Circular RNA Profiling Reveals Exosomal circ_0006156 as a Novel Biomarker in Papillary Thyroid Cancer

CircSEMA6A upregulates PRRG4 by targeting MiR-520h and recruiting ELAVL1 to affect cell invasion and migration in papillary thyroid carcinoma

Objective

As the most prevalent type of thyroid malignancy, papillary thyroid carcinoma (PTC) accounts for over 80% of all thyroid cancers. Circular RNAs (circRNAs) have been found to regulate multiple cancers, including PTC.

Materials and methods

Quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were used to analyse RNA and protein levels. Fluorescence in situ hybridization (FISH) was used to detect the distribution of the target genes. Functional experiments and animal experiments were implemented to analyse the biological functions of target genes in vitro and in vivo. Luciferase reporter, RNA pulldown, RNA binding protein immunoprecipitation (RIP) and mRNA stability assays were used to probe the underlying mechanisms.

Results

CircSEMA6Awas found to be upregulated in PTC tissues and cells, and its circular structure was verified. CircSEMA6A promotes PTC cell migration and invasion. Moreover, circSEMA6A functions as a competing endogenous RNA (ceRNA) to upregulate proline rich and Gla domain 4 (PRRG4) expression by sponging microRNA-520h (miR-520h). CircSEMA6A recruits ELAV1 to stabilize PRRG4 mRNA and drives PTC progression via PRRG4.

Conclusion

CircSEMA6A upregulates PRRG4 by targeting miR-520h and recruiting ELAVL1 to affect the invasion and migration of PTC cells, offering insight into the molecular mechanisms of PTC.

Extracellular vesicle-derived CircWhsc1 promotes cardiomyocyte proliferation and heart repair by activating TRIM59/STAT3/Cyclin B2 pathway

INTRODUCTION

Extracellular vesicles (EVs)-mediated cell-to-cell communication is crucial for hypoxia-induced cell proliferation and tissue repair, but its function in endogenous cardiac regeneration is still unknown.

OBJECTIVES

Herein, we aimed to determine whether hypoxia-inducible circWhsc1 in endothelial EVs promoted cardiomyocyte (CM) proliferation and cardiac regeneration.

METHODS

RNA-sequence data was used to identify EV circRNAs that were involved into endogenous cardiac regeneration. Quantitative polymerase chain reactions were conducted to determine circRNA expression in tissue, cells and EVs. Gain- and loss-of-function assays were performed to explore the function of EV-derived circWhsc1 during cardiac regeneration. Western blotting and RNA pulldown assays were used to investigate its underlying mechanism.

RESULTS

We found that circWhsc1 was enriched in neonatal mouse hearts, particularly in cardiac ECs, and was further upregulated both in ECs and EC-derived EVs under hypoxic conditions. When cocultured with hypoxia-preconditioned neonatal ECs or their secreted EVs, both neonatal and adult CMs exhibited an increased proliferation rate and G2/M ratio, which could be attenuated by knockdown of circWhsc1 in ECs. In vivo, EC-restricted overexpression of circWhsc1 and EV-mediated delivery of circWhsc1 induced CM proliferation, alleviated cardiac fibrosis and restored cardiac function following myocardial infarction in adult mice. Mechanistic studies revealed that EV-derived circWhsc1 activated TRIM59 by enhancing its phosphorylation, thereby reinforcing the binding of TRIM59 to STAT3, phosphorylating STAT3 and inducing CM proliferation.

CONCLUSION

The current study demonstrated that hypoxia-inducible circWhsc1 in EC-derived EVs induces CM proliferation and heart regeneration. EC-CM communication mediated by EV-derived circWhsc1 might represent a prospective therapeutic target for inducing cardiac repair post-myocardial infarction.

Circular RNAs in ferroptosis: regulation mechanism and potential clinical application in disease

Ferroptosis, an iron-dependent non-apoptotic form of cell death, is reportedly involved in the pathogenesis of various diseases, particularly tumors, organ injury, and degenerative pathologies. Several signaling molecules and pathways have been found to be involved in the regulation of ferroptosis, including polyunsaturated fatty acid peroxidation, glutathione/glutathione peroxidase 4, the cysteine/glutamate antiporter system Xc-, ferroptosis suppressor protein 1/ubiquinone, and iron metabolism. An increasing amount of evidence suggests that circular RNAs (circRNAs), which have a stable circular structure, play important regulatory roles in the ferroptosis pathways that contribute to disease progression. Hence, ferroptosis-inhibiting and ferroptosis-stimulating circRNAs have potential as novel diagnostic markers or therapeutic targets for cancers, infarctions, organ injuries, and diabetes complications linked to ferroptosis. In this review, we summarize the roles that circRNAs play in the molecular mechanisms and regulatory networks of ferroptosis and their potential clinical applications in ferroptosis-related diseases. This review furthers our understanding of the roles of ferroptosis-related circRNAs and provides new perspectives on ferroptosis regulation and new directions for the diagnosis, treatment, and prognosis of ferroptosis-related diseases.

Circular RNAs: biology and clinical significance of breast cancer

Circular RNAs (circRNAs) are novel noncoding RNAs with covalently closed-loop structures that can regulate eukaryotic gene expression. Due to their stable structure, circRNAs are widely distributed in the cytoplasm and have important biological functions, including as microRNA sponges, RNA-binding protein conjugates, transcription regulators, and translation templates. Breast cancer is among the most common malignant cancers diagnosed in women worldwide. Despite the development of comprehensive treatments, breast cancer still has high mortality rates. Recent studies have unmasked critical roles for circRNAs in breast cancer as regulators of tumour initiation, progression, and metastasis. Further, research has revealed that some circRNAs have the potential for use as diagnostic and prognostic biomarkers in clinical practice. Herein, we review the biogenesis and biological functions of circRNAs, as well as their roles in different breast cancer subtypes. Moreover, we provide a comprehensive summary of the clinical significance of circRNAs in breast cancer. CircRNAs are believed to be a hot focus in basic and clinical research of breast cancer, and innovative future research directions of circRNAs could be used as biomarkers, therapeutic targets, or novel drugs.Abbreviations: CeRNA: Competitive endogenous RNA; ciRNA: Circular intronic RNA; circRNA: Circular RNA; EIciRNA: Exon-intron circRNA; EMT: Epithelial-mesenchymal transition; IRES: Internal ribosome entry site; lncRNA: Long non-coding RNA; miRNA: MicroRNA; MRE: MiRNA response element; ncRNA: Non-coding RNA; RBP: RNA-binding protein; RNA-seq: RNA sequencing; RT-PCR: Reverse transcription-polymerase chain reaction.

Hsa_circ_0000877 facilitates the progression of diffuse large B-cell lymphoma by miR-370-3p/mitogen-activated protein kinase kinase kinase kinase 4/Hippo pathway

Diffuse large B-cell lymphoma (DLBCL) originates from B lymphocytes and is a fatal hematological malignancy. Circular RNAs have been increasingly reported as a promising biological target for cancer therapy, but their role in DLBCL remains poorly studied. Relative expression levels of has_circ_0000877 (circ_0000877), microRNA-370-3p (miR-370-3p), and mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4) were assessed by quantitative real-time PCR. Western blot analysis was employed to measure protein levels. Cell Counting Kit-8 assay and 5-ethynyl-2'-deoxyuridine (EdU) assay were used to detect the proliferation of TMD8 and U2932 cells. Cell cycle and apoptosis were investigated by flow cytometry. Transwell assay was used to analyze cell migration and invasion. Molecular interaction was determined by dual-luciferase reporter assay and RNA immunoprecipitation assay. The protein expression of Ki67 in tumor tissues of mice was detected by immunohistochemistry assay. The expression of circ_0000877 was markedly elevated in DLBCL tissues and cell lines. The decreased expression of circ_0000877 significantly inhibited proliferation, migration, and invasion of DLBCL cell lines. In addition, silencing circ_0000877 promoted cell apoptosis and induced cell cycle arrest in G0/G1 phase. Then, miR-370-3p directly interacted with circ_0000877 and MAP4K4. Circ_0000877 promoted MAP4K4 level by sponging miR-370-3p. MAP4K4 depletion inhibited the activation of Hippo pathway. Finally, circ_0000877 silencing significantly prevented the growth of DLBCL cells in vivo . Our findings revealed that circ_0000877 could regulate the malignant evolution of DLBCL by miR-370-3p/MAP4K4/Hippo pathway.

