Microarray profiling of circular RNAs and the potential regulatory role of hsa_circ_0071410 in the activated human hepatic stellate cell induced by irradiation

Upregulation of Circular RNA circATRNL1 to Sensitize Oral Squamous Cell Carcinoma to Irradiation

Accumulating evidence has demonstrated that circular RNAs (circRNAs) play important roles in regulating gene expression involved in tumor development. However, the role of circRNAs in modulating the radiosensitivity of oral squamous cell carcinoma (OSCC) and its potential mechanisms have not been documented. We performed high-throughput RNA sequencing (RNA-seq) to investigate the circRNA expression profile in OSCC patients and discovered that the circATRNL1 expression was significantly downregulated and closely related to tumor progression. The circATRNL1 was structurally validated via Sanger sequencing, RNase R treatment, and specific convergent and divergent primer amplification. Importantly, the expression levels of circATRNL1 decreased after irradiation treatment, and upregulation of circATRNL1 enhanced the radiosensitivity of OSCC through suppressing proliferation and the colony survival fraction, inducing apoptosis and cell-cycle arrest. Moreover, we observed that circATRNL1 could directly bind to microRNA-23a-3p (miR-23a-3p) and relieve inhibition for the target gene PTEN. In addition, the tumor radiosensitivity-promoting effect of circATRNL1 overexpression was blocked by miR-23a-3p in OSCC. Further experiments also showed that PTEN can reverse the inhibitory effect of OSCC radiosensitivity triggered by miR-23a-3p. We concluded that circANTRL1 may function as the sponge of miR-23a-3p to promote PTEN expression and eventually contributes to OSCC radiosensitivity enhancement. This study indicates that circANTRL1 may be a novel therapeutic target to improve the efficiency of radiotherapy in OSCC.

CircularRNA as novel biomarkers in liver diseases

The liver is an essential organ that is primarily responsible for digestion and eliminating toxic substances from the body. After the industrial revolution, Western diet and lifestyle changes have increased the incidence of several liver diseases, including non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), liver cirrhosis, and hepatocellular carcinoma (HCC). NAFLD and NASH are mostly asymptomatic at early stages, and the disease progression from NAFLD to life-threatening HCC remains not fully understood. Circular RNA (circRNA) is consist of a circular structure, and the circRNA-microRNA(miRNA)-mRNA axes have been shown to be involved in several cellular events, including apoptosis, vascularization, metastasis, etc. The highly stable structure of circRNAs has enabled themselves to be used as putative biomarkers of several diseases. Here, we conducted a literature review and discussed the identified roles of circRNAs in NAFLD, NASH, liver cirrhosis, and HCC. For example, deficiency of circRNA_0046366 and circRNA_0046367 has been shown as the characteristics of NAFLD, and restoration of these circRNAs ameliorates the oxidative stress, lipotoxicity, and disease severity in NAFLD. Silencing of circ_0071410 was shown to alleviate hepatic stellate activation, the key step of liver cirrhosis. CDR1 and circ_0067934 can facilitate the invasion and metastasis of HCC, while circMTO1 negatively regulates the progression of HCC. Although several research works have been conducted, the whole picture of circRNA-related underlying mechanisms is unclear. Future works using high-throughput bioinformatic approaches will be needed to delineate the role of circRNAs in liver diseases and to further develop novel diagnostics and therapeutics.

CircRNA_100367 regulated the radiation sensitivity of esophageal squamous cell carcinomas through miR-217/Wnt3 pathway

Background: Circular RNAs (circRNAs) play important roles in regulating the radioresistance of esophageal squamous cell carcinoma (ESCC). This study aimed to determine the role of hsa_circRNA_100367 in regulating radioresistance of ESCC.

Results: Higher expression and potency of endothelial to mesenchymal transformation (EMT) was found in radioresistant ESCC cells (KYSE-150R) than in ESCC cells (KYSE-150). Silencing circRNA_100367 inhibited the proliferation and migration of KYSE-150R cells, and decreased the expression of β-catenin (an important molecule in Wnt pathway) in KYSE-150R cells. Additionally, circRNA_100367 bound to miR-217, and miR-217 targeted Wnt3. Low Wnt3 expression was associated with the short survival time in patients with ESCC and Wnt3 knockdown inhibited the proliferation and migration of KYSE-150R cells. CircRNA_100367 enhanced the radioresistance of KYSE-150R cells through miR-217/Wnt3 pathway. In vivo, circRNA_100367 silence reduced the growth of KYSE-150R cells under radiation.

