The roles of circRNAs in cancers: Perspectives from molecular functions

Circular RNAs and the JAK/STAT pathway: New frontiers in cancer therapeutics

Circular RNAs, known as circRNAs, have drawn more attention to cancer biology in the last few years. Novel functions of circRNAs in cancer therapy open promising prospects for personalized medicine. This review focuses on the molecular properties and potential of circRNAs as biomarkers or therapeutic targets in cancer treatment. Unique properties of circular RNAs associated with a circular form provide stability and resilience to RNA exonuclease degradation. Circular RNAs' most important characteristic is that they are involved in the JAK/STAT pathway associated with oncogenesis. Notably, their deregulation has been reported in multiple carcinomas due to involvement in JAK/STAT signaling cascade modulation. Increased knowledge about circRNAs' interaction with the JAK/STAT pathway leads to the emergence of new possibilities for targeted cancer therapy. In addition, since circRNAs demonstrate tissue-relatedness of expression, they may be a reliable biomarker for predicting and diagnosing cancer. With the development of new technologies for targeting circRNAs, novel therapeutics can be produced that offer more personalized cancer treatment options based on the nature of the patient. The present review explores the exciting prospects of circRNAs for transforming cancer treatment into personalized medicine. It describes the current understanding of circRNA biology, its relationship to tumorigenesis, and possible targeting methods.

The quantification of circular RNA 0007841 during induction therapy helps estimate the response and survival benefits to bortezomib-based regimen in multiple myeloma

OBJECTIVE

Circular RNA_0007841 (Circ_0007841) facilitates multiple myeloma (MM) progression and resistance of the bortezomib by experimental studies, while its clinical implication in MM patients is still unclear. This study intended to evaluate the longitudinal change and prognostic role of circ_0007841 expression in MM patients receiving bortezomib-based induction therapy.

METHODS

In this prospective study, bone marrow plasma cell (BMPC) samples were gained from 97 MM patients at diagnosis and after bortezomib-based induction therapy, and from 30 healthy controls (HCs) proposing BM donation. Then, circ_0007841 expression in BMPC samples was measured by reverse transcription-quantitative polymerase chain reaction. Additionally, MM patients were followed up for a median of 29.4 months.

RESULTS

Circ_0007841 expression was increased in MM patients compared to HCs (P < 0.001), but it was decreased after bortezomib-based induction therapy in MM patients (P < 0.001). Moreover, circ_0007841 expression at diagnosis was associated with the presence of t (4; 14) (P = 0.034), while its expression after bortezomib-based induction therapy was linked with higher revised international staging system stage (P = 0.025) in MM patients. Interestingly, circ_0007841 expression after bortezomib-based induction therapy was lower in MM patients who achieved complete remissions (P = 0.001) and overall responses (P = 0.002) compared to those who did not. Prognostically, circ_0007841 expression after bortezomib-based induction therapy (over the median vs. below the median) independently predicted shorter progression-free survival (hazard ratio (HR): 2.497, P = 0.002) and overall survival (HR: 3.107, P = 0.008) in MM patients.

CONCLUSION

Circ_0007841 quantification during induction therapy may reflect the response and survival benefits to bortezomib-based regimen in MM patients.

Integrated whole transcriptome profiling revealed a convoluted circular RNA-based competing endogenous RNAs regulatory network in colorectal cancer

Recently, it has been identified that circRNAs can act as miRNA sponge to regulate gene expression in various types of cancers, associating them with cancer initiation and progression. The present study aims to identify colorectal cancer-related circRNAs and the underpinning mechanisms of circRNA/miRNA/mRNA networks in the development and progress of Colorectal Cancer. Differentially expressed circRNAs, miRNAs, and mRNAs were identified in GEO microarray datasets using the Limma package of R. The analysis of differentially expressed circRNAs resulted in 23 upregulated and 31 downregulated circRNAs. CeRNAs networks were constructed by intersecting the results of predicted and experimentally validated databases, circbank and miRWalk, and by performing DEMs and DEGs analysis using Cytoscape. Next, functional enrichment analysis was performed for DEGs included in ceRNA networks. Followed by survival analysis, expression profile assessment using TCGA and GEO data, and ROC curve analysis we identified a ceRNA sub-networks that revealed the potential regulatory effect of hsa_circ_0001955 and hsa_circ_0071681 on survival-related genes, namely KLF4, MYC, CCNA2, RACGAP1, and CD44. Overall, we constructed a convoluted regulatory network and outlined its likely mechanisms of action in CRC, which may contribute to the development of more effective approaches for early diagnosis, prognosis, and treatment of CRC.

