circRNAs and Exosomes: A Mysterious Frontier for Human Cancer

Engineering circular RNA for molecular and metabolic reprogramming

The role of messenger RNA (mRNA) in biological systems is extremely versatile. However, it's extremely short half-life poses a fundamental restriction on its application. Moreover, the translation efficiency of mRNA is also limited. On the contrary, circular RNAs, also known as circRNAs, are a common and stable form of RNA found in eukaryotic cells. These molecules are synthesized via back-splicing. Both synthetic circRNAs and certain endogenous circRNAs have the potential to encode proteins, hence suggesting the potential of circRNA as a gene expression machinery. Herein, we aim to summarize all engineering aspects that allow exogenous circular RNA (circRNA) to prolong the time that proteins are expressed from full-length RNA signals. This review presents a systematic engineering approach that have been devised to efficiently assemble circRNAs and evaluate several aspects that have an impact on protein production derived from. We have also reviewed how optimization of the key components of circRNAs, including the topology of vector, 5' and 3' untranslated sections, entrance site of the internal ribosome, and engineered aptamers could be efficiently impacting the translation machinery for molecular and metabolic reprogramming. Collectively, molecular and metabolic reprogramming present a novel way of regulating distinctive cellular features, for instance growth traits to neoplastic cells, and offer new possibilities for therapeutic inventions.

Pathways for macrophage uptake of cell-free circular RNAs

Circular RNAs (circRNAs) are stable RNAs present in cell-free RNA, which may comprise cellular debris and pathogen genomes. Here, we investigate the phenomenon and mechanism of cellular uptake and intracellular fate of exogenous circRNAs. Human myeloid cells and B cells selectively internalize extracellular circRNAs. Macrophage uptake of circRNA is rapid, energy dependent, and saturable. CircRNA uptake can lead to translation of encoded sequences and antigen presentation. The route of internalization influences immune activation after circRNA uptake, with distinct gene expression programs depending on the route of RNA delivery. Genome-scale CRISPR screens and chemical inhibitor studies nominate macrophage scavenger receptor MSR1, Toll-like receptors, and mTOR signaling as key regulators of receptor-mediated phagocytosis of circRNAs, a dominant pathway to internalize circRNAs in parallel to macropinocytosis. These results suggest that cell-free circRNA serves as an "eat me" signal and danger-associated molecular pattern, indicating orderly pathways of recognition and disposal.

Computational approaches and challenges in the analysis of circRNA data

Circular RNAs (circRNA) are a class of non-coding RNA, forming a single-stranded covalently closed loop structure generated via back-splicing. Advancements in sequencing methods and technologies in conjunction with algorithmic developments of bioinformatics tools have enabled researchers to characterise the origin and function of circRNAs, with practical applications as a biomarker of diseases becoming increasingly relevant. Computational methods developed for circRNA analysis are predicated on detecting the chimeric back-splice junction of circRNAs whilst mitigating false-positive sequencing artefacts. In this review, we discuss in detail the computational strategies developed for circRNA identification, highlighting a selection of tool strengths, weaknesses and assumptions. In addition to circRNA identification tools, we describe methods for characterising the role of circRNAs within the competing endogenous RNA (ceRNA) network, their interactions with RNA-binding proteins, and publicly available databases for rich circRNA annotation.

Prognostic and clinical value of circPRKCI expression in diverse human cancers

BACKGROUND

Highly expressed in various human cancers, circular RNA Protein Kinase C Iota (circPRKCI) has been reported to play an important role in cancer development and progression. Herein, we sought to reveal the prognostic and clinical value of circPRKCI expression in diverse human cancers.

METHODS

We searched the Pubmed, Web of Science, and the Cochrane Library databases from inception until May 16, 2021. The relationship between circPRKCI expression and cancer patients' survival, including overall survival (OS) and disease-free survival (DFS), was assessed by pooled hazard ratios (HR) with corresponding 95% confidence interval (CI). The correlation between circPRKCI expression and clinical outcomes was evaluated using odds ratios (OR) with corresponding 95% CI. The data were analyzed by STATA software (version 12.0) or Review Manager (RevMan 5.3).

RESULTS

A total of 15 studies with 1109 patients were incorporated into our meta-analysis. The results demonstrated that high circPRKCI expression was significantly related to poor OS (HR = 1.96, 95% CI: 1.61, 2.39, P <0.001) when compared with low circPRKCI expression in diverse human cancers. However, elevated circPRKCI expression was not associated with DFS (HR = 1.34, 95% CI: 0.93, 1.95, P = 0.121). Furthermore, the patient with a higher circPRKCI expression was prone to have a larger tumor size, advanced clinical stage, and lymph node metastasis, but it was not significantly correlated with age, gender, and distant metastasis.

CONCLUSION

Elevated circPRKCI expression was correlated with worse OS and unfavorable clinical features, suggesting a novel prognostic and predictive role of circPRKCI in diverse human cancers.

Exosomes derived from cancer-associated fibroblasts promote tumorigenesis, metastasis and chemoresistance of colorectal cancer by upregulating circ_0067557 to target Lin28

BACKGROUND

Cancer associated fibroblasts (CAFs) can remodel tumor microenvironment by secreting exosomes. This study aimed to investigate the role of exosomes derived from cancer-associated fibroblasts in colorectal cancer (CRC) progression.

METHODS

Circular RNA (circRNA) array was used to identify differentially expressed circRNAs in exosomes from normal fibroblasts (NFs) and CAFs, and confirmed one differentially expressed circRNA circ_0067557 by real-time PCR. The effect of circ_0067557 on proliferation, metastasis, chemoresistance and apoptosis was verified by wound heal, tranwell, CCK8, sphere-forming and flow cytometry assay.

RESULTS

Circ_0067557 expression in exosomes from CAFs was higher than those from NFs. CAF-derived exosomes promoted the proliferation, migration, invasion and chemoresistance of CRC cells while suppressed apoptosis. Silencing of circ_0067557 inhibited malignant phenotypes of CRC cells by targeting Lin28A and Lin28B. Moreover, CAF-derived exosomes enhanced the growth of CRC xenograft tumors.

CONCLUSION

Circ_0067557/Lin28A and Lin28B signal axis may be a potential therapy target for CRC.