Overexpression of circFNDC3B promotes the progression of oral tongue squamous cell carcinoma through the miR-1322/MED1 axis

BACKGROUND

The potential role of circFNDC3B in regulating oral tongue squamous cell carcinoma development (OTSCC) remains unknown.

METHODS

The level of circFNDC3B in OTSCC tissues or cell lines was measured and its function in vitro and in vivo was analyzed. Interactions among circFNDC3B, miR-1322, and MED1 were verified by luciferase reporter and RNA pull-down assays.

RESULTS

The level of circFNDC3B in tissues or cell lines of OTSCC was higher than that in control groups. siRNA-mediated circFNDC3B inhibition resulted in weakened proliferation, migration, and invasion, which was reversed by miR-1322. Overexpression of MED1 in OTSCC cells partially reversed the tumor suppression functions of si-circFNDC3B or miR-1322 mimics in vitro. circFNDC3B overexpression dramatically promoted tumor growth in vivo. circFNDC3B directly bound with miR-1322 and consequently promoted the MED1 expression in OTSCC cells.

CONCLUSIONS

The circFNDC3B/miR-1322/MED1 axis participates in OTSCC progression, which may provide novel therapeutic targets for OTSCC.

Circ_0000144 acts as a miR-1178-3p decoy to promote cell malignancy and angiogenesis by increasing YWHAH expression in papillary thyroid cancer

Papillary thyroid cancer (PTC) is the most common subtype of thyroid cancer. Circular RNA hsa_circ_0000144 (circ_0000144) is related to the progression of thyroid cancer. However, the mechanism by which circ_0000144 accelerates PTC progression is still unclear. Circ_0000144 and YWHAH were upregulated in PTC tissues and cells, while miR-1178-3p had an opposite result. Circ_0000144 silencing constrained PTC cell growth in vitro and in vivo and induced apoptosis and repressed migration, invasion, and angiogenesis of PTC cells in vitro. Circ_0000144 acted as a molecular sponge for miR-1178-3p, which targeted YWHAH. MiR-1178-3p inhibitor reversed circ_0000144 silencing-mediated influence on PTC cell malignancy and angiogenesis. Furthermore, YWHAH overexpression overturned miR-1178-3p mimic-mediated influence on malignant behaviors and angiogenesis of PTC cells. Notably, circ_0000144 regulated YWHAH expression by adsorbing miR-1178-3p. Circ_0000144 promoted cell malignancy and angiogenesis by regulating the miR-1178-3p/YWHAH axis in PTC, offering a novel mechanism for the malignancy and angiogenesis of PTC cells.

Inhibition of circ_0000144 repressed malignant behaviors and angiogenesis of PTC cells in vitro.

Knockdown of circ_0000144 constrained PTC cell proliferation in vivo.

Circ_0000144 acted as a miR-1178-3p sponge.

YWHAH acted as a downstream target for miR-1178-3p.

Function and Clinical Significance of Circular RNAs in Thyroid Cancer

Thyroid cancer (TC) is the leading cause and mortality of endocrine malignancies worldwide. Tumourigenesis involves multiple molecules including circular RNAs (circRNAs). circRNAs with covalently closed single-stranded structures have been identified as a type of regulatory RNA because of their high stability, abundance, and tissue/developmental stage-specific expression. Accumulating evidence has demonstrated that various circRNAs are aberrantly expressed in thyroid tissues, cells, exosomes, and body fluids in patients with TC. CircRNAs have been identified as either oncogenic or tumour suppressor roles in regulating tumourigenesis, tumour metabolism, metastasis, ferroptosis, and chemoradiation resistance in TC. Importantly, circRNAs exert pivotal effects on TC through various mechanisms, including acting as miRNA sponges or decoys, interacting with RNA-binding proteins, and translating functional peptides. Recent studies have suggested that many different circRNAs are associated with certain clinicopathological features, implying that the altered expression of circRNAs may be characteristic of TC. The purpose of this review is to provide an overview of recent advances on the dysregulation, functions, molecular mechanisms and potential clinical applications of circRNAs in TC. This review also aimes to improve our understanding of the functions of circRNAs in the initiation and progression of cancer, and to discuss the future perspectives on strategies targeting circRNAs in TC.

Roles of exosomal circRNAs in tumour immunity and cancer progression

Tumour immunity plays an important role in the development of cancer. Tumour immunotherapy is an important component of antitumour therapy. Exosomes, a type of extracellular vesicle, act as mediators of intercellular communication and molecular transfer and play an essential role in tumour immunity. Circular RNAs (circRNAs) are a new type of noncoding RNA that are enriched within exosomes. In this review, we describe the effects of exosomal circRNAs on various immune cells and the mechanisms of these effects, including macrophages, neutrophils, T cells, and Natural killer (NK) cells. Next, we elaborate on the latest progress of exosome extraction. In addition, the function of exosomal circRNAs as a potential prognostic and drug sensitivity marker is described. We present the great promise of exosomal circRNAs in regulating tumour immunity, predicting patient outcomes, and evaluating drug efficacy.

circRNF20 aggravates the malignancy of retinoblastoma depending on the regulation of miR-132-3p/PAX6 axis

Circular RNAs (circRNAs) serve as essential players in diverse human cancers, including retinoblastoma (RB). In this study, the function of circRNA Ring Finger Protein 20 (circRNF20) in RB progression was investigated. Quantitative real-time polymerase chain reaction, western blot assay or immunohistochemistry assay was performed to determine the expression of circRNF20, miR-132-3p and Paired Box 6 (PAX6). Dual-luciferase reporter assay, RNA immunoprecipitation assay and RNA pull-down assay were utilized to verify the relationships among circRNF20, miR-132-3p and PAX6. In vivo experiment was done for circRNF20 function in tumor formation. It was found that ircRNF20 level was increased in RB tissues and linked to advanced tumor, nodes, metastases (TNM) stage and poor overall survival rate. Deficiency of circRNF20 suppressed cell proliferation, migration and invasion and induced apoptosis in vitro, as well as blocked tumor growth in vivo. circRNF20 directly targeted miR-132-3p and miR-132-3p overexpression inhibited RB cell progression. PAX6 was the target gene of miR-132-3p. Moreover, miR-132-3p inhibition or PAX6 overexpression reversed circRNF20 deficiency-mediated effects on RB cell malignant behaviors. In addition, exosomal circRNF20 was able to promote RB cell progression. Thus, we concluded that circRNF20 served as an oncogene in RB progression through the circRNF20/miR-132-3p/PAX6 pathway.

Role of exosomal competitive endogenous RNA (ceRNA) in diagnosis and treatment of malignant tumors

Malignant tumors are a threat to human health, thus it is critical to better understand the mechanism of tumor occurrence and development and to find key therapeutic targets. Competitive endogenous RNA (ceRNA) is a type of RNA molecule that includes mRNA of coding-protein, pseudogenes, long non-coding RNA (lncRNA), and circular RNA (circRNA) etc. It is created through a competitive combination of common small RNA (miRNA) and has an inhibitory effect on mRNA translation. ceRNA regulate the post transcriptional expression of genes by competitively binding to common microRNAs (miRNAs).Studies have shown that cernas are involved in tumor cell proliferation, invasion and migration, drug resistance, angiogenesis, as well as tumor immunity, and so on, affecting the progression of tumor development. This article reviews the reported roles of exosomal ceRNA in the diagnosis and treatment of malignant tumors and the mechanisms underlying these.

