Circular RNA YAP1 inhibits the proliferation and invasion of gastric cancer cells by regulating the miR-367-5p/p27 Kip1 axis

Circular RNAs as key regulators in cancer hallmarks: New progress and therapeutic opportunities

Circular RNAs (circRNAs) have emerged as critical regulators in cancer biology, contributing to various cancer hallmarks, including cell proliferation, apoptosis, metastasis, and drug resistance. Defined by their covalently closed loop structure, circRNAs possess unique characteristics like high stability, abundance, and tissue-specific expression. These non-coding RNAs function through mechanisms such as miRNA sponging, interactions with RNA-binding proteins (RBPs), and modulating transcription and splicing. Advances in RNA sequencing and bioinformatics tools have enabled the identification and functional annotation of circRNAs across different cancer types. Clinically, circRNAs demonstrate high specificity and sensitivity in samples, offering potential as diagnostic and prognostic biomarkers. Additionally, therapeutic strategies involving circRNA mimics, inhibitors, and delivery systems are under investigation. However, their precise mechanisms remain unclear, and more clinical evidence is needed regarding their roles in cancer hallmarks. Understanding circRNAs will pave the way for novel diagnostic and therapeutic approaches, potentially improving patient outcomes.

Roles of gastric cancer-derived exosomes in the occurrence of metastatic hepatocellular carcinoma

Gastric cancer (GC), particularly in East Asia, is among the most prevalent cancers with high mortality rates. According to recent epidemiological data, patients with GC account for over a quarter of all cancer incidences and approximately one third of cancer-related deaths in East Asia. Liver metastasis (LM) is not only a common form of GC distant metastasis but also poses a major challenge to the prognosis and treatment of patients with advanced GC. Increasing evidence has shown that the gut-liver axis plays a pivotal role in maintaining the stomach-liver-gut homeostasis. Exosomes are small secreted vesicles enriched with specific proteins, lipids, and nucleic acids. These vesicles exhibit significant activities in signal transmission to adjacent or distant cells in the gut-liver axis, as well as in remodeling the tumor microenvironment. Some research have pointed out that exosomes promote LM of various cancers. However, there still lack of complete and systematic review on how exosomes affect GC-LM. In this article, we present a comprehensive description to explore the role of GC-derived exosomes in the occurrence and development of metastatic hepatocellular carcinoma (HCC).

The potential of circular RNAs as biomarkers and therapeutic targets for gastric cancer: A comprehensive review

BACKGROUND

Gastric cancer (GC) is a global health concern, contributing significantly to cancer-related mortality rates. Early detection is vital for improving patient outcomes. Recently, circular RNAs (circRNAs) have emerged as crucial players in the development and progression of various cancers, including GC.

AIM

This comprehensive review underscores the promising potential of circRNAs as innovative biomarkers for the early diagnosis of GC, as well as their possible utility as therapeutic targets for this life-threatening disease. Specifically, the review focuses on recent findings, mechanistic insights, and clinical applications of circRNAs in GC.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Dysregulation of circRNAs has been consistently observed in GC tissues, offering potential diagnostic value due to their stability in bodily fluids such as blood and urine. For instance, circPTPN22 and hsa_circ_000200. Furthermore, the expression levels of circRNAs such as circCUL2, hsa_circ_0000705 and circSHKBP1 have shown strong associations with critical clinical features of GC, including diagnosis, prognosis, tumor size, lymph node metastasis, tumor-node-metastasis (TNM) stage, and treatment response. Additionally, circRNAs such as circBGN, circLMO7, and circMAP7D1 have shown interactions with specific microRNAs (miRNAs), proteins, and other molecules that play key roles in development and progression of GC. This further highlighting their potential as therapeutic targets. Despite their potential, several challenges need to be addressed to effectively apply circRNAs as GC biomarkers. These include standardizing detection methods, establishing cutoff values for diagnostic accuracy, and validating findings in larger patient cohorts. Moreover, the functional mechanisms by which circRNAs contribute to GC pathogenesis and therapeutic resistance warrant further investigation. Advances in circRNAs research could provide valuable insights into the early detection and targeted treatment of GC, ultimately improving patient outcomes.

CircUGGT2 downregulation by METTL14-dependent m6A modification suppresses gastric cancer progression and cisplatin resistance through interaction with miR-186-3p/MAP3K9 axis

Chemoresistance is a major therapeutic challenge in advanced gastric cancer (GC). N6-methyladenosine (m6A) RNA modification has been shown to play fundamental roles in cancer progression. However, the underlying mechanisms by which m6A modification of circRNAs contributes to GC and chemoresistance remain unknown. We found that hsa_circ_0030632 (circUGGT2) was a predominant m6A target of METTL14, and METTL14 knockdown (KD) reduced circUGGT2 m6A levels but increased its mRNA levels. The expression of circUGGT2 was markedly increased in cisplatin (DDP)-resistant GC cells. CircUGGT2 KD impaired cell growth, metastasis and DDP-resistance in vitro and in vivo, but circUGGT2 overexpression prompted these effects. Furthermore, circUGGT2 was validated to sponge miR-186-3p and upregulate MAP3K9 and could abolish METTL14-caused miR-186-3p upregulation and MAP3K9 downregulation in GC cells. circUGGT2 negatively correlated with miR-186-3p expression and harbored a poor prognosis in patients with GC. Our findings unveil that METTL14-dependent m6A modification of circUGGT2 inhibits GC progression and DDP resistance by regulating miR-186-3p/MAP3K9 axis.

Potential therapeutic applications of circular RNA in acute kidney injury

Acute kidney injury (AKI) is a common clinical syndrome characterized by a rapid deterioration in renal function, manifested by a significant increase in creatinine and a sharp decrease in urine output. The incidence of morbidity and mortality associated with AKI is on the rise, with most patients progressing to chronic kidney disease or end-stage renal disease. Treatment options for patients with AKI remain limited. Circular RNA (circRNA) is a wide and diverse class of non-coding RNAs that are present in a variety of organisms and are involved in gene expression regulation. Studies have shown that circRNA acts as a competing RNA, is involved in disease occurrence and development, and has potential as a disease diagnostic and prognostic marker. CircRNA is involved in the regulation of important biological processes, including apoptosis, oxidative stress, and inflammation. This study reviews the current status and progress of circRNA research in the context of AKI.

YAP1-CPNE3 positive feedback pathway promotes gastric cancer cell progression

Hippo-Yes-associated protein 1 (YAP1) plays an important role in gastric cancer (GC) progression; however, its regulatory network remains unclear. In this study, we identified Copine III (CPNE3) was identified as a novel direct target gene regulated by the YAP1/TEADs transcription factor complex. The downregulation of CPNE3 inhibited proliferation and invasion, and increased the chemosensitivity of GC cells, whereas the overexpression of CPNE3 had the opposite biological effects. Mechanistically, CPNE3 binds to the YAP1 protein in the cytoplasm, inhibiting YAP1 ubiquitination and degradation mediated by the E3 ubiquitination ligase β-transducin repeat-containing protein (β-TRCP). Thereby activating the transcription of YAP1 downstream target genes, which creates a positive feedback cycle to facilitate GC progression. Immunohistochemical analysis demonstrated significant upregulation of CPNE3 in GC tissues. Survival and Cox regression analyses indicated that high CPNE3 expression was an independent prognostic marker for GC. This study elucidated the pivotal involvement of an aberrantly activated CPNE3/YAP1 positive feedback loop in the malignant progression of GC, thereby uncovering novel prognostic factors and therapeutic targets in GC.

