Elevated expression of circular RNA circ_0008450 predicts dismal prognosis in hepatocellular carcinoma and regulates cell proliferation, apoptosis, and invasion via sponging miR-548p

Circular RNAs as biomarkers and therapeutic targets for gastrointestinal cancers

Circular RNAs are a class of noncoding RNAs with covalently linked 5' and 3' ends that arise from backsplicing events. The absence of a 5' cap and a 3' poly(A) tail makes circular RNAs relatively more stable than their linear counterparts. They are evolutionary conserved and tissue-specific, and some show disease-specific expression patterns. Although their biological functions remain largely unknown, circular RNAs have been shown to play regulatory roles by acting as microRNA sponges, regulators of RNA-binding proteins, alternative splicing, and parental gene expression, and they could even encode proteins. Over the past few decades, circular RNAs have attracted wide attention in oncology owing to their implications in various tumors. Many circular RNAs have been characterized as key players in gastrointestinal cancers and influence cancer growth, progression, metastasis, and therapeutic resistance. Accumulating evidence reveals that their unique characteristics, coupled with their critical roles in tumorigenesis, make circular RNAs promising non-invasive clinical biomarkers for gastrointestinal cancers. In the present review, we summarized the biological roles of the emerging circular RNAs and their potential as biomarkers and therapeutic targets, which may help better understand their clinical significance in the management of gastrointestinal cancers.

Emerging Role of Circular RNAs in Hepatocellular Carcinoma Immunotherapy

Hepatocellular carcinoma (HCC) is a highly fatal malignancy with limited therapeutic options and high recurrence rates. Recently, immunotherapeutic agents such as immune checkpoint inhibitors (ICIs) have emerged as a new paradigm shift in oncology. ICIs, such as programmed cell death protein 1 (PD-1) inhibitors, have provided a new source of hope for patients with advanced HCC. Yet, the eligibility criteria of HCC patients for ICIs are still a missing piece in the puzzle. Circular RNAs (circRNAs) have recently emerged as a new class of non-coding RNAs that play a fundamental role in cancer pathogenesis. Structurally, circRNAs are resistant to exonucleolytic degradation and have a longer half-life than their linear counterparts. Functionally, circRNAs possess the capability to influence various facets of the tumor microenvironment, especially at the HCC tumor-immune synapse. Notably, circRNAs have been observed to control the expression of immune checkpoint molecules within tumor cells, potentially impeding the therapeutic effectiveness of ICIs. Therefore, this renders them potential cancer-immune biomarkers for diagnosis, prognosis, and therapeutic regimen determinants. In this review, the authors shed light on the structure and functional roles of circRNAs and, most importantly, highlight the promising roles of circRNAs in HCC immunomodulation and their potential as promising biomarkers and immunotherapeutic regimen determinants.

Circular RNAs in hepatocellular carcinoma: biogenesis, function, and pathology

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide. Both genetic and environmental factors through a multitude of underlying molecular mechanisms participate in the pathogenesis of HCC. Recently, numerous studies have shown that circular RNAs (circRNAs), an emerging class of non-coding RNAs characterized by the presence of covalent bonds linking 3' and 5' ends, play an important role in the initiation and progression of cancers, including HCC. In this review, we outline the current status of the field of circRNAs, with an emphasis on the functions and mechanisms of circRNAs in HCC and its microenvironment. We also summarize and discuss recent advances of circRNAs as biomarkers and therapeutic targets. These efforts are anticipated to throw new insights into future perspectives about circRNAs in basic, translational and clinical research, eventually advancing the diagnosis, prevention and treatment of HCC.

Review of novel functions and implications of circular RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent malignancies, with high incidence and mortality. As the majority of HCC patients are diagnosed at an advanced stage and die of recurrence and metastasis, its pathology and new biomarkers are needed. Circular RNAs (circRNAs) are a large subclass of long non-coding RNAs (lncRNAs) with covalently closed loop structures and abundant, conserved, stable, tissue-specific expression in mammalian cells. CircRNAs exert multiple functions in HCC initiation, growth and progression, serving as promising biomarkers for diagnosis, prognosis and therapeutic targets for this disease. This review briefly describes the biogenesis and biological functions of circRNAs and elucidates the roles of circRNAs in the development and progression of HCC, especially regarding epithelial-mesenchymal transition (EMT), drug resistance and interactions with epigenetic modifications. In addition, this review highlights the implications of circRNAs as potential biomarkers and therapeutic targets for HCC. We hope to provide novel insight into the roles of circRNAs in HCC.

The Role of miRNAs, circRNAs and Their Interactions in Development and Progression of Hepatocellular Carcinoma: An Insilico Approach

Hepatocellular carcinoma (HCC) is a type of malignant tumor. miRNAs are noncoding RNAs and their differential expression patterns are observed in HCC-induced by alcoholism, HBV and HCV infections. By acting as a competing endogenous RNA (ceRNA), circRNA regulates the miRNA function, indirectly controlling the gene expression and leading to HCC progression. In the present study, data mining was performed to screen out all miRNAs and circRNA involved in alcohol, HBV or HCV-induced HCC with statistically significant (≤0.05%) expression levels reported in various studies. Further, the interaction of miRNAs and circRNA was also investigated to explore their role in HCC due to various causative agents. Together, these study data provide a deeper understanding of the circRNA-miRNA regulatory mechanisms in HCC. These screened circRNA, miRNA and their interactions can be used as prognostic biomarkers or therapeutic targets for the treatment of HCC.

