Mobius strip in pancreatic cancer: biogenesis, function and clinical significance of circular RNAs

Advances on Senescence-associated secretory phenotype regulated by circular RNAs in tumors

The components that comprise the senescence-associated secretory phenotype (SASP) include growth factors, proteases, chemokines, cytokines, and bioactive lipids. It drives secondary aging and disrupts tissue homeostasis, ultimately leading to tissue repair and regeneration loss. It has a two-way regulatory effect on tumor cells, resisting cancer occurrence and promoting its progression. A category of single-stranded circular non-coding RNA molecules known as circular RNAs (circRNAs) carries out a series of cellular activities, including sequestering miRNAs and modulating gene editing and expression. Research has demonstrated that a large number of circRNAs exhibit aberrant expression in pathological settings, and play a part in the onset and progress of cancer via modulating SASP factors. However, the research related to SASP and circRNAs in tumors is still in its infancy at this stage. This review centers on the bidirectional modulation of SASP and the role of circRNAs in regulating SASP factors across different types of tumors. The aim is to present novel perspectives for the diagnosis and therapeutic management of malignancies.

Circ_0002395 promotes aerobic glycolysis and proliferation in pancreatic adenocarcinoma cells via miR-548c-3p/PDK1 axis

Circular RNAs (circRNAs) showing unusual expressions have been discovered in pancreatic adenocarcinoma (PAAD). However, the functions and underlying mechanisms of these circRNAs still remain largely unclear. Our current study discovered a notable increase in the expression of circRNA hsa_circ_0002395 (circ_0002395) in both PAAD tissues and cell lines. This up-regulation of circ_0002395 was found to be associated with larger tumor sizes and lymph node metastasis. Furthermore, our findings showed that circ_0002395 facilitated aerobic glycolysis and cell proliferation in PAAD cells by regulating the miR-548c-3p/PDK1 axis. Mechanistically, we identified circ_0002395 as a competing endogenous RNA (ceRNA) that sponged miR-548c-3p, thereby promoting PDK1 expression and aerobic glycolysis, and ultimately resulting in the enhancement of cell proliferation. Our findings found that circ_0002395 promoted proliferation of PAAD cells by enhancing PDK1 expression and aerobic glycolysis by sponging miR-548c-3p.

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.

Circ_0101692 knockdown retards the development of clear cell renal cell carcinoma through miR-384/FN1 pathway

PURPOSE

Circular RNA_0101692 (circ_0101692) is overexpressed in clear cell renal cell carcinoma (ccRCC) by microarray analyses. However, its function and action mechanism in ccRCC tumorigenesis is still elusive.

METHODS

Western blotting and qRT-PCR were executed to assess the circ_0101692, miR-384 and FN1 expression in ccRCC cells and tissues. Target relationships among them were determined via dual luciferase reporter and/or RNA immunoprecipitation assays. Cell proliferation was evaluated by CCK-8 assay. Caspase-3 activity assay was utilized to analyze cell apoptosis. To find out whether ccRCC cells might migrate, a transwell assay was performed. To assess the effects of circ_0101692 on tumor development in vivo, a mouse xenograft model was used.

RESULTS

High expression of circ_0101692 and FN1, and decreased miR-384 were determined in ccRCC. Cell growth, migration and viability were decreased whereas cell apoptosis was stimulated when circ_0101692 was knockdown. miR-384 inhibitor transfection attenuated the inhibiting impacts of circ_0101692 silencing on ccRCC cell progression. FN1 deletion further inverted the cancer-promoting effect of miR-384 downregulation on cell viability and migration. In addition, circ_0101692 could sponge miR-384 to relieve the inhibition of miR-384 on FN1 in ccRCC.

CONCLUSIONS

Circ_0101692 targeted miR-384/FN1 axis to facilitate cell proliferation, migration and repress apoptosis, thereby accelerating the development of ccRCC. This points out that circ_0101692/miR-384/FN1 axis might be a prospective target implemented for the future treatment of ccRCC.

Construction of a focal adhesion signaling pathway-related ceRNA network in pelvic organ prolapse by transcriptome analysis

Objective: Pelvic organ prolapse (POP) affects a large proportion of adult women, but the pathogenesis of POP remains unclear. The increase in global population aging will impose a substantial medical burden. Herein, we aimed to explore the related RNAs regulating the occurrence of POP and provide potential therapeutic targets.