Conclusion: Our results revealed that circRNA_100367 attenuated radioresistance of ESCC through miR-217/Wnt3 pathway.

Methods: CircRNAs related with the radioresistance of ESCC were analyzed by hierarchical cluster analysis. The relationship between circRNA_100367 and miR-217, Wnt3 was detected by RNA immunoprecipitation (RIP), RNA pull-down and luciferase reporte assays. The proliferation and migration ESCC cells were detected by MTT, Transwell and colony formation assays.

Curcumin enhances radiosensitization of nasopharyngeal carcinoma by regulating circRNA network

Circular RNAs (circRNAs) are involved in the regulation of gene expression in different physiological and pathological processes. These macromolecules can act as microRNA (miRNA) sponges and play an important role as gene regulators throughout the circRNA-miRNA pathway. In this study, we established a radioresistance model with the nasopharyngeal carcinoma cell line CNE-2, and then analyzed the differences in the circRNAs between radioresistant and normal nasopharyngeal carcinoma cell lines using a high-throughput microarray. Tested circRNAs included 1042 upregulated and 1558 downregulated circRNAs. Relevant signaling pathways associated with the circRNAs and their target miRNAs were analyzed using bioinformatics analysis to determine the radioresistance of the differentially expressed circRNAs. Curcumin was used to treat irradiated cell lines, and changes in the circRNA before and after curcumin treatment were analyzed to investigate the radiosensitization effects of curcumin. The results showed that curcumin could regulate the circRNA-miRNA-messenger RNA network and inhibit the epidermal growth factor receptor (EGFR), signal transducers and activators of transcription 3 (STAT3), and growth factor receptor-bound protein 2 (GRB2) to achieve radiosensitization. Thus, circRNA acted as a miRNA sponge and regulated the expression of miRNA, thereby affecting EGFR, STAT3, and GRB2 expression and radiosensitization.

TGF-β- and lipopolysaccharide-induced upregulation of circular RNA PWWP2A promotes hepatic fibrosis via sponging miR-203 and miR-223

Both transforming growth factor-beta (TGF-β) and lipopolysaccharide (LPS) can activate hepatic stellate cells (HSCs), thus increasing expressions of alpha smooth muscle actin (α-SMA) and type I collagen alpha 1 (Col1α1) and promoting liver fibrosis. However, whether TGF-β and LPS have a common downstream reactor remains unclear. Recently, a strong relationship of circular RNAs (circRNAs) and fibrogenesis has been elucidated. In this study, we compared the expressions of several circRNAs in TGF-β- and LPS-activated HSCs, and found that circ-PWWP2A was upregulated in both TGF-β- and LPS-activated HSCs and in mouse fibrotic liver tissues. Meanwhile, circ-PWWP2A was positively correlated with HSC activation and proliferation. Two microRNAs, miR-203 and miR-223, were identified to be the downstream targets of circ-PWWP2A using luciferase reporter assay and pull-down interaction assay. Circ-PWWP2A was suggested to promote HSC activation and proliferation via sponging miR-203 and miR-223, and subsequently increasing Fstl1 and TLR4, respectively. Furthermore, downregulating circ-PWWP2A was indicated to alleviate hepatic fibrosis in vivo. In conclusion, our findings indicated that circ-PWWP2A is the common downstream reactor of TGF-β and LPS in HSC activation, and that circ-PWWP2A plays a critical role in hepatic fibrogenesis via sponging miR-203 and miR-223.

TGF-β in Hepatic Stellate Cell Activation and Liver Fibrogenesis-Updated 2019

Liver fibrosis is an advanced liver disease condition, which could progress to cirrhosis and hepatocellular carcinoma. To date, there is no direct approved antifibrotic therapy, and current treatment is mainly the removal of the causative factor. Transforming growth factor (TGF)-β is a master profibrogenic cytokine and a promising target to treat fibrosis. However, TGF-β has broad biological functions and its inhibition induces non-desirable side effects, which override therapeutic benefits. Therefore, understanding the pleiotropic effects of TGF-β and its upstream and downstream regulatory mechanisms will help to design better TGF-β based therapeutics. Here, we summarize recent discoveries and milestones on the TGF-β signaling pathway related to liver fibrosis and hepatic stellate cell (HSC) activation, emphasizing research of the last five years. This comprises impact of TGF-β on liver fibrogenesis related biological processes, such as senescence, metabolism, reactive oxygen species generation, epigenetics, circadian rhythm, epithelial mesenchymal transition, and endothelial-mesenchymal transition. We also describe the influence of the microenvironment on the response of HSC to TGF-β. Finally, we discuss new approaches to target the TGF-β pathway, name current clinical trials, and explain promises and drawbacks that deserve to be adequately addressed.

