Functional role of circular RNAs in cancer development and progression

The regulatory roles of RNA-binding proteins in the tumour immune microenvironment of gastrointestinal malignancies

The crosstalk between the tumour immune microenvironment (TIME) and tumour cells promote immune evasion and resistance to immunotherapy in gastrointestinal (GI) tumours. Post-transcriptional regulation of genes is pivotal to GI tumours progression, and RNA-binding proteins (RBPs) serve as key regulators via their RNA-binding domains. RBPs may exhibit either anti-tumour or pro-tumour functions by influencing the TIME through the modulation of mRNAs and non-coding RNAs expression, as well as post-transcriptional modifications, primarily N6-methyladenosine (m6A). Aberrant regulation of RBPs, such as HuR and YBX1, typically enhances tumour immune escape and impacts prognosis of GI tumour patients. Further, while targeting RBPs offers a promising strategy for improving immunotherapy in GI cancers, the mechanisms by which RBPs regulate the TIME in these tumours remain poorly understood, and the therapeutic application is still in its early stages. This review summarizes current advances in exploring the roles of RBPs in regulating genes expression and their effect on the TIME of GI tumours, then providing theoretical insights for RBP-targeted cancer therapies.

CircATP5C1 promotes triple-negative breast cancer progression by binding IGF2BP2 to modulate CSF-1 secretion

Triple-negative breast cancer (TNBC) is a common malignant disease among females and severely threatens the health of women worldwide. Nowadays, circular RNAs (circRNAs) aroused our interest for their functions in human cancers, including TNBC. However, the mechanism of most circRNAs in the progression of TNBC remains unclear. We found a novel circRNA named circATP5C1, whose function in TNBC remains uncovered. Tissue microarray was used to analyze the association between the expression of circATP5C1 and the prognoses of TNBC patients. Gain-and loss-of-function experiments were performed to validate the biological functions of circATP5C1 in different TNBC cell lines. RNA-seq analyses were conducted to find out the target genes regulated by circATP5C1. RNA pull-down assay and mass spectrometry were used to select the proteins associated with circATP5C1. RNA FISH-immunofluorescence and RNA immunoprecipitation (RIP) were complemented to validate the interaction between circATP5C1 and its binding protein. CircATP5C1 was identified to have predictive function in prognosis of TNBC patients. CircATP5C1 advanced the progression of TNBC cells. Mechanistically, Colony stimulating factor 1 (CSF-1) is a vital downstream gene regulated by circATP5C1. The alteration of CSF-1 expression level was validated due to the interaction between circATP5C1 and insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2). Rescue experiments demonstrated that circATP5C1 accelerates the progression of TNBC partly via binding with IGF2BP2 to increase the secretion of CSF-1. This study uncovers a novel mechanism of circATP5C1/IGF2BP2/CSF-1 pathway in regulating progression of TNBC.

Circular RNA, A Molecule with Potential Chemistry and Applications in RNA-based Cancer Therapeutics: An Insight into Recent Advances

Non-coding RNAs (ncRNAs) are functional RNA molecules that do not code for proteins. Among these, circular RNAs (circRNAs) represent a recently identified class of endogenous ncRNAs with a pivotal role in gene regulation, alongside short ncRNAs (e.g., microRNAs or miRNAs) and long non-coding RNAs (lncRNAs). CircRNAs are characterized by their single-stranded, covalently closed circular structure, which lacks polyadenylated tails and 5'-3' ends. This unique circular conformation makes them resistant to exonuclease degradation, rendering them more stable than linear RNAs, such as mRNAs in human blood cells, which highlights their potential as biomarkers. Both linear and circular RNAs are derived from pre-mRNA precursors. However, while linear RNAs are produced through conventional splicing, circRNAs are primarily formed through a process known as reverse splicing. CircRNAs can be categorized into five basic types: exon circRNAs, circular intronic RNAs, exon-intron circRNAs, intergenic circRNAs, and fusion circRNAs. These molecules have been shown to significantly influence key hallmarks of cancer, including sustained growth signaling, proliferation, angiogenesis, resistance to apoptosis, unlimited replicative potential, and metastasis. This article will delve into the biogenesis and functions of circRNAs, explore their roles in cancer, and discuss their potential applications as therapeutic options and diagnostic biomarkers.

Non-coding RNAs as potential mediators of resistance to lung cancer immunotherapy and chemotherapy

Lung cancer is a common cause of cancer-related death globally. The majority of lung cancer patients initially benefit from chemotherapy and immunotherapy. However, as the treatment cycle progresses and the disease evolves, the emergence of acquired resistance leads to treatment failure. Many researches have shown that non-coding RNAs (ncRNAs) not only influence lung cancer progression but also act as potential mediators of immunotherapy and chemotherapy resistance in lung cancer, mediating drug resistance by regulating multiple targets and pathways. In addition, the regulation of immune response by ncRNAs is dualistic, forming a microenvironment for inhibits/promotes immune escape through changes in the expression of immune checkpoints. The aim of this review is to understand the effects of ncRNAs on the occurrence and development of lung cancer, focusing on the role of ncRNAs in regulating drug resistance of lung cancer.

SRSF3 and hnRNP A1-mediated m6A-modified circCDK14 regulates intramuscular fat deposition by acting as miR-4492-z sponge

The intramuscular fat (IMF) content of yak beef is critical for determining its quality. Circular RNAs (circRNAs) are a group of endogenous non-coding RNAs that have emerged as important factors in the regulation of IMF deposition. However, the molecular mechanisms through which circRNAs regulate IMF deposition, particularly in yaks, remain unclear. In the present study, a novel circRNA, circCDK14 (originating from the yak's CDK14 gene), was identified by sequencing and RNase R treatment. In our previous study, we successfully established a ceRNA network map and identified miR-4492-z, which interacts with circCDK14. Furthermore, using methylation prediction software, we predicted two genes, SRSF3 and hnRNP A1, that have a strong binding relationship with circCDK14; existing research has confirmed their close association with m6A methylation modifications. On the basis of these findings, we comprehensively evaluated the effects of circCDK14, miR-4492-z, SRSF3 and hnRNP A1 on the proliferation and differentiation of yak intramuscular pre-adipocytes using EdU, CCK-8, BODIPY, Oil Red O and qRT-PCR analyses. Mechanistically, the interaction between circCDK14 and miR-4492-z was validated using a dual-luciferase reporter gene assay and rescue experiments. RIP assays revealed the binding interaction of circCDK14 with SRSF3 and hnRNP A1. The MeRIP experiments showed modification of circCDK14 methylation, with SRSF3 and hnRNP A1 promoting the methylation and translocation of circCDK14 from the nucleus to the cytoplasm. In summary, our results suggest that m6A-modified circCDK14 plays a crucial role as an miR-4492-z sponge in regulating IMF deposition in yaks and that the nuclear export of circCDK14 correlates with the expression levels of SRSF3 and hnRNP A1. This study provides a theoretical basis for the improvement of yak meat quality and promotes the development of molecular yak breeding.

Role of circRNAs in regulating cell death in cancer: a comprehensive review

Despite multiple diagnostic and therapeutic advances, including surgery, radiation therapy, and chemotherapy, cancer preserved its spot as a global health concern. Prompt cancer diagnosis, treatment, and prognosis depend on the discovery of new biomarkers and therapeutic strategies. Circular RNAs (circRNAs) are considered as a stable, conserved, abundant, and varied group of RNA molecules that perform multiple roles such as gene regulation. There is evidence that circRNAs interact with RNA-binding proteins, especially capturing miRNAs. An extensive amount of research has presented the substantial contribution of circRNAs in various types of cancer. To fully understand the linkage between circRNAs and cancer growth as a consequence of various cell death processes, including autophagy, ferroptosis, and apoptosis, more research is necessary. The expression of circRNAs could be controlled to limit the occurrence and growth of cancer, providing a more encouraging method of cancer treatment. Consequently, it is critical to understand how circRNAs affect various forms of cancer cell death and evaluate whether circRNAs could be used as targets to induce tumor death and increase the efficacy of chemotherapy. The current study aims to review and comprehend the effects that circular RNAs exert on cell apoptosis, autophagy, and ferroptosis in cancer to investigate potential cancer treatment targets.

Circ_BLNK is a Unique Molecular Marker in Non-small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) patients are characterized by distant metastasis and poor prognosis. Growing evidence has implied that circular RNAs (circRNAs) are involved in multiple tumor progression, including NSCLC. The objective of the present study was to functionally dissect the role and mechanism of circ_BLNK in NSCLC development and progression. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the expression of circ_BLNK, miR-942-5p, and forkhead box protein O1 (FOXO1) in NSCLC tissues and cells. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, 5-ethynyl-2'-deoxyuridine (EdU) assay and colony formation assay detected cell proliferation; the protein expression levels were tested by western blot assay; cell apoptosis was measured by flow cytometry, and transwell assay detected cell migration and invasion. The molecular targeting relationship was determined by dual-luciferase reporter assay. The effect of circ_BLNK overexpression on tumor growth was detected by in vivo experiments and immunohistochemistry. Circ_BLNK was dramatically decreased in NSCLC, and overexpression of circ_BLNK inhibited proliferation, migration, and invasion of NSCLC cells and promoted cell apoptosis. Circ_BLNK level was negatively correlated with miR-942-5p expression and positively correlated with FOXO1 expression. Moreover, circ_BLNK acted as a sponge for miR-942-5p, which targeted FOXO1. Rescue assays presented that miR-942-5p reversed the anticancer action of circ_BLNK in NSCLC. Besides that, miR-942-5p inhibition suppressed the oncogenic behaviors, which were attenuated by FOXO1 knockdown. Animal experiments exhibited that circ_BLNK upregulation repressed tumor growth in vivo. Our study demonstrated a novel regulatory mechanism that circ_BLNK/miR-942-5p/FOXO1 axis adjusted non-small cell lung cancer development.