Astragaloside IV regulates circ_0001615 and miR-873-5p/LASP1 axis to suppress colorectal cancer cell progression

Astragaloside IV (AS-IV) has exhibited pivotal anti-cancer efficacy in multiple types of cancer, including colorectal cancer (CRC). Meanwhile, circular RNA (circRNA) circ_0001615 has been reported to be involved in the malignant development of CRC. Herein, this study is expected to figure out the interaction between circ_0001615 and AS-IV on CRC progression. The 50% inhibition concentration (IC50), proliferation, apoptosis, and migration were detected by Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, and wound healing assays. The expression of related proteins was examined by western blot. Circ_0001615, microRNA-873-5p (miR-873-5p), and LIM and SH3 protein 1 (LASP1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). The binding between miR-873-5p and circ_0001615, or LASP1, was predicted by Starbase, followed by verification by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The biological role of circ_0001615 and AS-IV on CRC tumor growth was detected by the xenograft tumor model in vivo. According to the IC50 of AS-IV in CRC cells, the 100 ng/mL AS-IV treatment for 24 h was chosen for the following research: Our data confirmed that AS-IV is a beneficial anti-cancer agent in CRC cells. Furthermore, circ_0001615 and LASP1 expression were increased, and miR-873-5p was decreased in CRC patients and cell lines, whereas their expression exhibited an opposite trend in AS-IV-treated cells. Functionally, applying AS-IV might act as a beneficial anti-cancer effect by downregulating circ_0001615 in CRC cells in vitro. Mechanically, circ_0001615 serves as a sponge for miR-873-5p to affect LASP1 expression. In addition, AS-IV inhibited CRC cell growth in vivo by modulating circ_0001615. Overall, AS-IV could mitigate CRC development, at least in part, through the circ_0001615/miR-873-5p/LASP1 axis. These findings support a theoretical basis for an in-depth study of the function of AS-IV and the clinical treatment of CRC.

Identification of circular RNA-Dcaf6 as a therapeutic target for optic nerve crush-induced RGC degeneration

The death of retinal ganglion cells (RGCs) can cause irreversible injury in visual function. Clarifying the mechanism of RGC degeneration is critical for the development of therapeutic strategies. Circular RNAs (circRNAs) are important regulators in many biological and pathological processes. Herein, we performed circRNA microarrays to identify dysregulated circRNAs following optic nerve crush (ONC). The results showed that 221 circRNAs were differentially expressed between ONC retinas and normal retinas. Notably, the levels of circular RNA-Dcaf6 (cDcaf6) expression in aqueous humor of glaucoma patients were higher than that in cataract patients. cDcaf6 silencing could reduce oxidative stress-induced RGC apoptosis in vitro and alleviate retinal neurodegeneration in vivo as shown by increased neuronal nuclei antigen (NeuN, neuronal bodies) and beta-III-tubulin (TUBB3, neuronal filaments) staining and reduced glial fibrillary acidic protein (GFAP, activated glial cells) and vimentin (activated glial cells) staining. Collectively, this study identifies a promising target for treating retinal neurodegeneration.

Hsa_circITGA4/ miR-1468/EGFR/ PTEN a Master Regulators Axis in Glioblastoma Development and Progression

In the fight against glioblastoma, circular RNA is emerging as a functional molecule. However, how circular RNA (circRNA) is regulated and what role it plays is still a mystery. In this research, different bioinformatics approaches were used to evaluate glioblastoma circRNA sequencing and array data, with the goal of developing a putative molecular sponge mechanism control network. The circRNAs were obtained from the Gene Expression Omnibus datasets. MicroRNA-circRNA interactions were predicted using CircInteractome. The microRNAs' expression and survival trends were screened using the TCGA database. MicroRNA gene targets were predicted using the MiRnet database. Sponge network gene candidates were screened using data from the GEPIA. The roles of the targeted genes were to be explained by analyzing data from Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes. To build the network and display the outcomes, we utilized python program, and enrichment online Bioinformatics databases. The circRNAs hsa_circITGA4_002, hsa_circITGA4_001, hsa_circITGA4_003, hsa_circ_0030855, hsa_circ_0030857 were chosen from among GBM patients and control group. Upregulation of hsa-miR-1468, hsa-miR-3683, hsa-miR-1273c, and hsa-miR-4665-3p were associated with a poor prognosis in GBM. MicroRNA targets such as ITGA4, LAMA2, EGFR, PTEN, COL1A4, and NCAM2 were analyzed using expression and survival data. The Apoptosis, cell adhesion molecules, PI3K/AKT and P53 signaling pathways were the most abundant functional categories among gene targets. The circRNA molecular sponge regulatory network includes hsa-miR-1468 and hsa-miR-4665-3p. In this network, hs hsa_circITGA4_002, hsa_circITGA4_001, hsa_circ_0030857, EGFR, PTEN, and ITGA4 may represent GBM therapeutic targets. Their role in GBM needs additional study.

