Global circular RNA expression profile of human gastric cancer and its clinical significance

Current prevalence status of gastric cancer and recent studies on the roles of circular RNAs and methods used to investigate circular RNAs

Gastric cancer is a malignant tumor with the fifth incidence and third mortality worldwide. There were 951,000 new cases and about 723,000 patients died of it in 2012. Undoubtedly, gastric cancer has been affecting people's living standards, and is already a major public health problem in China with its population growth and ageing. Even though the detection methods and medical standards have improved, the five-year survival rate of people is still very low. While circular RNA (circRNA) is increasingly attracting attention from researchers, at the same time, its mystery has gradually been uncovered. Many studies have shown that circRNA can act as molecular sponge of miRNA to regulate gene expression and has an obviously different expression profile between cancerous and normal groups, which arouse people's curiosity and provide new opportunities for early detection of gastric cancer to improve the quality of life of patients. This study reviews current prevalence of gastric cancer in the word and China, as well as the characteristics and functions of circRNA and common laboratory detection methods involving circRNA in gastric cancer.

Noncoding RNAs in Extracellular Fluids as Cancer Biomarkers: The New Frontier of Liquid Biopsies

The last two decades of cancer research have been devoted in two directions: (1) understanding the mechanism of carcinogenesis for an effective treatment, and (2) improving cancer prevention and screening for early detection of the disease. This last aspect has been developed, especially for certain types of cancers, thanks also to the introduction of new concepts such as liquid biopsies and precision medicine. In this context, there is a growing interest in the application of alternative and noninvasive methodologies to search for cancer biomarkers. The new frontiers of the research lead to a search for RNA molecules circulating in body fluids. Searching for biomarkers in extracellular body fluids represents a better option for patients because they are easier to access, less painful, and potentially more economical. Moreover, the possibility for these types of samples to be taken repeatedly, allows a better monitoring of the disease progression or treatment efficacy for a better intervention and dynamic treatment of the patient, which is the fundamental basis of personalized medicine. RNA molecules, freely circulating in body fluids or packed in microvesicles, have all the characteristics of the ideal biomarkers owing to their high stability under storage and handling conditions and being able to be sampled several times for monitoring. Moreover, as demonstrated for many cancers, their plasma/serum levels mirror those in the primary tumor. There are a large variety of RNA species noncoding for proteins that could be used as cancer biomarkers in liquid biopsies. Among them, the most studied are microRNAs, but recently the attention of the researcher has been also directed towards Piwi-interacting RNAs, circular RNAs, and other small noncoding RNAs. Another class of RNA species, the long noncoding RNAs, is larger than microRNAs and represents a very versatile and promising group of molecules which, apart from their use as biomarkers, have also a possible therapeutic role. In this review, we will give an overview of the most common noncoding RNA species detectable in extracellular fluids and will provide an update concerning the situation of the research on these molecules as cancer biomarkers.

Predicting human disease-associated circRNAs based on locality-constrained linear coding

Circular RNAs (circRNAs) are a new kind of endogenous non-coding RNAs, which have been discovered continuously. More and more studies have shown that circRNAs are related to the occurrence and development of human diseases. Identification of circRNAs associated with diseases can contribute to understand the pathogenesis, diagnosis and treatment of diseases. However, experimental methods of circRNA prediction remain expensive and time-consuming. Therefore, it is urgent to propose novel computational methods for the prediction of circRNA-disease associations. In this study, we develop a computational method called LLCDC that integrates the known circRNA-disease associations, circRNA semantic similarity network, disease semantic similarity network, reconstructed circRNA similarity network, and reconstructed disease similarity network to predict circRNAs related to human diseases. Specifically, the reconstructed similarity networks are obtained by using Locality-Constrained Linear Coding (LLC) on the known association matrix, cosine similarities of circRNAs and diseases. Then, the label propagation method is applied to the similarity networks, and four relevant score matrices are respectively obtained. Finally, we use 5-fold cross validation (5-fold CV) to evaluate the performance of LLCDC, and the AUC value of the method is 0.9177, indicating that our method performs better than the other three methods. In addition, case studies on gastric cancer, breast cancer and papillary thyroid carcinoma further verify the reliability of our method in predicting disease-associated circRNAs.

Clinical significances of hsa_circ_0067582 and hsa_circ_0005758 in gastric cancer tissues

BACKGROUND

Circular RNAs (circRNAs) are a special class of endogenous noncoding RNAs that have numerous biological functions in normal situation and diseases including cancers. However, the clinical significance of circRNAs in gastric cancer (GC) remains largely unknown. Here, we chose two representative circRNAs, hsa_circ_0067582 and hsa_circ_0005758, to investigate their clinical significance in GC patients.

METHODS

Using real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), we explored the expression levels of hsa_circ_0067582 and hsa_circ_0005758 in tissues with different stages of gastric tumorigenesis. Then, the relationships between their expression levels and GC patients' clinicopathological factors were further investigated. Receiver operating characteristic (ROC) curves were established for evaluating diagnostic values of hsa_circ_0067582 and hsa_circ_0005758.

RESULTS

Compared with healthy control tissues, both hsa_circ_0067582 and hsa_circ_0005758 were significantly decreased in GC tissues. Besides, hsa_circ_0067582 expression was associated with GC patients' tissue CEA level (P <.001) and stages (P = .037); and hsa_circ_0005758 expression was relevant to tissue CEA level (P < .001) and perineural invasion (P = .048). The area under the ROC curve (AUC) of hsa_circ_0067582 was up to 0.671. The cutoff value was set at 10.61, with which the sensitivity and specificity were 55.2% and 75.0%, respectively. Similar to hsa_circ_0005758, the AUC of hsa_circ_0005758 was 0.721. The cutoff value was set at 10.20, with which the sensitivity and specificity were 75.0% and 67.7%, respectively.

CONCLUSION

These results showed that both hsa_circ_0067582 and hsa_circ_0005758 may play an important role in gastric carcinogenesis; and they may be potential indicators for GC diagnosis.

Identification of circRNA-miRNA-mRNA regulatory network in gastric cancer by analysis of microarray data

Background

Evidence is increasingly indicating that circular RNAs (circRNAs) are closely involved in tumorigenesis and cancer progression. However, the function of circRNAs in gastric cancer (GC) are still unknown. Here, we aimed to determine the regulatory mechanism of circRNAs in GC.

Methods

Expression profiles of circRNAs were downloaded from four Gene Expression Omnibus (GEO) microarray datasets. Expression profiles of miRNAs and mRNAs were collected from The Cancer Genome Atlas (TCGA) database. We used the robust rank aggregation method to identify differentially expressed circRNAs (DEcircRNAs) and a ceRNA network was constructed based on circRNA–miRNA pairs and miRNA–mRNA pairs. Functional and pathway enrichment analyses were performed and interactions between proteins were predicted using Cytoscape. Aa subnetwork regulatory module was built using the MCODE plugin.

