Circular RNA expression in basal cell carcinoma

Regulatory miRNAs and lncRNAs in Skin Cancer: A Narrative Review

Non-coding RNAs (ncRNAs) have a significant regulatory role in the pathogenesis of skin cancer, despite the fact that protein-coding genes have generally been the focus of research efforts in the field. We comment on the actions of long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) in the current review with an eye toward potential therapeutic treatments. LncRNAs are remarkably adaptable, acting as scaffolding, guides, or decoys to modify key signaling pathways (i.e., the Wnt/β-catenin pathway) and gene expression. As post-transcriptional gatekeepers, miRNAs control gene expression by attaching to messenger RNAs and causing their degradation or suppression during translation. Cell cycle regulation, cellular differentiation, and immunological responses are all affected by the dysregulation of miRNAs observed in skin cancer. NcRNAs also show promise as diagnostic biomarkers and prognostic indicators. Unraveling the complexity of the regulatory networks governed by ncRNAs in skin cancer offers unprecedented opportunities for groundbreaking targeted therapies, revolutionizing the landscape of dermatologic care.

Screening differential circular RNA expression profiles and the potential role of hsa_circ_0085465 in liver cancer

Aims

This study aimed to screen the circular RNAs (circRNAs) that are differentially expressed between liver cancer and paired paracarcinoma tissues and then elucidate their role in cancer progression.

Materials and Methods

High-throughput sequencing of cancer and paired paracarcinoma tissues was followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of the parental genes of the differentially expressed circRNAs, which were also verified via real-time quantitative polymerase chain reaction analysis of the tissues. In addition, the function of selected circRNAs was determined using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4- sulfophenyl)-2H-tetrazolium (MTS) and transwell assays.

Results

Total 218 and 121 circRNAs were differentially upregulated and downregulated, respectively; these were mainly enriched with GO and KEGG terms related to biological functions. From five representatives of the differentially expressed circRNAs, we selected hsa_circ_0085465 for further analysis, discovering that its overexpression promoted the proliferation, migration, and invasion of 97 L cells.

Conclusion

Taken together, our results suggest that hsa_circ_0085465 is relevant to liver cancer progression.

Circ_CEA promotes the interaction between the p53 and cyclin-dependent kinases 1 as a scaffold to inhibit the apoptosis of gastric cancer

Circular RNAs (circRNAs) have been reported to play essential roles in tumorigenesis and progression. This study aimed to identify dysregulated circRNAs in gastric cancer (GC) and investigate the functions and underlying mechanism of these circRNAs in GC development. Here, we identify circ_CEA, a circRNA derived from the back-splicing of CEA cell adhesion molecule 5 (CEA) gene, as a novel oncogenic driver of GC. Circ_CEA is significantly upregulated in GC tissues and cell lines. Circ_CEA knockdown suppresses GC progression, and enhances stress-induced apoptosis in vitro and in vivo. Mechanistically, circ_CEA interacts with p53 and cyclin-dependent kinases 1 (CDK1) proteins. It serves as a scaffold to enhance the association between p53 and CDK1. As a result, circ_CEA promotes CDK1-mediated p53 phosphorylation at Ser315, then decreases p53 nuclear retention and suppresses its activity, leading to the downregulation of p53 target genes associated with apoptosis. These findings suggest that circ_CEA protects GC cells from stress-induced apoptosis, via acting as a protein scaffold and interacting with p53 and CDK1 proteins. Combinational therapy of targeting circ_CEA and chemo-drug caused more cell apoptosis, decreased tumor volume and alleviated side effect induced by chemo-drug. Therefore, targeting circ_CEA might present a novel treatment strategy for GC.

The emerging roles of circular RNA-mediated autophagy in tumorigenesis and cancer progression

Circular RNA (circRNA) is characterized by a specific covalently closed ring structure. The back-splicing of precursor mRNA is the main way of circRNA generation, and various cis/trans-acting elements are involved in regulating the process. circRNAs exhibit multiple biological functions, including serving as sponges of microRNAs, interacting with proteins to regulate their stabilities and abilities, and acting as templates for protein translation. Autophagy participates in many physiological and pathological processes, especially it plays a vital role in tumorigenesis and carcinoma progression. Increasing numbers of evidences have revealed that circRNAs are implicated in regulating autophagy during tumor development. Until now, the roles of autophagy-associated circRNAs in carcinoma progression and their molecular mechanisms remain unclear. Here, the emerging regulatory roles and mechanisms of circRNAs in autophagy were summarized. Furtherly, the effects of autophagy-associated circRNAs on cancer development were described. We also prospected the potential of autophagy-associated circRNAs as novel therapeutic targets of tumors and as biomarkers for cancer diagnosis and prognosis.

Non-coding RNAs in skin cancers:Biological roles and molecular mechanisms

Cutaneous malignancies, including basal cell carcinoma, cutaneous squamous cell carcinoma, and cutaneous melanoma, are common human tumors. The incidence of cutaneous malignancies is increasing worldwide, and the leading cause of death is malignant invasion and metastasis. The molecular biology of oncogenes has drawn researchers’ attention because of the potential for targeted therapies. Noncoding RNAs, including microRNAs, long noncoding RNAs, and circular RNAs, have been studied extensively in recent years. This review summarizes the aspects of noncoding RNAs related to the metastasis mechanism of skin malignancies. Continuous research may facilitate the identification of new therapeutic targets and help elucidate the mechanism of tumor metastasis, thus providing new opportunities to improve the survival rate of patients with skin malignancies.

hsa_circWDR37_016 Regulates Hypoxia-Induced Proliferation of Pulmonary Arterial Smooth Muscle Cells

Pulmonary arterial hypertension (PAH) is characterized by abnormal remodeling of pulmonary vessel walls caused by excessive pulmonary arterial smooth muscle cell (PASMC) proliferation. Our previous clinical studies have demonstrated the importance of the downregulated circRNA in PAH. However, the role of upregulated circRNAs is still elusive. Here, we identified the upregulated circRNA in PAH patients, hsa_circWDR37_016 (circWDR37), as a key regulator of hypoxic proliferative disorder of pulmonary arterial smooth muscle cells (PASMCs). Quantitative real-time PCR (qRT-PCR) analysis validated that exposure to hypoxia markedly increased the circWDR37 level in cultured human PASMCs. As evidenced by flow cytometry, 5-ethynyl-2′-deoxyuridine (EdU) incorporation, wound healing, and Tunel assay, silencing of endogenous circWDR37 attenuated proliferation and cell-cycle progression in hypoxia-exposed human PASMCs in vitro. Furthermore, bioinformatics and Luciferase assay showed that circWDR37 directly sponged hsa-miR-138-5p (miR-138) and was involved in the immunoregulatory and inflammatory processes of PAH. Together, these studies suggested new insights into circRNA regulated the pathology of PAH, providing a new potential therapeutic target for PAH treatment.