CircCDK1 blocking IGF2BP2-mediated m6A modification of CPPED1 promotes laryngeal squamous cell carcinoma metastasis via the PI3K/AKT signal pathway

BACKGROUND

Circular RNA (circRNA) is a novel noncoding RNA (ncRNA) that plays a critical role in various cancers. However, the clinical significance, biological function, and molecular mechanisms of circRNAs in laryngeal squamous cell carcinoma (LSCC) remain unclear.

METHODS

A circRNA array was performed to identify the differentially expressed circRNAs. In vitro and in vivo assays were proceeded to verify the biological function of circCDK1 in LSCC. RNA pulldown assays and RNA immunoprecipitation (RIP) were used to confirm the binding between circCDK1 and insulin-like growth factor 2 mRNA binding protein 2(IGF2BP2). The MeRIP assay was then used to identified the N6-methyladenisine (m6A) methylation of calcineurin like phosphatase domain containing1 (CPPED1).

RESULTS

Hsa_circ_0005774 (circCDK1) was found upregulated in LSCC tissues compared to adjacent normal tissues. The level of circCDK1 was positively correlated with poor prognosisof LSCC patients. In vitro and in vivo, circCDK1 promoted migration and invasion of LSCC cells. Mechanistically, eukaryotic translation initiation factor4A3(EIF4A3) induced biogenesis of circCDK1 by binding to its flanking. By competitively binding to IGF2BP2, circCDK1 blocked the m6A modification of CPPED1 in IGF2BP2-dependent manner. Moreover, the circCDK1-mediated decrease of CPPED1 activated the PI3K/AKT signal pathway to facilitate progression of LSCC.

CONCLUSIONS

Our findings demonstrated that EIF4A3-induced upregulation of circCDK1 promoted LSCC metastasis via EIF4A3-circCDK1-IGF2BP2-CPPED1 to activate PI3K-AKT signal pathway. CircCDK1 might serve as a new diagnostic and prognostic marker or potential therapeutic target for LSCC.

Differentially expressed non-coding RNAs and their regulatory networks in liver cancer

The vast majority of human transcriptome is represented by various types of small RNAs with little or no protein-coding capability referred to as non-coding RNAs (ncRNAs). Functional ncRNAs include microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), which are expressed at very low, but stable and reproducible levels in a variety of cell types. ncRNAs regulate gene expression due to miRNA capability of complementary base pairing with mRNAs, whereas lncRNAs and circRNAs can sponge miRNAs off their target mRNAs to act as competitive endogenous RNAs (ceRNAs). Each miRNA can target multiple mRNAs and a single mRNA can interact with several miRNAs, thereby creating miRNA-mRNA, lncRNA-miRNA-mRNA, and circRNA-miRNA-mRNA regulatory networks. Over the past few years, a variety of differentially expressed miRNAs, lncRNAs, and circRNAs (DEMs, DELs, and DECs, respectively) have been linked to cancer pathogenesis. They can exert both oncogenic and tumor suppressor roles. In this review, we discuss the recent advancements in uncovering the roles of DEMs, DELs, and DECs and their networks in aberrant cell signaling, cell cycle, transcription, angiogenesis, and apoptosis, as well as tumor microenvironment remodeling and metabolic reprogramming during hepatocarcinogenesis. We highlight the potential and challenges in the use of differentially expressed ncRNAs as biomarkers for liver cancer diagnosis and prognosis.

Hypoxia-responsive circular RNA circAAGAB reduces breast cancer malignancy by activating p38 MAPK and sponging miR-378 h

BACKGROUND

Breast cancer is a prevalent disease in women, with high prevalence worldwide. The hypoxic microenvironment of solid tumors develops during the progress of carcinogenesis and leads to greater malignancy and treatment resistance. Recently, accumulating evidence indicates that non-coding RNAs, such as circular RNAs (circRNAs), play a pivotal role in altering cellular functions. However, the underlying mechanisms of circRNAs in breast cancer are still unclear. Therefore, the purpose of this study was to investigate the role of a tumor-suppressive circRNA, circAAGAB, in breast cancer by assuming down-regulation of circAAGAB under hypoxia and the properties of a tumor suppressor.

