Emerging important roles of circRNAs in human cancer and other diseases

WNT/β-catenin signaling in hepatocellular carcinoma: The aberrant activation, pathogenic roles, and therapeutic opportunities

Hepatocellular carcinoma (HCC) is a liver cancer, highly heterogeneous both at the histopathological and molecular levels. It arises from hepatocytes as the result of the accumulation of numerous genomic alterations in various signaling pathways, including canonical WNT/β-catenin, AKT/mTOR, MAPK pathways as well as signaling associated with telomere maintenance, p53/cell cycle regulation, epigenetic modifiers, and oxidative stress. The role of WNT/β-catenin signaling in liver homeostasis and regeneration is well established, whereas in development and progression of HCC is extensively studied. Herein, we review recent advances in our understanding of how WNT/β-catenin signaling facilitates the HCC development, acquisition of stemness features, metastasis, and resistance to treatment. We outline genetic and epigenetic alterations that lead to activated WNT/β-catenin signaling in HCC. We discuss the pivotal roles of CTNNB1 mutations, aberrantly expressed non-coding RNAs and complexity of crosstalk between WNT/β-catenin signaling and other signaling pathways as challenging or advantageous aspects of therapy development and molecular stratification of HCC patients for treatment.

Biological role and regulation of circular RNA as an emerging biomarker and potential therapeutic target for cancer

Circular RNAs (circRNAs) are a unique family of endogenous RNAs devoid of 3' poly-A tails and 5' end caps. These single-stranded circRNAs, found in the cytoplasm, are synthesized via back-splicing mechanisms, merging introns, exons, or both, resulting in covalently closed circular loops. They are profusely expressed across the eukaryotic transcriptome and offer heightened stability against exonuclease RNase R compared to linear RNA counterparts. This review endeavors to provide a comprehensive overview of circRNAs' characteristics, biogenesis, and mechanisms of action. Furthermore, aimed to shed light on the potential of circRNAs as significant biomarkers in various cancer types. It has been performed an exhaustive literature review, drawing on recent studies and findings related to circRNA characteristics, synthesis, function, evaluation techniques, and their associations with oncogenesis. CircRNAs are intricately associated with tumor progression and development. Their multifaceted roles encompass gene regulation through the sponging of proteins and microRNAs, controlling transcription and splicing, interacting with RNA binding proteins (RBPs), and facilitating gene translation. Due to these varied roles, circRNAs have become a focal point in tumor pathology investigations, given their promising potential as both biomarkers and therapeutic agents. CircRNAs, due to their unique biogenesis and multifunctionality, hold immense promise in the realm of oncology. Their stability, widespread expression, and intricate involvement in gene regulation underscore their prospective utility as reliable biomarkers and therapeutic targets in cancer. As our understanding of circRNAs deepens, advanced techniques for their detection, evaluation, and manipulation will likely emerge. These advancements might catalyze the translation of circRNA-based diagnostics and therapeutics into clinical practice, potentially revolutionizing cancer care and prognosis.

circ_SIRT1 upregulates ATG12 to facilitate Imatinib resistance in CML through interacting with EIF4A3

Imatinib is the current gold standard for patients with chronic myeloid leukemia (CML). However, the primary and acquired drug resistance seriously limits the efficacy. To identify novel therapeutic target in Imatinib-resistant CML is of crucial clinical significance. CircRNAs have been demonstrated the essential regulatory roles in the progression and drug resistance of cancers. In this study, we identified a novel circRNA (circ_SIRT1), derived from the SIRT1, which is up-regulated in CML. The high expression of circ_SIRT1 is correlated with drug resistance in CML. Knockdown of circ_SIRT1 regulated K562/R cells viability, invasion and apoptosis. Besides, the inhibition of circ_SIRT1 attenuated autophagy level and reduced IC50 to Imatinib of K562/R cells. Mechanistically, circ_SIRT1 directly binds to the transcription factor Eukaryotic Translation Initiation Factor 4A3(EIF4A3) and regulated EIF4A3-mediated transcription of Autophagy Related 12 (ATG12), thereby affecting Imatinib resistance and autophagy level. Overexpression of ATG12 reversed the regulative effects induced by knockdown of circ_SIRT1. Taken together, our findings revealed circ_SIRT1 acted as a potential tumor regulator in CML and unveiled the underlying mechanism on regulating Imatinib resistance. circ_SIRT1 may serve as a novel therapeutic target and provide crucial clinical implications for Imatinib-resistant CML treatment.

Circular RNAs in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a term encompassing a few chronic inflammatory disorders that leads to damage of the intestinal tract. Although much progress has been made in understanding the pathology of IBD, the precise pathogenesis is not completely understood. Circular RNAs (circRNAs) are single-stranded, covalently closed, endogenous molecules in eukaryotes with a variety of biological functions. CircRNAs have been shown to have regulatory effects in many diseases, such as cancer, cardiovascular disease, and neurological disorders. CircRNAs have also been found to play important roles in IBD, and although they are not sufficiently investigated in the context of IBD, a few circRNAs have been identified as potential biomarkers for the diagnosis and prognosis of IBD and as potential therapeutic targets for IBD. Herein, we survey recent progress in understanding the functions and roles of circRNAs in IBD and discuss their potential clinical applications.