Exosome-mediated circGMPS facilitates the development of gastric cancer cells through miR-144-3p/PUM1

In recent years, gastric cancer (GC) is still one of the major public health burdens in the world. It is reported that exosome circular RNA (circRNA) is involved in the GC progression. However, the function and potential mechanism of circGMPS in GC remains unclear and needs further exploration. In this study, we isolated and identified exosomes from serum by TEM, NTA analysis and Western blot. RNA expression was evaluated by qRT-PCR. Western blot was employed to examine protein expression. Cell proliferation was measured using CCK-8. Transwell assay was adopted to analyze cell migration and invasion. The relationship between genes was explored through bioinformatics analysis, dual-luciferase reporter gene assay and spearman correlation coefficient. We found that circGMPS was elevated in GC exosomes, tissues and cells. Poor prognosis of GC patients was related to high circGMPS expression. Both exosome co-culture with cells and insertion of circGMPS clearly promoted cell progression. Mechanically, circGMPS sponged miR-144-3p to regulate PUM1. Inhibition of PUM1 or miR-144-3p overexpression inhibited the malignant GC cell progression. Our data confirmed that exosome-derived circGMPS boosted malignant progression by miR-144-3p/PUM1 axis in GC cells, providing strong evidences for circGMPS as a clinical biomarker of GC treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00597-9.

Dysregulated expression of miR‑367 in disease development and its prospects as a therapeutic target and diagnostic biomarker (Review)

MicroRNA (miR)-367 has a wide range of functions in gene regulation and as such plays a critical role in cell proliferation, differentiation and development, making it an essential molecule in various physiological processes. miR-367 belongs to the miR-302/367 cluster and is located in the intronic region of human chromosome 4 on the 4q25 locus. Dysregulation of miR-367 is associated with various disease conditions, including cancer, inflammation and cardiac conditions. Moreover, miR-367 has shown promise both as a tumor suppressor and a potential diagnostic biomarker for breast, gastric and prostate cancer. The elucidation of the essential role of miR-367 in inflammation, development and cardiac diseases emphasizes its versatility in regulating various physiological processes beyond cancer biology. However, further research is necessary to fully understand the complex regulatory mechanisms involving miR-367 in different physiological and pathological contexts. In conclusion, the versatility and significance of miR-367 makes it a promising candidate for further study and in the development of new diagnostic and therapeutic strategies.

Noncoding RNAs in tumorigenesis and tumor therapy

Tumorigenesis is a complicated process in which numerous modulators are involved in different ways. Previous studies have focused primarily on tumor-associated protein-coding genes such as oncogenes and tumor suppressor genes, as well as their associated oncogenic pathways. However, noncoding RNAs (ncRNAs), rising stars in diverse physiological and pathological processes, have recently emerged as additional modulators in tumorigenesis. In this review, we focus on two typical kinds of ncRNAs: long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs). We describe the molecular patterns of ncRNAs and focus on the roles of ncRNAs in cancer stem cells (CSCs), tumor cells, and tumor environmental cells. CSCs are a small subset of tumor cells and are generally considered to be cells that initiate tumorigenesis, and dozens of ncRNAs have been defined as critical modulators in CSC maintenance and oncogenesis. Moreover, ncRNAs are widely involved in oncogenetic processes, including sustaining proliferation, resisting cell death, genome instability, metabolic disorders, immune escape and metastasis. We also discuss the potential applications of ncRNAs in tumor diagnosis and therapy. The progress in ncRNA research greatly improves our understanding of ncRNAs in oncogenesis and provides new potential targets for future tumor therapy.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

Advances in high-throughput sequencing techniques and bioinformatic analysis have refuted the "junk" RNA hypothesis that was claimed against non-coding RNAs (ncRNAs). Circular RNAs (circRNAs); a class of single-stranded covalently closed loop RNA molecules have recently emerged as stable epigenetic regulators. Although the exact regulatory role of circRNAs is still to be clarified, it has been proven that circRNAs could exert their functions by interacting with other ncRNAs or proteins in their own physiologically authentic environment, regulating multiple cellular signaling pathways and other classes of ncRNAs. CircRNAs have also been reported to exhibit a tissue-specific expression and have been associated with the malignant transformation process of several hematological and solid malignancies. Along this line of reasoning, this review aims to highlight the importance of circRNAs in Breast Cancer (BC), which is ranked as the most prevalent malignancy among females. Notwithstanding the substantial efforts to develop a suitable anticancer therapeutic regimen against the heterogenous BC, inter- and intra-tumoral heterogeneity have resulted in an arduous challenge for drug development research, which in turn necessitates the investigation of other markers to be therapeutically targeted. Herein, the potential of circRNAs as possible diagnostic and prognostic biomarkers have been highlighted together with their possible application as novel therapeutic targets.

Expression analysis of circulating miR-22, miR-122, miR-217 and miR-367 as promising biomarkers of acute lymphoblastic leukemia

BACKGROUND

The role of serum-based biomarkers such as microRNAs in cancer diagnosis has been extensively established. This study aimed to determine the expression levels of bioinformatically selected miRNAs and whether they can be used as biomarkers or a new therapeutic target in patients with acute lymphoblastic leukemia (ALL).

MATERIALS AND METHODS

The expression levels of serum miR-22, miR-122, miR-217, and miR-367 in 21 ALL patients and 21 healthy controls were measured using quantitative real-time PCR. The receiver operating characteristic (ROC) curve and the associated area under the curve (AUC) was used to assess candidate miRNAs' diagnostic value as a biomarker.

RESULTS

The results showed that miR-217 was markedly decreased in patients with ALL compared to controls. Moreover, miR-22, miR-122, and miR-367 were found to be upregulated. Furthermore, ROC analysis showed that serum miR-217 and miR-367 could differentiate ALL patients from healthy individuals, while miR-22 has approximate discriminatory power that requires further investigation.

CONCLUSION

These results provide promising preliminary evidence that circulating miR-217 and miR-367 could be considered potent diagnostic biomarkers and therapeutic goals in this disease.

Functional properties of circular RNAs and research progress in gastric cancer

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

Role of Non-Coding RNAs in Colorectal Cancer: Focus on Long Non-Coding RNAs

Colorectal cancer is one of the most common causes of cancer-related deaths worldwide. Despite the advances in the knowledge of pathogenetic molecular mechanisms and the implementation of more effective drug treatments in recent years, the overall survival rate of patients remains unsatisfactory. The high death rate is mainly due to metastasis of cancer in about half of the cancer patients and the emergence of drug-resistant populations of cancer cells. Improved understanding of cancer molecular biology has highlighted the role of non-coding RNAs (ncRNAs) in colorectal cancer development and evolution. ncRNAs regulate gene expression through various mechanisms, including epigenetic modifications and interactions of long non-coding RNAs (lncRNAs) with both microRNAs (miRNAs) and proteins, and through the action of lncRNAs as miRNA precursors or pseudogenes. LncRNAs can also be detected in the blood and circulating ncRNAs have become a new source of non-invasive cancer biomarkers for the diagnosis and prognosis of colorectal cancer, as well as for predicting the response to drug therapy. In this review, we focus on the role of lncRNAs in colorectal cancer development, progression, and chemoresistance, and as possible therapeutic targets.

Circular RNAs as diagnostic biomarkers for gastric cancer: A comprehensive update from emerging functions to clinical significances

The incidence and mortality of gastric cancer ranks as a fouth leading cause of cancer death worldwide, especially in East Asia. Due to the lack of specific early-stage symptoms, the majority of patients in most developing nations are diagnosed at an advanced stage. Therefore, it is urgent to find more sensitive and reliable biomarkers for gastric cancer screening and diagnosis. Circular RNAs (circRNAs), a novel type of RNAs with covalently closed loops, are becoming a latest hot spot in the field of. In recent years, a great deal of research has demonstrated that abnormal expression of circRNAs was associated with the development of gastric cancer, and suggested that circRNA might serve as a potential biomarker for gastric cancer diagnosis. In this review, we summarize the structural characteristics, formation mechanism and biological function of circRNAs, and elucidate research progress and existing problems in early screening of gastric cancer.

Hsa_circ_0040809 and hsa_circ_0000467 promote colorectal cancer cells progression and construction of a circRNA-miRNA-mRNA network

Objective: Circular RNAs (circRNAs) have been demonstrated to be closely involved in colorectal cancer (CRC) pathogenesis and metastasis. More potential biomarkers are needed to be searched for colorectal cancer (CRC) diagnosis and treatment. The objective of this study is to seek differentially expressed circRNAs (DEcircRNAs), test their roles in CRC and construct a potential competing endogenous RNA (ceRNA) network.