METHODS

Firstly, circAAGAB was identified from expression profiling by next generation sequencing. Next, the stability of circAAGAB increased by interacting with the RNA binding protein FUS. Moreover, cellular and nuclear fractionation showed that most circAAGAB resided in the cytoplasm and that it up-regulated KIAA1522, NKX3-1, and JADE3 by sponging miR-378 h. Lastly, the functions of circAAGAB were explored by identifying its down-stream genes using Affymetrix microarrays and validated by in vitro assays.

RESULTS

The results showed that circAAGAB reduced cell colony formation, cell migration, and signaling through p38 MAPK pathway, as well as increased radiosensitivity.

CONCLUSION

These findings suggest that the oxygen-responsive circAAGAB acts as a tumor suppressor in breast cancer, and may contribute to the development of a more specific therapeutic regimen for breast cancer.

CircMAN1A2 contributes to nasopharyngeal carcinoma progression via enhancing the ubiquitination of ATMIN through miR-135a-3p/UBR5 axis

Recently, the dysregulation of circRNAs has been increasingly implicated in the pathogenesis of nasopharyngeal carcinoma (NPC). Among these circRNAs, circMAN1A2 has been highlighted for the up-regulated expression in NPC, whereas the underlying mechanisms have not been clearly established. Thus, the aim of this study was to delineate the tumor-supporting role of circMAN1A2 in the oncogenesis and metastases of NPC. We validated through qRT-PCR that circMAN1A2 was highly expressed in NPC tissues and NPC cells. Survival analysis through Kaplan-Meier method showed that the overall survival, disease-free survival, and distant metastasis-free survival of patients was negatively correlated with the expression of circMAN1A2. Then, gain- and loss-of function assays demonstrated that circMAN1A2 knockdown could impede the proliferation, migration, invasion, and EMT in NPC cells. Further, we conducted dual luciferase reporter gene, RIP, and RNA pull down assays, unveiling that circMAN1A2 functioned as a sponge of miR-135a-3p, and miR-135a-3p targeted UBR5. Additionally, UBR5 interacted with ATMIN to foster the ubiquitination of ATMIN, thereby expediting the malignant behaviors of NPC cells as well as the lung and inguinal lymph node metastases of NPC tumors in vivo. Together, our study uncovered the tumor-initiating and pro-metastatic role of circMAN1A2-miR-135a-3p-UBR5-ATMIN axis in NPC regulation that may be a potential therapeutic target for human NPC.

Hsa_circ_0005273 acts as a sponge of miR-509-3p to promote the malignant behaviors of breast cancer by regulating HMMR expression

BACKGROUND

Breast cancer (BC) is a common malignant tumor that threatens the health of women worldwide. Hsa_circ_0005273 has been identified as a carcinogenic factor in some solid tumors, including BC. However, the molecular mechanism of circ_0005273 in BC is poorly defined.

METHODS

The expression of circ_0005273, miR-509-3p, and hyaluronan-mediated motility receptor (HMMR) mRNA in BC was detected by quantitative real-time polymerase chain reaction. Cell proliferation, migration, invasion, and apoptosis were detected by 5-ethynyl-2'-deoxyuridine, transwell, and flow cytometry assays. The glycolysis level was detected via specific kits. Western blot was used to detect protein expression. Binding between miR-509-3p and circ_0005273 or HMMR was also verified by dual-luciferase reporter, RNA pull-down, and RNA immunoprecipitation assays. Xenograft tumor model was used to detect tumor changes in mice, and immunohistochemistry assay was employed to detect Ki-67 abundance.

RESULTS

Circ_0005273 was increased in BC tissues and cells. Circ_0005273 knockdown might inhibit BC cell proliferation, migration, invasion, glutamine metabolism, and induce apoptosis. Circ_0005273 was a miR-509-3p, and the repression role of circ_0005273 absence on BC cell development was weakened by miR-509-3p inhibitor or HMMR overexpression. Circ_0005273 up-regulated the expression of HMMR by sponging miR-509-3p. Additionally, circ_0005273 silencing might hinder tumor growth in vivo.

CONCLUSION

Circ_0005273 knockdown might repress BC cell malignant behaviors by regulating the miR-509-3p/HMMR axis, which might provide a potential therapeutic target for BC.

Exosomal circular RNA: a signature for lung cancer progression

Membrane vesicles having a diameter of 30-150 nm are known as exosomes. Several cancer types secrete exosomes, which may contain proteins, circular RNAs (circRNAs), microRNAs, or DNA. CircRNAs are endogenous RNAs that do not code for proteins and can create continuous and covalently closed loops. In cancer pathogenesis, especially metastasis, exosomal circRNAs (exo-circRNAs) have a crucial role mainly due to the frequently aberrant expression levels within tumors. However, neither the activities nor the regulatory mechanisms of exo-circRNAs in advancing lung cancer (LC) are obvious. A better understanding of the regulation and network connections of exo-circRNAs will lead to better treatment for LCs. The main objective of the current review is to highlight the functions and mechanisms of exo-circRNAs in LC and assess the relationships between exo-circRNA dysregulation and LC progression. In addition, underline the possible therapeutic targets based on exo-circRNA modulating.

