CircFAT1 sponges miR-375 to promote the expression of Yes-associated protein 1 in osteosarcoma cells

YAP1 promoter-associated noncoding RNA affects Ewing sarcoma cell tumorigenicity by regulating YAP1 expression

BACKGROUND

Ewing sarcomas (ESs) are aggressive paediatric tumours of bone and soft tissues afflicting children and adolescents. Despite current therapies having improved the 5-year survival rate to 70% in patients with localized disease, 25% of patients relapse and most have metastasis at diagnosis. Resistance to chemotherapy, together with the high propensity to metastasize, remain the main causes of treatment failure. Thus, identifying novel targets for alternative therapeutic approaches is urgently needed.

METHODS

Biochemical and functional analyses were carried out to elucidate the mechanism of regulation of YAP1 expression by pncRNA_YAP1-1 in ES cells.

RESULTS

Here, we identified a novel promoter-associated noncoding RNA, pncRNA_YAP1-1, transcribed from the YAP1 promoter in ES cells. We found that pncRNA_YAP1-1 level exerts antitumour effects on ES by destabilizing YAP1 protein. The molecular mechanism relies on the interaction of pncRNA_YAP1-1 with the RNA binding protein FUS, which stabilizes the transcript. Furthermore, pncRNA_YAP1-1 binding to TEAD impairs its interaction with YAP1, thus determining YAP1 translocation into the cytoplasm, its phosphorylation and degradation.

CONCLUSIONS

Overall, our findings reveal a novel layer of regulation of YAP1 protein expression by pncRNA_YAP1-1 in Ewing sarcoma. Considering the role of YAP1 in therapy response and cell propensity to metastasize, our results indicate pncRNA_YAP1-1 as an actionable target that could be exploited to enhance chemotherapy efficacy in Ewing sarcoma.

SIGNIFICANCE

PncRNA_YAP1-1 counteracts the YAP1 oncogenic transcriptional program in Ewing sarcoma cells by interfering with YAP1-TEAD interaction and impairing YAP1 protein stability. These findings uncover a novel treatment option for Ewing sarcoma.

Frequent dysregulation of multiple circular RNA isoforms with diverse regulatory mechanisms in cancer - Insights from circFNDC3B and beyond: Why unique circular RNA identifiers matter

Circular RNAs (circRNAs) are post-transcriptional regulators generated through backsplicing of pre-mRNAs, primarily comprising exons of host genes. A single host gene may produce multiple circRNA isoforms with distinct structures and sequences. Dysregulated circRNA expression has been implicated in tumorigenesis. This review aims to investigate the selection and regulatory roles of circRNA isoforms in cancer using the extensively studied hsa_circFNDC3B and thirteen other circRNAs as study models. Interrogation of literature and databases, particularly the circBase, confirms that host genes generate a plethora of circRNA isoforms; however, only a small subset of isoforms is validated as dysregulated in tumor tissues. Notably, two or more isoforms of the same circRNA are frequently dysregulated in cancer. Structurally, short isoforms retaining 5'-proximal exons are preferentially selected, but for long host genes, circRNAs may arise from mid- or 3'-regions. We identify dysregulation of seven circFNDC3B isoforms across twelve cancer types and multi-isoforms in nine of the other thirteen circRNAs also in multiple cancers. MicroRNA sponging appears to be the major regulatory mechanism, but possible biased study designs raise concerns. Using circFNDC3B and circZFR as examples, we show inconsistency and inadequacy in circRNA nomenclature in different databases and the literature, underscoring the urgent need for a universally accepted standardized central circRNA database. As an interim measure, we propose guidelines for circRNA nomenclature in journal publications. Our findings caution against indiscriminate clinical use of specific circRNA isoforms as biomarkers or therapeutic targets without further validation.

A Critical Review on microRNAs as Prognostic Biomarkers in Laryngeal Carcinoma

During the past decade, a vast number of studies were dedicated to unravelling the obscurities of non-coding RNAs in all fields of the medical sciences. A great amount of data has been accumulated, and consequently a natural need for organization and classification in all subfields arises. The aim of this review is to summarize all reports on microRNAs that were delineated as prognostic biomarkers in laryngeal carcinoma. Additionally, we attempt to allocate and organize these molecules according to their association with key pathways and oncogenes affected in laryngeal carcinoma. Finally, we critically analyze the common shortcomings and biases of the methodologies in some of the published papers in this area of research. A literature search was performed using the PubMed and MEDLINE databases with the keywords "laryngeal carcinoma" OR "laryngeal cancer" AND "microRNA" OR "miRNA" AND "prognostic marker" OR "prognosis". Only research articles written in English were included, without any specific restrictions on study type. We have found 43 articles that report 39 microRNAs with prognostic value associated with laryngeal carcinoma, and all of them are summarized along with the major characteristics and methodology of the respective studies. A second layer of the review is structural analysis of the outlined microRNAs and their association with oncogenes and pathways connected with the cell cycle (p53, CCND1, CDKN2A/p16, E2F1), RTK/RAS/PI3K cascades (EGFR, PI3K, PTEN), cell differentiation (NOTCH, p63, FAT1), and cell death (FADD, TRAF3). Finally, we critically review common shortcomings in the methodology of the papers and their possible effect on their results.

Interaction of noncoding RNAs with hippo signaling pathway in cancer cells and cancer stem cells

The Hippo signaling pathway has a regulatory function in the organogenesis process and cellular homeostasis, switching the cascade reactions of crucial kinases acts to turn off/on the Hippo pathway, altering the downstream gene expression and thereby regulating proliferation, apoptosis, or stemness. Disruption of this pathway can lead to the occurrence of various disorders and different types of cancer. Recent findings highlight the importance of ncRNAs, such as microRNA, circular RNA, and lncRNAs, in modulating the Hippo pathway. Defects in ncRNAs can disrupt Hippo pathway balance, increasing tumor cells, tumorigenesis, and chemotherapeutic resistance. This review summarizes ncRNAs' inhibitory or stimulatory role in - Hippo pathway regulation in cancer and stem cells. Identifying the relation between ncRNAs and the components of this pathway could pave the way for developing new biomarkers in the treatment and diagnosis of cancers.

Emerging role and function of Hippo-YAP/TAZ signaling pathway in musculoskeletal disorders

Hippo pathway is an evolutionarily conservative key pathway that regulates organ size and tissue regeneration by regulating cell proliferation, differentiation and apoptosis. Yes-associated protein 1 (YAP)/ WW domain-containing transcription regulator 1 (TAZ) serves as a pivotal transcription factor within the Hippo signaling pathway, which undergoes negative regulation by the Hippo pathway. The expression of YAP/TAZ affects various biological processes, including differentiation of osteoblasts (OB) and osteoclasts (OC), cartilage homeostasis, skeletal muscle development, regeneration and quality maintenance. At the same time, the dysregulation of the Hippo pathway can concurrently contribute to the development of various musculoskeletal disorders, including bone tumors, osteoporosis (OP), osteoarthritis (OA), intervertebral disc degeneration (IDD), muscular dystrophy, and rhabdomyosarcoma (RMS). Therefore, targeting the Hippo pathway has emerged as a promising therapeutic strategy for the treatment of musculoskeletal disorders. The focus of this review is to elucidate the mechanisms by which the Hippo pathway maintains homeostasis in bone, cartilage, and skeletal muscle, while also providing a comprehensive summary of the pivotal role played by core components of this pathway in musculoskeletal diseases. The efficacy and feasibility of Hippo pathway-related drugs for targeted therapy of musculoskeletal diseases are also discussed in our study. These endeavors offer novel insights into the application of Hippo signaling in musculoskeletal disorders, providing effective therapeutic targets and potential drug candidates for treating such conditions.

