as compared to adjacent tissues. The expression level of hsa_circ_0005986 in the patients who had used hair dye in the last 5 years was significantly lower. Moreover, a statistically significant negative correlation between body mass index (BMI) and hsa_circ_000839 expression was observed. In silico analysis of the ceRNA network of these circRNAs revealed mRNAs and miRNAs with crucial roles in BC.

Conclusion

Downregulation of hsa_circ_000839 and hsa_circ_0005986 in BC tumors suggests a tumor‐suppressive role for these circRNAs in BC, meriting the need for more experimentations to delineate the exact mechanism of their involvement in BC pathogenesis.

Dissecting the Role of Circular RNAs in Sarcomas with Emphasis on Osteosarcomas

Circular RNAs (circRNAs) are single-stranded RNAs generated from exons back-splicing from a single pre-mRNA, forming covalently closed loop structures which lack 5'-3'-polarity or polyadenylated tail. Ongoing research depicts that circRNAs play a pivotal role in tumorigenesis, tumor progression, metastatic potential and chemoresistance by regulating transcription, microRNA (miRNA) sponging, RNA-binding protein interactions, alternative splicing and to a lesser degree, protein coding. Sarcomas are rare malignant tumors stemming from mesenchymal cells. Due to their clinically insidious onset, they often present at advanced stage and their treatment may require aggressive chemotherapeutic or surgical options. This review is mainly focused on the regulatory functions of circRNAs on osteosarcoma progression and their potential role as biomarkers, an area which has prompted lately extensive research. The attributed oncogenic role of circRNAs on other mesenchymal tumors such as Kaposi Sarcoma (KS), Rhabdomyosarcoma (RMS) or Gastrointestinal Stromal Tumors (GISTs) is also described. The involvement of circRNAs on sarcoma oncogenesis and relevant emerging diagnostic, prognostic and therapeutic applications are expected to gain more research interest in the future.

CircRFX3 contributes to glioma progression through the circRFX3-miR-1179/miR-1229-VASP axis

Background

Circular RNAs (circRNAs) are implicated in the carcinogenesis of human cancers. However, the functional roles of circRFX3 in glioma are not elucidated.

Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed for the levels of circRFX3, RFX3, miR-1179, miR-1229 and vasodilator stimulated phosphoprotein (VASP). Actinomycin D assay and RNase R assay were employed to analyze the characteristics of circRFX3. Cell Counting Kit-8 (CCK-8) assay and colony formation assay were conducted for cell proliferation. Transwell assay was used for cell migration and invasion. Flow cytometry analysis was adopted for cell apoptosis. RNA pull-down assay, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were employed to analyze the interaction between miR-1179/miR-1229 and circRFX3 or VASP. Western blot assay was conducted for VASP protein level. Murine xenograft model assay was used to investigate the role of circRFX3 in vivo.

Results

CircRFX3 level was increased in glioma tissues and cells. Knockdown of circRFX3 suppressed glioma cell proliferation, migration and invasion and promoted apoptosis in vitro and repressed tumorigenesis of glioma in vivo. MiR-1179 and miR-1229 were identified to be the targets of circRFX3. MiR-1179 or miR-1229 inhibition reversed the impacts of circRFX3 knockdown on glioma cell malignant behaviors. Additionally, VASP was demonstrated to be the target gene of miR-1179 and miR-1229, and VASP overexpression abolished the effect of circRFX3 knockdown on glioma cell progression.

Conclusion

CircRFX3 served as a tumor promoter in glioma via modulating miR-1179/miR-1229-VASP axis, which might provide a novel target for glioma therapy.

Circ_0007534 Silencing Inhibits the Proliferation, Migration and Invasion and Induces the Apoptosis of Glioma Cells Partly Through Down-Regulating PROX1 Via Elevating miR-22-3p Level

Glioma is a common malignant brain neoplasm. The role and mechanism of circular RNA 0,007,534 (circ_0007534) in glioma progression were investigated in this study. The expression of circ_0007534, microRNA-22-3p (miR-22-3p) and prospero homeobox protein 1 (PROX1) messenger RNA (mRNA) was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The proliferation, migration and invasion abilities were analyzed by colony formation assay, transwell migration assay and transwell invasion assay. Cell apoptosis was assessed through measuring the activity of Caspase-3 using the Caspase-3 kit and the apoptosis rate using flow cytometry. Dual-luciferase reporter assay was used to confirm the target interaction between miR-22-3p and circ_0007534 or PROX1. The protein level of PROX1 was examined by Western blot assay. Animal studies were conducted to analyze the influence of circ_0007534 interference on xenograft tumor growth in vivo. Circ_0007534 was highly expressed in glioma tissues and cell lines relative to that in normal tissues and NHA cell line. Circ_0007534 knockdown suppressed the proliferation and motility while induced the apoptosis of glioma cells. Circ_0007534 negatively regulated miR-22-3p level through targeting it in glioma cells. Circ_0007534 interference-induced influences in glioma cells were partly overturned by the silencing of miR-22-3p. PROX1 was a target of miR-22-3p, and circ_0007534 interference-mediated effects in glioma cells were largely diminished by the overexpression of PROX1. Circ_0007534 interference restrained glioma development in vivo. Circ_0007534 aggravated glioma progression through elevating PROX1 expression via targeting miR-22-3p, which provided new targets for the diagnosis and treatment of glioma.

The Use of circRNAs as Biomarkers of Cancer

CircRNAs are a subclass of lncRNAs that have been found to be abundantly present in a wide range of species, including humans. CircRNAs are generally produced by a noncanonical splicing event called backsplicing that is dependent on the canonical splicing machinery, giving rise to circRNAs classified into three main categories: exonic circRNA, circular intronic RNA, and exon-intron circular RNA. Notably, circRNAs possess functional importance and display their functions through different mechanisms of action including sponging miRNAs, or even being translated into functional proteins. In addition, circRNAs also have great potential as biomarkers, particularly in cancer, thanks to their high stability, tissue type and developmental stage specificity, and their presence in biological fluids, which make them promising candidates as noninvasive biomarkers. In this chapter, we describe the most commonly used techniques for the study of circRNAs as cancer biomarkers, including high-throughput techniques such as RNA-Seq and microarrays, and other methods to analyze the presence of specific circRNAs in patient samples.