CircRNA-IGLL1/miR-15a/RNF43 axis mediates ammonia-induced autophagy in broilers jejunum via Wnt/β-catenin pathway

With the continued increase of global ammonia emission, the damage to human or animal caused by ammonia pollution has attracted wide attention. The noncoding RNAs have been reported to regulate a variety of biological processes under different environmental stimulation via ceRNA (competing endogenous RNA) networks. Autophagy is a hallmark of tissue damage from air pollution. However, the specific role of circular RNAs (circRNAs) in the injury of intestinal tissue caused by autophagy remains unclear. Here, we established 42-days old ammonia-exposed broiler models and observed that autophagy flux in broiler jejunum was activated under ammonia exposure. Meanwhile, a total of eight significantly dysregulated expressed circRNAs were obtained and a circRNAs-miRNAs-genes interaction networks were constructed by bioinformatics analysis. Furthermore, an axis named circRNA-IGLL1/miR-15a/RNF43 was predicted to participate in the excessive autophagy by targeting RNF43. The target relationship was proved by dual-luciferase reporter assay in vitro. Mechanistically, downregulated circRNA-IGLL1 could suppress the expression of RNF43 in ammonia-exposed jejunum and the Wnt/β-catenin pathway was activated. Inhibition of miR-15a reversed autophagy caused by downregulated circRNA-IGLL1. CircRNA-IGLL1 could competitively bind miR-15a to regulate RNF43 expression, thus modulating the occurrence of autophagy. Taken together, our results showed that circRNA-IGLL1/miR-15a/RNF43 axis is involved in ammonia-induced intestinal autophagy in broilers.

Hsa_circ_0023990 Promotes Tumor Growth and Glycolysis in Dedifferentiated TC via Targeting miR-485-5p/FOXM1 Axis

BACKGROUND

During the transformation to dedifferentiated thyroid cancer (TC) types, the ability of papillary thyroid carcinomas (PTCs) to concentrate radioactive iodine might be lost, raising difficulty for the current therapy. circRNAs were proved to be implicated in the progression of various cancers. In this study, we aimed to investigate the functional role and mechanism of hsa_circ_0023990 in dedifferentiated TC.

METHODS

The expression pattern of genes were detected using quantitative PCR or western blot assays. Cell proliferation was determined by CCK8, colony formation, EdU, and cell-cycle assays. Glycolysis was assessed using glucose uptake and lactate production assays. Luciferase reporter assay was performed to examine the interactions between miR-485-5p and hsa_circ_0023990 or FOXM1. Xenograft assay was allowed for observation of tumor growth in vivo.

RESULTS

Hsa_circ_0023990 and FOXM1 were upregulated in dedifferentiated TC tissues and cell lines. The higher level of hsa_circ_0023900 could stimulate the proliferation and glycolysis of dedifferentiated TC cells via positively regulating FOXM1. Mechanistically, miR-485-5p was demonstrated to interact with hsa_circ_0023990 and FOXM1 and involved in the regulation of has_circ_0023990 and FOXM1 in TC biological processes.

CONCLUSION

Our results discovered the functional network of hsa_circ_0023990 in dedifferentiated TC development by facilitating cell proliferation and glycolysis via miR-485-5p/FOXM1 axis, implying that hsa_circ_0023990 might be a potential therapeutic target for the dedifferentiated TC treatment.

Circular RNA-Is the Circle Perfect?

Circular RNA (circRNA) is a distinct class of non-coding RNA produced, in principle, using a back-splicing mechanism, conserved during evolution, with increased stability and a tissue-dependent expression. Circular RNA represents a functional molecule with roles in the regulation of transcription and splicing, microRNA sponge, and the modulation of protein–protein interaction. CircRNAs are involved in essential processes of life such as apoptosis, cell cycle, and proliferation. Due to the regulatory role (upregulation/downregulation) in pathogenic mechanisms of some diseases (including cancer), its potential roles as a biomarker or therapeutic target in these diseases were studied. This review focuses on the importance of circular RNA in cancer.

Characteristics of circRNA and its approach as diagnostic tool in melanoma

One of the most common types of cancer in the world is skin cancer, which has been divided into two groups: non-melanoma and melanoma skin cancer. Different external and internal agents are considered as risk factors for melanoma skin cancer pathogenesis but the exact mechanisms are not yet confirmed. Genetic and epigenetic changes, UV exposure, arsenic compounds, and chemical substances are contributory factors to the development of melanoma. A correlation has emerged between new therapies and the discovery of a basic molecular pattern for skin cancer patients. Circular RNAs (circRNAs) are described as a unique group of extensively expressed endogenous regulatory RNAs with closed-loop structure bonds connecting the 5' and 3' ends, which are commonly expressed in mammalian cells. In this review, we describe the biogenesis of circular RNAs and its function in cancerous conditions focusing on the crosstalk between different circRNAs and melanoma. Increasing evidence suggests that circRNAs appears to be relative to the origin and development of skin-related diseases like malignant melanoma. Different circular RNAs like hsa_circ_0025039, hsa_circRNA006612, circRNA005537, and circANRIL, by targeting different cellular and molecular targets (e.g., CDK4, DAB2IP, ZEB1, miR-889, and let-7 c-3p), can participate in melanoma cancer progression.

The Role of Circular RNAs in Keratinocyte Carcinomas

Keratinocyte carcinomas (KC) include basal cell carcinomas (BCC) and cutaneous squamous cell carcinomas (cSCC) and represents the most common cancer in Europe and North America. Both entities are characterized by a very high mutational burden, mainly UV signature mutations. Predominately mutated genes in BCC belong to the sonic hedgehog pathway, whereas, in cSCC, TP53, CDKN2A, NOTCH1/2 and others are most frequently mutated. In addition, the dysregulation of factors associated with epithelial to mesenchymal transition (EMT) was shown in invasive cSCC. The expression of factors associated with tumorigenesis can be controlled in several ways and include non-coding RNA molecules, such as micro RNAs (miRNA) long noncoding RNAs (lncRNA) and circular RNAs (circRNA). To update findings on circRNA in KC, we reviewed 13 papers published since 2016, identified in a PubMed search. In both BCC and cSCC, numerous circRNAs were identified that were differently expressed compared to healthy skin. Some of them were shown to target miRNAs that are also dysregulated in KC. Moreover, some studies confirmed the biological functions of individual circRNAs involved in cancer development. Thus, circRNAs may be used as biomarkers of disease and disease progression and represent potential targets of new therapeutic approaches for KC.

Non-coding RNAs in pancreatic ductal adenocarcinoma: New approaches for better diagnosis and therapy

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies with a 5-year survival rate less than 8%, which has remained unchanged over the last 50 years. Early detection is particularly difficult due to the lack of disease-specific symptoms and a reliable biomarker. Multimodality treatment including chemotherapy, radiotherapy (used sparingly) and surgery has become the standard of care for patients with PDAC. Carbohydrate antigen 19-9 (CA 19-9) is the most common diagnostic biomarker; however, it is not specific enough especially for asymptomatic patients. Non-coding RNAs are often deregulated in human malignancies and shown to be involved in cancer-related mechanisms such as cell growth, differentiation, and cell death. Several micro, long non-coding and circular RNAs have been reported to date which are involved in PDAC. Aim of this review is to discuss the roles and functions of non-coding RNAs in diagnosis and treatments of PDAC.

Role of Virally Encoded Circular RNAs in the Pathogenicity of Human Oncogenic Viruses

Human oncogenic viruses are a group of important pathogens that etiologically contribute to at least 12% of total cancer cases in the world. As an emerging class of non-linear regulatory RNA molecules, circular RNAs (circRNAs) have gained increasing attention as a crucial player in the regulation of signaling pathways involved in viral infection and oncogenesis. With the assistance of current circRNA enrichment and detection technologies, numerous novel virally-encoded circRNAs (vcircRNAs) have been identified in the human oncogenic viruses, initiating an exciting new era of vcircRNA research. In this review, we discuss the current understanding of the roles of vcircRNAs in the respective viral infection cycles and in virus-associated pathogenesis.