Circ_0004674 regulation of glycolysis and proliferation mechanism of osteosarcoma through miR-140-3p/TCF4 pathway

As a subclass of noncoding RNAs, circular RNA play an important role in tumour development. The aim of this study was to investigate the role of circ_0004674 in osteosarcoma glycolysis and the molecular mechanism of its regulation. We examined the expression of circ_0004674, miR-140-3p, TCF4 and glycolysis-related proteins (including HK2, PKM2, GLUT1 and LDHA) in osteosarcoma cells and tissues by quantitative reverse transcription-polymerase chain reaction and immunoblotting (Western blot analysis). The role of circ_0004674, miR-140-3p and TCF4 in the proliferation, apoptosis, migration and invasion of OS cells was examined using CCK8 assay, Apoptosis assay, Wound healing assay, Transwell migration and Matrigel invasion assay. The interaction of circ_0004674/miR-140-3p and miR-1543/TCF4 was also analysed using a dual luciferase reporter assay. Finally, the glycolytic process was assessed by glucose uptake assays and lactate production measurements. The results showed that the expression of circ_0004674 and TCF4 was significantly higher in MG63 and U2OS cells compared to hFOB1.19 cells, while the expression of miR-140-3p was downregulated. Silencing of circ_0004674 gene significantly inhibited the proliferation, migration and invasion of cancer cells and promoted apoptosis of cancer cells. Experiments such as dual luciferase reporter analysis showed that circ_0004674 regulates the expression of glycolysis-related proteins through the miR-140-3p/TCF4 pathway, and inhibition of this gene attenuated the depletion of glucose content and the production of lactate in cancer cells. Furthermore, inhibition of miR-140-3p or overexpression of TCF could reverse the phenotypic changes in cancer cells induced by circ_0004674 silencing. In summary, this study elucidated the specific function and potential mechanisms of circ_0004674 in osteosarcoma glycolysis. The findings demonstrate that miR-140-3p and TCF4 function respectively as a tumor suppressor gene and an oncogene in osteosarcoma. Notably, they influence glycolysis and associated pathways, regulating osteosarcoma proliferation. Therefore, circ_0004674 promotes osteosarcoma glycolysis and proliferation through the miR-140-3p/TCF4 pathway, enhancing the malignant behaviour of tumours, and it is expected to be a potential molecular target for osteosarcoma treatment.

Kaempferol inhibits colorectal cancer metastasis through circ_0000345 mediated JMJD2C/β-catenin signalling pathway

BACKGROUND

Recurrence and metastasis are the main causes of disease deterioration in colorectal cancer (CRC) patients, yet efficient therapeutic strategies are lacking. Natural compounds for efficient antitumour therapeutics are becoming increasingly prominent. Kaempferol, one of the main components of flavonoids in plants, displays a variety of pharmacological activities. Our preliminary experiments suggested that kaempferol could inhibit CRC metastasis and is significantly associated with the β-catenin signalling pathway. Moreover, we also defined the regulatory roles of JMJD2C in β-catenin signalling in our previous work.

PURPOSE

This study aims to reveal the mechanism by which kaempferol inhibits CRC progression and regulates the JMJD2C/β-catenin signalling pathway.

METHODS

The migratory capabilities of CRC cells after kaempferol intervention were measured by scratch wound healing and transwell assays. Circ_0000345 knockdown CRC stable cell lines were generated by lentivirus infection. The possible mechanism of kaempferol on circ_0000345 was verified by molecular-protein docking and verification program cellular thermal shift assay (CETSA). A dual luciferase reporter gene assay was carried out for the targeting relationship among circ_0000345, miR-205-5p and JMJD2C. Fluorescence in situ hybridization (FISH) was performed to determine the expression of circ_0000345 in tumour tissues. A pulmonary metastatic model of CRC in vitro was built to assess the antimetastatic effect and mechanism of kaempferol in vivo.

RESULTS

In vitro, kaempferol inhibits the ability to migrate of CRC cells by reducing the activation of the JMJD2C/β-catenin signalling pathway. MiR-205-5p is a key bridge for kaempferol to inhibit the expression of JMJD2C. The function of miR-205-5p is impeded by circ_0000345, which shows higher expression levels in human metastatic CRC tissues than nonmetastatic CRC tissues, and its formation is regulated by the RNA-binding proteins HNRNPK and HNRNPL. Mechanistically, kaempferol physically interacts with HNRNPK and HNRNPL to suppress JMJD2C by downregulating the expression of circ_0000345. In vivo, kaempferol suppresses CRC lung metastasis. Kaempferol inhibits the activation of JMJD2C/β-catenin signalling through reducing the expression of circ_0000345 in the CRC lung metastasis model.

CONCLUSION

Circ_0000345 enhances activation of the JMJD2C/β-catenin signalling pathway through miR-205-5p to promote CRC metastasis. Kaempferol inhibits CRC metastasis through the circ_0000345-mediated JMJD2C/β-catenin signalling pathway, and this effect is influenced as a direct consequence of the binding of kaempferol with HNRNPK and HNRNPL. This provides promising therapeutic and/or adjuvant agents for advanced CRC and sheds light on the multifaceted role of phytomedicine in cancer.

DNMT1 determines osteosarcoma cell resistance to apoptosis by associatively modulating DNA and mRNA cytosine-5 methylation

Cellular apoptosis is a central mechanism leveraged by chemotherapy to treat human cancers. 5-Methylcytosine (m5C) modifications installed on both DNA and mRNA are documented to regulate apoptosis independently. However, the interplay or crosstalk between them in cellular apoptosis has not yet been explored. Here, we reported that promoter methylation by DNMT1 coordinated with mRNA methylation by NSun2 to regulate osteosarcoma cell apoptosis. DNMT1 was induced during osteosarcoma cell apoptosis triggered by chemotherapeutic drugs, whereas NSun2 expression was suppressed. DNMT1 was found to repress NSun2 expression by methylating the NSun2 promoter. Moreover, DNMT1 and NSun2 regulate the anti-apoptotic genes AXL, NOTCH2, and YAP1 through DNA and mRNA methylation, respectively. Upon exposure to cisplatin or doxorubicin, DNMT1 elevation drastically reduced the expression of these anti-apoptotic genes via enhanced promoter methylation coupled with NSun2 ablation-mediated attenuation of mRNA methylation, thus rendering osteosarcoma cells to apoptosis. Collectively, our findings establish crosstalk of importance between DNA and RNA cytosine methylations in determining osteosarcoma resistance to apoptosis during chemotherapy, shedding new light on future treatment of osteosarcoma, and adding additional layers to the control of gene expression at different epigenetic levels.

Circular RNAs in renal cell carcinoma: from mechanistic to clinical perspective

CircRNAs, a special type of noncoding RNAs characterized by their stable structure and unique abilities to form backsplicing loops, have recently attracted the interest of scientists. These RNAs are abundant throughout the body and play important roles such as microRNA sponges, templates for transcription, and regulation of protein translation and RNA-binding proteins. Renal cancer development is highly correlated with abnormal circRNA expression in vivo. CircRNAs are currently considered promising targets for novel therapeutic approaches as well as possible biomarkers for prognosis and diagnosis of various malignancies. Despite our growing understanding of circRNA, numerous questions remain unanswered. Here, we address the characteristics of circRNAs and their function, focusing in particular on their impact on drug resistance, metabolic processes, metastasis, cell growth, and programmed cell death in renal cancer. In addition, the application of circRNAs as prognostic and diagnostic biomarkers will be discussed.