ATF2 accelerates the invasion and metastasis of hepatocellular carcinoma through targeting the miR-548p/TUFT1 axis

AIM

Due to high invasion and metastasis, hepatocellular carcinoma (HCC) is known as one of the most fatal carcinomas. We aim to further investigate regulatory mechanisms of invasion and metastasis to elucidate HCC pathogenesis and develop novel medications.

METHODS

Patient specimens were collected for assessing gene expression and correlation between gene expressions. The expression of Ki67 and E-cadherin in subcutaneous xenograft tumor were examined by immunohistochemistry staining. The expression of activating transcription factor 2 (ATF2), miR-548p and TUFT1 were determined using Real-time quantitative reverse transcription polymerase chain reaction. Epithelial-mesenchymal transition and PI3K/AKT signaling-associated markers were examined with western blot. The proliferation, migration and invasion were assessed by 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide, colony formation and transwell assays, respectively. Cell apoptosis was assessed via Annexin V and propidium iodide staining. Gene interaction was confirmed using chromatin immunoprecipitation and luciferase activity assays. Subcutaneous and intravenous xenograft mouse models were established for analyzing HCC growth and metastasis in vivo.

RESULTS

ATF2 was up-regulated in HCC patients and cells. ATF2 promoted HCC cell proliferation, migration and invasion and inhibited cell apoptosis through directly targeting miR-548p and controlling its expression. miR-548p suppressed HCC cell proliferation, migration and invasion and enhanced cell apoptosis. miR-548p directly bound to the 3'UTR of TUFT1 to restrain its expression and subsequently suppress the PI3K/AKT signaling. ATF2 knock-down significantly suppressed the growth and metastasis of HCC.

CONCLUSION

ATF2 accelerates HCC progression by promoting cell proliferation, migration, invasion and metastasis, which is dependent on regulating the miR-548p/TUFT1 axis.

Emerging roles of circular RNAs in liver cancer

Hepatocellular carcinoma and cholangiocarcinoma are the most common primary liver tumours, whose incidence and associated mortality have increased over recent decades. Liver cancer is often diagnosed late when curative treatments are no longer an option. Characterising new molecular determinants of liver carcinogenesis is crucial for the development of innovative treatments and clinically relevant biomarkers. Recently, circular RNAs (circRNAs) emerged as promising regulatory molecules involved in cancer onset and progression. Mechanistically, circRNAs are mainly known for their ability to sponge and regulate the activity of microRNAs and RNA-binding proteins, although other functions are emerging (e.g. transcriptional and post-transcriptional regulation, protein scaffolding). In liver cancer, circRNAs have been shown to regulate tumour cell proliferation, migration, invasion and cell death resistance. Their roles in regulating angiogenesis, genome instability, immune surveillance and metabolic switching are emerging. Importantly, circRNAs are detected in body fluids. Due to their circular structure, circRNAs are often more stable than mRNAs or miRNAs and could therefore serve as promising biomarkers - quantifiable with high specificity and sensitivity through minimally invasive methods. This review focuses on the role and the clinical relevance of circRNAs in liver cancer, including the development of innovative biomarkers and therapeutic strategies.

Clues for Improving the Pathophysiology Knowledge for Endometriosis Using Plasma Micro-RNA Expression

The pathophysiology of endometriosis remains poorly understood. The aim of the present study was to investigate functions and pathways associated with the various miRNAs differentially expressed in patients with endometriosis. Plasma samples of the 200 patients from the prospective "ENDO-miRNA" study were analyzed and all known human miRNAs were sequenced. For each miRNA, sensitivity, specificity, and ROC AUC values were calculated for the diagnosis of endometriosis. miRNAs with an AUC ≥ 0.6 were selected for further analysis. A comprehensive review of recent articles from the PubMed, Clinical Trials.gov, Cochrane Library, and Web of Science databases was performed to identify functions and pathways associated with the selected miRNAs. In total, 2633 miRNAs were found in the patients with endometriosis. Among the 57 miRNAs with an AUC ≥ 0.6: 20 had never been reported before; one (miR-124-3p) had previously been observed in endometriosis; and the remaining 36 had been reported in benign and malignant disorders. miR-124-3p is involved in ectopic endometrial cell proliferation and invasion and plays a role in the following pathways: mTOR, STAT3, PI3K/Akt, NF-κB, ERK, PLGF-ROS, FGF2-FGFR, MAPK, GSK3B/β-catenin. Most of the remaining 36 miRNAs are involved in carcinogenesis through cell proliferation, apoptosis, and invasion. The three main pathways involved are Wnt/β-catenin, PI3K/Akt, and NF-KB. Our results provide evidence of the relation between the miRNA profiles of patients with endometriosis and various signaling pathways implicated in its pathophysiology.