Circular RNAs: The star molecules in cancer

Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs with a closed loop structure. These RNAs are produced by pre-mRNA through variable shear processing and are highly conserved. Such highly conserved molecules play an important role in biology, especially in cancer biology. With the development of experimental techniques such as circRNA microarray screening and high-throughput sequencing technologies, the mystery of circRNAs has gradually been unveiled and the values of function and application have gradually emerged. Among them, cancer-related circRNAs are the most eye-catching. Numerous studies have shown that some circRNAs were involved in the pathogenesis of cancer. This review systematically introduced the cancer-related circRNAs and their origin, formation mechanisms, functions, and applications in the diagnosis and treatment of sixteen kinds of tumors.

The integrative regulatory network of circRNA and microRNA in keloid scarring

Circular RNA (circRNA), a novel type of non-coding RNA that consists of a circular loop, has been demonstrated to act as a "sponge" for microRNAs (miRNAs). However, the role of circRNAs in keloid remains unknown. In this study, we investigated circRNA expression profiles in keloid to identify potential diagnostic and therapeutic circRNAs. We performed a circRNA microarray assay to determine circRNA expression in keloid and paired normal skin tissues. Quantitative reverse transcription polymerase chain reaction was used to evaluate the expression levels of candidate circRNAs. The most significantly over-expressed circRNA was used to predict putative miRNA targets and the binding sites of miRNAs with this circRNA. Finally, we constructed a circRNA-miRNA interaction network and carried out gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. We found 52 significantly upregulated and 24 downregulated circRNAs in keloid compared with normal skin tissue. We confirmed that hsa_circ_0057452, hsa_circ_0007482, hsa_circ_0020792, hsa_circ_0057342, and hsa_circ_0043688 were significantly upregulated in keloid tissues. Analysis of the circRNA-miRNA interaction network revealed that circRNAs could interact with miRNAs, including miRNA-29a, miRNA-23a-5p and miRNA-1976. GO and KEGG analyses indicated that these target genes were involved in biological functions and signaling pathways that may play vital roles in the pathogenesis of keloid. This study revealed that circRNAs are potentially implicated in the development of keloid and could serve as novel diagnostic and therapeutic targets.

Circular RNA expression profile in the spinal cord of morphine tolerated rats and screen of putative key circRNAs

Morphine tolerance developed after repeated or continuous morphine treatment is a global health concern hindering the control of chronic pain. In our previous research, we have reported that the expression of lncRNAs and microRNAs have been greatly modified in the spinal cord of morphine tolerated rats, and the modulating role of miR-873a-5p, miR-219-5p and miR-365 have already been confirmed. However, whether circular RNAs, another essential kind of non-coding RNA, are involved in the pathogenesis of morphine tolerance is still beyond our knowledge. In this study, we conducted microarray analysis for circRNA profile and found a large number of circRNAs changed greatly in the spinal cord by morphine treatment. Among them, we selected nine circRNAs for validation, and seven circRNAs are confirmed. Gene Ontology/Kyoto Encyclopedia of Genes and Genomes (GO/KEGG) analysis were used for functional annotation. Besides, we confirmed the modified expression of seven circRNAs after validation by real-time PCR, selected 3 most prominently modulated ones among them and predicted their downstream miRNA-mRNA network and analyzed their putative function via circRNA-miRNA-mRNA pathway. Finally, we enrolled the differentially expressed mRNAs derived from the identical spinal cord, these validated circRNAs and their putative miRNA targets for ceRNA analysis and screened a promising circRNA-miRNA-mRNA pathway in the development of morphine tolerance. This study, for the first time, provided valuable information on circRNA profile and gave clues for further study on the circRNA mechanism of morphine tolerance.