Epigenetic regulation of cellular functions in wound healing

Stringent spatiotemporal regulation of the wound healing process involving multiple cell types is associated with epigenetic mechanisms of gene regulation, such as DNA methylation, histone modification and chromatin remodelling, as well as non-coding RNAs. Here, we discuss the epigenetic changes that occur during wound healing and the rapidly expanding understanding of how these mechanisms affect healing resolution in both acute and chronic wound milieu. We provide a focussed overview of current research into epigenetic regulators that contribute to wound healing by specific cell type. We highlight the role of epigenetic regulators in the molecular pathophysiology of chronic wound conditions. The understanding of how epigenetic regulators can affect cellular functions during normal and impaired wound healing could lead to novel therapeutic approaches, and we outline questions that can provide guidance for future research on epigenetic-based interventions to promote healing. Dissecting the dynamic interplay between cellular subtypes involved in wound healing and epigenetic parameters during barrier repair will deepen our understanding of how to improve healing outcomes in patients affected by chronic non-healing wounds.

Advances in the Identification of Circular RNAs and Research Into circRNAs in Human Diseases

Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs (ncRNAs) with a closed-loop structure that are mainly produced by variable processing of precursor mRNAs (pre-mRNAs). They are widely present in all eukaryotes and are very stable. Currently, circRNA studies have become a hotspot in RNA research. It has been reported that circRNAs constitute a significant proportion of transcript expression, and some are significantly more abundantly expressed than other transcripts. CircRNAs have regulatory roles in gene expression and critical biological functions in the development of organisms, such as acting as microRNA sponges or as endogenous RNAs and biomarkers. As such, they may have useful functions in the diagnosis and treatment of diseases. CircRNAs have been found to play an important role in the development of several diseases, including atherosclerosis, neurological disorders, diabetes, and cancer. In this paper, we review the status of circRNA research, describe circRNA-related databases and the identification of circRNAs, discuss the role of circRNAs in human diseases such as colon cancer, atherosclerosis, and gastric cancer, and identify remaining research questions related to circRNAs.

Hsa_circ_0000199 facilitates chemo-tolerance of triple-negative breast cancer by interfering with miR-206/613-led PI3K/Akt/mTOR signaling

Increasing attentions have been paid to the role of circRNAs in the etiology of triple-negative breast cancer (TNBC), and we strived to figure out the association of circRNA AKT3/miRNA axis with TNBC chemo-resistance. Altogether 207 BC patients were divided into TNBC group (n=83) and non-TNBC group (n=124), and MCF-10A, MDA-MB-231, MDA-MB-468, SK-BR-3 and MCF-7 cell lines were prepared in advance. Expressions of AKT3-derived circRNAs and relevant miRNAs in the TNBC tissues and cell lines were determined by employing real-time polymerase chain reaction (PCR). It was indicated that hsa_circ_0000199 expression was higher in TNBC tissues than in non-TNBC tissues, and high hsa_circ_0000199 expression was predictive of large tumor size, advanced TNM grade, high Ki-67 level and poor 3-year survival of TNBC patients (all P<0.05). Furthermore, miR-613 and miR-206 were sponged and negatively regulated by hsa_circ_0000199 (P<0.001), and PI3K/Akt/mTOR signaling was depressed by si-hsa_circ_0000199 in TNBC cell lines (P<0.01). Ultimately, miR-206/miR-613 inhibitor reversed impacts of si-hsa_circ_0000199 on PI3K/Akt/mTOR signaling, proliferation, migration, invasion, chemo-sensitivity and autophagy of TNBC cells (all P<0.01). Conclusively, silencing of hsa_circ_0000199 enhanced TNBC chemo-sensitivity by promoting miR-206/miR-613 expression and deactivating PI3K/Akt/mTOR signaling, which was conducive to improving chemotherapeutic efficacy of TNBC patients.

CircRNA_ACAP2 Suppresses EMT in Head and Neck Squamous Cell Carcinoma by Targeting the miR-21-5p/STAT3 Signaling Axis

Circular RNAs (circRNAs) contain microRNA (miRNA)-specific binding sites and can function as miRNA sponges to regulate gene expression by suppressing the inhibitory effect of miRNAs on their target genes. MiR-21-5p has been reported to be involved in the development of head and neck squamous cell carcinoma (HNSCC) and plays an important role in the activation of epithelial-mesenchymal transition (EMT). However, the upstream regulatory mechanism and downstream targets of miR-21-5p in tumor cells remain unknown. CircRNA_ACAP2 inhibits the function of miR-21-5p by binding to its specific binding sites in HNSCC cells. Overexpression of CircRNA_ACAP2 inhibits the proliferation and migration of HNSCC cells, while downregulation of CircRNA_ACAP2 has the opposite effect. STAT3 is a direct target gene of miR-21-5p and a transcription factor of ZEB1. We demonstrate that CircRNA_ACAP2 functions as a tumor suppressor gene in HNSCC and that its function is regulated via the miR-21-5p/STAT3 signaling axis.

Epigenetic regulation in the pathogenesis of non-melanoma skin cancer

Understanding of cancer with the help of ever-expanding cutting edge technological tools and bioinformatics is revolutionizing modern cancer research by broadening the space of discovery window of various genomic and epigenomic processes. Genomics data integrated with multi-omics layering have advanced cancer research. Uncovering such layers of genetic mutations/modifications, epigenetic regulation and their role in the complex pathophysiology of cancer progression could lead to novel therapeutic interventions. Although a plethora of literature is available in public domain defining the role of various tumor driver gene mutations, understanding of epigenetic regulation of cancer is still emerging. This review focuses on epigenetic regulation association with the pathogenesis of non-melanoma skin cancer (NMSC). NMSC has higher prevalence in Caucasian populations compared to other races. Due to lack of proper reporting to cancer registries, the incidence rates for NMSC worldwide cannot be accurately estimated. However, this is the most common neoplasm in humans, and millions of new cases per year are reported in the United States alone. In organ transplant recipients, the incidence of NMSC particularly of squamous cell carcinoma (SCC) is very high and these SCCs frequently become metastatic and lethal. Understanding of solar ultraviolet (UV) light-induced damage and impaired DNA repair process leading to DNA mutations and nuclear instability provide an insight into the pathogenesis of metastatic neoplasm. This review discusses the recent advances in the field of epigenetics of NMSCs. Particularly, the role of DNA methylation, histone hyperacetylation and non-coding RNA such as long-chain noncoding (lnc) RNAs, circular RNAs and miRNA in the disease progression are summarized.

<p>Microarray Expression Profiles and Bioinformatics Analyses Reveal Aberrant Circular RNAs Expression in Bladder Cancer</p>

Background

Increasing evidence shows that circular RNAs (circRNAs) are involved in many biological processes, functioning as microRNA (miRNA) sponges. The aim of this study is to identify differentially expressed circRNAs in bladder cancer (BCa).

Methods

The transcriptome of circRNAs in BCa was assayed by microarray. Quantitative real-time PCR was performed to verify the results. Then, potential miRNA response elements (MREs) between circRNAs and miRNAs were predicted. Pathway and ontology enrichment analyses were performed to identify mechanisms related to the gene regulation of differentially expressed circRNAs.

Results

Three hundred and eighty-six up-regulated and 394 down-regulated circRNAs were identified, and their potential MREs were predicted in BCa.