Down-regulation of hsa_circ_0006470 predicts tumor invasion: A new biomarker of gastric cancer

Background

Gastric cancer (GC) is a common cancer. Circular RNAs (circRNAs) regulate the pathogenesis of GC. This study aims to explore its potential as a GC biomarker.

Methods

The expression of hsa_circ_0006470 in GC tissues and GC cell lines was measured by quantitative reverse transcription‐polymerase chain reaction. The diagnostic value of hsa_circ_0006470 was estimated by the receiver operating characteristic (ROC) curve.

Results

Compared with adjacent normal tissues, the expression of hsa_circ_0006470 in GC tissues was significantly lower. The expression levels of hsa_circ_0006470 in different TNM stages and different invasion degrees were significantly different. The area under the ROC curve was 0.783, with sensitivity and specificity 0.725 and 0.750, respectively.

Conclusions

Hsa_circ_0006470 has a high value as a diagnostic biomarker for GC.

Circular RNAs as novel potential biomarkers for pancreatic cancer

Pancreatic cancer (PaCa) is the fourth leading cause of cancer-related deaths in the United States, and the vast majority of these malignancies are pancreatic ductal adenocarcinomas (PDAC), but there is still a lack of early detection biomarkers for PaCa. Unlike linear RNAs, circRNAs form covalently closed continuous loops and can act as mammalian gene regulators. They may be diagnostic or predictive biomarkers for some tumors, also be novel potential therapeutic targets in different diseases. This review focuses on (1) the biogenesis of circRNAs, RNA binding proteins (RBPs) and complementary sequences of circRNAs; (2) the characteristics of circRNAs which allow them to interact with miRNAs; (3) the roles of circRNAs playing in the regulation of gene expression, cell behavior and cancer, and their potential role as novel biomarkers and therapeutic targets in pancreatic cancer.

Circular RNA circAFF2 accelerates gastric cancer development by activating miR-6894-5p and regulating ANTXR 1 expression

BACKGROUND

Circular RNAs (circRNAs) contain a new class of non-coding RNAs that play an important role in adjusting biological function and gene expression. But the function of circRNAs in gastric cancer remains unclear. In the present research, we explored the functions of circular RNA AFF2(circAFF2, hsa_circ_0001947) in gastric cancer cells and an animal model of gastric cancer.

METHODS

The expression of circAFF2, microRNA-6894-5p (miR-6894-5p), and Anthrax toxin receptor 1 (ANTXR 1) were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Cell counting kit 8 (CCK-8) and transwell assays were used to analyze the knockdown effects of circAFF2, miR-6894-5p, and overexpression of ANTXR 1 on cell proliferation, migration, and invasion abilities. Binding interactions between, circAFF2 and miR-6894-5p and between, miR-6894-5p and ANTXR 1 were detected by Dual-luciferase reporter assays. Levels of protein expression were analyzed by Western blotting. Tumor models were established by subcutaneous injection of tumor cells in nude mice.

RESULT

The result showed that circAFF2 expression was significantly increased in gastric cancer cell lines and tissues. The knockdown of circAFF2 dramatically suppressed the cell migration, invasion and proliferation of gastric cancer cells. In vivo studies showed that knockdown of circAFF2 delayed tumor growth. Furthermore, we revealed that circAFF2 functioned as a sponge to absorb miR-6984-5p and elevated the expression of ANTXR 1.

CONCLUSION

CircAFF2 acts as an oncogene in gastric cancer and exerts its effects via miR-6894-5p/ANTXR 1 signaling.

Competing Endogenous RNA Networks in Glioma

Gliomas are the most common and malignant primary brain tumors. Various hallmarks of glioma, including sustained proliferation, migration, invasion, heterogeneity, radio- and chemo-resistance, contribute to the dismal prognosis of patients with high-grade glioma. Dysregulation of cancer driver genes is a leading cause for these glioma hallmarks. In recent years, a new mechanism of post-transcriptional gene regulation was proposed, i.e., "competing endogenous RNA (ceRNA)." Long non-coding RNAs, circular RNAs, and transcribed pseudogenes act as ceRNAs to regulate the expression of related genes by sponging the shared microRNAs. Moreover, coding RNA can also exert a regulatory role, independent of its protein coding function, through the ceRNA mechanism. In the latest glioma research, various studies have reported that dysregulation of certain ceRNA regulatory networks (ceRNETs) accounts for the abnormal expression of cancer driver genes and the establishment of glioma hallmarks. These achievements open up new avenues to better understand the hidden aspects of gliomas and provide new biomarkers and potential efficient targets for glioma treatment. In this review, we summarize the existing knowledge about the concept and logic of ceRNET and highlight the emerging roles of some recently found ceRNETs in glioma progression.

Circ_0000020 elevates the expression of PIK3CA and facilitates the malignant phenotypes of glioma cells via targeting miR-142-5p

BACKGROUND

Multiple circular RNAs (circRNAs) have been recently described as crucial oncogenic factors or tumor suppressors. This study aimed to investigate the role of circ_0000020 in glioma progression.

METHODS

Circ_0000020 and miR-142-5p expressions in glioma samples were assessed through qRT-PCR, and then the association between pathological indexes and circ_0000020 expressions was analyzed. Functional experiment was performed with human glioma cell lines U251 and U87. Gain-of-function and loss-of-function models were established. CCK-8 assay was used to detect glioma cell proliferation. Transwell assay was used to examine glioma cell migration and invasion. The regulatory relationships among circ_0000020, miR-142-5p and phosphatidylinositol 3-kinase C (PIK3CA) were investigated by bioinformatics analysis, luciferase reporter assay, qRT-PCR and Western blot. In vivo tumorigenesis assay was performed with nude mice to further validate the demonstrations of in vitro experiments.

