Preliminary investigation of the function of hsa_circ_0006215 in pancreatic cancer

Biological functions, mechanisms, and clinical significance of circular RNA in pancreatic cancer: a promising rising star

Pancreatic cancer (PC) is a highly malignant solid tumor with insidious onset and easy early metastasis. Despite tremendous efforts devoted to research in this field, the mechanisms underlying PC tumorigenesis and progression remain unclear. Additionally, robust biomarkers and satisfactory therapeutic strategies for clinical use in PC patients are still lacking. Circular RNAs (circRNAs) are a new type of non-coding RNA originating from precursor messenger RNAs, with a covalent continuous closed-loop structure, strong stability and high specificity. Accumulating evidence suggests that circRNAs may participate in PC development and progression. Abnormal expression of circRNAs in PC is considered a vital factor that affects tumor cell proliferation, migration, invasion, apoptosis, angiogenesis and drug resistance. In this review of relevant articles published in recent years, we describe the basic knowledge concerning circRNAs, including their classification, biogenesis, functions and research approaches. Moreover, the biological roles and clinical significance of circRNAs related to PC are discussed. Finally, we note the questions remaining from recent studies and anticipate that further investigations will address these gaps in knowledge in this field. In conclusion, we expect to provide insights into circRNAs as potential targets for specific PC diagnosis and treatment in the future.

Integrated Analysis of Glutathione Metabolic Pathway in Pancreatic Cancer

Metabolic enzyme-genes (MEs) play critical roles in various types of cancers. However, MEs have not been systematically and thoroughly studied in pancreatic cancer (PC). Global analysis of MEs in PC will help us to understand PC progressing and provide new insights into PC therapy. In this study, we systematically analyzed RNA sequencing data from The Cancer Genome Atlas (TCGA) (n = 180 + 4) and GSE15471 (n = 36 + 36) and discovered that metabolic pathways are disordered in PC. Co-expression network modules of MEs were constructed using weighted gene co-expression network analysis (WGCNA), which identified two key modules. Both modules revealed that the glutathione signaling pathway is disordered in PC and correlated with PC stages. Notably, glutathione peroxidase 2 (GPX2), an important gene involved in glutathione signaling pathway, is a hub gene of the key modules. Analysis of immune microenvironment components reveals that PC stage is associated with M2 macrophages, the marker gene of which is significantly correlated with GPX2. The results indicated that GPX2 is associated with PC progression, providing new insights for future targeted therapy.

Roles and clinical application of exosomal circRNAs in the diagnosis and treatment of malignant tumors

Exosomes are microvesicles secreted by cells. They contain a variety of bioactive substances with important roles in intercellular communication. Circular RNA (circRNA), a type of nucleic acid molecule found in exosomes, forms a covalently bonded closed loop without 5′ caps or 3′ poly(A) tails. It is structurally stable, widely distributed, and tissue specific. CircRNAs mainly act as microRNA sponges and have important regulatory roles in gene expression; they are superior to other non-coding RNAs as molecular diagnostic markers and drug treatment targets. Exosomal-derived circRNAs in the body fluids of tumor patients can modulate tumor proliferation, invasion, metastasis, and drug resistance. They can be used as effective biomarkers for early non-invasive diagnosis and prognostic evaluation of tumors, and also represent ideal targets for early precision therapeutic intervention. This review provides a theoretical basis for exploring the applications of exosomal circRNAs in malignant tumor diagnosis and treatment. We describe the biological functions of exosomal circRNAs in the occurrence and development of malignant tumors, their potential utility in diagnosis and treatment, and possible mechanisms.

Profiling of Serum Exosome MiRNA Reveals the Potential of a MiRNA Panel as Diagnostic Biomarker for Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease in the older adults. Although much effort has been made in the analyses of diagnostic biomarkers, such as amyloid-β, tau, and neurofilament light chain, identifying peripheral blood-based biomarkers is in extremely urgent need for their minimal invasiveness and more convenience. Here we characterized the miRNA profile by RNA sequencing in human serum exosomes from AD patients and healthy controls (HC) to investigate its potential for AD diagnosis. Subsequently, Gene Ontology analysis and pathway analysis were performed for the targeted genes from the differentially expressed miRNAs. These basic functions were differentially enriched, including cell adhesion, regulation of transcription, and the ubiquitin system. Functional network analysis highlighted the pathways of proteoglycans in cancer, viral carcinogenesis, signaling pathways regulating pluripotency of stem cells, and cellular senescence in AD. A total of 24 miRNAs showed significantly differential expression between AD and HC with more than ± 2.0-fold change at p value < 0.05 and at least 50 reads for each sample. Logistic regression analysis established a model for AD prediction by serum exosomal miR-30b-5p, miR-22-3p, and miR-378a-3p. Sequencing results were validated using quantitative reverse transcription PCR. The data showed that miR-30b-5p, miR-22-3p, and miR-378a-3p were significantly deregulated in AD, with area under the curve (AUC) of 0.668, 0.637, and 0.718, respectively. The combination of the three miRs gained a better diagnostic capability with AUC of 0.880. This finding revealed a miR panel as potential biomarker in the peripheral blood to distinguish AD from HC.