Conclusion

The differentially expressed circRNAs indicate that circRNAs could play important roles in the molecular pathogenesis of BCa.

hsa_circNFXL1_009 modulates apoptosis, proliferation, migration, and potassium channel activation in pulmonary hypertension

In this study, we explored the circular RNA (circRNA) profile in pulmonary arterial hypertension (PAH) patients caused by chronic obstructive pulmonary disease (COPD) and the effects of hsa_circNFXL1_009 on abnormal proliferation, apoptosis, and migration of human pulmonary arterial smooth muscle cells (hPASMCs) driven by hypoxia. Using microarrays, we screened the circRNA profile in whole-blood samples from three pairs of subjects and found 158 dysregulated circRNAs in patients with PAH-COPD. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis further validated that hsa_circNFXL1_009 was dramatically downregulated with the highest area under a receiver operating characteristic curve (ROC) in 21 pairs of subjects. Consistently, exposure to hypoxia markedly reduced the hsa_circNFXL1_009 level in cultured hPASMCs. Delivery of exogenous hsa_circNFXL1_009 attenuated hypoxia-induced proliferation, apoptotic resistance, and migration of hPASMCs, as evidenced by immunocytochemistry, 5-ethynyl-2′-deoxyuridine incorporation, wound healing, and a TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling) assay. A luciferase assay showed that hsa_circNFXL1_009 directly sponged hsa-miR-29b-2-5p (miR-29b) and positively regulated the expression of voltage-gated potassium (K⁺) channel subfamily B member 1 (KCNB1) at the mRNA level. Using patch-clamp electrophysiology, we proved that overexpression of hsa_circNFXL1_009 promoted a whole-cell K⁺ current in hPASMCs. Taken together, these studies identify hsa_circNFXL1_009 as a key regulator of PAH, and it may be used as a potential therapeutic target for the treatment of PAH.

Circular RNA: A novel potential biomarker for skin diseases

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

Upregulation of Circular RNA Itchy E3 Ubiquitin Protein Ligase Inhibits Cell Proliferation and Promotes Cell Apoptosis Through Targeting MiR-197 in Prostate Cancer

Objective:

This study aimed to investigate the effect of circular RNA itchy E3 ubiquitin protein ligase on cell proliferation and apoptosis and to explore its target micro-RNAs in prostate cancer cells.

Methods:

Circular RNA itchy E3 ubiquitin protein ligase expression in human prostate cancer cells and normal prostate epithelial cells was determined by real time-quantitative polymerase chain reaction assay. Circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids (circular RNA itchy E3 ubiquitin protein ligase(+) group and control overexpression plasmids group were transfected with PC-3 cells. Rescue experiment was performed by transfection of circular RNA itchy E3 ubiquitin protein ligase overexpression and micro-197 overexpression plasmids (circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids/micro RNA (+) group) into PC-3 cells. Cell Counting Kit-8 and annexin V/propidium iodide assays were conducted to evaluate cell proliferation and apoptosis, respectively. Western blot was performed to determine the expressions of apoptotic-related markers.

Results:

Circular RNA itchy E3 ubiquitin protein ligase expression was decreased in DU 145, 22RV1, VCaP, and PC-3 cells compared to RWPE cells. In PC-3 cells, cell proliferation rate was reduced in circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids group compared to control overexpression plasmids group at 48 hours and 72 hours. Cell apoptosis rate was elevated in circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids group compared to control overexpression plasmids group at 48 hours, and Western blot showed the similar results. Micro RNA-197 but not micro RNA-31 or micro RNA-432 was the target micro-RNA of circular RNA itchy E3 ubiquitin protein ligase. In rescue experiments, cell proliferation rate was elevated, but apoptosis rate was reduced in circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids/micro RNA (+) group compared to circular RNA itchy E3 ubiquitin protein ligase overexpression plasmids group, indicating that circular RNA itchy E3 ubiquitin protein ligase upregulation inhibited cell proliferation but promoted apoptosis through downregulating micro RNA-197.

Conclusion:

Circular RNA itchy E3 ubiquitin protein ligase upregulation suppresses cell proliferation but promotes apoptosis through targeting micro RNA-197 in prostate cancer. Our study may provide a new insight for the treatment of prostate cancer.

Microarray is an efficient tool for circRNA profiling

Circular RNAs (circRNAs) are emerging as a new class of endogenous and regulatory noncoding RNAs in latest years. With the widespread application of RNA sequencing (RNA-seq) technology and bioinformatics prediction, large numbers of circRNAs have been identified. However, at present, we lack a comprehensive characterization of all these circRNAs in interested samples. In this study, we integrated 87 935 circRNAs sequences that cover most of circRNAs identified till now represented in circBase to design microarray probes targeting back-splice site of each circRNA to profile expression of those circRNAs. By comparing the circRNA detection efficiency of RNA-seq with this circRNA microarray, we revealed that microarray is more efficient than RNA-seq for circRNA profiling. Then, we found ∼80 000 circRNAs were expressed in cervical tumors and matched normal tissues, and ∼25 000 of them were differently expressed. Notably, many of these circRNAs detected by this microarray can be validated by quantitative reverse transcription polymerase chain reaction (RT-qPCR) or RNA-seq. Strikingly, as many as ∼18 000 circRNAs could be robustly detected in cell-free plasma samples, and the expression of ∼2700 of them differed after surgery for tumor removal. Our findings provided a comprehensive and genome-wide characterization of circRNAs in paired normal tissues and tumors and plasma samples from multiple individuals. In addition, we also provide a rich resource with 41 microarray data sets and 10 RNA-seq data sets and strong evidences for circRNA expression in cervical cancer. In conclusion, circRNAs could be efficiently profiled by circRNA microarray to target their reported back-splice sites in interested samples.

Testicular biopsies microarray analysis reveals circRNAs are involved in the pathogenesis of non-obstructive azoospermia

Circular RNAs (circRNAs) have been reported to be involved in many diseases. But there is no report on circRNAs in non-obstructive azoospermia (NOA). The purpose of this paper is to explore the circular RNA expression profile and potential functions of circRNAs in NOA patients. We first preformed circRNA expression profiling analysis using a circRNA microarray in testicular samples from NOA and obstructive azoospermia (OA) patients. CircRNAs were validated by qRT-PCR. Bioinformatics analysis were used to construct the ceRNA network. GO and KEGG enrichment analysis were performed by using DAVID. Microarray analysis identified 82 differentially expressed circRNAs in NOA specimens. The differential expression of hsa_circRNA_402130, hsa_circRNA_072697, hsa_circRNA_030050, hsa_circRNA_100812 and hsa_circRNA_406168 was confirmed by qRT-PCR. Enrichment analysis revealed the association of hsa_circRNA_402130 and hsa_circRNA_072697 with multiple signaling pathways. The data indicated that circRNAs were significantly dysregulated in NOA specimens and might involve in the pathogenesis of NOA.

Circular RNA; a new biomarker for breast cancer: A systematic review

Circular RNAs (circRNAs) were recently discovered as a looped subset of competing endogenous RNAs, with an ability to regulate gene expression by microRNA sponging. There are several studies on their potential roles in cancer development, such as colorectal cancer and basal cell carcinoma. However, there is still a significant gap in the knowledge about circRNA functions in breast cancer (BC) progression. The current study systematically reviewed circRNA biogenesis and their potential roles as a novel biomarker in BC on published studies of the MEDLINE®/PubMed, Cochrane®, and Scopus® databases. The obtained results showed a general dysregulation of circRNAs expression in BC cells with a cell-type and stage-specific manner. The potential connection between circRNAs and BC cell proliferation, apoptosis, metastasis, and chemotherapy sensitivity and resistance were discussed.

Circular RNA circRHOBTB3 acts as a sponge for miR-654-3p inhibiting gastric cancer growth

Background

Circular RNAs (circRNAs) have recently emerged as a new family of noncoding RNAs that are involved in the causation and progression of various cancers. However, the roles of circRNAs in the tumorigenesis of gastric cancer (GC) are still largely unknown.

