Circular RNA USP1 regulates the permeability of blood-tumour barrier via miR-194-5p/FLI1 axis

Roles of circular RNAs in regulating the development of glioma

BACKGROUND

Glioma is the most common malignant tumor in the central nervous system. In patients with glioma, the prognosis is poor and median survival is only 12-15 months. With the recent development of sequencing technology, important roles of noncoding RNAs are being discovered in cells, especially those of circular RNAs (circRNAs). Because circRNAs are stable, abundant, and highly conserved, they are regarded as novel biomarkers in the early diagnosis and prognosis of diseases.

PURPOSE

In this review, roles and mechanisms of circRNAs in the development of glioma are summarized.

METHODS

This paper collects and reviews relevant PubMed literature.

CONCLUSION

Several classes of circRNAs are highly expressed in glioma and are associated with malignant biological behaviors of gliomas, including proliferation, migration, invasion, apoptosis, angiogenesis, and drug resistance. Further studies are needed to clarify the roles of circRNAs in glioma and to determine whether it is possible to increase therapeutic effects on tumors through circRNA intervention.

CircRNA: An emerging star in the progression of glioma

Circular RNAs (circRNAs), a class of single-stranded noncoding RNAs with a covalently closed loop structure, are recognized as promising biomarkers and targets for diagnosing and treating dozens of diseases, especially cancers. CircRNAs are extremely stable, abundant and conserved and have tissue- or developmental stage-specific expression. Currently, the biogenesis and biological functions of circRNAs have been increasingly revealed with deep sequencing and bioinformatics. Studies have indicated that circRNAs are frequently expressed in brain tissues and that their expression levels change in different stages of neural development, suggesting that circRNAs may play an important role in diseases of the nervous system, such as glioma. However, because the biogenesis and functions of circRNAs do not depend on a single mechanism but are coregulated by multiple factors, it is necessary to further explore the underlying mechanisms. In this review, we summarized the classification, mechanisms of biogenesis and biological functions of circRNAs. Meanwhile, we emphatically expounded on the process of abnormal expression of circRNAs, methods used in circRNA research, and their effects on the malignant biological capabilities of glioma.

Non-coding RNAs in the regulation of blood–brain barrier functions in central nervous system disorders

The blood–brain barrier (BBB) is an essential component of the neurovascular unit that controls the exchanges of various biological substances between the blood and the brain. BBB damage is a common feature of different central nervous systems (CNS) disorders and plays a vital role in the pathogenesis of the diseases. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNA (lncRNAs), and circular RNAs (circRNAs), are important regulatory RNA molecules that are involved in almost all cellular processes in normal development and various diseases, including CNS diseases. Cumulative evidences have demonstrated ncRNA regulation of BBB functions in different CNS diseases. In this review, we have summarized the miRNAs, lncRNAs, and circRNAs that can be served as diagnostic and prognostic biomarkers for BBB injuries, and demonstrated the involvement and underlying mechanisms of ncRNAs in modulating BBB structure and function in various CNS diseases, including ischemic stroke, hemorrhagic stroke, traumatic brain injury (TBI), spinal cord injury (SCI), multiple sclerosis (MS), Alzheimer's disease (AD), vascular cognitive impairment and dementia (VCID), brain tumors, brain infections, diabetes, sepsis-associated encephalopathy (SAE), and others. We have also discussed the pharmaceutical drugs that can regulate BBB functions via ncRNAs-related signaling cascades in CNS disorders, along with the challenges, perspective, and therapeutic potential of ncRNA regulation of BBB functions in CNS diseases.

The role of ubiquitin-specific peptidases in glioma progression

The balance between ubiquitination and deubiquitination is crucial for protein stability, function and location under physiological conditions. Dysregulation of E1/E2/E3 ligases or deubiquitinases (DUBs) results in malfunction of the ubiquitin system and is involved in many diseases. Increasing reports have indicated that ubiquitin-specific peptidases (USPs) play a part in the progression of many kinds of cancers and could be good targets for anticancer treatment. Glioma is the most common malignant tumor in the central nervous system. Clinical treatment for high-grade glioma is unsatisfactory thus far. Multiple USPs are dysregulated in glioma and have the potential to be therapeutic targets. In this review, we collected studies on the roles of USPs in glioma progression and summarized the mechanisms of USPs in glioma tumorigenesis, malignancy and chemoradiotherapy resistance.

Research Progress on Circular RNA in Glioma

The discovery of circular RNA (circRNA) greatly complements the traditional gene expression theory. CircRNA is a class of non-coding RNA with a stable cyclic structure. They are highly expressed, spatiotemporal-specific and conservative across species. Importantly, circRNA participates in the occurrence of many kinds of tumors and regulates the tumor development. Glioma is featured by limited therapy and grim prognosis. Cancer-associated circRNA compromises original function or creates new effects in glioma, thus contributing to oncogenesis. Therefore, this article reviews the biogenesis, metabolism, functions and properties of circRNA as a novel potential biomarker for gliomas. We elaborate the expression characteristics, interaction between circRNA and other molecules, aiming to identify new targets for early diagnosis and treatment of gliomas.