Methods: CircRNA microarrays were obtained from Gene Expression Omnibus, and differential expression was analyzed by R software. The relative expressions of DEcircRNAs were confirmed in CRC tissues and cell lines by qRT-PCR. MTs and Transwell experiments were performed for detecting the roles of circRNAs on CRC cell proliferation and migration, respectively. Targeted miRNAs of circRNAs and targeted mRNAs of miRNAs were predicted and screened by bioinformatics methods. A ceRNA network of DEcircRNAs was constructed by Cytoscape. To further verify the potential ceRNA network, the expressions of miRNAs and mRNAs in knockdown of DEcircRNAs CRC cells were detected by qRT-PCR.

Results: Two DEcircRNAs (hsa_circ_0040809 and hsa_circ_0000467) were identified and validated in CRC tissues and cell lines. The results of MTs and Transwell experiments showed that hsa_circ_0040809 and hsa_circ_0000467 promoted CRC proliferation and migration. Bioinformatics analysis screened 3 miRNAs (miR-326, miR-330-5p, and miR-330-3p) and 2 mRNAs (FADS1 and RUNX1), and a ceRNA network was constructed. In knockdown of hsa_circ_0040809 HCT-116 cells, the expression of miR-330-3p was significantly upregulated, while RUNX1 was significantly downregulated. In knockdown of hsa_circ_0000467 HCT-116 cells, the expressions of miR-326 and miR-330-3p were upregulated, while FADS1was downregulated.

Conclusion: We found that hsa_circ_0040809 and hsa_circ_0000467 were upregulated in CRC tissues and cell lines, and promoted CRC cell progression. A circRNA-miRNA-mRNA network based on hsa_circ_0040809 and hsa_circ_0000467 was constructed.

Research progress on the circRNA/lncRNA-miRNA-mRNA axis in gastric cancer

Gastric cancer is one of the most common malignant tumours worldwide. Genetic and epigenetic alterations are key factors in gastric carcinogenesis and drug resistance to chemotherapy. Competing endogenous RNA (ceRNA) regulation models have defined circRNA/lncRNA as miRNA sponges that indirectly regulate miRNA downstream target genes. The ceRNA regulatory network is related to the malignant biological behaviour of gastric cancer. The circRNA/lncRNA-miRNA-mRNA axis may be a marker for the early diagnosis and prognosis of gastric cancer and a potential therapeutic target for gastric cancer. Exosomal ncRNAs play an important role in gastric cancer and are expected to be ideal biomarkers for the diagnosis, prognosis, and treatment of gastric cancer. This review summarizes the specific ceRNA regulatory network (circRNA/lncRNA-miRNA-mRNA) discovered in gastric cancer in recent years, which may provide new ideas or strategies for early clinical diagnosis, further development, and application.

Circular RNA Controls Tumor Occurrence and Development via Cell Cycle Regulation

Circular RNAs (circRNAs) participate in the occurrence and development of various diseases through different mechanisms, such as by acting as a microRNA (miRNA) sponge, interacting with RNA-binding proteins, and regulating gene transcription and protein translation. For example, the abnormal expression of specific circRNAs in tumor cells can alter key regulatory factors and the cell cycle network, resulting in cell cycle disorders and the development and metastasis of tumors. Here, we summarize the mechanisms involved in the circRNA-mediated processes that lead to uncontrolled cell cycle and tumor cell proliferation. Extensive studies investigating the abnormal expression of circRNAs in different cancer types have been conducted. The unique characteristics of circRNAs and their ability to regulate the cell cycle through diverse mechanisms is extremely valuable in tumor diagnosis, treatment, and prognosis. Our review may assist in further understanding the circRNA-mediated regulation of the cell cycle in tumors and provide insights for research on circRNA-based therapeutic strategies and biological diagnosis for cancer.

CircGPR137B/miR-4739/FTO feedback loop suppresses tumorigenesis and metastasis of hepatocellular carcinoma

BACKGROUND

Emerging evidence indicates that circular RNAs (circRNAs) and m6A RNA methylation participate in the pathogenesis and metastasis of multiple malignancies including hepatocellular carcinoma (HCC). However, it remains undocumented how circRNAs form a feedback loop with the m6A modification contributing to HCC.

METHODS

A novel hsa_circ_0017114 (circGPR137B) was identified from three pairs of primary HCC and adjacent normal tissues by circRNA expression profiling. The association of circGPR137B and miR-4739 with clinicopathological parameters and prognosis in patients with HCC was analyzed by RT-qPCR, fluorescence in situ hybridization and TCGA cohorts. The role of circGPR137B in HCC was estimated in vitro and in vivo. RT-qPCR, western blot, m6A dot blot, RIP, MeRIP and dual-luciferase reporter assays were used to validate the reciprocal regulation of the feedback loop among circGPR137B, miR-4739 and m6A demethylase FTO. Meanwhile, the expression, function and prognosis of FTO in HCC were investigated by RT-qPCR, western blot, TCGA and rescue experiments.

RESULTS

We identified a new dramatically downregulated circGPR137B in HCC tissues, and found that downregulation of circGPR137B or upregulation of miR-4739 was associated with poor prognosis in patients with HCC. Ectopic expression of circGPR137B strikingly repressed the proliferation, colony formation and invasion, whereas knockdown of circGPR137B harbored the opposite effects. Moreover, restored expression of circGPR137B inhibited tumor growth and lung metastasis in vivo. Further investigations showed that circGPR137B, co-localized with miR-4739 in the cytoplasm, acted as a sponge for miR-4739 to upregulate its target FTO, which mediated m6A demethylation of circGPR137B and promoted its expression. Thus, a feedback loop comprising circGPR137B/miR-4739/FTO axis was formed. FTO suppressed cell growth and indicated favorable survival in patients with HCC.

CONCLUSION

Our results demonstrate that circGPR137B inhibits HCC tumorigenesis and metastasis through the circGPR137B/miR-4739/FTO feedback loop. This positive feedback mechanism executed by functional coupling between a circRNA sponge and an m6A modification event suggests a model for epigenetics.

Role of circRNA circ_0000080 in myocardial hypoxia injury

This study aimed to investigate the potential role of circRNA circ_0000080 in myocardial hypoxia injury and the underlying mechanisms. Patients with myocardial hypoxia injury who were admitted to Xi’an No. 1 Hospital, China, were included in this study. The expression levels of circ_0000080, miR-367-5p, and COX2 were analyzed by real-time quantitative PCR (RT-qPCR); cell viability was measured by cell counting kit-8 (CCK-8) assay; and apoptosis was detected by flow cytometry. In addition, the release of cytokines was determined by Enzyme-linked immunosorbent assay (ELISA), and the binding sites between miR-367-5p and circ_0000080/COX2 were predicted by bioinformatics analysis and confirmed by dual-luciferase reporter and RNA pull-down assays. circ_0000080 was upregulated in patients with MI and in H9c2 cells treated with H₂O₂ and hypoxia/reoxygenation (H/R). Silencing circ_0000080 reduced the H/R-mediated apoptosis of cardiomyocytes and secretion of pro-inflammatory cytokines. Moreover, circ_0000080 functioned as an miR-367-5p sponge to regulate the expression of COX2. Downregulated miR-367-5p or overexpressed COX2 degraded cellular functions of cardiomyocytes. circ_0000080 knockdown alleviated myocardial hypoxia injury through the miR-367-5p/COX2 axis.

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

METTL14-mediated m6A modification of circORC5 suppresses gastric cancer progression by regulating miR-30c-2-3p/AKT1S1 axis

Background

N6-methyladenosine (m6A) RNA methylation and circular RNAs (circRNAs) have been shown to act vital roles in multiple malignancies including gastric cancer (GC). However, there is little knowledge about how m6A modification of circRNAs contributes to GC progression.