Method: Tissue biopsies were collected from the anterior vaginal wall of six women with POP and six matched subjects without POP. The profiles of mRNAs, circRNAs, lncRNAs, and miRNAs were obtained by whole transcriptome RNA sequencing.

Result: The findings revealed that 71 circRNAs, 76 known lncRNAs, 84 miRNAs, and 931 mRNAs were significantly altered (p < 0.05 and |log2FC| > 1). GO and KEGG enrichment analyses indicated that the differentially expressed genes (DEGs) were mainly enriched in the focal adhesion signaling pathway. FLT, ITGA9, VEGFD, PPP1R12B, and ROCK2 were identified as focal adhesion signaling pathway-related hub genes by protein–protein interaction network analysis. Based on the relationships between the DEGs and miRNA, lncRNA and circRNA targets, we constructed a focal adhesion signaling pathway-related ceRNA network. The ceRNA network includes hsa_circ_0002190/hsa_circ_0046843/lnc-CARMN -miR-23a-3p - ROCK2 and hsa_circ_0001326/hsa_circ_0007733/lnc-AC107959/lnc-TPM1-AS - miR-205-5p - ROCK2/PPP1R12B/VEGFD. Moreover, abnormalities in the cytoskeleton in fibroblasts from individuals with POP were observed.

Conclusion: In this study, a focal adhesion signaling pathway-related ceRNA network was constructed, and this network may serve as a target for finding suitable drugs for the treatment of POP.

Hsa_circ_0046523 Mediates an Immunosuppressive Tumor Microenvironment by Regulating MiR-148a-3p/PD-L1 Axis in Pancreatic Cancer

Background

Circular RNAs (circRNAs) are a novel type of non-coding RNA, play an important role in the progression of tumors. However, the function and mechanism of circRNAs in regulating immune microenvironment of pancreatic cancer (PC) remain largely unclear.

Methods

The effects of hsa_circ_0046523 expression on proliferation, migration and invasion of PC cells were analyzed by CCK8 and Transwell assays. Flow cytometry was used to detect the proportion of CD4⁺ T cells, CD8⁺ T cells and Tregs in peripheral blood mononuclear cells (PBMCs) after co-culture, and the apoptosis, depletion and function of CD8⁺ T cells. The expression levels of immunoregulatory cytokines were detected by enzyme linked immunosorbent assay (ELISA). The dual-luciferase reporter was performed to determine the interaction between hsa_circ_0046523, miR-148a-3p, and PD-L1. Rescue experiments and PD-L1 blocking experiments were employed to investigate whether hsa_circ_0046523 exerts its biological function by miR-148a-3p/PD-L1 in PC. Furthermore, an immunocompetent murine PC model was established to confirm these findings.

Results

Hsa_circ_0046523 expression was remarkably upregulated in PC tissues and cell lines. Moreover, high expression of hsa_circ_0046523 was correlated with advanced pathological stage and poorer prognosis. Hsa_circ_0046523 overexpression promoted the proliferation, migration and invasion of PC cells in vitro. Co-culture experiments confirmed that forced expression of hsa_circ_0046523 could decrease the proportion of CD4⁺ and CD8⁺ T cells, as well as increase the proportion of Tregs among peripheral blood mononuclear cells (PBMCs). Meanwhile, hsa_circ_0046523 overexpression promoted the apoptosis and exhaustion of CD8⁺ T cells, inhibited CD8⁺ T cell function, increased the secretion of immunosuppressive cytokines IL-10 and TGF-β, and decreased the secretion of immune effector cytokines IFN-γ and IL-2 among PBMCs. Mechanistically, hsa_circ_0046523 exerted its biological function by binding to miR-148a-3p to upregulate PD-L1 expression in PC. Moreover, these immune modulating functions of miR-148a-3p/PD-L1 axis were also confirmed in an immunocompetent murine PC model.

Conclusions

Our study suggests that hsa_circ_0046523/miR-148a-3p/PD-L1 regulatory axis mediates PC immunosuppressive microenvironment and these molecules are expected to be new targets for remodeling tumor immune microenvironment of PC.