Circ_0067934: a circular RNA with roles in human cancer

A circular RNA (circRNA) is a non-coding RNA (ncRNA) derived from reverse splicing from pre-mRNA and is characterized by the absence of a cap structure at the 5' end and a poly-adenylated tail at the 3' end. Owing to the development of RNA sequencing and bioinformatics approaches in recent years, the important clinical value of circRNAs has been increasingly revealed. Circ_0067934 is an RNA molecule of 170 nucleotides located on chromosome 3q26.2. Circ_0067934 is formed via the reverse splicing of exons 15 and 16 in PRKCI (protein kinase C Iota). Recent studies revealed the upregulation or downregulation of circ_0067934 in various tumors. The expression of circ_0067934 was found to be correlated with tumor size, TNM stage, and poor prognosis. Based on experiments with cancer cells, circ_0067934 promotes cancer cell proliferation, migratory activity, and invasion when overexpressed or downregulated. The potential mechanism involves the binding of circ_0067934 to microRNAs (miRNAs; miR-545, miR-1304, miR-1301-3p, miR-1182, miR-7, and miR-1324) to regulate the post-transcriptional expression of genes. Other mechanisms include inhibition of the Wnt/β-catenin and PI3K/AKT signaling pathways. Here, we summarized the biological functions and possible mechanisms of circ_0067934 in different tumors to enable further exploration of its translational applications in clinical diagnosis, therapy, and prognostic assessments.

The potential role and mechanism of circRNAs in foam cell formation

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

Identification and characterization of circRNAs in peri-implantation endometrium between Yorkshire and Erhualian pigs

BACKGROUND

One of the most critical periods for the loss of pig embryos is the 12th day of gestation when implantation begins. Recent studies have shown that non-coding RNAs (ncRNAs) play important regulatory roles during pregnancy. Circular RNAs (circRNAs) are a kind of ubiquitously expressed ncRNAs that can directly regulate the binding proteins or regulate the expression of target genes by adsorbing micro RNAs (miRNA).

RESULTS

We used the Illumina Novaseq6,000 technology to analyze the circRNA expression profile in the endometrium of three Erhualian (EH12) and three Yorkshire (YK12) pigs on day 12 of gestation. Overall, a total of 22,108 circRNAs were identified. Of these, 4051 circRNAs were specific to EH12 and 5889 circRNAs were specific to YK12, indicating a high level of breed specificity. Further analysis showed that there were 641 significant differentially expressed circRNAs (SDEcircRNAs) in EH12 compared with YK12 (FDR < 0.05). Functional enrichment of differential circRNA host genes revealed many pathways and genes associated with reproduction and regulation of embryo development. Network analysis of circRNA-miRNA interactions further supported the idea that circRNAs act as sponges for miRNAs to regulate gene expression. The prediction of differential circRNA binding proteins further explored the potential regulatory pathways of circRNAs. Analysis of SDEcircRNAs suggested a possible reason for the difference in embryo survival between the two breeds at the peri-implantation stage.

CONCLUSIONS

Together, these data suggest that circRNAs are abundantly expressed in the endometrium during the peri-implantation period in pigs and are important regulators of related genes. The results of this study will help to further understand the differences in molecular pathways between the two breeds during the critical implantation period of pregnancy, and will help to provide insight into the molecular mechanisms that contribute to the establishment of pregnancy and embryo loss in pigs.

Biological functions of circRNAs and their advance on skeletal muscle development in bovine

The development of skeletal muscle in animals is a complex biological process, which are strictly and precisely regulated by many genes and non-coding RNAs. Circular RNA (circRNA) was found as a novel class of functional non-coding RNA with ring structure in recent years, which appears in the process of transcription and is formed by covalent binding of single-stranded RNA molecules. With the development of sequencing and bioinformatics analysis technology, the functions and regulation mechanisms of circRNAs have attracted great attention due to its high stability characteristics. The role of circRNAs in skeletal muscle development have been gradually revealed, where circRNAs were involved in various biological processes, such as proliferation, differentiation, and apoptosis of skeletal muscle cells. In this review, we summarized the current studies advance of circRNAs involved in skeletal muscle development in bovine, and hope to gain a deeper understanding of the functional roles of the circRNAs in muscle growth. Our results will provide some theoretical supports and great helps for the genetic breeding of this species, and aiming at improving bovine growth and development and preventing muscle diseases.

Understanding the roles and regulation patterns of circRNA on its host gene in tumorigenesis and tumor progression

Circular RNAs (circRNAs) are a novel type of endogenous non-coding RNAs, which are covalently closed loop structures formed by precursor mRNAs (pre-mRNAs) through back-splicing. CircRNAs are abnormally expressed in many tumors, and play critical roles in a variety of tumors as oncogenes or tumor suppressor genes by sponging miRNAs, regulating alternative splicing and transcription, cis-regulating host genes, interacting with RNA binding proteins (RBPs) or encoding polypeptides. Among them, the regulation of circRNAs on their corresponding host genes is a critical way for circRNAs to exit their functions. Accumulating evidence suggests that circRNAs are able to regulate the expression of host genes at the transcriptional level, post-transcriptional level, translational level, post-translational level, or by encoding polypeptides. Therefore, this paper mainly summarized the roles and association of circRNAs and their corresponding host genes in tumorigenesis and tumor progression, generalized the circRNAs that function synergistically or antagonistically with their host genes, and elaborated the mechanisms of mutual regulation between circRNAs and their host genes. More importantly, this review provides specific references for revealing the potential application of circRNAs combined with their host genes in tumor diagnosis, treatment and prognosis.