Results

A total of eight DEcircRNAs, 240 DEmiRNAs, and 4578 DEmRNAs were identified. The circRNA–miRNA–mRNA network was constructed based on seven circRNAs, 33 miRNAs, 69 mRNAs in GC. GO and KEGG pathway analysis indicated DEmRNAs might be associated with GC onset and progression. A PPI network was established and four hub genes (MCM4, KIF23, MCM8, and NCAPD2) were determined from the network. Then a circRNA–miRNA-hub gene subnetwork was constructed based on the four DEcircRNAs, three DEmiRNAs, and four DEmRNAs.

Conclusions

Our findings provide a deeper understanding the circRNA-related competing endogenous RNA regulatory mechanism in GC pathogenesis.

Diagnostic performance of circular RNAs in human cancers: A systematic review and meta-analysis

BACKGROUND

Recently, accumulating evidence have revealed that circular RNA (circRNA) was deregulated in multiple types of cancer, suggesting that circRNA might serve as a novel candidate biomarker of cancer diagnosis. However, inconsistent results have become an obstacle in applying circRNAs to clinical practice. The aim of this study is to evaluate diagnostic value of circRNAs among cancers.

METHODS

A literature search was systematically performed among PubMed, Sciencedirect, Cochrane Library, Web of Science, Wanfang, and Chinese National Knowledge Infrastructure databases up to February 15, 2019. The pooled sensitivity (SEN), specificity (SPE), positive likelihood ratios, negative likelihood ratios, diagnostic odds ratio, and area under the SROC curve (AUC) were applied to evaluate diagnostic performance of circRNAs.

RESULTS

In total, the study included 64 studies with single circRNA and 13 studies with combined circRNAs. Overall, the study presented that a single circRNA had moderate diagnostic value, with a SEN of 0.75, a SPE of 0.76, and an AUC of 0.82. The plasma circRNAs had higher diagnostic accuracy than tissue (AUC: 0.87, 95% confidence interval [CI]: 0.83-0.89 for plasma/serum subgroup; AUC: 0.79, 95% CI: 0.75-0.82 for tissue subgroup). Furthermore, the combined circRNAs had good diagnostic efficacy for GC, with a SEN of 0.89, a SPE of 0.94, and an AUC of 0.97, respectively.

CONCLUSION

This study confirmed that circRNAs may be candidate biomarkers for cancer diagnosis. In particular, diagnosis of combined circRNAs will be a new alternative applied to clinical research and practice for cancer.

Emerging roles of circular RNAs in colorectal cancer

Circular RNAs (circRNAs) are a newly discovered class of endogenous non-coding RNAs. Owing to the development of high-throughput sequencing, researchers have identified thousands of circRNAs. Emerging evidence suggests that circRNAs are involved in various tumor cell processes, including proliferation, apoptosis, invasion and migration. Because of their high stability and abundance, tissue-specific expression, and easy detection, circRNAs are considered ideal biomarkers for cancer diagnosis and prognosis. An increasing number of studies have recently demonstrated that circRNAs are closely associated with colorectal cancer (CRC). CRC is the third most common cancer and the second leading cause of cancer-related death globally. Thus, understanding the molecular mechanisms involved in the development and progression of CRC is vital. In this review, we summarize the current literature regarding human circRNAs related to CRC and present an overview of the potential clinical implications of circRNAs with respect to CRC.

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.

Expression profiles of circular RNAs in human colorectal cancer based on RNA deep sequencing

Background

Circular RNAs (circRNAs) are a novel group of RNAs and play essential roles in cancers. However, the expression profiles of circRNAs in human colorectal cancer (CRC) are largely unclear.

Methods

The differentially expressed circRNAs, mRNAs, and microRNAs (miRNAs) between CRC tissues and paired adjacent normal tissues were first screened. Then, gene ontology and pathway analyses were performed to predict the possible functions. In addition, we identified the differentially expressed circRNAs in CRC correlated with Krüppel‐like factor 4 (KLF4) and validated their expression levels in CRC tissues. Finally, the correlations between hsa_circ_0142527 expression levels and clinicopathological features of patients with CRC were also analyzed.

Results

After filtered 4735 circRNAs by RNA deep sequencing, 67 differentially expressed circRNAs (fold change >2.0, P < 0.05) were selected. The top two pathways were cell cycle and other glycan degradation. Hsa_circ_0142527 and KLF4 mRNA were significantly lower expressed in CRC tissues in both training and confirm groups and have high positive correlation (r = 0.754). We further found that the expression levels of hsa_circ_0142527 were significantly associated with age (P = 0.004), differentiation (P = 0.008), invasion (P = 0.029), distal metastasis (P = 0.004), TNM stage (P = 0.005), and carcinoembryonic antigen (CEA; P = 0.037).

Conclusions

The circRNA expression profile of CRC provided new clues for understanding the occurrence of CRC. Hsa_circ_0142527 may be served as a potential biomarker for the diagnosis of CRC.

Current Status of Functional Studies on Circular RNAs in Bladder Cancer and their Potential Role as Diagnostic and Prognostic Biomarkers: A Review

Worldwide, bladder cancer represents the ninth most common malignancy and is the 13^th cause of cancer-associated death. Although surgery combined with chemotherapy and radiotherapy has improved patient outcomes, the prognosis remains poor for most patients with muscle-invasive bladder cancer. The exact mechanisms and critical regulators of bladder cancer remain unknown. Circular RNAs (circRNAs) are a distinct type of endogenous non-coding RNA. Recent studies have shown that circRNAs participate in many processes, including proliferation, invasion, migration, and apoptosis in multiple types of malignancy, including bladder cancer. Some circRNAs are dysregulated in bladder cancer and play essential roles in cancer progression. Importantly, some circRNAs may serve as diagnostic and prognostic biomarkers for bladder cancer. This review aims to summarize the findings from recent studies that have focused on the roles of human circRNAs in bladder cancer and discusses the clinical roles for circRNAs, including their potential roles as diagnostic or prognostic biomarkers.

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.

Hsa_circ_0067997 promotes the progression of gastric cancer by inhibition of miR-515-5p and activation of X chromosome-linked inhibitor of apoptosis (XIAP)

Circular RNAs (circRNAs) have been revealed to play vital roles in modulating gene expression and participate in several pathological responses including gastric cancer (GC). However, the larger numbers of the circRNAs in GC progression remain undetermined. In the present study, four GC related circRNAs expression profiles from the Gene Expression Omnibus (GEO) database were enrolled. We identified hsa_ circRNA_00067997 (circ_0067997) as an oncogene in GC. qRT-PCR was used to validate the expression of circ_0067997 in GC tissues and cell lines. The results revealed that circ_0067997 was upregulated in GC, and high circ_0067997 expression was associated with the poor overall survival rate of GC patients. Knockdown of circ_0067997 significantly reduced cell viability, inhibited colony formation, and attenuated invasive ability, whereas overexpression of circ_0067997 exhibited opposed effects. Circ_0067997 was identified to be a sponge for miR-515-5p directly. Moreover, XIAP was demonstrated to be targeted and regulated by miR-515-5p. In conclusion, circ_0067997 was identified to be an oncogene in GC by regulating miR-515-5p/XIAP axis.