Circular RNA circ_0008450 regulates the proliferation, migration, invasion, apoptosis and chemosensitivity of CDDP-resistant nasopharyngeal carcinoma cells by the miR-338-3p/SMAD5 axis

Circular RNAs have recently been implicated in the tumorigenesis and chemoresistance of nasopharyngeal carcinoma (NPC). In this report, we identified the precise action of circ_0008450 in NPC progression and cisplatin (CDDP) resistance. The levels of circ_0008450, microRNA (miR)-338-3p and SMAD family member 5 (SMAD5) were gauged by quantitative real-time PCR or western blot. Cell proliferation and IC50 value for CDDP were detected by the Cell Counting Kit-8 assay. Cell colony formation, cell cycle progression, apoptosis, migration and invasion were assessed by colony formation, flow cytometry and transwell assays, respectively. Targeted relationships among circ_0008450, miR-338-3p and SMAD5 were determined by dual-luciferase reporter and RNA immunoprecipitation assays. Tumor models were assayed to evaluate the role of circ_0008450 in tumor growth. Our data indicated that up-regulated circ_0008450 was correlated with NPC CDDP resistance. Moreover, the knockdown of circ_0008450 suppressed cell proliferation, migration, invasion, and promoted apoptosis and CDDP sensitivity in vitro, as well as weakened tumor growth in vivo. Mechanistically, circ_0008450 directly bound to miR-338-3p, and the regulatory effects of circ_0008450 on cell malignant behaviors and CDDP sensitivity were mediated by miR-338-3p in vitro. SMAD5 was a direct target of miR-338-3p and circ_0008450 mediated SMAD5 expression through miR-338-3p. Furthermore, the enforced level of miR-338-3p regulated cell malignant behaviors and CDDP sensitivity in vitro via down-regulating SMAD5. Additionally, the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway was modulated by the circ_0008450/miR-338-3p axis in the two CDDP-resistant NPC cell lines. Our current study suggested that circ_0008450 modulated the malignant behaviors and drug sensitivity of CDDP-resistant NPC cells at least in part by targeting the miR-338-3p/SMAD5 axis, providing potential targets for improving the treatment of chemoresistant NPC.

Circular RNA circ_0073181 contributes to tumorigenesis by regulating protein tyrosine phosphatase receptor type E via miR-548p in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major world public problem in the world, with high morbidity and mortality rates. Circular RNA (circRNA) circ_0073181 has been reported to be related to HCC development. However, the mechanism of circ_0073181 in HCC is far from being addressed. Circ_0073181, microRNA-548p (miR-548p) and protein tyrosine phosphatase receptor type E (PTPRE) level were detected by real-time quantitative PCR (RT-qPCR). Cell proliferation, migration, invasion and apoptosis were detected by Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine, wound healing, transwell and flow cytometry assay. Protein levels of proliferating cell nuclear antigen, Bcl-2 related X protein (Bax) and PTPRE were examined by western blot assay. The binding relationship between miR-548p and circ_0073181 or PTPRE was predicted by circular RNA interactome and targetScan and then verified by a dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The biologic role of circ_0073181 on HCC tumor growth was examined by the xenograft tumor model in vivo. Circ_0073181 and PTPRE were upregulated, and miR-548p was decreased in HCC tissues and cells. Furthermore, circ_0073181 knockdown could boost proliferation, migration, invasion and repress apoptosis of HCC cells in vitro. The mechanical analysis suggested that circ_0073181 could regulate PTPRE expression by sponging miR-548p. In addition, circ_0073181 knockdown suppressed cell growth of HCC in vivo. Circ_0073181 silencing could inhibit HCC cell growth and metastasis partly by regulating the miR-548p/ PTPRE axis, providing a promising therapeutic target for the HCC treatment.

Circular noncoding RNA hsa_circ_0005986 as a prognostic biomarker for hepatocellular carcinoma

Circular RNAs (circRNAs) represent potential biomarkers because of their highly stable structure and robust expression pattern in clinical samples. The aim of this study was to evaluate the expression of a recently identified circRNA, hsa_circ_0005986; determine its clinical significance; and evaluate its potential as a biomarker of hepatocellular carcinoma (HCC). We evaluated hsa_circ_0005986 expression in 123 HCC tissue samples, its clinical significance, and its association with patients’ clinicopathological characteristics and survival. Hsa_circ_0005986 expression was downregulated in HCC tissues. Low hsa_circ_0005986 expression was more common in tumors larger than 5 cm [odds ratio (OR), 3.19; 95% confidence interval (CI), 1.51–6.76; p = 0.002], advanced TNM stage (III/IV; OR, 2.39; 95% CI, 1.16–4.95; p = 0.018), and higher BCLC stage (B/C; OR, 2.71; 95% CI, 1.30–5.65; p = 0.007). High hsa_circ_0005986 expression was associated with improved survival and was an independent prognostic factor for overall [hazard ratio (HR), 0.572; 95% CI, 0.339–0.966; p = 0.037] and progression-free (HR, 0.573; 95% CI, 0.362–0.906; p = 0.017) survival. Moreover, the circRNA–miRNA–mRNA network was constructed using RNA-seq/miRNA-seq data and clinical information from TCGA-LIHC dataset. Our findings indicate a promising role for hsa_circ_0005986 as a prognostic biomarker in patients with HCC.

Current Molecular Biology and Therapeutic Strategy Status and Prospects for circRNAs in HBV-Associated Hepatocellular Carcinoma

Circular RNAs (circRNAs) are newly classified noncoding RNA (ncRNA) members with a covalently closed continuous loop structure that are involved in immune responses against hepatitis B virus (HBV) infections and play important biological roles in the occurrence and pathogenesis of HCC progression. The roles of circRNAs in HBV-associated HCC (HBV-HCC) have gained increasing attention. Substantial evidence has revealed that both tissue and circulating circRNAs may serve as potential biomarkers for diagnostic, prognostic and therapeutic purposes. So far, at least four circRNA/miRNA regulatory axes such as circRNA_101764/miR-181, circRNA_100338/miR-141-3p, circ-ARL3/miR-1305, circ-ATP5H/miR-138-5p, and several circulating circRNAs were reported to be associated with HBV-HCC development. Notably, TGF/SMAD, JAK/STAT, Notch and Wnt/β-catenin signaling pathways may play pivotal roles in this HBV-driven HCC via several circRNAs. Moreover, in non-HBV HCC patients or HCC patients partially infected by HBV, numerous circRNAs have been identified to be important regulators impacting the malignant biological behavior of HCC. Furthermore, the role of circRNAs in HCC drug resistance has become a focus of research with the aim of reversing chemoresistance and immune resistance. Herein, we review the molecular biology of circRNAs in HBV-HCC and their potential in therapeutic strategies.