The Relationship Between the Expression of circFAT1 and Immune Cell in Patients with Non-Small Cell Lung Cancer

Objective

To analyze the correlation between the expression of circFAT1 in serum and immune cells in patients with non-small cell lung cancer (NSCLC).

Methods

A total of 96 patients with NSCLC admitted to our hospital from November 2019 to November 2022 were regarded as the study subjects. In the meantime, 96 volunteers who had physical examination in our hospital were regarded as the control group. The expression level of circFAT1 in serum was detected by real-time fluorescence quantitative PCR. NSCLC cancer tissue (NSCLC group) and paracancerous tissue (tissue ≥ 2cm away from the focus) (paracancerous group) were collected during the operation, the expression of CD4+, CD8+ and Foxp3+ in tissues was determined by immunohistochemistry; the expression level of circFAT1 mRNA in NSCLC tissue was analyzed using the Ualcan database. Spearman correlation was applied to analyze the correlation between the expression of circFAT1 and immune cells (CD4+, Foxp3+, CD8+).

Results

The level of circFAT1 in NSCLC tissue was higher than that in normal tissue (P < 0.05). Compared with the control group, the expression level of circFAT1 in serum of NSCLC group was obviously higher (P < 0.05). The expression level of circFAT1 was related to lymph node metastasis, TNM stage and differentiation (P < 0.05). Compared with the paracancerous group, the positive expression rate of CD8+ in NSCLC group was obviously lower, and the positive expression rates of CD4+ and Foxp3+ were obviously higher (P < 0.05). The expression of CD4+, Foxp3+ and CD8+ in NSCLC patients' cancer tissue was related to lymph node metastasis, TNM stage and differentiation degree (P < 0.05). Spearman correlation analysis showed that circFAT1 was positively correlated with the expression of CD4+ and Foxp3+ and negatively correlated with the expression of CD8+ (P < 0.05).

Conclusion

CircFAT1 is highly expressed in the serum of NSCLC patients and is closely related to immune cells.

Targeting signaling pathways in osteosarcoma: Mechanisms and clinical studies

Osteosarcoma (OS) is a highly prevalent bone malignancy among adolescents, accounting for 40% of all primary malignant bone tumors. Neoadjuvant chemotherapy combined with limb-preserving surgery has effectively reduced patient disability and mortality, but pulmonary metastases and OS cells' resistance to chemotherapeutic agents are pressing challenges in the clinical management of OS. There has been an urgent need to identify new biomarkers for OS to develop specific targeted therapies. Recently, the continued advancements in genomic analysis have contributed to the identification of clinically significant molecular biomarkers for diagnosing OS, acting as therapeutic targets, and predicting prognosis. Additionally, the contemporary molecular classifications have revealed that the signaling pathways, including Wnt/β-catenin, PI3K/AKT/mTOR, JAK/STAT3, Hippo, Notch, PD-1/PD-L1, MAPK, and NF-κB, have an integral role in OS onset, progression, metastasis, and treatment response. These molecular classifications and biological markers have created new avenues for more accurate OS diagnosis and relevant treatment. We herein present a review of the recent findings for the modulatory role of signaling pathways as possible biological markers and treatment targets for OS. This review also discusses current OS therapeutic approaches, including signaling pathway-based therapies developed over the past decade. Additionally, the review covers the signaling targets involved in the curative effects of traditional Chinese medicines in the context of expression regulation of relevant genes and proteins through the signaling pathways to inhibit OS cell growth. These findings are expected to provide directions for integrating genomic, molecular, and clinical profiles to enhance OS diagnosis and treatment.

Non-coding RNAs: emerging roles in the characterization of immune microenvironment and immunotherapy of prostate cancer

Prostate cancer is the most common tumor among men. Although the prognosis for early-stage prostate cancer is good, patients with advanced disease often progress to metastatic castration-resistant prostate cancer (mCRPC), which usually leads to death owing to resistance to existing treatments and lack of long-term effective therapy. In recent years, immunotherapy, especially immune checkpoint inhibitors (ICIs), has made great progress in the treatment of various solid tumors, including prostate cancer. However, the ICIs have only shown modest outcomes in mCRPC compared with other tumors. Previous studies have suggested that the suppressive tumor immune microenvironment (TIME) of prostate cancer leads to poor anti-tumor immune response and tumor resistance to immunotherapy. It has been reported that non-coding RNAs (ncRNAs) are capable of regulating upstream signaling at the transcriptional level, leading to a "cascade of changes" in downstream molecules. As a result, ncRNAs have been identified as an ideal class of molecules for cancer treatment. The discovery of ncRNAs provides a new perspective on TIME regulation in prostate cancer. ncRNAs have been associated with establishing an immunosuppressive microenvironment in prostate cancer through multiple pathways to modulate the immune escape of tumor cells which can promote resistance of prostate cancer to immunotherapy. Targeting these related ncRNAs presents an opportunity to improve the effectiveness of immunotherapy in this patient population.

The FAT1 Cadherin Drives Vascular Smooth Muscle Cell Migration

Vascular smooth muscle cells (VSMCs) are normally quiescent and non-migratory, regulating the contraction and relaxation of blood vessels to control the vascular tone. In response to arterial injury, these cells become active; they proliferate, secrete matrix proteins, and migrate, and thereby contribute importantly to the progression of several cardiovascular diseases. VSMC migration specifically supports atherosclerosis, restenosis after catheter-based intervention, transplant vasculopathy, and vascular remodeling during the formation of aneurysms. The atypical cadherin FAT1 is expressed robustly in activated VSMCs and promotes their migration. A positive role of FAT1 in the migration of other cell types, including neurons, fibroblasts, podocytes, and astrocyte progenitors, has also been described. In cancer biology, however, the effect of FAT1 on migration depends on the cancer type or context, as FAT1 either suppresses or enhances cancer cell migration and invasion. With this review, we describe what is known about FAT1's effects on cell migration as well as the factors that influence FAT1-dependent migration. In VSMCs, these factors include angiotensin II, which activates FAT1 expression and cell migration, and proteins of the Atrophin family: Atrophin-1 and the short isoform of Atrophin-2, which promote VSMC migration, and the long isoform of Atrophin-2, which exerts negative effects on FAT1-dependent VSMC migration.

Extracellular Vesicles Derived circSH3PXD2A Inhibits Chemoresistance of Small Cell Lung Cancer by miR-375-3p/YAP1

Introduction

Small cell lung cancer (SCLC) is a subtype of lung cancer with high malignancy and poor prognosis. Rapid acquisition of chemoresistance is one of the main reasons leading to clinical treatment failure of SCLC. Studies have indicated that circRNAs participate in multiple processes of tumor progression, including chemoresistance. However, the molecular mechanisms of circRNAs driving the chemoresistance of SCLC are not well specified.

Methods

The differentially expressed circRNAs were screened by transcriptome sequencing of chemoresistant and chemosensitive SCLC cells. The EVs of SCLC cells were isolated and identified by ultracentrifugation, Western blotting, transmission electron microscopy, nanoparticle tracking analysis and EVs uptake assays. The expression levels of circSH3PXD2A in serum and EVs of SCLC patients and healthy individuals were detected by qRT‒PCR. The characteristics of circSH3PXD2A were detected by Sanger sequencing, RNase R assay, nuclear-cytoplasmic fraction assay, and fluorescence in situ hybridization assay. The mechanisms of circSH3PXD2A inhibiting SCLC progression were studied by bioinformatics analysis, chemoresistance assay, proliferation assay, apoptosis assay, transwell assay, pull-down assay, luciferase reporting assay, and mouse xenograft assay.