RESULTS

Circ_0000020 expression in glioma samples was remarkably increased compared with that in normal brain tissues and its high expression was associated with unfavorable pathological indexes. Circ_0000020 overexpression remarkably accelerated proliferation, migration and invasion of glioma cells. Accordingly, circ_0000020 knockdown suppressed the malignant phenotypes of glioma cells. Circ_0000020 overexpression significantly reduced miR-142-5p expression by sponging it, and circ_0000020 could enhance the expression of PIK3CA, which was a target gene of miR-142-5p.

CONCLUSIONS

Circ_0000020 promotes glioma progression via miR-142-5p/PIK3CA axis.

Down-regulation of circular RNA hsa_circ_0007534 suppresses cell growth by regulating miR-219a-5p/SOX5 axis in osteosarcoma

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The interaction between circ_0007534 and miR-219a-5p is confirmed for the first time.

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The interaction between miR-219a-5p and SOX5 is confirmed for the first time.

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Circ_0007534 knockdown inhibits the progression of osteosarcoma cells.

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Circ_0007534 regulates the growth of osteosarcoma cells through modulating miR-219a-5p/SOX5 axis.

Introduction

Circular RNA circ_0007534 and microRNA-219a (miR-219a-5p) were reported to be involved in osteosarcoma (OS) development. Osteosarcoma (OS) is one of the most common malignant bone tumors, which was more prone to occur in the metaphysis of long bones, including distal femur and proximal tibia. However, the detailed mechanisms were not fully clear. The purpose of this research was to reveal the functional mechanisms of circ_0007534 and miR-219a-5p in OS.

Methods

The levels of genes were determined by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell proliferation ability was detected by cell counting kit-8 (CCK-8) and colony formation assay. Cell migration and invasion abilities were measured using the transwell assay. Furthermore, the interaction between miR-219a-5p and circ_0007534 or SRY (sex-determining region Y)-box 5 (SOX5) was predicted by starbaseV3.0, and confirmed by the dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Besides, tumor xenograft experiment was performed to analyze the effect of circ_0007534 depletion on tumor growth in vivo.

Results

The levels of circ_0007534 and SOX5 were increased, while the miR-219a-5p level was decreased in OS tissues and cells. Circ_0007534 knockdown repressed the proliferation, colony formation, migration, and invasion in OS cells. Circ_0007534 targeted miR-219a-5p, and miR-219a-5p interacted with SOX5. Furthermore, circ_0007534 regulated the growth of OS cells through modulating the levels of miR-219a-5p and SOX5.

Conclusion

Our finding demonstrated that circ_0007534 knockdown suppressed the growth of OS cells via regulating miR-219a-5p/SOX5 axis, providing a potential target for OS treatment and diagnosis.

Knockdown of circRNA_0007534 suppresses the tumorigenesis of cervical cancer via miR-206/GREM1 axis

BACKGROUND

Increasing evidence manifested that circular RNAs (circRNAs) acted as crucial regulators in human cancers by targeting the miRNA/mRNA axis, including cervical cancer (CC). Circ_0007534 was reported to promote CC cell proliferation and invasion by the miR-498/BMI-1 axis. The aim of this study was to explore a novel miRNA/mRNA network underlying circ_0007534 in CC regulation.

METHODS

The quantitative real-time polymerase chain reaction (qRT-PCR) was implemented to examine the levels of circ_0007534, miR-206 and Gremlin1 (GREM1). Cell viability was determined using MTT assay. BrdU and colony formation assays were performed for analyzing cell proliferation. Cell apoptosis was assessed by flow cytometry. The protein levels of GREM1 and apoptotic markers (Bcl-2, Bax, C-Caspase3) were measured via western blot. Cell invasion was detected by transwell assay. The target relationship was analyzed by dual-luciferase reporter assay. The impact of circ_0007534 on CC growth in vivo was ascertained by xenograft assay.

RESULTS

Circ_0007534 expression was aberrantly increased in CC tissues and cells. Functionally, knockdown of circ_0007534 reduced CC cell growth and invasion but motivated apoptosis. In the mechanism, circ_0007534 targeted miR-206 and its regulatory function was associated with sponging miR-206. Moreover, circ_0007534 was found to regulate GREM1 level by targeting miR-206. The inhibitory effect of si-circ_0007534 on the malignant progression of CC was reversed after GREM1 was overexpressed. Furthermore, circ_0007534 inhibition also reduced tumor growth of CC in vivo partially by regulating miR-206/GREM1 axis.

CONCLUSION

These results suggested that knockdown of circ_0007534 promoted the level of miR-206 to induce the expression downregulation of GREM1, consequently inhibiting the progression of CC.

Preliminary RNA-microarray analysis of long non-coding RNA expression in abnormally invasive placenta

Long non-coding RNAs (lncRNAs) are reported to have important roles in placental development and function, but the role of lncRNAs in abnormally invasive placenta (AIP) remains elusive. In the present study, the differential expression profiles of lncRNAs were analyzed to identify novel targets for further study of AIP. A total of 10 lncRNAs were chosen for validation by reverse transcription-quantitative PCR. To further determine the functions of dysregulated lncRNAs and their corresponding mRNAs, functional enrichment analysis, coexpression analysis were performed. A total of 329 lncRNAs and 179 mRNAs were identified to be differently expressed between the invasive and control group. Gene ontology analysis revealed that the 10 most significantly enriched functions included upregulated mRNAs and the most significantly enriched term was related to the proteinaceous extracellular matrix (ECM). In the pathway analysis, the two most significantly enriched pathways were the TGF-β signaling pathway for upregulated mRNAs and the pentose phosphate pathway for downregulated mRNAs. Furthermore, for certain dysregulated lncRNAs, their associated mRNAs were also dysregulated. Of note, BMP and activin membrane-bound inhibitor and TGF-β-induced, as the target genes of the TGF-β pathway, were indicated to be closely related to the ECM and invasive placental cells. Their nearby lncRNAs G008916 and vault RNA2-1 were also significantly dysregulated. In conclusion, significant lncRNAs with the potential to serve as biomarkers for AIP were identified.

