Circular RNAs: Biogenesis, Mechanism, and Function in Human Cancers

CircRNAs are a class of noncoding RNA species with a circular configuration that is formed by either typical spliceosome-mediated or lariat-type splicing. The expression of circRNAs is usually abnormal in many cancers. Several circRNAs have been demonstrated to play important roles in carcinogenesis. In this review, we will first provide an introduction of circRNAs biogenesis, especially the regulation of circRNA by RNA-binding proteins, then we will focus on the recent findings of circRNA molecular mechanisms and functions in cancer development. Finally, some open questions are also discussed.

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The expanding world of metabolic enzymes moonlighting as RNA binding proteins

Biochemical Society Transactions ◽

10.1042/bst20200664 ◽

2021 ◽

Author(s):

Nicole J. Curtis ◽

Constance J. Jeffery

Keyword(s):

Gene Expression ◽

Regulatory Networks ◽

Binding Proteins ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Molecular Structures ◽

Intermediary Metabolism ◽

The Many ◽

And Function

RNA binding proteins play key roles in many aspects of RNA metabolism and function, including splicing, transport, translation, localization, stability and degradation. Within the past few years, proteomics studies have identified dozens of enzymes in intermediary metabolism that bind to RNA. The wide occurrence and conservation of RNA binding ability across distant branches of the evolutionary tree suggest that these moonlighting enzymes are involved in connections between intermediary metabolism and gene expression that comprise far more extensive regulatory networks than previously thought. There are many outstanding questions about the molecular structures and mechanisms involved, the effects of these interactions on enzyme and RNA functions, and the factors that regulate the interactions. The effects on RNA function are likely to be wider than regulation of translation, and some enzyme–RNA interactions have been found to regulate the enzyme's catalytic activity. Several enzyme–RNA interactions have been shown to be affected by cellular factors that change under different intracellular and environmental conditions, including concentrations of substrates and cofactors. Understanding the molecular mechanisms involved in the interactions between the enzymes and RNA, the factors involved in regulation, and the effects of the enzyme–RNA interactions on both the enzyme and RNA functions will lead to a better understanding of the role of the many newly identified enzyme–RNA interactions in connecting intermediary metabolism and gene expression.

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RNA-binding proteins in hematopoiesis and hematological malignancy

Blood ◽

10.1182/blood-2018-10-839985 ◽

2019 ◽

Vol 133 (22) ◽

pp. 2365-2373 ◽

Cited By ~ 8

Author(s):

Daniel J. Hodson ◽

Michael Screen ◽

Martin Turner

Keyword(s):

Noncoding Rna ◽

Binding Proteins ◽

Hematological Malignancies ◽

Rna Binding ◽

Rna Binding Proteins ◽

Dynamic Control ◽

Disease Biomarkers ◽

Therapeutic Modalities ◽

And Function ◽

Multiple Signaling

Abstract RNA-binding proteins (RBPs) regulate fundamental processes, such as differentiation and self-renewal, by enabling the dynamic control of protein abundance or isoforms or through the regulation of noncoding RNA. RBPs are increasingly appreciated as being essential for normal hematopoiesis, and they are understood to play fundamental roles in hematological malignancies by acting as oncogenes or tumor suppressors. Alternative splicing has been shown to play roles in the development of specific hematopoietic lineages, and sequence-specific mutations in RBPs lead to dysregulated splicing in myeloid and lymphoid leukemias. RBPs that regulate translation contribute to the development and function of hematological lineages, act as nodes for the action of multiple signaling pathways, and contribute to hematological malignancies. These insights broaden our mechanistic understanding of the molecular regulation of hematopoiesis and offer opportunities to develop disease biomarkers and new therapeutic modalities.