Specific Circular RNA Signature of Endothelial Cells: Potential Implications in Vascular Pathophysiology

Circular RNAs (circRNAs) are a recently characterized family of gene transcripts forming a covalently closed loop of single-stranded RNA. The extent of their potential for fine-tuning gene expression is still being discovered. Several studies have implicated certain circular RNAs in pathophysiological processes within vascular endothelial cells and cancer cells independently. However, to date, no comparative study of circular RNA expression in different types of endothelial cells has been performed and analysed through the lens of their central role in vascular physiology and pathology. In this work, we analysed publicly available and original RNA sequencing datasets from arterial, veinous, and lymphatic endothelial cells to identify common and distinct circRNA expression profiles. We identified 4713 distinct circRNAs in the compared endothelial cell types, 95% of which originated from exons. Interestingly, the results show that the expression profile of circular RNAs is much more specific to each cell type than linear RNAs, and therefore appears to be more suitable for distinguishing between them. As a result, we have discovered a specific circRNA signature for each given endothelial cell type. Furthermore, we identified a specific endothelial cell circRNA signature that is composed four circRNAs: circCARD6, circPLXNA2, circCASC15 and circEPHB4. These circular RNAs are produced by genes that are related to endothelial cell migration pathways and cancer progression. More detailed studies of their functions could lead to a better understanding of the mechanisms involved in physiological and pathological (lymph)angiogenesis and might open new ways to tackle tumour spread through the vascular system.

Exosomal non-coding RNAs: Blueprint in colorectal cancer metastasis and therapeutic targets

Colorectal cancer (CRC) is ranked as the world's third-most prevalent cancer, and metastatic CRC considerably increases cancer-related fatalities globally. A number of complex mechanisms that are strictly controlled at the molecular level are involved in metastasis, which is the primary reason for death in people with CRC. Recently, it has become clear that exosomes, which are small extracellular vesicles released by non-tumorous and tumorigenic cells, play a critical role as communication mediators among tumor microenvironment (TME). To facilitate communication between the TME and cancer cells, non-coding RNAs (ncRNAs) play a crucial role and are recognized as potent regulators of gene expression and cellular processes, such as metastasis and drug resistance. NcRNAs are now recognized as potent regulators of gene expression and many hallmarks of cancer, including metastasis. Exosomal ncRNAs, like miRNAs, circRNAs, and lncRNAs, have been demonstrated to influence a number of cellular mechanisms that contribute to CRC metastasis. However, the molecular mechanisms that link exosomal ncRNAs with CRC metastasis are not well understood. This review highlights the essential roles that exosomal ncRNAs play in the progression of CRC metastatic disease and explores the therapeutic choices that are open to patients who have CRC metastases. However, exosomal ncRNA treatment strategy development is still in its early phases; consequently, additional investigation is required to improve delivery methods and find novel therapeutic targets as well as confirm the effectiveness and safety of these therapies in preclinical and clinical contexts.

Decrypting the circular RNAs does a favor for us: Understanding, diagnosing and treating diabetes mellitus and its complications

Circular RNAs (circRNAs), a novel type of single-stranded noncoding RNAs with a covalently closed loop structure, are generated in a circular conformation via non-canonical splicing or back-splicing events. Functionally, circRNAs have been elucidated to soak up microRNAs (miRNAs) and RNA binding proteins (RBPs), serve as protein scaffolds, maintain mRNA stability, and regulate gene transcription and translation. Notably, circRNAs are strongly implicated in the regulation of β-cell functions, insulin resistance, adipocyte functions, inflammation as well as oxidative stress via acting as miRNA sponges and RBP sponges. Basic and clinical studies have demonstrated that aberrant alterations of circRNAs expressions are strongly associated with the initiation and progression of diabetes mellitus (DM) and its complications. Here in this review, we present a summary of the biogenesis, transportation, degradation and functions of circRNAs, and highlight the recent findings on circRNAs and their action mechanisms in DM and its complications. Overall, this review should contribute greatly to our understanding of circRNAs in DM pathogenesis, offering insights into the further perspectives of circRNAs for DM diagnosis and therapy.

miRNAs as short non-coding RNAs in regulating doxorubicin resistance

The treatment of cancer patients has been prohibited by chemoresistance. Doxorubicin (DOX) is an anti-tumor compound disrupting proliferation and triggering cell cycle arrest via inhibiting activity of topoisomerase I and II. miRNAs are endogenous RNAs localized in cytoplasm to reduce gene level. Abnormal expression of miRNAs changes DOX cytotoxicity. Overexpression of tumor-promoting miRNAs induces DOX resistance, while tumor-suppressor miRNAs inhibit DOX resistance. The miRNA-mediated regulation of cell death and hallmarks of cancer can affect response to DOX chemotherapy in tumor cells. The transporters such as P-glycoprotein are regulated by miRNAs in DOX chemotherapy. Upstream mediators including lncRNAs and circRNAs target miRNAs in affecting capacity of DOX. The response to DOX chemotherapy can be facilitated after administration of agents that are mostly phytochemicals including curcumol, honokiol and ursolic acid. These agents can regulate miRNA expression increasing DOX's cytotoxicity. Since delivery of DOX alone or in combination with other drugs and genes can cause synergistic impact, the nanoparticles have been introduced for drug sensitivity. The non-coding RNAs determine the response of tumor cells to doxorubicin chemotherapy. microRNAs play a key role in this case and they can be sponged by lncRNAs and circRNAs, showing interaction among non-coding RNAs in the regulation of doxorubicin sensitivity.

New insight into circRNAs: characterization, strategies, and biomedical applications

Circular RNAs (circRNAs) are a class of covalently closed, endogenous ncRNAs. Most circRNAs are derived from exonic or intronic sequences by precursor RNA back-splicing. Advanced high-throughput RNA sequencing and experimental technologies have enabled the extensive identification and characterization of circRNAs, such as novel types of biogenesis, tissue-specific and cell-specific expression patterns, epigenetic regulation, translation potential, localization and metabolism. Increasing evidence has revealed that circRNAs participate in diverse cellular processes, and their dysregulation is involved in the pathogenesis of various diseases, particularly cancer. In this review, we systematically discuss the characterization of circRNAs, databases, challenges for circRNA discovery, new insight into strategies used in circRNA studies and biomedical applications. Although recent studies have advanced the understanding of circRNAs, advanced knowledge and approaches for circRNA annotation, functional characterization and biomedical applications are continuously needed to provide new insights into circRNAs. The emergence of circRNA-based protein translation strategy will be a promising direction in the field of biomedicine.

The role of ncRNA in the co-regulation of autophagy and exosome pathways during cancer progression

Since its discovery a few decades ago, autophagy has been recognized as a crucial signaling pathway, linked to the recycling of cellular components in nutrient stress. Autophagy is a two-way sword, playing a dual role in tumorigenesis. In this catabolic process, dysfunctional organelles, biomolecules, and misfolded proteins are sequestered in the autophagosome and sent to the lysosome for degradation. Alongside, there are cellular messengers called exosomes, which are released from cells and are known to communicate and regulate metabolism in recipient cells. Multivesicular bodies (MVB) act as the intricate link between autophagy and exosome pathways. The continuous crosstalk between the two pathways is coordinated and regulated by multiple players among which ncRNA is the emerging candidates. The exosomes carry varied cargo of which non-coding RNA exerts an immediate regulatory effect on recipient cells. ncRNA is known to exhibit dual behavior in both promoting and inhibiting tumor growth. There is increasing evidence for the involvement of ncRNAs' in the regulation of different hallmarks of cancer. Different ncRNAs are involved in the co-regulation of autophagy and exosome pathways and therefore represent a superior therapeutic approach to target cancer chemoresistance. Here, we will discuss the ncRNA involved in regulating autophagy, and exosomes pathways and its relevance in cancer therapeutics.