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

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

CircDDX42 Accelerates the Development of Pancreatic Cancer via miR-613/ID4/PI3K/AKT Axis

Background

Pancreatic cancer (PC) is one of the fatal cancers globally. CircDEAD-box helicase 42 (circDDX42) has been reported to play an oncogenic role in many cancers. The purpose of our study was to explore the relationship between circDDX42 and PC development and the potential mechanism by which circDDX42 modulating the progression of PC.

Methods

The enrichment of circDDX42, miR-613 and inhibitor of DNA binding 4 (ID4) was determined by quantitative real-time polymerase chain reaction (qRT-PCR) in PC tissues and cells. The proliferation, apoptosis and metastasis of PC cells were examined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Western blot, flow cytometry and transwell migration and invasion assays, respectively. The binding sites between miR-613 and circDDX42 or ID4 were predicted by Starbase bioinformatic software, and dual-luciferase reporter assay was conducted to verify the combination between miR-613 and circDDX42 or ID4. Western blot was carried out to detect the abundance of ID4, p-phosphatidylinositol 3-kinase (p-PI3K), PI3K, p-AKT serine/threonine kinase (p-AKT) and AKT in PC cells. The in vivo role of circDDX42 was verified through using murine xenograft model.

Results

The level of circDDX42 was enhanced in PC tissues and cells compared with that in matching normal tissues and HPDE cells. CircDDX42 promoted the proliferation and metastasis and suppressed the apoptosis of PC cells. CircDDX42 could sponge miR-613, and miR-613 was negatively regulated by circDDX42 in PC cells. MiR-613 suppressed the progression of PC. ID4 was a direct target of miR-613. ID4 was inversely modulated by miR-613 and positively regulated by circDDX42 in PC cells. ID4 played an oncogenic role in the tumorigenesis of PC. CircDDX42/miR-613/ID4 axis regulated the activation of PI3K/AKT pathway in PC cells. ID4 facilitated the progression of PC via activating PI3K/AKT signal pathway. CircDDX42 promoted the tumor growth of PC in vivo.

Conclusion

CircDDX42 accelerated the proliferation and metastasis while impeded the apoptosis of PC cells via circDDX42/miR-613/ID4/PI3K/AKT axis. This axis might be a promising target for PC therapy.

Down-regulated microRNA-223 or elevated ZIC1 inhibits the development of pancreatic cancer via inhibiting PI3K/Akt/mTOR signaling pathway activation

Objective: MicroRNAs (miRNAs) are known to participate in the progression of human cancers, such as pancreatic cancer (PC), while the mechanisms of miR-223 in PC remain largely unknown. This study was for the investigation of the status of microRNA (miR)-223 in the growth of PC with the involvement of ZIC1 and the PI3K/Akt/mTOR pathway. Methods: MiR-223 and ZIC1 expression in PC tissue and cell lines was detected. PANC-1 cells and SW1990 cells were screened for subsequent experiments. Screened cells were transfected with miR-223- or ZIC1-related  oligonucleotides or plasmids, or AZD8055, the dual inhibitor of the PI3K/Akt/mTOR signaling pathway to test the functions of miR-223, ZIC1 or PI3K/Akt/mTOR signaling pathway in the biological functions of PC cells. The expression of miR-223, ZIC1, or PI3K/Akt/mTOR signaling pathway-related proteins was examined. Tumor xenograft in nude mice was conducted for the detection of tumor growth of PC. Results: Up-regulated miR-223 and declined ZIC1 existed in PC tissues of patients and cell lines. ZIC1 was determined to be a target gene of miR-223. Down-regulated miR-223 or up-regulated ZIC1 led to suppressed proliferation, migration, invasion, and cell cycle entry, volume and weight of tumors, while elevated apoptosis in PC cells through declining phosphorylation levels of PI3K, Akt and mTOR. MiR-223 up-regulation or ZIC1 down-regulation induced opposite results on PC cells. Conclusion: This study highlights that down-regulated miR-223 or elevated ZIC1 inhibits the development of PC via restricting activation of the PI3K/Akt/mTOR pathway, which has important meanings for exploring the mechanism of PC.

Circular RNAs and cancer: Opportunities and challenges

Circular RNAs (circRNAs) are covalently circularized RNA moieties that despite being relatively abundant were only recently identified and have only begun to be investigated within the last couple of years. Even though there are many thousands of genes that appear capable of producing circRNAs, and the fact that many circRNAs appear to be highly evolutionarily conserved, the function of all but a few remain to be fully explored. What has been determined, however, is that circRNAs play key regulatory roles in many aspects of biology with focus being given to their function in cancer. Most of the studies to date have found that circRNAs act as master regulator of gene expression most often than not acting to regulate levels though sequestration or "sponging" of other gene expression regulators, particularly miRNAs. They can also function directly modulating transcription, or by interfering with splicing mechanisms. Some circRNAs can also be translated into functional proteins or peptides. A combination of tissue and developmental stage specific expression along with an innate resistance to RNAse activity means that circRNAs show perhaps their greatest potential as novel biomarkers of cancer. In this chapter we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We also consider some of the challenges that remain to be overcome to allow this emerging class of RNAs to fulfill their potential in clinical practice.