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Identification of Novel RNA Binding Proteins Influencing Circular RNA Expression in Hepatocellular Carcinoma

International Journal of Molecular Sciences ◽

10.3390/ijms22147477 ◽

2021 ◽

Vol 22 (14) ◽

pp. 7477

Author(s):

Rok Razpotnik ◽

Petra Nassib ◽

Tanja Kunej ◽

Damjana Rozman ◽

Tadeja Režen

Keyword(s):

Hepatocellular Carcinoma ◽

Binding Proteins ◽

Rna Binding ◽

Rna Binding Proteins ◽

Regulatory Protein ◽

Circular Rna ◽

Differentially Expressed ◽

Circular Rnas ◽

Bioinformatics Analyses ◽

Published Evidence

Circular RNAs (circRNAs) are increasingly recognized as having a role in cancer development. Their expression is modified in numerous cancers, including hepatocellular carcinoma (HCC); however, little is known about the mechanisms of their regulation. The aim of this study was to identify regulators of circRNAome expression in HCC. Using publicly available datasets, we identified RNA binding proteins (RBPs) with enriched motifs around the splice sites of differentially expressed circRNAs in HCC. We confirmed the binding of some of the candidate RBPs using ChIP-seq and eCLIP datasets in the ENCODE database. Several of the identified RBPs were found to be differentially expressed in HCC and/or correlated with the overall survival of HCC patients. According to our bioinformatics analyses and published evidence, we propose that NONO, PCPB2, PCPB1, ESRP2, and HNRNPK are candidate regulators of circRNA expression in HCC. We confirmed that the knocking down the epithelial splicing regulatory protein 2 (ESRP2), known to be involved in the maintenance of the adult liver phenotype, significantly changed the expression of candidate circRNAs in a model HCC cell line. By understanding the systemic changes in transcriptome splicing, we can identify new proteins involved in the molecular pathways leading to HCC development and progression.

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Comprehensive landscape and future perspectives of circular RNAs in colorectal cancer

Molecular Cancer ◽

10.1186/s12943-021-01318-6 ◽

2021 ◽

Vol 20 (1) ◽

Author(s):

Fei Long ◽

Zhi Lin ◽

Liang Li ◽

Min Ma ◽

Zhixing Lu ◽

...

Keyword(s):

Colorectal Cancer ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Circular Rnas ◽

Future Perspectives ◽

Cis Acting ◽

New Class ◽

Functional Peptides ◽

Mirna Sponges

AbstractColorectal cancer (CRC) is a common hereditary tumor that is often fatal. Its pathogenesis involves multiple genes, including circular RNAs (circRNAs). Notably, circRNAs constitute a new class of noncoding RNAs (ncRNAs) with a covalently closed loop structure and have been characterized as stable, conserved molecules that are abundantly expressed in tissue/development-specific patterns in eukaryotes. Based on accumulating evidence, circRNAs are aberrantly expressed in CRC tissues, cells, exosomes, and blood from patients with CRC. Moreover, numerous circRNAs have been identified as either oncogenes or tumor suppressors that mediate tumorigenesis, metastasis and chemoradiation resistance in CRC. Although the regulatory mechanisms of circRNA biogenesis and functions remain fairly elusive, interesting results have been obtained in studies investigating CRC. In particular, the expression of circRNAs in CRC is comprehensively modulated by multiple factors, such as splicing factors, transcription factors, specific enzymes and cis-acting elements. More importantly, circRNAs exert pivotal effects on CRC through various mechanisms, including acting as miRNA sponges or decoys, interacting with RNA binding proteins, and even translating functional peptides. Finally, circRNAs may serve as promising diagnostic and prognostic biomarkers and potential therapeutic targets in the clinical practice of CRC. In this review, we discuss the dysregulation, functions and clinical significance of circRNAs in CRC and further discuss the molecular mechanisms by which circRNAs exert their functions and how their expression is regulated. Based on this review, we hope to reveal the functions of circRNAs in the initiation and progression of cancer and highlight the future perspectives on strategies targeting circRNAs in cancer research.

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The effective function of circular RNA in colorectal cancer

Cancer Cell International ◽

10.1186/s12935-021-02196-0 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Mandana Ameli-Mojarad ◽

Melika Ameli-Mojarad ◽

Mahrooyeh Hadizadeh ◽

Chris Young ◽

Hosna Babini ◽

...