Results

It was identified that the circSH3PXD2A was a prominently downregulated circRNA in chemoresistant SCLC cells. The expression level of circSH3PXD2A in EVs of SCLC patients was negatively associated with chemoresistance, and the combination of EVs-derived circSH3PXD2A and serum ProGRP (Progastrin-releasing peptide) levels had better indications for DDP-resistant SCLC patients. CircSH3PXD2A inhibited the chemoresistance, proliferation, migration, and invasion of SCLC cells through miR-375-3p/YAP1 axis in vivo and in vitro. SCLC cells cocultured with EVs secreted by circSH3PXD2A-overexpressing cells exhibited decreased chemoresistance and cell proliferation.

Conclusion

Our results manifest that EVs-derived circSH3PXD2A inhibits the chemoresistance of SCLC through miR-375-3p/YAP1 axis. Moreover, EVs-derived circSH3PXD2A may serve as a predictive biomarker for DDP-resistant SCLC patients.

Signal Pathways and microRNAs in Osteosarcoma Growth and the Dual Role of Mesenchymal Stem Cells in Oncogenesis

The major challenges in Osteosarcoma (OS) therapy are its heterogeneity and drug resistance. The development of new therapeutic approaches to overcome the major growth mechanisms of OS is urgently needed. The search for specific molecular targets and promising innovative approaches in OS therapy, including drug delivery methods, is an urgent problem. Modern regenerative medicine focuses on harnessing the potential of mesenchymal stem cells (MSCs) because they have low immunogenicity. MSCs are important cells that have received considerable attention in cancer research. Currently, new cell-based methods for using MSCs in medicine are being actively investigated and tested, especially as carriers for chemotherapeutics, nanoparticles, and photosensitizers. However, despite the inexhaustible regenerative potential and known anticancer properties of MSCs, they may trigger the development and progression of bone tumors. A better understanding of the complex cellular and molecular mechanisms of OS pathogenesis is essential to identify novel molecular effectors involved in oncogenesis. The current review focuses on signaling pathways and miRNAs involved in the development of OS and describes the role of MSCs in oncogenesis and their potential for antitumor cell-based therapy.

The function and mechanisms of action of circular RNAs in Urologic Cancer

Kidney, bladder, and prostate cancer are the three major tumor types of the urologic system that seriously threaten human health. Circular RNAs (CircRNAs), special non-coding RNAs with a stabile structure and a unique back-splicing loop-forming ability, have received recent scientific attention. CircRNAs are widely distributed within the body, with important biologic functions such as sponges for microRNAs, as RNA binding proteins, and as templates for regulation of transcription and protein translation. The abnormal expression of circRNAs in vivo is significantly associated with the development of urologic tumors. CircRNAs have now emerged as potential biomarkers for the diagnosis and prognosis of urologic tumors, as well as targets for the development of new therapies. Although we have gained a better understanding of circRNA, there are still many questions to be answered. In this review, we summarize the properties of circRNAs and detail their function, focusing on the effects of circRNA on proliferation, metastasis, apoptosis, metabolism, and drug resistance in kidney, bladder, and prostate cancers.

Circ_0001060 Upregulates and Encourages Progression in Osteosarcoma

Circular RNA (circRNA) is involved in the occurrence and development of various cancers. To this day, the expression and mechanism of circRNA in osteosarcoma (OS) remain unclear. We previously found that circ_0001060 was highly expressed in OS tumor tissues. In this work, we identified that high level expression of circ_0001060 was significantly associated with late clinical stage, larger tumor volume, higher frequency of metastasis, and poor prognosis in OS patients. Furthermore, we confirmed that silencing circ_0001060 inhibited the proliferation and migration of OS cell. Using bioinformatics analysis, we built three circRNA-miRNA-mRNA regulatory modules (circ_0001060-miR-203a-5p-TRIM21, circ_0001060-miR-208b-5p-MAP3K5, and circ_0001060-miR-203a-5p-PRKX), suggesting that these signaling axes may be involved in the inhibitory effect of circ_0001060 on OS. To sum up, circ_0001060 is a novel tumor biomarker for OS as well as a potential therapeutic target.

CircFAT1 Promotes the Proliferation and Invasion of Malignant Melanoma through miR375-SLC7A11 Signal Axis

BACKGROUND

Circular RNA, as a member of noncoding RNA, plays an important role in the occurrence, development and metastasis of tumor cells. So far, the correlation between circular RNA and malignant melanoma remains obscure.

METHODS

RNA expression of circFAT1 and miR-375 in malignant melanoma (MM) tissues and cell lines was detected by RT-PCR. The proliferation, cloning, migration and invasion of SK-Mel-28 and A375 cells were assessed using CCK-8 test, clone formation and Transwell assay, respectively. CircRNA immunoprecipitation was used to validate the relationship between circFAT1 and miR-375. The binding between circFAT1 and miR-375, as well as SLC7A11 and miR-375 were verified by luciferase assay.

RESULTS

In our study，the circFAT1 was significantly overexpressed in the MM tissue than melanocytic nevi. Conversely, the expression of miR-375 in MM tissue was lower than in melanocytic nevi tissue. The underexpression of circFAT1 with siRNA plasmids significantly suppressed the proliferation, invasion and clone formation of MM cell line. Mechanistically, circFAT1 positively regulates the expression level of SLC7A11 by sponging miR-375. The promotive effects of circFAT1 on the proliferation and invasion ability of MM cells were reversed by the upregulation of miR-375.

CONCLUSION

circFAT1 promotes the proliferation, invasion and clone formation of malignant melanoma cells by improving the expression level of SLC7A11 via sponging miR-375.

Genetic Alterations and Deregulation of Hippo Pathway as a Pathogenetic Mechanism in Bone and Soft Tissue Sarcoma

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

Downregulation of hsa_circ_0000885 suppressed osteosarcoma metastasis and progression via regulating E2F3 expression and sponging miR-16-5p

Introduction

Accumulating evidence has shown that circular RNAs (circRNAs) have indispensable functions during tumor progression by regulating gene expression. A previous study found that upregulation of hsa_circ_0000885 indicated a poor clinical outcome of osteosarcoma (OS). However, the regulatory mechanism of this process is unclear.

Methods

This investigation aimed to elucidate how hsa_circ_0000885 regulated OSs. The study used RT-qPCR to investigate hsa_circ_0000885 expression in OS cells. We conducted luciferase reporter assays and analyses to confirm the hsa_circ_0000885 downstream target. We transfected OS cells using different vectors and used Transwell migration, colony formation, western blotting, Matrigel invasion, proliferation, in vivo tumorigenesis, and metastasis assays to identify the role of hsa_circ_0000885 in OS.

Results

The results showed that hsa_circ_0000885 expression altered OS cell lines, and that hsa_circ_0000885 downregulation suppressed OS cell proliferation and invasion using in vivo and in vitro experiments. Luciferase reporter assays verified that miR-16-5p and E2F3 were downstream targets of hsa_circ_0000885. E2F3 overexpression or miR-16-5p inhibition reversed OS cell invasion and proliferation after silencing hsa_circ_0000885. Furthermore, hsa_circ_0000885 affected cancer stem cell differentiation by regulating miR-16-5p/E2F3.