Long Noncoding RNA KCNQ1OT1 Confers Gliomas Resistance to Temozolomide and Enhances Cell Growth by Retrieving PIM1 From miR-761

Many studies have found that the dysregulation of long noncoding RNA (lncRNA) contributed to cancer initiation, progression, and recurrence via multiple signaling pathways. However, the underlying mechanisms of lncRNA in temozolomide (TMZ)-resistant gliomas were not well understood, hindering the improvement of TMZ-based therapies. The present study demonstrated that the lncRNA KCNQ1OT1 increased in TMZ-resistant glioma cells compared to the TMZ-sensitive cells. The introduction of KCNQ1OT1 promoted cell viability, clonogenicity, and rhodamine 123 efflux while hampering TMZ-induced apoptosis. Moreover, KCNQ1OT1 directly sponged miR-761, which decreased in TMZ-resistant sublines. The overexpression of miR-761 attenuated cell viability and clonogenicity, while triggering apoptosis and rhodamine 123 accumulation post-TMZ exposure, leading to a response to TMZ. The interaction between miR-761 and 3'-untranslated region of PIM1 attenuated PIM1-mediated signaling cascades. Furthermore, the knockdown of KCNQ1OT1 augmented the TMZ-induced tumor regression in TMZ-resistant U251 mouse models. Briefly, the present study evaluated that KCNQ1OT1 conferred TMZ resistance by releasing PIM1 expression from miR-761, resulting in the upregulation of PIM-mediated MDR1, c-Myc, and Survivin. The present findings demonstrated that the interplay of KCNQ1OT1: miR-761: PIM1 regulated chemoresistance in gliomas and provided a promising therapeutic target for TMZ-resistant glioma patients.

Circular RNAs as diagnostic biomarker in pancreatic cancer

Pancreatic cancer is one of the causes of death in the world. Unfortunately, common imaging technologies did not succeed in identifying this disease, and because of the absence of sensitive and specific biomarkers, it is not possible to screen and diagnose the disease. Therefore, this disease is usually diagnosed when patient is at an advanced stage of cancer and has lost the chance of surgery, and routine treatments such as radiotherapy and chemotherapy are not very effective. For this reason, the discovery of new biomarkers to overcome the diagnostic and therapeutic problems of pancreatic cancer is essential. Recently, circular RNAs (circRNAs) have been introduced as a group of noncoding RNAs that can play the role of critical regulators in various human diseases including cancer. A lot of studies revealed that circRNAs can have diverse roles in various cancers, including breast, colorectal, lung, renal, gastric, and hepatocellular carcinoma. The results of these researches have demonstrated that change in circRNAs expression levels in the tumor cells affects carcinogenesis, the stages of progression and metastasis of cancer through various mechanisms. Given that several studies have tested the role of circRNAs in pancreatic cancer, we decided to review the mechanisms proposed in these studies to conclude and summarize the work done in this regard.

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.

Predicting novel CircRNA-disease associations based on random walk and logistic regression model

Circular RNAs (circRNAs), a large group of small endogenous noncoding RNA molecules, have been proved to modulate protein-coding genes in the human genome. In recent years, many experimental studies have demonstrated that circRNAs are dysregulated in a number of diseases, and they can serve as biomarkers for disease diagnosis and prognosis. However, it is expensive and time-consuming to identify circRNA-disease associations by biological experiments and few computational models have been proposed for novel circRNA-disease association prediction. In this study, we develop a computational model based on the random walk and the logistic regression (RWLR) to predict circRNA-disease associations. Firstly, a circRNA-circRNA similarity network is constructed by calculating their functional similarity of circRNA based on circRNA-related gene ontology. Then, a random walk with restart is implemented on the circRNA similarity network, and the features of each pair of circRNA-disease are extracted based on the results of the random walk and the circRNA-disease association matrix. Finally, a logistic regression model is used to predict novel circRNA-disease associations. Leave one out validation (LOOCV), five-fold cross validation (5CV) and ten-fold cross validation (10CV) are adopted to evaluate the prediction performance of RWLR, by comparing with the latest two methods PWCDA and DWNN-RLS. The experiment results show that our RWLR has higher AUC values of LOOCV, 5CV and 10CV than the other two latest methods, which demonstrates that RWLR has a better performance than other computational methods. What's more, case studies also illustrate the reliability and effectiveness of RWLR for circRNA-disease association prediction.

Hsa_circ_0038646 promotes cell proliferation and migration in colorectal cancer via miR-331-3p/GRIK3

Increasing evidence supports the essential roles of circular RNAs (circRNAs) and microRNAs (miRNAs/miRs) in different types of human cancer. For example, hsa_circ_0137008 functions as a sponge for mi-338-5p and inhibits the malignant phenotype in colorectal cancer. Furthermore, hsa_circ_RNA_0011780 downregulates FBXW7 by targeting miR-554a and suppressing the progression of non-small cell lung cancer. Thus far, only a single report has identified that the miRNA miR-331-3p exerts a pivotal effect on human colorectal cancer (CRC) evolution. However, both the up- and downstream regulatory mechanisms of miR-331-3p are unclear. In the present study, it was predicted via bioinformatics analysis that the circRNA, hsa_circ_0038646, and the glutamate receptor ionotropic kainate 3 (GRIK3) gene contain binding sites that can interact with miR-331-3p. Thus, hsa_circ_0038646/miR-331-3p/GRIK3 may be a novel therapeutic pathway for CRC. Reverse transcription-quantitative PCR and western blotting analyses were performed, as well as cell proliferation, luciferase reporter and Transwell migration assays. Hsa_circ_0038646 was overexpressed in both CRC cells and tissues, and this aberrant expression was positively related with increasing tumor grade. Knockdown of hsa_circ_0038646 significantly weakened human CRC cell proliferation and migration. It was shown that hsa_circ_0038646 can sponge miR-331-3p to suppress its expression, and that suppression of miR-331-3p can reverse the effects of hsa_circ_0038646 inhibition in CRC cells. It was determined that GRIK3 is a downstream target of miR-331-3p, and that hsa_circ_0038646 could increase the levels of GRIK3 by suppressing miR-331-3p in CRC cells. Restoring GRIK3 expression rescued the weakened CRC cell proliferation and migration following hsa_circ_0038646 knockdown. The present study indicated that hsa_circ_0038646 functions as a tumor promoter in CRC by increasing GRIK3 expression via sponging of miR-331-3p. The hsa_circ_0038646/miR-331-3p/GRIK3 axis may be a novel therapeutic and diagnostic target of CRC.