Circular RNA Circ_0008450 Regulates the Invasion, Migration, and Proliferation of Oral Squamous Carcinoma Human Oral Squamous Cell 3 Cells by Targeting miR-1294

To determine the role of the circ_0008450/miR-1294 molecular axis in the proliferation, migration, and invasion of oral squamous cell carcinoma (OSCC) cells, the expression levels of circ_0008450 and miR-1294 in OSCC and neighboring non-cancerous tissues were detected by real-time quantitative polymerase chain reaction. Human OSCC HSC3 cells were transfected with negative control (NC) small interfering (Si) RNA (Si-NC), Si-circ_0008450, micro RNA (miR)-NC, miR-1294 mimics, anti-miR-1294, anti-Si-circ_0008450, or anti-miR-NC. The activity of HSC3 cells was detected with the CCK-8 assay. The transwell assay was used to assess the invasion and migration of HSC3 cells. The targeted relationship between miR-1294 and CIRc_0008450 was detected with the dualluciferase report assay. Western blot analysis was performed to measure the protein expression levels of matrix metalloproteinase (MMP)-2, MMP-9, and Ki-67 (also known as MKI67). As compared to neighboring non-cancerous tissues, the expression levels of circ_0008450 in OSCC tissues were significantly increased (P < 0.05), while miR-1294 levels were significantly decreased (P < 0.05). As compared to the Si-NC group, cell activity was significantly decreased (P < 0.05), the numbers of migrating and invading cells were significantly decreased (P < 0.05), and the protein levels of Ki-67, MMP-2, and MMP-9 were significantly decreased (P < 0.05) in the Si-circ_0008450 group. The results of the double luciferase assay confirmed targeted binding of circ_0008450 to miR-1294. As compared to the miR-NC group, cell activity was significantly decreased (P < 0.05) in the miR-1294 group, as were the numbers of migrating and invading cells (P < 0.05), and the protein levels of Ki-67, MMP-2, and MMP-9 (P < 0.05). As compared to the Si-circ_0008450+anti-miR-NC group, cell activity was significantly increased (P < 0.05) in the Si-circ_0008450+anti-miR-1294 group, as were the numbers of migrating and invading cells (P < 0.05), and the protein levels (P < 0.05) of Ki-67, MMP-2, and MMP-9. Interference with circ_0008450 reduced the invasion, migration, and proliferation of OSCC cells on account of upregulation via binding with miR-1294.

Genome-wide identification and characterization of circular RNA in resected hepatocellular carcinoma and background liver tissue

Circular RNA (circRNA) is a type of non-coding RNA known to affect cancer-related micro RNAs and various transcription factors. circRNA has promise as a cancer-related biomarker because its circular structure affords high stability. We found using high-throughput sequencing that seven candidate circRNAs (hsa_circ_0041150, hsa_circ_0025624, hsa_circ_0001020, hsa_circ_0028129, hsa_circ_0008558, hsa_circ_0036683, hsa_circ_0058087) were downregulated in HCC. The expression of these circRNAs was examined by quantitative PCR in 233 sets of HCC and matched background normal liver tissues, and correlations between candidate circRNA expression and prognosis were evaluated. The results of quantitative PCR showed that expression of hsa_circ_0041150, hsa_circ_0001020 and hsa_circ_0008558 was significantly lower in HCC than in background normal liver tissues. Kaplan–Meier analysis revealed that low expression of hsa_circ_0001020, hsa_circ_0036683, and hsa_circ_0058087 was associated with poor recurrence-free (RFS) and overall survival (OS) in HCC. Additionally, multivariate analysis revealed that low hsa_circ_0036683 expression was a significant prognostic factor, independent from other clinicopathological features, for inferior RFS and OS. There was no significant association between the expression of these circRNAs and hepatitis B/C status or cirrhosis. This study therefore identified circRNAs as potential prognostic markers for patients who undergo curative surgery for HCC and highlighted hsa_circ_0036683 as the most useful biomarker.

The Roles of circRNAs in Liver Cancer Immunity

Circular RNAs (circRNAs) are stable covalently closed non-coding RNAs (ncRNAs). Many studies indicate that circRNAs are involved in the pathological and physiological processes of liver cancer. However, the functions of circRNAs in liver cancer immunity are less known. In this review, we summarized the functions of circRNAs in liver cancer, including proliferative, metastasis and apoptosis, liver cancer stemness, cell cycle, immune evasion, glycolysis, angiogenesis, drug resistance/sensitizer, and senescence. Immune escape is considered to be one of the hallmarks of cancer development, and circRNA participates in the immune escape of liver cancer cells by regulating natural killer (NK) cell function. CircRNAs may provide new ideas for immunotherapy in liver cancer.