Circular RNAs as diagnostic biomarkers in gastric cancer: A meta-analysis review

PURPOSE

Gastric cancer is a malignant tumor in the world and circRNA has a close connection with it. However, the effects of circRNA on gastric cancer is still not clear.

METHODS

A comprehensive search of PubMed, Web of Science and Embase for published experimental studies about circRNA from 2013 to June 2018 was conducted with two investigators. Diagnostic OR (DOR) was calculated to evaluate the diagnostic efficacy by STATA 12.0.

RESULTS

Total 11 studies were found, including 12 kinds of circRNAs, 11 in tissues, 5 in plasma, and all down regulated. The combined DOR and AUC (Area Under the Curve of Receiver Operating Characteristic) with their 95%CI were 8.778 [6.108, 12.614] and 0.81 [0.78, 0.84] respectively, indicating that circRNAs can reflect gastric cancer as well. Subgroup analysis revealed that circRNAs in plasma were higher than tissues as well as in subgroup with different sample sizes. We speculated that the heterogeneity of the literatures was mainly due to the different backgrounds of gastric cancer and the differences in experimental design and operation process. And the Deeks' funnel map revealed there was no obvious public biasness in the literature.

CONCLUSION

CircRNAs have high sensitivity and specificity in the diagnosis of gastric cancer, and it may become an auxiliary diagnostic biomarker of gastric cancer.

FNDC3B circular RNA promotes the migration and invasion of gastric cancer cells via the regulation of E-cadherin and CD44 expression

Circular RNAs (circRNAs) are a new class of RNAs, and many studies have identified thousands of circRNAs in tumor cells. Fibronectin type III domain‐containing protein 3B (FNDC3B) circular RNA (circFNDC3B, circBase ID: hsa_circ_0006156) circularizes with exons 5 and 6. Gibson Assembly DNA technology was used to construct a circFNDC3B expression vector without a splice site and restriction enzyme site. We showed that circFNDC3B increased migration and invasion in gastric cancer (GC). Ectopic expression of circFNDC3B reduced the level of E‐cadherin protein to promote the epithelial–mesenchymal transition in GC. RNA immunoprecipitation assays and RNA pull‐down assays confirmed that circFNC3B increased CD44 expression, which was associated with cell adhesion, via the formation of a ternary complex of circFNDC3B‐IGF2BP3‐CD44 mRNA. These results indicated that circFNDC3B was associated with the degree of malignancy to highlight the specific characteristics of cell invasion.

Identification of Key Genes and Circular RNAs in Human Gastric Cancer

Background

Globally, gastric cancer (GC) is the third most common source of cancer-associated mortality. The aim of this study was to identify key genes and circular RNAs (circRNAs) in GC diagnosis, prognosis, and therapy and to further explore the potential molecular mechanisms of GC.

Material/Methods

Differentially expressed genes (DEGs) and circRNAs (DE circRNAs) between GC tissues and adjacent non-tumor tissues were identified from 3 mRNA and 3 circRNA expression profiles. Functional analyses were performed, and protein–protein interaction (PPI) networks were constructed. The significant modules and key genes in the PPI networks were identified. Kaplan-Meier analysis was performed to evaluate the prognostic value of these key genes. Potential miRNA-binding sites of the DE circRNAs and target genes of these miRNAs were predicted and used to construct DE circRNA–miRNA–mRNA networks.

Results

A total of 196 upregulated and 311 downregulated genes were identified in GC. The results of functional analysis showed that these DEGs were significantly enriched in a variety of functions and pathways, including extracellular matrix-related pathways. Ten hub genes (COL1A1, COL3A1, COL1A2, COL5A2, FN1, THBS1, COL5A1, SPARC, COL18A1, and COL11A1) were identified via PPI network analysis. Kaplan-Meier analysis revealed that 7 of these were associated with a poor overall survival in GC patients. Furthermore, we identified 2 DE circRNAs, hsa_circ_0000332 and hsa_circ_0021087. To reveal the potential molecular mechanisms of circRNAs in GC, DE circRNA–microRNA–mRNA networks were constructed.

Conclusions

Key candidate genes and circRNAs were identified, and novel PPI and circRNA–microRNA–mRNA networks in GC were constructed. These may provide useful information for the exploration of potential biomarkers and targets for the diagnosis, prognosis, and therapy of GC.

Circular RNA ARHGAP26 is over-expressed and its downregulation inhibits cell proliferation and promotes cell apoptosis in gastric cancer cells

BACKGROUND/AIMS

This study aimed to explore the effect of circular RNA ARHGAP26 (circ-ARHGAP26) on cell proliferation and apoptosis in gastric cancer (GC) cell lines.

MATERIALS AND METHODS

Human GC cell lines including HGC-27, AGS, SGC-7901, BGC-823, NCI-N87 and human normal gastric mucosal cells GSE-1 were cultured. The circ-ARHGAP26 expression was determined by quantitative polymerase chain reaction assay. Blank inhibitor and circ-ARHGAP26 inhibitor plasmids were transfected into HGC-27 or AGS cells as NC (-) and circ-ARHGAP26(-) groups. Counting Kit-8 (CCK-8) and Annexin V (AV)/propidium iodide (PI) were conducted to evaluate cell proliferation and cell apoptosis, respectively. Western blot was performed to determine the expressions of apoptotic markers (C-Caspase3 and Bcl-2).

RESULTS

The circ-ARHGAP26 expression was elevated in HGC-27 (P < 0.001), AGS (P < 0.001), SGC-7901 (P < 0.01), BGC-823 (P < 0.05) and NCI-N87 (P < 0.05) GC cell lines compared to GSE-1 cells. In HGC-27 cells, CCK8 assay revealed that cell proliferation was decreased at 48 h (P < 0.05) and 72 h (P < 0.01), while AV/PI assay disclosed that cell apoptosis rate was increased at 72 h in circ-ARHGAP26 (-) group compared to NC (-) group (P < 0.01). Western blot assay also illuminated that apoptotic marker C-Caspase 3 was raised, while anti-apoptotic marker Bcl-2 was reduced at 72 h in circ-ARHGAP26 (-) group compared to NC (-) group. In addition, further validation in AGS cells also exhibited that cells proliferation was repressed, while apoptosis was enhanced in circ-ARHGAP26 (-) group compared to NC (-) group.