Circular RNAs and Their Role in Exosomes

As a novel class of endogenous non-coding RNAs discovered in recent years, circular RNAs (circRNAs) are highly conserved and stable covalently closed ring structures with no 5'-end cap or 3'-end poly(A) tail. CircRNAs are formed by reverse splicing, mainly by means of a noose structure or intron complementary pairing. Exosomes are tiny discoid vesicles with a diameter of 40-100 nm that are secreted by cells under physiological and pathological conditions. Exosomes play an important role in cell-cell communication by carrying DNA, microRNAs, mRNAs, proteins and circRNAs. In this review, we summarize the biological functions of circRNAs and exosomes, and further reveal the potential roles of exosomal circRNAs in different diseases, providing a scientific basis for the diagnosis, treatment, and prognosis of a wide variety of diseases.

Emerging Roles of Extracellular Vesicle-Delivered Circular RNAs in Atherosclerosis

Atherosclerosis (AS) is universally defined as chronic vascular inflammation induced by dyslipidaemia, obesity, hypertension, diabetes and other risk factors. Extracellular vesicles as information transmitters regulate intracellular interactions and their important cargo circular RNAs are involved in the pathological process of AS. In this review, we summarize the current data to elucidate the emerging roles of extracellular vesicle-derived circular RNAs (EV-circRNAs) in AS and the mechanism by which EV-circRNAs affect the development of AS. Additionally, we discuss their vital role in the progression from risk factors to AS and highlight their great potential for use as diagnostic biomarkers of and novel therapeutic strategies for AS.

Roles and clinical application of exosomal circRNAs in the diagnosis and treatment of malignant tumors

Exosomes are microvesicles secreted by cells. They contain a variety of bioactive substances with important roles in intercellular communication. Circular RNA (circRNA), a type of nucleic acid molecule found in exosomes, forms a covalently bonded closed loop without 5′ caps or 3′ poly(A) tails. It is structurally stable, widely distributed, and tissue specific. CircRNAs mainly act as microRNA sponges and have important regulatory roles in gene expression; they are superior to other non-coding RNAs as molecular diagnostic markers and drug treatment targets. Exosomal-derived circRNAs in the body fluids of tumor patients can modulate tumor proliferation, invasion, metastasis, and drug resistance. They can be used as effective biomarkers for early non-invasive diagnosis and prognostic evaluation of tumors, and also represent ideal targets for early precision therapeutic intervention. This review provides a theoretical basis for exploring the applications of exosomal circRNAs in malignant tumor diagnosis and treatment. We describe the biological functions of exosomal circRNAs in the occurrence and development of malignant tumors, their potential utility in diagnosis and treatment, and possible mechanisms.

Hsa_circ_0058129 regulates papillary thyroid cancer development via miR‐873‐5p/follistatin‐like 1 axis

Background

Papillary thyroid cancer (PTC) is an endocrine malignancy with a high incidence. Circular RNAs (circRNAs) participate in regulating PTC. Here, we analyzed the role of hsa_circ_0058129 (circ_0058129) in PTC.

Methods

The expression of circ_0058129, fibronectin 1 (FN1) mRNA, microRNA‐873‐5p (miR‐873‐5p), and follistatin‐like 1 (FSTL1) was detected by qRT‐PCR and western blot. Cell proliferation was analyzed by CCK‐8, EdU, and flow cytometry analysis assays. Cell migration and invasion were evaluated by Transwell assay. The targeting relationship of miR‐873‐5p and circ_0058129 or FSTL1 was identified through dual‐luciferase reporter assay, RIP assay, and RNA pull‐down assay. Xenograft mouse model assay was implemented to determine the effect of circ_0058129 on tumor formation in vivo.

Results

The circ_0058129 and FSTL1 abundances were increased, while the miR‐873‐5p content was decreased in PTC tissues and cells compared with control groups. Circ_0058129 shortage inhibited PTC cell proliferation, migration, and invasion. Moreover, miR‐873‐5p repressed PTC cell malignancy by binding to FSTL1. Circ_0058129 targeted miR‐873‐5p to regulate FSTL1.

Conclusion

Circ_0058129 expedited PTC progression through the miR‐873‐5p/FSTL1 pathway.

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

Molecular functions and therapeutic applications of exosomal noncoding RNAs in cancer

Cancer is one of the most difficult diseases in human society. Therefore, it is urgent for us to understand its pathogenesis and improve the cure rate. Exosomes are nanoscale membrane vesicles formed by a variety of cells through endocytosis. As a new means of intercellular information exchange, exosomes have attracted much attention. Noncoding RNAs exist in various cell compartments and participate in a variety of cellular reactions; in particular, they can be detected in exosomes bound to lipoproteins and free circulating molecules. Increasing evidence has suggested the potential roles of exosomal noncoding RNAs in the progression of tumors. Herein, we present a comprehensive update on the biological functions of exosomal noncoding RNAs in the development of cancer. Specifically, we mainly focus on the effects of exosomal noncoding RNAs, including microRNAs, circular RNAs, long noncoding RNAs, small nuclear RNAs, and small nucleolar RNAs, on tumor growth, metastasis, angiogenesis, and chemoresistance. Moreover, we outline the current clinical implications concerning exosomal noncoding RNAs in cancer treatment.

Circular RNAs and thyroid cancer: closed molecules, open possibilities

Thyroid neoplasms requiring differential diagnosis between thyroid cancer and benign tumors can be detected in more than half of the healthy population. A generally accepted method that allows assessing the risk of malignant potential and determining the indications for surgical treatment of thyroid tumor is a fine-needle aspiration biopsy followed by a cytological examination. Nevertheless, in patients with indeterminate categories of cytological conclusions according to Bethesda system, the positive predictive value of the cytology result is significantly lower than desired and often leads to unjustified surgical treatment. In this regard, the search for alternative diagnostic solutions continues. Circular RNAs are a group of non-coding RNAs distinguished by a closed structure formed by covalent bonding of the nucleotide chain ends. Recent studies allow us to conclude that many different circular RNAs are involved in processes mediating oncogenesis in the thyroid gland, and their altered expression in tissue, blood, and exosomes of plasma may be a characteristic sign of thyroid cancer and certain clinicopathological features of its course. The purpose of this review is to analyze the accumulated data on the association of various circular RNAs with thyroid cancer and to discuss possible ways to improve the diagnosis and treatment of the disease based on the assessment of the expression of these molecules.

Extracellular Vesicles as Signal Carriers in Malignant Thyroid Tumors?

Extracellular vesicles (EVs) are small, membranous structures involved in intercellular communication. Here, we analyzed the effects of thyroid cancer-derived EVs on the properties of normal thyroid cells and cells contributing to the tumor microenvironment. EVs isolated from thyroid cancer cell lines (CGTH, FTC-133, 8505c, TPC-1 and BcPAP) were used for treatment of normal thyroid cells (NTHY), as well as monocytes and endothelial cells (HUVEC). EVs' size/number were analyzed by flow cytometry and confocal microscopy. Gene expression, protein level and localization were investigated by qRT-PCR, WB and ICC/IF, respectively. Proliferation, migration and tube formation were analyzed. When compared with NTHY, CGTH and BcPAP secreted significantly more EVs. Treatment of NTHY with cancer-derived EVs changed the expression of tetraspanin genes, but did not affect proliferation and migration. Cancer-derived EVs suppressed tube formation by endothelial cells and did not affect the phagocytic index of monocytes. The number of 6 μm size fraction of cancer-derived EVs correlated negatively with the CD63 and CD81 expression in NTHY cells, as well as positively with angiogenesis in vitro. Thyroid cancer-derived EVs can affect the expression of tetraspanins in normal thyroid cells. It is possible that 6 μm EVs contribute to the regulation of NTHY gene expression and angiogenesis.