Advances in circular RNAs and their role in glioma (Review)

Glioma is the most common primary tumour of the central nervous system, and is associated with a high postoperative recurrence rate and resistance to chemotherapy. High‑grade glioblastoma in particular has a very poor prognosis and poses a serious threat to human health. Related studies have confirmed that the occurrence and development of gliomas are closely associated with the abnormal expression and regulation of genes. Moreover, the number of studies on the association of the expression of non‑coding RNAs [linear RNAs, microRNAs and circular RNAs (circRNAs)] in human cells with glioma has been gradually increasing in recent years. Among those, circRNAs, previously considered to be 'splicing errors', have been shown to be highly expressed in eukaryotic cells and regulate the biological behaviour of gliomas. circRNAs are highly abundant and stable, and have become a research hotspot in the field of glioma molecular biology. The aim of the present review was to focus on the research progress regarding the association between circRNA expression and gliomas, and to provide a theoretical basis according to the currently available literature for further exploring this association. The present study may be of value for the early diagnosis, pathological grading, targeted therapy and prognostic evaluation of gliomas.

The circ_VCAN with radioresistance contributes to the carcinogenesis of glioma by regulating microRNA-1183

Circular RNAs (circRNAs), a widespread type of noncoding RNA, are produced by reverse splicing with a circular loop structure. Circ_VCAN (hsa_circ_0073237) acts as a novel circRNA, although its roles in the progression and radioresistance of glioma remain unknown.Expressions of circ_VCAN and microRNA-1183 (miR-1183) were analyzed by quantitative real-time PCR, and the functions of circ_VCAN and irradiate in glioma cell proliferation, apoptosis, migration, and invasion were assessed using cell counting kit-8, flow cytometry, Wound healing, and Transwell assays. The interaction between circ_VCAN and miR-1183 was validated dual-luciferase reporter assay.Our results revealed that circ_VCAN was significantly upregulated in radioresistant glioma tissues compared with radiosensitive tissues, and that circ_VCAN expression was negatively correlated with miR-1183 expression in glioma tissues. We also determined that circ_VCAN expression was decreased and miR-1183 expression was increased in U87 and U251 cells after irradiation. Both knockdown of circ_VCAN and treatment with miR-1183 mimics inhibited proliferation, migration, and invasion, and accelerated apoptosis of the irradiated U87 and U251 cells. In addition, luciferase reporter assays revealed that circ_VCAN might function as a sponge for miR-1183. Finally, overexpression of circ_VCAN expedited carcinogenesis and reduced glioma radiosensitivity by regulating miR-1183.Circ_VCAN serves as a potential oncogene of glioma by regulating miR-1183, and plays an essential role in the radioresistance of glioma.

Plasma MicroRNA Expression Profiles in Psoriasis

Background

Psoriasis is an immune-mediated inflammatory chronic skin disease characterized by chronic inflammation in the dermis, parakeratosis, and excessive epidermal growth. MicroRNAs (miRNAs) are key regulators of immune responses. Although differential expression of miRNAs has been reported in certain inflammatory autoimmune diseases, their role in psoriasis has not been fully illuminated. Our aims were to confirm plasma miRNA expression signatures in psoriasis and to examine their potential influence on psoriasis pathogenesis.

Methods

A miRNome PCR array was used to analyse the plasma of psoriasis patients and healthy donors. We performed miRNA pathway enrichment and target gene network analyses on psoriasis plasma samples.

Results

We found several specific plasma miRNA signatures relevant to psoriasis. The miRNAs targeted pathways associated with psoriasis, such as the VEGF, MAPK, and WNT signaling pathways. Network analysis revealed pivotal deregulated plasma miRNAs and their relevant target genes and pathways regulating psoriasis pathogenesis.

Conclusions

This study analysed the expression of plasma miRNAs and their target pathways, elucidating the pathogenesis of psoriasis; these results may be used to design novel therapeutic strategies and to identify diagnostic biomarkers for psoriasis.

Star Circular RNAs In Human Cancer: Progress And Perspectives

Circular RNAs (circRNAs) are a recently discovered subclass of non-coding RNAs (ncRNAs) characterized by a covalently closed loop structure created by reverse splicing. Because they do not have a 5' cap structure and a 3' poly A tail, circRNAs have higher stability, abundance and evolutionary conservation than linear RNA between species. These features produce various potential biological functions of circRNAs, such as miRNA sponges, RNA-binding proteins that form RNA protein complexes. In recent years, more and more studies have shown that circRNAs play a vital role in the occurrence and development of human diseases. At the same time, their enormous potential as a biomarker and therapeutic target is also evolving. The purpose of this review is to summarize existing cancer-associated circRNAs and to try to find circRNAs that are abnormally expressed in many cancers. Therefore, we reviewed previous circRNAs studies related to cancer and selected them by statistics. The eight circRNAs that have the highest frequency in different cancers or involve key pathways are called star circRNAs. Here, we review the classification, features, and functions of emerging star circRNAs, with particular attention to the role of circRNAs in various cancers.