CircRNAs: A Promising Star for Treatment and Prognosis in Oral Squamous Cell Carcinoma

CircRNAs are a class of endogenous long non-coding RNAs with a single-stranded circular structure. Most circRNAs are relatively stable, highly conserved, and specifically expressed in tissue during the cell and developmental stages. Many circRNAs have been discovered in OSCC. OSCC is one of the most severe and frequent forms of head and neck cancer today, with a poor prognosis and low overall survival rate. Due to its prevalence, OSCC is a global health concern, characterized by genetic and epigenomic changes. However, the mechanism remains vague. With the advancement of biotechnology, a large number of circRNAs have been discovered in mammalian cells. CircRNAs are dysregulated in OSCC tissues and thus associated with the clinicopathological characteristics and prognosis of OSCC patients. Research studies have demonstrated that circRNAs can serve as biomarkers for OSCC diagnosis and treatment. Here, we summarized the properties, functions, and biogenesis of circRNAs, focusing on the progress of current research on circRNAs in OSCC.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: An Emerging Diagnostic and Therapeutic Biomolecules for Neurodegenerative Disabilities

Mesenchymal stem cells (MSCs) are a type of versatile adult stem cells present in various organs. These cells give rise to extracellular vesicles (EVs) containing a diverse array of biologically active elements, making them a promising approach for therapeutics and diagnostics. This article examines the potential therapeutic applications of MSC-derived EVs in addressing neurodegenerative disorders such as Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). Furthermore, the present state-of-the-art for MSC-EV-based therapy in AD, HD, PD, ALS, and MS is discussed. Significant progress has been made in understanding the etiology and potential treatments for a range of neurodegenerative diseases (NDs) over the last few decades. The contents of EVs are carried across cells for intercellular contact, which often results in the control of the recipient cell's homeostasis. Since EVs represent the therapeutically beneficial cargo of parent cells and are devoid of many ethical problems connected with cell-based treatments, they offer a viable cell-free therapy alternative for tissue regeneration and repair. Developing innovative EV-dependent medicines has proven difficult due to the lack of standardized procedures in EV extraction processes as well as their pharmacological characteristics and mechanisms of action. However, recent biotechnology and engineering research has greatly enhanced the content and applicability of MSC-EVs.

Functional Involvement of circRNAs in the Innate Immune Responses to Viral Infection

Effective viral clearance requires fine-tuned immune responses to minimize undesirable inflammatory responses. Circular RNAs (circRNAs) are a class of non-coding RNAs that are abundant and highly stable, formed by backsplicing pre-mRNAs, and expressed ubiquitously in eukaryotic cells, emerging as critical regulators of a plethora of signaling pathways. Recent progress in high-throughput sequencing has enabled a better understanding of the physiological and pathophysiological functions of circRNAs, overcoming the obstacle of the sequence overlap between circRNAs and their linear cognate mRNAs. Some viruses also encode circRNAs implicated in viral replication or disease progression. There is increasing evidence that viral infections dysregulate circRNA expression and that the altered expression of circRNAs is critical in regulating viral infection and replication. circRNAs were shown to regulate gene expression via microRNA and protein sponging or via encoding small polypeptides. Recent studies have also highlighted the potential role of circRNAs as promising diagnostic and prognostic biomarkers, RNA vaccines and antiviral therapy candidates due to their higher stability and lower immunogenicity. This review presents an up-to-date summary of the mechanistic involvement of circRNAs in innate immunity against viral infections, the current understanding of their regulatory roles, and the suggested applications.

Cisplatin in Liver Cancer Therapy

Hepatocellular carcinoma (HCC) is the most common primary liver tumor and is often diagnosed at an unresectable advanced stage. Systemic chemotherapy as well as transarterial chemoembolization (TACE) and hepatic arterial infusion chemotherapy (HAIC) are used to treat advanced HCC. TACE and HAIC have long been the standard of care for patients with unresectable HCC but are limited to the treatment of intrahepatic lesions. Systemic chemotherapy with doxorubicin or chemohormonal therapy with tamoxifen have also been considered, but neither has demonstrated survival benefits. In the treatment of unresectable advanced HCC, cisplatin is administered transhepatic arterially for local treatment. Subsequently, for cisplatin-refractory cases due to drug resistance, a shift to systemic therapy with a different mechanism of action is expected to produce new antitumor effects. Cisplatin is also used for the treatment of liver tumors other than HCC. This review summarizes the action and resistance mechanism of cisplatin and describes the treatment of the major hepatobiliary cancers for which cisplatin is used as an anticancer agent, with a focus on HCC.

Smoking-Induced M2-TAMs, via circEML4 in EVs, Promote the Progression of NSCLC through ALKBH5-Regulated m6A Modification of SOCS2 in NSCLC Cells

Lung cancer is a commonly diagnosed disease worldwide, with non-small cell lung cancers (NSCLCs) accounting for ≈ 85% of cases. Cigarette smoke is an environmental exposure promoting progression of NSCLC, but its role is poorly understood. This study reports that smoking-induced accumulation of M2-type tumor-associated macrophages (M2-TAMs) surrounding NSCLC tissues promotes malignancy. Specifically, extracellular vesicles (EVs) from cigarette smoke extract (CSE)-induced M2 macrophages promoted malignancy of NSCLC cells in vitro and in vivo. circEML4 in EVs from CSE-induced M2 macrophages is transported to NSCLC cells, where it reduced the distribution of ALKBH5 in the nucleus by interacting with Human AlkB homolog H5 (ALKBH5), resulting in elevated N6-methyladenosine (m6A) modifications. m6A-seq and RNA-seq revealed suppressor of cytokine signaling 2 (SOCS2)-mediated activation of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway by regulating m6A modification of SOCS2 via ALKBH5. Down-regulation of circEML4 in EVs from CSE-induced M2 macrophages reversed EVs-enhanced tumorigenicity and metastasis in NSCLC cells. Furthermore, this study found that smoking patients showed an increase in circEML4-positive M2-TAMs. These results indicate that smoking-induced M2-TAMs via circEML4 in EVs promote the NSCLC progression through ALKBH5-regulated m6A modification of SOCS2. This study also reveals that circEML4 in EVs from TAMs acts as a diagnostic biomarker for NSCLC, especially for patients with smoking history.