Circ_0058063 regulates the development of esophageal cancer through miR-377-3p/HOXA1 axis

Esophageal cancer is one of the deadliest cancers. Circular RNA (CircRNA) can be used as a tumor marker. Therefore, this provides an important idea for our research. Real-time quantitative PCR (RT-qPCR) was used to analyze the expression of circ_0058063, miR-377-3p and homeobox protein Hox-A1 (HOXA1), western blot was used to analyze the protein levels of HOXA1 and cyclinD1, B cell leukemia/lymphoma 2 associated X (Bax). Cell Counting Kit-8 (CCK-8) assay, colony formation assay and wound healing assay were used to analyze cell proliferation and migration; apoptosis was analyzed by flow cytometry. Dual-luciferase reporter assays were performed to analyze the luciferase activities. Transwell assay was used to analyze the cell invasion. A glycolysis metabolism assay was used to analyze cell glycolysis ability. Xenograft models were used to validate the effect of circ_0009035 in the growth of esophageal cancer in vivo . Circ_0009035 and HOXA1 were upregulated, while miR-377 was downregulated in esophageal cancer.. Circ_0058063 targeted miR-377-3p, and HOX4 was a target of miR-377-3p. Knockdown of circ_0058063 inhibited migration, invasion and proliferation and promoted apoptosis of esophageal cancer cells. MiR-377-3p inhibition or HOXA1 overexpression could restore the effect of si-circ_0058063 on esophageal cancer cells. Knockdown of circ_0058063 repressed the growth of esophageal cancer tumors in vivo. Our study found that circ_0058063 could regulate the expression of HOXA1 by targeting miR-377-3p, thereby affecting the progress of esophageal cancer.

CircSHOC2 Knockdown Alleviates High Glucose-Induced Vascular Endothelial Cell Pyroptosis via Targeting miR-145/FOXO1 Axis In Vitro Condition

Emerging evidence indicates that pyroptosis participates in the pathogenic process of vascular endothelial cells in cardiovascular system complications of diabetes. The roles of circular RNAs (circRNAs) in high glucose (HG)-induced vascular endothelial cells are still unclear. Here, our research investigated the function and mechanism of circRNA circSHOC2 in pyroptosis of vascular endothelial cells. Results indicated that circSHOC2 was up-regulated in HG-induced human umbilical vein endothelial cells (HUVECs). Functionally, cellular assays indicated that circSHOC2 silencing repressed HG-induced HUVECs pyroptosis. Moreover, circSHOC2 targeted miR-145 through miRNA sponge, and FOXO1 functioned as downstream target of miR-145. In conclusion, these findings suggested the potential roles of circSHOC2 on HG-induced vascular endothelial cells in vitro condition, providing new insights for cardiovascular system complications of diabetes.

The malignancy of chordomas is enhanced via a circTLK1/miR-16-5p/Smad3 positive feedback axis

CircRNAs play crucial roles in various malignancies via an increasing number of reported regulatory mechanisms, including the classic sponging mechanism between circRNAs and micro RNAs (miRNAs). We performed bioinformatic analyses and identified circTLK1 as a regulator of malignant chordoma progression. Moreover, we observed that circTLK1 showed high expression in chordoma cells and tissues, while circTLK1 interference suppressed chordoma cell proliferation and invasion. In addition, circTLK1 directly interacted with miR-16-5p, which has previously been shown to repress chordoma, and circTLK1 knockdown suppressed Smad3 expression. Chromatin immunoprecipitation sequencing further demonstrated that Smad3 acts as a positive regulator by interacting with TLK1, thereby mediating the circTLK1/miR-16-5p/Smad3 positive feedback axis. Taken together, our findings suggested that the disruption of the circTLK1/miR-16-5p/Smad3 positive feedback pathway, particularly via the Smad3 inhibitor SIS3, could be a promising therapeutic strategy.

CircADSS contributes to hepatocellular carcinoma development by regulating miR-431-5p/TOP2A

CircRNAs participated in regulating hepatocellular carcinoma (HCC), and the regulation function of circRNA adenylosuccinate synthase (circADSS) on HCC development is not clear. RT-qPCR and western blot were performed to detect RNA expression. Cell proliferation was analysed by CCK-8 and EdU assay. Cell cycle distribution was analysed by flow cytometry assay. Cell migration and invasion were measured by transwell assay. Mechanism assays were employed to examine the interaction between miR-431-5p and circADSS, or TOP2A. Xenograft mouse model was constructed for in vivo assay. CircADSS and TOP2A expression were boosted, while miR-431-5p was limited in tumour tissues and cells. CircADSS silencing decreased HCC cell proliferation, cell cycle progression, migration, invasion, as well as EMT. MiR-431-5p inhibitors or ectopic TOP2A expression could restore the effect of circADSS knockdown on HCC progression. There was target relationship between miR-431-5p and circADSS, or TOP2A. Knockdown of circADSS suppressed tumour growth in vivo. CircADSS could regulate HCC cell malignancy by miR-431-5p/TOP2A axis.

circITGB1 Regulates Adipocyte Proliferation and Differentiation via the miR-23a/ARRB1 Pathway

Adipose tissues represent an important energy storage organ in animals and are the largest endocrine organ. It plays an important regulatory role in the pathogenesis of insulin resistance, cardiovascular disease, and metabolic syndrome. Adipose development is a complex biological process involving multiple key genes, signaling pathways, and non-coding RNAs, including microRNAs and circular RNAs. In this study, we characterized circITGB1 and named its host gene ITGB1, which is differentially expressed in sheep of different months based on sequencing data. We collated and analyzed the sequencing data to select miRNA-23a with strong binding to ARRB1. We found that miRNA-23a regulates the development and differentiation of sheep adipocytes by targeting ARRB1. As a competing endogenous RNA, circITGB1 overexpression effectively alleviated the inhibitory effect of miR-23a on ARRB1. Conclusively, we provide evidence that circITGB1 regulates the proliferation and differentiation of sheep adipocytes via the miR-23a/ARRB1 pathway. This study provides a scientific basis for further studies on adipose tissue development at the circRNA level.