Methods

The expression profiles of circRNAs in GC were identified in open GEO database and were evaluated at the mRNA level in clinical GC samples compared with paired non-tumorous tissues. Kaplan-Meier survival curve was used to analyze the correlation of circRNA and patients’ prognosis. Subsequently, the circular structures of candidate circRNAs were validated by Sanger sequencing, divergent primer PCR, and RNase R treatments. Gain- and loss-of-function analyses were performed to evaluate the functional significance of it in GC initiation and progression. Dual-luciferase reporter and RNA pull-down assays were used to identify the microRNA (miRNA) sponge mechanism of circRNAs.

Results

The expression of circRHOBTB3 was lower in GC tissues and cell lines. Downregulation of circRHOBTB3 was significantly correlated with poor differentiation and unfavorable prognosis in patients with GC. Overexpression of circRHOBTB3 in GC cells led to decreased proliferation and induced G₁/S arrest in vitro, accompanied with inhibited xenograft tumor growth in vivo, while the opposite effects were achieved in circRHOBTB3-silenced cells. Furthermore, we demonstrated that circRHOBTB3 acts as a sponge for miR-654-3p and verified that p21 is a novel target of miR-654-3p.

Conclusion

Taken together, this study revealed that circRHOBTB3 might function as competing endogenous RNA (ceRNA) for miR-654-3p, which could contribute to growth inhibition of GC through activating p21 signaling pathway. Our data suggested that circRHOBTB3 would serve as a novel promising diagnosis marker and therapeutic target for GC.

Next-generation sequencing reveals hsa_circ_0058092 being a potential oncogene candidate involved in gastric cancer

Gastric cancer is a serious problem for human health. As part of noncoding RNA, circular RNA (circRNA) plays a key role in the occurrence and development of malignant tumor. We used next generation sequencing technology to detect circRNA expression profiles in 5 paired human gastric cancer tissues. Then, bioinformatics analysis was carried out to analyze the function of dysregulated circRNAs. Hsa_circ_0058092 was selected as the object of follow-up analysis. After using the Cistrome DB dataset the data was used to predict specific transcription factors of hsa_circ_0058092. The relationship between hsa_circ_0058092 and PODXL was further validated using RT-PCR and immunohistochemical techniques. Survival data were collected using a Kaplan-Meier analysis of hsa_circ_0058092. We identified 319 aberrantly expressed circRNAs, Hsa_circ_0058092 was selected for our studies. Functional analysis of hsa_circ_0058092 revealed that it was related to metabolic processes. The prediction results suggested that hsa_circ_0058092 has a relationship with hsa-miR-4269 which could specifically bind to the PODXL sequence. Transcription factor CEBPB may regulate the transcription process of hsa_circ_0058092. The expression of hsa_circ_0058092 was positively correlated with PODXL expression. Immunohistochemical analysis of PODXL showed that the expression of PODXL protein in cancer tissues is higher than that in adjacent tissues. Kaplan-Meier analysis suggested that hsa_circ_0058092 was associated with survival of gastric cancer patients. All of these results showed that hsa_circ_0058092 was a potential oncogene.

Selective downregulation of distinct circRNAs in the tissues and plasma of patients with primary hepatic carcinoma

Multiple studies have indicated that circular RNAs (circRNAs) are closely associated with malignant tumor development and metastasis. However, the significance of circRNAs in primary hepatic carcinoma (PHC), particularly in the plasma, remains largely undetermined. In the current study, circRNA expression profiles in three pairs of tumor and adjacent normal samples from patients with PHC, were examined using circRNA chip screening. A total of 80 circRNAs were upregulated, while 75 circRNAs were downregulated in PHC tissues, relative to para-tumor tissues (fold change, ≥1.5). A total of two upregulated circRNAs and three downregulated circRNAs were selected as candidates for further validation of their differential expression. This was performed using reverse transcription-quantitative PCR with 11 pairs of PHC tissues and para-tumor tissues. The results indicated that hsa_circ_0003056 exhibited reduced expression in PHC tissues. Moreover, hsa_circ_0003056 and hsa_circ_0067127 were quantified in the plasma samples of 35 PHC patients and 32 healthy donors. The results revealed that hsa_circ_0067127 was significantly downregulated in the patients' plasma. Finally, a competing endogenous RNA network was constructed, which consisted of one circRNA (hsa_circ_0003056 or has_circ_0067127), five miRNAs and miRNA-targeted genes (mRNAs). Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that differentially expressed (DE) genes were significantly enriched in the pathway associated with ‘regulation of the pluripotency of stem cells’ for hsa_circ_0003056, and ‘ubiquitin-mediated proteolysis’ and ‘prostate cancer’ for hsa_circ_0067127. Gene ontology analysis revealed that DE genes were primarily associated with the ‘modulation of kinase activity’ and ‘intracellular and transmembrane-ephrin receptor activity’ for hsa_circ_0003056, ‘artery morphogenesis activity’, ‘HOPS complex and transferase activity’ and in ‘transferring acyl groups’ for hsa_circ_0067127. This approach indicated that hsa_circ_0003056 in PHC tissue, and hsa_circ_0067127 in PHC plasma, are downregulated and may be implicated in the tumorigenesis of PHC.

Circular RNA MAT2B Promotes Glycolysis and Malignancy of Hepatocellular Carcinoma Through the miR-338-3p/PKM2 Axis Under Hypoxic Stress

Glucose metabolism reprogramming, which is a well-established characteristic of multiple cancers, demands a higher rate of glycolysis to meet the increasing demands for macromolecular synthesis and to maintain rapid proliferation in a hypoxic environment. However, the mechanism underlying this switch remains to be elucidated. In this study, we investigated the function of circular RNA MAT2B (circMAT2B) in hepatocellular carcinoma (HCC) glucose metabolism reprogramming and malignancy. CircMAT2B was identified by bioinformatics analysis of Gene Expression Omnibus data sets. CircMAT2B expression was up-regulated in HCC tissues and cell lines. HCC patients with high circMAT2B expression had shortened overall survival. We analyzed the positive correlation between glycolysis and circMAT2B expression in HCC using a maximum standardized uptake value determined by preoperative positron emission tomography/computed tomography scanning combined with high-performance liquid chromatography assessment of the metabolites of glycolysis and the citric acid cycle. The effect of circMAT2B on glycolysis was validated in vitro and in vivo under hypoxic (1% O₂ ) conditions. Functional assays were performed in HCC cells, HCC organoids, and nude mice to explore the tumor-promoting roles of circMAT2B in HCC. Biotin-coupled probe pull-down assays, biotin-coupled microRNA capture, luciferase reporter assays, fluorescence in situ hybridization, and RNA immunoprecipitation assays were performed to confirm the interaction among different RNAs. Mechanistically, we demonstrated that circMAT2B up-regulated expression levels of the microRNA (miR)-338-3p target gene PKM2, which encodes a key enzyme in the process of glycolysis, through "sponging" miR-338-3p; thus, glycolysis and HCC progression are promoted through this mechanism. Conclusion: CircMAT2B promoted HCC progression by enhanced glycolysis by activating the circMAT2B/miR-338-3p/PKM2 axis under hypoxia, which may provide a therapeutic target for HCC.