The miRNA Content of Bone Marrow-Derived Extracellular Vesicles Contributes to Protein Pathway Alterations Involved in Ionising Radiation-Induced Bystander Responses

Extracellular vesicles (EVs), through their cargo, are important mediators of bystander responses in the irradiated bone marrow (BM). MiRNAs carried by EVs can potentially alter cellular pathways in EV-recipient cells by regulating their protein content. Using the CBA/Ca mouse model, we characterised the miRNA content of BM-derived EVs from mice irradiated with 0.1 Gy or 3 Gy using an nCounter analysis system. We also analysed proteomic changes in BM cells either directly irradiated or treated with EVs derived from the BM of irradiated mice. Our aim was to identify key cellular processes in the EV-acceptor cells regulated by miRNAs. The irradiation of BM cells with 0.1 Gy led to protein alterations involved in oxidative stress and immune and inflammatory processes. Oxidative stress-related pathways were also present in BM cells treated with EVs isolated from 0.1 Gy-irradiated mice, indicating the propagation of oxidative stress in a bystander manner. The irradiation of BM cells with 3 Gy led to protein pathway alterations involved in the DNA damage response, metabolism, cell death and immune and inflammatory processes. The majority of these pathways were also altered in BM cells treated with EVs from mice irradiated with 3 Gy. Certain pathways (cell cycle, acute and chronic myeloid leukaemia) regulated by miRNAs differentially expressed in EVs isolated from mice irradiated with 3 Gy overlapped with protein pathway alterations in BM cells treated with 3 Gy EVs. Six miRNAs were involved in these common pathways interacting with 11 proteins, suggesting the involvement of miRNAs in the EV-mediated bystander processes. In conclusion, we characterised proteomic changes in directly irradiated and EV-treated BM cells, identified processes transmitted in a bystander manner and suggested miRNA and protein candidates potentially involved in the regulation of these bystander processes.

Circ_0000395 Promoted CRC Progression via Elevating MYH9 Expression by Sequestering miR-432-5p

Colorectal cancer (CRC) has been listed as the fourth deadly cancer. Circular RNA hsa_circRNA_001046, also termed as hsa_circ_0000395 (circ_0000395), has been shown to be upregulated in CRC. Nevertheless, the function of circ_0000395 in CRC progression is unclear. 42 CRC patients were enrolled in the study. Detection of circ_0000395 expression in tissues and cells was executed using real-time quantitative polymerase chain reaction (RT-qPCR). Evaluation of circ_0000395 function was performed using loss-of-function experiments in vitro and in vivo. The regulatory mechanism of circ_0000395 was predicted by bioinformatics analysis and validated by dual-luciferase reporter and RIP assays. Exosomes were isolated by ultracentrifugation and validated by western blotting, TEM, and NTA. Circ_0000395 was strongly expressed in CRC samples and cell lines. Also, circ_0000395 repressed CRC growth in mouse models in vivo and induced CRC cell apoptosis, restrained CRC cell proliferation, migration, invasion, and EMT in vitro. Mechanistically, circ_0000395 sequestered miR-432-5p to regulate MYH9 expression. Furthermore, miR-432-5p knockdown reversed circ_0000395 silencing-mediated effects on CRC cell malignant phenotypes. MYH9 overexpression counteracted the inhibiting effects of miR-432-5p upregulation on CRC cell malignant phenotypes. Additionally, CRC cells derived from exosomal circ_0000395 promoted cancer cell malignant phenotypes. Our findings demonstrated that circ_0000395 sequestered miR-432-5p to elevate MYH9 expression, resulting in facilitating CRC progression, manifesting a potential therapeutic target for CRC.

Tumor-Derived Extracellular Vesicles: Multifunctional Entities in the Tumor Microenvironment

Tumor cells release extracellular vesicles (EVs) that can function as mediators of intercellular communication in the tumor microenvironment. EVs contain a host of bioactive cargo, including membrane, cytosolic, and nuclear proteins, in addition to noncoding RNAs, other RNA types, and double-stranded DNA fragments. These shed vesicles may deposit paracrine information and can also be taken up by stromal cells, causing the recipient cells to undergo phenotypic changes that profoundly impact diverse facets of cancer progression. For example, this unique form of cellular cross talk helps condition the premetastatic niche, facilitates evasion of the immune response, and promotes invasive and metastatic activity. These findings, coupled with those demonstrating that the number and content of EVs produced by tumors can vary depending on their tumor of origin, disease stage, or response to therapy, have raised the exciting possibility that EVs can be used for risk stratification, diagnostic, and even prognostic purposes. We summarize recent developments and the current knowledge of EV cargoes, their impact on disease progression, and implementation of EV-based liquid biopsies as tumor biomarkers.

Recent Advances of Circular RNAs as Biomarkers for Osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor in young adult, which is prone to early metastasis and poor prognosis. The current treatment methods need to be improved. Circular RNA is a covalently blocked circular, non-coding RNA that plays an essential role in the occurrence, development, clinical diagnosis, and treatment of various diseases. Recently, an increasing number of circRNAs have been identified in osteosarcoma. Understanding its role in osteosarcoma is conducive to the early detection, diagnosis, and treatment of osteosarcoma. In this paper, we reviewed the mechanism of action of circular RNA in the occurrence and development of osteosarcoma and its clinical application in recent years.

The emerging role of noncoding RNAs in systemic lupus erythematosus: new insights into the master regulators of disease pathogenesis

Auto-immune diseases are a form of chronic disorders in which the immune system destroys the body's cells due to a loss of tolerance to self-antigens. Systemic lupus erythematosus (SLE), identified by the production of autoantibodies in different body parts, is one of the most well-known examples of these diseases. Although the etiology of SLE is unclear, the disease's progression may be affected by genetic and environmental factors. As studies in twins provide adequate evidence for genetic involvement in the SLE, other phenomena such as metallization, histone modifications, and alterations in the expression of noncoding RNAs (ncRNAs) also indicate the involvement of epigenetic factors in this disease. Among all the epigenetic alterations, ncRNAs appear to have the most crucial contribution to the pathogenesis of SLE. The ncRNAs' length and size are divided into three main classes: micro RNAs, long noncoding RNAs (LncRNA), and circular RNAs (circRNAs). Accumulating evidence suggests that dysregulations in these ncRNAs contributed to the pathogenesis of SLE. Hence, clarifying the function of these groups of ncRNAs in the pathophysiology of SLE provides a deeper understanding of the disease. It also opens up new opportunities to develop targeted therapies for this disease.

Exosomes in bone remodeling and breast cancer bone metastasis

Exosomes are endosome-derived microvesicles that carry cell-specific biological cargo, such as proteins, lipids, and noncoding RNAs (ncRNAs). They play a key role in bone remodeling by enabling the maintenance of a balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Recent evidence indicates that exosomes disrupt bone remodeling that occurs during breast cancer (BC) progression. The bone is a preferred site for BC metastasis owing to its abundant osseous reserves. In this review, we aimed to highlight the roles of exosomes derived from bone cells and breast tumor in bone remodeling and BC bone metastasis (BCBM). We also briefly outline the mechanisms of action of ncRNAs and proteins carried by exosomes secreted by bone and BCBM. Furthermore, this review highlights the potential of utilizing exosomes as biomarkers or delivery vehicles for the diagnosis and treatment of BCBM.