MicroRNA-761 inhibits the metastasis of gastric cancer by negatively regulating Ras and Rab interactor 1

Gastric cancer (GC), the second most common malignant cancer worldwide, gives rise to a number of cancer-associated fatalities annually. Accumulating evidence has shown that microRNAs (miRs) may serve as oncogenes or tumor suppressors in GC development. The aim of this study was to discover the expression, function and mechanism of miR-761 in GC progression. First, the findings revealed that the expression level of miR-761 was significantly decreased in GC cell lines and tissues. The functional studies showed that miR-761 in GC cells inhibited tumor proliferation and metastasis. In the mechanistic study, through an online database search and luciferase assay, Ras and Rab interactor 1 (RIN1), which has been demonstrated as an oncogene in various types of cancer, including GC, was identified as a target of miR-761. Notably, miR-761 expression was demonstrated to be negatively correlated with RIN1 mRNA levels in GC tissues. Simultaneously, overexpression of RIN1 partially rescued the inhibitory effect of miR-761 mimic in the GC cells. The present study provided new insights into the role of miR-761 in the progression of GC, and implicated the potential application of miR-761 in GC cell therapy.

Circular RNA circSCAF11 Accelerates the Glioma Tumorigenesis through the miR-421/SP1/VEGFA Axis

Circular RNAs (circRNAs) are a novel category of non-coding RNAs, and they have been identified to participate in glioma tumorigenesis. Here we investigated the functions of circRNA circSCAF11 in glioma genesis, and we unveiled its molecular mechanism in the pathophysiological process. Expression levels of circSCAF11, miR-421, and SP1 mRNA were measured using RT-PCR. Proteins were measured using western blotting. The tumor phenotypes of glioma cells were detected using flow cytometry and Cell Counting Kit-8 (CCK-8), transwell, and xenograft mouse assays. The combination within circSCAF11, miR-421, and SP1 was validated using luciferase reporter assay or RNA pull-down assay. The binding of transcription factor SP1 with vascular endothelial cell growth factor A (VEGFA) promoter was inspected using chromatin immunoprecipitation (ChIP). circSCAF11 expression was found to be significantly upregulated in the glioma tissue specimens and cell lines. The ectopic overexpression of circSCAF11 was closely correlated with the poor clinical outcome of glioma patients. Functionally, knockdown of circSCAF11 inhibited the proliferation, invasion, and tumor growth and induced the G0/G1 phase arrest. Mechanically, circSCAF11 positively regulated the SP1 expression through sponging miR-421. Moreover, transcription factor SP1 activated the transcription of VEGFA, constructing the circSCAF11/miR-421/SP1/VEGFA axis in the glioma genesis. The findings in this research illustrate that circSCAF11 accelerates glioma tumorigenesis through the miR-421/SP1/VEGFA axis, providing a potential target for circRNA and glioma treatment.

Emerging roles of circular RNAs in colorectal cancer

Circular RNAs (circRNAs) are a newly discovered class of endogenous non-coding RNAs. Owing to the development of high-throughput sequencing, researchers have identified thousands of circRNAs. Emerging evidence suggests that circRNAs are involved in various tumor cell processes, including proliferation, apoptosis, invasion and migration. Because of their high stability and abundance, tissue-specific expression, and easy detection, circRNAs are considered ideal biomarkers for cancer diagnosis and prognosis. An increasing number of studies have recently demonstrated that circRNAs are closely associated with colorectal cancer (CRC). CRC is the third most common cancer and the second leading cause of cancer-related death globally. Thus, understanding the molecular mechanisms involved in the development and progression of CRC is vital. In this review, we summarize the current literature regarding human circRNAs related to CRC and present an overview of the potential clinical implications of circRNAs with respect to CRC.

CircPCMTD1 Acts as the Sponge of miR-224-5p to Promote Glioma Progression

Glioma is the most common malignant tumor of the central nervous system with high morbidity and mortality. Circular RNAs (circRNAs) are abundant non-coding RNAs, which contribute to tumor progression by competing with other endogenous RNAs such as microRNA (miRNA). MiRNA are a class of small non-coding RNAs, which interrupt the translation of target mRNAs. CircPCMTD1 (hsa-circ-0001801) is a newly discovered circRNA that was found to be significantly upregulated in glioma. However, its function is unclear. In this study, circPCMTD1 upregulation promoted the cell viability, migration and invasion dramatically, while the inhibition of circPCMTD1 led to a significant reduction of tumor growth in vivo. MiRNAs microarray analyses on circPCMTD1 silencing models in U251 and U118MG cells were performed, and the results suggested that circPCMTD1 knockdown could upregulate the expression of miR-224-5p and downregulate the expression of mTOR, one of miR-224-5p targets, in both cell lines. According to the prediction from circular RNA interactome and Targetscan, there was a complementary sequence in circPCMTD1 for miR-224-5p. Dual-luciferase reporter assay demonstrated that circPCMTD1 were targets of miR-224-5p. RIP assay was also performed to further confirm their directly interaction. Overexpression of miR-224-5p inhibited the viability and proliferation, migration, and invasion of U251 and U118MG glioma cells. In conclusion, circPCMTD1 could contribute to the promotion of glioma progression, and it may serve as the sponge of miR-224-5p to exert its function.

Circ-ZNF264 Promotes the Growth of Glioma Cells by Upregulating the Expression of miR-4493 Target Gene Apelin

Glioma is the most common malignant tumor in the brain and nervous system, with high recurrence and high mortality rate. Recent researches have shown that circular RNAs (circRNAs) play key roles in the genesis and progress of glioma. Detection of circRNAs in glioma cells revealed that the expression of circ-ZNF264 was upregulated. At the same time, the expression of miR-4493 was downregulated in glioma cells and had multiple binding sites on the circ-ZNF264 sequence. Dual luciferase reporter gene assay confirmed that miR-4493 could bind to circ-ZNF264 and apelin specifically. MiR-4493 expression was not changed, but its target gene apelin expression could be significantly upregulated by circ-ZNF264. MiR-4493 could inhibit the expression of circ-ZNF264 and apelin. Biological behaviors of glioma cells were detected; circ-ZNF264 promoted cell proliferation and invasion and inhibited apoptosis. MiR-4493 had the opposite effects and could terminate the above effects of circ-ZNF264. When the expression of apelin was downregulated and that of circ-ZNF264 was upregulated, the changes of the above biological behaviors were not obvious. Therefore, in glioma cells, circ-ZNF264 can inhibit the function of miR-4493 and then upregulate its target gene apelin expression, thus regulating glioma cell proliferation, apoptosis, and invasion. This finding provides more evidence for the role of circRNAs in glioma.