Circ_0004491 stimulates guanine nucleotide-binding protein alpha subunit to inhibit the malignant progression of oral squamous cell carcinoma by sponging miR-2278

Background/purpose

Circular RNA origin recognition complex subunit 4 (circORC4; ID: hsa_circ_0004491) have been confirmed to be a novel potential biomarker of oral squamous cell carcinoma (OSCC). This study aimed to explore the molecular mechanism of circ_0004491 in OSCC progression.

Materials and methods

Levels of circ_0004491, microRNA (miR)-2278, guanine nucleotide-binding protein alpha subunit (GNAS), Bax, Bcl-2, E-cadherin and ki-67 were detected by quantitative real-time PCR, western blotting and immunohistochemistry. The proliferation of OSCC cells was measured using colony formation assay and EdU staining. Cell apoptosis and motility were detected by flow cytometry and transwell assays respectively. Interaction between miR-2278 and circ_0004491 or GNAS was predicted by bioinformatics analysis and confirmed via luciferase reporter assay and RNA immunoprecipitation assay. Xenograft tumor model was used to analyze the role of circ_0004491 in tumor growth in vivo.

Results

Circ_0004491 was downregulated in OSCC tissues and cell lines. Circ_0004491 overexpression suppressed the proliferation, migration and invasion whereas facilitated the apoptosis of OSCC cells. Circ_0004491 acted as a molecular sponge for miR-2278, and circ_0004491 overexpression-mediated effect was partly reversed by miR-2278 mimic in OSCC cells. MiR-2278 interacted with the 3'UTR of GNAS. Circ_0004491 contributed to GNAS level by sponging miR-2278 in OSCC cells. GNAS knockdown restored miR-2278 inhibitor-mediated effect in OSCC cells. Circ_0004491 overexpression repressed xenograft tumor growth in vivo.

Conclusion

Circ_0004491 can repress OSCC progression by regulation of miR-2278/GNAS axis, providing a possible circRNA-targeted therapy for OSCC.

Unraveling the significance of exosomal circRNAs in cancer therapeutic resistance

Exosomes are nanoscale extracellular vesicles secreted by a variety of cells, affecting the physiological and pathological homeostasis. They carry various cargoes including proteins, lipids, DNA, and RNA and have emerged as critical mediators of intercellular communication. During cell-cell communication, they can internalize either by autologous or heterologous recipient cells, which activate different signaling pathways, facilitating malignant progression of cancer. Among different types of cargoes in exosomes, the endogenous non-coding RNAs, such as circular RNAs (or circRNAs), have gained tremendous attention for their high stability and concentration, playing promising functional roles in cancer chemotherapeutic response by regulating the targeted gene expression. In this review, we primarily described the emerging evidence demonstrating the important roles of circular RNAs derived from exosomes in the regulation of cancer-associated signaling pathways that were involved in cancer research and therapeutic interventions. Additionally, the relevant profiles of exosomal circRNAs and their biological implications have been discussed, which is under investigation for their potential effect on the control of cancer therapeutic resistance.

Recent advances in cancer fusion transcript detection

Extensive investigation of gene fusions in cancer has led to the discovery of novel biomarkers and therapeutic targets. To date, most studies have neglected chromosomal rearrangement-independent fusion transcripts and complex fusion structures such as double or triple-hop fusions, and fusion-circRNAs. In this review, we untangle fusion-related terminology and propose a classification system involving both gene and transcript fusions. We highlight the importance of RNA-level fusions and how long-read sequencing approaches can improve detection and characterization. Moreover, we discuss novel bioinformatic tools to identify fusions in long-read sequencing data and strategies to experimentally validate and functionally characterize fusion transcripts.

Hsa_circ_0074158 regulates the endothelial barrier function in sepsis and its potential value as a biomarker

Background: Sepsis is one of the main causes of death in critically ill patients with high morbidity and mortality. Circular RNAs (CircRNAs) are aberrantly expressed, and play significant regulatory roles in many diseases. However, the expression profiles and functions of circRNAs in sepsis have not yet been fully clarified.

Methods: Our present study performed an RNA sequencing (RNA-seq) analysis to assess the expression profiles of circRNAs in vitro. We applied the quantitative real-time polymerase chain reaction (RT-qPCR) to verify the RNA-seq results. The analyses of Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, the competitive endogenous RNA (ceRNA) regulatory networks, were performed to explore the potential mechanism in sepsis. And then, significantly up-regulated differentially expressed (DE) circRNA, hsa_circ_0074158, was selected for further study. Hsa_circ_0074158 was silenced to investigate its regulatory function in sepsis, and the barrier function was also examined in vitro. Endothelial cell junctions were valued using Vascular endothelial cadherin (VE-cadherin), which was detected by immunofluorescence staining. We measured endothelial permeability by transendothelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC)-dextran extravasation.

Results: In total, 203 significantly DE circRNAs, including 77 up-regulated and 126 down-regulated, were identified. In vitro, the RT-qPCR assay showed that the expression pattern of hsa_circ_0074158, hsa_circ_RSBN1L_11059, hsa_circ_0004188, and hsa_circ_0005564 were consistent with the results from RNA-seq analysis. The expression of hsa_circ_0074158 detected by RT-qPCR in vivo was also consistent with the RNA-seq results. The ceRNA networks, GO enrichment, and the KEGG pathway analyses revealed that circRNAs may be related to the barrier function in sepsis. The immunofluorescence assay showed that the suppression of hsa_circ_0074158 expression significantly enhanced the expression of VE-cadherin, which was suppressed in lipopolysaccharide (LPS)-induced sepsis. Additionally, hsa_circ_0074158 knockdown could partially reverse the LPS-induced TEER reduction and FITC-dextran extravasation elevation in sepsis.