Identification of potential circular RNA biomarkers in lung adenocarcinoma: A bioinformatics analysis and retrospective clinical study

Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer-associated mortality. Lung adenocarcinoma (LAC) is the most prevalent pathological subtype of NSCLC and accounts for ~40% of all lung cancer mortalities. There remains an urgent demand for the identification of novel biomarkers for the diagnosis and development of therapeutic strategies for LAC. In the present study, the profiles of the differentially-expressed circular RNAs (circRNAs) in LAC tissues compared with those in their corresponding non-cancerous tissues were obtained after analyzing the circRNA microarray dataset GSE101586. The expression pattern of the indicated circRNAs in the LAC tissues were subsequently verified using reverse transcription-quantitative PCR (RT-qPCR). The potential prognostic significance of these circRNAs in patients with LAC were then analyzed in a retrospective clinical study. A circRNA-microRNA (miR or miRNA)-mRNA regulatory network in LAC was established by using Cytoscape. In addition, a protein-protein interaction (PPI) network was plotted using the Search Tool for the Retrieval of Interacting Genes/Proteins and visualized through Cytoscape. The prognostic value of the hub genes found was then analyzed based on the Gene Expression Profiling Interactive Analysis database. In total, four differentially-expressed circRNAs were obtained from the GSE101586 microarray dataset, three of which (hsa_circ_0006220, hsa_circ_0072088 and hsa_circ_0001666) were confirmed by RT-qPCR to be highly expressed in LAC tissues. This retrospective clinical study revealed that higher expression levels of these three circRNAs were associated with poorer prognoses in patients with LAC. In addition, siRNA-mediated knockdown of these circRNAs was found to inhibit cell proliferation, migration and invasion in LAC cells. Following analysis of the molecular mechanism underlying these circRNAs, eight miRNAs, namely miR-520f, miR-1261, miR-1270, miR-620, miR-188-3p, miR-516b, miR-940 and miR-661, were identified with potential binding sites for these three circRNAs. Subsequently, 232 overlapped genes from the 795 upregulated genes in the LAC samples from The Cancer Genome Atlas database and 7,829 predicted target genes of the list of eight aforementioned miRNAs were obtained. A circRNA-miRNA-mRNA network was then constructed. A PPI network was established, with six hub genes, namely kinesin family member (KIF) 2C, KIF18B, maternal embryonic leucine zipper kinase, baculoviral IAP repeat-containing 5, polo-like kinase 1 and cytoskeleton-associated protein 2-like, determined from this network. Higher expression levels of each of these hub genes were found to be associated with poorer prognoses of patients with LAC. To conclude, data from the present study suggested that circRNAs hsa_circ_0006220, hsa_circ_0072088 and hsa_circ_0001666 have the potential to be viable biomarkers and therapeutic targets for LAC.

Recent advances in crosstalk between N6-methyladenosine (m6A) modification and circular RNAs in cancer

N6-methyladenosine (m6A), as the most common RNA modification, plays a vital role in the development of cancers. Circular RNAs (circRNAs) are a class of single-stranded covalently closed RNA molecules. Recently, m6A modification has been identified as performing biological functions for regulating circRNAs. Increasing evidence also shows that circRNAs are involved in cancer progression by targeting m6A regulators. In this review, we describe the functional crosstalk between m6A and circRNAs, and illustrate their roles in cancer development. m6A methylation mediates the biogenesis, stability, and cytoplasmic export of circRNAs in different cancer types. Moreover, circRNAs regulate the expression of m6A regulators, participate in the degradation of m6A regulators, and regulate the m6A modification of target mRNAs. Finally, we discuss the potential applications and future research directions of m6A modification and circRNAs in cancer. Further understanding of the biological roles of m6A and circRNAs will provide new insight into the diagnosis and treatment of cancer patients.

Exosomal RNAs: Novel Potential Biomarkers for Diseases-A Review

Exosomes are a subset of nano-sized extracellular vesicles originating from endosomes. Exosomes mediate cell-to-cell communication with their cargos, which includes mRNAs, miRNAs, lncRNAs, and circRNAs. Exosomal RNAs have cell specificity and reflect the conditions of their donor cells. Notably, their detection in biofluids can be used as a diagnostic marker for various diseases. Exosomal RNAs are ideal biomarkers because their surrounding membranes confer stability and they are detectable in almost all biofluids, which helps to reduce trauma and avoid invasive examinations. However, knowledge of exosomal biomarkers remains scarce. The present review summarizes the biogenesis, secretion, and uptake of exosomes, the current researches exploring exosomal mRNAs, miRNAs, lncRNAs, and circRNAs as potential biomarkers for the diagnosis of human diseases, as well as recent techniques of exosome isolation.

circRNA is a potential target for cardiovascular diseases treatment

Circular RNAs (circRNAs), a novel class of endogenous noncoding RNA, are characterized by their covalently closed-loop structures without a 5' cap or a 3' poly(A) tail. With the evolution of high-throughput sequencing technology and bioinformatics, an increasing number of circRNAs have been discovered, and their functions were highlighted. Cardiovascular diseases (CVDs) have become the world's leading killers, with serious impacts on human health. Although significant progress has been made in clarifying the development of CVDs from the molecular to the cellular level, CVDs remain one of the leading causes of death in humans. circRNAs mainly function as a "sponge" to absorb microRNAs, which results in the positive control of downstream proteins. They play important regulatory roles in the development of CVDs. This paper reviews current knowledge on the biogenesis, detection and validation, translation, translocation and degradation, and general functions of circRNAs, with a focus on their roles in CVDs.

Circular RNA hsa_circ_0006091 as a novel biomarker for hepatocellular carcinoma

Circular RNAs (circRNAs) are stable and extensively distributed non-coding RNA molecules that are differentially expressed in liver cancer tissues in the human body. In this study, we aimed to investigate circRNA as a novel candidate biomarker for hepatocellular carcinoma (HCC). For three groups of HCC and neighboring healthy tissues, the differentially expressed circRNAs were identified through high-throughput sequencing analysis. Reverse transcription PCR (RT-PCR) and quantitative polymerase chain reaction (qPCR) were employed for the evaluation of circRNAs that show an elevated expression level in HCC. The obtained results revealed the significantly differential expression of hsa_circ_0006091 in HCC. Then we obtained their target genes through biological analysis, followed by verifying the underlined target genes, and the regulator of G-protein signaling 12 (RGS12) showed an elevated expression level in HCC tissues. Finally, receiver operating characteristic (ROC) curve analysis was conducted on AFP, RGS12, and hsa_circ_0006091, and combined analysis was performed. Furthermore, hsa_circ_0006091 is a novel candidate biomarker for HCC and could improve the diagnostic strategies, prediction, and follow-up of HCC patients. The joint diagnosis of the hsa_circ_0006091&AFP and hsa_circ_0006091&RGS12 has diagnostic significance and can be used as a molecular marker for HCC diagnosis.

Abbreviations: AUC:area under the ROC curve; ROC:Receptor Operating Characteristics; bp:base pair;mRNA:Messenger Ribonucleic acid;ceRNA:Competing endogenous RNA; RT-qPCR: Real time-quantitativen PCR technology; circRNA: circular RNA; HCC:Hepatocellular carcinoma;miRNA:microRNA;KEGG:Kyoto Encyclopedia of Genes and Genomes; RGS12:regulator of G-protein signaling 12; AFP:alpha fetoprotein; ncRNAs:non-coding RNAs; GEO:Gene Expression Omnibus; FDR:false discovery rate

Exosomal circRELL1 serves as a miR-637 sponge to modulate gastric cancer progression via regulating autophagy activation

Circular RNAs (circRNAs) play a vital role in the occurrence and development of tumors, including gastric cancer (GC). However, there are still many circRNAs related to GC whose functions and molecular mechanisms remain undetermined. Herein, we discover circRNA RELL1, which has not been investigated in GC, and it is markedly downregulated in GC tissues, which is related with poor prognosis, more pronounced lymph node metastasis and poor TNM stage. After confirming the circular structure of circRELL1, we found that circRELL1 could block cell proliferation, invasion, migration, and anti-apoptosis in patients with GC by a series of in vivo and in vitro function-related studies. Further mechanism investigation demonstrated that circRELL1 could sponge miR-637 and indirectly unregulated the expression of EPHB3 via modulating autophagy activation in GC. Additionally, circRELL1 can be transmitted by exosomal communication, and exosomal circRELL1 suppressed the malignant behavior of GC in vivo and in vitro. Taken together, this study elucidates the suppressive roles of circRELL1/miR-637/EPHB3 axis through autophagy activation in GC progression, inspiring for further understanding of the underlying molecular mechanisms of GC and providing a promising novel diagnostic circulating biomarker and therapeutic target in GC.