Recent Update on the Role of Circular RNAs in Hepatocellular Carcinoma

After being overlooked for decades, circular RNAs (circRNAs) have recently generated considerable interest. circRNAs play a role in a variety of normal and pathological biological processes, including hepatocarcinogenesis. Many circRNAs contribute to hepatocarcinogenesis through sponging of microRNAs (miRs) and disruption of cellular signaling pathways that play a part in control of cell proliferation, metastasis and apoptosis. In most cases, overexpressed circRNAs sequester miRs to cause de-repressed translation of mRNAs that encode oncogenic proteins. Conversely, low expression of circRNAs has also been described in hepatocellular carcinoma (HCC) and is associated with inhibited production of tumor suppressor proteins. Other functions of circRNAs that contribute to hepatocarcinogenesis include translation of truncated proteins and acting as adapters to regulate influence of transcription factors on target gene expression. circRNAs also affect hepatocyte transformation indirectly. For example, the molecules regulate immune surveillance of cancerous cells and influence the liver fibrosis that commonly precedes HCC. Marked over- or under-expression of circRNA expression in HCC, with correlating plasma concentrations, has diagnostic utility and assays of these RNAs are being developed as biomarkers of HCC. Although knowledge in the field has recently surged, the myriad of described effects suggests that not all may be vital to hepatocarcinogenesis. Nevertheless, investigation of the role of circRNAs is providing valuable insights that are likely to contribute to improved management of a serious and highly aggressive cancer.

Hypoxia-induced circular RNA hsa_circ_0008450 accelerates hepatocellular cancer progression via the miR-431/AKAP1 axis

Hypoxia facilitates the progression of numerous cancers. Circular RNAs (circRNA) have been revealed to be involved in the process of tumors mediated by hypoxia. However, the role and molecular mechanism of circular RNA hsa_circ_0008450 (circ_0008450) in hepatocellular cancer (HCC) under hypoxic conditions has been rarely reported. Expression levels of circ_0008450, microRNA(miR)-431 and A-kinase anchor protein 1 (AKAP1) were examined using reverse transcription-quantitative PCR. Cell viability, apoptosis and glycolysis were assessed via Cell Counting Kit-8, flow cytometry and glycolysis assays, respectively. The association between circ_0008450 or AKAP1 and miR-431 was verified via dual-luciferase reporter assays. Protein levels of AKAP1 were detected by western blotting. Effect of hsa_circ_0008450 on tumor growth in vivo was confirmed by xenograft assays. Circ_0008450 was upregulated in HCC tissues and hypoxia-disposed HCC cells. Depletion of circ_0008450 suppressed tumor growth in vivo and reversed the repression of apoptosis and the acceleration of viability and glycolysis of HCC cells induced by hypoxia treatment in vitro. Notably, circ_0008450 regulated AKAP1 expression by sponging miR-431. Furthermore, miR-431 inhibition reversed the circ_0008450 silencing-mediated effects on viability, apoptosis and glycolysis in hypoxia-treated HCC cells. Additionally, AKAP1 enhancement abolished the effects of miR-431 upregulation on the viability, apoptosis and glycolysis in hypoxia-treated HCC cells. In conclusion, circ_0008450 repression mitigated the progression of HCC under hypoxia by downregulating AKAP1 via miR-431, providing a potential target for HCC treatment.

Circ_0008450 downregulates Runx3 to promote the proliferation and epithelial-mesenchymal transition of human keratinized epithelial cells

Keloid is an extremely common and often overlooked benign neoplastic disease, but its consequences should not be underestimated. Therefore, a deep exploration of the pathological mechanism of keloid becomes very essential. After 22 samples were collected from each patient's keloid tissues and normal skin tissues, circ_0008450 and Runx3 expression was tested by qRT-PCR. When primary human keratinized epithelial cells were transfected by sh-circ_0008450 or sh-Runx3, cell proliferation, apoptosis, migration, and EMT process were assessed by CCK-8, BrdU assay, apoptosis assay, migration assay, and Western blot. Finally, transfection was performed to explore the effect of circ_0008450 on the TGF-β/Smad signal pathway by adopting western blot. Circ_0008450 was highly expressed in keratinized epithelial tissues. After the transfection of sh-circ_0008450 into primary human keratinized epithelial cells, cell proliferation, migration, and EMT process were inhibited, and apoptosis was stimulated. Moreover, circ_0008450 silence-induced above changes were partly reversed by transfecting sh-Runx3. In addition, transfecting sh-circ_0008450 could repress TGF-β/Smad pathway, while transfecting sh-Runx3 activated the above pathway. Circ_0008450 down-regulated Runx3 to promote the proliferation and EMT process of human keratinized epithelial cells. This discovery may be related to the activation of the TGF-β/Smad pathway.

Circular RNAs in gastrointestinal cancer: Current knowledge, biomarkers and targeted therapy (Review)

Circular RNAs (circRNAs) are a type of endogenous non‑coding RNAs that are connected at the 3' and 5' ends by exon or intron cyclization, which forms a covalently closed loop. They are stable, well conserved, exhibit specific expression in mammalian cells and can function as microRNA (miRNA or miR) sponges to regulate the target genes of miRNAs, which influences biological processes. Such as tumor proliferation, invasion, metastasis, apoptosis and tumor stage. circRNAs represent promising candidates for clinical diagnosis and treatment. In the present review, the biogenesis, classification and functions of circRNAs in tumors are briefly summarized and discussed. In addition, the participation of circRNAs in signal transduction pathways regulating gastrointestinal cancer cellular functions is highlighted.