Conclusion: In conclusion, we have found DE circRNAs could serve as potential biomarkers and therapeutic targets for sepsis. Hsa_circ_0074158 plays a vital role in sepsis and is related to the disruption of the endothelial barrier.

circ-LIMK1 regulates cisplatin resistance in lung adenocarcinoma by targeting miR-512-5p/HMGA1 axis

This study aimed to unveil the detailed role and new mechanism of circ-LIMK1 in lung adenocarcinoma. Real-time quantitative polymerase chain reaction was performed to analyze the expression of circ-LIMK1, miR-512-5p, and HMGA1. 3-(4,5)-Dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide assay was employed to test the half maximal inhibitory concentration of cisplatin (DDP). Western blot was used to measure the expression of HMGA1, multidrug resistance protein 1, mitochondrial 37S ribosomal protein, and vascular endothelial growth factor A. Colony formation assay, flow cytometry, transwell assay, and tube formation assay were performed to analyze cell functions. Animal models were established to assay the role of circ-LIMK1 in vivo. The expression of circ-LIMK1 was up-regulated in DDP-resistant tumor tissues and cells. Knockdown of circ-LIMK1 reduced DDP resistance, impaired cancer cell growth, migration, invasion, and angiogenesis. circ-LIMK1 targeted miR-512-5p, and HMGA1 was targeted by miR-512-5p. MiR-512-5p absence could restore the repressive effects of circ-LIMK1 knockdown on lung adenocarcinoma cell phenotypes. Overexpression of HMGA1 could restore the inhibitory effects of miR-512-5p enrichment on lung adenocarcinoma cell malignant phenotypes. Knockdown of circ-LIMK1 could reduce growth of DDP-resistant tumors in vivo. Collectively, circ-LIMK1 regulated DDP resistance in lung adenocarcinoma by targeting miR-512-5p/HMGA1 axis.

Fuzheng Xiaozheng prescription exerts anti-hepatocellular carcinoma effects by improving lipid and glucose metabolisms via regulating circRNA-miRNA-mRNA networks

BACKGROUND

Hepatocellular carcinoma (HCC) is a major threat to human health due to its high lethality. Our previous studies suggested that Fuzheng Xiaozheng prescription (FZXZP), an effective Chinese medicine, demonstrated significant suppressive effects on HCC. However, its underlying mechanism remains largely unclear.

PURPOSE

This study aimed to investigate the anti-HCC mechanisms of FZXZP from transcriptomic sequencing based on a holistic perspective.

METHODS

Rat HCC model was induced by diethylnitrosamine, and then the model was administered with two doses of FZXZP, high and low. Sodium demethylcantharidate was used as a positive control. Subsequently, microarrays of circRNA, miRNA and mRNA were performed on the blank, model, high and low dose groups, respectively, and the competitive binding mechanisms among them were further analyzed by bioinformatics. Then, the circRNA-miRNA-mRNA networks were constructed to mine the targeted-RNAs of FZXZP in HCC, as well as to explore their potential regulatory mechanisms. Finally, functions and pathways of the FZXZP targeted genes in rat HCC were annotated with GO and KEGG, and qRT-PCR was performed to validate the accuracy of the above analyses in this study.

RESULTS

The results showed that FZXZP significantly inhibited the development and progression of HCC in rats, improved the pathological conditions and suppressed the proliferation of HCC cells. Subsequently, after a series of screening, the competing endogenous RNA networks (circRNA-miRNA-mRNA), consisting of 2 circRNAs, 7 miRNAs and 104 mRNAs, were finally established. KEGG and GO analyses of the networks revealed that lipid metabolism related pathways, such as fatty acid metabolism, bile secretion and PPAR pathway, were significantly enriched. In the further hubgene network analysis, in addition to lipid metabolism, aberrant glucose metabolism was found to be ameliorated by G6pc and Pklr in hubgenes. Finally, the qRT-PCR analyses confirmed that the expression tendencies of the above targeted genes were correct and believable in transcriptomic sequencings, and qRT-PCR results of the genes closely related to proliferation, invasion and apoptosis of HCC also indicated the inhibitory effects of FZXZP on HCC obviously.

CONCLUSION

FZXZP demonstrated significant anti-HCC effects through improving lipid and glucose metabolism, restoring the metabolic homeostasis of the liver via circRNA-miRNA-mRNA networks.

Circ_0058063 contributes to oral squamous cell carcinoma development by sponging miR-145-5p and upregulating SERPINE1

BACKGROUND

We aimed to demonstrate the effects circ_0058063 exerted on oral squamous cell carcinoma (OSCC) and its downstream mechanism associated with miR-145-5p and SERPINE1.

METHODS

The relevant contents of miR-145-5p, circ 0058063, and SERPINE1 mRNAs in OSCC were evaluated using RT-qPCR. Functional experiments including CCK-8, Transwell, Western blot and in vivo experiment were implemented to investigate the biological impacts on OSCC cells. Using dual-luciferase reporter, RIP, and RNA pull-down assays, the direct binding relationship between miR-145-5p, circ 0058063, and SERPINE1, SMAD3, CYR61, and IGF1R mRNAs was verified.