Keyword(s):

Colorectal Cancer ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Circular Rna ◽

Circular Rnas ◽

Colorectal Tumorigenesis ◽

Non Coding Rnas ◽

Mirna Sponges ◽

Mechanisms Of Development

AbstractColorectal cancer (CRC) is the 3rd most common type of cancer worldwide. Late detection plays role in one-third of annual mortality due to CRC. Therefore, it is essential to find a precise and optimal diagnostic and prognostic biomarker for the identification and treatment of colorectal tumorigenesis. Covalently closed, circular RNAs (circRNAs) are a class of non-coding RNAs, which can have the same function as microRNA (miRNA) sponges, as regulators of splicing and transcription, and as interactors with RNA-binding proteins (RBPs). Therefore, circRNAs have been investigated as specific targets for diagnostic and prognostic detection of CRC. These non-coding RNAs are also linked to metastasis, proliferation, differentiation, migration, angiogenesis, apoptosis, and drug resistance, illustrating the importance of understanding their involvement in the molecular mechanisms of development and progression of CRC. In this review, we present a detailed summary of recent findings relating to the dysregulation of circRNAs and their potential role in CRC.

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Insights into the multifaceted role of circular RNAs: implications for Parkinson’s disease pathogenesis and diagnosis

npj Parkinson s Disease ◽

10.1038/s41531-021-00265-9 ◽

2022 ◽

Vol 8 (1) ◽

Author(s):

Epaminondas Doxakis

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Rna Binding ◽

Rna Binding Proteins ◽

Clinical Manifestations ◽

Alpha Synuclein ◽

Circular Rnas ◽

Age Related ◽

And Function ◽

The Brain

AbstractParkinson’s disease (PD) is a complex, age-related, neurodegenerative disease whose etiology, pathology, and clinical manifestations remain incompletely understood. As a result, care focuses primarily on symptoms relief. Circular RNAs (circRNAs) are a large class of mostly noncoding RNAs that accumulate with aging in the brain and are increasingly shown to regulate all aspects of neuronal and glial development and function. They are generated by the spliceosome through the backsplicing of linear RNA. Although their biological role remains largely unknown, they have been shown to regulate transcription and splicing, act as decoys for microRNAs and RNA binding proteins, used as templates for translation, and serve as scaffolding platforms for signaling components. Considering that they are stable, diverse, and detectable in easily accessible biofluids, they are deemed promising biomarkers for diagnosing diseases. CircRNAs are differentially expressed in the brain of patients with PD, and growing evidence suggests that they regulate PD pathogenetic processes. Here, the biogenesis, expression, degradation, and detection of circRNAs, as well as their proposed functions, are reviewed. Thereafter, research linking circRNAs to PD-related processes, including aging, alpha-synuclein dysregulation, neuroinflammation, and oxidative stress is highlighted, followed by recent evidence for their use as prognostic and diagnostic biomarkers for PD.

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Structural basis for recognition of human 7SK long noncoding RNA by the La-related protein Larp7

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1806276115 ◽

2018 ◽

Vol 115 (28) ◽

pp. E6457-E6466 ◽

Cited By ~ 20

Author(s):

Catherine D. Eichhorn ◽

Yuan Yang ◽

Lucas Repeta ◽

Juli Feigon

Keyword(s):