Circular RNAs: history, metabolism, mechanisms of function, and regulatory roles at a glance

Circular RNAs (circRNAs) are non-coding RNA (ncRNA) molecules that, due to their covalent ring structure and lack of free ends, have a very high intracellular stability compared to their linear counterparts. In general, circRNAs are expressed in mammalian cells and exhibit tissue/cell-specific expression patterns. Mounting evidence is indicative that circRNAs regulate a variety of cellular processes by acting as miRNA sponges, transcriptional regulators, protein sponges, molecular scaffolds, and protein/peptide translators. The emergence of the biological functions of circRNAs has brought a novel outlook to our better understanding of cellular physiology and disease pathogenesis. CircRNAs have also been shown to play a critical role in the occurrence, development and progression of cancers. Their participation in the pathophysiology of various diseases including cardiovascular diseases, diabetes and neurological disorders is very important. Such characteristics have led to more studies investigating circRNAs as promising tools in molecular medicine and targeted therapy.

Recent Advances in the Role of Non-coding RNAs in Fetal Alcohol Spectrum Disorders

Despite numerous preclinical studies modeling fetal alcohol spectrum disorder (FASD)-associated neurodevelopmental deficits to date, a comprehensive molecular landscape dictating these deficits remains poorly understood. Non-coding RNAs constitute a substantial layer of epigenetic regulation of gene expression at the transcriptional, post-transcriptional, translational, and post-translational levels. Yet, little is known about the differential expression of non-coding RNAs in the context of prenatal alcohol exposure (PAE) that are mechanistically linked with FASD-related neurobehavior deficits. This chapter reviews our current knowledge from preclinical studies in non-coding RNA-mediated molecular mechanisms that may underlie FASD pathophysiology. This chapter also summarizes relevant clinical evidence and current efforts in utilizing these non-coding RNA molecules as biomarkers of PAE-associated deficits impacting central nervous system (CNS) function. Unraveling the diverse roles of various species of non-coding RNAs is critical to enhancing our comprehension of these intricate molecular pathways. Understanding these pathways would likely contribute to identifying critical molecular target(s) for developing efficient treatment strategies and prognostic and diagnostic markers fostering advancements in treating and managing FASD-related CNS dysfunction.

Circ-Luc7l Absence Attenuates Diabetic Nephropathy Progression by Reducing Mesangial Cell Excessive Proliferation, Inflammation, and Extracellular Matrix Accumulation via Mediating the miR-205-5p/Tgfbr1 Pathway

Diabetic nephropathy (DN) threatens the survival quality of patients, with complex pathogenesis. Circular RNA (circRNA) dysregulation occurs in DN development. This work aimed to investigate the role of circ-Luc7l in DN cell models and related molecular mechanisms. The expression of circ-Luc7l, microRNA (miR)-205-5p, and transforming growth factor-beta receptor 1 (Tgfbr1) was examined by real-time quantitative PCR (RT-qPCR). Cell viability and proliferation were detected by Cell Counting Kit-8 (CCK-8) assay and EdU assay. The expression of extracellular matrix (ECM)-related markers and Tgrbr1 protein was measured by Western blot. The binding between miR-205-5p and circ-Luc7l or Tgfbr1 was validated by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, or RNA pull-down assay. Experimental animal models were established to elucidate the function of circ-Luc7l in vivo. Circ-Luc7l expression was notably enhanced in high glucose (HG)-treated mesangial cells. Knockdown of circ-Luc7l attenuated HG-induced cell proliferation, inflammation, and ECM accumulation in vitro and relieved inflammation and ECM accumulation of kidneys of diabetic mice in vivo. Circ-Luc7l targeted miR-205-5p, and miR-205-5p inhibition rescued the depletion effects of circ-Luc7l knockdown on cell proliferation, inflammation, and ECM accumulation. MiR-205-5p bound to Tgfbr1 whose expression was negatively regulated by circ-Luc7l. Tgfbr1 overexpression also rescued the depletion effects of circ-Luc7l knockdown on cell proliferation, inflammation, and ECM accumulation. In HG conditions, increased circ-Luc7l upregulated Tgfbr1 expression via targeting miR-205-5p to induce DN progression.

Hsa_circ_0078767 Enhances Osteosarcoma Chemoresistance to Doxorubicin Through the Regulation of the miR-188-3p/GPX4 Axis

Background

Osteosarcoma (OS) is a primary malignancy of bone. The emergence of chemoresistance represents a persistent barrier to effective cancer patient care. This analysis sought to examine hsa_circ_0078767 as a mediator of doxorubicin (DOX) resistance in OS.

Methods

Levels of hsa_circ_0078767, miR-188-3p, and glutathione peroxidase 4 (GPX4) in OS clinical tissue samples and cell lines were evaluated by quantitative polymerase chain reaction (qPCR) and Western blotting. Associations between hsa_circ_0078767 levels in clinical samples and patient overall survival were assessed with Kaplan-Meier curves. CCK-8 assays were utilized as a means of examining DOX half-inhibitory concentration (IC50) values. RNA immunoprecipitation and pull-down, as well as reporter assays, investigated interactions between hsa_circ_0078767, miR-188-3p, and GPX4 within OS cells exhibiting DOX resistance.

Results

OS patient tissues and cell lines resistant to DOX exhibited elevated hsa_circ_0078767 and GPX4 expression together with a reduction in miR-188-3p levels. Inhibiting hsa_circ_0078767 expression contributed to a profound decrease in the ability of OS tumors to resist DOX. Mechanistically, it was determined that hsa_circ_0078767 can enhance DOX chemoresistance through its ability to bind and sequester miR-188-3p, which otherwise negatively modulates GPX4 to enhance chemosensitivity. Accordingly, the sequestration of miR-188-3p by hsa_circ_0078767 led to the derepression and upregulation of GPX4.

Conclusion

Hsa_circ_0078767 was found to modulate miR-188-3p/GPX4 signaling to enhance OS cell resistance to DOX treatment and facilitate disease progression. As such, hsa_circ_0078767 may represent a valuable biomarker or target for use in the context of OS patient management.

Analysis of hsa_circ_0136256 as a biomarker for fibrosis in systemic sclerosis

BACKGROUND

Exploration of whether circRNAs in the skin of systemic sclerosis (SSc) model mice interact with 4E-BP1 protein to mediate the mTOR signaling pathway to regulate SSc fibrosis is crucial to identify homologous human circRNAs as markers to guide the diagnosis and treatment of SSc.

METHODS

C57BL/6 mice aged 6-8 weeks and weighing approximately 20 g were subcutaneously injected with bleomycin (BLM) to establish an SSc model. High-throughput sequencing was used to screen the differentially expressed circRNA in the skin of SSc model mice and control mice. RNA immunoprecipitation and RNA pulldown confirmed the interaction between circRNA and 4E-BP1 protein. SSc model mice were treated with empty plasmid (OE-NC), overexpression plasmid of mmu_circ_0005372 (OE-circ_0005372), interference plasmid of mmu_circ_0005372 (sh-circ5372), mutant plasmid of mmu_circ_0005372 (circ5372-MT), mTOR activator (MHY1485), mTOR inhibitor (omipalisib), or JAK1/2 inhibitor (ruxolitinib). Sections of mouse skin tissue were stained with Hematoxylin and eosin and Masson's stain. The collagen volume fraction (CVF) was calculated as CVF = area of blue collagen/total area with ImageJ. The correlation between homologous human circRNAs and clinical data was analyzed.

RESULTS

Compared to the control group, 21,839 circRNAs were upregulated and 27, 946 circRNAs were downregulated in the skin tissue of mice in the SSc model group. Among them was mmu_circ_0005372, which is derived from the FZD3 gene, is closely related to fibrosis, and is involved in the mTOR signaling pathway. Hsa_circ_0136256 was identified as the homologous human circRNA of mmu_circ_0005372. RT-qPCR confirmed that the expression of mmu_circ_0005372 was significantly reduced in the skin tissue of SSc mice, and the expression of hsa_circ_0136256 was significantly reduced in the peripheral blood mononuclear cells of patients with SSc. The interaction between mmu_circ_0005372 and 4E-BP1 protein was inhibited in the skin tissue of SSc model mice. The results showed that the CVF of OE-circ_0005372 group was significantly lower than that of the sh-circ5372, circ5372-MT, and MHY1485 groups, indicating that OE-circ5372 significantly improved skin fibrosis in the SSc mice. ROC curve analysis was performed on hsa_circ_0136256 (AUC = 0.719, P = 0.035). The expression of hsa_circ_0136256 was negatively correlated with COL IV, RDW-SD, and RDW-CV, and positively correlated with VC, PLT, and PCT. The results suggested that hsa_circ_0136256 may have important roles in the clinical diagnosis of SSc.