Methods

The association of METTL14 expression with the clinicopathological characteristics and prognosis in patients with GC was assessed by Western blot, Immunohistochemistry and public datasets. In vitro and vivo function experiments were conducted to investigate the role of METTL14 in GC. Furthermore, m6A-circRNA epitranscriptomic microarray was utilized to identify METTL14-mediated m6A modification of circRNAs, which were validated by methylated RNA immunoprecipitation (Me-RIP), RT-qPCR and rescue experiments in GC cells. The sponge of circORC5 with miR-30c-2-3p was confirmed by luciferase gene report and RNA immunoprecipitation assays. The expression, localization and prognosis of circORC5 in GC were evaluated by fluorescence in situ hybridization. The effects of METTL14 and (or) circORC5 on miR-30c-2-3p-mediated AKT1S1 and EIF4B were estimated by RT-qPCR and Western blot analyses.

Results

We found that METTL14 was downregulated in GC tissue samples and its low expression acted as a prognostic factor of poor survival in patients with GC. Ectopic expression of METTL14 markedly repressed growth and invasion of GC cells in vitro and in vivo, whereas knockdown of METTL14 harbored the opposite effects. Mechanically, m6A-circRNA epitranscriptomic microarray and Me-RIP identified circORC5 as the downstream target of METTL14. Silencing of METTL14 reduced the m6A level of circORC5, but increased circORC5 expression. Moreover, circORC5 could sponge miR-30c-2-3p, and reverse METTL14-caused upregulation of miR-30c-2-3p and downregulation of AKT1S1 and EIF4B. In addition, circORC5 possessed a negative correlation with miR-30c-2-3p and indicated a poor survival in GC.

Conclusion

Our findings demonstrate that METTL14-mediated m6A modification of circORC5 suppresses gastric cancer progression by regulating miR-30c-2-3p/AKT1S1 axis.

Circular RNAs Modulate Cancer Hallmark and Molecular Pathways to Support Cancer Progression and Metastasis

Simple Summary

Circular RNAs (circRNA) are a type of RNA molecule of circular shape that are now being extensively studied due to the important roles they play in different biological processes. In addition, they were also shown to be implicated in disease such as cancer. Cancer is a complex process which is often defined by a combination of specific processes called cancer hallmarks. In this review, we summarize the literature on circRNAs in cancer and classify them as being implicated in specific cancer hallmarks.

Abstract

Circular RNAs (circRNAs) are noncoding products of backsplicing of pre-mRNAs which have been established to possess potent biological functions. Dysregulated circRNA expression has been linked to diseases including different types of cancer. Cancer progression is known to result from the dysregulation of several molecular mechanisms responsible for the maintenance of cellular and tissue homeostasis. The dysregulation of these processes is defined as cancer hallmarks, and the molecular pathways implicated in them are regarded as the targets of therapeutic interference. In this review, we summarize the literature on the investigation of circRNAs implicated in cancer hallmark molecular signaling. First, we present general information on the properties of circRNAs, such as their biogenesis and degradation mechanisms, as well as their basic molecular functions. Subsequently, we summarize the roles of circRNAs in the framework of each cancer hallmark and finally discuss the potential as therapeutic targets.

Diagnostic efficacy of circular RNAs as noninvasive, liquid biopsy biomarkers for early detection of gastric cancer

BACKGROUND

Majority of gastric cancers (GC) are diagnosed at advanced stages which contributes towards their poor prognosis. In view of this clinical challenge, identification of non-invasive biomarker for early diagnosis is imperative. Herein, we aimed to develop a non-invasive, liquid-biopsy based assay by using circular RNAs (circRNAs) as molecular biomarkers for early detection of GC.

METHODS

We performed systematic biomarker discovery and validation of the candidate circRNAs in matched tissue specimens of GC and adjacent normal mucosa. Next, we translated the discovered circRNA based biomarker panel into serum samples in a training and validation cohort of GC patients (n = 194) and non-disease controls (n = 94) and evaluated their diagnostic performance. In addition, we measured the expression of circRNAs in serum samples of pre- and post-surgical GC patients and evaluated the specificity of circRNAs biomarker panel with respect to other gastro-intestinal (GI) malignancies.

RESULTS

We identified 10-circRNAs in the discovery phase with subsequent validation in a pilot cohort of GC tissue specimens. Using a training cohort of patients, we developed an 8-circRNA based risk-prediction model for the diagnosis of GC. We observed that our biomarker panel robustly discriminated GC patients from non-disease controls with an AUC of 0.87 in the training, and AUC of 0.83 in the validation cohort. Notably, the biomarker panel could robustly identify even early-stage GC patients, regardless of their tumor histology (diffuse vs. intestinal). The decreased expression of circRNAs in post-surgery serum specimens indicated their tumor-specificity and their potential source of origin in the systemic circulation.

CONCLUSIONS

We identified a panel of 8-circRNAs as non-invasive, liquid-biopsy biomarkers which might serve as potential diagnostic biomarkers for the early detection of GC.

Designing strategies of small-molecule compounds for modulating non-coding RNAs in cancer therapy

Non-coding RNAs (ncRNAs) have been defined as a class of RNA molecules transcribed from the genome but not encoding proteins, such as microRNAs, long non-coding RNAs, Circular RNAs, and Piwi-interacting RNAs. Accumulating evidence has recently been revealing that ncRNAs become potential druggable targets for regulation of several small-molecule compounds, based on their complex spatial structures and biological functions in cancer therapy. Thus, in this review, we focus on summarizing some new emerging designing strategies, such as high-throughput screening approach, small-molecule microarray approach, structure-based designing approach, phenotypic screening approach, fragment-based designing approach, and pharmacological validation approach. Based on the above-mentioned approaches, a series of representative small-molecule compounds, including Bisphenol-A, Mitoxantrone and Enoxacin have been demonstrated to modulate or selectively target ncRNAs in different types of human cancers. Collectively, these inspiring findings would provide a clue on developing more novel avenues for pharmacological modulations of ncRNAs with small-molecule drugs for future cancer therapeutics.

CircRNA circTIAM1 promotes papillary thyroid cancer progression through the miR-646/HNRNPA1 signaling pathway

Papillary thyroid cancer (PTC) is a common endocrine tumor with a rapidly increasing incidence in recent years. Although the majority of PTCs are relatively indolent and have a good prognosis, a certain proportion is highly aggressive with lymphatic metastasis, iodine resistance, and easy recurrence. Circular RNAs (circRNAs) are a class of noncoding RNAs that are linked to a variety of tumor processes in several cancers, including PTC. In the current study, circRNA high-throughput sequencing was performed to identify alterations in circRNA expression levels in PTC tissues. circTIAM1 was then selected because of its increased expression in PTC and association with apoptosis, proliferation, and migration of PTC cells in vitro and in vivo. Mechanistically, circTIAM1 acted as a sponge of microRNA-646 and functioned in PTC by targeting miR-646 and heterogeneous ribonucleoprotein A1. Fluorescence in situ hybridization and dual-luciferase reporter assays further confirmed these connections. Overall, our results reveal an important oncogenic role of circTIAM1 in PTC and may represent a potentially therapeutic target against PTC progression.

Circular RNA hsa_circ_0009172 suppresses gastric cancer by regulation of microRNA-485-3p-mediated NTRK3

Gastric cancer is the third leading cause of cancer-related death worldwide, with relapse and metastasis being major contributors to the mortality. Circular RNAs (circRNAs) have been at the center of several researches and some circRNAs have been indicated to be involved in gastric cancer as sponges. Nevertheless, the mechanism underlying the function of circRNA remains largely unclear. Therefore, this study was conducted with the main objective of screening the associated circRNA in gastric cancer and exploring its mechanism. Expression of hsa_circRNA_0009172 was validated in gastric cancer tissues and cell lines after the correlation between hsa_circRNA_0009172 and prognosis was determined. Moreover, the binding site between miR-485-3p and hsa_circRNA_0009172 or NTRK3 was verified using dual luciferase assay and RNA pull down. Function-gain and -loss experiments were performed for the purpose of detecting the effect of hsa_circRNA_0009172 in vivo and in vitro as well as its mechanism with microRNA (miRNA)-485-3p and NTRK3 in gastric cancer. The hsa_circRNA_0009172 expression was downregulated in gastric cancer tissues and cell lines, indicating a positive association with patient prognosis. Functionally, hsa_circ_0009172 overexpression inhibited proliferative, invasive and migrative potential of gastric cancer cells as well as epithelial-mesenchymal transition (EMT)-related proteins by sponging miR-485-3p to inhibit NTRK3, while miR-485-3p overexpression could reverse the inhibitory effect of hsa_circ_0009172 on gastric cancer. Furthermore, either up-regulation of hsa_circ_0009172 or down-regulation of miR-485-3p led to the suppression of xenograft tumor growth in nude mice. In conclusion, hsa_circ_0009172 serves as a tumor suppressor in gastric cancer by targeting miR-485-3p/NTRK3 axis.