Role of exosomal competitive endogenous RNA (ceRNA) in diagnosis and treatment of malignant tumors

Malignant tumors are a threat to human health, thus it is critical to better understand the mechanism of tumor occurrence and development and to find key therapeutic targets. Competitive endogenous RNA (ceRNA) is a type of RNA molecule that includes mRNA of coding-protein, pseudogenes, long non-coding RNA (lncRNA), and circular RNA (circRNA) etc. It is created through a competitive combination of common small RNA (miRNA) and has an inhibitory effect on mRNA translation. ceRNA regulate the post transcriptional expression of genes by competitively binding to common microRNAs (miRNAs).Studies have shown that cernas are involved in tumor cell proliferation, invasion and migration, drug resistance, angiogenesis, as well as tumor immunity, and so on, affecting the progression of tumor development. This article reviews the reported roles of exosomal ceRNA in the diagnosis and treatment of malignant tumors and the mechanisms underlying these.

Liquid biopsy at the frontier of detection, prognosis and progression monitoring in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide and a leading cause of carcinogenic death. To date, surgical resection is regarded as the gold standard by the operator for clinical decisions. Because conventional tissue biopsy is invasive and only a small sample can sometimes be obtained, it is unable to represent the heterogeneity of tumor or dynamically monitor tumor progression. Therefore, there is an urgent need to find a new minimally invasive or noninvasive diagnostic strategy to detect CRC at an early stage and monitor CRC recurrence. Over the past years, a new diagnostic concept called “liquid biopsy” has gained much attention. Liquid biopsy is noninvasive, allowing repeated analysis and real-time monitoring of tumor recurrence, metastasis or therapeutic responses. With the advanced development of new molecular techniques in CRC, circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), exosomes, and tumor-educated platelet (TEP) detection have achieved interesting and inspiring results as the most prominent liquid biopsy markers. In this review, we focused on some clinical applications of CTCs, ctDNA, exosomes and TEPs and discuss promising future applications to solve unmet clinical needs in CRC patients.

Circular RNA sterile alpha motif domain containing 4A contributes to cell 5-fluorouracil resistance in colorectal cancer by regulating the miR-545-3p/6-phosphofructo-2-kinase/fructose-2,6-bisphosphataseisotype 3 axis

Colorectal cancer (CRC) is one of the most fatal cancers in the world. Circular RNA sterile alpha motif domain containing 4A (circSAMD4A) was found to be highly expressed in CRC and promoted the tumorigenesis of CRC. However, the role of circSAMD4A in 5-fluorouracil (5-Fu) resistance of CRC is yet to be clarified. This study is designed to investigate the function of circSAMD4A in 5-Fu resistance of CRC and its potential molecular mechanism. Quantitative real-time PCR was used to detect the expression levels of circSAMD4A, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isotype 3 (PFKFB3) mRNA, and miR-545-3p, and western blot was used to detect the protein expression. For functional analysis, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, colony formation/5-ethynyl-2'-deoxyuridine assay, flow cytometry analysis, and glycolysis metabolism analysis were used to assess the capacities of cell viability, proliferation, apoptosis, and glycolysis in 5-Fu-resistant cells of CRC. The dual-luciferase reporter assay was used to verify the interaction between miR-545-3p and circSAMD4A or PFKFB3. Xenograft tumor model was established to confirm the biological role of circSAMD4A in 5-Fu resistance of CRC in vivo. CircSAMD4A was upregulated in 5-Fu-resistant CRC tissues and cells. Functionally, circSAMD4A knockdown inhibited the proliferation and glycolysis mechanism but promoted apoptosis in 5-Fu-resistant cells of CRC. CircSAMD4A was identified as a molecular sponge of miR-545-3p to upregulate PFKFB3 expression. Mechanistically, circSAMD4A knockdown-induced 5-Fu sensitivity was mediated by miR-545-3p/PFKFB3 axis. Moreover, circSAMD4A knockdown improved 5-Fu sensitivity of CRC in vivo. CircSAMD4A contributed to 5-Fu resistance of CRC cells partly through upregulating PFKFB3 expression by sponging miR-545-3p, providing a possible circRNA-targeted therapy for CRC.