CONCLUSION

Mmu_circ_0005372 and homologous human hsa_circ_0136256 may be biomarkers and therapeutic targets for SSc fibrosis.

Insights about exosomal circular RNAs as novel biomarkers and therapeutic targets for hepatocellular carcinoma

One of the most prevalent pathological types of Primary Liver Cancer (PLC) is the Hepatocellular Carcinoma (HCC) poses a global health issue. The high recurrence and metastasis rate of HCC, coupled with a low 5-year survival rate, result in a bleak prognosis. Exosomes, small extracellular vesicles released by various cells, contain diverse non-coding RNA molecules, including circular RNAs (circRNAs), which play a significant role in intercellular communication and can impact HCC progression. Studies have revealed the potential clinical applications of exosomal circRNAs as biomarkers and therapeutic targets for HCC. These circRNAs can be transferred via exosomes to nearby non-cancerous cells, thereby regulating HCC progression and influencing malignant phenotypes, such as cell proliferation, invasion, metastasis, and drug resistance. This review provides a comprehensive overview of the identified exosomal circRNAs, highlighting their potential as non-invasive biomarkers for HCC, and suggesting new perspectives for HCC diagnosis and treatment. The circRNA from exosomal organelles promotes metastasis and immune scape because of their unique chirality which is different from the Biomolecular Homochirality.

CircANXA4 (hsa_circ_0055087) regulates the miR-1256/PRM1 axis to promote tumor progression in colorectal cancer

Colorectal cancer (CRC) incidence ranks third among malignant cancers with a high propensity for distant metastasis. Despite continuous efforts to improve treatment, the prognosis especially in patients with advanced distant metastasis is low. The mechanism of development and progression of CRC is not fully understood. Non-coding RNAs (ncRNAs) have emerged as essential regulators in cancer progression. Here, we aim to dissect the role of one critical ncRNA, circANXA4, in CRC progression. CircANXA4 expression was analyzed by the GEO database. Differentially expressed circRNAs were identified by the Limma package R software. Expression of circANXA4 and miR-1256 was detected by qRT-PCR. The regulation of circANXA4 on cell proliferation and progression was confirmed with the cell viability assay using cell counting kit-8 (CCK-8) and transwell migration assay. RNA pull-down assay, RNA immunoprecipitation (RIP), and western blot were used to determine the interaction between circANXA4, miR-1256, and protamine1 (PRM1). CircANXA4 was upregulated in both CRC tissues and cell lines. Knockdown of circANXA4 effectively reduced cell proliferation, progression, and migration. Additionally, silencing circANXA4 remarkably increased miR-1256 expression, while reducing PRM1 expression, thereby demonstrating that circANXA4 downregulates miR-1256 expression through a complementary binding site. Rescue experiments revealed the interactions between circANXA4, miR-1256, and PRM1. Pearson correlation analysis revealed that circANXA4 expression positively correlated with PRM1 expression and miR-1256 expression inversely correlated with PRM1 expression. In sum, we demonstrated that circANXA4 promotes cancer cell proliferation and progression by sponging miR-1256 and upregulating PRM1 in CRC.

LGCDA: Predicting CircRNA-Disease Association Based on Fusion of Local and Global Features

CircRNA has been shown to be involved in the occurrence of many diseases. Several computational frameworks have been proposed to identify circRNA-disease associations. Despite the existing computational methods have obtained considerable successes, these methods still require to be improved as their performance may degrade due to the sparsity of the data and the problem of memory overflow. We develop a novel computational framework called LGCDA to predict circRNA-disease associations by fusing local and global features to solve the above mentioned problems. First, we construct closed local subgraphs by using k-hop closed subgraph and label the subgraphs to obtain rich graph pattern information. Then, the local features are extracted by using graph neural network (GNN). In addition, we fuse Gaussian interaction profile (GIP) kernel and cosine similarity to obtain global features. Finally, the score of circRNA-disease associations is predicted by using the multilayer perceptron (MLP) based on local and global features. We perform five-fold cross validation on five datasets for model evaluation and our model surpasses other advanced methods.

circ-ATAD1 as Competing Endogenous RNA for miR-191-5p Forces Non-small Cell Lung Cancer Progression

The association of circular RNAs (circRNAs) with non-small cell lung cancer (NSCLC) has been recognized extensively. In view of this, our study particularly surveyed the underlying mechanism of circ-ATAD1 in the disease. First, an analysis of the clinical expression of circ-ATPase family AAA domain containing 1 (ATAD1) was performed, followed by further evaluation of the relationship between circ-ATAD1 expression and prognosis. Then, A549 cells were treated with single transfection or combined transfection with the plasmid vectors that interfere with circ-ATAD1 or miR-191-5p. circ-ATAD1 and miR-191-5p levels were detected by reverse transcription quantitative polymerase chain reaction to verify the transfection success. Then, cell proliferation was checked by cell count kit-8 and clonal formation test. Cell apoptosis was analyzed by flow cytometry. Cell migration and invasion were examined by wound healing assay and Transwell. Finally, the targeting of miR-191-5p to circ-ATAD1 or Forkhead Box K1 (FOXK1) was verified by bioinformation website starBase analysis and dual-luciferase reporter assay. circ-ATAD1 was expressed abundantly in tumor tissues of NSCLC patients and had a predictive value in poor prognosis. circ-ATAD1 underexpression or miR-191-5p overexpression could obstruct A549 cells to behave aggressively, while circ-ATAD1 upregulation or miR-191-5p depletion resulted in the promotion of aggressiveness of A549 cells. Interestingly, circ-ATAD1 could decoy miR-191-5p. miR-191-5p negatively regulated FOXK1 expression, and downregulating miR-191-5p or upregulating FOXK1 rescued circ-ATAD1 downregulation-mediated influences on NSCLC cells. circ-ATAD1 accelerates NSCLC progression by absorbing miR-191-5p to upregulate FOXK1 expression.

Circ_100549 promotes tumor progression in lung adenocarcinoma through upregulation of BIRC6

Lung adenocarcinoma (LUAD) is a subtype of lung cancer with high incidence and mortality globally. Emerging evidence suggests that circular RNAs (circRNAs) exert critical functions in human cancers, including LUAD. CircRNA_100549 (circ_100549) has been reported to be significantly upregulated in non-small cell lung cancer (NSCLC) samples, while its role in modulating LUAD progression remains to be explored. The current study aims at investigating the functional roles of circ_100549 in LUAD and its downstream molecular mechanism. First, we found that the expression of circ_100549 was higher in LUAD cell lines. Loss-of-function assays verified that depletion of circ_100549 repressed LUAD cell proliferation but accelerated cell apoptosis. Furthermore, in vivo experiments demonstrated that silencing of circ_100549 suppressed tumor growth. Subsequently, based on database analysis, we carried out a series of experiments to explore the mechanisms and effects of circ_100549 underlying LUAD progression, including RNA-binding protein immunoprecipitation (RIP), RNA/DNA pull-down, luciferase reporter, and chromatin immunoprecipitation (ChIP) assays. The results indicated that circ_100549 serves as a ceRNA by sponging miR-95-5p to upregulate BPTF expression, thus upregulating BIRC6 expression at a transcriptional level in LUAD. In summary, our study demonstrated that circ_100549 facilitates LUAD progression by upregulating BIRC6 expression.

Circular RNA circMAN1A2 promotes ovarian cancer progression through the microRNA-135a-3p/IL1RAP/TAK1 pathway

Background

Ovarian cancer (OC) is the most lethal malignancy in women owing to its diagnosis only at the advanced stage. Elucidation of its molecular pathogenesis may help identify new tumor markers and targets for therapy. Circular RNAs (circRNAs) are stable, conserved, and functional biomolecules that can be used as effective biomarkers for various cancers.

Methods

In this study, a potential circRNA related to early diagnosis of OC, circMAN1A2, was analyzed. Overexpression/knockdown of circMAN1A2 in OC cells was used to decipher its effects on cell proliferation with a Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine (EdU), cell cycle, clone formation, and wound healing assay. RNA pull-down and Dual luciferase assay were used to explain the underlying mechanism by which circMAN1A2 regulates OC cell proliferation. In vivo, the effect of circMAN1A2 in OC was evaluated using nude mouse xenograft experiments.

Results

CircMAN1A2 was highly expressed in OC and promoted proliferation, clone formation, and tumorigenicity of OC cells. In addition, we found that circMAN1A2 acted as a sponge for microRNA (miR)-135a-3p; miR-135a-3p directly targeted the 3' untranslated region of interleukin 1 receptor accessory protein (IL1RAP) in OC cells, thereby regulating the phosphorylation of transforming growth factor-beta activated kinase 1 (TAK1), which resulted in promotion of OC cell growth.

Conclusions

CircMAN1A2 promotes OC cell proliferation by inhibiting the miR-135a-3p/IL1RAP/TAK1 axis. In conclusion, circMAN1A2 may be a biomarker for early detection of OC and a target for subsequent therapy.