Recent Advances in the Potential Use of Circular RNA for the Diagnosis and Treatment of Pancreatic Cancer

There are few biomarkers available for the early diagnosis and prognostic evaluation of pancreatic cancer. In addition, the development of targeted therapy for pancreatic cancer is an unmet need due to the lack of molecular targets. With the continuous progress in circular RNA (circRNA)-related research, its role in the occurrence and development of pancreatic cancer has been discovered and gradually recognized. Therefore, circRNA may represent a novel marker for early diagnosis of this disease and a focus of targeted clinical therapy. CircRNA is a type of non-coding RNA with a closed circular structure formed by covalent bonds. Some circRNAs can act as “sponges” to adsorb microRNAs (miRNAs) and play the role of competitive endogenous RNA (ceRNA) to remove their inhibitory effects on the target genes of miRNA. Thus, they can indirectly restore the expression of target genes. The circRNA–miRNA–mRNA network plays a regulatory role in the proliferation, invasion, metastasis, and other biological behaviors of pancreatic cancer. Given the recent advances in circRNA, this review seeks to provide an overview of the biological function of circRNA and highlights the recent research progress regarding the molecular mechanism of circRNA for the clinical diagnosis and treatment of pancreatic cancer.

Circ-MBOAT2 knockdown represses tumor progression and glutamine catabolism by miR-433-3p/GOT1 axis in pancreatic cancer

BACKGROUND

Pancreatic cancer is a malignant tumor and ranks the sixth in incidence among cancers. Circular RNA (circRNA) has been reported to regulate the progression of pancreatic cancer. However, the effects of circ-membrane bound O-acyltransferase domain containing 2 (circ-MBOAT2) on regulating pancreatic cancer process were unclear.

METHODS

The expression levels of circ-MBOAT2, microRNA-433-3p (miR-433-3p) and glutamic-oxaloacetic transaminase 1 (GOT1) mRNA were detected by quantitative real-time polymerase chain reaction (qRT-PCR). GOT1 protein expression was determined by western blot analysis. Cell proliferation was illustrated by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) and cell colony formation assay. Cell apoptosis was demonstrated by flow cytometry analysis. Cell invasion and migration were investigated by transwell invasion and wound-healing assays. Glutamine catabolism was explained by detecting glutamine consumption, alpha ketoglutarate (α-KG) production and glutamate production. In vivo assay was performed to illustrate the impacts of circ-MBOAT2 silencing on tumor formation in vivo. The binding relationship between miR-433-3p and circ-MBOAT2 or GOT1 was predicted by circinteractome or starbase online databases, and identified by dual-luciferase reporter assay.

RESULTS

Circ-MBOAT2 and GOT1 expression were significantly upregulated, while miR-433-3p expression was downregulated in pancreatic cancer tissues and cells compared with normal pancreatic tissues or cells. Circ-MBOAT2 silencing repressed cell proliferation, migration, invasion and glutamine catabolism, whereas promoted cell apoptosis in pancreatic cancer. Additionally, circ-MBOAT2 acted as a sponge of miR-433-3p, which was found to be associate with GOT1. MiR-433-3p inhibitors hindered circ-MBOAT2 silencing-mediated impacts on pancreatic cancer progression and glutamine catabolism. Furthermore, circ-MBOAT2 silencing repressed tumor formation in vivo.

CONCLUSION

Circ-MBOAT2 modulated tumor development and glutamine catabolism by miR-433-3p/GOT1 axis in pancreatic cancer. This finding suggests that circ-MBOAT2 may be a therapeutic target for pancreatic cancer.