AhR Antagonist Promotes Differentiation of Papillary Thyroid Cancer via Regulating circSH2B3/miR-4640-5P/IGF2BP2 Axis

Abnormally high expression of aryl hydrocarbon receptor (AhR) has been implicated in dedifferentiation of radioiodine-refractory papillary thyroid cancer (RR-PTC). This study aimed to evaluate the differentiation effect of AhR antagonist in PTC, and to explore the potential mechanism of it. Results showed that AhR antagonists promoted differentiation of PTC, as shown as increase in ¹²⁵I uptake and Na/I symporter (NIS) expression level. CircRNA microarray in K1 cells treated with StemRegenin 1(SR1) revealed that hsa_circ_0006741 (circSH2B3) was down-regulated in SR1 treated K1 cells. Downregulation of circSH2B3 increased ¹²⁵I uptake and NIS expression levels. CircSH2B3 acted as an endogenous sponge of hsa-miR-4640-5p and modulated IGF2BP2 expression. IGF2BP2 overexpression induced dedifferentiation of PTC, while silencing IGF2BP2 accelerated differentiation of PTC cells. Rescue studies showed that the dedifferentiation activity of AhR was modulated by the circSH2B3/miR-4640-5p/IGF2BP2 axis. Our findings confirmed for the first time that AhR antagonists promote differentiation of PTC via inhibiting the circSH2B3/miR-4640-5p/IGF2BP2 axis, offering a novel therapeutic approach and a potential marker for differentiation of PTC.

The potential role of exosomal circRNAs in the tumor microenvironment: insights into cancer diagnosis and therapy

Exosomes are multifunctional regulators of intercellular communication by carrying various messages under both physiological and pathological status of cancer patients. Accumulating studies have identified the presence of circular RNAs (circRNAs) in exosomes with crucial regulatory roles in diverse pathophysiological processes. Exosomal circRNAs derived from donor cells can modulate crosstalk with recipient cells locally or remotely to enhance cancer development and propagation, and play crucial roles in the tumor microenvironment (TME), leading to significant enhancement of tumor immunity, metabolism, angiogenesis, drug resistance, epithelial mesenchymal transition (EMT), invasion and metastasis. In this review, we describe the advances of exosomal circRNAs and their roles in modulating cancer hallmarks, especially those in the TME. Moreover, clinical application potential of exosomal circRNAs in cancer diagnosis and therapy are highlighted, bridging the gap between basic knowledge and clinical practice.

CircRNA circ_0006156 inhibits the metastasis of prostate cancer by blocking the ubiquitination of S100A9

Circular RNAs (circRNAs) have been demonstrated to play vital roles in cancer development and progression. However, studies on the association between circRNAs and prostate cancer (PCa) are still lacking. CircRNA sequencing of two pairs of PCa tissues and adjacent normal tissues was conducted in the present study, and qRT-PCR was performed to verify the results. Functional experiments were performed to investigate cellular functions after specific changes. Mass spectrometry analysis after RNA pull-down experiments and Co-IP assays were further conducted. Downstream target proteins were predicted via online databases and detected in vitro by Western blot analysis and in vivo by immunohistochemistry. Hsa_circ_0006156 (subsequently named circ_0006156) expresses at low levels in both PCa tissues and cells, and it significantly inhibits the migration and invasion of PCa cells. Circ_0006156 binds to and blocks the ubiquitination of S100A9. Moreover, functional assays revealed that circ_0006156 represses the malignant progression of PCa by binding to S100A9. Finally, in vivo experiments showed that circ_0006156 suppresses PCa migration and invasion by increasing S100A9, revealing circ_0006156 as a potential novel effective target for PCa treatment.

Exosomal circular RNA hsa_circ_007293 promotes proliferation, migration, invasion, and epithelial-mesenchymal transition of papillary thyroid carcinoma cells through regulation of the microRNA-653-5p/paired box 6 axis

Circular RNAs (circRNAs) or exosomes have been reported to exert key regulatory and/or communication functions in human cancer. Nevertheless, current literature on the effects of exosomal circRNAs on tumor invasion and metastasis in thyroid cancer is incomplete. The role of tumor-derived exosomes in driving in vitro papillary thyroid carcinoma (PTC) progression and metastasis requires further investigation. In our study, Exosomes were harvested from PTC patient serum and PTC cell culture medium. Gene expression analysis in PTC cell lines and exosomes was performed with quantitative reverse-transcription polymerase chain reaction. Transwell, wound healing, Western blot assays, and the cell counting kit-8 were applied for functional analysis. Dual-luciferase reporter assay was used to examine the interaction between hsa_circ_007293 (circ007293), microRNA (miR)-653-5p, and paired box 6 (PAX6). Results showed that circ007293 was enriched in exosomes derived from PTC patient serum and cell culture media. Moreover, circ007293 could enter PTC cells through exosomes, and exosomal circ007293 promoted PTC cell epithelial-mesenchymal transition, invasion, migration, and proliferation. circ007293 knockdown reversed the malignant phenotype of PTC cells in vitro. Additionally, circ007293 could competitively bind with miR-653-5p to regulate PAX6 expression. Notably, miR-653-5p overexpression or PAX6 inhibition suppressed the malignant effects of exosomal circ007293. These results evidenced that exosomal circ007293 induced EMT and augmented the invasive and migratory abilities of PTC cells via the miR-653-5p/PAX6 axis, suggesting that it may serve as a promising biomarker for cancer progression.

Identification of Circ-FNDC3B, an Overexpressed circRNA in Abdominal Aortic Aneurysm, as a Regulator of Vascular Smooth Muscle Cells

Circular RNAs (circRNAs) have been implicated in the dysfunction of vascular smooth muscle cells (VSMCs), which is linked with the development of abdominal aortic aneurysm (AAA). Herein, we explored the precise action of circRNA fibronectin type III domain containing 3B (circ-FNDC3B) in VSMC injury triggered by angiotensin II (Ang-II).Circ-FNDC3B, microRNA (miR) -143-3p, and a disintegrin and metalloproteinase 10 (ADAM10) were quantified by quantitative real-time polymerase chain reaction or western blot assay. Ribonuclease R and subcellular localization assays were applied to characterize circ-FNDC3B. Cell viability, apoptosis, and proliferation were assessed by the Cell Counting Kit-8 assay, flow cytometry, and 5-Ethynyl-2' -Deoxyuridine assay, respectively. The levels of tumor necrosis factor alpha, interleukin-6, superoxide dismutase, and malonaldehyde were estimated by enzyme-linked immunosorbent assay. Direct relationship miR-143-3p and circ-FNDC3B or ADAM10 was verified by dual-luciferase reporter and RNA immunoprecipitation assays.Circ-FNDC3B was highly expressed in AAA tissues and Ang-II-treated VSMCs. Knocking down circ-FNDC3B alleviated Ang-II-induced VSMC injury. Mechanistically, circ-FNDC3B directly targeted miR-143-3p, and miR-143-3p was a downstream mediator of circ-FNDC3B in regulating cell injury induced by Ang-II. ADAM10 was directly targeted and inhibited by miR-143-3p. MiR-143-3p-mediated inhibition of ADAM10 relieved Ang-II-induced VSMC injury. Furthermore, circ-FNDC3B acted as a competing endogenous RNA for miR-143-3p to modulate ADAM10 expression.Our findings suggested that circ-FNDC3B silencing ameliorated cytotoxicity triggered by Ang-II in VSMCs at least partially depending on the regulation of the miR-143-3p/ADAM10 axis.