Circular RNAs: epigenetic regulators in cancerous and noncancerous skin diseases

The most frequent kind of malignancy in the universe is skin cancer, which has been categorized into non-melanoma and melanoma skin cancer. There are no complete information of the skin carcinogenesis process. A variety of external and internal agents contribute to the non-melanoma and melanoma skin cancer pathogenesis. These factors are epigenetic changes, X-rays, genetic, arsenic compounds, UV rays, and additional chemical products. It was found that there could be a relationship between the appearing novel and more suitable therapies for participants in this class of diseases and detection of basic molecular paths. A covalently closed loop structure bond connecting the 5' and 3' ends characterizes a new group of extensively expressed endogenous regulatory RNAs, which are called circular RNAs (circRNAs). Mammals commonly express circRNAs. They are of high importance in tumorigenesis. Multiple lines evidence indicated that a variety of circular RNAs are associated with initiation and development of skin-related diseases such as skin cancers. Given that different circular RNAs (hsa_circ_0025039, hsa_circRNA006612, circRNA005537, and circANRIL) via targeting various cellular and molecular targets (e.g., CDK4, DAB2IP, ZEB1, miR-889, and let-7c-3p) exert their effects on skin cancers progression. Herein, for first time, we summarized different circular RNAs in skin cancers and noncancerous diseases. Moreover, we highlighted crosstalk between circular RNAs and ceRNAs in cancerous conditions.

Potential Diagnostic and Prognostic Biomarkers of Circular RNAs for Lung Cancer in China

Emerging evidence demonstrated that circular RNAs (circRNAs) were dysregulated in lung cancer, indicating that circRNAs might serve as novel diagnostic and prognostic biomarkers for lung cancer. However, the clinical value of circRNAs on lung cancer remains unclear. This study aimed to evaluate the efficiency of circRNAs in the diagnosis and prognosis for lung cancer in China. 2122 Chinese individuals were enrolled in this investigation for assessment of diagnostic value and examination of prognostic analysis. In the diagnostic analysis, the pooled sensitivity, specificity, PLR, NLR, DOR, and AUC of the sROC curve with their 95% CIs were 0.80 (95%CI: 0.74-0.84), 0.80 (95%CI: 0.73-0.86), 3.97 (95%CI: 2.80-5.62) and 0.26 (95%CI: 0.19-0.34), 15.51 (95%CI: 8.76-24.47), and 0.85 (95%CI: 0.82-0.88), respectively. As for the prognostic power of circRNAs, lung cancer patients with higher expression levels of circRNAs tend to possess lower overall survival with the overall pooled HR (1.70, 95%CI: 1.26-2.29). Furthermore, in stratified analysis, upregulated and downregulated circRNAs were manifested to exert significant effects on prognosis with HR values of 2.17 (95%CI: 1.74-2.72) and 0.52 (95%CI: 0.34-0.80). This study validates that circRNAs are promising diagnostic and predictive biomarkers for lung cancer patients in China.

Circular RNA expression profiles in cisplatin-induced acute kidney injury in mice

Aim: This study was carried out to identify the expression profile and role of circRNAs in cisplatin-induced acute kidney injury (AKI). Materials & methods: In this study, an AKI model was established in cisplatin-treated mice, and the expression of circRNAs was profiled by next-generation sequencing. The differential expression levels of selected circRNAs were determined by quantitative real-time polymerase chain reaction. Bioinformatics analysis was conducted to predict the functions. Results: In total, 368 circRNAs were detected to be differentially expressed in response to cisplatin treatment. Bioinformatics analysis indicated that the parental genes of the differentially expressed circRNAs were predominantly implicated in the cell and cell part, cellular process and cancer pathways. Conclusion: CircRNAs might be differentially expressed in AKI, which are potentially involved in pathophysiology of cisplatin-induced nephrotoxicity.

Circular RNA expression in pancreatic ductal adenocarcinoma

The regulatory roles of circular RNAs (circRNAs) in cancer are attracting increasing attention. The aim of the present study was to explore the roles of circRNAs in pancreatic ductal adenocarcinoma (PDAC) using microarray data. The circRNA and microRNA (miRNA) microarray data were downloaded from Gene Expression Omnibus. A total of 256 differentially expressed circRNAs were obtained by analyzing the circRNA microarray data from 26 pairs of PDAC and adjacent normal tissues. Differentially expressed miRNAs were analyzed using a dataset of 6 PDAC tissues and 5 non-neoplastic pancreas samples (GSE43796); 20 differentially expressed miRNAs were detected. circRNA/miRNA interactions were predicted between differentially expressed circRNAs and miRNAs using miRanda and RNAhybrid algorithms and 51 circRNA/miRNA interactions were obtained. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis using gene symbols of differentially expressed circRNAs demonstrated that 41 circRNAs were enriched in 17 pathways. Subnetworks that were associated with apoptosis or proliferation were extracted from the 17 pathways and a new network was constructed using Cytoscape software, which identified that mitogen-activated protein kinase, PI3K/AKT and WNT/β-catenin signaling pathways may be associated with PDAC development. In conclusion, 256 differentially expressed circRNAs and 20 differentially expressed miRNAs were identified in PDAC tissues compared with normal tissues; the circRNA/miRNA interactions and the networks of KEGG pathways provided a global view of the function of these differentially expressed circRNAs and miRNAs.

circRNA and gastrointestinal cancer

Circular RNAs (circRNAs) are a novel class of endogenous noncoding RNAs that form covalently closed continuous loops without 3' end poly (A) tails and 5' end caps. circRNAs are more conservative and stable than linear RNA. circRNAs can specifically bind to microRNAs as competing endogenous RNA, thereby directly or indirectly regulating the expression of related genes. circRNAs have been implicated in several cancers including gastrointestinal (GI) cancers. Some circRNAs have the potential to become biological biomarkers and therapeutic targets of GI cancers. However, the multiple functional roles of circRNAs in GI cancers remain largely unclear.

Computational approaches for circular RNA analysis

Circular RNAs (circRNAs) are a recent addition to the expanding universe of RNA species and originate through back-splicing events from linear primary transcripts. CircRNAs show specific expression profiles with regards to cell type and developmental stage. Importantly, only few circRNAs have been functionally characterized to date. The detection of circRNAs from RNA sequencing data is a complex computational workflow that, depending on tissue and condition typically yields candidate sets of hundreds or thousands of circRNA candidates. Here, we provide an overview on different computational analysis tools and pipelines that became available throughout the last years. We outline technical and experimental requirements that are common to all approaches and point out potential pitfalls during the computational analysis. Although computational prediction of circRNAs has become quite mature in recent years, we provide a set of valuable validation strategies, in silico as well as in vitro-based approaches. In addition to circRNA detection via back-splicing junction, we present available analysis pipelines for delineating the primary sequence and for predicting possible functions of circRNAs. Finally, we outline the most important web resources for circRNA research. This article is categorized under: RNA Methods > RNA Analyses in vitro and In Silico RNA Evolution and Genomics > Computational Analyses of RNA.

Circular RNA cTFRC acts as the sponge of MicroRNA-107 to promote bladder carcinoma progression

BACKGROUND

Circular RNA (circRNA) represents a broad and diverse endogenous RNAs that can regulate gene expression in cancer. However, the regulation and function of bladder cancer (BC) circRNAs remain largely unknown.

METHODS

Here we generated circRNA microarray data from three BC tissues and paired non-cancerous matched tissues, and detected circular RNA-cTFRC up-regulated and correlated with tumor grade and poor survival rate of BC patients. We subsequently performed functional analyses in cell lines and an animal model to support clinical findings. Mechanistically, we demonstrated that cTFRC could directly bind to miR-107 and relieve suppression for target TFRC expression.