RESULTS

In OSCC, Circ 0058063 was significantly overexpressed. Knockdown of circ_0058063 suppressed OSCC cell migration and proliferation, but enhanced cell apoptosis. Functionally and mechanistically, circ_0058063 could specifically bind with miR-145-5p and thus up-regulated expression of downstream target SERPINE1, which together contributed to the progression of OSCC.

CONCLUSION

Circ_0058063 could promote malignant behavior of OSCC by upregulating SERPINE1 through sponging miR-145-5p.

CircRNAs: novel therapeutic targets in multiple myeloma

BACKGROUND

Circular RNA (circRNA) is a type of non-coding RNA that has recently attracted the attention of researchers. Multiple myeloma (MM) is a hematological malignancy with a dismal prognosis that indicates a pressing need for better treatment alternatives, particularly in terms of biological indicators. According to recent research findings, the presence of circRNA is also closely related to the incidence and progression of malignant hemopathy. There have been, however, only a few investigations of circRNA in MM.

MATERIAL AND METHODS

This review will be on the biological properties and functions of circRNA in MM and a discussion of the clinical utility of circRNA in the diagnosis, prognosis, and treatment of MM.

CONCLUSIONS

CircRNA is involved in gene transcription, translation, and epigenetic modification as well as the regulation of cancer cell proliferation, invasion, and metastasis, and hence, promotes or inhibits the occurrence and progression of MM. Therefore, circRNA holds promise as a potential future MM biomarker.

Identification and functional analysis of circRNAs in the skeletal muscle of juvenile and adult largemouth bass (Micropterus salmoides)

Circular RNA (circRNA) is a novel emerging type of endogenous regulatory non-coding RNA molecules with a covalent closed-loop configuration, which exerts important functions in multiple biological processes. CircRNAs are known to regulate gene expression as functional regulators interacting with miRNAs by sponge, which have been reported to regulate skeletal muscle development. Nevertheless, the information of circRNAs involved in regulating muscle growth and development in fish is largely unknown. Here, we first identified 312 and 511 circRNAs in skeletal muscle of juvenile and adult largemouth bass (LMB) using RNA sequencing, respectively. The differentially expressed circRNAs (DE-circRNAs) analysis showed that there are 44 DE-circRNAs at two different skeletal muscle growth stages. Six circRNAs were chosen randomly and their relative expression levels in juvenile and adult LMB were confirmed by real-time PCR, indicating that these circRNAs were existed authenticity. In addition, Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis showed that these hose genes (their linear mRNAs) of DE-circRNAs were mainly enriched in the regulation of actin cytoskeleton signaling pathways. The circRNA-miRNA interaction regulatory networks indicated that one circRNA can regulate one or more miRNA. For instance, more than 30 miRNAs were regulated by two circRNAs (circRNA389 and circRNA399). Of them, the muscle-related miRNAs including the let-7 family, miR-133 and miR-26 and so on were found acting as miRNAs sponge regulated by circRNAs, indicating the roles of circRNAs in regulating muscle growth-related genes expression. Overall, these findings will not only broaden our understanding of circRNAs regulation mechanisms underlying muscle growth and development in LMB but also provides a novel clue for further functional research in carnivorous fish genetic breeding.

Diagnostic and prognostic value of circRNAs expression in head and neck squamous cell carcinoma: A meta-analysis

Background

Circular RNAs (circRNAs) have been found to have potential biological applications against tumors in humans. This study aimed to evaluate the diagnostic, prognostic, and clinicopathological value of circRNAs in head and neck squamous cell carcinoma (HNSCC).

Methods

The PubMed, Web of Science, EMBASE, and the Cochrane Library were comprehensively searched for the relevant studies before October 20, 2021. Statistical analysis was performed based on STATA 15.0, Meta‐DiSc 1.4, and RevMan 5.3 software.

Results

A total of 55 reports regarding 56 kinds of circRNA were studied in this meta‐analysis, including 23, 38, and 26 articles on diagnosis, prognosis, and clinicopathological features, respectively. The pooled sensitivity, specificity, and area under the curve (AUC) of the summary receiver‐operating characteristic curve (SROC) were 0.78, 0.84, and 0.87, respectively. Besides, the upregulation of oncogenic circRNAs was significantly associated with poorer overall survival (OS) (HR=2.25, p < 0.05) and disease‐free interval (DFS) (HR=1.92, p < 0.05). In contrast, the elevated expression of tumor suppressor circRNAs was associated with a favorable prognosis (HR=0.50, p < 0.05). In addition, the high expression of oncogenic circRNAs was associated with the tumor size (OR=3.59, p < 0.05), degree of differentiation (OR=1.89, p < 0.05), TNM stage (OR=2.35, p < 0.05), lymph node metastasis (OR=1.85, p < 0.05), and distant metastasis (OR=3.42, p < 0.05). Moreover, the expression of tumor suppressor circRNAs was associated with improved clinicopathological features (lymph node metastasis: OR=0.25, p < 0.05).

Conclusions

CircRNAs could serve as potential predictive indicators and be useful for the diagnosis, prognosis, and identification of clinicopathological features in HNSCC.