Hsa_circ_0013290 Acts as Cancer-Promoting Gene in Hepatocellular Carcinoma

Background

As a new class of non-coding RNAs, circRNAs have been recently reported to be involved in the tumorigenesis and progression of human cancers. In the current study, we attempted to explore the potential function of a novel circRNA (hsa_circ_0013290) in hepatocellular carcinoma (HCC).

Methods

Relative hsa_circ_0013290 expression was analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The subcellular location of hsa_circ_0013290 was performed by RNA subcellular isolation and fluorescence in situ hybridization (FISH) assays. The effect of hsa_circ_0013290 on proliferation was detected by Cell Counting Kit-8 (CCK-8) assays. The effect of hsa_circ_0013290 on cell cycle distribution and apoptosis was detected by flow cytometry. The invasion and migration abilities of hsa_circ_0013290 were detected by transwell assays.

Results

Hsa_circ_0013290 is significantly upregulated in HCC cell lines and mainly located in cytoplasm of HCC cells. Hsa_circ_0013290 overexpression promotes cell invasion and migration and inhibits cell apoptosis. In contrast, hsa_circ_0013290 knockdown impedes cell invasion and migration and accelerates cell apoptosis. However, hsa_circ_0013290 did not affect cell proliferation.

Conclusions

Hsa_circ_0013290 is overexpressed in HCC cell lines and is mainly located in the cytoplasm of HCC cells. Hsa_circ_0013290 promotes cell invasion and migration, and inhibits cell apoptosis.

Tumor Suppressive Circular RNA-102450: Development of a Novel Diagnostic Procedure for Lymph Node Metastasis from Oral Cancer

Circular RNAs (circRNAs), which form as covalently closed loop structures, have several biological functions such as regulation of cellular behavior by adsorbing microRNAs. However, there is limited information of circRNAs in oral squamous cell carcinoma (OSCC). Here, we aimed to elucidate the roles of aberrantly expressed circRNAs in OSCC. CircRNA microarray showed that circRNA-102450 was down-regulated in OSCC cells. Clinical validation of circRNA-102450 was performed using highly sensitive droplet digital PCR in preoperative liquid biopsy samples from 30 OSCC patients. Interestingly, none of 16 studied patients with high circRNA-102450 had regional lymph node metastasis (RLNM), whereas 4 of 14 studied patients (28.5%) with low expression had pathologically proven RLNM. Overexpressed circRNA-102450 significantly inhibited the tumor metastatic properties of cell proliferation, migration, and invasion. Furthermore, circRNA-102450 directly bound to, and consequently down-regulated, miR-1178 in OSCC cells. Taken together, circRNA-102450 has a tumor suppressive effect via the circRNA-102450/miR-1178 axis and may be a novel potential marker of RLNM in OSCC patients.

Five genes involved in circular RNA-associated competitive endogenous RNA network correlates with metastasis in papillary thyroid carcinoma

This study aimed to identify potential circular RNA (circRNA), microRNA (miRNA) and mRNA biomarkers as well as their underlying regulatory mechanisms in papillary thyroid carcinoma (PTC). Three microarray datasets from the Gene Expression Omnibus database as well as expression data and clinical phenotype from The Cancer Genome Atlas (TCGA) were downloaded, followed by differential expression, functional enrichment, protein-protein interaction (PPI), and module analyses. The support vector machine (SVM)-recursive feature elimination (RFE) algorithm was used to screen the key circRNAs. Finally, the mRNA-miRNA-circRNA regulatory network and competitive endogenous RNA (ceRNA) network were constructed. The prognostic value and clinical correlations of key mRNAs were investigated using TCGA dataset, and their expression was validated using the UALCAN database. A total of 1039 mRNAs, 18 miRNAs and 137 circRNAs were differentially expressed in patients with PTC. A total of 37 key circRNAs were obtained using the SVM-RFE algorithm, whereas 46 key mRNAs were obtained from significant modules in the PPI network. A total of 11 circRNA-miRNA pairs and 40 miRNA-mRNA pairs were predicted. Based on these interaction pairs, 46 circRNA-miRNA-mRNA regulatory pairs were integrated, of which 8 regulatory pairs in line with the ceRNA hypothesis were obtained, including two circRNAs (circ_0004053 and circ_0028198), three miRNAs (miR-199a-5p, miR-199b-5p, and miR-7-5p), and five mRNAs, namely APOA2, CCL20, LPAR5, MFGE8, and TIMP1. Survival analysis showed that LPAR5 expression was associated with patient survival. APOA2 expression showed significant differences between metastatic and non-metastatic tumors, whereas CCL20, LPAR5, MFGE8 and TIMP1 showed significant differences between metastatic and non-metastatic lymph nodes. Overall, we identified several potential targets and regulatory mechanisms involved in PTC. APOA2, CCL20, LPAR5, MFGE8, and TIMP1 may be correlated with PTC metastasis.

Regulation of cancer progression by circRNA and functional proteins

Circular RNAs (circRNAs) are closed back-splicing products of precursor mRNA in eukaryotes. Compared with linear mRNAs, circRNAs have a special structure and stable expression. A large number of studies have provided different regulatory mechanisms of circRNAs in tumors. Challenges exist in understanding the control of circRNAs because of their sequence overlap with linear mRNA. Here, we survey the most recent progress regarding the regulation of circRNA biogenesis by RNA-binding proteins, one of the vital functional proteins. Furthermore, substantial circRNAs exert compelling biological roles by acting as protein sponges, by being translated themselves or regulating posttranslational modifications of proteins. This review will help further explore more types of functional proteins that interact with circRNA in cancer and reveal other unknown mechanisms of circRNA regulation.

CircRNA Microarray Profiling Reveals hsa_circ_0058493 as a Novel Biomarker for Imatinib-Resistant CML

Background: CircRNA has appeared as a critical molecular in the development of various cancers. However, the cellular function of circRNAs and exosomal circRNAs has not been well explored in Chronic myeloid leukemia (CML). Methods: Differentially expressed circRNAs were identified by a human circRNA microarray analysis. The expression of hsa_circ_0058493 in peripheral blood mononuclear cells (PBMCs) and exosomes was verified using quantitative real-time PCR. Short hairpin RNAs against hsa_circ_0058493 were constructed to silence the expression of circ_0058493. CCK8, flow cytometry and EdU assay were performed to investigate the biological functions of circ_0058493. Results: Hsa_circ_0058493 was significantly overexpressed in the PBMCs of CML patients and high level of circ_0058493 was associated with the poor clinical efficacy of imatinib. Silencing the expression of circ_0058493 significantly inhibited the development of imatinib-resistant CML cells. miR-548b-3p was overexpressed in circ_0058493-downregulated CML cells. Bioinformatic analysis revealed that circ_0058493 might exert its regulatory function acting as a "sponge" of miR-548b-3p. Moreover, hsa_circ_0058493 was significantly enriched in the exosomes derived from imatinib-resistant CML cells. Conclusion: Hsa_circ_0058493 in PBMCs could be a promising prognostic biomarker and might provide a therapeutic target for CML treatment.