Conclusions

Overall, the results showed that hsa_circ_0000885 downregulation suppressed OS progression and metastasis via regulating E2F3 expression and sponging miR-16-5p.

Circ_0136666 aggravates osteosarcoma development through mediating miR-1244/CEP55 axis

Background

Accumulating articles demonstrate that circular RNAs play pivotal functions in tumorigenesis. However, the working mechanism of circ_0136666 in osteosarcoma (OS) progression remains to be further clarified.

Methods

Real time-quantitative polymerase chain reaction and western blot assay were applied to determine RNA and protein expression, respectively. Cell proliferation was assessed by 5-Ethynyl-2′-deoxyuridine assay and colony formation assay. Transwell assays were carried out to assess cell migration and invasion abilities. Flow cytometry was performed to analyze cell apoptosis. Cell glycolysis was evaluated by analyzing the uptake of glucose and the production of lactate using the corresponding kits. Dual-luciferase reporter assay and biotinylated RNA-pull down assay were performed to confirm the target interaction between microRNA-1244 (miR-1244) and circ_0136666 or centrosomal protein 55 (CEP55). Xenograft tumor model was utilized to explore the role of circ_0136666 in tumor growth in vivo.

Results

Circ_0136666 expression was prominently elevated in OS tissues and cell lines. Circ_0136666 absence restrained the proliferation, migration, invasion and glycolytic metabolism and promoted the apoptosis of OS cells. Circ_0136666 negatively regulated miR-1244 expression by binding to it in OS cells. MiR-1244 overexpression suppressed the malignant behaviors of OS cells. CEP55 was a target of miR-1244 in OS cells. Circ_0136666 positively regulated CEP55 expression partly by sequestering miR-1244 in OS cells. CEP55 overexpression largely reversed circ_0136666 silencing-mediated influences in OS cells. Circ_0136666 silencing significantly suppressed tumor growth in vivo.

Conclusion

Circ_0136666 silencing inhibited OS progression partly by targeting miR-1244/CEP55 signaling. Silencing circ_0136666 and CEP55 or restoring miR-1244 level might be a potential therapeutic strategy for OS.

Circular RNA circFIRRE drives osteosarcoma progression and metastasis through tumorigenic-angiogenic coupling

Background

Disappointing clinical efficacy of standard treatment has been proven in refractory metastatic osteosarcoma, and the emerging anti-angiogenic regimens are still in the infantile stage. Thus, there is an urgent need to develop novel therapeutic approach for osteosarcoma lung metastasis.

Methods

circFIRRE was selected from RNA-sequencing of 4 matched osteosarcoma and adjacent samples. The expression of circFIRRE was verified in clinical osteosarcoma samples and cell lines via quantitative real-time polymerase chain reaction (RT-qPCR). The effect of circFIRRE was investigated in cell lines in vitro models, ex vivo models and in vivo xenograft tumor models, including proliferation, invasion, migration, metastasis and angiogenesis. Signaling regulatory mechanism was evaluated by RT-qPCR, Western blot, RNA pull-down and dual-luciferase reporter assays.

Results

In this article, a novel circular RNA, circFIRRE (hsa_circ_0001944) was screened out and identified from RNA-sequencing, and was upregulated in both osteosarcoma cell lines and tissues. Clinically, aberrantly upregulated circFIRRE portended higher metastatic risk and worse prognosis in osteosarcoma patients. Functionally, in vitro, ex vivo and in vivo experiments demonstrated that circFIRRE could drive primary osteosarcoma progression and lung metastasis by inducing both tumor cells and blood vessels, we call as “tumorigenic-angiogenic coupling”. Mechanistically, upregulated circFIRRE was induced by transcription factor YY1, and partially boosted the mRNA and protein level of LUZP1 by sponging miR-486-3p and miR-1225-5p.

Conclusions

We identified circFIRRE as a master regulator in the tumorigenesis and angiogenesis of osteosarcoma, which could be purposed as a novel prognostic biomarker and therapeutic target for refractory osteosarcoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01624-7.

The diverse functions of FAT1 in cancer progression: good, bad, or ugly?

FAT atypical cadherin 1 (FAT1) is among the most frequently mutated genes in many types of cancer. Its highest mutation rate is found in head and neck squamous cell carcinoma (HNSCC), in which FAT1 is the second most frequently mutated gene. Thus, FAT1 has great potential to serve as a target or prognostic biomarker in cancer treatment. FAT1 encodes a member of the cadherin-like protein family. Under normal physiological conditions, FAT1 serves as a molecular "brake" on mitochondrial respiration and acts as a receptor for a signaling pathway regulating cell-cell contact interaction and planar cell polarity. In many cancers, loss of FAT1 function promotes epithelial-mesenchymal transition (EMT) and the formation of cancer initiation/stem-like cells. However, in some types of cancer, overexpression of FAT1 leads to EMT. The roles of FAT1 in cancer progression, which seems to be cancer-type specific, have not been clarified. To further study the function of FAT1 in cancers, this review summarizes recent relevant literature regarding this protein. In addition to phenotypic alterations due to FAT1 mutations, several signaling pathways and tumor immune systems known or proposed to be regulated by this protein are presented. The potential impact of detecting or targeting FAT1 mutations on cancer treatment is also prospectively discussed.

circRNA: A New Biomarker and Therapeutic Target for Esophageal Cancer

Circular RNAs (circRNAs) comprise a large class of endogenous non-coding RNA with covalently closed loops and have independent functions as linear transcripts transcribed from identical genes. circRNAs are generated by a “back-splicing” process regulated by regulatory elements in cis and associating proteins in trans. Many studies have shown that circRNAs play important roles in multiple processes, including splicing, transcription, chromatin modification, miRNA sponges, and protein decoys. circRNAs are highly stable because of their closed ring structure, which prevents them from degradation by exonucleases, and are more abundant in terminally differentiated cells, such as brains. Recently, it was demonstrated that numerous circRNAs are differentially expressed in cancer cells, and their dysfunction is involved in tumorigenesis and metastasis. However, the crucial functions of these circRNAs and the dysregulation of circRNAs in cancer are still unknown. In this review, we summarize the recent reports on the biogenesis and biology of circRNAs and then catalog the advances in using circRNAs as biomarkers and therapeutic targets for cancer therapy, particularly esophageal cancer.

The interplay between noncoding RNA and YAP/TAZ signaling in cancers: molecular functions and mechanisms

The Hippo signaling pathway was found coordinately modulates cell regeneration and organ size. Its dysregulation contributes to uncontrolled cell proliferation and malignant transformation. YAP/TAZ are two critical effectors of the Hippo pathway and have been demonstrated essential for the initiation or growth of most tumors. Noncoding RNAs (ncRNAs), including miRNAs, lncRNAs, and circRNAs, have been shown to play critical roles in the development of many cancers. In the past few decades, a growing number of studies have revealed that ncRNAs can directly or indirectly regulate YAP/TAZ signaling. YAP/TAZ also regulate ncRNAs expression in return. This review summarizes the interactions between YAP/TAZ signaling and noncoding RNAs together with their biological functions on cancer progression. We also try to describe the complex feedback loop existing between these components.