Biological roles and potential clinical values of circular RNAs in gastrointestinal malignancies

Circular RNAs (circRNAs), a class of endogenous RNA molecules, are produced by alternative splicing of precursor RNA and are covalently linked at the 5' and 3' ends. Recent studies have revealed that dysregulated circRNAs are closely related to the occurrence and progression of gastrointestinal malignancies. Accumulating evidence indicates that circRNAs, including circPVT1, circLARP4, circ-SFMBT2, cir-ITCH, circRNA_100782, circ_100395, circ-DONSON, hsa_circ_0001368, circNRIP1, circFAT1(e2), circCCDC66, circSMARCA5, circ-ZNF652, and circ_0030235 play important roles in the proliferation, differentiation, invasion, and metastasis of cancer cells through a variety of mechanisms, such as acting as microRNA sponges, interacting with RNA-binding proteins, regulating gene transcription and alternative splicing, and being translated into proteins. With the characteristics of high abundance, high stability, extensive functions, and certain tissue-, time- and disease-specific expressions, circRNAs are expected to provide novel perspectives for the diagnoses and treatments of gastrointestinal malignancies.

Current State of "Omics" Biomarkers in Pancreatic Cancer

Pancreatic cancer is one of the most fatal malignancies and the seventh leading cause of cancer-related deaths related to late diagnosis, poor survival rates, and high incidence of metastasis. Unfortunately, pancreatic cancer is predicted to become the third leading cause of cancer deaths in the future. Therefore, diagnosis at the early stages of pancreatic cancer for initial diagnosis or postoperative recurrence is a great challenge, as well as predicting prognosis precisely in the context of biomarker discovery. From the personalized medicine perspective, the lack of molecular biomarkers for patient selection confines tailored therapy options, including selecting drugs and their doses or even diet. Currently, there is no standardized pancreatic cancer screening strategy using molecular biomarkers, but CA19-9 is the most well known marker for the detection of pancreatic cancer. In contrast, recent innovations in high-throughput techniques have enabled the discovery of specific biomarkers of cancers using genomics, transcriptomics, proteomics, metabolomics, glycomics, and metagenomics. Panels combining CA19-9 with other novel biomarkers from different "omics" levels might represent an ideal strategy for the early detection of pancreatic cancer. The systems biology approach may shed a light on biomarker identification of pancreatic cancer by integrating multi-omics approaches. In this review, we provide background information on the current state of pancreatic cancer biomarkers from multi-omics stages. Furthermore, we conclude this review on how multi-omics data may reveal new biomarkers to be used for personalized medicine in the future.

Circular RNA in pancreatic cancer: a novel avenue for the roles of diagnosis and treatment

Pancreatic cancer (PC), an important cause of cancer-related deaths worldwide, is one of the most malignant cancers characterized by a dismal prognosis. Circular RNAs (circRNAs), a class of endogenous ncRNAs with unique covalently closed loops, have attracted great attention in regard to various diseases, especially cancers. Compelling studies have suggested that circRNAs are aberrantly expressed in different cancer tissues and cell types, including PC. More specifically, circRNAs can modify the proliferation, progression, tumorigenesis and chemosensitivity of PC, and some circRNAs could serve as biomarkers for diagnosis and prognosis. Herein, we summarize what is currently known to be related to the biogenesis, functions and potential roles of human circRNAs in PC and their application prospects for PC clinical treatments.

The Role of Circular RNAs in Pancreatic Ductal Adenocarcinoma and Biliary-Tract Cancers

Simple Summary

Pancreatic and biliary tract cancers often present with non-specific symptoms, resulting in diagnosis at a late stage. This may be too late for curative surgery. Earlier detection and characterisation may guide treatment options and increase survival. Natural “circles” of RNA (circRNAs) are shown to regulate cancer-related genes, and act as cancer “biomarkers”. Recent research has shown that circRNAs are both abundant and stable, both of which are desirable characteristics for clinically useful biomarkers. In this systematic review, we describe the roles of circRNAs in pancreatic and biliary tract cancers, summarise the current published research and explore their utility as a biomarker. A total of 32 articles were included: 22 considering Pancreatic Cancer, 7 for Bile Duct Cancer and 3 for Gallbladder Cancer. CircRNA proved an exciting prospect as a biomarker for these cancers and future work should continue to develop and expand this field of research.