The functions, oncogenic roles, and clinical significance of circular RNAs in renal cell carcinoma

Renal cell carcinoma (RCC) is the most common form of malignancy affecting the kidneys. Circular RNAs (circRNAs) are non-coding RNAs that are derived from exonic or intronic sequences through a selective shearing process. There is growing evidence that these circRNAs can influence a range of biological pathways by serving as protein decoys, microRNA sponges, regulators of transcriptional activity, or templates for protein translation. The dysregulation of circRNA expression patterns is a hallmark of RCC and other cancer types, and there is strong evidence that these RNA species can play central roles in the onset and progression of RCC tumors. In the present review, we summarized recent findings on the functional roles and clinical impacts of circRNAs in RCC. Further, we discussed their potential utility as diagnostic biomarkers or targets for therapeutic intervention.

Circ_0001093 promotes glutamine metabolism and cancer progression of esophageal squamous cell carcinoma by targeting miR-579-3p/glutaminase axis

Increasing studies indicate that circular RNAs (circRNAs) play critical roles in tumor metabolism of multiple cancers. However, the contribution of circRNAs in glutamine metabolism of esophageal squamous cell carcinoma (ESCC) remains elusive. The objective of this research was to investigate the role and mechanism of circRNA hsa_circ_0001093 (circ_0001093) in the glutamine metabolism and tumorigenesis of ESCC. Circ_0001093, microRNA-579-3p (miR-579-3p) and glutaminase (GLS) expressions in ESCC tissues and cell lines were measured by qRT-PCR, tissue array or Western blot. Cell proliferation, invasion and migration were assessed by CCK-8 or transwell assays. Glutamine consumption, glutamate and ATP production were detected by indicated assay kits. The relationships between circ_0001093 and miR-579-3p or GLS mRNA were investigated by bioinformatics analysis, RNA pull-down, luciferase reporter and RNA immunoprecipitation (RIP) assays. Here, we found that circ_0001093 expression was up-regulated in ESCC tissues and cell lines. Increased circ_0001093 expression predicted an unfavourable prognosis, and was associated with the lymph node metastasis, TNM staging and tumor size in ESCC tissues. Circ_0001093 knockdown suppressed cell proliferation, invasion, migration and glutamine metabolism of ESCC cells, while circ_0001093 over-expression showed the opposite effects. Mechanistically, circ_0001093 acted as a competing endogenous RNA (ceRNA) by sponging miR-579-3p, thereby increasing GLS expression. Furthermore, the inhibitory effects of circ_0001093 knockdown on the invasion, migration and glutamine metabolism were partly rescued by miR-579-3p inhibition or GLS over-expression in ESCC cells. Additionally, miR-579-3p expression was down-regulated in ESCC tissues, while GLS expression was up-regulated. In conclusion, this study first provides evidence that the circ_0001093/miR-579-3p/GLS regulatory network can affect glutamine metabolism and malignant phenotype of ESCC, which can further impact ESCC progression.

Circular RNA ITCH: An Emerging Multifunctional Regulator

In the last decade, numerous circRNAs were discovered by virtue of the RNA-Seq technique. With the deepening of experimental research, circRNAs have brought to light the key biological functions and progression of human diseases. CircRNA ITCH has been demonstrated to be a tumor suppressor in numerous cancers, and recently it was found to play an important role in bone diseases, diabetes mellitus, and cardiovascular diseases. However, the functions of circ-ITCH have not been completely understood. In this review, we comprehensively provide a conceptual framework to elucidate circ-ITCH biological functions of cell proliferation, apoptosis and differentiation, and the pathological mechanisms of inflammation, drug resistance/toxicity, and tumorigenesis. Finally, we summarize its clinical applications in various diseases. This research aimed at clarifying the role of circ-ITCH, which could be a promising therapeutic target.

Presence of cell-free fetal circRNA in maternal plasma

INTRODUCTION

There is an urgent need to find novel stable cell-free fetal (cff-) RNA in the maternal circulation to facilitate the advance of non-invasive prenatal testing (NIPT) to more effectively avoid birth defects.

METHODS

CircRNA microarray was used to detect the cff-circRNA in plasma.

RESULTS

There were cff-circRNAs from the fetus in the peripheral blood of pregnant women and they persisted even until at least 24 h after delivery. In addition, we found that cff-circRNA might have a specific expression pattern in gestational disease.

CONCLUSIONS

We demonstrated the presence of cff-circRNA in the maternal circulation, which may shed new light on the development of NIPT.

Extracellular vesicles as a new hope for diagnosis and therapeutic intervention for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer with a high mortality rate. Early diagnosis and treatment before tumor progression into an advanced stage is ideal. The current diagnosis of HCC is mainly based on imaging modalities such as ultrasound, computed tomography, and magnetic resonance imaging. These methods have some limitations including diagnosis in the case of very small tumors with atypical imaging patterns. Extracellular vesicles (EVs) are nanosized vesicles which have been shown to act as an important vector for cell-to-cell communication. In the past decade, EVs have been investigated with regard to their roles in HCC formation. Since these EVs contain biomolecular cargo such as nucleic acid, lipids, and proteins, it has been proposed that they could be a potential source of tumor biomarkers and a vector for therapeutic cargo. In this review, reports on the roles of HCC-derived EVs in tumorigenesis, and clinical investigations using circulating EVs as a biomarker for HCC and their potential diagnostic roles have been comprehensively summarized and discussed. In addition, findings from in vitro and in vivo reports investigating the potential roles of EVs as therapeutic interventions are also presented. These findings regarding the potential benefits of EVs will encourage further investigations and may allow us to devise novel strategies using EVs in the early diagnosis as well as for treatment of HCC in the future.