Exosomal microRNAs shuttling between tumor cells and macrophages: cellular interactions and novel therapeutic strategies

Extracellular vesicles secreted by tumor microenvironment (TME) cells are vital players in tumor progression through transferring nucleic acids and proteins. Macrophages are the main immune cells in TME and tumor associated macrophages (TAM) express M2 phenotype, which induce tumor proliferation, angiogenesis, invasion, metastasis and immune elimination, resulting in the subsequent evolution of malignancies. There are a high number of studies confirmed that tumor cells and TAM interact with each other through extracellular vesicles in various cancers, like pancreatic ductal adenocarcinoma, gastric cancer, breast cancer, ovarian cancer, colon cancer, glioblastoma, hepatocellular cancer, and lung cancer. Herein, this review summarizes the current knowledge on mechanisms of communications between tumor cells and TAM via extracellular vesicles, mainly about microRNAs, and targeting these events might represent a novel approach in the clinical implications of this knowledge into successful anti-cancer strategies.

FAT1 and MSH2 Are Predictive Prognostic Markers for Chinese Osteosarcoma Patients Following Chemotherapeutic Treatment

Osteosarcoma is characterized by diverse genetic mutations, including single-nucleotide variants (SNVs), which can complicate clinical outcomes of the treatment. This study identified key mutations or polymorphisms in genes that correlate with osteosarcoma prognoses. A total of 110 patients with osteosarcoma were assigned to "good" or "poor" cohorts depending on their 5-year disease-free survival (DFS) after surgery and chemotherapeutic treatment. We performed next-generation sequencing analysis of tumor tissues for prognosis-associated SNVs in 315 tumorigenesis-related genes, followed by modeling of clinical outcomes for these patients using random forest classification via a support vector machine (SVM). Data from the Chinese Millionome Database were used to compare SNV frequency in osteosarcoma patients and healthy people. SVM screening identified 17 nonsynonymous SNVs located in 15 genes, of which rs17224367 and rs3733406 (located in MSH2 and FAT1, respectively) were strongly correlated with osteosarcoma prognosis. These results were verified in a 26-patient validation cohort, confirming that these SNVs could be used to predict prognosis. These results demonstrated that two SNVs located in MSH2 and FAT1 are associated with prognosis of osteosarcoma patients. © 2022 American Society for Bone and Mineral Research (ASBMR).

Non-coding RNAs in ferroptotic cancer cell death pathway: meet the new masters

Despite the recent advances in cancer therapy, cancer chemoresistance looms large along with radioresistance, a major challenge in dire need of thorough and minute investigation. Not long ago, cancer cells were reported to have proven refractory to the ferroptotic cell death, a newly discovered form of regulated cell death (RCD), conspicuous enough to draw attention from scholars in terms of targeting ferroptosis as a prospective therapeutic strategy. However, our knowledge concerning the underlying molecular mechanisms through which cancer cells gain immunity against ferroptosis is still in its infancy. Of late, the implication of non-coding RNAs (ncRNAs), including circular RNAs (circRNAs), microRNAs (miRNAs), and long non-coding RNAs (lncRNAs) in ferroptosis has been disclosed. Nevertheless, precisely explaining the molecular mechanisms behind the contribution of ncRNAs to cancer radio/chemotherapy resistance remains a challenge, requiring further clarification. In this review, we have presented the latest available information on the ways and means of regulating ferroptosis by ncRNAs. Moreover, we have provided important insights about targeting ncRNAs implicated in ferroptosis with the hope of opening up new horizons for overcoming cancer treatment modalities. Though a long path awaits until we make this ambitious dream come true, recent progress in gene therapy, including gene-editing technology will aid us to be optimistic that ncRNAs-based ferroptosis targeting would soon be on stream as a novel therapeutic strategy for treating cancer.

MiR-590 suppresses the progression of non-small cell lung cancer by regulating YAP1 and Wnt/β-catenin signaling

OBJECTIVE

Accumulating evidence has been revealed that miR-590 is involved in the progression and carcinogenesis of various cancers. However, the molecular mechanism of miR-590 in non-small-cell lung cancer (NSCLC) remains unclear.

METHODS

Quantitative reverse transcription-PCR (qRT-PCR), western blot, MTT, and transwell assay were applied to investigate the functional role of miR-590 in this study. Dual luciferase reporter assay was utilized to investigate the interaction between YAP1 and miR-590 expression. Cells transfected with miR-590 mimic or inhibitor were subjected to western blot to investigate the role of Wnt/β-catenin signaling in NSCLC modulated by miR-590.

RESULTS

MiR-590 was down-regulated in NSCLC tissues and cells. Kaplan-Meier analysis found that the higher expression of miR-590 in NSCLC patients, the more improved survival rate of NSCLC patients. Over-expression of miR-590 inhibited NSCLC cell proliferation, migration, and invasion. Moreover, increasing miR-590 suppressed Yes-associated protein 1 (YAP1) expression and inhibited the Wnt/β-catenin pathway in NSCLC cells. Furthermore, miR-590 was negatively correlated with YAP1 expression.

CONCLUSION

These findings demonstrated that the miR-590/YAP1 axis exerted an important role in the progression of NSCLC, suggesting that miR-590 might be the appealing prognostic marker for NSCLC treatment.

Activation of YAP1 by N6-Methyladenosine-Modified circCPSF6 Drives Malignancy in Hepatocellular Carcinoma

Circular RNAs (circRNA) and N6-methyladenosine (m6A) modification are extensively involved in the progression of diverse tumors, including hepatocellular carcinoma (HCC). However, the cross-talk between circRNAs and m6A remains elusive in the pathogenesis of HCC. Here we investigated m6A-mediated regulation of circRNAs in HCC. m6A-related circRNAs were identified by integrating information from two published studies, revealing circular cleavage and polyadenylation specific factor 6 (circCPSF6) as a novel m6A-modified circRNA. circCPSF6 was dominated by ALKBH5-mediated demethylation, followed by the recognization and destabilization by YTHDF2. Meanwhile, circCPSF6 was upregulated in HCC specimens, and elevated circCPSF6 expression served as an independent prognostic factor for worse survival of patients with HCC. Loss-of-function assays demonstrated that circCPSF6 maintained cell proliferation and tumorigenicity and reinforced cell motility and tumor metastasis. circCPSF6 triggered expression of YAP1, further activating its downstream cascade. Mechanistically, circCPSF6 competitively bound PCBP2, blunting its binding to YAP1 mRNA, thereby sustaining the stability of YAP1. Functionally, removal of YAP1 reversed the effects of circCPSF6 in vitro and in vivo. Aberrant activation of the circCPSF6-YAP1 axis promoted HCC malignancy. These findings offer novel insights into the regulation of circRNAs by m6A modifications and the role of this epigenetic reprogramming in HCC.

SIGNIFICANCE

This study advances the understanding of the interplay between m6A methylation and circRNAs in hepatocellular carcinoma, highlighting the potential of circCPSF6 as a therapeutic target.

CircRNA-miRNA networks in regulating bone disease

Circular RNA (circRNA) is a class of endogenous noncoding RNA (ncRNA), presenting as a special covalent closed loop without a 5' cap or 3' tail, maintaining resistance to RNA exonuclease and keeping high stability. Although lowly expressed in most situations, circRNA makes an active difference in regulating physiological or pathological processes by modulating gene expression by regulation of transcription, protein, and miRNA functions through various mechanisms in particular tissues. Recent studies have demonstrated the roles of the miRNA-circRNA network in the development of several bone diseases such as osteoporosis, a multiple-mechanism disease resulting from defective bone quality and low bone mass, osteoarthritis, whose main pathomechanism is inflammation and articular cartilage degradation, as well as osteosarcoma, known as one of the most common bone cancers. However, the specific mechanism of how circRNA along with miRNA influences those diseases is not well documented, showing potential for the development of new therapies for those bone diseases.