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

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

CircFADS2: A potential prognostic biomarker of colorectal cancer

IMPACT STATEMENT

Colorectal cancer (CRC) is the third most common malignancy worldwide with the second highest mortality rate. Although multidisciplinary cooperative therapies are helpful for improving the survival of CRC patients, the prognosis remains poor. Therefore, it is imperative to seek new biomarkers for the development of individualized treatment for each CRC patient. Circular RNA, an endogenous transcript with specific covalent closed loop, exhibits higher stability, conservation and expression abundance than the corresponding linear component and thus may be utilized as a promised biomarker. Although the majority of studies have focused on circular RNA expression profiling in various types of cancers, evidence supporting their critical role in the diagnosis and prognosis of CRC is limited. This study aimed to screen and identify novel circular RNA biomarkers of CRC by chip analysis and qPCR verification, and to highlight their potential as targets for CRC prognosis, and therapy.

Circular RNAs in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a geographical distributed epithelial tumor of head and neck, which is prevalent in east Africa and Asia, especially southern China. Moreover, NPC has an unfavorable clinical effect and is prone to metastasis at an advanced stage. Although the recovery rate of patients has been improved due to concurrent chemoradiotherapy, poor curative effects and low overall survival remain key issues. The precise mechanisms and pivotal regulators of NPC remain still unclear. To improve the therapeutic efficacy, we focused on related-NPC circular RNAs (circRNAs). CircRNAs are a unique type of endogenous non-coding RNAs (ncRNAs) with a covalent closed-loop structure. Their expression is rich, stable and conservative. Different circRNA have specific tissue and developmental stages and can be detected in body fluids. In addition, circRNAs are involved in multiple pathological processes, especially in cancers. In recent years, using high-throughput indicator technology and bioinformatics technology, a large number of circRNAs have been identified in NPC cells and verified to have biological functions and mechanisms of action. This article aims to provide a retrospective review of the latest research on the proliferation and migration of related-NPC circRNA. Specifically, we focused on the roles and mechanisms of circRNAs in the development and progression of NPC.

CONCLUSION

CircRNA can act as an oncogene or tumor suppressor gene and participate in NPC progression (e.g., proliferation, apoptosis, migration, and invasion). In short, circRNAs have potential as biomarkers for the diagnosis, prognosis and treatment of NPC.

Diagnostic and prognostic value of circular RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common malignant tumour, which has posed a heavy health and financial burden worldwide. Due to limited symptoms at the early stage and the limitation in current biomarkers, HCC patients are usually diagnosed at the advanced stage with a pessimistic overall survival rate. Circular RNAs (circRNAs) are a subclass of single‐stranded RNAs characterized by a covalently closed loop structure without 3’‐ or 5’‐end. With advances in high‐throughput sequencing technology and bioinformatics, accumulating studies have demonstrated the promotor or suppressor roles of circRNAs in the carcinogenesis, progression, and metastasis of HCC. Moreover, circRNAs are characteristic of higher abundance, stability and conservation compared with linear RNAs. Therefore, circRNAs have emerged as one of the most promising diagnostic and prognostic biomarkers for HCC with reliable accuracy, sensitivity and specificity. In this review, we briefly introduce the characteristics of circRNAs and summarize the roles of circRNAs in the biological procedures of HCC. Furthermore, we provide an overview on the potential diagnostic and prognostic value of circRNAs as biomarkers for patients with HCC. Finally, we discuss future perspectives of circRNAs in cancer research.

Circular RNA MTO1 suppresses tumorigenesis of gastric carcinoma by sponging miR-3200-5p and targeting PEBP1

Gastric carcinoma (GC) is one of the most common cancers with the fifth highest incidence of malignant tumors and the second highest death rate in the world. Ever-increasing investigations have shown that circular RNAs (circRNAs) are involved in the development of numerous cancers. But so far, the recognization for circMTO1 that is realized and studied as a cancer-suppressing gene is a small part and the regulatory mechanism of circMTO1 in GC has yet to be further explored. In this study, our experimental results delineated that circMTO1 exhibited much lower expression level in GC tissues and cells. CircMTO1 overexpression slowed down GC progression via inhibiting cell proliferation, migration, invasion and epithelial-mesenchymal transition (EMT) process. Besides, circMTO1 acted as a sponge for miR-3200-5p as well as it could negatively regulate the expression of miR-3200-5p. Moreover, circMTO1 was verified to compete with PEBP1 to bind to miR-3200-5p, thus decelerating the development of GC. In a word, this study was the first to indagate the underlying mechanism of circMTO1 in GC and confirmed circMTO1 exerted its anti-cancer effects by miR-3200-5p/PEBP1 axis, implying that circMTO1 may become a new promising therapeutic target for GC patients.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

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

Silencing Of hsa_circ_0008450 Represses Hepatocellular Carcinoma Progression Through Regulation Of microRNA-214-3p/EZH2 Axis

Purpose

Circular RNA (circRNA) hsa_circ_0008450 has been shown to be up-regulated in hepatocellular carcinoma (HCC). However, the functional role of hsa_circ_0008450 and its molecular mechanism are still unknown.

Patients and methods

We used qRT-PCR and Western blot to examine the expression levels of hsa_circ_0008450, microRNA-214-3p (miR-214-3p), and enhancer of zeste homolog 2 (EZH2) protein. CCK8 assay and wound healing assay were used to detect cell viability and cell migration capability. Cell apoptosis was assessed by flow cytometry. Luciferase reporter assay was used to explore the interaction among hsa_circ_0008450, miR-214-3p, and EZH2.