CONCLUSION

The circ-ARHGAP26 is over-expressed and its downregulation inhibits cell proliferation and promotes cells apoptosis in GC cells.

Circular RNA: a novel biomarker and therapeutic target for human cancers

Circular (circ)RNAs, a newly recognized class of noncoding RNA, have been implicated in the occurrence and development of several diseases, including neurological and cardiovascular diseases. Studies of human tumors, including those of liver cancer, gastric cancer, lung cancer and colorectal cancer, have shown differential expression profiles of circRNAs, suggesting regulatory roles in cancer pathogenesis and metastasis. In this review, we discuss the most recent research into tumor-related circRNAs, providing a comprehensive summary of the expression or/and function of these circRNAs and proposing rational perspectives on the potential clinical application of circRNAs as helpful biomarkers or therapeutic targets in human tumors.

A novel circular RNA, circFAT1(e2), inhibits gastric cancer progression by targeting miR-548g in the cytoplasm and interacting with YBX1 in the nucleus

In the present study, two circular RNA (circRNA) expression profiles in paired gastric cancer (GC) tissues from the GEO database were examined. We identified a novel circRNA, has_circ_0001461, which we termed circFAT1(e2). We verified that circFAT1(e2) was significantly downregulated in GC tissues and cell lines and was correlated with overall survival of GC patients. Fluorescence in situ hybridization (FISH) analysis showed that circFAT1(e2) was distributed in the cytoplasm of GC cells, as well as in the nucleus. Functional assays indicated that overexpression of circFAT1(e2) inhibited GC cell proliferation, migration and invasion. Then, we investigated whether circFAT1(e2) acts as a sponge of microRNA-549g(miR-548g) and regulates the expression of tumor suppressor RUNX1 in GC cells. Moreover, we found that nucleus-located circFAT1(e2) could directly interact with Y-box binding protein-1 (YBX1) and inhibit its function. In conclusion, circFAT1(e2) may play a role as a tumor suppressor in GC cells by regulating the miR-548g/RUNX1 axis in the cytoplasm and targeting YBX1 in the nucleus.

CRISPR-Cpf1-mediated genome editing and gene regulation in human cells

Clustered regularly interspaced short palindromic repeat (CRISPR) system is being championed as a robust and flexible tool for genome editing. Compared with CRISPR associated protein 9 (Cas9), the CRISPR from Prevotella and Francisella 1 (Cpf1) protein has some distinct characteristics, including RNase activity, T-rich protospacer adjacent motif (PAM) preference and generation of sticky cutting ends. The extremely low propensity of off-target effects and relatively high editing efficiency represent prominent advantages of Cpf1 over Cas9. CRISPR-Cpf1, alone or fused with function domains, has broadly expanded the applications such as multiplex gene knockout, transcriptional repression or activation and epigenome editing in a drug controlled way. Meanwhile, the modification of CRISPR RNAs (crRNAs) with aptamer RNA achieves great promotion on genome editing. Moreover, disease-associated gene manipulation in mice, tumor mutation detection in patients with cancers, and more yet to come, represent growing demands of CRISPR-Cpf1 in clinical genome therapy. In this review, we summarized the unique properties of Cpf1 and the molecular mechanisms underlying CRISPR-Cpf1 on gene editing and regulation in human cells.

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.

RNAs as Candidate Diagnostic and Prognostic Markers of Prostate Cancer-From Cell Line Models to Liquid Biopsies

The treatment landscape of prostate cancer has evolved rapidly over the past five years. The explosion in treatment advances has been witnessed in parallel with significant progress in the field of molecular biomarkers. The advent of next-generation sequencing has enabled the molecular profiling of the genomic and transcriptomic architecture of prostate and other cancers. Coupled with this, is a renewed interest in the role of non-coding RNA (ncRNA) in prostate cancer biology. ncRNA consists of several different classes including small non-coding RNA (sncRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA). These families are under active investigation, given their essential roles in cancer initiation, development and progression. This review focuses on the evidence for the role of RNAs in prostate cancer, and their use as diagnostic and prognostic markers, and targets for treatment in this disease.

Circ_0056618 and CXCR4 act as competing endogenous in gastric cancer by regulating miR-206

Circular RNAs (circRNAs) have proved to play an important role in gastric cancer. In this study, we found that circ_0056618 took part in gastric cancer cell proliferation and survival. The real-time polymerase chain reaction result showed that circ_0056618 was overexpressed in tumor tissues or cells compared with adjacent normal tissues or normal cells and had a negative relationship to gastric cancer patients' survival time. Meanwhile, the inhibition of circ_0056618 suppressed the proliferation and metastasis of gastric cancer cells. Further bioinformatical analysis indicated that circ_0056618 sponged miR-206 to regulate CXCR4 according to the prediction of TargetScan and miRanda. Dual-luciferase reporter assay and Western blot analysis revealed the underlying relationship of circ_0056618, miR-206, and CXCR4. Hence, circ_0056618 negatively regulated miR-206 expression promoting CXCR4 expression. Altogether, circ_0056618 is a potential gastric cancer prognostic marker, as well as a potential therapeutic target to inhibit gastric cancer metastasis.

Circular RNA: new star, new hope in cancer

BACKGROUND

Circular RNAs are a new class of endogenous non-coding RNA that can function as crucial regulators of diverse cellular processes. The diverse types of circular RNAs with varying cytogenetics in cancer have also been reported. Circular RNAs can act as a microRNA sponge or through other mechanisms to regulate gene expression as either tumor inhibitors or accelerators, suggesting that circular RNAs can serve as newly developed biomarkers with clinic implications. Here, we summerized recent advances on circular RNAs in cancer and described a circular RNA network associated with tumorigenesis. The clinical implications of circular RNAs in cancer were also discussed in this paper.

SHORT CONCLUSION

Growing evidence has revealed the crucial regulatory roles of circular RNAs in cancer and the elucidation of functional mechanisms involving circular RNAs would be helpful to construct a circRNA-miRNA-mRNA regulatory network. Moreover, circular RNAs can be easily detected due to their relative stability, widespread expression, and abundance in exosomes, blood and saliva; thus, circular RNAs have potential as new and ideal clinical biomarkers in cancer.

Global microarray profiling identified hsa_circ_0064428 as a potential immune-associated prognosis biomarker for hepatocellular carcinoma

BACKGROUND

Increasing evidence has shown that circular RNAs (circRNAs) are involved tumourigenesis and metastasis of hepatocellular carcinoma (HCC); however, progression about its function in HCC is relatively slow. Here, we aimed to investigate whether plasma circRNAs could reflect the tumour-infiltrating lymphocytes (TILs) in HCC tumour tissues and serve as prognosis biomarker for HCC.