Identification of Potential Immune-Related circRNA-miRNA-mRNA Regulatory Network in Intestine of Paralichthys olivaceus During Edwardsiella tarda Infection

Olive flounder (Paralichthys olivaceus) is an important economical flatfish in Japan, Korea, and China, but its production has been greatly threatened by disease outbreaks. In this research, we aimed to explore the immune responsive mechanism of P. olivaceus against Edwardsiella tarda infection by profiling the expression of circRNA, miRNA, and mRNA by RNA-seq and constructing a regulatory circular circRNA–miRNA–mRNA network. Illumina sequencing of samples from normal control (H0), 2 h (H2), 8 h (H8), and 12 h (H12) post-challenge was conducted. Differentially expressed (DE) circRNA (DE–circRNAs), miRNAs (DE–miRNAs), and mRNAs [differential expression genes (DEGs)] between challenge and control groups were identified, resulting in a total of 62 DE–circRNAs, 39 DE–miRNAs, and 3,011 DEGs. Based on the differentially expressed gene results, miRNA target interactions (circRNA–miRNA pairs and miRNA–mRNA pairs) were predicted by MiRanda software. Once these paired were combined, a preliminary circRNA–miRNA–mRNA network was generated with 198 circRNA–miRNA edges and 3,873 miRNA–mRNA edges, including 44 DE–circRNAs, 32 DE–miRNAs, and 1,774 DEGs. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was performed to evaluate the function of the DEGs in this network, and we focused and identified two important intestinal immune pathways (herpes simplex infection and intestinal immune network for IgA production) that showed statistical significance between the challenge and control groups. Furthermore, three critical DEGs (nectin2, MHC II α-chain, and MHC II β-chain) were identified, mapped into the preliminary circRNA–miRNA–mRNA network, and new circRNA–miRNA–mRNA regulatory networks were constructed. In conclusion, we, for the first time, identified circRNA–miRNA–mRNA network from P. olivaceus in the pathogenesis of E. tarda and provided valuable resources for further analyses of the molecular mechanisms and signaling networks.

Circular RNAs as novel regulators, biomarkers and potential therapies in fibrosis

Fibrosis is the excess deposition of extracellular matrix components which ultimately leads to the disruption of organ architecture and loss of function. Circular RNAs (circRNAs) are a newly discovered type of long noncoding RNAs with single-stranded covalently closed loops. It is known that circRNAs are novel regulators of gene expression via various ways, including miRNA sponge, protein sponge, regulation of transcription and post transcription. Recently, a growing body of evidence suggests that circular RNAs are also involved in tissue fibrosis in several organs. In this review, we summarized current studies of circular RNAs in fibrosis and hopefully aid in better understanding the molecular mechanism of fibrosis and provide a basis to explore new therapeutic targets of fibrosis.

Regulatory Non-coding RNAs Network in Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) spectrum comprises simple steatosis and non-alcoholic steatohepatitis (NASH) that can lead to fibrosis and cirrhosis. The patients usually have no history of excessive alcohol consumption and other etiologies that can cause fatty liver. Understanding of the pathophysiology of NAFLD has revealed that non-coding RNAs (ncRNAs) play significant roles in modulating the disease susceptibility, pathogenesis and progression. Currently, the ncRNAs are grouped according to their sizes and their regulatory or housekeeping functions. Each of these ncRNAs has a wide range of involvement in the regulation of the genes and biological pathways. Here, we briefly review the current literature the regulatory ncRNAs in NAFLD pathogenesis and progression, mainly the microRNAs, long non-coding RNAs and circular RNAs. We also discuss the co-regulatory functions and interactions between these ncRNAs in modulating the disease pathogenesis. Elucidation of ncRNAs in NAFLD may facilitate the identification of early diagnostic biomarkers and development of therapeutic strategies for NAFLD.

Differential expression of circular RNAs in hepatic tissue in a model of liver fibrosis and functional analysis of their target genes

AIM

To measure the expression profile of circular RNA (circRNA) in hepatic tissues in a liver fibrosis model and to explore their function using molecular biology and bioinformatic techniques.