Results

hsa_circ_0008450 was significantly increased in HCC tissues and cells. Furthermore, knockdown of hsa_circ_0008450 in HCC cells inhibited cell proliferation, invasion, and migration. Mechanically, hsa_circ_0008450 promoted the expression of EZH2 protein through sponging miR-214-3p. Knockdown of circ_0008450 suppressed tumorigenesis of HCC cells in vivo.

Conclusion

Knockdown of hsa_circ_0008450 inhibits HCC progression by regulating miR-214-3p/EZH2 axis. This study suggests that hsa_circ_0008450 may serve as a novel target for the treatment of HCC.

Circular RNA expression and circPTPRM promotes proliferation and migration in hepatocellular carcinoma

Circular RNAs (circRNAs) play a critical role during hepatocellular carcinoma (HCC) development. CircRNA PTPRM (circPTPRM) has not been reported to cause disease and its role in HCC is unclear. This study explored circRNA expression and the function of circPTPRM in HCC. RNA sequencing (RNA-seq) was performed on 3 randomly selected pairs of HCC tissues and their corresponding adjacent non-tumor tissues. Three differentially expressed circRNAs, circPTPRM, circSMAD2 and circPTBP3 were selected and verified by real-time quantitative reverse transcription-polymerase chain reactions in 30 pairs of tissue samples, In vitro cultured hepatoma cells, and normal liver cells. Clinical data analysis was performed to select target circRNAs. Anti-target circRNA siRNAs were transfected into hepatoma cell lines, and the biological behavior of hepatoma cells following silencing of the target circRNA were detected by cell proliferation, plate cloning, and transwell assays. There were 86 differentially expressed circRNAs from RNA-seq, of which 53 were significantly upregulated and 33 were significantly downregulated in HCC. CircPTPRM expression was significantly upregulated in HCC tissue (p = 0.023) based on the analysis of 30 paired samples. CircPTPRM expression positively correlated with HCC recurrence and metastasis (p = 0.039). CircPTPRM silencing reduced HCC cell proliferation, migration and invasion. CircRNAs were differentially expressed in HCC samples. CircPTPRM was significantly upregulated in HCC and may function during the tumorigenesis and metastasis of HCC.

Emerging roles of circRNA in formation and progression of cancer

Circular RNAs (circRNAs) are recently discovered as a special novel type of endogenous noncoding RNAs (ncRNAs), which form a covalently closed continuous loop and are highly represented in the eukaryotic transcriptome. Recent research revealed that circRNAs can function as microRNA (miRNA) sponges, regulators of splicing and transcription, as well as interact with RNA-binding proteins (RBPs). In this review, not only the function and mechanism, but also the experimental methods of circRNA are summarized. The summary of the current state of circRNA will help us in the discovery of novel biomarkers, the therapeutic targets and their potential significance in diagnosis and treatment of diseases. CircRNAs might play important roles in cancers especially in hepatocellular carcinoma, gastric carcinoma and colorectal cancer as well as serving as diagnostic or predictive biomarkers of some diseases and providing new treatments of diseases.

Role of CircRNAs_100395 in Proliferation and Metastases of Liver Cancer

BACKGROUND Circular RNAs (circRNAs) are a kind of noncoding RNA with high cancer-specific expression, and great potential in regulating tumorigenesis. Among these, circRNA_100395 (circ_100395) has been reported to be downregulated in lung cancer, and participates in the process of tumor cell proliferation and metastasis. However, its expression and function in liver cancer remain unknown. MATERIAL AND METHODS Quantitative real-time polymerase chain reaction (RT-qPCR) was used to evaluate the expression level of circ_100395 and microRNAs-1228 (miR-1228) in liver cancer samples and the adjacent non-tumor tissues. Cell proliferation, apoptosis, invasion, migration, and epithelial-mesenchymal transition (EMT) pathway of circ_100395 upregulated cells were analyzed using a Cell Counting Kit-8 (CCK-8), flow cytometry, Transwell assay, and Western blot analysis. RESULTS We found that circ_100395 was downregulated in cancerous liver tissues relative to the adjacent normal tissues. The overexpression of circ_100395 was negatively associated with tumor differentiation, microvascular invasion, and portal vein tumor thrombosis. However, patients with higher circ_10039 expression tended to have better postoperative disease-free survival time. Moreover, upregulation of circ_100395 in liver cancer cells inhibited cell proliferation, induced apoptosis, then silenced the EMT pathway and reduced migration and invasion abilities, while this anti-tumor effect was significantly reversed by the downstream target, miR-1228. CONCLUSIONS circ_100395 appears to be a promising therapeutic target for liver cancer.

Molecular network-based identification of competing endogenous RNAs in bladder cancer

BACKGROUND

Circular RNAs (circRNAs) have been shown to interact with microRNAs (miRNA) as competitive endogenous RNAs (ceRNAs) to regulate target gene expression and participate in tumorigenesis. However, the role of circRNA-mediated ceRNAs in bladder cancer (BC) remains unknown. Accordingly, the aim of this study was to elucidate the regulatory mechanisms in BC based on construction of the ceRNA network.

METHODS

The RNA expression profiles were obtained from public datasets in the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) database, and were used to establish a circRNA-miRNA-mRNA network. The interactions among proteins were analyzed using the STRING database and hubgenes were extracted using the cytoHubba application. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses of differentially expressed mRNAs in BC and normal tissue samples were performed to determine the functions of the intersecting mRNAs.