Circular RNA circRNA_0067934 promotes glioma development by modulating the microRNA miR-7/ Wnt/β-catenin axis

Glioma, one of the most prevalent malignant tumors, is well-known for its poor prognosis and low survival rate among patients. As a type of non-coding RNA, circular RNAs (circRNAs) play a significant role in tumor progression. However, the function and role of circRNAs in glioma development remain unclarified. In our experiments, the relative expression level of circRNA_0067934 and miR-7 in glioma tissue was detected by qRT-PCR, and specific gene knockdown was mediated by siRNA and miRNA-inhibitor. Dual-luciferase reporter assay was carried out to determine whether miR-7 successfully targeted circRNA_0067934. Also, CCK-8 and Transwell were performed to evaluate the malignant behaviors of glioma tissues. Western blotting and immunofluorescence were used to evaluate relative protein expression levels. The results of qRT-PCR indicated that circRNA_0067934 was over-expressed in glioma tissues, and down regulation of circRNA_0067934 reduced the tumor progression by inhibiting cell proliferation, invasion, and migration. The relative expression level of miR-7 was significantly reduced in glioma tissues, which showed a negative association with the expression of circRNA_0067934. CircRNA_0067934 could tagete the miR-7 to regulate progression of glioma cell. In addition, the Wnt/β-catenin signaling pathway might involve in down stream regulation of circRNA_0067934 and miR-7. In conclusion, our results revealed that circRNA_0067934 regulates glioma cells progression by targeting miR-7/ Wnt/β-catenin axis.

Comprehensive Analysis of Circular RNA Expression in ceRNA Networks and Identification of the Effects of hsa_circ_0006867 in Keloid Dermal Fibroblasts

Circular RNAs (circRNAs) play a crucial role in the pathogenesis of various fibrotic diseases, but the potential biological function and expression profile of circRNAs in keloids remain unknown. Herein, microarray technology was applied to detect circRNA expression in four patient-derived keloid dermal fibroblasts (KDFs) and normal dermal fibroblasts (NDFs). A total of 327 differentially expressed (DE) circRNAs (fold change &gt; 1.5, p &lt; 0.05) were identified with 195 upregulated and 132 downregulated circRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the upregulated circRNAs were mainly enriched in the cytoskeleton and tight junctions, while the downregulated circRNAs were related to morphogenesis of the epithelium and axonal guidance. To explore the function of DE circRNAs, a circRNA-miRNA-mRNA network, including five circRNAs, nine miRNAs, and 235 correlated mRNAs, was constructed using bioinformatics analyses. The expression of five DE circRNAs was validated by qRT–PCR in 18 pairs of KDFs and NDFs, and hsa_circ_0006867 showed promising regulatory function in keloids in vitro. Silencing hsa_circ_00006867 suppressed the proliferation, migration, and invasion of keloid fibroblasts. RNA-binding protein immunoprecipitation (RIP) assays indicated that hsa_circ_00006867 may serve as a platform for miRNA binding to Argonaute (AGO) 2. In addition, hsa-miR-29a-5p may be a potential target miRNA of hsa_circ_00006867. Taken together, our research provided multiple novel clues to understand the pathophysiologic mechanism of keloids and identified hsa_circ_0006867 as a biomarker of keloids.

Emerging Role and Mechanism of circRNAs in Pediatric Malignant Solid Tumors

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures and are widely distributed in eukaryotes, conserved and stable as well as tissue-specific. Malignant solid tumors pose a serious health risk to children and are one of the leading causes of pediatric mortality. Studies have shown that circRNAs play an important regulatory role in the development of childhood malignant solid tumors, hence are potential biomarkers and therapeutic targets for tumors. This paper reviews the biological characteristics and functions of circRNAs as well as the research progress related to childhood malignant solid tumors.

Research Progress of circRNAs in Glioblastoma

Circular RNAs (circRNAs) are a class of single-stranded covalently closed non-coding RNAs without a 5' cap structure or 3' terminal poly (A) tail, which are expressed in a variety of tissues and cells with conserved, stable and specific characteristics. Glioblastoma (GBM) is the most aggressive and lethal tumor in the central nervous system, characterized by high recurrence and mortality rates. The specific expression of circRNAs in GBM has demonstrated their potential to become new biomarkers for the development of GBM. The specific expression of circRNAs in GBM has shown their potential as new biomarkers for GBM cell proliferation, apoptosis, migration and invasion, which provides new ideas for GBM treatment. In this paper, we will review the biological properties and functions of circRNAs and their biological roles and clinical applications in GBM.