Long non-coding RNA LINC00649 regulates YES-associated protein 1 (YAP1)/Hippo pathway to accelerate gastric cancer (GC) progression via sequestering miR-16-5p

Although long non-coding RNA (LncRNA) LINC00649 is reported to be closely associated with acute myeloid leukemia (AML), prostate cancer and colorectal cancer, its role in regulating other types of cancer, such as gastric cancer (GC), has not been studied. This study analyzed the expression status of LINC00649 in GC tissues and cells by performing Real-Time qPCR analysis, and we found that LINC00649 tended to be enriched in cancerous tissues and cells but not in their normal counterparts, which were supported by the data from TCGA dataset. Next, by performing the gain- and loss-of-function experiments, we expectedly found that LINC00649 acted as an oncogene to accelerate GC cell proliferation, migration and epithelial-mesenchymal transition (EMT) in vitro and promote its tumorigenesis in vivo. Moreover, the online miRDB software predicted that miR-16-5p bound to both LINC00649 and 3' untranslated region (3'UTR) of YAP1 mRNA, which were validated by the following dual-luciferase reporter gene system assay and RNA pull-down assay. Finally, we proved that LINC00649 exerted its tumor-promoting effects in GC by regulating the miR-16-5p/YES-associated protein 1 (YAP1)/Hippo pathway. Mechanistically, knock-down of LINC00649 suppressed YAP1 expressions by releasing miR-16-5p, resulting in the recovery of the Hippo pathway, which suppressed the expression levels of the downstream oncogenes, including EGFR, SOX2 and OCT4, leading to the inhibition of the malignant phenotypes in GC cells. In conclusion, this study, for the first time, evidenced that LINC00649 promoted GC progression by targeting the miR-16-5p/YAP1/Hippo signaling pathway, which provided potential diagnostic and therapeutic indicators for GC treatment for clinical utilization.

Hsa_circ_0013290 Acts as Cancer-Promoting Gene in Hepatocellular Carcinoma

Background

As a new class of non-coding RNAs, circRNAs have been recently reported to be involved in the tumorigenesis and progression of human cancers. In the current study, we attempted to explore the potential function of a novel circRNA (hsa_circ_0013290) in hepatocellular carcinoma (HCC).

Methods

Relative hsa_circ_0013290 expression was analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The subcellular location of hsa_circ_0013290 was performed by RNA subcellular isolation and fluorescence in situ hybridization (FISH) assays. The effect of hsa_circ_0013290 on proliferation was detected by Cell Counting Kit-8 (CCK-8) assays. The effect of hsa_circ_0013290 on cell cycle distribution and apoptosis was detected by flow cytometry. The invasion and migration abilities of hsa_circ_0013290 were detected by transwell assays.

Results

Hsa_circ_0013290 is significantly upregulated in HCC cell lines and mainly located in cytoplasm of HCC cells. Hsa_circ_0013290 overexpression promotes cell invasion and migration and inhibits cell apoptosis. In contrast, hsa_circ_0013290 knockdown impedes cell invasion and migration and accelerates cell apoptosis. However, hsa_circ_0013290 did not affect cell proliferation.

Conclusions

Hsa_circ_0013290 is overexpressed in HCC cell lines and is mainly located in the cytoplasm of HCC cells. Hsa_circ_0013290 promotes cell invasion and migration, and inhibits cell apoptosis.

CircRNAs in gastric cancer: current research and potential clinical implications

Gastric cancer (GC) has a dismal prognosis and is also one of the most commonly diagnosed malignancies worldwide. circRNAs are covalently closed circular RNA molecules without 5'-cap and a 3'-tail, currently listed among the broad noncoding RNA family. circRNAs participate in a variety of pathophysiological processes relevant to human diseases, especially malignancies, including GC. Compelling evidence has shown that circRNAs can function by sponging miRNAs, interacting with RNA binding proteins, and encoding proteins or peptides. Yet, our current understanding of these RNA circles remains very limited. Here, we overview the biogenesis, characteristics, functions, and degradation of circRNAs. Moreover, we give an account of the circRNAs that have been linked with GC, describing their functions and mechanisms of action in the context of GC. Next, we discuss the potential value of circRNAs as diagnostic or prognostic GC biomarkers and summarize future prospects, important questions, and challenges of circRNA-based therapeutics.

CircPTK2 inhibits the tumorigenesis and metastasis of gastric cancer by sponging miR-134-5p and activating CELF2/PTEN signaling

BACKGROUND

CircRNAs are a new subset of noncoding RNAs formed by covalent closed loops and play crucial roles in the regulation of cancer gene expression. However, the roles and underlying mechanisms of circRNAs in gastric cancer (GC) remain indistinct. This study aimed to explore the role and mechanism of hsa_circ_0006421 (circPTK2) in GC.

METHODS

The differential expression of circRNAs between GC tissues and adjacent normal tissues were identified by a circRNA expression profiling. Associations of circPTK2 or miR-134-5p expression with clinicopathological characteristics and prognosis of GC patients were analyzed by chi-square of Fisher's exact tests and Kaplan-Meier analysis. CCK8, colony formation, EdU assays and animal models were performed to assess the effects of circPTK2 on proliferation and invasion of GC cells. CircPTK2-specific probes were used to purify the RNA pulled down from the circPTK2, and enrichment of circPTK2 and miR-134-5p was detected by qRT-PCR. The effects of circPTK2 on miR-134-5p expression and CELF2/PTEN signaling were examined by qRT-PCR and Western blotting analysis.

RESULTS

Low expression of circPTK2 and high expression of miR-134-5p were related to the poor survival, and high expression of miR-134-5p was related to the tumor recurrence in GC patients. Overexpressing circPTK2 suppressed the proliferation, colony formation, DNA synthesis and cell invasion as well as xenograft tumor growth and lung metastasis in vitro and in vivo, whereas silencing circPTK2 had the opposite effects. Moreover, circPTK2 was negatively correlated and co-localized with miR-134-5p in the cytoplasm of GC tissue cells. circPTK2 bound to and sponged miR-134-5p in GC cells, and miR-134-5p facilitated cell growth and invasion but attenuated circPTK2 induced tumor suppressive effects and CELF2/PTEN signaling activation in GC cells.

CONCLUSIONS

circPTK2 functions as a tumor suppressor in GC by sponging miR-134-5p and activating the CELF2/PTEN axis.

Circular RNAs in cell cycle regulation: Mechanisms to clinical significance

Circular RNAs (circRNAs), a type of non‐coding RNA, are single‐stranded circularized molecules characterized by high abundance, evolutionary conservation and cell development‐ and tissue‐specific expression. A large body of studies has found that circRNAs exert a wide variety of functions in diverse biological processes, including cell cycle. The cell cycle is controlled by the coordinated activation and deactivation of cell cycle regulators. CircRNAs exert mutifunctional roles by regulating gene expression via various mechanisms. However, the functional relevance of circRNAs and cell cycle regulation largely remains to be elucidated. Herein, we briefly describe the biogenesis and mechanistic models of circRNAs and summarize their functions and mechanisms in the regulation of critical cell cycle modulators, including cyclins, cyclin‐dependent kinases and cyclin‐dependent kinase inhibitors. Moreover, we highlight the participation of circRNAs in cell cycle‐related signalling pathways and the clinical value of circRNAs as promising biomarkers or therapeutic targets in diseases related to cell cycle disorder.

