The comprehensive expression analysis of circular RNAs in gastric cancer and its association with field cancerization

The role of ASXL1 mutations and ASXL1 CircRNAs in cancer

BACKGROUND

Mutations in the Additional Sex Combs Like 1 (ASXL1) gene were first reported in myelodysplastic syndromes. Recent studies have clarified the relationship between ASXL1 mutations and the development of cancers.

OBJECTIVE

This study aims to review the roles of ASXL1 and ASXL1 CircRNAs, such as epigenetic regulation, chromatin modification, and transcription factor function in malignancies.

METHOD

This study is a review of articles related to the role of ASXL1 and ASXL1 CircRNAs in malignancies, retrieved from PubMed and Scopus.

RESULTS

ASXL1 plays a role in malignancies and is also related to poor overall survival and cancer metastasis. ASXL1 encodes conserved and abundant Circular RNAs (circRNAs) that act as post-transcriptional regulators, regulating tumorigenesis and progression in cancer. ASXL1 circRNA was identified in the top 10% of differentially expressed circRNAs in clinically relevant tissues. Additionally, the role of ASXL1 gene circRNAs in cancer development is reviewed in this study.

CONCLUSION

ASXL1 and ASXL1circRNA have dual functions in combination with different proteins, being involved in both transcriptional activation and repression in a context-dependent manner. Moreover, studies indicate these genes play an important role in epithelial-mesenchymal transition (EMT) and metastasis. Ongoing research is aimed at determining this gene family's function in biological events.

AHNAK Contributes to Hepatocellular Carcinoma Growth by Interacting with IGF-1R

Neuroblast differentiation-associated protein AHNAK, a large structural scaffold protein, remains mysterious in biological processes. AHNAK plays a suppressive or progressive role in different types of cancers. To investigate the role of the AHNAK in hepatocellular carcinoma (HCC), cell viability assays were performed to determine the cell proliferation of the stable AHNAK-knockdown HepG2 cell line; co-immunoprecipitation (Co-IP) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) were performed on HCC and matched paracancerous (MPC) tissues. The Metascape platform was used for enrichment analyses; the "ComplexHeatmap" package was applied for cluster analyses and visualization. Co-IP, Western botting and immunofluorescence double staining were performed to assess the interactions between AHNAK and insulin-like growth factor 1 receptor (IGF-1R). AHNAK silencing reduced the viability of HepG2 cells; the interactome in HCC and MPC tissues enriched 204 pathways and processes, which partially reflected the signature of HCC field cancerization. AHNAK could co-localize and interact with IGF-1R. These results suggested that the AHNAK complex contributes to HCC growth, potentially by interacting with IGF-1R.

Functional properties of circular RNAs and research progress in gastric cancer

Circular RNAs (circRNAs) are a class of closed circular non-coding RNAs widely exist in eukaryotes, with high stability and species conservation. A large number of studies have shown that circRNAs are abnormally expressed in various tumor tissues, and are abundant in plasma with long half-life and high specificity, which may be served as potential tumor biomarkers for early diagnosis, treatment and prognosis of malignant tumors. However, the role of circRNAs is still poorly understood in gastric cancer. This article reviews the research progress of circRNAs in gastric cancer in recent years so as to explore the relationship between circRNAs and the occurrence and the development of gastric cancer, and provide new ideas for the diagnosis and treatment of gastric cancer.

Triple-Negative Breast Cancer circRNAome Reveals Hsa_circ_0072309 as a Potential Risk Biomarker

Simple Summary

Triple Negative Breast Cancer (TNBC) is a highly aggressive type of cancer that lacks biomarkers for its early discovery, leading to overall poor prognosis after its diagnosis. Circular RNAs (circRNAs) are a new class of regulatory RNAs and are promising biomarkers for several human diseases, including TNBC. In this study, we profiled the expression of all circRNAs present in TNBC in order to identify new biomarkers for this disease and it was possible to observe that 16 were deregulated, among them hsa_circ_0072309. In two distinct sets of samples, hsa_circ_0072309 was able to distinguish TNBC from healthy controls, making it a promising risk biomarker for this disease. Additionaly, since circRNAs are known to interact with RNA-Binding Proteins (RBPs), we investigated its probable function in this cancer and found that by interacting with such RBPs, this circRNA is acting in several cancer-related biological pathways. Recognizing these differentially expressed circRNAs and identifying their role can lead to a better understanding of dysregulated pathways in TNBC and ultimately allow the development of personalized therapies in this molecular subtype of breast cancer.