RESULTS

A total of 27 circRNAs, 76 miRNAs, and 4744 mRNAs were found to be differentially expressed between BC and normal tissues. The circRNA-miRNA-mRNA ceRNA network was established based on 21 circRNAs, 14 miRNAs, and 150 mRNAs differentially expressed in BC. We also established a protein-protein interaction network and identified 10 hubgenes, which were used to construct circRNA-miRNA-hubgene regulatory modules. The most enriched biological process GO term was strand displacement (P<0.05), and the homologous recombination and Fanconi anemia pathways were significantly enriched (P<0.05) for the differentially expressed genes in BC.

CONCLUSIONS

We screened several dysregulated circRNAs and established a circRNA-associated ceRNA network by bioinformatics analysis. The identified ceRNAs are likely critical in the pathogenesis of BC and may serve as future therapeutic biomarkers.

Circular RNA circ_0008450 upregulates CXCL9 expression by targeting miR-577 to regulate cell proliferation and invasion in nasopharyngeal carcinoma

As a kind of malignant tumor, nasopharyngeal carcinoma (NPC) has attracted increasing attention from researchers. As a member of the circular RNA (circRNA) family, circ_0008450 has been investigated in hepatocellular carcinoma but not in NPC. This study aims to reveal the special biologic role and mechanism of circ_0008450 in NPC. qRT-PCR analysis was conducted to test the level of circ_0008450 in different tissues and cells. Loss/Gain of function assay was utilized to detect the influence of silenced/overexpressed circ_0008450 on the proliferation, apoptosis, migration, and invasion of NPC cells. The mechanism of circ_0008450 was assessed by performing qRT-PCR and luciferase reporter experiments. The results showed that circ_0008450 was elevated in NPC tissues and cells. Silenced circ_0008450 could inhibit cell proliferation, and metastatic properties and increased the number of apoptotic cells. Ectopically expressed circ_0008450 strengthened the abovementioned malignant biological behaviors. Mechanistically, circ_0008450 reduced miR-577-mediated repression of CXCL9, resulting in facilitating the oncogenic functions of NPC. In conclusion, circ_0008450 acts as an oncogene in NPC cells through regulating miR-577/CXCL9 signaling. Our findings might provide a new therapeutic target for treating NPC.

Circular RNAs in hepatocellular carcinoma: Biomarkers, functions and mechanisms

Hepatocellular carcinoma (HCC), a leading cause of cancer-related death with high invasive and metastatic potential, has a low survival rate. To improve the survival and quality of life in HCC patients, it is urgently needed to explore novel biomarkers for early diagnosis and prognosis of HCC, as well as therapeutic strategies. Circular RNAs (circRNAs) are a class of highly conserved, stable and abundant non-coding RNAs (ncRNAs) that can regulate gene expression at transcriptional or post-transcriptional levels. Recently, some circRNAs are identified to be potential biomarkers for HCC diagnosis and prognosis. Furthermore, some circRNAs are found to play oncogenic or suppressive roles in HCC progression by regulating various biological processes, including cell proliferation, migration, invasion and metastasis, epithelial-mesenchymal transition (EMT), as well as apoptosis. In this review, we summarize recent findings of deregulated circRNAs, their functions and molecular mechanisms in HCC, and discuss their potential roles as diagnostic biomarkers, prognostic biomarkers, as well as therapeutic targets for HCC.

Circular RNA circ-DONSON facilitates gastric cancer growth and invasion via NURF complex dependent activation of transcription factor SOX4

Background

Circular RNAs (circRNAs) are a novel type of noncoding RNAs and play important roles in tumorigenesis, including gastric cancer (GC). However, the functions of most circRNAs remain poorly understood. In our study, we aimed to investigate the functions of a new circRNA circ-DONSON in GC progression.

Methods

The expression of circ-DONSON in gastric cancer tissues and adjacent normal tissues was analyzed by bioinformatics method, qRT-PCR, Northern blotting and in situ hybridization (ISH). The effects of circ-DONSON on GC cell proliferation, apoptosis, migration and invasion were measured by using CCK8, colony formation, EdU, immunofluorescence (IF), FACS and Transwell assays. qRT-PCR and Western blotting were utilized to validate how circ-DONSON regulates SOX4 expression. ChIP, DNA fluorescence in situ hybridization (DNA-FISH) and DNA accessibility assays were used to investigate how circ-DONSON regulates SOX4 transcription. The interaction between circ-DONSON and NURF complex was evaluated by mass spectrum, RNA immunoprecipitation (RIP), pulldown and EMSA assays. Xenograft mouse model was used to analyze the effect of circ-DONSON on GC growth in vivo.

Results

Elevated expression of circ-DONSON was observed in GC tissues and positively associated with advanced TNM stage and unfavorable prognosis. Silencing of circ-DONSON significantly suppressed the proliferation, migration and invasion of GC cells while promoting apoptosis. circ-DONSON was localized in the nucleus, recruited the NURF complex to SOX4 promoter and initiated its transcription. Silencing of the NURF complex subunit SNF2L, BPTF or RBBP4 similarly attenuated GC cell growth and increased apoptosis. circ-DONSON knockdown inhibited GC growth in vivo.

Conclusion

circ-DONSON promotes GC progression through recruiting the NURF complex to initiate SOX4 expression.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1006-2) contains supplementary material, which is available to authorized users.