Upregulation of circ_0008812 and circ_0001583 predicts poor prognosis and promotes breast cancer proliferation

Background: Accumulating evidence suggests that circular RNAs (circRNAs) are highly correlated with tumor progression and pathogenesis in breast cancer. Whereas, their regulatory roles and corresponding mechanisms in breast cancer are still not exhaustive. Thus, we intended to establish circRNA-mediated competive endogenous RNA (ceRNA) network to uncover the possible roles and clinical implications of circRNAs in breast cancer.

Methods: Microarray and RNA-sequencing (RNA-seq) data were download from GEO and TCGA database to screen for differentially expressed RNAs (DEcircRNAs, DEmiRNAs, DEmRNAs) in breast cancer. By implementing online databases, we established ceRNA networks, performed gene set enrichment analysis, constructed protein-protein interaction (PPI) networks, and assessed the expression levels and prognostic significance of hub genes. Subsequently, we explored the functions of prognosis-related genes and constructed gene-drug interaction networks. Finally, the functional roles of DEcircRNAs in breast cancer were revealed via MTT and colony formation assay.

Results: Based on the identified 8 DEcircRNAs, 25 miRNAs and 216 mRNAs, a ceRNA regulatory network was established. Further analysis revealed that prominent enrichments were transcription factor binding, transforming growth factor-beta (TGF-β) and Apelin signaling pathway etc. PPI network and survival curves analysis showed that elevated levels of hub genes (RACGAP1 and KPNA2) were associated with poorer prognosis. They were found to be positively relevant to cell cycle and proliferation. Then a prognostic sub-network of ceRNA was constructed, consisting of 2 circRNAs, 4 miRNAs and 2 mRNAs. The gene-drug interaction network showed that numerous drugs could regulate the expression of these two prognosis-related genes. Functional experiments showed that depletion of circ_0008812 and circ_0001583 could significantly inhibit the proliferation of MCF-7 cells.

Conclusion: Our study constructed 4 prognostic regulatory axes that are significantly correlated with tumor prognosis in breast cancer patients, and uncover the roles of circ_0008812 and circ_0001583 in breast cancer, providing a new perspective into the molecular mechanisms of breast cancer pathogenesis.

Stem cell-derived exosomal transcriptomes for wound healing

Wound healing is a complex and integrated process of the interaction of various components within the injured tissue. Accumulating evidence suggested that stem cell-derived exosomal transcriptomes could serve as key regulatory molecules in wound healing in stem cell therapy. Stem cell-derived exosomal transcriptomes mainly consist of long noncoding RNAs (lncRNAs), microRNAs (miRNAs), circular RNAs (circRNAs) and messenger RNAs (mRNAs). In this article we presented a brief introduction on the wound repair process and exosomal transcriptomes. Meanwhile, we summarized our current knowledge of the involvement of exosomal transcriptomes in physiological and pathological wound repair process including inflammation, angiogenesis, and scar formation.

circ_0008797 attenuates non-small cell lung cancer proliferation, metastasis, and aerobic glycolysis by sponging miR-301a-3p/SOCS2

PURPOSE

This paper firstly reported the exact function of circ_0008797 on non-small cell lung cancer (NSCLC) progression.

METHODS

NSCLC tissues/matched normal tissues were harvested from 88 NSCLC patients. RNA fluorescence in situ hybridization experiment was applied to detect circ_0008797 localization in NSCLC cells. circ_0008797 effect on NSCLC cells proliferation, migration, invasion, glucolysis, and apoptosis was researched by cell counting kit-8 assay, 5-ethynyl-2'deoxyuridine assay, Transwell experiment, glycolysis assay, and TUNEL assay. Dual luciferase reporter gene assay, RNA pull-down assay and RNA immunoprecipitation assay were used to verify the binding relationship between two genes. In vivo tumorigenesis and lung metastasis was performed using nude mice. Quantitative reverse transcription-polymerase chain reaction, immunohistochemistry and western blot were applied for genes expression detection. Hematoxylin and eosin staining was performed on lung tissues.