Abstract

Circular RNAs (circRNAs) are a class of long non-coding RNAs that have the ability to sponge RNA-Binding Proteins (RBPs). Triple-negative breast cancer (TNBC) has very aggressive behavior and poor prognosis for the patient. Here, we aimed to characterize the global expression profile of circRNAs in TNBC, in order to identify potential risk biomarkers. For that, we obtained RNA-Seq data from TNBC and control samples and performed validation experiments using FFPE and frozen tissues of TNBC patients and controls, followed by in silico analyses to explore circRNA-RBP interactions. We found 16 differentially expressed circRNAs between TNBC patients and controls. Next, we mapped the RBPs that interact with the top five downregulated circRNAs (hsa_circ_0072309, circ_0004365, circ_0006677, circ_0008599, and circ_0009043) and hsa_circ_0000479, resulting in a total of 16 RBPs, most of them being enriched to pathways related to cancer and gene regulation (e.g., AGO1/2, EIF4A3, ELAVL1, and PTBP1). Among the six circRNAs, hsa_circ_0072309 was the one that presented the most confidence results, being able to distinguish TNBC patients from controls with an AUC of 0.78 and 0.81, respectively. This circRNA may be interacting with some RBPs involved in important cancer-related pathways and is a novel potential risk biomarker of TNBC.

Marek's Disease Virus Virulence Genes Encode Circular RNAs

Circular RNAs (circRNAs) are a recently rediscovered class of functional noncoding RNAs that are involved in gene regulation and cancer development. Next-generation sequencing approaches identified circRNA fragments and sequences underlying circularization events in virus-induced cancers. In the present study, we performed viral circRNA expression analysis and full-length sequencing in infections with Marek’s disease virus (MDV), which serves as a model for herpesvirus-induced tumorigenesis. We established inverse PCRs to identify and characterize circRNA expression from the repeat regions of the MDV genome during viral replication, latency, and reactivation. We identified a large variety of viral circRNAs through precise mapping of full-length circular transcripts and detected matching sequences with several viral genes. Hot spots of circRNA expression included the transcriptional unit of the major viral oncogene encoding the Meq protein and the latency-associated transcripts (LATs). Moreover, we performed genome-wide bioinformatic analyses to extract back-splice junctions from lymphoma-derived samples. Using this strategy, we found that circRNAs were abundantly expressed in vivo from the same key virulence genes. Strikingly, the observed back-splice junctions do not follow a unique canonical pattern, compatible with the U2-dependent splicing machinery. Numerous noncanonical junctions were observed in viral circRNA sequences characterized from in vitro and in vivo infections. Given the importance of the genes involved in the transcription of these circRNAs, our study contributes to our understanding and complexity of this deadly pathogen.

IMPORTANCE Circular RNAs (circRNAs) were rediscovered in recent years both in physiological and pathological contexts, such as in cancer. Viral circRNAs are encoded by at least two human herpesviruses, the Epstein Barr virus and the Kaposi’s Sarcoma-associated herpesvirus, both associated with the development of lymphoma. Marek’s disease virus (MDV) is a well-established animal model to study virus-induced lymphoma but circRNA expression has not been reported for MDV yet. Our study provided the first evidence of viral circRNAs that were expressed at key steps of the MDV lifecycle using genome-wide analyses of circRNAs. These circRNAs were primarily found in transcriptional units that corresponded to the major MDV virulence factors. In addition, we established a bioinformatics pipeline that offers a new tool to identify circular RNAs in other herpesviruses. This study on the circRNAs provided important insights into major MDV virulence genes and herpesviruses-mediated gene dysregulation.

Screening Differential CircRNAs Expression Profiles Reveals the Regulatory Role of the has_circTPT1_003-has-miR-218-5p-CCNE2/SMC4 Signaling Axis in Bladder Carcinoma Progression

Circular RNAs (circRNAs) are a class of noncoding RNAs closely related to the development and progression of various human cancers. However, it is unclear whether circRNAs play an important role in the development of bladder cancer. We utilized human circRNA array V2 microarrays to screen circRNA expression profiles in bladder cancer tissues. Bioinformatic tools including circBank, dbDEMC 2.0, miRCancer, TarBase v7.0, miRtarbase, TCGA-BLCA, Cytoscape-MCODE, String, ENCORI, and Venny 2.1 were then employed to construct the circRNA-miRNA-mRNA regulatory networks. In total, 105 upregulated circRNAs and 167 downregulated circRNAs (fold change >2 and p < 0.001) were filtered out. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of filtered dysregulated circRNAs disclosed that the circRNAs regulatory network was closely related with mRNA processing and cell cycle, etc. Further excavation analysis showed that seven differentially overexpressed circRNAs including hsa_circ_0000133, hsa_circ_0023610, hsa_circ_0005615, hsa_circ_0030162, hsa_circ_0077007, hsa_circ_0001140, and hsa_circ_0107031 were associated with bladder cancer invasiveness, and the cell cycle signal axis. has_circTPT1_003-has-miR-218-5p-CCNE2/SMC4 was finally clarified as a possible mechanism for bladder cancer progression. Based on results derived from multiple approaches, we identified that has_circTPT1_003-has-miR-218-5p-CCNE2/SMC4 signal axis may be involved in the invasion process of bladder cancer.