Osteosarcoma and Metastasis

Osteosarcoma is the most common primary bone malignancy in adolescents. Its high propensity to metastasize is the leading cause for treatment failure and poor prognosis. Although the research of osteosarcoma has greatly expanded in the past decades, the knowledge and new therapy strategies targeting metastatic progression remain sparse. The prognosis of patients with metastasis is still unsatisfactory. There is resonating urgency for a thorough and deeper understanding of molecular mechanisms underlying osteosarcoma to develop innovative therapies targeting metastasis. Toward the goal of elaborating the characteristics and biological behavior of metastatic osteosarcoma, it is essential to combine the diverse investigations that are performed at molecular, cellular, and animal levels from basic research to clinical translation spanning chemical, physical sciences, and biology. This review focuses on the metastatic process, regulatory networks involving key molecules and signaling pathways, the role of microenvironment, osteoclast, angiogenesis, metabolism, immunity, and noncoding RNAs in osteosarcoma metastasis. The aim of this review is to provide an overview of current research advances, with the hope to discovery druggable targets and promising therapy strategies for osteosarcoma metastasis and thus to overcome this clinical impasse.

circATP2A2 promotes osteosarcoma progression by upregulating MYH9

Osteosarcoma (OS) is a highly metastatic primary malignant tumor. CircRNA hsa_circ_0028173 (circATP2A2) has been uncovered to be related to the advancement of OS. However, the biological role of circATP2A2 in OS has not been validated. circATP2A2 and MYH9 were upregulated while miR-335-5p was downregulated in OS. OS patients with high circATP2A2 expression displayed a shorter overall survival and the area under curve of circATP2A2 was 0.77, manifesting that circATP2A2 might be a diagnostic and prognostic biomarker. circATP2A2 silencing repressed OS cell proliferation and glycolysis in vivo and constrained OS cell proliferation, glycolysis, migration, and invasion in vitro. circATP2A2 regulated MYH9 expression through sponging miR-335-5p. MiR-335-5p inhibitor reversed the repressive effect of circATP2A2 knockdown on OS cell malignancy and glycolysis. MYH9 overexpression overturned miR-335-5p upregulation-mediated OS cell malignancy and glycolysis. circATP2A2 accelerated OS cell malignancy and glycolysis through upregulating MYH9 via sponging miR-335-5p, offering a promising target for OS treatment.

circGNAQ, a circular RNA enriched in vascular endothelium, inhibits endothelial cell senescence and atherosclerosis progression

Endothelial cell senescence is one of the most important causes of vascular dysfunction and atherosclerosis. Circular RNAs (circRNAs) are endogenous RNA molecules with covalently closed-loop structures, which have been reported to be abnormally expressed in many human diseases. However, the potential role of circRNAs in endothelial cell senescence and atherosclerosis remains largely unknown. Here, we compared the expression patterns of circRNAs in young and senescent human endothelial cells with RNA sequencing. Among the differentially expressed circRNAs, circGNAQ, a circRNA enriched in vascular endothelium, was significantly downregulated in senescent endothelial cells. circGNAQ silencing triggered endothelial cell senescence, as determined by a rise in senescence-associated β-galactosidase activity, reduced cell proliferation, and suppressed angiogenesis; circGNAQ overexpression showed the opposite effects. Mechanistic studies revealed that circGNAQ acted as an endogenous miR-146a-5p sponge to increase the expression of its target gene PLK2 by decoying the miR-146a-5p, thereby delaying endothelial cell senescence. In vivo studies showed that circGNAQ overexpression in the endothelium inhibited endothelial cell senescence and atherosclerosis progression. These results suggest that circGNAQ plays critical roles in endothelial cell senescence and consequently the pathogenesis of atherosclerosis, implying that the management of circGNAQ provides a potential therapeutic approach for limiting the progression of atherosclerosis.

Hsa_circ_0024093 accelerates VSMC proliferation via miR-4677-3p/miR-889-3p/USP9X/YAP1 axis in in vitro model of lower extremity ASO

Arteriosclerosis obliterans (ASO) of the lower extremities is identified as a kind of cardiovascular disease with aberrant proliferation and apoptosis of vascular smooth muscle cells (VSMCs). Accumulating studies have demonstrated the vital role of Yes1-associated transcriptional regulator (YAP1) in VSMCs, while its upstream regulatory mechanism in VSMCs in ASO of the lower extremities needs to be further elucidated. Herein, hsa_circ_0024093, a circular RNA (circRNA) from YAP1, was identified to positively regulate the protein level of YAP1 in VSMCs. Functionally, silencing of hsa_circ_0024093 obviously impeded cell proliferation and migration and promoted apoptosis in VSMCs in the in vitro model of ASO of the lower extremities. Mechanistically, it was found that hsa_circ_0024093 could regulate the expression of USP9X, which further induced YAP1 deubiquitination to stabilize YAP1 protein. In depth, it was revealed from mechanism experiments that hsa_circ_0024093 sequestered miR-889-3p or miR-4677-3p to enhance USP9X expression. Further, rescue assays validated that hsa_circ_0024093 regulated the miR-4677-3p/miR-889-3p/USP9X axis to accelerate the proliferation and migration of VSMCs in the in vitro model of ASO of the lower extremities. These findings may provide a novel perspective for better understanding of ASO of the lower extremities.

Circular RNA 0102049 suppresses the progression of osteosarcoma through modulating miR-520g-3p/PLK2 axis

Circular RNAs (circRNAs) are a type of non-coding RNAs generated from back splicing to enhance or inhibit the progression of multiple human cancers including osteosarcoma (OS). Although circ_0102049 has been found to be highly expressed in OS cell lines, the role and specific mechanism of circ_0102049 in OS remains unclear. Here, we found that silence of circ_0102049 could significantly exacerbate the tumorigenesis of OS in vivo through sponging microRNA-520g-3p. Polo-like kinase 2 (PLK2) was predicted to be a target of miR-520g-3p, and luciferase reporter assay revealed that overexpression of miR-520g-3p dramatically suppressed the expression of PLK2, whereas miR-520g-3p inhibitor promoted the PLK2 expression. Moreover, the silence of circ_0102049 could markedly promote the proliferation, invasion, migration and cell-cycle promotion while inhibiting the apoptosis of OS cell line MG63 cells in vitro through regulating miR-520g-3p/PLK2 axis. Taken together, the present study indicated that circ_0102049 suppressed the progression of osteosarcoma via modulating miR-520g-3p/PLK2/TAp73 axis, providing a potential therapeutic target for OS.

A Previously Undiscovered Circular RNA, circTNFAIP3, and Its Role in Coronavirus Replication

Circular RNAs (circRNAs) are a newly discovered class of noncoding RNAs (ncRNAs) present in various tissues and cells. However, the functions of most circRNAs have not been verified experimentally. Here, using deltacoronavirus as a model, differentially expressed circRNAs in cells with or without deltacoronavirus infection were analyzed by RNA sequencing to characterize the cellular responses to RNA virus infection. More than 57,000 circRNA candidates were detected, and seven significantly dysregulated circRNAs were quantitated by real-time reverse transcription-PCR. We discovered a previously unidentified circRNA derived from the TNFAIP3 gene, named circTNFAIP3, which is distributed and expressed widely in various tissues. RNA viruses, including deltacoronaviruses, rather than DNA viruses tend to activate the expression of endogenous circTNFAIP3. Overexpression of circTNFAIP3 promoted deltacoronavirus replication by reducing the apoptosis, while silencing of circTNFAIP3 inhibited deltacoronavirus replication by enhancing the apoptosis. In summary, our work provides useful circRNA-related information to facilitate investigation of the underlying mechanism of deltacoronavirus infection and identifies a novel circTNFAIP3 that promotes deltacoronavirus replication via regulating apoptosis.