RESULTS

circ_0008797 was low expressed in NSCLC tissues and cell lines, associating with poor outcome (p <.05). circ_0008797 was mainly expressed in NSCLC cells cytoplasm. circ_0008797 inhibited proliferation, migration, invasion, and glycolysis, but enhanced apoptosis of NSCLC cells (p <.05). circ_0008797 attenuated malignant phenotype of NSCLC cells by sponging miR-301a-3p. circ_0008797 facilitated SOCS2 expression by sponging miR-301a-3p. SOCS2 knockdown partially reversed the inhibitory effect of miR-301a-3p inhibition on NSCLC cells malignant phenotype (p <.05). circ_0008797 attenuated NSCLC prolifearion and metastasis in vivo (p <.05).

CONCLUSION

circ_0008797 attenuates NSCLC proliferation, metastasis and aerobic glycolysis by sponging miR-301a-3p/SOCS2.

RNMFLP: Predicting circRNA-disease associations based on robust nonnegative matrix factorization and label propagation

Circular RNAs (circRNAs) are a class of structurally stable endogenous noncoding RNA molecules. Increasing studies indicate that circRNAs play vital roles in human diseases. However, validating disease-related circRNAs in vivo is costly and time-consuming. A reliable and effective computational method to identify circRNA-disease associations deserves further studies. In this study, we propose a computational method called RNMFLP that combines robust nonnegative matrix factorization (RNMF) and label propagation algorithm (LP) to predict circRNA-disease associations. First, to reduce the impact of false negative data, the original circRNA-disease adjacency matrix is updated by matrix multiplication using the integrated circRNA similarity and the disease similarity information. Subsequently, the RNMF algorithm is used to obtain the restricted latent space to capture potential circRNA-disease pairs from the association matrix. Finally, the LP algorithm is utilized to predict more accurate circRNA-disease associations from the integrated circRNA similarity network and integrated disease similarity network, respectively. Fivefold cross-validation of four datasets shows that RNMFLP is superior to the state-of-the-art methods. In addition, case studies on lung cancer, hepatocellular carcinoma and colorectal cancer further demonstrate the reliability of our method to discover disease-related circRNAs.

CircZDBF2 up-regulates RNF145 by ceRNA model and recruits CEBPB to accelerate oral squamous cell carcinoma progression via NFκB signaling pathway

Background

Oral squamous cell carcinoma (OSCC), as one of the commonest malignancies showing poor prognosis, has been increasingly suggested to be modulated by circular RNAs (circRNAs). Through GEO (Gene Expression Omnibus) database, a circRNA derived from ZDBF2 (circZDBF2) was uncovered to be with high expression in OSCC tissues, while how it may function in OSCC remains unclear.

Methods

CircZDBF2 expression was firstly verified in OSCC cells via qRT-PCR. CCK-8, along with colony formation, wound healing, transwell and western blot assays was performed to assess the malignant cell behaviors in OSCC cells. Further, RNA pull down assay, RIP assay, as well as luciferase reporter assay was performed to testify the interaction between circZDBF2 and RNAs.

Results

CircZDBF2 expressed at a high level in OSCC cells and it accelerated OSCC cell proliferation, migration, invasion as well as EMT (epithelial-mesenchymal transition) process. Further, circZDBF2 sponged miR-362-5p and miR-500b-5p in OSCC cells to release their target ring finger protein 145 (RNF145). RNF145 expressed at a high level in OSCC cells and circZDBF2 facilitated RNF145 transcription by recruiting the transcription factor CCAAT enhancer binding protein beta (CEBPB). Moreover, RNF145 activated NFκB (nuclear factor kappa B) signaling pathway and regulated IL-8 (C-X-C motif chemokine ligand 8) transcription.

Conclusion

CircZDBF2 up-regulated RNF145 expression by sponging miR-362-5p and miR-500b-5p and recruiting CEBPB, thereby promoting OSCC progression via NFκB signaling pathway. The findings recommend circZDBF2 as a probable therapeutic target for OSCC.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03347-1.

Biogenesis, functions, and clinical implications of circular RNAs in non-small cell lung cancer

Lung cancer (LC) is the leading cause of cancer-related deaths worldwide, with high morbidity and mortality. Non-small cell lung cancer (NSCLC) is a major pathological type of LC and accounts for more than 80% of all cases. Circular RNAs (circRNAs) are a large class of non-coding RNAs (ncRNAs) with covalently closed-loop structures, a high abundance, and tissue-specific expression patterns. They participate in various pathophysiological processes by regulating complex gene networks involved in proliferation, apoptosis, migration, and epithelial-to-mesenchymal transition (EMT), as well as metastasis. A growing number of studies have revealed that the dysregulation of circRNAs contributes to many aspects of cancer progression, such as its occurrence, metastasis, and recurrence, suggesting their great potential as efficient and specific biomarkers in the diagnosis, prognosis, and therapeutic targeting of NSCLC. In this review, we systematically elucidate the characteristics, biogenesis, and functions of circRNAs and focus on their molecular mechanisms in NSCLC progression. Moreover, we highlight their clinical implications in NSCLC treatment.