Alteration in the Expression of Circular Rnas and its association with the Development and Progression of Osteosarcoma, an Integrative Review with High Sensitivity Research

BACKGROUND

Osteosarcoma is the most common primary malignant bone tumor, mainly affecting children, young adults, and the elderly. It is an aggressive cancer with a poor prognosis, exhibiting low survival rates even with standard treatment. Recently, circular RNA molecules capable of influencing gene expression through various functions, with their main role being acting as microRNA sponges and reducing their intracellular expression, have been identified. Recent studies have linked circular RNAs to osteosarcoma development and progression. Therefore, the present study aimed to investigate the alteration in circular RNA expression during osteosarcoma development and progression.

METHODS

An integrative literature review was conducted from September 10th to November 12th, 2021, using the following databases: PubMed/MEDLINE, SCOPUS, Web of Science, OVID, and EMBASE. 129 full articles were included in the review. The obtained data were organized using a standardized data collection instrument, which included the following information: altered expression profile of circular RNAs, associated cancer hallmarks, clinical-pathological relationships of circular RNAs, and perspectives on the studied circular RNAs.

RESULTS

A total of 94 distinct circular RNAs were identified, predominantly showing an increased expression pattern. Approximately 91% of the studies that aimed to identify the mechanisms of action of circular RNAs highlighted the function of circular RNAs as microRNA sponges. The most associated cancer hallmarks with the identified circular RNAs were proliferative signaling induction, invasion and metastasis, and resistance to cell death. The altered expression of these circular RNAs generally correlated with a worse prognosis for patients, as evidenced by clinical features such as shorter survival, advanced Enneking and/or TNM stage, higher incidence of metastasis, larger tumor size, and increased chemoresistance.

CONSLUSION

These findings indicate the significance of circular RNA molecules in osteosarcoma carcinogenesis, suggesting their potential as new prognostic and/or diagnostic biomarkers, as well as alternative therapeutic targets in the fight against osteosarcoma.

Functional relevance of circRNA aberrant expression in pediatric acute leukemia with KMT2A::AFF1 fusion

ABSTRACT

Circular RNAs (circRNAs) are emerging molecular players in leukemogenesis and promising therapeutic targets. In KMT2A::AFF1 (MLL::AF4)-rearranged leukemia, an aggressive disease compared with other pediatric B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), data about circRNAs are limited. Here, we disclose the circRNA landscape of infant patients with KMT2A::AFF1 translocated BCP-ALL showing dysregulated, mostly ectopically expressed, circRNAs in leukemia cells. Most of these circRNAs, apart from circHIPK3 and circZNF609, previously associated with oncogenic behavior in ALL, are still uncharacterized. An in vitro loss-of-function screening identified an oncogenic role of circFKBP5, circKLHL2, circNR3C1, and circPAN3 in KMT2A::AFF1 ALL, whose silencing affected cell proliferation and apoptosis. Further study in an extended cohort disclosed a significantly correlated expression of these oncogenic circRNAs and their putative involvement in common regulatory networks. Moreover, it showed that circAFF1 upregulation occurs in a subset of cases with HOXA KMT2A::AFF1 ALL. Collectively, functional analyses and patient data reveal oncogenic circRNA upregulation as a relevant mechanism that sustains the malignant cell phenotype in KMT2A::AFF1 ALL.

Biological role and regulation of circular RNA as an emerging biomarker and potential therapeutic target for cancer

Circular RNAs (circRNAs) are a unique family of endogenous RNAs devoid of 3' poly-A tails and 5' end caps. These single-stranded circRNAs, found in the cytoplasm, are synthesized via back-splicing mechanisms, merging introns, exons, or both, resulting in covalently closed circular loops. They are profusely expressed across the eukaryotic transcriptome and offer heightened stability against exonuclease RNase R compared to linear RNA counterparts. This review endeavors to provide a comprehensive overview of circRNAs' characteristics, biogenesis, and mechanisms of action. Furthermore, aimed to shed light on the potential of circRNAs as significant biomarkers in various cancer types. It has been performed an exhaustive literature review, drawing on recent studies and findings related to circRNA characteristics, synthesis, function, evaluation techniques, and their associations with oncogenesis. CircRNAs are intricately associated with tumor progression and development. Their multifaceted roles encompass gene regulation through the sponging of proteins and microRNAs, controlling transcription and splicing, interacting with RNA binding proteins (RBPs), and facilitating gene translation. Due to these varied roles, circRNAs have become a focal point in tumor pathology investigations, given their promising potential as both biomarkers and therapeutic agents. CircRNAs, due to their unique biogenesis and multifunctionality, hold immense promise in the realm of oncology. Their stability, widespread expression, and intricate involvement in gene regulation underscore their prospective utility as reliable biomarkers and therapeutic targets in cancer. As our understanding of circRNAs deepens, advanced techniques for their detection, evaluation, and manipulation will likely emerge. These advancements might catalyze the translation of circRNA-based diagnostics and therapeutics into clinical practice, potentially revolutionizing cancer care and prognosis.

Effects of extracellular vesicle-derived noncoding RNAs on pre-metastatic niche and tumor progression

A pre-metastatic niche (PMN) is a protective microenvironment that facilitates the colonization of disseminating tumor cells in future metastatic organs. Extracellular vesicles (EVs) play a role in intercellular communication by delivering cargoes, such as noncoding RNAs (ncRNAs). The pivotal role of extracellular vesicle-derived noncoding RNAs (EV-ncRNAs) in the PMN has attracted increasing attention. In this review, we summarized the effects of EV-ncRNAs on the PMN in terms of immunosuppression, vascular permeability and angiogenesis, inflammation, metabolic reprogramming, and fibroblast alterations. In particular, we provided a comprehensive overview of the effects of EV-ncRNAs on the PMN in different cancers. Finally, we discussed the promising clinical applications of EV-ncRNAs, including their potential as diagnostic and prognostic markers and therapeutic targets.

circSSPO boosts growth of esophageal squamous cell carcinoma through upregulation of micrRNA-6820-5p-mediated KLK8 and PKD1 expression

Investigation on a competitive endogenous RNA (ceRNA) network attracted lots of attention due its function in cancer regulation. Here, we probed into the possible molecular mechanism of circSSPO/microRNA-6820-5p (miR-6820-5p)/kallikrein-related peptidase 8 (KLK8)/PKD1 network in the esophageal squamous cell carcinoma (ESCC). Following whole-transcriptome sequencing and differential analysis in collected ESCC tissue samples, circRNA-miRNA-mRNA regulatory network affecting ESCC was investigated. After interaction measurement among circSSPO/miR-6820-5p/KLK8/PKD1, their regulatory roles in ESCC cell functions in vitro and xenograft tumor growth and lung metastasis in vivo were analyzed. The bioinformatics prediction and sequencing results screened that circSSPO, miR-6820-5p, KLK8, and PKD1 were associated with ESCC development. In ESCC, miR-6820-5p was expressed at very low levels, while circSSPO, KLK8, and PKD1 were highly expressed. In vitro cell experiments further proved that circSSPO competitively inhibited miR-6820-5p to induce ESCC cell malignant properties. Moreover, knockdown of KLK8 or PKD1 inhibited ESCC cell malignant properties. circSSPO also promoted the tumorigenic and metastasis of ESCC through the upregulation of KLK8 and PKD1 expression in vivo. We found that circSSPO was an oncogenic circRNA that was significantly abundant in ESCC tissues and circSSPO exhibited an oncogenic activity in ESCC by elevating expression of KLK8 and PKD1 through suppressing miR-6820-5p expression.

Newly discovered circRNAs encoding proteins: recent progress

Circular RNA (circRNA) is a special class of noncoding RNA molecules and the latest research hotspot in the field of RNA. CircRNA molecules have a closed loop structure, which is not affected by RNA exonuclease and has the characteristics of more stable expression. Previous studies have shown that circRNA molecules are rich in microRNA (miRNA) binding sites and act as miRNA sponges in cells. By interacting with miRNAs associated with tumors and other diseases, circRNAs play an important regulatory role. However, circRNAs have recently been found to have small open reading frames that enable them to encode peptides/proteins. These proteins have been reported to play an important role in the mechanism of regulation of a variety of diseases and have great potential in the diagnosis and treatment of diseases. In this review, we summarize the mechanism of action of the newly discovered circRNA-coding proteins since 2022 and briefly describe their research process. In addition, we also discuss the prediction model of the functional sites and encoded proteins of circRNAs, which provides a potential idea for future research on circRNAs.

Competitive endogenous network of circRNA, lncRNA, and miRNA in osteosarcoma chemoresistance

Osteosarcoma is the most prevalent and fatal type of bone tumor. Despite advancements in the treatment of other cancers, overall survival rates for patients with osteosarcoma have stagnated over the past four decades Multiple-drug resistance-the capacity of cancer cells to become simultaneously resistant to multiple drugs-remains a significant obstacle to effective chemotherapy. The recent studies have shown that noncoding RNAs can regulate the expression of target genes. It has been proposed that "competing endogenous RNA" activity forms a large-scale regulatory network across the transcriptome, playing important roles in pathological conditions such as cancer. Numerous studies have highlighted that circular RNAs (circRNAs) and long noncoding RNAs (lncRNAs) can bind to microRNA (miRNA) sites as competitive endogenous RNAs, thereby affecting and regulating the expression of mRNAs and target genes. These circRNA/lncRNA-associated competitive endogenous RNAs are hypothesized to play significant roles in cancer initiation and progression. Noncoding RNAs (ncRNAs) play an important role in tumor resistance to chemotherapy. However, the molecular mechanisms of the lncRNA/circRNA-miRNA-mRNA competitive endogenous RNA network in drug resistance of osteosarcoma remain unclear. An in-depth study of the molecular mechanisms of drug resistance in osteosarcoma and the elucidation of effective intervention targets are of great significance for improving the overall recovery of patients with osteosarcoma. This review focuses on the molecular mechanisms underlying chemotherapy resistance in osteosarcoma in circRNA-, lncRNA-, and miRNA-mediated competitive endogenous networks.