CircRNAs as Potential Blood Biomarkers and Key Elements in Regulatory Networks in Gastric Cancer

Gastric cancer (GC) is the fifth most common type of cancer and the third leading cause of cancer death in the world. It is a disease that encompasses a variety of molecular alterations, including in non-coding RNAs such as circular RNAs (circRNAs). In the present study, we investigated hsa_circ_0000211, hsa_circ_0000284, hsa_circ_0000524, hsa_circ_0001136 and hsa_circ_0004771 expression profiles using RT-qPCR in 71 gastric tissue samples from GC patients (tumor and tumor-adjacent samples) and volunteers without cancer. In order to investigate the suitability of circRNAs as minimally invasive biomarkers, we also evaluated their expression profile through RT-qPCR in peripheral blood samples from patients with and without GC (n = 41). We also investigated the predicted interactions between circRNA-miRNA-mRNA and circRNA-RBP using the KEGG and Reactome databases. Overall, our results showed that hsa_circ_0000211, hsa_circ_0000284 and hsa_circ_0004771 presented equivalent expression profiles when analyzed by different methods (RNA-Seq and RT-qPCR) and different types of samples (tissue and blood). Further, functional enrichment results identified important signaling pathways related to GC. Thus, our data support the consideration of circRNAs as new, minimally invasive biomarkers capable of aiding in the diagnosis of GC and with great potential to be applied in clinical practice.

The circular RNA hsa_circ_000780 as a potential molecular diagnostic target for gastric cancer

Background

The present study aimed to identify a specific circular RNA (circRNA) for early diagnosis of gastric cancer (GC).

Methods

Totally 82 patients with GC, 30 with chronic nonatrophic gastritis and 30 with chronic atrophic gastritis were included in this study. Four of the 82 GC patients were selected for screening. Total RNA from malignant and adjacent tissue samples was extracted, and circRNAs in four patients were screened. According to the screening results, the eight most upregulated and downregulated circRNAs with a statistically significant association with GC were identified by real-time fluorescent quantitative polymerase chain reaction (PCR). Then, the most regulated circRNA was selected for further sensitivity and specificity assessments. CircRNA expression was examined by quantitative reverse transcriptase PCR in 78 GC (21 and 57 early and advanced GC, respectively) and adjacent tissue samples, as well as in gastric fluid samples from 30 patients with chronic nonatrophic gastritis, 30 with chronic atrophic gastritis, and 78 GC.

Results

A total of 445 circRNAs, including 69 upregulated and 376 downregulated circRNAs, showed significantly altered expression in GC tissue samples. Hsa_circ_000780 was significantly downregulated in 80.77% of GC tissue samples, with levels in GC tissue samples correlating with tumor size, tumor stage, T stage, venous invasion, carcinoembryonic antigen amounts, and carbohydrate antigen 19–9 levels. Strikingly, this circRNA was found in the gastric fluid of patients with early and advanced GC.

Conclusions

The present study uncovered a new circRNA expression profile in human GC, with hsa_circ_000780 significantly downregulated in GC tissue and gastric fluid specimens. These findings indicate that hsa_circ_000780 should be considered a novel biomarker for early GC screening.

Nuclear and Mitochondrial Genome, Epigenome and Gut Microbiome: Emerging Molecular Biomarkers for Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is currently the second most common neurodegenerative disorder, burdening about 10 million elderly individuals worldwide. The multifactorial nature of PD poses a difficult obstacle for understanding the mechanisms involved in its onset and progression. Currently, diagnosis depends on the appearance of clinical signs, some of which are shared among various neurologic disorders, hindering early diagnosis. There are no effective tools to prevent PD onset, detect the disease in early stages or accurately report the risk of disease progression. Hence, there is an increasing demand for biomarkers that may identify disease onset and progression, as treatment-based medicine may not be the best approach for PD. Over the last few decades, the search for molecular markers to predict susceptibility, aid in accurate diagnosis and evaluate the progress of PD have intensified, but strategies aimed to improve individualized patient care have not yet been established.

CONCLUSIONS

Genomic variation, regulation by epigenomic mechanisms, as well as the influence of the host gut microbiome seem to have a crucial role in the onset and progress of PD, thus are considered potential biomarkers. As such, the human nuclear and mitochondrial genome, epigenome, and the host gut microbiome might be the key elements to the rise of personalized medicine for PD patients.

Nanopore sequencing of brain-derived full-length circRNAs reveals circRNA-specific exon usage, intron retention and microexons

Circular RNA (circRNA) is a class of covalently joined non-coding RNAs with functional roles in a wide variety of cellular processes. Their composition shows extensive overlap with exons found in linear mRNAs making it difficult to delineate their composition using short-read RNA sequencing, particularly for long and multi-exonic circRNAs. Here, we use long-read nanopore sequencing of nicked circRNAs (circNick-LRS) and characterize a total of 18,266 and 39,623 circRNAs in human and mouse brain, respectively. We further develop an approach for targeted long-read sequencing of a panel of circRNAs (circPanel-LRS), eliminating the need for prior circRNA enrichment and find >30 circRNA isoforms on average per targeted locus. Our data show that circRNAs exhibit a large number of splicing events such as novel exons, intron retention and microexons that preferentially occur in circRNAs. We propose that altered exon usage in circRNAs may reflect resistance to nonsense-mediated decay in the absence of translation.