CircRNA: A novel potential strategy to treat thyroid cancer (Review)

Thyroid cancer (TC) is the most common type of endocrine cancer. Over the last 50 years, the global incidence of TC has been increasing. The survival rate of TC is higher than that of most other types of cancer, but it depends on numerous factors, including the specific type of TC and stage of the disease. Circular RNAs (circRNAs) are a new class of long noncoding RNA with a closed loop structure that have a critical role in the complex gene regulatory network that controls the emergence of TC. The most important function of circRNAs is their ability to specifically bind to microRNAs. In addition, the biological functions of circRNAs also include interactions with proteins, regulation of the transcription of genes and acting as translation templates. Based on the characteristics of circRNAs, they have been identified as potential biomarkers for the diagnosis of tumors. In the present review, the function and significance of circRNAs and their potential clinical implications for TC were summarized. Furthermore, possible treatment approaches involving the use of mesenchymal stem cells (MSCs) and exosomes derived from MSCs as carriers to load and transport circRNAs were discussed.

Upregulated circRAD18 promotes tumor progression by reprogramming glucose metabolism in papillary thyroid cancer

Background

By regulating complex functional processes, circRNAs are crucial in the development of different cancers. Nevertheless, most circRNAs in papillary thyroid cancer metabolic reprogramming remain unknown.

Methods

The expression of circRNA was assessed by qRT-PCR in papillary thyroid cancer tissues and cell lines. Cell proliferation and glucose intake experiments were performed by certain kit. Transwell assays and wound healing assays were performed to investigate the function of circRNA in metastasis. In addition, a serious of molecular experiments were conducted to determine the exact mechanism of circRAD18. Luciferase reporter and RNA immunoprecipitation assay were conducted to determine the molecular interaction between circRNA and miRNA.

Results

We characterized circRAD18 as a significantly upregulated circRNA in papillary thyroid tissues and cell lines and found its downregulation could inhibit the growth and metastasis ability of papillary thyroid cancer. Interestingly, we found that circRAD18 was involved in glucose metabolism reprogramming of papillary thyroid cancer, and its silence could remarkably inhibit cell glucose uptake and lactate production in papillary thyroid cancer cells. Inhibition of circRAD18 could decrease the expression level of PDK1 protein by sponging miR-516b.

Conclusions

This study verified the novel function of the circRAD18-miR-516b-PDK1 axis in papillary thyroid cancer metabolic reprogramming progression, which has potential to be a novel therapeutic target.

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.

Serum Exosomal Circular RNA Expression Profile and Regulative Role in Proliferative Diabetic Retinopathy

Background

Proliferative diabetic retinopathy (PDR), as one of the main microvascular complications of diabetes mellitus, seriously threatens the visual function of the working-age population; yet, the underlying pathogenesis is still poorly understood. This study aimed to identify the distinct exosomal circular RNA (circRNA) expression in PDR serum and preliminarily explore the potential pro-angiogenic mechanism of specific exosomal circRNAs.

Methods

We collected serum samples from 10 patients with PDR and 10 patients with age-matched senile cataract to detect the exosomal differentially expressed genes (DEGs) of circRNAs via high-throughput sequencing, followed by validation with quantitative real-time PCR (qRT-PCR). Next, bioinformatics analyses including competitive endogenous RNA (ceRNA) network, protein-protein interaction network (PPI), and functional enrichment analyses were performed. In addition, the potential function of circFndc3b (hsa_circ_0006156) derived from high-glucose-induced endothelial cells was analyzed in human retinal vascular endothelial cells (HRVECs).

Results

In total, 26 circRNAs, 106 microRNAs (miRNAs), and 2,264 messenger RNAs (mRNAs) were identified as differentially expressed in PDR serum exosomes compared with cataract serum exosomes (fold change > 1, P < 0.05). A circRNA-miRNA-mRNA ceRNA network was established. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the mRNAs were mainly enriched in the PI3K-Akt signaling pathway, MAPK signaling pathway, Wnt signaling pathway, and VEGF signaling pathway. The PPI network and module analysis identified 10 hub genes, including RhoA, Cdc42, and RASA1. Finally, circFndc3b and exosomes derived from high-glucose-induced endothelial cells were identified with the capability to facilitate angiogenesis in vitro.

Conclusion

Aberrant profiling of exosomal circRNAs in PDR serum was identified. CircFndc3b derived from high-glucose-induced endothelial cells may play an important role in the angiogenesis of PDR.

The Diagnostic Value of Serum Exosomal Has_circ_0000615 for Breast Cancer Patients

Background

To explore the expression level of has_circ_0000615 in peripheral blood samples and evaluate its diagnostic value for breast cancer patients.

Methods

The peripheral blood samples of 95 breast cancer patients who underwent curative surgical resection and 95 age-matched healthy volunteers in our institutions from September 2019 to November 2020 were systematically collected. The expression level of has_circ_0000615 in the plasma was amplified and detected by qRT-PCR, and its correlation to clinicopathological characteristics of breast cancer patients were analyzed.

Results

Breast cancer patients had a significantly higher expression level of has_circ_0000615 in the plasma than healthy controls (P < 0.01), and its high expression was closely associated with advanced tumor stage (P=0.010), lymph node metastasis (P = 0.001) and high grade of recurrence risk (P=0.012). The receiver operator characteristic (ROC) curves showed that the area under curve (AUC) value, sensitivity and specificity of has_circ_0000615 for the diagnosis of non-metastatic breast cancer was 0.904 (95% CI: 0.863–0.944), 76.8% and 88.4%, respectively. Serum has_circ_0000615 expression had a better diagnostic efficiency than routine tumor biomarkers such as CA153, CA125 and CEA for distinguishing breast cancer patients from healthy individuals. TEM revealed that isolated exosomes from the culture medium of breast cancer cells had a disk-like appearance with a diameter of 80–200 nm vesicles, and the expression of exosome markers CD9 and CD81 was markedly increased. More importantly, the expression of has_circ_0000615 was detected in the exosomes and its expression level was markedly upregulated in breast cancer cell lines compared with normal ductal epithelial cells. The stability assay showed that there was no difference between RNA extraction at 0 hour and 24 hours in terms of the expression of has_circ_0000615 (P =0.327). Has_circ_0000615 might as exosomes be secreted into the circulating blood of breast cancer patients, resulting in a high expression level in plasma samples.

Conclusion

The detection of has_circ_0000615 might be a promising diagnostic method for breast cancer.

Circular RNA Protein Tyrosine Kinase 2 Promotes Cell Proliferation, Migration and Suppresses Apoptosis via Activating MicroRNA-638 Mediated MEK/ERK, WNT/β-Catenin Signaling Pathways in Multiple Myeloma

Our previous study observed that circular RNA protein tyrosine kinase 2 (circ-PTK2) was upregulated and correlated with worse clinical features and unfavorable prognosis in multiple myeloma (MM) patients. Thus, this study aimed to further characterize the regulatory function of circ-PTK2 on cell malignant activities and its target microRNA-638 (miR-638) as well as downstream MEK/ERK, WNT/β-catenin signaling pathways in MM. The effect of circ-PTK2 on MM cell proliferation, apoptosis, migration, invasion and its potential target miRNAs was assessed by transfecting circ-PTK2 overexpression plasmids into U226 cells and circ-PTK2 knock-down plasmids into LP-1 cells. Furthermore, the interaction between circ-PTK2 and miR-638 mediated MEK/ERK and WNT/β-catenin signaling pathways was validated by rescue experiments. Circ-PTK2 was overexpressed in most MM cell lines compared to normal plasma cells. Overexpressing circ-PTK2 promoted proliferation and migration, inhibited apoptosis in U266 cells, but did not affect cell invasion; knocking down circ-PTK2 achieved opposite effect in LP-1 cells. Besides, circ-PTK2 reversely regulated miR-638 expression but not miR-4690, miR-6724, miR-6749 or miR-6775. The following luciferase reporter assay illustrated the direct bind of circ-PTK2 towards miR-638. In rescue experiments, overexpressing miR-638 suppressed proliferation, migration, while promoted apoptosis in both wild U266 cells and circ-PTK2-overexpressed U266 cells; meanwhile, overexpressing miR-638 also suppressed MEK/ERK and WNT/β-catenin pathways in both wild U266 cells and circ-PTK2-overexpressed U266 cells. Knocking down miR-638 achieved opposite effect in both wild LP-1 cells and circ-PTK2-knocked-down LP-1 cells. In conclusion, circ-PTK2 promotes cell proliferation, migration, suppresses cell apoptosis via miR-638 mediated MEK&ERK and WNT&β-catenin signaling pathways in MM.