Circular RNA ATP2C1 (has_circ_0005797) sponges miR-432/miR-335 to promote breast cancer progression through regulating CCND1 expression

Breast cancer (BC) is the most frequently diagnosed malignancy in the world. Accumulating evidence has indicated that circular RNAs (circRNAs) play essential roles in BC. Here we investigated the biological functions of circATP2C as a competing endogenous RNA (ceRNA) in BC development. We found that circATP2C1 expression was upregulated in BC cells and tissues and was significantly associated with the poor overall survival in BC patients. CircATP2C1 is more resistant to RNase R exonuclease and Actinomycin D than is the linear mRNA of ATP2C1. CircATP2C1-knockdown inhibited the viability, colony proliferation and invasion abilities, while increasing the apoptosis rates of BC cells in vitro, as well as inhibiting tumor mass, size and weight in vivo. Upregulation of miR-432 and miR-335 inhibited CCND1 expression in BC cells. Both miR-432/miR-335 specifically bind to the 3'-UTR of circATP2C1 and CCND1 (CyclinD1). The inhibition of the aggression of BC cells by circATP2C1-knockdown was rescued by co-transfection of miR-432/miR-335 inhibitors. In conclusion, circATP2C1 promotes BC oncogenesis and metastasis by sponging miR-432/miR-335 to abolish the inhibition of the target gene, CCND1. This study suggests that circATP2C1 has implications for BC diagnosis and treatment.

Prenatal alcohol exposure dysregulates spinal and circulating immune cell circular RNA expression in adult female rats with chronic sciatic neuropathy

Alcohol consumption during pregnancy is associated with Fetal Alcohol Spectrum Disorders (FASD) that results in a continuum of central nervous system (CNS) deficits. Emerging evidence from both preclinical and clinical studies indicate that the biological vulnerability to chronic CNS disease in FASD populations is driven by aberrant neuroimmune actions. Our prior studies suggest that, following minor nerve injury, prenatal alcohol exposure (PAE) is a risk factor for developing adult-onset chronic pathological touch sensitivity or allodynia. Allodynia in PAE rats occurs concurrently with heightened proinflammatory peripheral and spinal glial-immune activation. However, minor nerve-injured control rats remain non-allodynic, and corresponding proinflammatory factors are unaltered. A comprehensive molecular understanding of the mechanism(s) that underlie PAE-induced proinflammatory bias during adulthood remains elusive. Non-coding circular RNAs (circRNAs) are emerging as novel modulators of gene expression. Here, we hypothesized that PAE induces dysregulation of circRNAs that are linked to immune function under basal and nerve-injured conditions during adulthood. Utilizing a microarray platform, we carried out the first systematic profiling of circRNAs in adult PAE rats, prior to and after minor nerve injury. The results demonstrate a unique circRNA profile in adult PAE rats without injury; 18 circRNAs in blood and 32 spinal circRNAs were differentially regulated. Following minor nerve injury, more than 100 differentially regulated spinal circRNAs were observed in allodynic PAE rats. Bioinformatic analysis identified that the parental genes of these circRNAs are linked to the NF-κB complex, a central transcription factor for pain-relevant proinflammatory cytokines. Quantitative real-time PCR was employed to measure levels of selected circRNAs and linear mRNA isoforms. We have validated that circVopp1 was significantly downregulated in blood leukocytes in PAE rats, concurrent with downregulation of Vopp1 mRNA levels. Spinal circVopp1 levels were upregulated in PAE rats, regardless of nerve injury. Additionally, PAE downregulated levels of circItch and circRps6ka3, which are linked to immune regulation. These results demonstrate that PAE exerts long-lasting dysregulation of circRNA expression in blood leukocytes and the spinal cord. Moreover, the spinal circRNA expression profile following peripheral nerve injury is differentially modulated by PAE, potentially contributing to PAE-induced neuroimmune dysregulation.

Therapeutic and diagnostic applications of exosomal circRNAs in breast cancer

Circular RNAs (circRNAs) are regulatory elements that are involved in orchestrating gene expression and protein functions and are implicated in various biological processes including cancer. Notably, breast cancer has a significant mortality rate and is one of the most common malignancies in women. CircRNAs have been demonstrated to contribute to the pathogenesis of breast cancer including its initiation, progression, metastasis, and resistance to drugs. By acting as miRNA sponges, circRNAs can indirectly influence gene expression by disrupting miRNA regulation of their target genes, ultimately altering the course of cancer development and progression. Additionally, circRNAs can interact with proteins and modulate their functions including signaling pathways involved in the initiation and development of cancer. Recently, circRNAs can encode peptides that play a role in the pathophysiology of breast cancer and other diseases and their potential as diagnostic biomarkers and therapeutic targets for various cancers including breast cancer. CircRNAs possess biomarkers that differentiate, such as stability, specificity, and sensitivity, and can be detected in several biological specimens such as blood, saliva, and urine. Moreover, circRNAs play an important role in various cellular processes including cell proliferation, differentiation, and apoptosis, all of which are integral factors in the development and progression of cancer. This review synthesizes the functions of circRNAs in breast cancer, scrutinizing their contributions to the onset and evolution of the disease through their interactions with exosomes and cancer-related intracellular pathways. It also delves into the potential use of circRNA as a biomarker and therapeutic target against breast cancer. It discusses various databases and online tools that offer crucial circRNA information and regulatory networks. Lastly, the challenges and prospects of utilizing circRNAs in clinical settings associated with breast cancer are explored.

Circular RNA hsa_circ_0000519 contributes to angiogenesis and tumor progression in hepatocellular carcinoma through the miR-1296/E2F7 axis

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy. Uncontrolled angiogenesis plays a critical role in hepatocellular tumor growth and metastasis. In this study, we aimed to investigate the effects of circular RNA hsa_circ_0000519 and the potential involvement of microRNA (miR)-1296 and E2F transcription factor 7 (E2F7) in HCC development. Hsa_circ_0000519 was highly expressed in HCC cells and hepatocellular tumor tissues, and correlated with poor prognosis of HCC patients. Knockdown of hsa_circ_0000519 significantly reduced HCC cell viability, suppressed cell proliferation, and induced cell cycle arrest in G0/G1. Downregulation of hsa_circ_0000519 also inhibited formation of capillary-like endothelial structures in vitro and impeded microvessel formation in mice bearing HCC tumors. The migration and invasive capacities of HCC cells were markedly reduced by hsa_circ_0000519 knockdown. Hsa_circ_0000519 possessed a binding site for microRNA (miR)-1296. Upregulation of hsa_circ_0000519 significantly decreased the miR-1296 expression in both HCC cells and mouse xenografts. Furthermore, E2F7 was a target of miR-1296. Hsa_circ_0000519 positively regulated E2F7 via acting as a miR-1296 sponge. Upregulation of E2F7 abolished the inhibitory effects of hsa_circ_0000519 knockdown on HCC cell proliferation and angiogenesis. In conclusion, hsa_circ_0000519 promoted tumor progression and angiogenesis in HCC through the miR-1296/E2F7 axis. These data suggest the potential clinical application of hsa_circ_0000519 in HCC treatment.

Emerging landscape of circFNDC3B and its role in human malignancies

In recent years, more attention has been paid to expanding the abundance of Circular RNAs (circRNAs), while the circRNAs that have been found to have significant functions have not been studied in different diseases. CircFNDC3B is one of the most researched circRNAs generated from fibronectin type III domain-containing protein 3B (FNDC3B) gene. Accumulating researches have reported the multiple functions of circFNDC3B in different cancer types and other non-neoplastic diseases, and predicted that circFNDC3B might be a potential biomarker. Notably, circFNDC3B can play roles in different diseases by binding to various microRNAs (miRNAs), binding to RNA-binding proteins (RBPs), or encoding functional peptides. This paper systematically summarizes the biogenesis and function of circRNAs, reviews and discusses the roles and molecular mechanisms of circFNDC3B and its target genes in different cancers and non-neoplastic diseases, which will do favor to broaden our comprehension of the function of circRNAs and facilitate subsequent research on circFNDC3B.

Role of circRNAs in gastric cancer

Circular RNAs (circRNAs) are a large class of non-coding RNAs with single-strand covalently closed loops, formed by reverse splicing, which widely exist in many cell lines and diverse species. Some circRNAs have highly evolutionarily conserved sequences, or tissue-specific or cell-specific expression patterns, and many circRNAs are extremely stable. In the past decades, accumulating evidence has indicated that circRNAs participate in the mechanisms associated with the development of many kinds of tumors, exert important biological functions by acting as microRNA or protein ‘sponges’, transcriptional regulatory factors, and protein translation templates, and play key roles in the occurrence and development of gastric cancer. This review comprehensively summarizes the biogenesis, characteristics, and biological functions of circRNAs, and the molecular mechanisms underlying the role of circRNAs in the carcinogenesis and progression of gastric cancer.