Geospatial Assessments of DNA Adducts in the Human Stomach: A Model of Field Cancerization

BACKGROUND

Field cancerization is a popular concept regarding where cancer cells arise in a plane, such as the opened-up gastrointestinal mucosa. The geospatial distribution of DNA adducts, some of which are believed to initiate mutation, may be a clue to understanding the landscape of the preferred occurrence of gastric cancer in the human stomach, such that the occurrence is much more frequent in the lesser curvature than in the greater curvature.

METHODS

Seven DNA adducts, C5-methyl-2'-deoxycytidine, 2'-deoxyinosine, C5-hydroxymethyl-2'-deoxycytidine, N6-methyl-2'-deoxyadenosine, 1,N6-etheno-2'-deoxyadenosine, N6-hydroxymethyl-2'-deoxyadenosine, and C8-oxo-2'-deoxyguanosine, from different points and zones of the human stomach were semi quantitatively measured by liquid chromatography/tandem mass spectrometry. The differences in the quantity of these DNA adducts from the lesser and greater curvature, the upper, middle and lower third zones, the anterior and posterior wall of the stomach, and the mucosae distant from and near the tumor were compared to determine whether the location preference of cancer in the stomach could be explained by the distribution of these DNA adducts. Comparisons were conducted considering the tumor locations and operation methods.

CONCLUSIONS

Regarding the DNA adducts investigated, significant differences in quantities and locations in the whole stomach were not noted; thus, these DNA adducts do not explain the preferential occurrence of cancer in particular locations of the human stomach.

Depletion of Circular RNA circ_CORO1C Suppresses Gastric Cancer Development by Modulating miR-138-5p/KLF12 Axis

Background

Gastric cancer (GC) is a common and deadly malignancy in the world. CircRNAs have emerged as important regulators in human diseases, including GC. In this work, we intended to explore the role of circ_CORO1C in GC progression and potential mechanism.

Methods

Quantitative real-time PCR (qRT-PCR) or Western blot assay was performed to examine the expression of circRNA coronin-like actin-binding protein 1C (circ_CORO1C), microRNA (miR)-138-5p and Krueppel-like factor 12 (KLF12) in clinical samples and cells. Cell colony formation ability and viability were measured by colony formation assay and methyl thiazolyl tetrazolium (MTT) assay, respectively. Expression of cell proliferation and epithelia-mesenchymal transition (EMT) biomarker was detected by Western blot analysis. And cell metastasis, including migration and invasion, and apoptosis were analyzed via Transwell assay and flow cytometry, respectively. Target relationship among circ_CORO1C, miR-138-5p and KLF12 was validated by dual-luciferase reporter assay. The in vivo role of circ_CORO1C was investigated by tumor xenograft assay.

Results

Circ_CORO1C and KLF12 were upregulated, while miR-138-5p was downregulated in GC tissues and cells. Circ_CORO1C knockdown suppressed colony formation ability, viability, migration, invasion and EMT in GC cells, while promoted cell apoptosis in vitro. Circ_CORO1C targeted miR-138-5p, the inhibition of which could attenuate silenced circ_CORO1C-induced inhibitory effects on GC progression. MiR-138-5p repressed the aggressive malignant behaviors of GC cells by directly targeting KLF12. Circ_CORO1C deficiency inhibited GC tumor growth in vivo.

Conclusion

Depletion of circ_CORO1C suppressed GC progression by regulating miR-138-5p/KLF12 axis, offering a potential molecular target for GC therapy.

Molecular risk markers related to local tumor recurrence at histological margin-free endoscopically resected early gastric cancers: A pilot study

Local recurrences in early gastric cancers (EGCs) after complete endoscopic submucosal dissection (ESD) remain problematic. Here, we investigated the spatially sequential molecular changes in various cancer-related proteins along the axis of the histologically clear but recurrent resection margins (TRM) to determine the appropriate tumor-free margin distance and potential molecular risk markers related to local recurrence. Five eligible patients with recurrent EGCs after complete ESD were selected from 548 EGC patients. The specimens, including recurrent resection margin axis, were divided into 5 zones. Digital spatial profiling assay was performed to quantify the expression level of 31 cancer-related proteins along each zone. p-Chk1 level was significantly reduced in TRM zone than non-recurrent resection margin. The expression of p44/42 ERK and p-Chk1 were significantly decreased along the lateral axis of the recurrent resection margin, with no significance toward the normal zone, which may suggest that p44/42 ERK and p-Chk1 may be involved in the recurrent side compared to non-recurrent margin. Although we could not evaluate more than 5.5 mm, the significant linear decreases in p44/42 ERK and p-Chk1 were maintained until at least 5.5 mm from the tumor zone in the TRM direction. We estimated the possible margin distance using scatterplots and linear regression analyses, which also showed the estimated distance more than 5.5 mm. In conclusion, the p-Chk1 and p44/42 ERK may be potential candidates of molecular risk markers that may be related to the local recurrence after complete ESD, and a tumor-free distance of 5.5 mm is not enough for safety margin.