The diagnostic significance of blood-derived circRNAs in NSCLC: Systematic review and meta-analysis

Background

Using blood-derived circular RNAs (circRNAs) may be an efficient tool for noninvasive fluid biopsy in diagnosing non-small cell lung cancer (NSCLC). However, no relevant systemic meta-analysis has been conducted so far to support the diagnostic value of using blood-derived circRNAs in NSCLC clinically. The aim of this study is to clarify the issue through a meta-analysis.

Methods

A systematic search strategy was used to search relevant literature in the databases of PubMed, Web of Science, and Cochrane Library from 2017 to 2022. The relationship between the diagnostic accuracy of circRNAs and NSCLC was analyzed. For the purpose of evaluating the quality of the literature, Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) was used. Statistical analyses were assessed using Stata software (version 17.0) and META-DISC (version 1.4).

Results

The meta-analysis included 1,093 patients with NSCLC and 959 controls. Results are as follows: pooled sensitivity, 0.78 (95% CI = 0.71–0.83, I² = 71.86); pooled specificity, 0.76 (95% CI = 0.70–0.82, I² = 70.12); pooled positive likelihood ratio (PLR), 3.3 (95% CI = 2.6–4.2, I² = 37.56); pooled negative likelihood ratio (NLR), 0.29 (95% CI = 0.23–0.37, I² = 64.67); diagnostic odds ratio (DOR), 11.42 (95% CI = 7.88–16.56, I² = 99.05); area under the receiver operating characteristic curve (AUC), 0.84 (95% CI = 0.80–0.87). Based on the subgroup analysis, it appears that the heterogeneity is primarily caused by the NSCLC subgroup.

Conclusion

circRNAs are highly useful diagnostic biomarkers for NSCLC in China. Further prospective studies on the diagnostic value of circRNAs should be conducted in multiple countries.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42022323804.

New insights on circular RNAs and their potential applications as biomarkers, therapeutic agents, and preventive vaccines in viral infections: with a glance at SARS-CoV-2

The occurrence of viral infections and approaches to handling them are very challenging and require prompt diagnosis and timely treatment. Recently, genomic medicine approaches have come up with the discovery of the competing endogenous RNA (ceRNA) network, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) on the basis of gene silencing. CircRNAs, as a group of non-encoded RNAs, make a loop-like structure by back-splicing through 3′ and 5′ ends. They are stable, abundant, specific, and highly conserved and can be quickly generated at large scales in vitro. CircRNAs have the potential to contribute in several cellular processes in a way that some serve as microRNA sponges, cellular transporters, protein-binding RNAs, transcriptional regulators, and immune system modulators. CircRNAs can even play an important role in modulating antiviral immune responses. In the present review, circRNAs’ biogenesis, function, and biomarker and therapeutic potential as well as their prospective applications as vaccines against viral infections such as SARS-CoV-2 are explained. By considering their unique properties, their potential to be used as novel vaccines, biomarkers, and a therapeutic approach appears possible.

Recent advances in biological membrane-based nanomaterials for cancer therapy

Nanomaterials have shown significant advantages in cancer theranostics, owing to their enhanced permeability and retention effect in tumors and multi-function integration capability. Biological membranes, which are collected from various cells and their secreted membrane structures, can further be applied to establish membrane-based nanomaterials with perfect biocompatibility, tumor-targeting capacity, immune-stimulatory activity and adjustable versatility for cancer therapy. In this review, according to their source, membranes are divided into four groups: (1) cell membranes; (2) secretory membranes; (3) engineered membranes; and (4) hybrid membranes. First, cell membranes can be extracted from natural cells of the body, tumor tissue cells, and bacteria. Furthermore, secretory membranes mainly refer to exosome, apoptotic body and bacterial outer membrane vesicle, and membranes with specific protein/peptide expression or therapeutic inclusions are obtained from engineered cells. Finally, a hybrid membrane will be constituted by two or more of the abovementioned membranes. These membranes can form drug-carrying nanoparticles themselves or coat multi-functional nanoparticles, further realizing efficient cancer therapy. We summarize the application of various biological membrane-based nanomaterials in cancer therapy and point out their advantages as well as the places that need to be further improved, providing systematic knowledge of this field and a strategy for further optimization.

Prognostic and clinicopathologic significance of circZFR in multiple human cancers

Background

Abnormally expressed in diverse cancers, circZFR has been correlated with clinical outcomes of cancer patients. Aim of this meta-analysis was to elucidate the prognostic role of circZFR in multiple human malignancies.

Methods

Literature retrieval was conducted by systematically searching on Pubmed, Web of Science, and the Cochrane Library up to December 2nd, 2021. Hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs) were pooled to evaluate the association between circZFR expression and overall survival (OS). The reliability of the pooled results was assessed through sensitivity analysis and the publication bias was measured by Begg’s and Egger’s test.

Results

A total of seventeen studies comprising 1098 Chinese patients were enrolled in this meta-analysis. Results demonstrated that high circZFR expression was correlated with an unfavorable OS (HR = 2.14, 95% CI 1.74, 2.64). High circZFR expression predicted larger tumor size (OR = 2.79, 95% CI 1.52, 5.12), advanced clinical stage (OR = 3.38, 95% CI 1.49, 7.65), tendentiousness of lymph node metastasis (LNM) (OR = 3.08, 95% CI 2.01, 4.71), and malignant grade (OR = 3.18, 95% CI 1.09, 9.30), but not related to age, gender, and distant metastasis (DM).

Conclusions

High circZFR expression was associated with unfavorable OS and clinicopathologic parameters including tumor size, clinical stage, LNM, and histology grade, implicating a promising prognostic factor in cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12957-022-02733-9.

Circular RNA PVT1 promotes progression of thyroid cancer by competitively binding miR‑384

Plasmacytoma variant translocation 1 circular RNA (circPVT1) is involved in the initiation and development of several types of cancer. However, the underlying molecular role of circPVT1 in tumorigenesis of thyroid cancer remains to be elucidated. In the present study, relative expression of circPVT1 was markedly upregulated in thyroid cancer compared with adjacent normal tissue. circPVT1 expression was associated with clinical stage and lymph node metastasis. Furthermore, Cell Counting Kit-8, colony formation and Transwell chamber assays demonstrated that knockdown of circPVT1 decreased proliferation, migration and invasion of thyroid cancer cells in vitro. Moreover, circPVT1 directly interacted with microRNA (miR)-384, as shown by bioinformatics prediction and dual luciferase and RNA pull-down assay. miR-384 inhibition partially reversed the circPVT1 knockdown-mediated inhibitory effect on proliferation, migration and invasion of thyroid cancer cells. In summary, these findings demonstrated that circPVT1 may be a potential therapeutic target for thyroid cancer.