RESULTS

We detected circular RNA-cTFRC up-regulated and correlated with tumor grade and poor survival rate of BC patients. Knock down of cTFRC inhibited invasion and proliferation of BC cell lines in vitro and tumor growth in vivo. Furthermore, the expression of cTFRC correlated with TFRC and negatively correlated with miR-107 both in BC cell lines and BC clinical samples. In addition, up-regulation of cTFRC promoted TFRC expression and contributed to an epithelial to mesenchymal transition phenotype in BC cells. Finally, we found that cTFRC acts as a competing endogenous RNA (ceRNA) for miR-107 to regulate TFRC expression.

CONCLUSIONS

cTFRC may exert regulatory functions in BC and may be a potential marker of BC diagnosis or progression.

[Differences in expression profiles of circular RNA between luminal breast cancer cells and normal breast cells]

OBJECTIVE

To investigate the differences in the expression profiles of circular RNA (circRNA) between luminal breast cancer cells and normal breast cells.

METHODS

Total RNA extracted from luminal breast cancer cells MCF7 and normal breast cells MCF10A was digested with Rnase R to remove linear RNAs and enrich circRNAs. The enriched circRNAs were amplified and transcribed into fluorescent cRNAs using a random priming method, and were hybridized onto the circRNA hybridization array. The circRNA expression profiles of MCF7 and MCF10A cells were analyzed using Agilent Feature Extraction software. Quantile normalization and subsequent data processing were performed, and volcano plot filtering and hierarchical clustering were utilized to analyze the circRNA expression patterns. The expressions of 3 circRNAs with significant log fold changes were validated using qPCR.

RESULTS

The hybridization array data revealed significant differences in the circRNA expression profiles between MCF7 and MCF10A cells. Compared with those of MCF10A cells, the 12910 circRNAs expressed in MCF7 cells showed 5964 up-regulated, 81 consistently regulated, and 6865 down-regulated circRNAs; 343 circRNAs showed a log fold change by more than 2 folds, among which 213 circRNAs were up-regulated and 130 were down-regulated. Nine circRNAs showed differential expressions by more than 2 folds, including 8 up-regulated ones, namely hsa_circRNA_061260 (6.02 folds), hsa_circRNA_103933 (5.96 folds), hsa_circRNA_005239 (5.84 folds), hsa_circRNA_100689 (5.69 folds), hsa_circRNA_004087 (5.60 folds), hsa_circRNA_104420 (5.25 folds), hsa_circRNA_104421 (5.13 folds) and hsa_circRNA_101222 (5.03 folds); only one circRNA was down-regulated, namely hsa_circRNA_104864 (5.09 folds). The expressions of hsa_circRNA_100689, hsa_circRNA_005239 and hsa_circRNA_104864 were further validated by qPCR, which yielded consistent results with the microarray data.

CONCLUSIONS

The circRNA expression profiles differ significantly between luminal breast cancer cells and normal breast cells. These differentially expressed circRNAs may serve as potential novel targets for the diagnosis of luminal breast cancer.

The potential role of circRNA_004229 in hair/epidermal regulation after MED1 ablation in keratinocytes

Background/Aims: Mediator complex subunit 1 (MED1) is an important transcriptional co-activator involved in multiple signaling pathways. Previous studies indicated an essential role of MED1 in hair cycling and wound repair through regulating the transcription of mRNAs. Circular RNAs (circRNAs), as a novel class of non-coding RNAs, are involved in various skin biological functions. Our study aimed to investigate the circRNAs expression profile in MED1 epidermal conditional knockout mice (KO), and provide potential candidates as well as the mechanism underlying the circRNAs regulation in both hair follicles and epidermis. Method: Microarray based circRNA expression was determined in MED1 KO mice and wild type mice (WT). The expression level was further confirmed by qRT-PCR. We predicted a possible interaction network of circRNA/microRNA/mRNA by bioinformatics and constructed them with Cytoscape software. Expression of several candidate target mRNAs was verified using qRT-PCR. A TUNEL assay was performed to assess the apoptosis level of MED1 KO and WT skin. Results: Here we identified 109 (34-up, 75-down) distinct circRNAs through microarrays that are differently expressed in MED1 KO mice compared with WT mice (FC > 2 and p-value < 0.05), suggesting a potential role of circRNAs in epidermal regulation. Among these circRNAs, circRNA_004229 was found to decrease significantly after MED1 deletion. The most likely potential targets miRNA for circRNA_004229 include miR-149-5p and miR-207, which possibly further impede the expression of their target mRNA, Tnfrsf19 and Perp, respectively. Apoptosis was suppressed in MED1 KO mice, which implies a potential role of circRNAs in regulating epidermal biological processes including apoptosis. Conclusion: Our study determined the expression profile of circRNAs in MED1 KO skin, and provided hints that circRNA_004229 might be involved in the regulation of keratinocytes in both hair follicles and interfollicular epidermis through a ceRNA mechanism.

We demonstrated that circRNA_004229 might inhibit apoptosis through binding miR-207 and miR-149-5p after MED1 deletion in keratinocytes.

Present Scenario of Circular RNAs (circRNAs) in Plants

Circular RNAs (circRNAs) are new endogenous non-coding RNA family members that arise during pre-mRNA splicing in a reversed order in which the 3' and 5' ends are covalently closed. Compared to the comprehensive investigation of circRNAs in animals, circRNA research in plants is still in its infancy. Genome-wide identification and characterization of circRNAs have recently been performed in several plant species. CircRNAs are ubiquitously expressed and abundant in plants. The expression of circRNAs is often dependent on cell-type, tissue, and developmental stage, and it is particularly stress-inducible in plants. CircRNAs might play important roles in various biological processes in plants, including development and the response to biotic and abiotic stresses. Here, we review the current literature and provide a brief overview of circRNAs and their research status in plants, as well as the bioinformatic tools and database resources for circRNA analysis.

The profile analysis of circular RNAs in human placenta of preeclampsia

IMPACT STATEMENT

The abnormal expression of many regulatory factors may be involved in the development of PE. circRNAs are proved to have a series of important biological functions; however, reports about circRNA and PE are rare. In this work, we evaluated the profile analysis of circRNAs in human placenta of PE by RNA-seq and found some newly differentially expressed circRNAs which might be involved in PE. Combined with bioinformatics analysis, their possible functions were preliminarily discussed.

Circular RNA: new star, new hope in cancer

BACKGROUND

Circular RNAs are a new class of endogenous non-coding RNA that can function as crucial regulators of diverse cellular processes. The diverse types of circular RNAs with varying cytogenetics in cancer have also been reported. Circular RNAs can act as a microRNA sponge or through other mechanisms to regulate gene expression as either tumor inhibitors or accelerators, suggesting that circular RNAs can serve as newly developed biomarkers with clinic implications. Here, we summerized recent advances on circular RNAs in cancer and described a circular RNA network associated with tumorigenesis. The clinical implications of circular RNAs in cancer were also discussed in this paper.

SHORT CONCLUSION

Growing evidence has revealed the crucial regulatory roles of circular RNAs in cancer and the elucidation of functional mechanisms involving circular RNAs would be helpful to construct a circRNA-miRNA-mRNA regulatory network. Moreover, circular RNAs can be easily detected due to their relative stability, widespread expression, and abundance in exosomes, blood and saliva; thus, circular RNAs have potential as new and ideal clinical biomarkers in cancer.