Circular RNAs as important players in human gastric cancer

As one of the most prevalent gastrointestinal diseases, gastric cancer (GC) is the second leading cause of cancer-related deaths worldwide. Since GC has no clinical manifestations in the early stage of the disease, most patients are detected in the later phases of disease and have an unfortunately lower chance of recovery. Circular RNAs (circRNAs), a novel category of non-coding RNAs (ncRNAs), are mainly engaged in the regulation of gene expression at the transcriptional and post-transcriptional levels. Numerous evidences have revealed that circRNAs play key roles in GC as they are involved in cell proliferation, growth, and apoptosis via modulating the expression of some target genes, miRNAs, and proteins. Many studies have addressed the impact of circRNA dysregulation on GC initiation, progression, and invasion via binding to miRNAs or RNA binding proteins. Moreover, changes in circRNA expression are associated with pathological and clinical features of GC highlighting their potentials as diagnostic or prognostic biomarkers in GC. In the current study, the recent findings on the significance of circRNAs in the development and progression of GC are reviewed. We focus on the implications of circRNAs as potential diagnostic or prognostic biomarkers in this malignancy.

Vidal A, Pinto P, Ribeiro-dos-Santos AM, Cruz RLS, Fonseca Cabral G, Anaissi AKM, Lopes KDP, Ribeiro-dos-Santos A, Demachki S, de Assumpção PP, Ribeiro-dos-Santos Â, Santos S. Global Analyses of Expressed Piwi-Interacting RNAs in Gastric Cancer

Gastric cancer (GC) represents a notable amount of morbidity and mortality worldwide. Understanding the molecular basis of CG will offer insight into its pathogenesis in an attempt to identify new molecular biomarkers to early diagnose this disease. Therefore, studies involving small non-coding RNAs have been widely explored. Among these, PIWI-interacting RNAs (piRNAs) are an emergent class that can play important roles in carcinogenesis. In this study, small-RNA sequencing was used to identify the global piRNAs expression profile (piRNome) of gastric cancer patients. We found 698 piRNAs in gastric tissues, 14 of which were differentially expressed (DE) between gastric cancer (GC), adjacent to gastric cancer (ADJ), and non-cancer tissues (NC). Moreover, three of these DE piRNAs (piR-48966*, piR-49145, piR-31335*) were differently expressed in both GC and ADJ samples in comparison to NC samples, indicating that the tumor-adjacent tissue was molecularly altered and should not be considered as a normal control. These three piRNAs are potential risk biomarkers for GC, especially piR-48966* and piR-31335*. Furthermore, an in-silico search for mRNAs targeted by the differentially expressed piRNAs revealed that these piRNAs may regulate genes that participate in cancer-related pathways, suggesting that these small non-coding RNAs may be directly and indirectly involved in gastric carcinogenesis.

Non-Invasive Early Molecular Detection of Gastric Cancers

Gastric cancer (GC) is a significant source of global cancer death with a high mortality rate, because the majority of patients with GC are diagnosed at a late stage, with limited therapeutic choices and poor outcomes. Therefore, development of minimally invasive or noninvasive biomarkers which are specific to GC is crucially needed. The latest advancements in the understanding of GC molecular landscapes and molecular biological methods have accelerated attempts to diagnose GC at an early stage. Body fluids, including peripheral blood, saliva, gastric juice/wash, urine, and others, can be a source of biomarkers, offering new methods for the early detection of GC. Liquid biopsy-based methods using circulating sources of cancer nucleic acids could also be considered as alternative strategies. Moreover, investigating gastric juices/washes could represent an alternative for the detection of GC via invasive biopsy. This review summarizes recently reported biomarkers based on DNA methylation, microRNA, long noncoding RNA, circular RNA, or extracellular vesicles (exosomes) for the detection of GC. Although the majority of studies have been conducted to detect these alterations in advanced-stage GC and only a few in population studies or early-stage GC, some biomarkers are potentially valuable for the development of novel approaches for an early noninvasive detection of GC.