Noncoding RNAs in tumor metastasis: molecular and clinical perspectives

Metastasis is the main culprit of cancer-associated mortality and involves a complex and multistage process termed the metastatic cascade, which requires tumor cells to detach from the primary site, intravasate, disseminate in the circulation, extravasate, adapt to the foreign microenvironment, and form organ-specific colonization. Each of these processes has been already studied extensively for molecular mechanisms focused mainly on protein-coding genes. Recently, increasing evidence is pointing towards RNAs without coding potential for proteins, referred to as non-coding RNAs, as regulators in shaping cellular activity. Since those first reports, the detection and characterization of non-coding RNA have explosively thrived and greatly enriched the understanding of the molecular regulatory networks in metastasis. Moreover, a comprehensive description of ncRNA dysregulation will provide new insights into novel tools for the early detection and treatment of metastatic cancer. In this review, we focus on discussion of the emerging role of ncRNAs in governing cancer metastasis and describe step by step how ncRNAs impinge on cancer metastasis. In particular, we highlight the diagnostic and therapeutic applications of ncRNAs in metastatic cancer.

Curcumin suppresses the progression of gastric cancer by regulating circ_0056618/miR-194-5p axis

Curcumin has been demonstrated to be an anti-tumor agent in many types of cancers, including gastric cancer (GC). However, the molecular mechanisms by which curcumin performs its anti-tumor effects remain elusive. circ_0056618 and miR-194-5p are reported to be involved in GC progression, but their relationships with curcumin are unclear. In this study, circ_0056618 was elevated, and miR-194-5p was reduced in GC tissues and cells. Curcumin treatment led to a decrease in circ_0056618 level in GC cells. Overexpression of circ_0056618 promoted cell proliferation, migration, and invasion and suppressed cell cycle arrest and apoptosis in curcumin-treated GC cells. Moreover, miR-194-5p was identified as the target of circ_0056618, and its expression in GC cells increased after curcumin treatment. Overexpression of miR-194-5p reversed the promotional effect of circ_0056618 on cell progression in curcumin-treated GC cells. Additionally, curcumin treatment repressed the tumorigenesis of GC in vivo through regulating circ_0056618. Curcumin treatment delayed the development of GC partly through decreasing circ_0056618 and increasing miR-194-5p.

Effect of circular RNA, mmu_circ_0000296, on neuronal apoptosis in chronic cerebral ischaemia via the miR-194-5p/Runx3/Sirt1 axis

Chronic cerebral ischaemia (CCI) is a common pathological disorder, which is associated with various diseases, such as cerebral arteriosclerosis and vascular dementia, resulting in neurological dysfunction. As a type of non-coding RNA, circular RNA is involved in regulating the occurrence and development of diseases, such as ischaemic brain injury. Here, we found that HT22 cells and hippocampus treated with CCI had low expression of circ_0000296, Runx3, Sirt1, but high expression of miR-194-5p. Overexpression of circ_0000296, Runx3, Sirt1, and silenced miR-194-5p significantly inhibited neuronal apoptosis induced by CCI. This study demonstrated that circ_0000296 specifically bound to miR-194-5p; miR-194-5p bound to the 3'UTR region of Runx3 mRNA; Runx3 directly bound to the promoter region of Sirt1, enhancing its transcriptional activity. Overexpression of circ_0000296 by miR-194-5p reduced the negative regulatory effect of miR-194-5p on Runx3, promoted the transcriptional effect of Runx3 on Sirt1, and inhibited neuronal apoptosis induced by CCI. mmu_circ_0000296 plays an important role in regulating neuronal apoptosis induced by CCI through miR-194-5p/Runx3/Sirt1 pathway.

Tight junctions and their regulation by non-coding RNAs

Tight junction (TJ) is a “zippering up” junction structure located at the uppermost portion of adjacent epithelial/endothelial cells in organs and tissues. TJs maintain the relative stability of intracellular substances and functions by closing or opening intercellular pathways, coordinating the entry and exit of molecules of different sizes and charges, and regulating the permeability of paracellular barrier. TJs also prevent microbial invasion, maintain epithelial/endothelial cell polarity, and regulate cell proliferation. TJs are widely present in the skin and mucosal epithelial barriers, intestinal epithelial barrier, glomerular filtration barrier, bladder epithelial barrier, blood-brain barrier, brain-blood tumor barrier, and blood-testis barrier. TJ dysfunction in different organs can lead to a variety of diseases. In addition to signal pathways, transcription factors, DNA methylation, histone modification, TJ proteins can also be regulated by a variety of non-coding RNAs, such as micro-RNAs, long-noncoding RNAs, and circular RNAs, directly or indirectly. This review summarizes the structure of TJs and introduces the functions and regulatory mechanisms of TJs in different organs and tissues. The roles and mechanisms of non-coding RNAs in the regulation of TJs are also highlighted in this review.