METHODS

The classic CCl₄ mouse liver fibrosis model was established alongside a normal control group. The circRNA expression profile of hepatic tissue from the two groups was compared using a high-throughput circRNA microarray. The differentially expressed circRNAs were identified, and real-time quantitative polymerase chain reaction (RT-qPCR) was used to verify a subset of the differentially expressed circRNAs (target genes). At the same time, the mouse oxidative stress injury, macrophage inflammation, and hepatic stellate cell activation models were established, and the expression of target circRNA in the above cells was measured by RT-qPCR. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to predict the biological functions of target genes. Finally, one of the circRNAs was selected and its cellular function was verified using siRNA.

RESULTS

A total of 10 389 circRNAs were analyzed by microarray. Compared with the normal group, there were 69 circRNAs that were differentially expressed in the liver fibrosis model group (>2-fold differential expression, P < 0.05), of which 14 were upregulated and 55 were downregulated. Five circRNAs and their differential expression were verified by RT-qPCR, and the findings were consistent with the microarray results. Of these, three circRNAs were differentially expressed (P < 0.05) in the JS1 model, one circRNA was differentially expressed (P < 0.05) in the AML12 model, and four circRNAs were differentially expressed (P < 0.05) in the RAW264.7 model. The GO analysis showed that the differentially expressed circRNAs might be involved in cell autophagy, composition of extracellular matrix components, synthesis and metabolism of retinoic acid, retinol dehydrogenase activity, ubiquitin-like protein ligase activity, histone methylation, and other biological functions. The KEGG analysis showed that the target genes of the differentially expressed circRNAs might be involved in transforming growth factor-β1/smads, Hippo, Rap1, vascular endothelial growth factor, and other signaling pathways. Lipofection experiments showed that the expression of α-smooth muscle actin (α-SMA) in JS1 cells increased significantly after the expression of mmu_circ_34116 was decreased.

CONCLUSION

The circRNA expression profile in liver fibrosis tissue shows significant changes. Partially differentially expressed circRNA could be involved in hepatic fibrosis related to hepatic oxidative stress injury, macrophage inflammation, and stellate cell activation. For instance, mmu_circ_34116 can significantly inhibit the activation of hepatic stellate cells.

Reactive Oxygen Species Drive Epigenetic Changes in Radiation-Induced Fibrosis

Radiation-induced fibrosis (RIF) develops months to years after initial radiation exposure. RIF occurs when normal fibroblasts differentiate into myofibroblasts and lay down aberrant amounts of extracellular matrix proteins. One of the main drivers for developing RIF is reactive oxygen species (ROS) generated immediately after radiation exposure. Generation of ROS is known to induce epigenetic changes and cause differentiation of fibroblasts to myofibroblasts. Several antioxidant compounds have been shown to prevent radiation-induced epigenetic changes and the development of RIF. Therefore, reviewing the ROS-linked epigenetic changes in irradiated fibroblast cells is essential to understand the development and prevention of RIF.

Comprehensive circular RNA expression profiles in a mouse model of nonalcoholic steatohepatitis

Recent studies have revealed that circular RNAs (circRNAs) are involved in the development of various liver diseases. However, the regulatory role of circRNAs in nonalcoholic steatohepatitis (NASH) has not been fully elucidated. In the present study, the circRNA profiles in a NASH mouse model were investigated, and their functions in NASH were predicted using bioinformatics analysis, with the aim of providing novel clues for delineating the mechanisms of action. A NASH mouse model was established by feeding mice with a methionine and choline‑deficient diet. The liver circRNA profile was screened using a circRNA microarray, and the differentially expressed circRNAs were verified by reverse transcription‑quantitative polymerase chain reaction. Subsequently, circRNA‑microRNA (miRNA) interactions were predicted. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to annotate the biological functions of host linear transcripts of circRNA. A total of 450 circRNAs were revealed to be dysregulated, with 298 circRNAs upregulated and 152 circRNAs downregulated in the NASH model mice. circRNA_29981 was identified as a significantly differentially expressed circRNA. The results from the circRNA‑miRNA pathway interaction analysis revealed that circRNA_29981 was a potential regulator of hepatic stellate cell activation. The host linear transcripts were also analyzed, and the top 10 enriched GO entries and KEGG pathways were annotated. These findings suggested that circRNAs may be important regulators of NASH. Taken together, the results of the present study demonstrated that the circRNA profile in NASH may provide potential candidates for future studies aimed at elucidating the pathogenic mechanism(s) involved in the disease.