Circular RNAs as New Regulators in Gastric Cancer: Diagnosis and Cancer Therapy

Gastric cancer (GC) is one of the most commonly diagnosed cancers that causes high mortality in the world. Although the surgery tools and chemotherapies have significantly improved the overall survival of patients with GC, the early diagnosis of GC remains insufficient and many patients diagnosed with advanced stages of GC are not able to benefit from curative therapy. Circular RNAs (circRNAs), novel members of the non-coding cancer genome, are being explored with regards to various cancer types including GC. CircRNAs could work as miRNA sponges to regulate cell proliferation, cell migration, and cell cycle in GC. In addition, it was found that abnormal expression of circRNAs was associated with pathological characteristics in GC tissues, which could help to act as potential markers of early diagnosis or predictors of prognosis. Although various functional circRNAs have been discovered and characterized, the studies of circRNAs in GC are still at early stages compared with other RNAs. In order to provide a whole view to better understand the circRNAs in the occurrence and development of GC, we review the current knowledge on circRNAs in relation to their expression and regulation in GC as well as their potential to be diagnosis markers, and their role in drug resistance will be mentioned. It is helpful to address their possibility from basic research into practical application.

The Biological Role of Sponge Circular RNAs in Gastric Cancer: Main Players or Coadjuvants?

Circular RNAs (circRNAs) are a new class of long noncoding RNAs able to perform multiple functions, including sponging microRNAs (miRNAs) and RNA-Binding Proteins (RBPs). They play an important role in gastric carcinogenesis, but its involvement during gastric cancer (GC) development and progression are not well understood. We gathered miRNA and/or RBPs sponge circRNAs present in GC, and accessed their biological roles through functional enrichment of their target genes or ligand RBPs. We identified 54 sponge circRNAs in GC that are able to sponge 51 miRNAs and 103 RBPs. Then, we evaluated their host gene expression using The Cancer Genome Atlas (TCGA) database and observed that COL1A2 is the most overexpressed gene, which may be due to circHIPK3/miR-29b-c/COL1A2 axis dysregulation. We identified 27 GC-related pathways that may be affected mainly by circPVT1, circHIPK3 and circNF1. Our results indicate that circHIPK3/miR-107/BDNF/LIN28 axis may mediate chemoresistance in GC, and that circPVT1, circHIPK3, circNF1, ciRS-7 and circ_0000096 appear to be involved in gastrointestinal cancer development. Lastly, circHIPK3, circNRIP1 and circSMARCA5 were identified in different ethnic populations and may be ubiquitous modulators of gastric carcinogenesis. Overall, the studied sponge circRNAs are part of a complex RBP-circRNA-miRNA-mRNA interaction network, and are involved in the establishment, chemoresistance and progression of GC.

The Expression, Functions and Mechanisms of Circular RNAs in Gynecological Cancers

Circular RNAs (circRNAs) are covalently closed, endogenous non-coding RNAs and certain circRNAs are linked to human tumors. Owing to their circular form, circRNAs are protected from degradation by exonucleases, and therefore, they are more stable than linear RNAs. Many circRNAs have been shown to sponge microRNAs, interact with RNA-binding proteins, regulate gene transcription, and be translated into proteins. Mounting evidence suggests that circRNAs are dysregulated in cancer tissues and can mediate various signaling pathways, thus affecting tumorigenesis, metastasis, and remodeling of the tumor microenvironment. First, we review the characteristics, biogenesis, and biological functions of circRNAs, and describe various mechanistic models of circRNAs. Then, we provide a systematic overview of the functional roles of circRNAs in gynecological cancers. Finally, we describe the potential future applications of circRNAs as biomarkers for prognostic stratification and as therapeutic targets in gynecological cancers. Although the function of most circRNAs remains elusive, some individual circRNAs have biologically relevant functions in cervical cancer, ovarian cancer, and endometrial cancer. Certain circRNAs have the potential to serve as biomarkers and therapeutic targets in gynecological cancers.

CircRNA: a rising star in gastric cancer

In recent years, a large number of circRNAs have been identified in mammalian cells with high-throughput sequencing technologies and bioinformatics. The aberrant expression of circRNAs has been reported in many human diseases including gastric cancer (GC). The number of GC-related circRNAs with validated biological functions and mechanisms of action is growing. CircRNAs are critically involved in GC cell proliferation, apoptosis, migration, and invasion. CircRNAs have been shown to function as regulators of parental gene transcription and alternative splicing and miRNA sponges. Moreover, circRNAs have been suggested to interact with proteins to regulate their expression level and activities. Several circRNAs have been identified to encode functional proteins. Due to their great abundance, high stability, tissue- and developmental-stage-specific expression patterns, and wide distribution in various body fluids and exosomes, circRNAs exhibit a great potential to be utilized as biomarkers for GC. Herein, we briefly summarize their biogenesis, properties and biological functions and discuss about the current research progress of circRNAs in GC with a focus on the potential application for GC diagnosis and therapy.

Circular RNA CCDC66 promotes gastric cancer progression by regulating c-Myc and TGF-β signaling pathways

Background: CircRNAs play important roles in cancer development and progression and have the potential to serve as cancer biomarkers. The aim of this study was to investigate the role of circular RNA CCDC66 (circCCDC66) in gastric cancer and to reveal the underlying mechanisms.