Andrographolide suppresses osteoarthritis progression by regulating circ_Rapgef1/miR-383-3p/NLRP3 signaling axis

BACKGROUND

Andrographolide (AD) has been reported to play a potential anti-arthritic role by facilitating the proliferation and inhibiting the apoptosis of chondrocytes. However, the molecular mechanism underlying the protective role of AD in osteoarthritis (OA) remains to be elucidated.

METHODS

OA mice model was established via anterior cruciate ligament transection (ACLT) operation. OA cell model was established through treating mice primary chondrocytes with LPS (1 μg/mL, 24 h). Enzyme-linked immunosorbent assay (ELISA) was performed to measure the concentrations of inflammatory cytokines in the supernatant. Cell proliferation was assessed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and 5-Ethynyl-2'-deoxyuridine (EdU) assay. Cell apoptosis was evaluated by flow cytometry. The intermolecular interaction was verified by dual-luciferase reporter assay.

RESULTS

AD administration reduced the infiltration of inflammatory cells in the synovial tissues of ankle joint and suppressed the inflammatory response in OA mice model in vivo. Lipopolysaccharide (LPS) stimulation suppressed the proliferation and induced the apoptosis and inflammation of chondrocytes, and AD treatment protected chondrocytes from LPS-induced dysfunction. Circular RNA (circRNA) Rap guanine nucleotide exchange factor 1 (circ_Rapgef1) overexpression attenuated AD-mediated protective effects in OA cell model. Circ_Rapgef1/microRNA-383-3p (miR-383-3p)/Nod-like receptor pyrin domain 3 (NLRP3) axis was identified in this study for the first time. Circ_Rapgef1 overexpression-mediated effects were partly reversed by the overexpression of miR-383-3p in chondrocytes. NLRP3 silencing partly overturned miR-383-3p knockdown-mediated effects in chondrocytes. Circ_Rapgef1 overexpression up-regulated the expression of NLRP3 partly by targeting miR-383-3p in chondrocytes.

CONCLUSION

Circ_Rapgef1 suppressed AD-mediated protective effects in OA partly by regulating miR-383-3p/NLRP3 signaling.

The Emerging Roles of Circular RNAs in the Chemoresistance of Gastrointestinal Cancer

Gastrointestinal (GI) cancer represents a major global health problem due to its aggressive characteristics and poor prognosis. Despite the progress achieved in the development of treatment regimens, the clinical outcomes and therapeutic responses of patients with GI cancer remain unsatisfactory. Chemoresistance arising throughout the clinical intervention is undoubtedly a critical barrier for the successful treatment of GI cancer. However, the precise mechanisms associated with chemoresistance in GI cancer remain unclear. In the past decade, accumulating evidence has indicated that circular RNAs (circRNAs) play a key role in regulating cancer progression and chemoresistance. Notably, circRNAs function as molecular sponges that sequester microRNAs (miRNAs) and/or proteins, and thus indirectly control the expression of specific genes, which eventually promote or suppress drug resistance in GI cancer. Therefore, circRNAs may represent potential therapeutic targets for overcoming drug resistance in patients with GI cancer. This review comprehensively summarizes the regulatory roles of circRNAs in the development of chemoresistance in different GI cancers, including colorectal cancer, gastric cancer and esophageal cancer, as well as deciphers the underlying mechanisms and key molecules involved. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies against GI cancer.

Advances on biological functions of exosomal non-coding RNAs in osteoarthritis

Exosomes can be secreted by various cells and function as intercellular communication vehicles by delivering specific cargoes from the donor cells to the recipient cells through their paracrine activity. Recently, an increasing number of studies have shown that non-coding RNAs (ncRNAs) could be entrapped in and transferred between cartilage-related cells as exosomal cargoes to modulate the expression of various target genes by regulation at post-transcriptional and post-translational levels. They are mainly comprised of microRNAs, long non-coding RNAs, and circular RNAs. Articular cartilage degeneration is one of the main pathological features of osteoarthritis. Exosomal ncRNAs are involved in pathological processes of osteoarthritis, such as proliferation, migration, chondrogenesis, chondrocyte differentiation induction, extracellular matrix formation, apoptosis, and inflammation. In this review, we summarize the biological functions of exosomal ncRNAs in cartilage homeostasis and osteoarthritis progression and discuss the perspectives and challenges of exosomal ncRNAs application for osteoarthritis patients in the future. Exosomal ncRNA has an important regulatory role in the pathogenesis of osteoarthritis, but more evidence is needed for clinical application.