Emerging Roles of Circ-ZNF609 in Multiple Human Diseases

Circular RNAs (circRNAs) are a special type of endogenous RNAs with extensive roles in multiple human diseases. They are formed by back-splicing of partial sequences of the parental precursor mRNAs. Unlike linear RNAs, their covalently closed loop structure without a 5′ cap and a 3′ polyadenylated tail confers on them high stability and they are difficult to be digested by RNase R. Increasing evidence has proved that aberrant expressions of many circRNAs are detected and that circRNAs exert essential biological functions in disease development and progression via acting as a molecular sponge of microRNA, interacting with proteins as decoys or scaffolds, or self-encoding small peptides. Circular RNA zinc finger protein 609 (circ-ZNF609) originates from exon2 of ZNF609, which is located at chromosome 15q22.31, and it has recently been proved that it can translate into a protein. Being aberrantly upregulated in various diseases, it could promote malignant progression of human tumors, as well as tumor cell proliferation, migration, and invasion. Here in this review, we concluded the biological functions and potential mechanisms of circ-ZNF609 in multiple diseases, which could be further explored as a targetable molecule in future accurate diagnosis and prognosis.

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.

Exosome-Derived Non-Coding RNAs in the Tumor Microenvironment of Colorectal Cancer: Possible Functions, Mechanisms and Clinical Applications

Colorectal cancer (CRC) is the second leading cause of cancer death and the third most prevalent malignancy. Colorectal tumors exchange information with the surrounding environment and influence each other, which collectively constitutes the tumor microenvironment (TME) of CRC. Many studies have shown that exosome-derived non-coding RNAs (ncRNAs) play important roles in various pathophysiological processes by regulating the TME of CRC. This review summarizes recent findings on the fundamental roles of exosomal ncRNAs in angiogenesis, vascular permeability, tumor immunity, tumor metabolism and drug resistance. Certainly, the in-depth understanding of exosomal ncRNAs will provide comprehensive insights into the clinical application of these molecules against CRC.

Extracellular Vesicles in Cardiovascular Diseases: Diagnosis and Therapy

Cardiovascular diseases (CVDs) are the leading cause of global mortality. Therapy of CVDs is still a great challenge since many advanced therapies have been developed. Multiple cell types produce nano-sized extracellular vesicles (EVs), including cardiovascular system-related cells and stem cells. Compelling evidence reveals that EVs are associated with the pathophysiological processes of CVDs. Recently researches focus on the clinical transformation in EVs-based diagnosis, prognosis, therapies, and drug delivery systems. In this review, we firstly discuss the current knowledge about the biophysical properties and biological components of EVs. Secondly, we will focus on the functions of EVs on CVDs, and outline the latest advances of EVs as prognostic and diagnostic biomarkers, and therapeutic agents. Finally, we will introduce the specific application of EVs as a novel drug delivery system and its application in CVDs therapy. Specific attention will be paid to summarize the perspectives, challenges, and applications on EVs’ clinical and industrial transformation.

Circ_0006790 carried by bone marrow mesenchymal stem cell-derived exosomes regulates S100A11 DNA methylation through binding to CBX7 in pancreatic ductal adenocarcinoma

Extracellular vesicles, particularly exosomes, play a vital role via their cargoes. Their potential in pancreatic ductal adenocarcinoma (PDAC), one of the leading causes of cancer-related mortality worldwide is attracting interests. However, the roles and underlying mechanisms of exosomal circular RNAs (circRNAs) in the development of PDAC remain unclear yet. We aimed to illuminate the mechanisms of exosomal hsa_circ_0006790 (thereafter termed circ_6790) released by exosomes (Exo) derived from bone marrow mesenchymal stem cell (BM-MSC) during immune escape in PDAC in this study. BM-MSC-derived Exo inhibited growth, metastasis, and immune escape in PDAC. Exo enhanced circ_6790 expression in PDAC cells. Knockdown of circ_6790 in Exo significantly attenuated the anti-tumor effect of Exo. Circ_6790 facilitated the nuclear translocation of chromobox 7 (CBX7). CBX7 increased the DNA methylation of S100A11 by recruiting DNA methyltransferases to its promoter region, thereby inhibiting the transcription of S100A11. Inhibition of CBX7 or overexpression of S100A11 annulled the inhibitory effects of Exo on PDAC growth, metastasis, and immune escape. In conclusion, our results suggest that MSC-derived exosomal circ_6790 could downregulate S100A11 in PDAC cells and hamper immune escape via CBX7-catalyzed DNA hypermethylation.

The Emerging Roles of Circ-ABCB10 in Cancer

Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) without 5′ caps and 3′ tails, which are formed from precursor mRNAs (pre-mRNAs) that are inversely back-spliced by exons. CircRNAs are characterized by a covalently closed circular structure and are abundantly expressed in eukaryotic cells. With the development of RNA-sequencing, it was discovered that circRNAs play important roles in the regulation of numerous human genes and are related to the occurrence, development, and prognosis of diseases. Studies in various cancers have revealed that circRNAs have both positive and negative effects on the occurrence and development of tumors. Circ-ABCB10, a circular RNA originating from exons of ABCB10 located on chromosome 1q42, has been proven to play an important role in different types of cancers. Here, we report the primary findings of recent research studies by many contributors about the roles of circ-ABCB10 in cancer and clearly formulate its influence and functions in different aspects of cancer biology, which gives us a broad picture of circ-ABCB10. Thus, this study aimed to generalize the roles of circ-ABCB10 in the diagnosis and treatment of different types of tumors and its related miRNA genes. In this way, we wish to provide a sufficient understanding and assess the future development direction of the research on circ-ABCB10.

The emerging landscape of exosomal CircRNAs in solid cancers and hematological malignancies

Circular RNAs (circRNAs) are a type of recently discovered noncoding RNA. They exert their biological functions by competitively binding to microRNAs (miRNAs) as miRNA sponges, promoting gene transcription and participating in the regulation of selective splicing, interacting with proteins and being translated into proteins. Exosomes are derived from intracavitary vesicles (ILVs), which are formed by the inward budding of multivesicular bodies (MVBs), and exosome release plays a pivotal role in intercellular communication. Accumulating evidence indicates that circRNAs in exosomes are associated with solid tumor invasion and metastasis. Additionally, emerging studies in the last 1 ~ 2 years have revealed that exosomal circRNA also have effect on hematological malignancies. In this review, we outline the properties and biological functions of circRNAs and exosomes. In particular, we summarize in detail the mechanism and roles of exosomal circRNAs and highlight their application as novel biomarkers in malignant tumors.