Circular RNA CircCACTIN Promotes Gastric Cancer Progression by Sponging MiR-331-3p and Regulating TGFBR1 Expression

Background: Circular RNAs (circRNAs) are a new class of RNAs that play a significant role in regulating gene expression and biological function. However, the expression profile and function of circRNAs in gastric cancer (GC) remain mostly uncertain. In the present study, we researched the expression profile of circRNAs in human GC tissues and explored the role of circCACTIN (hsa_circ_0092303).

Methods: Circular RNA microarray assays were performed to detect circular RNA expression profiles of GC and circCACTIN was identified for further investigation. Quantitative real-time PCR was used to detect the expression of circCACTIN, miR-331-3p and TGFBR1 in GC specimens and cell lines. CircCACTIN was stably silenced and overexpressed in GC cells, and cell proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), as well as tumorigenesis in nude mice were performed to assess the effect of circCACTIN on GC.

Results: CircCACTIN expression was obviously up-regulated in GC tissues and cell lines. Knockdown of circCACTIN inhibited GC cells proliferation, migration, invasion and EMT. Enforced-expression of circCACTIN promoted GC cells migration, invasion and EMT, but had no effect on GC cells proliferation. Moreover, in vivo experiments, circCACTIN up-regulation promoted GC tumor growth and EMT, and circCACTIN down-regulation inhibited GC tumor growth and EMT. Binding interactions were detected between circCACTIN and miR-331-3p, and between miR-331-3p and TGFBR1 by Dual-luciferase reporter assays. Mechanistically, we demonstrated that circCACTIN promoted gastric cancer progression by sponging miRNA-331-3p and regulating TGFBR1 mRNA expression.

Conclusion: The circCACTIN/miR-331-3p/TGFBR1 axis affected the proliferation, migration, invasion and EMT of GC through the mechanism of competing endogenous RNAs (ceRNA). Furthermore, our results identified circCACTIN as a novel oncogenic circRNA in GC.

Hsa_circ_0000467 promotes cancer progression and serves as a diagnostic and prognostic biomarker for gastric cancer

BACKGROUND

Emerging evidence indicates that dysregulation of circular RNAs (circRNAs) is implicated in the development of malignancies. However, the diagnostic value and functional role of circRNAs in gastric cancer (GC) remain largely elusive.

METHODS

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was performed to detect the expression of hsa_circ_0000467 in tissues, cell lines, and plasma. A receiver operating characteristic (ROC) curve was constructed to estimate the diagnostic value of hsa_circ_0000467. The association between the expression level of hsa_circ_0000467 and the clinicopathological features was analyzed. Moreover, cell functional assays were performed.

RESULTS

Hsa_circ_0000467 was significantly upregulated in GC tissue compared to adjacent nontumor tissue (n = 51, P < 0.05). Similar results were detected in the HGC-27, MGC-803, AGS, NUGC-3, GES-1 cell lines (n = 15, P < 0.001), and in the plasma samples from GC patients (n = 20, P < 0.05). The area under the ROC curve of hsa_circ_0000467 was 0.790, which is superior to commonly used biomarkers including CEA and CA-724. We found that the expression levels of hsa_circ_0000467 in the same patient were significantly lower after surgery (n = 20, P < 0.05). Moreover, the hsa_circ_0000467 expression level is closely associated with TNM stage. Additionally, Cox multivariate analysis showed that hsa_circ_0000467 is a novel independent prognostic factor. Furthermore, in vitro experiments demonstrated that knockdown of hsa_circ_0000467 markedly inhibited the proliferation, migration, and invasion of GC cells. Moreover, hsa_circ_0000467 silencing increased tumor apoptosis in vitro.

CONCLUSION

Hsa_circ_0000467 can act as a novel noninvasive biomarker for the diagnosis and prognosis of GC and may be a potential therapeutic target for GC.

circLARP4 induces cellular senescence through regulating miR-761/RUNX3/p53/p21 signaling in hepatocellular carcinoma

Circular RNAs (circRNAs), a novel class of non-coding RNAs, have emerged as indispensable modulators in human malignancies. Aberrant cellular senescence is a phenotype observed in various cancers. The association of circRNAs with cellular senescence in tumors is yet to determined. Here, we investigated the role of circLARP4 in cellular senescence and cell proliferation in hepatocellular carcinoma (HCC). Downregulated circLARP4 level was observed in HCC tissues and cell lines. Low expression level of circLARP4 independently predicted poor survival outcome. Gain-of-function and loss-of-function assays demonstrated that circLARP4 suppressed HCC cell proliferation, mediated cell cycle arrest and induced senescence in vitro. Levels of p53 and p21, 2 key regulatory molecules in cellular senescence, were increased in circLARP4-overexpressed HCC cells and decreased in circLARP4-silenced HCC cells. In vivo experiments further confirmed the tumor-suppressing activity of circLARP4. Further mechanistic studies showed that circLARP4 dampened HCC progression by sponging miR-761, thereby promoting the expression level of RUNX3 and activating the downstream p53/p21 signaling. Our study revealed the role of circLARP4/miR-761/RUNX3/p53/p21 signaling in HCC progression, providing a potential survival predictor and therapeutic candidate for HCC.