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.

Circular RNAs: biology and clinical significance of breast cancer

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

Discovery of fusion circular RNAs in leukemia with KMT2A::AFF1 rearrangements by the new software CircFusion

Chromosomal translocations in cancer genomes, key players in many types of cancers, generate chimeric proteins that drive oncogenesis. Genomes with chromosomal rearrangements can also produce fusion circular RNAs (f-circRNAs) by backsplicing of chimeric transcripts, as first shown in leukemias with PML::RARα and KMT2A::MLLT3 translocations and later in solid cancers. F-circRNAs contribute to the oncogenic processes and reinforce the oncogenic activity of chimeric proteins. In leukemia with KMT2A::AFF1 (MLL::AF4) fusions, we previously reported specific alterations of circRNA expression, but nothing was known about f-circRNAs. Due to the presence of two chimeric sequences, fusion and backsplice junctions, the identification of f-circRNAs with available tools is challenging, possibly resulting in the underestimation of this RNA species, especially when the breakpoint is not known. We developed CircFusion, a new software tool to detect linear fusion transcripts and f-circRNAs from RNA-seq data, both in samples for which the breakpoints are known and when the information about the joined exons is missing. CircFusion can detect linear and circular chimeric transcripts deriving from the main and reciprocal translocations also in the presence of multiple breakpoints, which are common in malignant cells. Benchmarking tests on simulated and real datasets of cancer samples with previously experimentally determined f-circRNAs showed that CircFusion provides reliable predictions and outperforms available methods for f-circRNA detection. We discovered and validated novel f-circRNAs in acute leukemia harboring KMT2A::AFF1 rearrangements, leading the way to future functional studies aimed to unveil their role in this malignancy.

Up-Regulation of SH3TC2 Induced by YTHDF1 Predicts Poor Outcome and Facilitates Cell-Cycle Progress in Colorectal Cancer

N6-methyladenosine (m6A) modification plays a crucial role in determining the fate and function of RNA transcripts in tumor cells. Nevertheless, how m6A regulates the expression of key molecules and coordinates its involvement in the development of colorectal cancer (CRC) remains largely unclear. Here, we report that the m6A reading protein YTHDF1-mediated up-regulation of SH3TC2 promotes CRC growth both in vitro and in vivo. In a pan-cancer analysis across more than thirty types of cancer, we found that SH3TC2 was dysregulated in nine cancers, including BLCA, CHOL, COAD, LAML, PAAD, READ, SKCM, BRCA, and TGCT, and was closely associated with patient prognosis in four cancers, including COAD, MESO, PAAD, and READ. In particular, SH3TC2 was overexpressed in CRC as confirmed by six independent study cohorts. Clinically, high expression of SH3TC2 predicted worse disease-free survival (DFS) in CRC patients. SH3TC2 showed fascinating diagnostic value and was correlated with immunosuppression in CRC. Functionally, RNA-sequencing combined with experiments revealed that knockdown of SH3TC3 significantly inhibited cell-cycle progress of CRC, impairing cell growth. Mechanistically, YTHDF1 protein directly binds with SH3TC2 mRNA and promotes its elevation in an m6A-dependent manner. Thus, our findings provide a mechanism to target the YTHDF1/SH3TC2 axis for CRC therapy.

Anesthetic propofol suppresses growth and metastasis of lung adenocarcinoma in vitro through downregulating circ-MEMO1-miR-485-3p-NEK4 ceRNA axis

BACKGROUND

Recently, circular RNAs (circRNAs) have been emerging as new regulators in the propofol-induced tumor-suppressive role. Here, we intended to investigate the involvement of circRNA-Mediator of cell motility 1 (circ-MEMO1; hsa_circ_0007385) in propofol role in cancer hallmarks of lung adenocarcinoma (LUAD).

METHODS

Real-time quantitative PCR and western blotting examined transcriptional and translational levels of circ-MEMO1, microRNA (miR)-485-3p, and NIMA-related kinase-4 (NEK4), and markers of growth and metastasis including E-cadherin, CyclinD1, and Vimentin. Cancer hallmarks were measured by 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, flow cytometry, 5-ethynyl-2-deoxyuridine assay, and transwell assay. The interaction among circ-MEMO1, miR-485-3p, NEK4 was determined by dual-luciferase reporter assay and Pearson's correlation analysis.

RESULTS

Circ-MEMO1 and NEK4 were high-expressed, and miR-485-3p was low-expressed in LUAD patients and cells; moreover, circ-MEMO1 and NEK4 expression in LUAD cells could be suppressed, whereas miR-485-3p could be elevated with propofol anesthesia. Functionally, propofol restrained cell viability, cell cycle entrance, cell proliferation, migration, and invasion of LUAD cells, accompanied by promoted E-cadherin and depressed CyclinD1 and Vimentin. Coincidently, high circ-MEMO1 was associated with low overall survival of LUAD patients, and overexpressing circ-MEMO1 could overall attenuate propofol effects in LUAD cells. Of note, upregulating miR-485-3p and/or interfering NEK4 could partially countermand the adverse impacts of circ-MEMO1 on propofol's role in LUAD cells. Importantly, circ-MEMO1 acted as a sponge for miR-485-3p to modulate the expression of miR-485-3p-targeted oncogene NEK4.

CONCLUSION

Promoting the circ-MEMO1-miR-485-3p-NEK4 axis might halt the tumor-inhibiting role of propofol in LUAD cells in vitro, suggesting a potential epigenetic pathway of propofol.

The FUS/circEZH2/KLF5/ feedback loop contributes to CXCR4-induced liver metastasis of breast cancer by enhancing epithelial-mesenchymal transition

Background

Metastasis of breast cancer have caused the majority of cancer-related death worldwide. The circRNAs are associated with tumorigenesis and metastasis in breast cancer according to recent research. However, the biological mechanism of circRNAs in liver metastatic breast cancer remains ambiguous yet.

Methods

Microarray analysis of three pairs of primary BC tissues and matched hepatic metastatic specimens identified circEZH2. We used RT-qPCR and FISH assays to confirm circEZH2 existence, characteristics, and expression. Both in vivo and in vitro, circEZH2 played an oncogenic role which promoted metastasis as well. A range of bioinformatic analysis, Western blot, RNA pull-down, RIP, ChIP, and animal experiments were used to define the feedback loop involving FUS, circEZH2, miR-217-5p, KLF5, FUS, CXCR4 as well as epithelial and mesenchymal transition.

Results

In our research, circEZH2 was proved to be upregulated in liver metastases in BC and predicted the worse prognosis in breast cancer patients. Overexpression of circEZH2 notably accentuated the vitality and invasion of BC cells, whereas knockdown of circEZH2 elicited the literally opposite effects. Besides, overexpressed circEZH2 promoted tumorigenesis and liver metastasis in vivo. Moreover, circEZH2 could adsorb miR-217-5p to upregulate KLF5 thus leading to activate FUS transcription which would facilitate the back-splicing program of circEZH2. Meanwhile, KLF5 could upregulated CXCR4 transcriptionally to accelerate epithelial and mesenchymal transition of breast cancer.

Conclusions

Consequently, a novel feedback loop FUS/circEZH2/KLF5/CXCR4 was established while circEZH2 could be novel biomarker and potential target for BC patients’ therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01653-2.

Circ_0000189 Promotes the Malignancy of Glioma Cells via Regulating miR-192-5p-ZEB2 Axis

Background

Some recent studies have reported the role of circular RNAs (circRNAs) in modulating the tumorigenesis of human malignancies. Nevertheless, the expression characteristics, biological functions, and regulatory mechanism of circ_0000189 in glioma are unclear.

Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) was utilized to detect the expression levels of circ_0000189, miR-192-5p, and ZEB2 mRNA in glioma tissues and cells. The association between the expression of circ_0000189 and the clinicopathological indicators and the features of magnetic resonance imaging (MRI) images of glioma patients were analyzed. Western blot was utilized to evaluate ZEB2 expression and epithelial-mesenchymal transition (EMT-)-related proteins (E-cadherin, N-cadherin, as well as Vimentin) in glioma cells. Cell proliferation was assessed employing cell counting kit-8 (CCK-8) and EdU experiments. Flow cytometry was used to detect the apoptotic rate of the cells. Cell migration and invasion were accessed employing Transwell assay. Moreover, dual luciferase reporter gene assay and RNA immunoprecipitation assay were employed to investigate the targeting relationship between miR-192-5p and circ_0000189, miR-192-5p, and ZEB2. Subcutaneous tumorigenesis experiment and lung metastasis experiment in nude mice were conducted to verify the regulatory function of circ_0000189 on the proliferation and metastasis of glioma cells in vivo.

Results

circ_0000189 was markedly overexpressed in glioma tissues and cell lines. Its high expression was associated with poor clinical pathological indicators and adverse MRI signs. Gain-of-function experiments and loss-of-function experiments confirmed that circ_0000189 overexpression facilitated the proliferation and migration, as well as invasion of glioma cells, and suppressed apoptosis, and facilitated epithelial-mesenchymal transition (EMT) process. Compared to the control group, knocking down circ_0000189 suppressed the malignant phenotypes of glioma cells both in vivo and in vitro. Working as a competitive endogenous RNA, circ_0000189 directly targeted miR-192-5p, and repressed its expression, and circ_0000189 positively modulated ZEB2 expression indirectly via repressing miR-192-5p.