Silencing circ-USP1 protects the renal tubular from kidney injury induced by hypoxia via modulating miR-194-5p/DNMT3A axis in acute renal allografts

Recent studies indicate that circular RNAs are involved in dysregulation of kidney injury. Nevertheless, the underlying mechanisms remain largely unclear. Therefore, this study sought to investigate the role of circ-USP1 in the pathogenesis of early renal allografts. Thirty-two male C57BL/6J mice aged between 6 and 8 weeks were divided into the sham and allograft groups. Thereafter, the association between miR-194-5p, circ-USP1 and DNMT3A was confirmed using a combination of bioinformatics and the luciferase reporter gene assay. Additionally, the expression of circ-USP1, miR-194-5p and DNMT3A mRNA was detected through qPCR. Afterwards, the Western blot assay was performed to examine the expression of DNMT3A protein. Finally, the TUNEL assay was conducted to determine the rate of apoptosis in DNMT3A cells. The expression of circ-USP1 increased, while that of miR-194-5p decreased in renal allografts. Additionally, silencing circ-USP1 reduced kidney injuries caused by renal allografts in mice. Moreover, miR-194-5p was a target for circ-USP1, and DNMT3A was a target of miR-194-5p. Finally, it was shown that silencing circ-USP1 reduced DNMT3A expression in the kidney of mice that received renal allografts. Circ-USP1 functions as a competing endogenous RNA for miR-194-5p. This occurs in order to regulate DNMT3A expression in kidney injury induced by hypoxia in acute renal allografts.

Circular RNA circ_0003645 silencing alleviates inflammation and apoptosis via the NF-κB pathway in endothelial cells induced by oxLDL

Atherosclerosis (AS) is a serious threat to the cardiovascular system. Circular RNA circ_0003645 was found to be differentially expressed in the process of AS. Our study tried to unravel the effect and underlying mechanism of circ_0003645 in endothelial cells treated with oxidized low-density lipoprotein (oxLDL). Si-RNAs and over-circ0003645 were transfected into human umbilical vein endothelial cells (HUVECs), and the expression levels of circ_0003645 and NF-κB mRNA were measured. The protein level of NF-κB, lactate dehydrogenase leakage (LDH leakage), cell viability, and apoptosis were detected. Further, the expression of interleukin (IL)-6, tumor necrosis factor (TNF)-α, ICAM-1, and VCAM-1 were measured. Circ_0003645 was found up-regulated in AS patients and in HUVECs treated with oxLDL. The LDH leakage, cell apoptosis, and expression levels of IL-6, TNF-α, ICAM-1, VCAM-1, NF-κB mRNA, NF-κB protein were all inhibited by circ_0003645 silencing, while cell viability was promoted, and the opposite effects were observed by the overexpression of circ_0003645. In conclusion, circ_0003645 silencing alleviated inflammation and apoptosis, while promoted the viability in oxLDL-induced endothelial cells by the NF-κB pathway.

Circular RNA USP1 regulates the permeability of blood-tumour barrier via miR-194-5p/FLI1 axis

Recent studies indicate circular RNAs are related to dysregulation of vascular endothelial cell function, yet the underlying mechanisms have remained elusive. Here, we characterized the functional role of circular RNA USP1 (circ‐USP1) in the regulation of the blood‐tumour barrier (BTB) permeability and the potential mechanisms. In the current study, the circ‐USP1 expressing level was up‐regulated in glioma cerebral microvascular endothelial cells (GECs) of the BTB model in vitro. Knockdown of circ‐USP1 disrupted the barrier integrity, increased its permeability as well as reduced tight junction‐related protein claudin‐5, occludin and ZO‐1 expressions in GECs. Bioinformatic prediction and luciferase assay indicated that circ‐USP1 bound to miR‐194‐5p and suppressed its activity. MiR‐194‐5p contributed to circ‐USP1 knockdown‐induced increase of BTB permeability via targeting and down‐regulating transcription factor FLI1. Furthermore, FLI1 regulated the expressions of claudin‐5, occludin and ZO‐1 in GECs through binding to their promoter regions. Single or combined treatment of circ‐USP1 and miR‐194‐5p effectively promoted anti‐tumour drug doxorubicin across BTB to induce apoptosis of glioma cells. Overall, this present study identified the crucial regulation of circ‐USP1 on BTB permeability via miR‐194‐5p/FLI1 axis‐mediated regulation of tight junction proteins, which might facilitate the development of therapeutics against human gliomas.