Abstract

Pancreatic Ductal Adenocarcinoma (PDAC) and biliary-tract cancers (BTC) often present at a late stage, and consequently patients have poor survival-outcomes. Circular RNAs (circRNAs) are non-coding RNA molecules whose role in tumourigenesis has recently been realised. They are stable, conserved and abundant, with tissue-specific expression profiles. Therefore, significant interest has arisen in their use as potential biomarkers for PDAC and BTC. High-throughput methods and more advanced bioinformatic techniques have enabled better profiling and progressed our understanding of how circRNAs may function in the competing endogenous RNA (ceRNA) network to influence the transcriptome in these cancers. Therefore, the aim of this systematic review was to describe the roles of circRNAs in PDAC and BTC, their potential as biomarkers, and their function in the wider ceRNA network in regulating microRNAs and the transcriptome. Medline, Embase, Scopus and PubMed were systematically reviewed to identify all the studies addressing circRNAs in PDAC and BTC. A total of 32 articles were included: 22 considering PDAC, 7 for Cholangiocarcinoma (CCA) and 3 for Gallbladder Cancer (GBC). There were no studies investigating Ampullary Cancer. Dysregulated circRNA expression was associated with features of malignancy in vitro, in vivo, and ex vivo. Overall, there have been very few PDAC and BTC tissues profiled for circRNA signatures. Therefore, whilst the current studies have demonstrated some of their functions in these cancers, further work is required to elucidate their potential role as cancer biomarkers in tissue, biofluids and biopsies.

CircRHOT1 mediated cell proliferation, apoptosis and invasion of pancreatic cancer cells by sponging miR-125a-3p

Pancreatic cancer patients are asymptomatic at early stages and leading to late diagnoses. Additionally, pancreatic cancer easily metastasizes and is resistant to radiotherapy and chemotherapy. Therefore, it is critical to understand the underlying molecular mechanisms involved in pancreatic cancer to develop more efficient diagnostic and treatment strategies. In this study, we demonstrated that circRHOT1 was overexpressed in pancreatic cancer tissues and cell lines, and it was found to directly bind to miR-125a-3p, acting as an endogenous sponge to inhibit its activity. Knockdown of circRHOT1 expression significantly inhibited proliferation as well as invasion, and it promoted apoptosis of pancreatic cancer cells via the regulation of E2F3 through the targeting of miR-125a-3p. Taken together, our results showed that circRHOT1 plays critical roles in regulating the biological functions of pancreatic cancer cells, suggesting that circRHOT1 may serve as a potential diagnostic marker and therapeutic target for patients with pancreatic cancer.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

The Regulatory Functions of Circular RNAs in Digestive System Cancers

Circular ribonucleic acids (circRNAs), which are a type of covalently closed circular RNA, are receiving increasing attention. An increasing amount of evidence suggests that circRNAs are involved in the biogenesis and development of multiple diseases such as digestive system cancers. Dysregulated circRNAs have been found to act as oncogenes or tumour suppressors in digestive system cancers. Moreover, circRNAs are related to ageing and a wide variety of processes in tumour cells, such as cell apoptosis, invasion, migration, and proliferation. Moreover, circRNAs can perform a remarkable multitude of biological functions, such as regulating splicing or transcription, binding RNA-binding proteins to enable function, acting as microRNA (miRNA) sponges, and undergoing translated into proteins. However, in digestive system cancers, circRNAs function mainly as miRNA sponges. Herein, we summarise the latest research progress on biological functions of circRNAs in digestive system cancers. This review serves as a synopsis of potential therapeutic targets and biological markers for digestive system cancer.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

Circular RNA (circRNA) is an intriguing class of RNA with covalently closed-loop structure and is highly stable and conservative. As new members of the ncRNAs, the function, mechanism, potential diagnostic biomarker, and therapeutic target have raised increased attention. Most circRNAs are presented with characteristics of abundance, stability, conservatism, and often exhibiting tissue/developmental-stage-specific manner. Over 30,000 circRNAs have been identified with their unique structures to maintain stability more easily than linear RNAs. An increased numbers of circRNAs are dysregulated and involved in several biological processes of malignance, such as tumorigenesis, growth, invasion, metastasis, apoptosis, and vascularization. Emerging evidence suggests that circRNAs play important roles by acting as miRNA sponge or protein scaffolding, autophagy regulators, and interacting with RNA-binding protein (RBP), which may potentially serve as a novel promising biomarker for prevention, diagnosis and therapeutic target for treatment of human cancer with great significance either in scientific research or clinic arena. This review introduces concept, major features of circRNAs, and mainly describes the major biological functions and clinical relevance of circRNAs, as well as expressions and regulatory mechanisms in various types of human cancer, including pathogenesis, mode of action, potential target, signaling regulatory pathways, drug resistance, and therapeutic biomarkers. All of which provide evidence for the potential utilities of circRNAs in the diagnosis and treatment of cancer.