Contribution of circRNAs in gastric cancer

Gastric cancer (GC) is one of the most commonly diagnosed neoplasms in the world. A number of environmental and lifestyle factors, particularly chronic infection with Helicobacter pylori, have been found to partake in the pathogenesis of GC. The advent of high-throughput genome and transcriptome analysis has enhanced the knowledge about molecular mechanisms of the pathogenesis of GC. However, data regarding the expression of several circRNAs, such as circLMTK2, are not consistent. We explain the role of circRNAs in the development of GC. We searched databases for the newest publications using the terms gastric cancer and circRNA. Each circRNA alteration, downstream targets, its impacts on cancer cells, and the prognostic and diagnostic roles of these circRNAs have been discussed. Taken together, circRNAs can be putative biomarkers in GC and potential targets for the treatment of this cancer. Yet, this field is still in its infancy and needs further experiments for reaching the clinical application. As these transcripts are stable in circulation, they can be used in non-invasive methods of cancer detection and patients' follow-up.

miR-497 defect contributes to gastric cancer tumorigenesis and progression via regulating CDC42/ITGB1/FAK/PXN/AKT signaling

Gastric cancer (GC) is one of the leading causes of cancer-related death worldwide. MicroRNAs (miRNAs) are known to be important regulators of GC. This study aims to investigate the role of miRNA (miR)-497 in GC. We demonstrated that the expression of miR-497 was downregulated in human GC tissues. After N-methyl-N-nitrosourea treatment, the incidence of GC in miR-497 knockout mice was significantly higher than that in wild-type mice. miR-497 overexpression suppressed GC cell proliferation, cell-cycle progression, colony formation, anti-apoptosis ability, and cell migration and invasion capacity. Additionally, miR-497 overexpression decreased the expression levels of cell division cycle 42 (CDC42) and integrin β1 (ITGB1) and inhibited the phosphorylation of focal adhesion kinase (FAK), paxillin (PXN), and serine-threonine protein kinase (AKT). Furthermore, overexpression of miR-497 inhibited the metastasis of GC cells in vivo, which could be counteracted by CDC42 restoration. Furthermore, the focal adhesion of GC cells was found to be regulated by miR-497/CDC42 axis via ITGB1/FAK/PXN/AKT signaling. Collectively, it is concluded that miR-497 plays an important role in the repression of GC tumorigenesis and progression, partly via the CDC42/ITGB1/FAK/PXN/AKT pathway.

The Use of circRNAs as Biomarkers of Cancer

CircRNAs are a subclass of lncRNAs that have been found to be abundantly present in a wide range of species, including humans. CircRNAs are generally produced by a noncanonical splicing event called backsplicing that is dependent on the canonical splicing machinery, giving rise to circRNAs classified into three main categories: exonic circRNA, circular intronic RNA, and exon-intron circular RNA. Notably, circRNAs possess functional importance and display their functions through different mechanisms of action including sponging miRNAs, or even being translated into functional proteins. In addition, circRNAs also have great potential as biomarkers, particularly in cancer, thanks to their high stability, tissue type and developmental stage specificity, and their presence in biological fluids, which make them promising candidates as noninvasive biomarkers. In this chapter, we describe the most commonly used techniques for the study of circRNAs as cancer biomarkers, including high-throughput techniques such as RNA-Seq and microarrays, and other methods to analyze the presence of specific circRNAs in patient samples.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

Circular RNAs regulate cancer-related signaling pathways and serve as potential diagnostic biomarkers for human cancers

Circular RNAs (circRNAs) are RNAs that have an important role in various pathological processes, including cancer. After the usage of high-throughput RNA sequencing, many circRNAs were found to be differentially expressed in various cancer cell lines and regulate cell signaling pathways by modulating particular gene expressions. Understanding their role in these pathways and what cancers they are found in can set the stage for identifying diagnostic and prognostic biomarkers and therapeutic targets of cancer. This paper will discuss which circRNAs are found in different cancers and what mechanisms they use to upregulate or downregulate certain cellular components.

Exosomal circRNA as a novel potential therapeutic target for multiple myeloma-related myocardial damage

Introduction

Myocardial damage is a mostly incurable complication of multiple myeloma (MM) that seriously affects the treatment outcome and quality of life of patients. Exosomal circular RNAs (exo-circRNAs) play an important role in tumor occurrence and development and are considered key factors in MM pathogenesis. However, the role and mechanism of action of exo-circRNAs in MM-related myocardial damage are still unclear. This study aimed to investigate correlations between exo-circRNAs and MM and to preliminarily explore the role of exo-circRNAs in MM-related myocardial damage.

Methods

Six MM patients and five healthy controls (HCs) were included in the study. High-throughput sequencing and qRT-PCR verification were used to obtain a profile of abnormally expressed exo-circRNAs. GO, KEGG, miRanda, TargetScan and Metascape were used for bioinformatics analyses. H9C2 cells treated with exosomes from U266 cells were used in cell experiments. CCK-8, PCR, immunofluorescence and western blotting assays were used to detect cell proliferation and expression of autophagy-related indicators. Electron microscopy was used to observe the number of autophagic vesicles.

Results

Bioinformatics analysis showed that circRNAs with upregulated expression had the potential to promote MM-related myocardial damage. In addition, PCR results confirmed that circ-G042080 was abundantly expressed in the serum exosomes of 20 MM patients. Correlation analysis showed that the expression level of circ-G042080 was positively correlated with the clinical level of MM and MM-related myocardial damage and that circ-G042080 might interfere with MM-related myocardial damage through a downstream miRNA/TLR4 axis. Cell experiments demonstrated that the circ-G042080/hsa-miR-4268/TLR4 axis might exist in H9C2 cells incubated with exosomes and cause abnormal autophagy.

Conclusion

Abnormal expression of serum exo-circRNAs was found to be associated with MM-related myocardial damage, suggesting that exo-circRNAs might become a new diagnostic marker of MM-related myocardial damage and a therapeutic target.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02011-w.

Identification of circRNA-miRNA-mRNA networks contributes to explore underlying pathogenesis and therapy strategy of gastric cancer

Background

Circular RNAs (circRNAs) are a new class of noncoding RNAs that have gained increased attention in human tumor research. However, the identification and function of circRNAs are largely unknown in the context of gastric cancer (GC). This study aims to identify novel circRNAs and determine their action networks in GC.

Methods

A comprehensive strategy of data mining, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and computational biology were conducted to discover novel circRNAs and to explore their potential mechanisms in GC. Promising therapeutic drugs for GC were determined by connectivity map (CMap) analysis.

Results

Six overlapped differentially expressed circRNAs (DECs) were screened from selected microarray and RNA-Seq datasets of GC, and the six DECs were then validated by sanger sequencing and RNase R treatment. Subsequent RT-qPCR analysis of GC samples confirmed decreased expressions of the six DECs (hsa_circ_0000390, hsa_circ_0000615, hsa_circ_0001438, hsa_circ_0002190, hsa_circ_0002449 and hsa_circ_0003120), all of which accumulated preferentially in the cytoplasm. MiRNA binding sites and AGO2 occupation of the six circRNAs were predicted using online databases, and circRNA–miRNA interactions including the six circRNAs and 33 miRNAs were determined. Then, 5320 target genes of the above 33 miRNAs and 1492 differently expressed genes (DEGs) from The Cancer Genome Atlas (TCGA) database were identified. After intersecting the miRNA target genes and the 889 downregulated DEGs, 320 overlapped target genes were acquired. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis indicated that these target genes were related to two critical tumor-associated signaling pathways. A protein–protein interaction network with the 320 target genes was constructed using STRING, and fifteen hubgenes (ATF3, BTG2, DUSP1, EGR1, FGF2, FOSB, GNAO1, GNAI1, GNAZ, GNG7, ITPR1, ITPKB, JUND, NR4A3, PRKCB) in the network were identified. Finally, bioactive chemicals (including vorinostat, trichostatin A and astemizole) based on the fifteen hubgenes were identifed as therapeutic agents for GC through the CMap analysis.