Functional role of circular RNAs in cancer development and progression

Circular RNAs (circRNAs) are a large class of endogenously expressed non-coding RNAs formed by covalently closed loops through back-splicing. High throughput sequencing technologies have identified thousands of circRNAs with high sequence conservation and cell type specific expression in eukaryotes. CircRNAs play multiple important roles in cellular physiology functioning as miRNA sponges, transcriptional regulators, RBP binding molecules, templates for protein translation, and immune regulators. In a clinical context, circRNAs expression is correlated with patient's clinicopathological features in cancers including breast, liver, gastric, colorectal, and lung cancer. Additionally, distinct properties of circRNAs, such as high stability, exonuclease resistance, and existence in body fluids, show promising role for circRNAs as molecular biomarkers for tumor diagnosis, non-invasive monitoring, prognosis, and therapeutic intervention. Therefore, it is critical to further understand the molecular mechanism underlying circRNAs interaction in tumors and the recent progress of this RNA species in cancer development. In this review, we provide a detailed description of biological functions, molecular role of circRNAs in different cancers, and its potential role as biomarkers in a clinical context.

Function and clinical significance of circRNAs in solid tumors

Circular RNA (circRNA) is a new type of endogenous non-coding RNAs (ncRNAs). circRNA regulates gene expression in many biological processes, and it also participates in the initiation and development of various diseases, including tumors, which are the focus of present research. With the development of high-throughput sequencing technique, an increasing number of circRNAs closely related to tumors have been discovered. According to numerous studies, there is a significant difference in the expressions of circRNAs among a variety of tumor tissues and para-carcinoma normal tissues. Some specifically expressed circRNAs may potentially serve as new biomarkers for tumor diagnosis and prognosis. This systemic review briefly introduces the characteristics, biogenesis, and functions of circRNAs, as well as discusses their relationship with cancer in detail. In addition, this article also describes several research strategies for circRNAs.

Overexpressed CDR1as functions as an oncogene to promote the tumor progression via miR-7 in non-small-cell lung cancer

Background

Circular RNA (circRNA) is a novel member of the noncoding RNA and function as efficient microRNA sponges with gene-regulatory potential, especially the circular RNA ciRS-7 (CDR1as)/tumor suppressor miRNA-7 (miR-7) signals. However, the function of CDR1as/miR-7 in non-small cell lung cancer (NSCLC) is unknown.

Methods

Normal lung tissues (n=20), adjacent non-tumor tissues (n=60), and NSCLC tissues (n=60) were collected to determine the expression and significance of CDR1as/miR-7. Lung cancer cell lines A549 and H460 were overexpressed or knocked down of CDR1as, miR-7 to determine the tumor growth etc. The CDR1as/miR-7-related pathway were analyzed.

Results

CDR1as levels was robustly increased with the development of NSCLC (P<0.001) and the NSCLC tissues harbored highest expression of CDR1as, which negatively correlated to the expression of miR-7. Patients with high expression of CDR1as had high TNM stage (P=0.004), more lymph nodes metastasis (LNM) (P=0.021) and shorted overall survival time (OS) (P=0.0135). The CDR1as level was an independent prognostic factor for the patients with NSCLC. Overexpression of CDR1as induced increased cell vitalities and growth, which could be abrogated by knockdown of CDR1as or overexpressed miR-7 to induce apoptosis and G1/S arrest. Mechanistically, CDR1as functioned as miR-7 sponges to up-regulate the key target genes of miR-7 including EGFR, CCNE1 and PIK3CD. The results in vivo further confirmed that CDR1as functioned as oncogene to inhibit the anti-tumor effects of tumor suppressor miR-7 by up-regulation of proliferation index Ki-67, EGFR, CCNE1 and PIK3CD levels.

Conclusion

Overexpressed CDR1as in NSCLC functions promotes the tumor progression via miR-7 signals.

Circular RNAs in Cancer - Lessons Learned From microRNAs

Circular RNAs (circRNA) are RNA molecules built from fragments of linear pre-messenger RNAs and other linear RNA species through a process termed "back-splicing" in which the 3' and 5' ends are joined together giving rise to a covalently uninterrupted loop. circRNAs are not new members of the RNA world; they were first discovered in the early 1990s. The novelty is their abundance in the mammalian cells, as recently thousands of circRNAs were discovered and annotated. The biogenesis of circRNAs is a partially characterized process, regulated by three different mechanisms: exon skipping, intron pairing, and RNA-binding proteins. On the other hand, the function of circRNAs remains largely unknown and only a handful of singular reports describe in detail the biological roles of some circular transcripts. In a very short period of time, numerous circRNAs were associated with various cancer types and were also identified in bodily fluids with the potential of being disease-specific biomarkers. In this review, we briefly describe the biogenesis and function of circRNAs and present the circular transcripts that were more than once reported in literature to be associated with cancer. Finally, we point out some of the difficulties encountered in the study of circRNAs in cancer, as we consider that taking these into account could accelerate and improve our understanding of the biologic and translational use of circRNAs in human diseases.

Preliminary investigation of the function of hsa_circ_0006215 in pancreatic cancer

The incidence of pancreatic cancer is increasing annually in Asia as a whole. Pancreatic cancer ranks sixth in terms of incidence of all malignant tumors. Circular RNA (circRNA) is a type of non-coding RNA which forms a covalently closed continuous loop. CircRNA is extensively expressed in the cytoplasm, and is markedly conservative and stable. MicroRNA (miR)-378a-3p and human (hsa)_circ_0006215 were detected using the reverse transcription-quantitative polymerase chain reaction (RT-qPCR) in tissue and cells. Western blot analysis detected the SERPINA4 and hsa_circ_0006215 expression in tissue. A Cell Counting Kit-8 assay was used to determine cell stability. Flow cytometry was used to determine the cell apoptotic rate. Transwell assays were used to determine cell migration. hsa_circ_0006215 was identified as a significantly upregulated circRNA. RT-qPCR results verified that, in 30 samples of pancreatic cancer tissue and paracancerous tissue, hsa_circ_0006215 expression was increased in pancreatic cancer tissue, miR-378a-3p expression was decreased in pancreatic cancer tissue, and SERPINA4 expression was increased in pancreatic cancer tissue (P<0.05). Using bioinformatics database and bioinformatics analysis, the interaction network of hsa_circ_0006215 indicated that this circRNA was most likely to regulate the expression of miR-378a-3p. Further interaction analysis revealed that the SERPINA4 gene was a regulatory target gene most likely to have an influence. The present study identified the effects of hsa_circ_0006215, miR-378a-3p and SERPINA4 signaling pathways in pancreatic cancer cells.

Polymorphisms and expression pattern of circular RNA circ-ITCH contributes to the carcinogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) ranks the sixth most common cancer and the third cause of cancer-related mortality worldwide. Recent studies identified that circ-ITCH Suppresses mutiple cancers proliferation via inhibiting the Wnt/beta-Catenin pathway. In current study, conducted a genetic association study together with epidemiological follow-up study to delineate the role of circ-ITCH in the development and progression of HCC. we found rs10485505 (adjusted OR =1.18; 95% CI=1.06-1.31; P value =3.1×10^-3) and rs4911154 (adjusted OR =1.27; 95% CI=1.14-1.43; P value =3.7×10^-5) were significantly associated with increased HCC risk. The expression level of circ-ITCH was significantly lower in HCC tissues, compared with that in adjacent tissues (P value < 0.001). Cox regression analysis indicated that high expression of circ-ITCH was associated with favorable survival of HCC (HR=0.45; 95% CI=0.29-0.68; P value < 0.001). These results indicate that circ-ITCH may have an inhibitory effect on HCC, and could serve as susceptibility and prognostic biomarkers for HCC patients.