METHODS

Tissue samples of patients with HCC were subjected to immunohistochemistry staining against CD8 to examine the TILs. Then, we investigated the expression profile of circRNAs by microarray between plasma of patients with HCC with high TILs and low TILs, and the differentially expressed circRNAs were validated with qRT-PCR. Statistical analysis was performed with SPSS software and GraphPad Prism.

RESULTS

We have demonstrated that patients with HCC with high TILs exhibit a significant better overall survival, suggesting clinical outcome could be predicted by TILs. Global circRNA microarray between plasma of patients with HCC with high TILs and low TILs successfully identified six differentially expressed novel circRNAs. Among them, the expression of hsa_circ_0064428 was significantly reduced in patients with HCC with high TILs but increased in patients with low TILs. Moreover, hsa_circ_0064428 was negatively correlated with patient's survival, tumour size and metastasis.

CONCLUSION

These findings together imply that hsa_circ_0064428 could be considered as a potential HCC prognosis biomarker. Future in-depth research is required to further illustrate the involvement of hsa_circ_0064428 in HCC tumourigenesis and metastasis.

The expression profile and clinical application potential of hsa_circ_0000711 in colorectal cancer

Introduction

Circular RNAs, as a class of long-time-ignored non-coding RNA, have been revealed as multifunctional RNAs in recent years, especially in the cancer research. However, the mechanism of most circular RNAs and their clinical application values in human cancers remain unknown, including in colorectal cancer (CRC).

Methods

In this study, we focused on the expression pattern and clinical values of hsa_circ_0000711 in CRC. The expression level of hsa_circ_0000711 in 101 paired CRC tissues and 3 CRC cell lines (HCT116, COLO205, and H-T29), as well as human normal colon epithelial cell line NCM460, were measured by quantitative real-time polymerase chain reaction.

Results

Our results revealed that the expression level of hsa_circ_0000711 was significantly downregulated in CRC tissues (P=9.35E-16) and CRC cell lines (P<0.01). In addition, the area under the receiver characteristic curves was 0.81. The sensitivity and specificity were 0.91 and 0.58, respectively. Meanwhile, our study showed that low expression of hsa_circ_0000711 could serve as an independent prediction biomarker associated with poor overall survival of CRC patients (hazard ratio =2.409; 95% CI: 1.276–4.547; P=0.004).

Conclusion

All of these results indicated that hsa_circ_0000711 may play a crucial role in CRC carcinogenesis and could be a potential effective biomarker for the diagnosis and prognosis of CRC.

Upregulated hsa_circ_0004458 Contributes to Progression of Papillary Thyroid Carcinoma by Inhibition of miR-885-5p and Activation of RAC1

BACKGROUND Circular RNAs (circRNAs), a class of noncoding RNAs, may act as biomarkers and therapeutic targets of various cancers. However, the effects of hsa_circ_0004458 in papillary thyroid carcinoma (PTC) are still very much unclear. We aimed to demonstrate the potential roles of hsa_circ_0004458 in the progression of PTC. MATERIAL AND METHODS In our study, qRT-PCR assay was performed to assess hsa_circ_0004458, miR-885-5p and RAC1 expressions. Dual-luciferase reporter assay was used to detect the regulatory effects of hsa_circ_0004458 on miR-885-5p, and miR-885-5p on RAC1. MTT and flow cytometry assays were used to measure the cell proliferation, cycle, and apoptosis abilities. Tumor formation assay in nude mice was performed to measure the tumor growth in vivo. RESULTS Our results indicated that hsa_circ_0004458 was upregulated in PTC tissues and cells, while silencing of hsa_circ_0004458 suppressed PTC cell proliferation and promoted PTC cell cycle arrest and apoptosis in vitro. Tumor formation assay in nude mice showed that knockdown of hsa_circ_0004458 by siRNAs inhibited the growth of PTC tumor in vivo. In addition, we found that miR-885-5p was a direct target of hsa_circ_0004458, and silencing of hsa_circ_0004458 inhibited PTC cell proliferation by miR-885-5p. We also demonstrated that RAC1 was a direct target of miR-885-5p and silencing of RAC1 suppressed PTC cell proliferation. CONCLUSIONS We found that hsa_circ_0004458 promoted the progression of PTC by inhibition of miR-885-5p and activation of RAC1, and hsa_circ_0004458 may serve as a potential therapeutic target and biomarker for PTC.

Functional role of circular RNAs in cancer development and progression

Circular RNAs (circRNAs) are a large class of endogenously expressed non-coding RNAs formed by covalently closed loops through back-splicing. High throughput sequencing technologies have identified thousands of circRNAs with high sequence conservation and cell type specific expression in eukaryotes. CircRNAs play multiple important roles in cellular physiology functioning as miRNA sponges, transcriptional regulators, RBP binding molecules, templates for protein translation, and immune regulators. In a clinical context, circRNAs expression is correlated with patient's clinicopathological features in cancers including breast, liver, gastric, colorectal, and lung cancer. Additionally, distinct properties of circRNAs, such as high stability, exonuclease resistance, and existence in body fluids, show promising role for circRNAs as molecular biomarkers for tumor diagnosis, non-invasive monitoring, prognosis, and therapeutic intervention. Therefore, it is critical to further understand the molecular mechanism underlying circRNAs interaction in tumors and the recent progress of this RNA species in cancer development. In this review, we provide a detailed description of biological functions, molecular role of circRNAs in different cancers, and its potential role as biomarkers in a clinical context.

Circular RNAs: Characteristics, Function and Clinical Significance in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. HCC patients are commonly diagnosed at an advanced stage, for which highly effective therapies are limited. Moreover, the five-year survival rate of HCC patients remains poor due to high frequency of tumor metastasis and recurrence. These challenges give rise to the emergent need to discover promising biomarkers for HCC diagnosis and identify novel targets for HCC therapy. Circular RNAs (circRNAs), a class of long-overlook non-coding RNA, have been revealed as multi-functional RNAs in recent years. Growing evidence indicates that circRNA expression alterations have a broad impact in biological characteristics of HCC. Most of these circRNAs regulate HCC progression by acting as miRNA sponges, suggesting that circRNAs may function as promising diagnostic biomarkers and ideal therapeutic targets for HCC. In this review, we summarize the current progress in studying the functional role of circRNAs in HCC pathogenesis and present their potential values as diagnostic biomarkers and therapeutic targets. In-depth investigations on the function and mechanism of circRNAs in HCC will enrich our knowledge of HCC pathogenesis and contribute to the development of effective diagnostic biomarkers and therapeutic targets for HCC.