Methods: The expression of circCCDC66 in GC tissues and cell lines was examined by qRT-PCR. The correlation between circCCDC66 expression level and clinicopathological characteristics was analyzed. The biological roles of circCCDC66 in GC cell apoptosis, proliferation, migration and invasion were determined by flow cytometry, cell counting, cell colony formation, wound healing, transwell migration and matrigel invasion assays. The role of circCCDC66 in GC growth was further confirmed by mouse xenograft tumor model. Western blot and qRT-PCR were used to explore the effects of circCCDC66 on epithelial-mesenchymal transition (EMT)-related gene and protein expression.

Results: CircCCDC66 expression was elevated in both GC tissues and cell lines compared to adjacent normal tissues and normal gastric epithelial cell line. The upregulation of circCCDC66 in GC tissues was related to tumor stage and lymphatic metastasis. CircCCDC66 knockdown significantly inhibited GC cell proliferation, migration and invasion and induced cell apoptosis in GC cells. On the contrary, circCCDC66 overexpression had the opposite effects. In addition, circCCDC66 knockdown suppressed the tumorigenesis of GC cells in nude mice. Furthermore, circCCDC66 knockdown inhibited the activation of c-Myc and TGF-β signaling pathways and reversed EMT in GC cells. c-Myc and TGF-β interference blocked circCCDC66-mediated promotion of gastric cancer cell proliferation, migration and invasion.

Conclusion: CircCCDC66 promotes GC growth and metastasis by activating c-Myc and TGF-β signaling pathways, suggesting that it may serve as a potential biomarker for GC.

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.

miRNome Reveals New Insights Into the Molecular Biology of Field Cancerization in Gastric Cancer

BACKGROUND

MicroRNAs (miRNAs) play an important role in gastric carcinogenesis and have been associated with gastric field cancerization; however, their role is not fully understood in this process. We performed the miRNome sequencing of non-cancerous, adjacent to tumor and gastric cancer samples to understand the involvement of these small RNAs in gastric field cancerization.

METHODS

We analyzed samples of patients without cancer as control (non-cancerous gastric samples) and adjacent to cancer and gastric cancer paired samples, and considered miRNAs with |log2(fold change)| > 2 and Padj < 0.05 to be statistically significant. The identification of target genes, functional analysis and enrichment in KEGG pathways were realized in the TargetCompare, miRTargetLink, and DAVID tools. We also performed receiver operating characteristic (ROC) curves and miRNAs that had an AUC > 0.85 were considered to be potential biomarkers.

RESULTS

We found 14 miRNAs exclusively deregulated in gastric cancer, of which six have potential diagnostic value for advanced disease. Nine miRNAs with known tumor suppressor activities (TS-miRs) were deregulated exclusively in adjacent tissue. Of these, five have potential diagnostic value for the early stages of gastric cancer. Functional analysis of these TS-miRs revealed that they regulate important cellular signaling pathways (PI3K-Akt, HIF-1, Ras, Rap1, ErbB, and MAPK signaling pathways), that are involved in gastric carcinogenesis. Seven miRNAs were differentially expressed in both gastric cancer and adjacent regarding to non-cancerous tissues; among them, hsa-miR-200a-3p and hsa-miR-873-5p have potential diagnostic value for early and advanced stages of the disease. Only hsa-miR-196a-5p was differentially expressed between adjacent to cancer and gastric cancer tissues. In addition, the other miRNAs identified in this study were not differentially expressed between adjacent to cancer and gastric cancer, suggesting that these tissues are very similar and that share these molecular changes.

CONCLUSION

Our results show that gastric cancer and adjacent tissues have a similar miRNA expression profile, indicating that studied miRNAs are intimately associated with field cancerization in gastric cancer. The overexpression of TS-miRs in adjacent tissues may be a barrier against tumorigenesis within these pre-cancerous conditions prior to the eventual formation or relapse of a tumor. Additionally, these miRNAs have a great accuracy in discriminating non-cancerous from adjacent to tumor and cancer tissues and can be potentially useful as biomarkers for gastric cancer.

Role of circular RNAs in gastric cancer: Recent advances and prospects

Circular RNA (circRNA) is a newly discovered non-coding RNA with special structure, which is widely expressed in eukaryotic organisms and mainly located in the cytoplasm. circRNAs participate in gene regulation by working as miRNA sponges that block the inhibitory effect of miRNA on its target genes. In addition, circRNAs can bind to RNA binding proteins to regulate gene expression. Based on characteristics of stability, expression specificity and participation in gene regulation, circRNAs are expected to be biomarkers for early diagnosis of cancer or potential targets for cancer therapy. With the help of bioinformatics analysis, circRNA microarray analysis and high-throughput sequencing technology, more circRNAs were discovered to participate in the progression of gastric cancer (GC) over the past three years. This article gives an overview of these recent research focusing on the roles of circRNAs in GC and highlights the advances.