Circular RNA hsa_circ_105039 promotes cardiomyocyte differentiation by sponging miR‑17 to regulate cyclinD2 expression

Previously it was found that hsa_circ_105039 was underexpressed in the heart tissue of patients with congenital heart disease (CHD). However, the function and mechanism of hsa_circ_105039 in CHD are unclear. In the present study, induced pluripotent stem (iPS) cells were differentiated into cardiomyocytes using 1% dimethyl sulfoxide (DMSO). Cell differentiation, viability, migration and apoptosis were measured before and following hsa_circ_105039 knockdown or overexpression. The results indicated that hsa_circ_105039 overexpression promoted cell differentiation, viability and migration; whereas apoptosis was simultaneously repressed. A luciferase reporter assay verified that hsa_circ_105039 acted as a sponge for microRNA (miR)‑17 and that cyclinD2 was a direct target of miR‑17. Furthermore, differentiation‑related genes and proteins were analyzed by reverse transcription‑quantitative PCR and western blotting, respectively. The results showed that hsa_circ_105039 could also upregulate the expression of differentiation‑related genes and proteins, including natriuretic peptide A, cardiac troponin I, GATA‑binding protein 4 and homobox transcription factor, in iPS cells. The results suggested that hsa_circ_105039 exerted a protective effect by promoting miR‑17/cyclinD2 in DMSO‑induced iPS cardiomyocytes, which indicated that hsa_circ_105039 is a potential key molecule for the diagnosis of CHD.

Circular RNAs in Hedgehog Signaling Activation and Hedgehog-Mediated Medulloblastoma Tumors

Simple Summary

Here the expression profile of circular RNAs in Hedgehog signaling-dependent cell lines and medulloblastoma cells was interrogated. Using stringent criteria, a reduced expression of seven circular RNAs in Hedgehog-dependent medulloblastoma versus cerebellum was clearly established. Depletion and/or overexpression of these deregulated RNA circles in two medulloblastoma cell lines revealed minimal effects in cellular proliferation based on two independent assays. These findings highlight the complexity of gene expression outcomes and the possibility that gene products may not necessarily have an obvious phenotypic impact on the cellular context where they are present. It is not inconceivable that a substantial number of differentially expressed circular RNAs may represent “passenger molecules” with little impact on a cell, reflecting the stochasticity of the gene expression and splicing processes.

Abstract

Within the past decade, circular RNAs have largely emerged as novel regulators of human biology, including brain function and cancer development. On the other hand, the Hedgehog pathway has established roles in regulating biological processes, including tumorigenesis. Here, the circular RNA transcriptome, in the context of Hedgehog signaling activation of medulloblastoma Daoy and human embryonic palatal mesenchyme HEPM cells, was determined. In total, 29 out of the 30 selected circular RNAs were validated by Sanger sequencing, with some regulated to a limited extent by Hedgehog signaling. Interestingly, back-spliced junctions, the marker of exonic RNA circles, were also identified at a low frequency within poly (A) mRNAs, reflecting exon repetition events. Thirteen circular RNAs had reduced expression in human medulloblastoma tumors in comparison to normal cerebellum. For seven out of these thirteen RNA circles, the linear mRNAs originating from the same genes did not exhibit a reduced expression. Depletion and/or overexpression of these seven circular RNAs minimally affected medulloblastoma cell proliferation. These findings highlight that differential expression of a gene product may not necessarily elicit an obvious phenotypic impact. Consequently, further analysis is required to determine the possible subtle contributions to the development of this cerebellar tumor.

CircRNAs as potent biomarkers in ovarian cancer: a systematic scoping review

More powerful prognostic and diagnostic tools are urgently needed for identifying and treating ovarian cancer (OC), which is the most fatal malignancy in women in developed countries. Circular RNAs (circRNAs) are conservative and stable looped molecules that can regulate gene expression by competing with other endogenous microRNA sponges. This discovery provided new insight into novel methods for regulating genes that are involved in many disorders and cancers. This review focuses on the dysregulated expression of circRNAs as well as their diagnostic and prognostic values in OC. We found that studies have identified twenty-one downregulated circRNAs and fifty-seven upregulated ones. The results of these studies confirm that circRNAs might be potent biomarkers with diagnostic, prognostic and therapeutic target value for OC. We also consider the connection between circRNAs and OC cell proliferation, apoptosis, metastasis, and chemotherapy resistance and sensitivity.

Circular RNAs and their role in renal cell carcinoma: a current perspective

Circular RNAs (circRNAs) are a new class of long non-coding RNAs, that results from a special type of alternative splicing referred to as back-splicing. They are widely distributed in eukaryotic cells and demonstrate tissue-specific expression patterns in humans. CircRNAs actively participate in various important biological activities like gene transcription, pre-mRNA splicing, translation, sponging miRNA and proteins, etc. With such diverse biological functions, circRNAs not only play a crucial role in normal human physiology, as well as in multiple diseases, including cancer. In this review, we summarized our current understanding of circRNAs and their role in renal cell carcinoma (RCC), the most common cancer of kidneys. Studies have shown that the expression level of several circRNAs are considerably varied in RCC samples and RCC cell lines suggesting the potential role of these circRNAs in RCC progression. Several circRNAs promote RCC development and progression mostly via the miRNA/target gene axis making them ideal candidates for novel anti-cancer therapy. Apart from these, there are a few circRNAs that are significantly downregulated in RCC and overexpression of these circRNAs leads to suppression of RCC growth. Differential expression patterns and novel functions of circRNAs in RCC suggest that circRNAs can be utilized as potential biomarkers and therapeutic targets for RCC therapy. However, our current understanding of the role of circRNA in RCC is still in its infancy and much comprehensive research is needed to achieve clinical translation of circRNAs as biomarkers and therapeutic targets in developing effective treatment options for RCC.