Circular RNAs in immune responses and immune diseases

Circular RNAs (circRNAs) are novel clusters of endogenous noncoding RNAs (ncRNAs) that are widely expressed in eukaryotic cells. In contrast to the generation of linear RNA transcripts, circRNAs undergo a "back-splicing" process to form a continuous, covalently closed, stable loop structure without 5' or 3' polarities and poly (A) tails during posttranscriptional modification. Due to the widespread availability of several technologies, especially high-throughput RNA sequencing, numerous circRNAs have been discovered not only in mammals but also in plants and insects. Notably, due to their abilities to serve as microRNA (miRNA) "sponges", miRNA "reservoirs", regulate gene expression and encode proteins, circRNAs participate in the development and progression of different immune responses and immune diseases by enriching various forms of epigenetic modification. CircRNAs have been demonstrated to be expressed in a tissue-specific and pathogenesis-related manner during the occurrence of multiple immune diseases. Additionally, because of their circular configurations, expression in blood and peripheral tissues and coexistence with exosomes, circRNAs show inherent conservation along with environmental resistance stability and may be regarded as potential biomarkers or therapeutic targets for some immune diseases. In this review, we summarize the characteristics, functions and mechanisms of circRNAs and their involvement in immune responses and diseases. Although our knowledge of circRNAs remains preliminary, this field is worthy of deeper exploration and greater research efforts.

Hsa_circ_101280 promotes hepatocellular carcinoma by regulating miR-375/JAK2

In this study, we sought to predict the effects of a certain circular RNA (circRNA), hsa_circ_101280 (also known as hsa_circ_0100929 and hsa_circ_SLAIN1), on hepatocellular carcinoma (HCC) cells and to determine the potential mechanism. After screening differentially expressed circRNAs in HCC tissues through Gene Expression Omnibus data analysis, hsa_circ_101280 was found to be highly expressed, and its high expression was verified in HCC cell lines with qRT-PCR along with the low expression of its downstream miRNA miR-375. Colony formation and flow cytometry assays showed that both hsa_circ_101280 silencing and miR-375 overexpression restrained proliferation and promoted apoptosis in HCC cells. JAK2 was identified as a downstream mRNA target of miR-375 by RNA pull-down and dual-luciferase reporter gene assays, its expression in HCC cell lines were positively regulated by hsa_circ_101280 and negatively by miR-375 expression. Furthermore, the silencing of hsa_circ_101280 significantly inhibited the growth of HCC xenografts in nude mice, with the downregulated expression of JAK2. Overall, both the in vitro and in vivo studies revealed that hsa_circ_101280 largely facilitated the tumorigenesis of HCC, characterized by the promoted proliferation and suppressed apoptosis of HCC cells, by sponging miR-375 and upregulating JAK2.

Circular RNA 101368/miR-200a axis modulates the migration of hepatocellular carcinoma through HMGB1/RAGE signaling

Hepatocellular carcinoma (HCC), one of the most common type of cancers, is highly refractory to most systemic therapies. Understanding the genomic dysregulations, in particularly non-coding RNA (ncRNA) dysregulations, in HCC may provide novel strategies to HCC treatment. In our previous study, we demonstrated the key role of miR-200a-mediated HMGB1/RAGE signaling in HCC carcinogenesis. In the present study, we identified circular RNA (circRNA)-miRNA pair that might modulate the migration of HCC cell lines based on previously reported GEO database (GSE78520 and GSE43445) and investigated the function and molecular mechanism. circRNA-101368 was predicted by lncTar to target miR-200a, and the expression of circRNA-101368 was significantly upregulated in HCC tissue samples; the overexpression of circRNA-101368 was correlated with poorer prognosis in patients with HCC. Moreover, circRNA-101368 knockdown suppressed the migration and the protein levels of HMGB1, RAGE and NF-κB, while increased the E-Cadherin expression in HCC cell lines. As confirmed by luciferase reporter and RNA immunoprecipitation assays, circRNA-101368 directly bound to miR-200a to negatively regulate each other. The effect of circRNA-101368 knockdown on cell migration and HMGB1/RAGE signaling could be partially attenuated by miR-200a inhibition. In tissue samples, miR-200a was negatively correlated with circRNA-101368 and HMGB1, respectively, whereas circRNA-101368 and HMGB1 was positively correlated. Taken together, we demonstrated a network of circRNAs-miRNA-mRNA in HCC and provided a novel mechanism of HCC cell migration regulation.