Conclusions

This study provides a novel insight for further exploration of the pathogenesis and therapy of GC from the circRNA-miRNA-mRNA network perspective.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02903-5.

Circular RNA circPVT1 Contributes to Doxorubicin (DXR) Resistance of Osteosarcoma Cells by Regulating TRIAP1 via miR-137

Background

Chemoresistance is a major obstacle to the treatment of osteosarcoma patients. Circular RNA (circRNA) circPVT1 has been reported to be related to the doxorubicin (DXR) resistance in osteosarcoma. This study is designed to explore the role and mechanism of circPVT1 in the DXR resistance of osteosarcoma.

Methods

circPVT1, microRNA-137 (miR-137), and TP53-regulated inhibitor of apoptosis 1 (TRIAP1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). The protein levels of ATP-binding cassette, subfamily C, member 1 (ABCC1), multidrug resistance-associated protein 1 (MRP-1), cleaved- (c-) caspase-3, B-cell lymphoma-2 (Bcl-2), and TRIAP1 were examined by a western blot assay. Cell viability, proliferation, and apoptosis were detected by cell counting kit-8 (CCK-8), colony formation, and flow cytometry assays, severally. The binding relationship between miR-137 and circPVT1 or TRIAP1 was predicted by starbase 3.0 and then verified by dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. The biological role of circPVT1 in osteosarcoma tumor growth and drug resistance was examined by the xenograft tumor model in vivo. Results. circPVT1 and TRIAP1 were highly expressed, and miR-137 was decreased in DXR-resistant osteosarcoma tissues and cells. Moreover, circPVT1 knockdown could boost DXR sensitivity by inhibiting DXR-caused proliferation and DXR-induced apoptosis in DXR-resistant osteosarcoma cells in vitro. The mechanical analysis discovered that circPVT1 acted as a sponge of miR-137 to regulate TRIAP1 expression. circPVT1 silencing increased the drug sensitivity of osteosarcoma in vivo. Conclusion. circPVT1 boosted DXR resistance of osteosarcoma cells partly by regulating the miR-137/TRIAP1 axis, hinting a promising therapeutic target for the osteosarcoma treatment.

The circACC1/miR-29c-3p/FOXP1 network plays a key role in gastric cancer by regulating cell proliferation

Although substantial progress has been made in early detection and treatment of GC, this disease remains a major burden worldwide. CircRNAs have potential as prognostic and diagnostic biomarkers in tumorigenesis. Therefore, we aimed to clarify the role and mechanism of circACC1 in GC cell proliferation. The expression levels of circACC1, miR-29c-3p and FOXP1 were validated in GC tissue samples and adjacent tissue samples. The impact of circACC1 and miR-29c-3p on overall survival was evaluated in GC specimens. A functional study was performed on MKN-45 and BGC823 cells transfected with different vectors. Cell proliferation was assayed by CCK-8 and colony formation assays. The interactions among circACC1, miR-29c-3p and FOXP1 were tested by RNA immunoprecipitation and luciferase reporter assays. This study demonstrated that circACC1 is upregulated in GC tissues, and its upregulation predicts poorer OS in GC patients. Upregulation of circACC1 promoted GC cell proliferation, as indicated by CCK-8 and colony formation assays. A mechanistic study revealed that the pro-oncogenic effect of circACC1 was mainly caused by binding to miR-29c-3p, thus regulating expression of its downstream target FOXP1. The circACC1/miR-29c-3p/FOXP1 network plays a key role in gastric cancer by regulating cell proliferation.

CircANKRD52 Promotes the Tumorigenesis of Hepatocellular Carcinoma by Sponging miR-497-5p and Upregulating BIRC5 Expression

CircRNAs participate in the pathogenesis of a variety of cancers. Previous studies showed that baculoviral IAP repeat containing 5 (BIRC5) can promote tumor progression. But, the mechanisms by which circRNAs regulate BIRC5 expression in hepatocellular carcinoma (HCC) remain unknown. The clinical prognosis of BIRC5 or miR-497-5p expression in patients with HCC was assessed by TCGA RNA-seq dataset. hsa_circ_0026939 (circANKRD52) or BIRC5 was identified to bind with miR-497-5p by luciferase gene report, RIP and circRIP assays. MTT, colony formation, Transwell assays and a xenograft tumor model were used to estimate the role of miR-497-5p or circANKRD52 in HCC cells. As a result, we found that elevated expression of BIRC5 or decreased expression of miR-497-5p was linked to poor survival in HCC. Restored expression of miR-497-5p repressed cell proliferation, colony formation and invasiveness by targeting BIRC5, but its inhibitor showed the opposite results. Furthermore, circANKRD52 possessed a tumor-promoting effect by acting as a sponge of miR-497-5p and thereby upregulated BIRC5 in HCC cells. In conclusion, our findings demonstrated that circANKRD52 enhances the tumorigenesis of HCC by sponging miR-497-5p and upregulating BIRC5 expression.

Circular RNA CircEPB41L2 Functions as Tumor Suppressor in Hepatocellular Carcinoma Through Sponging miR-590-5p

Background

Circular RNAs (circRNAs) could interact with miRNAs to regulate gene expression, participating in hepatocellular carcinoma (HCC) initiation and development. This work aimed to determine the potential function and molecular mechanism of circEPB41L2 (hsa_circ_0077837) during HCC progression.

Materials and Methods

The expression of circEPB41L2 in HCC tissues and HCC cell lines was quantified using real-time quantitative PCR (qRT-PCR). CCK-8 assays and colony formation assays were utilized to detect the proliferation of HCC cells. Wound healing assay and transwell assay were performed to determine the capability of migration and invasion for HCC cells. Western blot was conducted to determine gene expression on protein levels. The effect of circEPB41L2 on HCC in vivo was investigated via xenograft experiment. Interaction between circEPB41L2 and miR-590-5p was predicted through bioinformatics methods and confirmed via luciferase reporter assay.

Results

Extensive analysis of circRNA profiles in tumor and matched para-tumor tissues collected from 61 HCC patients identified that circEPB41L2 was significantly down-regulated in HCC, which was further confirmed in another HCC group by qRT-PCR analysis. The clinicopathological analysis revealed that down-regulation of circEPB41L2 was negatively associated with tumor size, vascular invasion and alpha-fetoprotein, while positively correlated with HCC prognosis. The biological function experiments showed that overexpression of circEPB41L2 could obviously inhibit the proliferation and metastasis of HCC cells in vitro, while knockdown of circEPB41L2 induced opposite results. Moreover, we also found that circEPB41L2 inhibited HCC migration and invasion though EMT signaling pathway. Similarly, overexpression of circEPB41L2 can also significantly inhibit the proliferation of HCC cells in vivo. Bioinformatic analysis and luciferase reporter assay revealed that circEPB41L2 interacts directly with miR-590-5p and the corresponding biological functions were also verified in miRNA rescue experiments.

Conclusion

Our results suggest that circEPB41L2 might function as a tumor suppressor during HCC progression by sponging miR-590-5p.

The m6A Reader YTHDF1 Facilitates the Tumorigenesis and Metastasis of Gastric Cancer via USP14 Translation in an m6A-Dependent Manner

Objectives

N⁶-methyladenosine (m⁶A) RNA methylation is implicated in the progression of multiple cancers via influencing mRNA modification. YTHDF1 can act as an oncogene in gastric cancer (GC), while the biological mechanisms via which YTHDF1 regulates gastric tumorigenesis through m⁶A modification remain largely unknown.

Methods

GEO and TCGA cohorts were analyzed for differentially expressed m⁶A modification components in GC clinical specimens and their association with clinical prognosis. Transwell and flow cytometry assays as well as subcutaneous xenograft and lung metastasis models were used to evaluate the phenotype of YTHDF1 in GC. Intersection of RNA/MeRIP-seq, luciferase assay, RIP-PCR, RNA pull-down and MeRIP-PCR was used to identify YTHDF1- modified USP14 and its m⁶A levels in GC cells.