Conclusion

circ_0000189 facilitates the progression of glioma by modulating miR-192-5p/ZEB2 axis.

CircMMP9 accelerates the progression of hepatocellular carcinoma through the miR-149/CCND2 axis

BACKGROUND

This study aimed to verify the hypothesis that circular RNA MMP9 (circMMP9) promotes hepatocellular carcinoma (HCC) progression through targeting miR-149 and regulating cyclin D2 (CCND2) expression.

METHODS

Expression of circMMP9, miR-149 and CCND2 was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR) or protein blotting. Cell Counting Kit-8 (CCK-8) was used to evaluate cell proliferation. The HCC cell migration and invasion were evaluated using wound healing and transwell assays. The interaction among circMMP9, miR-149, and CCND2 was evaluated using luciferase, RNA-pull down, and RNA immunoprecipitation (RIP) assays, respectively. Cell apoptosis and cycle were examined by flow cytometry. A subcutaneous HCC xenograft mouse model was established for analyzing the role of circMMP9 in regulating the progression of HCC in vivo.

RESULTS

The expression of circMMP9 was elevated in HCC tissues and its high expression correlated with poor prognosis (P<0.05). Knockdown of circMMP9 restrained the proliferation, migration, and invasion of HCC cells and led to arrested cell cycle and increased apoptosis (all P<0.05). Furthermore, knockdown of circMMP9 attenuated HCC growth in vivo (P<0.05). Mechanically, circMMP9 acted as a sponge for miR-149 and enhanced CCND2 expression in HCC cells (P<0.05). Inhibition of miR-149 or overexpression of CCND2 abrogated knockdown of circMMP9-mediated alleviation of the malignant phenotypes of HCC (P<0.05).

CONCLUSIONS

For the first time, we demonstrated that circMMP9 exacerbated HCC progression through the miR-149/CCND2 axis, which suggested that circMMP9 could be potentially targeted for HCC treatment.

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.

Exosomal Circsafb2 Reshaping Tumor Environment to Promote Renal Cell Carcinoma Progression by Mediating M2 Macrophage Polarization

Background

Macrophages are the most abundant infiltrating immune-related stromal cells present in and around tumors, showing different phenotypes and functions. M2 macrophages mainly exert immunosuppressive functions and promote tumor growth. Exosomes are emerging as important mediators of cross-talk between tumor cells and the microenvironment. CircRNAs are novel members of non-coding RNAs that regulate cancer proliferation and progression. However, the mechanism by which exosomal circRNA regulates macrophage polarization in renal cell carcinoma (RCC) is still largely unknown.

Methods

RCC-derived exosomes were characterized using transmission electron microscopy and nanoparticle tracking analysis (NTA). CCK-8, wound healing, and Transwell assays were performed to assess whether exosomes would affect the proliferation, migration, and invasion of RCC. Furthermore, we performed a bioinformatics analysis to identify circRNAs in RCC serum-derived exosomes from the GEO database. The fluorescence in situ hybridization (FISH) assay was used to detect the cellular distribution of circSAFB2. Bioinformatics analyses (StarBase 2.0) were used to pool the miRNA targets of circSAFB2. Luciferase assays were performed to verify the direct interactions. Western blotting was used to detect markers of macrophage M2 polarization. Lastly, mouse xenograft and bioluminescence imaging were used to examine the clinical relevance of exosomal circSAFB2 in vivo.

Results

We report the circRNA derived from SAFB2 and evaluate its biological function in promoting the immune escape of RCC. We found that circSAFB2 was highly expressed in RCC tissues and RCC-derived exosomes. Furthermore, we demonstrated that exosomal circSAFB2 mediates the polarization of M2 macrophages through the miR-620/JAK1/STAT3 axis to promote RCC metastasis.

Conclusions

Our data first demonstrated that circSAFB2 leads to immune escape from RCC by mediating M2 macrophage polarization via the miR-620/JAK1/STAT3 axis. These findings indicate a novel molecular mechanism of exosomal circSAFB2 in the progression of RCC and implicate circSAFB2 as a target for exosome-mediated tumor immune evasion.

Circular RNA_0078767 upregulates Kruppel-like factor 9 expression by targeting microRNA-889, thereby inhibiting the progression of osteosarcoma

Among kids and juveniles, osteosarcoma (OS) is a common bone malignancy. Circular RNAs (circs, circRNAs) play important roles in multiple malignancies including OS, yet circ_0078767ʹs biological functions in OS are far from well elucidated. This study is targeted at understanding circ_0078767ʹs biological functions in OS and its molecular mechanisms. This study confirmed that circ_0078767 expression was reduced in OS cell lines and tissues. Circ_0078767 overexpression remarkably inhibited OS cell growth, migration, invasion, epithelial-mesenchymal transition (EMT), and promoted apoptosis, whereas circ_0078767 knockdown resulted in the opposite effects. MicroRNA-889 (miR-889) was targeted and regulated by circ_0078767, and miR-889 could negatively modulate Kruppel-like factor 9 (KLF9) expression. Besides, circ_0078767 positively regulated KLF9 expression in OS cells via repressing miR-889. In conclusion, circ_0078767 enhances KLF9 expression by targeting miR-889 to inhibit OS progression.

Circular RNA circ_0006948 Promotes Esophageal Squamous Cell Carcinoma Progression by Regulating microRNA-3612/LASP1 Axis

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is the most prevalent malignancy worldwide. Circular RNAs (circRNAs) circ_0006948 is reported to be upregulated in ESCC cells.

AIMS

This study is designed to explore the role and mechanism of circ_0006948 in ESCC progression.

METHODS

Circ_0006948, linear FNDC3B, microRNA-3612 (miR-3612), and LIM and SH3 protein 1 (LASP1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell viability, colony number, migration, invasion, and apoptosis were examined by Cell Counting Kit-8 (CCK-8), colony formation, transwell, and flow cytometry assays, severally. Glucose consumption, lactate production, and ATP level were measured by the corresponding kits. Protein levels of hexokinase 2 (HK2) and lactate dehydrogenase A (LDHA), and LASP1 were assessed by western blot assay. The cytoplasmic localization of circ_0006948 was identified by the subcellular fractionation assay. The binding relationship between miR-3612 and circ_0006948 or LASP1 was predicted by starBase or TargetScan and then verified by a dual-luciferase reporter assay. The biological role of circ_0006948 on ESCC tumor growth was examined by the xenograft tumor model in vivo.

RESULTS

Circ_0006948 and LASP1 were increased, and miR-3612 was decreased in ESCC tissues and cells. Furthermore, circ_0006948 knockdown could suppress cell viability, colony number, migration, invasion, glycolysis, and boost apoptosis in ESCC cells. Mechanically, circ_0006948 could act as a sponge of miR-3612 to regulate LASP1 expression. In addition, circ_0006948 silencing inhibited ESCC tumor growth in vivo.

CONCLUSION

Circ_0006948 boosted ESCC progression partly by regulating the miR-3612/LASP1 axis, providing an underlying therapeutic target for the ESCC treatment.

Whole Transcriptome Sequencing Identified CircRNA Profiles and the Related Networks in Schizophrenia

Schizophrenia (SCZ) is a complex psychiatric syndrome with uncertain etiology. This study aimed to uncover the expression profiles and related regulatory networks of circular RNA (circRNA) in SCZ. Whole transcriptome sequencing was performed to assess the expression profiles of circRNAs and microRNAs (miRNAs) in the peripheral blood of three patients with SCZ and three healthy controls. Five circRNAs were validated by quantitative real-time PCR (RT-qPCR). TargetScan, RNAhybrid, and miRanda were performed to predict the target miRNAs of the top 10 dysregulated circRNAs. MiRTarBase was applied to predict the target mRNAs of miRNAs to construct circRNA-miRNA-mRNA (ceRNA) networks. CatRAPID and StarBase were used to predict the target RNA-binding proteins (RBPs) of circRNAs to construct circRNA-RBP networks. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to predict the potential functions of the maternal genes of circRNAs and target mRNAs. In total, 450 circRNAs and 160 miRNAs were found to be significantly differentially expressed, with hsa_circ_0003999 and hsa_circ_0030042 being significantly different between patients with SCZ and healthy controls (P < 0.05). The PI3K-AKT, MAPK, and cell cycle pathways were predicted to be associated with SCZ. GO analysis showed that focal adhesion was related to SCZ. The ceRNA networks, especially hsa_circ_0006151/hsa-miR-4685-3p/ZBTB16, hsa_circ_0000008/hsa-miR-1976/ZBTB16, and the hsa_circ_0007963/hsa-miR-3127-3p/UBE2K axes have the greatest probability of being involved in the pathophysiology of SCZ. The RBP networks, FXR1, FXR2, DGCR8, XRN2, FMR1, and QKI were the RBPs associated with SCZ. In conclusion, the circRNAs, ceRNAs, and RBP network expression patterns and related pathways indicate the potential role of circRNAs in the pathogenesis and development of SCZ.