Preliminary screening and functional analysis of circular RNAs associated with hepatic stellate cell activation

OBJECTIVE

To screen for circular RNAs (circRNAs) that are associated with the activation of hepatic stellate cell (HSC) by monitoring changes in liver circRNA expression in a model of liver fibrosis.

METHODS

The classic mouse model of CCl₄-induced liver fibrosis was established and validated by histopathological examination. JS1 cells were activated by TGF-β1 to model HSC activation in vitro. Differentially expressed circRNAs in the fibrotic liver tissues and JS1 cells were determined using circRNA microarray, and some of those circRNAs were verified by RT-qPCR. The target genes of the above circRNAs were then predicted by bioinformatics analysis and summarized into a "circRNA-miRNA-mRNA" network diagram. Constructed plasmid mmu_circ_34116 siRNA was transfected to JS1 cells by Lipo2000, then we detected the expression changes of α-SMA.

RESULTS

A total of 10,389 circRNAs were identified by microarray screening, and 69 differentially expressed circRNAs were detected in the fibrotic liver tissues with >2-fold difference in expression level relative to normal liver tissues (P < 0.05); 14 circRNAs were up-regulated and 55 were down-regulated. Five differentially expressed circRNAs in fibrotic liver and JS1 cells were verified by RT-qPCR, while all five showed similar trends with the microarray results in the liver, only 3 circRNAs in the JS1 activation model were consistent with the microarray results while one showed no significant change and one circRNA was not detected. Bioinformatics analysis predicted that the "mmu_circ_34116/miR-22-3P/BMP7" signal axis might be involved in the activation of HSC. Transfection experiment confirmed that the expression of α-SMA is significantly elevated as a result of inhibitory expression of mmu_circ_34116.

CONCLUSION

The circRNAs expression profile of liver tissue had changed in fibrosis mouse model, and some of these circRNAs may be associated with HSC activation. For instance, mmu_circ_34116 would inhibit HSC activation.

Decreased circular RNA hsa_circ_0001649 predicts unfavorable prognosis in glioma and exerts oncogenic properties in vitro and in vivo

Glioma is a devastating disease with increasing incidence worldwide. Circular RNAs (circRNAs) was demonstrated to be involved in a wide range of pathophysiological processes, including tumorigenesis and development. Recently, the abnormally expressed hsa_circ_0001649 was found in several malignancies. In the current study, the expression levels of hsa_circ_0001649 in glioma and its clinical significance were explored. The biological functions including cell growth, colony-forming ability and apoptosis altered by hsa_circ_0001649 were further investigated in vitro. Tumor formation assay was also carried out to elucidate the oncogenic properties of hsa_circ_0001649. The data documented a decrease of hsa_circ_0001649 expression in glioma specimens and cell lines. In addition, down-regulated hsa_circ_0001649 is linked to larger tumor size (p = 0.002) and advanced WHO grade (p = 0.023). Additionally, hsa_circ_0001649 may be an independent prognostic marker for glioma patients after surgery (p = 0.046). Moreover, up-regulated hsa_circ_0001649 inhibits glioma cell growth in vitro and in vivo. Importantly, increased expression of hsa_circ_0001649 facilitates apoptosis by regulating Bcl-2/caspase-3 pathway. Ultimately, this study suggests that hsa_circ_0001649 may be a potential glioma-related prognostic/therapeutic target.

Identification of Potentially Functional CircRNA-miRNA-mRNA Regulatory Network in Hepatocellular Carcinoma by Integrated Microarray Analysis