Recent advances in gastric cancer early diagnosis

Gastric cancer (GC) remains an important cause of cancer death worldwide with a high mortality rate due to the fact that the majority of GC cases are diagnosed at an advanced stage when the prognosis is poor and the treatment options are limited. Unfortunately, the existing circulating biomarkers for GC diagnosis and prognosis display low sensitivity and specificity and the GC diagnosis is based only on the invasive procedures such as upper digestive endoscopy. There is a huge need for less invasive or non-invasive tests but also highly specific biomarkers in case of GC. Body fluids such as peripheral blood, urine or saliva, stomach wash/gastric juice could be a source of specific biomarkers, providing important data for screening and diagnosis in GC. This review summarized the recently discovered circulating molecules such as microRNAs, long non-coding RNAs, circular RNAs, which hold the promise to develop new strategies for early diagnosis of GC.

Epigenetic Field Cancerization in Gastric Cancer: microRNAs as Promising Biomarkers

Background: The biological role of microRNAs (miRNAs) in field cancerization is unknown. To investigate the involvement of miRNAs in gastric field cancerization, we evaluated the expression profile of ten miRNAs and their diagnostic value.

Methods: We used three groups of FFPE gastric samples: non-cancer (NC), cancer adjacent (ADJ) and gastric cancer (GC). The expression profiles of hsa-miR-10a, -miR-21, -miR-29c, -miR-135b, -miR-148a, -miR-150, -miR-204, -miR-215, -miR-483 and -miR-664a were investigated using qRT-PCR. The results obtained by qRT-PCR were validated in Small RNA-Seq data from the TCGA database. The search for target genes of the studied miRNAs was performed in the miRTarBase public database and miRTargetLink tool, using experimentally validated interactions. In addition, we also performed the functional analysis of these genes using enrichment in KEGG pathways. The potential as biomarker was evaluated using a receiver operating characteristic (ROC) curve and the derived area under the curve (AUC>0.85) analysis.

Results: The miRNAs hsa-miR-10a, -miR-21, -miR-135b, hsa-miR-148a, -miR-150, -miR-215, -miR-204, -miR-483 and -miR-664a were up-regulated in ADJ and GC compared to NC (P<0.03); and hsa-miR-21 and -miR-135b were up-regulated in GC compared to ADJ (P<0.01). Hsa-miR-148a, -miR-150, -miR-215, -miR-483 and -miR-664a were not differentially expressed between GC and ADJ, suggesting that both share similar changes (P>0.1). The TS-miR hsa-miR-29c was up-regulated in ADJ compared to NC and GC (P<0.01); we did not observe a significant difference in the expression of this miRNA between NC and GC. This feature may be an antitumor mechanism used by cancer-adjacent tissue because this miRNA regulates the BCL-2, CDC42 and DMNT3A oncogenes. The expression level of hsa-miR-204 was associated with Helicobacter pylori infection status (P<0.05). Functional analysis using the genes regulated by the studied miRNAs showed that they are involved in biological pathways and cellular processes that are critical for the establishment of H. pylori infection and for the onset, development and progression of GC. hsa-miR-10a, -miR-21, -miR-135b, -miR-148a, -miR-150, -miR-215, -miR-483 and -miR-664a were able to discriminate NC from other tissues with great accuracy (AUC>0.85).

Conclusion: The studied miRNAs are closely related to field cancerization, regulate genes important for gastric carcinogenesis and can be potentially useful as biomarkers in GC.

CircRNAs and cancer: Biomarkers and master regulators

Circular RNAs (circRNAs) are a novel class of regulatory RNAs that despite being relatively abundant have only recently begun to be explored. There are many thousands of genes that appear capable of producing circRNAs, however the function of all but a handful remain to be determined. What is emerging about these highly conserved molecules is that they play important roles in biology and cancer biology in particular. The most explored function of circRNAs is as master regulators of gene expression that act to sequester or ´sponge´ other gene expression regulators, in particular miRNAs. They have also been demonstrated to function via direct modulation of transcription, and by interfering with splicing mechanisms. Although generally expressed in low abundance when compared to their linear counterparts, they are often expressed in a tissue- and developmental stage- specific manner. Coupled with their remarkable resistance to RNAse activity due to a covalent closed cyclic structure, circRNAs show great promise as novel biomarkers of cancer and other diseases. In this review we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We will also review some of the challenges that remain to be resolved if this emerging class of RNAs are really to become useful in the clinic.

The emerging role of circular RNAs in gastric cancer

Gastric cancer (GC) ranks as the fourth most common cancer and the third leading cause of cancer-related death worldwide. Circular RNAs (circRNAs) are a new class of long noncoding RNAs characterized by a single-stranded covalently closed loop structure. Emerging evidence reveals the essential function of circRNAs in the occurrence and development of human diseases. Among these, circRNAs are aberrantly expressed in GC and are involved in the progression of GC. In this review, we briefly summarize the current knowledge of the classification, biogenesis and biological functions of circRNAs, with an emphasis on their relationship with GC. As our understanding of the relation between circRNAs and GC advances, more diagnostic and therapeutic protocols will be developed for the prevention and treatment of GC.