The circular RNA circHMGB2 drives immunosuppression and anti-PD-1 resistance in lung adenocarcinomas and squamous cell carcinomas via the miR-181a-5p/CARM1 axis

BACKGROUND

Previous studies have confirmed the oncogenic role of HMGB2 in various cancers, but the biological functions of HMGB2-derived circRNAs remain unknown. Thus, we intended to investigate the potential role of HMGB2-derived circRNAs in lung adenocarcinomas (LUAD) and squamous cell carcinomas (LUSC).

METHODS

The expression profiles of HMGB2-derived circRNAs in LUAD and LUSC tissues and matched normal tissues were assessed using qRT-PCR. The role of circHMGB2 in the progression of the LUAD and LUSC was determined in vitro by Transwell, CCK-8, flow cytometry and immunohistochemistry assays, as well as in vivo in an immunocompetent mouse model and a humanized mouse model. In addition, in vivo circRNA precipitation assays, luciferase reporter assays and RNA pulldown assays were performed to explore the underlying mechanism by which circHMGB2 promotes anti-PD-1 resistance in the LUAD and LUSC.

RESULTS

The expression of circHMGB2 (hsa_circ_0071452) was significantly upregulated in NSCLC tissues, and survival analysis identified circHMGB2 as an independent indicator of poor prognosis in the LUAD and LUSC patients. We found that circHMGB2 exerted a mild effect on the proliferation of the LUAD and LUSC cells, but circHMGB2 substantially reshaped the tumor microenvironment by contributing to the exhaustion of antitumor immunity in an immunocompetent mouse model and a humanized mouse model. Mechanistically, circHMGB2 relieves the inhibition of downstream CARM1 by sponging miR-181a-5p, thus inactivating the type 1 interferon response in the LUAD and LUSC. Moreover, we found that the upregulation of circHMGB2 expression decreased the efficacy of anti-PD-1 therapy, and we revealed that the combination of the CARM1 inhibitor EZM2302 and an anti-PD-1 antibody exerted promising synergistic effects in a preclinical model.

CONCLUSION

circHMGB2 overexpression promotes the LUAD and LUSC progression mainly by reshaping the tumor microenvironment and regulating anti-PD-1 resistance in the LUAD and LUSC patients. This study provides a new strategy for the LUAD and LUSC treatment.

Lidocaine represses the malignant behavior of lung carcinoma cells via the circ_PDZD8/miR-516b-5p/GOLT1A axis

Lung carcinoma is the most prevalent malignancy in adults. Lidocaine (Lido) has been confirmed to exert an anti-tumor role in many human cancers. However, the role and underlying mechanism of Lido in lung carcinoma remain poorly understood. Cell proliferation ability, migration, invasion, and apoptosis were measured by Colony formation, 5-ethynyl-2'-deoxyuridine (EdU), Cell Counting Kit-8 (CCK-8), transwell, and flow cytometry assays. Circ_PDZD8, microRNA-516b-5p (miR-516b-5p), and Golgi transport 1A (GOLT1A) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Protein levels of proliferating cell nuclear antigen (PCNA) and GOLT1A were examined by western blot assay. The binding relationship between miR-516b-5p and circ_PDZD8 or GOLT1A was predicted by circular RNA Interactome or Starbase 3.0 and then verified by a dual-luciferase reporter assay. The biological roles of circ_PDZD8 and Lido on lung carcinoma cell growth were examined by the xenograft tumor model in vivo. Lido suppressed proliferation, migration, invasion, and induced apoptosis in lung carcinoma cells. Circ_PDZD8 and GOLT1A were increased, miR-516b-5p was decreased in lung carcinoma tissues and cell lines. Their expression presented the opposite trend in Lido-triggered lung carcinoma cells. Circ_PDZD8 might overturn the repression of Lido on cell growth ability and metastasis in this tumor. Mechanically, circ_PDZD8 might regulate GOLT1A expression by sponging miR-516b-5p. Circ_PDZD8 weakened the anti-lung carcinoma effect of Lido in vivo. Circ_PDZD8 might mitigate the inhibitory effect of Lido on tumor cell malignancy by modulating the miR-516b-5p/GOLT1A axis, providing a novel insight for lung carcinoma treatment.

A Circ-0007022/miR-338-3p/Neuropilin-1 Axis Reduces the Radiosensitivity of Esophageal Squamous Cell Carcinoma by Activating Epithelial-To-Mesenchymal Transition and PI3K/AKT Pathway

Radiotherapy resistance is an important cause of treatment failure in esophageal squamous cell carcinoma (ESCC). Circular RNAs have attracted a lot of attention in cancer research, but their role in ESCC radiosensitivity has not been elucidated yet. Here, we aimed to evaluated the functional impacts of circ-0007022 on ESCC radiosensitivity. In this study, a stable radiotherapy-resistant cell line was established and verified by a series of functional experiments. Subsequently, high-throughput sequencing revealed that circ-0007022 was significantly overexpressed in the radiotherapy-resistant cell line and this conclusion was verified in ESCC patients’ tumor tissues by real-time quantitative PCR. Moreover, loss-of-function and overexpression experiments in vitro and in vivo revealed that, after irradiation, the abilities of proliferation and migration in circ-0007022-overexpressing stable transgenic strain were significantly higher than that in circ-0007022-knockdown stable transgenic strain. Additionally, RNA Immunoprecipitation, RNA pull-down, luciferase reporter assays, and fluorescence in situ hybridization experiments demonstrated the mechanism of how circ-0007022 could sponge miR-338-3p and upregulate downstream target of miR-338-3p, neuropilin-1 (NRP1). Moreover, NRP1 led to poor prognosis for ESCC patients receiving radiotherapy, and NRP1 knock-down enhanced radiosensitivity of ESCC cells. Furthermore, circ-0007022 overexpression activated Epithelial-to-mesenchymal transition and PI3K/Akt pathway, and NRP1 knock-down could reversed this phenomenon. Finally, Akt Inhibitor reversed circ-0007022s role in radiotherapy in ESCC cells. Taken together, the circ-0007022/miR-338-3p/NRP1 axis enhances the radiation resistance of ESCC cells via regulating EMT and PI3K/Akt pathway. The new circRNA circ-0007022 is thus expected to be a therapeutic target for ESCC patients.

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 RNA circ-PLCD1 functions as a tumor suppressor in non-small cell lung cancer by inactivation of PI3K/AKT signaling pathway

Circular RNAs (circRNAs) are emerging as crucial regulators in tumorigenesis and aggressive progression. However, their biological roles in non-small cell lung cancer (NSCLC) remain largely unknown. Here, by performing circRNA high throughput sequencing in 4 paired NSCLC and normal tissues, we found a NSCLC-associated circRNA, circ-PLCD1, which was evidently downregulated in NSCLC tissues and cell lines. Circ-PLCD1 was transcriptionally activated by tumor-inhibiting protein p53, and exogenous expression of circ-PLCD1 inhibited NSCLC cell proliferation, invasion and induced apoptosis. Mechanistically, circ-PLCD1 acted as a competitive endogenous RNA (ceRNA) to sponge miR-375 and miR-1179 and elevate PTEN, a well-known inhibitor of oncogenic PI3K/AKT signaling, thereby repressing NSCLC tumorigenesis. Importantly, we also identified this ceRNA regulatory axis of circ-PLCD1/miR-375/miR-1179/PTEN in vivo by establishing a xenograft tumor model. Clinically, NSCLC patients with low circ-PLCD1 expression had larger tumor size, later clinical stage and shorter survival time than those with high circ-PLCD1 expression. Altogether, our findings reveal the important tumor suppressive role of circ-PLCD1 in NSCLC, reactivation of this circRNA may be considered as a novel therapeutic avenue for patient with NSCLC.

EIF4A3-induced circCCNB1 (hsa_circ_0001495) promotes glioma progression by elevating CCND1 through interacting miR-516b-5p and HuR

To explore the functions of circRNA cyclin B1 (circCCNB1) in glioma and its possible mechanisms. The expression of circCCNB1, eukaryotic translation initiation factor 4A3 (EIF4A3), cyclin D1 (CCND1) and miR-516b-5p was determined by qRT-PCR, western blot or immunohistochemistry (IHC) assay. The feature of circCCNB1 was analyzed by Actinomycin D (ActD), RNase R and subcellular fraction assays. The molecule relationships were analyzed by RIP, dual-luciferase reporter and RNA pull-down assays. CCK-8, EdU and colony formation assays were performed to analyze cell proliferation. Flow cytometry analysis was executed to estimate the cell cycle. Murine xenograft model assay was used for the role of circCCNB1 in vivo. CircCCNB1 was overexpressed in glioma tissues and cells. EIF4A3 positively regulated circCCNB1 expression. CircCCNB1 knockdown repressed glioma cell proliferation and cell cycle process in vitro and blocked tumor growth in vivo. CircCCNB1 knockdown reduced CCND1 expression in glioma cells and CCND1 overexpression bated the effect of circCCNB1 knockdown on glioma cell growth. CircCCNB1 interacted with HuR to elevate CCND1 expression. miR-516b-5p could interact with circCCNB1 and CCND1. CircCCNB1 regulated glioma cell progression and CCND1 expression by miR-516b-5p and HuR. CircCCNB1 aggravated glioma cell growth by elevating CCND1 through targeting miR-516b-5p and HuR.