Function and clinical significance of circRNAs in solid tumors

Circular RNA (circRNA) is a new type of endogenous non-coding RNAs (ncRNAs). circRNA regulates gene expression in many biological processes, and it also participates in the initiation and development of various diseases, including tumors, which are the focus of present research. With the development of high-throughput sequencing technique, an increasing number of circRNAs closely related to tumors have been discovered. According to numerous studies, there is a significant difference in the expressions of circRNAs among a variety of tumor tissues and para-carcinoma normal tissues. Some specifically expressed circRNAs may potentially serve as new biomarkers for tumor diagnosis and prognosis. This systemic review briefly introduces the characteristics, biogenesis, and functions of circRNAs, as well as discusses their relationship with cancer in detail. In addition, this article also describes several research strategies for circRNAs.

Circular RNA, a novel marker for cancer determination (Review)

Circular RNAs are abundant and conserved endogenous RNAs that are formed by exon skipping or back‑splicing events and occur in all forms of life. They have been proven to exhibit tissue‑ or cell‑type specificity and to be able to regulate cell behavior through multiple pathways. In cancer research, numerous studies have indicated that circular RNAs serve as potential biomarkers and therapeutic targets. Furthermore, differential expression of certain circular RNAs clearly predicts the clinical outcomes of cancer patients. Circular RNAs regulate carcinogenesis and cancer progression by acting as a microRNA sponge, coding for proteins and interacting with proteins. The present review mainly focuses on the recent literature regarding the role of circular RNAs in cancer, which may suggest novel strategies for cancer prognosis, diagnosis and clinical treatment.

[Research Progress of Circular RNA in Lung Cancer]

Lung cancer is one of the most important malignant tumors of human health and life in the world, and is the leading cause of death in the world. At present, it is believed that it is caused by many factors. Circular RNA (circRNA), as a class of non-coding RNA family, has covalently closed loop structure. CircRNA is abundant in different cells. CircRNAs due to the special structure, with a high degree of specificity, conservation and stability, may have a potential clinical value in the development of lung cancer. The biological function of circRNA is multi-faceted, including miRNA sponge, transcriptional and alternative splicing, protein coding , and so on. Currently, the role and mechanism of circRNA in lung cancer is not very clear. In this paper, the characteristics, function, mechanism and the role of circRNAs in the occurrence and development of lung cancer are reviewed.
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The emerging role of circRNAs and their clinical significance in human cancers

Circular RNA (circRNA), a recently discovered subclass of non-coding RNAs (ncRNAs), forms a covalently closed loop with neither a 5' cap structure nor a 3' polyadenylated tail. Generated from precursor mRNA (pre-mRNA) through "backsplicing" (a type of alternative RNA splicing), the majority of circRNAs are located in the cytoplasm and are widespread among living organisms. They are stable and conserved and exhibit spatiotemporal-specific expression. CircRNAs are known to be involved in the development and progression of multiple diseases, including cancer, by acting as microRNA (miRNA) sponges and by regulating processes such as transcription and translation. The extensively aberrant expression profiles of circRNAs in multiple cancerous tissues make these molecules promising diagnostic biomarkers and therapeutic targets for cancer. Here, we briefly review the characteristics, biogenesis, classification, and functions of circRNAs, with a particular focus on the role of circRNAs in various cancers.

The progress of circular RNAs in various tumors

Circular RNAs (circRNAs), a novel type of non-coding RNAs, presented as covalently closed continuous loops. Recent researches had found that circRNAs could function as microRNA sponges, regulators of gene transcription and encoding proteins. They were relatively stable and expressed widely in cytoplasm, which played important roles in carcinogenesis of cancers, such as esophageal cancer, gastric cancer, colorectal cancer, hepatocarcinoma, bladder cancer, glioma, breast cancer, osteosarcoma and so on. Furthermore, they were involved in many biological functions, like cell proliferation, drug resistance, cell cycle, invasion and metastasis. Therefore, the further studies were meaningful on the mechanism of cancers and circRNAs. In the review, we will summarize the current biogenesis of circRNAs and the roles of them in various cancers, which might be a novel biomarker and therapeutic avenue.

Circular RNAs in hepatocellular carcinoma: Functions and implications

At present, as hotspot members of the noncoding RNA network, circular RNAs (circRNAs) with distinct properties and diverse pathophysiological functions are being increasingly delineated. CircRNAs play roles at the epigenetic, transcriptional and posttranscriptional regulatory levels. Major studies have focused on their functions as efficient microRNA sponges. The validated number of endogenous circRNAs involved in hepatocellular carcinoma (HCC) continues to increase. Altered circRNA expression is associated with HCC occurrence, invasion, and metastasis. Moreover, the aberrant expression of circRNAs is also significantly related to HCC tumor stage, size, differentiation and metastasis. Because they are exceptionally stable, highly conserved and have tissue‐specific expression patterns, some circRNAs, including hsa_circ_0004018, hsa_circ_0003570, and hsa_circ_0005075, may be potential markers for the diagnosis of HCC. We herein summarize the current knowledge of HCC‐associated circRNAs and present their implications for carcinogenesis and their potential value as diagnostic and prognostic biomarkers. Finally, we discuss the future directions of studies on HCC‐associated circRNAs.

Gene microarray analysis of the circular RNAs expression profile in human gastric cancer

Human gastric cancer is a common malignant neoplasm of the digestive system and represents a threat to human health worldwide. The mechanisms underlying gastric cancer germination and development are not yet fully understood. Circular RNAs (circRNAs) serve crucial roles in various physiological and pathological processes, particularly cancer. However, few studies have focused on the mechanisms involving circRNAs in gastric cancer. Therefore the present study set out to identify the differentially expressed circRNAs in gastric cancer. Three specimens of gastric cancer and normal gastric tissue were selected and circRNA microarray analysis was performed to detect the differentially expressed circRNAs. The changes in circRNAs were confirmed by reverse transcription-quantitative polymerase chain reaction analysis. A total of 347 upregulated and 603 downregulated circRNAs (fold-change, >2.0) were identified in gastric cancer compared with the normal gastric tissue. A total of 20 selected circRNAs were dysregulated during gastric cancer, which suggests their potential role in gastric cancer. The present study identified circRNAs in the expression profile of human gastric cancer that were potentially involved in the underlying molecular mechanisms of its development.

Circular RNAs as novel biomarkers with regulatory potency in human diseases

Circular RNAs (circRNAs) are a large class of noncoding RNAs characterized with closed loop structures without 3′ and 5′ polar ends. They can roughly be divided into exonic circRNAs, exon–intron circRNAs and circular intronic RNAs. CircRNAs are characterized with stability, prevalence, specificity and conservation, which arouse great interest in circRNAs as disease biomarkers. Their abilities to sponge to miRNAs, cis-regulate parent genes, bind to proteins and encode proteins endow circRNAs a critical role of regulation in eukaryotic cells. This concise review focuses on circRNAs as functional biomarkers and therapeutic targets in both tumor and nontumorous diseases.