Noncoding Rna ◽

Rna Binding ◽

Rna Binding Proteins ◽

Transcription Elongation ◽

Structural Basis ◽

Titration Calorimetry ◽

Rna Recognition Motif ◽

Related Protein ◽

Binding Interface ◽

And Function

The La and the La-related protein (LARP) superfamily is a diverse class of RNA binding proteins involved in RNA processing, folding, and function. Larp7 binds to the abundant long noncoding 7SK RNA and is required for 7SK ribonucleoprotein (RNP) assembly and function. The 7SK RNP sequesters a pool of the positive transcription elongation factor b (P-TEFb) in an inactive state; on release, P-TEFb phosphorylates RNA Polymerase II to stimulate transcription elongation. Despite its essential role in transcription, limited structural information is available for the 7SK RNP, particularly for protein–RNA interactions. Larp7 contains an N-terminal La module that binds UUU-3′OH and a C-terminal atypical RNA recognition motif (xRRM) required for specific binding to 7SK and P-TEFb assembly. Deletion of the xRRM is linked to gastric cancer in humans. We report the 2.2-Å X-ray crystal structure of the human La-related protein group 7 (hLarp7) xRRM bound to the 7SK stem-loop 4, revealing a unique binding interface. Contributions of observed interactions to binding affinity were investigated by mutagenesis and isothermal titration calorimetry. NMR 13C spin relaxation data and comparison of free xRRM, RNA, and xRRM–RNA structures show that the xRRM is preordered to bind a flexible loop 4. Combining structures of the hLarp7 La module and the xRRM–7SK complex presented here, we propose a structural model for Larp7 binding to the 7SK 3′ end and mechanism for 7SK RNP assembly. This work provides insight into how this domain contributes to 7SK recognition and assembly of the core 7SK RNP.

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Evolution of the Small Family of Alternative Splicing Modulators Nuclear Speckle RNA-Binding Proteins in Plants

Genes ◽

10.3390/genes11020207 ◽

2020 ◽

Vol 11 (2) ◽

pp. 207 ◽

Cited By ~ 2

Author(s):

Leandro Lucero ◽

Jeremie Bazin ◽

Johan Rodriguez Melo ◽

Fernando Ibañez ◽

Martín D. Crespi ◽

...

Keyword(s):

Alternative Splicing ◽

Medicago Truncatula ◽

Noncoding Rna ◽

Binding Proteins ◽

Rna Binding ◽

Rna Binding Proteins ◽

Nodule Development ◽

Nuclear Speckle ◽

Symbiotic Nodule

RNA-Binding Protein 1 (RBP1) was first identified as a protein partner of the long noncoding RNA (lncRNA) ENOD40 in Medicago truncatula, involved in symbiotic nodule development. RBP1 is localized in nuclear speckles and can be relocalized to the cytoplasm by the interaction with ENOD40. The two closest homologs to RBP1 in Arabidopsis thaliana were called Nuclear Speckle RNA-binding proteins (NSRs) and characterized as alternative splicing modulators of specific mRNAs. They can recognize in vivo the lncRNA ALTERNATIVE SPLICING COMPETITOR (ASCO) among other lncRNAs, regulating lateral root formation. Here, we performed a phylogenetic analysis of NSR/RBP proteins tracking the roots of the family to the Embryophytes. Strikingly, eudicots faced a reductive trend of NSR/RBP proteins in comparison with other groups of flowering plants. In Medicago truncatula and Lotus japonicus, their expression profile during nodulation and in specific regions of the symbiotic nodule was compared to that of the lncRNA ENOD40, as well as to changes in alternative splicing. This hinted at distinct and specific roles of each member during nodulation, likely modulating the population of alternatively spliced transcripts. Our results establish the basis to guide future exploration of NSR/RBP function in alternative splicing regulation in different developmental contexts along the plant lineage.

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P5398CircRNAs deregulation in heart failure patients

European Heart Journal ◽

10.1093/eurheartj/ehz746.0358 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

S Greco ◽

A Made' ◽

M Longo ◽

R Tikhomirov ◽

S Castelvecchio ◽

...