Circular RNAs With Efficacy in Preclinical In Vitro and In Vivo Models of Esophageal Squamous Cell Carcinoma

Esophageal cancer is associated with a dismal prognosis. The armamentarium of approved drugs is focused on chemotherapy with modest therapeutic benefit. Recently, checkpoint inhibitory monoclonal antibody Pembrolizumab was approved. In order to identify new targets and modalities for the treatment of esophagus squamous cell carcinoma (ESCC) we searched the literature for circRNAs involved in the pathogenesis of ESCC. We identified two down-regulated and 17 up-regulated circRNAs as well as a synthetic circRNA with efficacy in preclinical in vivo systems. Down-regulated circRNAs sponge microRNAs directed against tumor suppressor genes. Up-regulated circRNAs sponge microRNAs directed against mRNAs, which encode proteins with pro-tumoral functions. We discuss issues such as reconstitution of down-regulated circRNAs and inhibition of up-regulated circRNAs with short interfering RNA (siRNA)- related entities. Also, we address druggability issues of the identified targets.

Circular RNA as a Novel Biomarker for Diagnosis and Prognosis and Potential Therapeutic Targets in Multiple Myeloma

Circular RNAs (circRNAs) are a novel type of covalently closed RNAs involved in several physiological and pathological processes. They display tissue-specific expression and are constant, abundant, and highly conserved, making them perfect markers for diagnosis and prognosis. Several studies have proposed that circRNAs are also differentially produced in malignancies where they have oncogenic effects. Furthermore, circRNAs affecting microRNAs modify the expression profile of several transcription factors which play essential roles in tumors. CircRNAs within the hematopoietic compartment were identified as modulators of mechanisms able to enhance or suppress tumor progression in blood malignancies. Moreover, several circRNAs were suggested to confer resistance to the conventional drugs employed in hematopoietic cancers. In this review, we highlight the growing role and the controlling mechanisms by which circRNAs modify multiple myeloma genesis. We propose that circRNAs can be considered as potential diagnostic and prognostic markers, can induce chemoresistance, and might represent novel therapeutic targets for multiple myeloma.

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.

Cancer metabolism and tumor microenvironment: fostering each other?

The changes associated with malignancy are not only in cancer cells but also in environment in which cancer cells live. Metabolic reprogramming supports tumor cell high demand of biogenesis for their rapid proliferation, and helps tumor cell to survive under certain genetic or environmental stresses. Emerging evidence suggests that metabolic alteration is ultimately and tightly associated with genetic changes, in particular the dysregulation of key oncogenic and tumor suppressive signaling pathways. Cancer cells activate HIF signaling even in the presence of oxygen and in the absence of growth factor stimulation. This cancer metabolic phenotype, described firstly by German physiologist Otto Warburg, insures enhanced glycolytic metabolism for the biosynthesis of macromolecules. The conception of metabolite signaling, i.e., metabolites are regulators of cell signaling, provides novel insights into how reactive oxygen species (ROS) and other metabolites deregulation may regulate redox homeostasis, epigenetics, and proliferation of cancer cells. Moreover, the unveiling of noncanonical functions of metabolic enzymes, such as the moonlighting functions of phosphoglycerate kinase 1 (PGK1), reassures the importance of metabolism in cancer development. The metabolic, microRNAs, and ncRNAs alterations in cancer cells can be sorted and delivered either to intercellular matrix or to cancer adjacent cells to shape cancer microenvironment via media such as exosome. Among them, cancer microenvironmental cells are immune cells which exert profound effects on cancer cells. Understanding of all these processes is a prerequisite for the development of a more effective strategy to contain cancers.

Accentuating CircRNA-miRNA-Transcription Factors Axis: A Conundrum in Cancer Research

Circular RNAs (circRNAs) are the newly uncovered class of non-coding RNAs being cognized as profound regulators of gene expression in developmental and disease biology. These are the covalently closed RNAs synthesized when the pre-mRNA transcripts undergo a back-splicing event. In recent years, circRNAs are gaining special attention in the scientific world and are no longer considered as "splicing noise" but rather structurally stable molecules having multiple biological functions including acting as miRNA sponges, protein decoys/scaffolds, and regulators of transcription and translation. Further, emerging evidence suggests that circRNAs are also differentially expressed in multiple cancers where they play oncogenic roles. In addition, circRNAs in association with miRNAs change the expression patterns of multiple transcription factors (TFs), which play important roles in cancer. Thus, the circRNA-miRNA-TFs axis is implicated in the progression or suppression of various cancer types and plays a role in cell proliferation, invasion, and metastasis. In this review article, we provide an outline of the biogenesis, localization, and functions of circRNAs specifically in cancer. Also, we highlight the regulatory function of the circRNA-miRNA-TFs axis in the progression or suppression of cancer and the targeting of this axis as a potential therapeutic approach for cancer management. We anticipate that our review will contribute to expanding the knowledge of the research community about this recent and rapidly growing field of circRNAs for further thorough investigation which will surely help in the management of deadly disease cancer.

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.

A novel circRNA-miRNA-mRNA network reveals hsa-circ-0040039 as a biomarker for intervertebral disc degeneration

Objective

Alterations in the structure and function of intervertebral discs by multifaceted chronic processes can result in intervertebral disc degeneration (IDD). The mechanisms involved in IDD are still unknown.

Methods

We investigated the possible mechanisms underlying IDD using a bioinformatics analysis of publicly available microarray expression datasets and built a circular RNA–microRNA–mRNA (circRNA–miRNA–mRNA) network based on the results. Datasets GSE67566 and GSE116726 were downloaded from the Gene Expression Omnibus (GEO) and analyzed using the limma package in R. The CircInteractome database was used to detect miRNAs related to circRNA, and TargetScan, miRDB, and miRTarBase were used to predict target mRNAs. Key target genes were annotated using Gene Ontology terms.

Results

The circRNA hsa-circ-0040039 was found to have the top log fold-change score. Analysis using Metascape showed that the associated genes were enriched mainly in the cell cycle. The Cytoscape plugin MCODE predicted that two members of the RAS oncogene family—RAB1A and RAB1B—and multiple coagulation factor deficiency (MCFD2) may play key roles in IDD.

Conclusion

Our results suggested that hsa-circ-0040039 and the related network may be potential biomarkers for IDD.

Autophagy and ncRNAs: Dangerous Liaisons in the Crosstalk between the Tumor and Its Microenvironment

Simple Summary

Tumor cells communicate with the stromal cells within the tumor microenvironment (TME) to create a conducive environment for tumor growth. One major avenue for mediating crosstalk between various cell types in the TME involves exchanges of molecular payloads in the form of extracellular vesicles/exosomes. Autophagy is a fundamental mechanism to maintain intracellular homeostasis but recent reports suggest that secretory autophagy plays an important role in promoting secretion of exosomes that are packaged with non-coding RNAs (ncRNAs) and other biomolecules from the donor cell. Uptake of exosomal autophagy-modulating ncRNAs by recipient cells may further perpetuate tumor progression.