Inhibition of circular RNA_0000285 prevents cell proliferation and induces apoptosis in thyroid cancer by sponging microRNA-654-3p

Thyroid cancer is derived from follicular or thyroid cells and has become the most prevalent malignant tumor of endocrine organs, with increased morbidity and mortality. Circular RNAs (circRNAs) are used as prognostic and predictive markers for different types of cancer. However, the role of circRNA_0000285 in thyroid cancer and its potential molecular mechanism remain unclear. The present study aimed to investigate the roles and underlying molecular mechanism of circRNA_0000285 in thyroid cancer to identify novel treatments for this disease. The target binding site of circRNA_0000285 and microRNA-654-3p (miR-654-3p) were predicted and confirmed via the dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. Thyroid cancer cell viability and apoptosis were determined via the MTT assay and flow cytometric analysis, respectively, whereas the expression levels of circRNA_0000285 and miR-654-3p were determined via reverse transcription-quantitative PCR analysis. In addition, the protein expression levels of the apoptosis-associated proteins, Bax and B-cell lymphoma 2 (Bcl-2), were detected via western blotting. The results of the dual-luciferase reporter and RIP assays demonstrated that miR-654-3p directly targeted circRNA_0000285. The expression levels of circRNA_0000285 and miR-654-3p in thyroid cancer cells (TPC-1 and FTC133) were upregulated and downregulated, respectively. Knockdown of circRNA_0000285 via small interfering (si)RNA inhibited circRNA_0000285 levels and increased miR-654-3p levels. In addition, miR-654-3p expression decreased following transfection with miR-654-3p inhibitor. Functional experiments demonstrated that circRNA_0000285-siRNA decreased thyroid cancer cell proliferation, promoted cell apoptosis, enhanced Bax expression and suppressed Bcl-2 expression. All these effects were reversed following transfection with miR-654-3p inhibitor. Taken together, the results of the present study suggest that circRNA_0000285 plays a vital role in thyroid cancer progression by regulating miR-654-3p, which provides a potential therapeutic target for this disease.

Silencing circRNA protein kinase C iota (circ-PRKCI) suppresses cell progression and glycolysis of human papillary thyroid cancer through circ-PRKCI/miR-335/E2F3 ceRNA axis

The circular RNA PRKCI (circ-PRKCI; ID: hsa_circ_0122683) is highly expressed in human papillary thyroid cancer (PTC) tumors according to GSE93522 dataset. However, its role in PTC tumorigenesis remains to be documented. Here, quantitative real-time PCR showed that expression of circ-PRKCI was abnormally upregulated in human PTC patients' tumors and cells, and higher circ-PRKCI might predict lymph node metastasis and recurrence. Functionally, cell behaviors were measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay, colony formation assay, fluorescence-activated cell sorting method, scratch wound assay, transwell assay, western blotting, and assay kits for glucose and lactate. As a result, circ-PRKCI knockdown could suppress cell cycle progression of PTC cells and restrain the abilities of cell proliferation, colony formation, wound closure, invasion, glucose consumption and lactate production, accompanied with decreased levels of matrix metalloproteinase-2 (MMP2), MMP9 and Snail. Moreover, above-mentioned inhibition could be imitated by overexpressing microRNA-335-5p (miR-335). Molecularly, circ-PRKCI functioned as a sponge for miR-335 and miR-335 could further targeted E2F transcription factor-3 (E2F3), according to dual-luciferase reporter assay and RNA immunoprecipitation. However, downregulating miR-335 diminished the effects of circ-PRKCI role on cell growth, metastasis and glycolysis in PTC cells; besides, there was a counteractive effect between miR-335 upregulation and E2F3 upregulation in PTC cells as well. Furthermore, xenograft experiment revealed that silencing circ-PRKCI could retard tumor growth of PTC cells in vivo. Collectively, circ-PRKCI exerted oncogenic role in PTC by antagonizing cell progression and glycolysis via regulating miR-335/E2F3 axis, suggesting circ-PRKCI was a potential biomarker and target for PTC.

Circular RNA circKIF4A facilitates the malignant progression and suppresses ferroptosis by sponging miR-1231 and upregulating GPX4 in papillary thyroid cancer

Circular RNAs (circRNAs) are one type of non-coding RNA. They act as important role in regulating various biological processes in the malignant progression. But we don't clearly know the specific mechanism of the majority circRNAs in papillary thyroid tumor progression. In the current study, we explored circKIF4A and the result showed that it had high expression in papillary thyroid cancer. The functions of circKIF4A were explored by CCK-8, transwell, and mouse xenograft experiments. Knockdown of circKIF4A could suppress papillary thyroid cell growth and migration. In addition, RIP assays and dual luciferase vector reporter assays were further conducted. Our consequence showed circKIF4A facilitated the malignant progress of papillary thyroid tumor by sponging miR-1231 and upregulating GPX4 expression. In conclusion, our study proved that circKIF4A-miR-1231-GPX4 axis played a vital role in cancer proliferation and ferroptosis by competing endogenous RNAs. Therefore, targeting circKIF4A is very likely to be a potential method for treatment of papillary thyroid cancer in the future.

Interaction between non-coding RNAs and Toll-like receptors

Toll-like receptors (TLRs) are a large group of pattern recognition receptors which are involved in the regulation of innate immune responses. Based on the interplay between TLRs and adapter molecules, two distinctive signaling cascades, namely the MyD88-dependent and TRIF-dependent pathways have been recognized. TLRs are involved in the development of a wide variety of diseases including cancer and autoimmune disorders. A large body of evidence has shown interaction between two classes of non-coding RNAs, namely microRNAs (miRNAs) and long noncoding RNAs (lncRNAs). These interactions have prominent roles in the pathogenesis of several disorders including infectious disorders, autoimmune conditions and neoplastic disorders. This review aims at description of the interaction between these non-coding RNAs and TLRs.

Emerging roles of circular RNAs in thyroid cancer

As the most common endocrine-related malignant tumor, the prevalence of thyroid cancer (TC) has soared strikingly over the past thirty years then verged to stabilization or even descension temporally. Distributed in a cell-specific manner, circular RNAs (circRNAs) is a novel class of non-coding RNAs characterized by its covalently closed loop without 5'-terminal cap and 3'-terminal poly A tail, which guarantee its distinctive evolutionary conservation and exonucleases resistance. Emerging evidence indicates that circRNA participates in the pathogenesis and carcinogenesis of several cancers including thyroid cancer. In this review, we concentrated on the connection between circRNAs and thyroid cancer so as to obtain a more profound understanding. We aim to discuss this relationship between TC and circRNAs by summarizing the effect of various circRNAs on tumor biological behaviors and clinical application, and systematically outlook the conceivable application of circRNAs in TC diagnosis and therapy.

Advances of circular RNAs in thyroid cancer: An overview

Circular RNA (circRNA) is a general term for a type of single-stranded RNAs, they are primarily generated via exon back-splice process in precursor mRNAs (pre-mRNAs). circRNAs refer to an emerging type of endogeneity-correlated closed molecules of RNA in a covalent manner. They mainly function as microRNA sponges, protein brackets, and regulatory element in transcription and splicing process. Recently, it has also starting been noticed that they serve as extraordinary models involved in polypeptides producing process. Although circRNAs have been extensively studied, their function in thyroid carcinoma is still lacking. Thus, we present the latest advances in circRNA research and summarize their fundamental rules of regulating process as well as the mechanism. More importantly, We mainly review the role and mechanism of circRNA in thyroid cancer, which provides an emerging perspective and theoretically supports the treatment of thyroid cancer.