Keyword(s):

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Functional Characterization ◽

Enrichment Analysis ◽

Host Gene ◽

Circular Rnas ◽

Amplification Efficiency ◽

Rna Seq ◽

Bioinformatics Pipeline

Abstract Background Circular RNAs (circRNAs) are an emerging class of noncoding RNAs stemming from the splicing and circularization of pre-mRNAs exons. CircRNAs can regulate transcription and splicing, sequester microRNAs acting as “sponge” and inducing the respective targets, and bind to RNA binding proteins. Recently, they have been found deregulated in dilated cardiomyopathies (DCM), one of the cardiovascular diseases with the worst rate of morbidity and mortality, and whose molecular mechanisms are only partially known. Purpose Therein, we will evaluate in ischemic DCM patients the modulation of 17 circRNAs, 14 out of them obtained from literature data on DCM ischemic or not, while the other 3 were circRNAs not characterized in the heart previously. The study aims to identify circRNAs candidates for further functional characterization in DCM. In addition, as differential expression (DE) analysis is not easily performed for circRNAs in RNA-seq datasets, the validated circRNAs will be used to set up the most specific and sensitive bioinformatics pipeline for circRNA-DE analysis. Methods We designed divergent and convergent specific primers for 17 circRNAs and their host gene, respectively, and their amplification efficiency was measured by RT-qPCR. Transcripts expression was measured in left ventricle biopsies of 12 patients affected by non end-stage ischemic HF and of 12 matched controls. Results We identified cPVT1, cANKRD17, cBPTF as DE, and validated the modulation of 5 out of the 14 DCM-related circRNAs (cHIPK3, cALPK2, cPCMTD1, cNEBL, cSLC8A1), while cPDRM5, cTTN1 showed opposite modulation, which may be due to the specific disease condition. All of them were modulated differently from the respective host gene. CircRNA/miRNA interactions were predicted using Starbase 3.0. Next, mRNAs-targets of the identified miRNAs were predicted by mirDIP 4.1 and intersected with gene expression datasets of the same patients, previously obtained by microarray analysis. We found that cBPTF and cANKRD17 might sponge 12 and 2 miRNAs, respectively. Enrichment analysis of the relevant targets identified several important pathways implicated in DCM, such as MAPK, FoxO, EGFR, VEGF and Insulin/IGF pathways. In addition, deep RNA-Seq analysis that is currently ongoing and the validated circRNAs will be used to optimize the bioinformatics pipeline for circRNA DE analysis. Conclusions We identified a subset of circRNAs deregulated in ischemic HF potentially implicated in HF pathogenesis.

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First Identification of RNA-Binding Proteins That Regulate Alternative Exons in the Dystrophin Gene

International Journal of Molecular Sciences ◽

10.3390/ijms21207803 ◽

2020 ◽

Vol 21 (20) ◽

pp. 7803

Author(s):

Julie Miro ◽

Anne-Laure Bougé ◽

Eva Murauer ◽

Emmanuelle Beyne ◽

Dylan Da Cunha ◽

...

Keyword(s):

Large Scale ◽

Binding Proteins ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Dystrophin Gene ◽

Rna Seq ◽

Spatio Temporal ◽

Dmd Gene ◽

Shed Light

The Duchenne muscular dystrophy (DMD) gene has a complex expression pattern regulated by multiple tissue-specific promoters and by alternative splicing (AS) of the resulting transcripts. Here, we used an RNAi-based approach coupled with DMD-targeted RNA-seq to identify RNA-binding proteins (RBPs) that regulate splicing of its skeletal muscle isoform (Dp427m) in a human muscular cell line. A total of 16 RBPs comprising the major regulators of muscle-specific splicing events were tested. We show that distinct combinations of RBPs maintain the correct inclusion in the Dp427m of exons that undergo spatio-temporal AS in other dystrophin isoforms. In particular, our findings revealed the complex networks of RBPs contributing to the splicing of the two short DMD exons 71 and 78, the inclusion of exon 78 in the adult Dp427m isoform being crucial for muscle function. Among the RBPs tested, QKI and DDX5/DDX17 proteins are important determinants of DMD exon inclusion. This is the first large-scale study to determine which RBP proteins act on the physiological splicing of the DMD gene. Our data shed light on molecular mechanisms contributing to the expression of the different dystrophin isoforms, which could be influenced by a change in the function or expression level of the identified RBPs.

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