Abstract

Autophagy is a fundamental cellular homeostasis mechanism known to play multifaceted roles in the natural history of cancers over time. It has recently been shown that autophagy also mediates the crosstalk between the tumor and its microenvironment by promoting the export of molecular payloads such as non-coding RNA (ncRNAs) via LC3-dependent Extracellular Vesicle loading and secretion (LDELS). In turn, the dynamic exchange of exosomal ncRNAs regulate autophagic responses in the recipient cells within the tumor microenvironment (TME), for both tumor and stromal cells. Autophagy-dependent phenotypic changes in the recipient cells further enhance tumor growth and metastasis, through diverse biological processes, including nutrient supplementation, immune evasion, angiogenesis, and therapeutic resistance. In this review, we discuss how the feedforward autophagy-ncRNA axis orchestrates vital communications between various cell types within the TME ecosystem to promote cancer progression.

Exosomal circRNAs: Emerging Players in Tumor Metastasis

Metastasis is an important feature of malignant tumors, and is the primary cause of poor prognosis and treatment failure, in addition to representing a potentially fatal challenge for cancer patients. Exosomes are small extracellular vesicles 30–150 nm in diameter that transmit cargo, such as DNA, RNA, and proteins, as a means of intercellular communication. Exosomes play crucial roles in a range of human diseases, especially malignant tumors. A growing number of studies have verified that circRNAs can be enveloped in exosomes and transferred from secretory cells to recipient cells, thereby regulating tumor progression, especially tumor metastasis. Exosomal circRNAs regulate tumor cell metastasis not only by regulating the signaling pathways, but also by affecting the tumor microenvironment. Moreover, exosomal circRNAs have the potential to serve as valuable diagnostic biomarkers and novel therapeutic targets in cancer patients. In this review, we summarize the mechanism by which exosomal circRNAs modulate metastatic phenomena in various types of tumors, and put forward the prospects of clinical applications of exosomal circRNAs in tumor therapy.

Diverse Roles and Therapeutic Potentials of Circular RNAs in Urological Cancers

Circular RNAs (circRNAs) are a novel class of noncoding RNAs, which are mainly formed as a loop structure at the exons caused by noncanonical splicing; they are much more stable than linear transcripts; recent reports have suggested that the dysregulation of circRNAs is associated with the occurrence and development of diseases, especially various human malignancies. Emerging evidence demonstrated that a large number of circRNAs play a vital role in a series of biological processes such as tumor cell proliferation, migration, drug resistance, and immune escape. Additionally, circRNAs were also reported to be potential prognostic and diagnostic biomarkers in cancers. In this work, we systematically summarize the biogenesis and characteristics of circRNAs, paying special attention to potential mechanisms and clinical applications of circRNAs in urological cancers, which may help develop potential therapy targets for urological cancers in the future.

Novel circular RNA circATRNL1 accelerates the osteosarcoma aerobic glycolysis through targeting miR-409-3p/LDHA

In recent researches, circular RNAs (circRNAs) have been shown to exert critical functions in osteosarcoma biology. Nevertheless, the contribution of circRNAs to osteosarcoma remains largely unclear. Results indicated that expression of circATRNL1 was higher in osteosarcoma tissues and cells. The high-expression of circATRNL1 was significantly correlated with aggressive features and acted as an independent risk factor for osteosarcoma patients' overall survival. Functionally, our findings demonstrate that circATRNL1 promotes the osteosarcoma aerobic glycolysis in vitro. Mechanistically, circATRNL1 up-regulated the expression level of LDHA, which was also targeted by miR-409-3p. Therefore, circATRNL1 exerted the accelerative roles of osteosarcoma aerobic glycolysis through miR-409-3p/LDHA axis. In conclusion, circATRNL1 promoted osteosarcoma progression by enhancing glycolysis via circATRNL1/miR-409-3p/LDHA axis, which may inspire a novel therapeutic target for osteosarcoma.

Circular RNAs in kidney disease and cancer

Circular RNAs (circRNAs) are a class of endogenously expressed regulatory RNAs with a single-stranded circular structure. They are generated by back splicing and their expression can be tightly regulated by RNA binding proteins. Cytoplasmic circRNAs can function as molecular sponges that inhibit microRNA-target interactions and protein function or as templates for the efficient generation of peptides via rolling circle amplification. They can also act as molecular scaffolds that enhance the reaction kinetics of enzyme-substrate interactions. In the nucleus, circRNAs might facilitate chromatin modifications and promote gene expression. CircRNAs are resistant to degradation and can be packaged in extracellular vesicles and transported in the circulation. Initial studies suggest that circRNAs have roles in kidney disease and associated cardiovascular complications. They have been implicated in hypertensive nephropathy, diabetic kidney disease, glomerular disease, acute kidney injury and kidney allograft rejection, as well as in microvascular and macrovascular complications of chronic kidney disease, including atherosclerotic vascular disease. In addition, several circRNAs have been reported to have oncogenic or tumour suppressor roles or to regulate drug resistance in kidney cancer. The available data suggest that circRNAs could be promising diagnostic and/or prognostic biomarkers and potential therapeutic targets for kidney disease, cardiovascular disease and kidney cancer.

Circular RNAs as potential regulators in bone remodeling: a narrative review

Objective

In this review, we focus on the recent progress of circular ribonucleic acids (circRNAs)-related molecular mechanisms in the processes of osteogenesis and osteoclastogenesis, and explore their roles in the development of bone-remodeling disorders.

Background

The well-coupled bone-formation and bone-resorption processes are vital in bone remodeling. Once the balance is disrupted, bone-remodeling disorders (e.g., osteoporosis and osteopetrosis) occur, severely affecting patients’ quality of life. CircRNAs, the newly discovered members of the non-coding RNA family, have been reported to act as key checkpoints of various signaling pathways that influence osteoblasts and osteoclasts functions, thus regulating the physiological and pathological processes of bone homeostasis.

Methods

Three English and three Chinese databases [i.e., PubMed, Embase, MEDLINE (via Ovid), Chinese Biomedical Literature, China National Knowledge Infrastructure, and VIP databases] were searched to June 2021 without language restrictions. Studies exploring the roles of circRNAs in key bone remodeling mediators, such as Smad-dependent bone morphogenetic protein (BMP)/transforming growth factor beta (TGF-β), Wnts, runt-related transcription factor (RUNX), forkhead boxes (FOXs), colony-stimulating factor 1 (CSF-1), receptor activator of nuclear factor kappa B ligand (RANKL)/osteoprotegerin (OPG), and circRNA-related bone-remodeling disorders, were included.

Conclusions

Many circRNAs have been shown to promote osteogenesis and facilitate osteoclast differentiation via diverse mechanisms, and thus modulate the process of bone homeostasis. The imbalance or impairment of these two parts causes diseases, such as osteoporosis, and osteonecrosis of the femoral head, which are also closely correlated to the aberrant presence of circRNAs. Current evidence provides us with promising diagnosis and treatment methods for some bone homeostasis disorders.