Although they were discovered in 1970s, circular RNAs (circRNAs) have attracted great interest only relatively recently. Instead of genome ‘junk matters’, circRNAs are now considered as promising biomarkers and treatment targets. CircRNAs are involved in numerous cancer-related and noncancer diseases, such as lung cancer, gastric cancer, cardiovascular diseases, diabetes mellitus and so on. This review outlines the classification, characterization and function of circRNAs, with a specific focus on recent studies concerning the role of circRNAs in human diseases.

Circular RNA 0068669 as a new biomarker for hepatocellular carcinoma metastasis

BACKGROUND

Circular RNAs (circRNAs) play important roles in disease occurrence. However, the roles of circRNAs in the diagnosis of hepatocellular carcinoma (HCC) are largely unknown. The aim of this study is to investigate the clinical diagnostic values of hsa_circ_0068669 (Alias: hsa_circ_103561), one of the representative HCC-associated circRNAs.

METHODS

Hsa_circ_0068669 expression levels in HCC tissues, HCC cell lines, and chronic hepatitis tissues were detected by real-time quantitative reverse transcription-polymerase chain reaction. Its expression levels between HCC tissues and adjacent non-tumorous tissues were analyzed using paired t test. Independent t test and one-way analysis of variance (ANOVA) were performed to analyze the relationships between hsa_circ_0068669 expression levels and clinicopathological factors of patients with HCC. A receiver operating characteristic (ROC) curve was established to estimate the value of hsa_circ_0068669 as a biomarker in HCC.

RESULTS

Hsa_circ_0068669 expression was significantly downregulated in HCC tissues and HCC cell lines compared with paired non-tumorous tissues and normal hepatic cell line, respectively. Moreover, hsa_circ_0068669 expression in HCC tissues was decreased comparing with chronic hepatitis tissues. Furthermore, hsa_circ_0068669 expression was correlated with microvascular invasion and TNM stages.

CONCLUSIONS

Our findings indicate that hsa_circ_0068669 might be served as a novel potential biomarker for HCC metastasis.

Identification and functional characterization of circRNA-0008717 as an oncogene in osteosarcoma through sponging miR-203

Circular RNA (circRNA) is a key regulator in the development and progression of human cancers, however its role in osteosarcoma tumorigenesis is not well understood. The present study aims to investigate the expression profiles and potential modulation of circRNA on osteosarcoma carcinogenesis. Human circRNA microarray was performed to screen for abnormally expressed circRNA in osteosarcoma tissue and circRNA-0008717 was identified as one circRNA significantly upregulated in osteosarcoma tissue. Osteosarcoma patients with high circRNA-0008717 expression had shortened survival. Gain and loss functional assays suggested that knockdown of circRNA-0008717 suppressed cell proliferation, migration and invasion, but promoted cell apoptosis. By using biotin-labeled circRNA-0008717 probe to perform RNA precipitation in osteosarcoma cells, we identified miR-203 as the circ0008717-associated microRNA. Subsequently, Bmi-1 was identified as the functional target of miR-203. In addition, overexpression of circRNA-0008717 in osteosarcoma could elevate Bmi-1 expression, resulting in the promotion of osteosarcoma cell proliferation and invasion. Furthermore, the tumor promoting effect of circRNA-0008717 was abolished by miR-203 mimics or Bmi-1 silencing vector. In conclusion, circRNA-0008717 plays an oncogenic role in osteosarcoma and may serve as a promising prognostic biomarker for osteosarcoma patients. Therefore, silence of circRNA-0008717 could be a future direction to develop a novel treatment strategy.

Hsa_circ_0005986 inhibits carcinogenesis by acting as a miR-129-5p sponge and is used as a novel biomarker for hepatocellular carcinoma

Circular RNAs (circRNAs), a class of long-time-ignored noncoding RNA, have been revealed as multifunctional RNAs in recent years. However, the diagnostic values and the mechanism of most circRNAs in hepatocellular carcinoma (HCC) remain unknown. In this study, we revealed that the expression level of hsa_circ_0005986 in HCC was significantly lower than that in adjacent non-tumorous tissues (P < 0.001). Its levels in HCC cell lines, HepG2, SMMC7721, Huh7, MHCC97L, MHCC97H, and HCCLM3 were significantly lower than those in human normal hepatic cell line L02 (P < 0.001). In addition, the low expression level of hsa_circ_0005986 was correlated with chronic hepatitis B family history (P = 0.001), tumor diameters (P < 0.001), microvascular invasion (P = 0.026), and Barcelona Clinic Liver Cancer (BCLC) stage (P < 0.001). Further experiments demonstrated that both hsa_circ_0005986 and Notch1mRNA were targets of miR-129-5p, and that hsa_circ_0005986 downregulation liberated miR-129-5p and decreased the expression level of Notch1mRNA. More importantly, hsa_circ_0005986 downregulation accelerated cell proliferation by promoting the G0/G1 to S phase transition. We conclude that hsa_circ_0005986 function as microRNA sponge in tumorigenesis and can be used as a novel biomarker for HCC.

CircRNAs as biomarkers of cancer: a meta-analysis

Background

The expression of circular RNA (circRNA) may affect tumor progression. However, there have been no systemic meta-analysis for cancer diagnosis by using circRNAs in clinical till now. Herein, we aimed to collect and examined all the evidence on the potential role of circRNA as novel biomarker in human cancers.

Methods

A comprehensive search strategy was used to search relevant literatures in the databases of PubMed, Embase, and the Web of Science from 2015 to August 2017. The correlation between circRNA expression and the diagnostic accuracy of tumor markers was analyzed. The methodological quality of each study was assessed by quality assessment for the diagnostic accuracies of the eligible studies (QUADAS-2). Statistical analysis was performed by applying the STATA (version 12.0) software.

Results

The present meta-analysis included 1752 patients with circRNA expression data of tumor and paired adjacent non-tumorous tissues from 17 publications (19 studies). The pooled sensitivity, specificity, positive likelihood ratios (PLR), negative likelihood ratios (NLR), and diagnostic OR (DOR) with their 95% confidential intervals (95%CIs), and AUC values were 0.72 (0.67–0.76), 0.74 (0.69–0.78), 2.80 (2.40–3.10), 0.38 (0.33–0.44), 7.00 (6.00–9.00), and 0.79, respectively. Subgroup analyses showed that the expression of circRNA in tissues of hepatocellular carcinoma (HCC) group was more prone to be detected than other tumor types, with a high values of the specificity, DOR, and AUC.

Conclusions

circRNAs might be suitable as diagnostic biomarkers for tumors, especially in HCC diagnosis. Further prospective studies on the diagnostic value of circRNAs from the different tumors are needed in the future.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4213-0) contains supplementary material, which is available to authorized users.