BACKGROUND Hepatocellular carcinoma (HCC) is the most common malignancy of the liver and recent studies have revealed that circular RNA (circRNA) plays an important role in the pathogenesis of HCC. Some circRNAs may act as a microRNA (miRNA) sponge to affect miRNA activities in the regulation of messenger RNA (mRNA) expression. However, the circRNA-miRNA-mRNA network in HCC remains largely unknown. MATERIAL AND METHODS The circRNA expression profiles (GSE94508 and GSE97332), miRNA and mRNA expression profile (GSE22058) were downloaded from Gene Expression Omnibus microarray data and then a circRNA-miRNA-mRNA regulatory network in HCC was constructed. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of differentially expressed (DE) genes were performed. The functional circRNA-miRNA-mRNA regulatory modules were constructed using cytoHubba plugin based on Cytoscape and KEGG enrichment analysis. RESULTS The network contained 60 circRNA-miRNA pairs and 4982 miRNA-mRNA pairs, including 29 circRNAs, 16 miRNAs, and 1249 mRNAs. GO and KEGG pathway analysis revealed the network might be involved in the procession of carcinogenesis such as cell proliferation, cell cycle, and p53 signaling pathway. In addition, 3 top ranked circRNAs (hsa_circ_0078279, hsa_circ_0007456, and hsa_circ_0004913) related networks were identified to be highly correlated with the pathogenesis of HCC. Furthermore, the functional circRNA-miRNA-mRNA regulatory modules were constructed based on the 3 top-ranked circRNAs and those DE genes enriched in carcinogenesis related pathways. CONCLUSIONS This study suggests that a specific circRNA-miRNA-mRNA network is associated with the carcinogenesis of HCC, which might aid in the identification of molecular biomarkers and therapeutic targets for HCC.

Microarray profiles reveal that circular RNA hsa_circ_0007385 functions as an oncogene in non-small cell lung cancer tumorigenesis

OBJECTIVE

Circular RNAs (circRNAs) are a novel class of non-protein-coding RNA. Emerging evidence indicates that circRNAs participate in the regulation of many pathophysiological processes. This study aims to explore the expression profiles and pathological effects of circRNAs in non-small cell lung cancer (NSCLC).

METHODS

Human circRNAs microarray analysis was performed to screen the expression profile of circRNAs in NSCLC tissue. Expressions of circRNA and miRNA in NSCLC tissues and cells were quantified by qRTPCR. Functional experiments were performed to investigate the biological functions of circRNA, including CCK-8 assay, colony formation assay, transwell assay and xenograft in vivo assay.

RESULTS

Human circRNAs microarray revealed a total 957 abnormally expressed circRNAs (> twofold, P < 0.05) in NSCLC tissue compared with adjacent normal tissue. In further studies, hsa_circ_0007385 was significantly up regulated in NSCLC tissue and cells. In vitro experiments with hsa_circ_0007385 knockdown resulted in significant suppression of the proliferation, migration and invasion of NSCLC cells. In vivo xenograft assay using hsa_circ_0007385 knockdown, significantly reduced tumor growth. Bioinformatics analysis and luciferase reporter assay verified the potential target miR-181, suggesting a possible regulatory pathway for hsa_circ_0007385.

CONCLUSION

In summary, results suggest hsa_circ_0007385 plays a role in NSCLC tumorigenesis, providing a potential therapeutic target for NSCLC.

Circular RNA and its mechanisms in disease: From the bench to the clinic

The emerging recognition of the functional roles of circular RNAs (circRNAs) has given rise to a new perspective regarding our understanding of cellular physiology and disease pathogenesis. Unlike linear RNAs, circRNAs are covalently closed continuous loops that act as gene regulators in mammals, and their sequence composition determines the mode of circRNA biogenesis. The availability and integrated use of advanced genome analysis platforms have allowed the identification of a large number of these molecules. Their high abundance, stability and evolutionary conservation among species endow circRNAs with numerous potential functions, such as acting as microRNA (miRNA) sponges or binding to RNA-associated proteins to form RNA-protein complexes that regulate gene transcription. Moreover, circRNAs have been shown to be expressed in a tissue-specific manner and in pathological conditions, which has stimulated significant interest in their role in human disease and cancer. In this concise review, we outline the characteristics, functions and mechanisms of action of circRNAs as well as their involvement in different diseases. Although their exact roles and mechanisms of gene regulation remain to be clarified, circRNAs have potential applications as disease biomarkers and novel therapeutic targets.

Circular RNA in Liver: Health and Diseases

Circular RNA (circRNA) is an important class of noncoding RNA characterized by covalently closed continuous loop structures. In recent years, the various functions of circRNAs have been continuously documented, including effects on cell proliferation and apoptosis and nutrient metabolism. The liver is the largest solid organ in mammals, and it also performs many functions in the body, which is considered to be the busiest organ in the body. At the same time, the liver is vulnerable to multiple pathogenic factors, causing various acute and chronic liver diseases. The pathogenesis of liver disease is still not fully understood. As a rising star for the past few years, circRNAs have been proven involved in the regulation of liver homeostasis and disease. This chapter will explain the role of circRNAs in liver health and diseases and sort out the confusion in the present study.