A survey of circular RNAs in complex diseases: databases, tools and computational methods

Circular RNAs (circRNAs) are a category of novelty discovered competing endogenous non-coding RNAs that have been proved to implicate many human complex diseases. A large number of circRNAs have been confirmed to be involved in cancer progression and are expected to become promising biomarkers for tumor diagnosis and targeted therapy. Deciphering the underlying relationships between circRNAs and diseases may provide new insights for us to understand the pathogenesis of complex diseases and further characterize the biological functions of circRNAs. As traditional experimental methods are usually time-consuming and laborious, computational models have made significant progress in systematically exploring potential circRNA-disease associations, which not only creates new opportunities for investigating pathogenic mechanisms at the level of circRNAs, but also helps to significantly improve the efficiency of clinical trials. In this review, we first summarize the functions and characteristics of circRNAs and introduce some representative circRNAs related to tumorigenesis. Then, we mainly investigate the available databases and tools dedicated to circRNA and disease studies. Next, we present a comprehensive review of computational methods for predicting circRNA-disease associations and classify them into five categories, including network propagating-based, path-based, matrix factorization-based, deep learning-based and other machine learning methods. Finally, we further discuss the challenges and future researches in this field.

A Novel circRNA-miRNA-mRNA Hub Regulatory Network in Lung Adenocarcinoma

The growing evidence suggests that circular RNAs (circRNAs) have significant associations with tumor occurrence and progression, yet the regulatory mechanism of circRNAs in lung adenocarcinoma (LUAD) remains unclear. This study clarified the potentially regulatory network and functional mechanism of circRNAs in LUAD. The expression data of circRNAs, microRNAs (miRNAs), and messenger RNAs (mRNAs) were obtained from the Gene Expression Omnibus (GEO) database. Relying on GSE101586, GSE101684, and GSE112214, we identified differentially expressed circRNAs (DEcircRNAs). Depending on GSE135918 and GSE32863, we screened out differentially expressed miRNAs (DEmiRNAs) and mRNAs (DEmRNAs), respectively. Then, a novel competing endogenous RNA (ceRNA) regulatory network related to LUAD was constructed. We also revealed biological processes and signal pathways regulated by these DEcircRNAs. Based on gene expression data and survival information of LUAD patients in The Cancer Genome Atlas (TCGA) and GEO, we implemented survival analysis to select DEmRNAs related to prognosis and build a novel circRNA-miRNA-mRNA hub regulatory network. Meanwhile, quantitative real-time PCR (qRT-PCR) was utilized to validate DEcircRNAs in the ceRNA hub regulatory network. As a result, a total of 8 DEcircRNAs, 19 DEmiRNAs, and 85 DEmRNAs were identified. The novel ceRNA regulatory network included 5 circRNAs, 8 miRNAs, and 22 mRNAs. The final ceRNA hub regulatory network contained two circRNAs, two miRNAs, and two mRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that the five DEcircRNAs may affect LUAD onset and progression through Wnt signaling pathway and Hippo signaling pathway. All in all, this study revealed the regulatory network and functional mechanism of circRNA-related ceRNAs in LUAD.

Circular RNA: A novel type of biomarker for glioma (Review)

With the rapid development of sequencing technologies, the characteristics and functions of circular RNAs (circRNAs) in different tissues, and their underlying pathophysiological mechanisms, have been identified. circRNAs are significantly enriched in the brain and are continually expressed from the embryonic stage to the adult stage in rats. Previous studies have reported that certain circRNAs are differentially expressed in glioma and regulate a number of biological processes, such as cell proliferation, metastasis and oncogenesis of glioma. Furthermore, certain circRNAs have been associated with tumor size, World Health Organization tumor grade and poor prognosis in patients with glioma. It has been hypothesized that circRNAs may be involved in the onset and progression of glioma through transcriptional regulation, protein translation and binding to microRNAs. These properties and functions suggest the potential of circRNAs as prognostic biomarkers and therapeutic targets for glioma. For the present review, published studies were examined from PubMed, Embase, Cochrane Central and the reference lists of the retrieved articles. The aim of the present review was to summarize the progress of circRNA research in glioma, discuss the potential diagnostic and prognostic values, and the roles of circRNAs in glioma, and provide a novel theoretical basis and research concepts for the prediction, diagnosis and treatment of glioma.