Results

High-expressed YTHDF1 was found in GC tissues and was related to poor prognosis, acting as an independent prognostic factor of poor survival in GC patients. YTHDF1 deficiency inhibited cell proliferation and invasion (in vitro), and gastric tumorigenesis and lung metastasis (in vivo) and also induced cell apoptosis. Intersection assays revealed that YTHDF1 promoted USP14 protein translation in an m⁶A-dependent manner. USP14 upregulation was positively correlated with YTHDF1 expression and indicated a poor prognosis in GC.

Conclusion

Our data suggested that m⁶A reader YTHDF1 facilitated tumorigenesis and metastasis of GC by promoting USP14 protein translation in an m⁶A-dependent manner and might provide a potential target for GC treatment.

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

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

Circular RNA 0081146 facilitates the progression of gastric cancer by sponging miR-144 and up-regulating HMGB1

OBJECTIVES

Recent studies have revealed that circular RNA (circRNA) plays a pivotal role in cancer development. The study aimed to investigate the role of circ_0081146 in gastric cancer (GC).

RESULTS

Circ_0081146 was upregulated in GC tissues and cells. Patients with high expression of circ_0081146 had a significantly reduced 5-year overall survival rate. Circ_0081146 knockdown restrained the growth, migration and invasion of GC cells in vitro as well as tumorigenesis in vivo. Circ_0081146 targeted miR-144 and HMGB1 was targeted by miR-144. Circ_0081146 was negatively correlated with miR-144 expression, while positively correlated with HMGB1 expression in GC tissues. Moreover, the inhibitory effect of circ_0081146 knockdown on the progression of GC cells were reversed by silencing miR-144 or HMGB1 overexpression. Mechanically, circ_0081146 increased HMGB1 expression by targeting miR-144.

CONCLUSION

Circ_0081146 functions as an oncogene in GC to promote cell growth, migration and invasion via modulating the miR-144/HMGB1 axis.

Circular RNA circRUNX1 promotes papillary thyroid cancer progression and metastasis by sponging MiR-296-3p and regulating DDHD2 expression

Papillary thyroid cancer (PTC) has a continuously increasing incidence and imposes a heavy medical burden to individuals and society due to its high proportion of lymph node metastasis and recurrence in recent years. Circular RNAs, a class of noncoding RNAs, participate in the progression of many cancers, but the role of circRNAs in PTC is still rarely reported. In this study, circRNA deep sequencing was performed to identify differentially expressed circRNAs in PTC. CircRUNX1 was selected for its high expression in PTC, and circRUNX1 silencing was directly associated with the week potential for migration, invasion and proliferation of PTC in vivo and in vitro. Fluorescence in situ hybridization (FISH) was further used to confirm the cytoplasmic localization of circRUNX1, indicating the possible function of circRUNX1 as a ceRNAs in PTC progression through miRNA binding. MiR-296-3p was then confirmed to be regulated by circRUNX1 and to target DDHD domain containing 2 (DDHD2) by luciferase reporter assays. The strong antitumor effect of miR-296-3p and the tumor-promoting effect of DDHD2 were further investigated in PTC, indicating that circRUNX1 modulates PTC progression through the miR-296-3p/DDHD2 pathway. Overall, circRUNX1 plays an oncogenic role in PTC and provides a potentially effective therapeutic strategy for PTC progression.

Circular RNA circDLC1 inhibits MMP1-mediated liver cancer progression via interaction with HuR

Rationale: circular RNAs (circRNAs) have been demonstrated to play a crucial role in cancer progression. KIAA1429, a key component of the m6A methyltransferase complex, has recently been reported to promote hepatocellular carcinoma (HCC) progression by regulating the m6A methylation. The aim of present study is to investigate the role of circular RNAs in KIAA1429-mediated HCC progression. Methods: RNA sequencing (RNA-seq) and methylated RNA immunoprecipitation sequencing (m6A-seq) were utilized to identify KIAA1429-regulated circRNAs. The effects of circDLC1 on proliferation and metastasis of hepatoma cells were examined in vitro and in vivo. RT-qPCR was used to measure the expression of circDLC1 in HCC tissues and hepatoma cells. RNA FISH, RIP assays and biotin-labeled RNA pull-down were used to investigate the downstream effector of circDLC1. The downstream targets of circDLC1 were identified using RNA-seq. Results: Our data demonstrated that circDLC1 was downregulated in HCC tissues and closely relevant to favorable prognosis. Overexpression of circDLC1 inhibited the proliferation and motility of hepatoma cells in vitro and in vivo, while silencing of circDLC1 played the opposite role. Mechanistic investigations revealed that circDLC1 could bind to RNA-binding protein HuR, which subsequently reduced the interaction between HuR and MMP1 mRNAs, and thus inhibited the expression of MMP1, ultimately contributing to inhibition of HCC progression. Conclusion: Our work suggests that circDLC1, a downstream target of KIAA1429, is a promising prognostic marker for HCC patients, and the circDLC1-HuR-MMP1 axis may serve as a potential therapeutic target for HCC treatment.

Circular RNAs as important players in human gastric cancer

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

hsa_circ_0023409 Accelerates Gastric Cancer Cell Growth and Metastasis Through Regulating the IRS4/PI3K/AKT Pathway

Gastric cancer (GC) is a big threat to human life and health. Circular RNAs (circRNAs), a subclass of noncoding RNAs, were reported to play a critical role in GC progression. Here, we investigated the role of a novel circRNA named hsa_circ_0023409 in GC and its mechanism. Hsa_circ_0023409 expression in GC and adjacent tissues was examined by quantitative real-time polymerase chain reaction and in situ hybridization. The functions of hsa_circ_0023409 in GC cells were assessed both in vitro and in vivo. Immunofluorescence staining was performed for the localization of hsa_circ_0023409 and miR-542-3p in cells. The interaction between hsa_circ_0023409 and miR-542-3p, and miR-542-3p and insulin receptor substrate 4 (IRS4) was detected by dual-luciferase reporter assay. The effect of hsa_circ_0023409, miR-542-3p, and IRS4 on IRS4/phosphatidylinositol 3-kinase (PI3K)/AKT pathway was detected by western blot. The results showed that hsa_circ_0023409 was mainly located in cytoplasm and highly expressed in GC tissues and cells. Moreover, hsa_circ_0023409 showed positive correlation with tumor size, histological grade, and tumor-node-metastasis staging of GC patients. Functional studies showed that hsa_circ_0023409 promoted cell viability, proliferation, migration, and invasion and suppressed apoptosis in GC. Mechanism studies demonstrated that hsa_circ_0023409 upregulated IRS4 via sponging miR-542-3p in GC cells. Furthermore, IRS4 overexpression activated the PI3K/AKT pathway and reversed the inhibitory effect of hsa_circ_0023409 knockdown on the PI3K/AKT pathway. Taken together, we prove that hsa_circ_0023409 activates IRS4/PI3K/AKT pathway by acting as a sponge for miR-542-3p, thus promoting GC progression, indicating that hsa_circ_0023409 may serve as a potential target for treatment of GC and prognosis of GC patients.

Circular RNAs emerge as important regulators with great potential for clinical application in gastric cancer

Gastric cancer (GC) is a common digestive malignancy with a high-ranking morbidity and mortality. Therefore, it is urgent to identify novel indicators and develop new strategies for clinical diagnosis and treatment of GC. As a type of noncoding RNA, circular RNAs (circRNAs) have received increased attention in GC during recent years. To more comprehensively understand current research progress on circRNAs in GC, in this review, we introduce basic knowledge of circRNAs, summarize abnormally expressed circRNAs and discuss their functions and regulatory molecular mechanisms in GC. Then, we review potential applications of circRNAs for GC diagnosis, prognosis and treatment. Finally, we conclude by highlighting major advancements of circRNAs in GC research, and we discuss existing challenges and possible future research directions of GC-associated circRNAs.