Comprehensive analysis of differentially expressed non-coding RNAs and mRNAs in gastric cancer cells under hypoxic conditions

Hypoxia commonly occurs in solid cancers, especially in gastric cancer due to its rapid growth. The ability of gastric cancer cells to survive and progress under hypoxic conditions has been known for decades, but the mechanisms underlying this characteristic remain poorly understood. As cancer cells undergo changes in their genetic profile under certain conditions, we investigated the expression profile of non-coding RNAs (circRNAs, lncRNAs, and miRNAs) and mRNAs in gastric cancer MKN-28 cells under hypoxic conditions via sequencing and subsequent bioinformatic analyses. In addition, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to validate the results. We identified a number of significantly differentially expressed circRNAs, lncRNAs, miRNAs, and mRNAs in hypoxia-exposed MKN-28 cells relative to the normoxia control, and results of qRT-PCR were consistent with sequencing data. Pathway enrichment analyses revealed the principal functions of the significantly deregulated genes. Furthermore, examination of co-expression and competing endogenous RNA (ceRNAs) networks illustrated the complex regulatory pathways among non-coding RNAs and mRNAs, implicating these pathways in gastric cancer. In conclusion, our findings provide a novel perspective on non-coding RNAs and mRNAs and lay the foundation for future research on the potential roles of non-coding RNAs in gastric cancer under hypoxic conditions.

circHECTD1 promotes the silica-induced pulmonary endothelial-mesenchymal transition via HECTD1

Excessive proliferation and migration of fibroblasts contribute to pulmonary fibrosis in silicosis, and both epithelial cells and endothelial cells participate in the accumulation of fibroblasts via the epithelial–mesenchymal transition (EMT) and the endothelial–mesenchymal transition (EndMT), respectively. A mouse endothelial cell line (MML1) was exposed to silicon dioxide (SiO₂, 50 μg/cm²), and immunofluorescence and western blot analyses were performed to evaluate levels of specific endothelial and mesenchymal markers and to elucidate the mechanisms by which SiO₂ induces the EndMT. Functional changes were evaluated by analyzing cell migration and proliferation. The mRNA and circular RNA (circRNA) levels were measured using qPCR and fluorescent in situ hybridization (FISH). Lung tissue samples from both Tie2-GFP mice exposed to SiO₂ and silicosis patients were applied to confirm the observations from in vitro experiments. Based on the results from the current study, SiO₂ increased the expression of mesenchymal markers (type I collagen (COL1A1), type III collagen (COL3A1) and alpha smooth muscle actin (α-SMA/Acta2)) and decreased the expression of endothelial markers (vascular endothelial cadherin (VE-Cad/Cdh 5) and platelet endothelial cell adhesion molecule-1 (PECAM1)), indicating the occurrence of the EndMT in response to SiO₂ exposure both in vivo and in vitro. SiO₂ concomitantly increased circHECTD1 expression, which, in turn, inhibited HECTD1 protein expression. SiO₂-induced increases in cell proliferation, migration, and changes in marker levels were restored by either a small interfering RNA (siRNA) targeting circHECTD1 or overexpression of HECTD1 via the CRISPR/Cas9 system, confirming the involvement of the circHECTD1/HECTD1 pathway in the EndMT. Moreover, tissue samples from SiO₂-exposed mice and silicosis patients confirmed the EndMT and change in HECTD1 expression. Our findings reveal a potentially new function for the circHECTD1/HECTD1 pathway and suggest a possible mechanism of fibrosis in patients with pulmonary silicosis.

Hsa_circ_0007534 as a blood-based marker for the diagnosis of colorectal cancer and its prognostic value

BACKGROUND

Many studies have shown that differentially expressed circular RNA (circRNA) in plasma can serve as biomarkers in non-invasive detection of cancers during screening. However, the clinical significance of plasma circRNA in the diagnosis of colorectal cancer (CRC) is still not clear. Therefore, we examined expression of hsa_circ_0007534 in plasma to verify whether it can be utilized to diagnose and monitor CRC in routine clinical practice.

METHODS

112 CRC patients and 46 healthy controls were recruited to participate in our study. The levels of hsa_circ_0007534 in plasma samples and tumor tissues were identified by real-time quantitative polymerase chain reaction (RT-qPCR). The diagnostic value was evaluated using receiver operating characteristics (ROC) curves and the area under the ROC curves (AUC). The Kaplan-Meier survival curve was used to evaluate whether the expression level of hsa_circ_0007534 was associated with overall survival rate.

RESULTS

Compared with the healthy control group, hsa_circ_0007534 expression was significantly increased in plasma from CRC patients. Increased hsa_circ_0007534 expression level in plasma was associated with progression of clinical classifications, metastatic phenotype, and poor differentiation in CRC patients. ROC analysis showed that hsa_circ_0007534 could distinguish CRC patients from healthy controls with high AUC (0.780), sensitivity (0.92) and specificity (0.522). Finally, high hsa_circ_0007534 expression was positively correlated with poor prognosis in CRC patients.

CONCLUSION

All of the results suggest that hsa_circ_0007534 may be a potential cancer marker of patients with CRC and may associate with poor prognosis.

Circular RNAs: a new frontier for cancer diagnosis and therapy

In recent years, circular RNAs (circRNAs) have attracted considerable attention because they play a significant role in many fields of cancer biology. Additionally, it has become increasingly clear that circRNAs have the potential to make contributions to the successful application of individualized cancer medicine. This brief review introduces circRNAs by describing their potential as a biomarker and therapeutic target and discussing the possible strategies to target them. This review also presents the challenges that are encountered by circRNAs for their definitive entry into clinical practice. Clearly, our understanding of circRNAs helps to add a new dimension to the molecular structure of cancer and will provide many new opportunities for cancer treatment.

Circular RNAs as Biomarkers for Cancer

As a type of novel noncoding RNAs, circular RNAs (circRNAs) have attracted great interest due to its different characteristics from linear RNAs. They are abundantly and stably present in the transcriptome of eukaryotic cells, with development stage specificity and high conservatism. Because circRNAs are not easily degraded by exonuclease RNase R, they can exist more stably in body fluids than linear RNAs. Based on these unique conditions, circRNAs have great potential value as clinical diagnostic and prognostic markers. As the research deepens, more and more evidences suggest that circRNAs may be closely associated with many diseases, especially cancer. Numerous studies have demonstrated the abnormal expression of circRNAs in cancer, and they can regulate the occurrence and progression of cancer by targeting key genes. Abundant circRNAs in tissues and cells can be released into saliva and blood. It is undeniable that circRNAs are a class of promising future biomarkers for cancer diagnosis and prognosis. Here we summarize the researches on circRNAs and cancer over the past few years. We expect this summary to be a stepping stone to further exploration of possible circRNAs as cancer biomarkers.