Circular RNAs and gastrointestinal cancers: Epigenetic regulators with a prognostic and therapeutic role

Both environmental and genetic factors are involved in the initiation and development of gastrointestinal cancer. Covalent closed circular RNAs (circRNAs) are produced by a mechanism called "back-splicing" from mRNAs. They are highly stable and show cell and tissue specific expression patterns. Although some functions such as "microRNA sponge" and "RNA binding protein sponge" have been reported for a small number of circRNAs, the function of thousands of other circRNAs is still unknown. Dysregulation of circRNAs has been reported in many GI cancers and are involved in metastasis and invasion. CircRNAs have been reported to be useful as prognostic markers and targets for developing new treatments. We first describe the properties and biogenesis of circRNAs. We then summarize recent reports about circRNA functions, expression status, and their potential to be used as biomarkers in GI cancers including, gastric cancer, colorectal cancer, esophageal cancer, hepatocellular carcinoma, gallbladder cancer and pancreatic cancer.

Research progress on circularRNAs in pancreatic cancer: emerging but promising

There is currently no diagnostic modality for early-stage pancreatic cancer. Given that adjuvant therapies require further development, the overall survival of pancreatic cancer remains unsatisfactory. Circular RNAs (circRNAs) are a class of noncoding RNAs that play an important role in the progression of many diseases including cancer. CircRNAs mainly bind to microRNAs as microRNA sponges to restore the expression of targeted genes and regulate tumor invasion, metastasis, proliferation, and apoptosis. CircRNAs also play roles in the diagnosis and targeted therapy of tumors. Studies on the mechanisms of action of circRNAs in pancreatic cancer are still in their infancy, but it is anticipated that this field will gradually advance. In this review, we provide a brief introduction to circRNAs from four perspectives: biogenesis, functions, and mechanisms of action, tumor therapy with circRNAs, and circRNAs' roles in pancreatic cancer.

Exo-circRNAs: a new paradigm for anticancer therapy

CircRNAs, as new members of long noncoding RNAs, have been the focus of recent investigation. CircRNAs feature a closed continuous loop structure without 5′-3′ polarity or a poly A tail. Many studies have reported the potential application of circRNAs in the clinic as new biomarkers and therapeutic targets in different diseases, especially for cancer. Additionally, the exosomes are important vehicles in cell-to-cell communication. And exo-circRNAs are circRNAs in exosomes which can be detected to provide additional evidence for conventional diagnostic methods and can be applied to suppress the malignant progress in cancer. In this review, we describe the biogenesis, characteristics, and functions of circRNAs and exosomes. Specifically, we present a comprehensive update of the promising role of exo-circRNAs in anticancer therapy.

circRAPGEF5 Contributes to Papillary Thyroid Proliferation and Metastatis by Regulation miR-198/FGFR1

The circular RNA RAPGEF5 (circRAPGEF5) is generated from five exons of the RAPGEF5 gene and abnormal expression in papillary thyroid cancer (PTC). However, whether circRAPGEF5 plays a role in PTC tumorigenesis remains unclear. The aim of the present study was to investigate the role of circRAPGEF5 in PTC. The results showed that circRAPGEF5 was upregulated in PTC tissues and cell lines. circRAPGEF5 knockdown inhibited cell proliferation, migration, and invasion in vitro; and circRAPGEF5 silencing downregulated fibroblast growth factor receptor 1 (FGFR1) expression by “sponging” miR-198, suppressing the aggressive biological behaviors of PTC. Luciferase reporter assays confirmed that circRAPGEF5 interacted with miR-198 and that miR-198 interacted with the 3′ UTR of FGFR1 to downregulate its expression. Xenograft experiments confirmed that circRAPGEF5 knockdown suppressed FGFR1-mediated tumor growth by promoting miR-198 expression. circRAPGEF5 acts as a tumor promoter via a novel circRAPGEF5/miR-198/FGFR1 axis, providing a potential biomarker and therapeutic target for the management of PTC.