Dissecting the Role of Circular RNAs in Sarcomas with Emphasis on Osteosarcomas

Circular RNAs (circRNAs) are single-stranded RNAs generated from exons back-splicing from a single pre-mRNA, forming covalently closed loop structures which lack 5'-3'-polarity or polyadenylated tail. Ongoing research depicts that circRNAs play a pivotal role in tumorigenesis, tumor progression, metastatic potential and chemoresistance by regulating transcription, microRNA (miRNA) sponging, RNA-binding protein interactions, alternative splicing and to a lesser degree, protein coding. Sarcomas are rare malignant tumors stemming from mesenchymal cells. Due to their clinically insidious onset, they often present at advanced stage and their treatment may require aggressive chemotherapeutic or surgical options. This review is mainly focused on the regulatory functions of circRNAs on osteosarcoma progression and their potential role as biomarkers, an area which has prompted lately extensive research. The attributed oncogenic role of circRNAs on other mesenchymal tumors such as Kaposi Sarcoma (KS), Rhabdomyosarcoma (RMS) or Gastrointestinal Stromal Tumors (GISTs) is also described. The involvement of circRNAs on sarcoma oncogenesis and relevant emerging diagnostic, prognostic and therapeutic applications are expected to gain more research interest in the future.

EIF4A3-induced circular RNA PRKAR1B promotes osteosarcoma progression by miR-361-3p-mediated induction of FZD4 expression

Emerging evidence indicates that circRNAs are broadly expressed in osteosarcoma (OS) cells and play a crucial role in OS progression. Recently, cancer-specific circRNA circPRKAR1B has been identified by high-throughput sequencing and is recorded in publicly available databases. Nevertheless, the detailed functions and underlying mechanisms of circPRKAR1B in OS remains poorly understood. By functional experiments, we found that circPRKAR1B enhanced OS cell proliferation, migration, and promotes OS epithelial–mesenchymal transition (EMT). Mechanistic investigations suggested that circPRKAR1B promotes OS progression through sponging miR-361-3p to modulate the expression of FZD4. Subsequently, we identified that EIF4A3 promoted cirPRKAR1B formation through binding to the downstream target of circPRKAR1B on PRKAR1B mRNA. Further rescue study revealed that overexpression of the Wnt signalling could impair the onco-suppressor activities of the silencing of circPRKAR1B. Interestingly, further experiments indicated that circPRKAR1B is involved in the sensitivity of chemoresistance in OS. On the whole, our results demonstrated that circPRKAR1B exerted oncogenic roles in OS and suggested the circPRKAR1B/miR-361-3p/FZD4 axis plays an important role in OS progression and might be a potential therapeutic target.

MicroRNA-375: potential cancer suppressor and therapeutic drug

MiR-375 is a conserved noncoding RNA that is known to be involved in tumor cell proliferation, migration, and drug resistance. Previous studies have shown that miR-375 affects the epithelial-mesenchymal transition (EMT) of human tumor cells via some key transcription factors, such as Yes-associated protein 1 (YAP1), Specificity protein 1 (SP1) and signaling pathways (Wnt signaling pathway, nuclear factor κB (NF-κB) pathway and transforming growth factor β (TGF-β) signaling pathway) and is vital for the development of cancer. Additionally, recent studies have identified microRNA (miRNA) delivery system carriers for improved in vivo transportation of miR-375 to specific sites. Here, we discussed the role of miR-375 in different types of cancers, as well as molecular mechanisms, and analyzed the potential of miR-375 as a molecular biomarker and therapeutic target to improve the efficiency of clinical diagnosis of cancer.

The Role of miRNA in the Pathophysiology of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) represent a tumor group that is both rare and heterogeneous. Prognosis is largely determined by the tumor grading and the site of the primary tumor and metastases. Despite intensive research efforts, only modest advances in diagnostic and therapeutic approaches have been achieved in recent years. For patients with non-respectable tumor stages, prognosis is poor. In this context, the development of novel diagnostic tools for early detection of NETs and prediction of tumor response to therapy as well as estimation of the overall prognosis would greatly improve the clinical management of NETs. However, identification of novel diagnostic molecules is hampered by an inadequate understanding of the pathophysiology of neuroendocrine malignancies. It has recently been demonstrated that microRNA (miRNA), a family of small RNA molecules with an established role in the pathophysiology of quite different cancer entities, may also play a role as a biomarker. Here, we summarize the available knowledge on the role of miRNAs in the development of NET and highlight their potential use as serum-based biomarkers in the context of this disease. We discuss important challenges currently preventing their use in clinical routine and give an outlook on future directions of miRNA research in NET.

Long non-coding RNA SNHG5 regulates ulcerative colitis via microRNA-375 / Janus kinase-2 axis

Ulcerative colitis (UC) is an intestinal inflammatory disorder. Long non-coding RNAs (lncRNAs) are collectively involved in UC. This study is designed to explore the roles of lncRNA (small nucleolar RNA host gene 5) SNHG5 in UC. Gene or microRNA (miRNA) expression was detected using RT-qPCR and western blot, respectively. Cellular functions were analyzed by cell counting kit 8 (CCK8), 5-ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry, and the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) assays. Lactate dehydrogenase (LDH) content was determined by a cell cytotoxicity assay. The interactions between miR-375 and SNHG5 or Janus kinase-2 (JAK2) were verified by a luciferase reporter assay. SNHG5 was up-regulated in intestinal mucosa tissues of UC patients as well as tumor necrosis factor alpha-treated (TNF-α-treated) young adult mouse colon (YAMC) cells. Down-regulated SNHG5 promoted cell proliferation and inhibited apoptosis of YAMC cells. miR-375 was verified to be a target of SNHG5 and was suppressed by TNF-α treatment in YAMC cells. Over-expression of miR-375 restored YAMC cellular functions. Additionally, miR-375 targeted JAK2, which was up-regulated by TNF-α treated YAMC cells. Up-regulation of JAK2 induced the dysfunction of YAMC cells. Knockdown of SNHG5 promoted the proliferation and suppressed the apoptosis of YAMC cells via regulating miR-375/JAK2 axis. Therefore, knockdown of SNHG5 may be a promising therapy for UC.

Circular RNA FAT atypical cadherin 1 (circFAT1)/microRNA-525-5p/spindle and kinetochore-associated complex subunit 1 (SKA1) axis regulates oxaliplatin resistance in breast cancer by activating the notch and Wnt signaling pathway

Increasing evidence has confirmed the vital roles of circular RNAs (CircRNAs) in the drug resistance of breast cancer (BC). Herein, we intended to study the effect of circular RNA FAT atypical cadherin 1 (circFAT1) on BC oxaliplatin (OX) resistance and find out the potential molecular mechanism in it. In this study, mRNA and protein levels of genes were measured by RT-qPCR and western blotting, respectively. Luciferase reporter assay confirmed the relationship between microRNA-525-5p (miR-525-5p) and circFAT1 or spindle and kinetochore-associated complex subunit 1 (SKA1). CCK-8, transwell, and flow cytometry experiments were utilized to investigate the chemosensitivity, migration, invasion, and apoptosis of BC cells. Gene Set Enrichment Analysis (GSEA) was applied to discover possible pathways related to SKA1. It was uncovered that circFAT1 was overexpressed in OX-resistant BC tissues and cells. Functional experiments showed that circFAT1 depletion reduced the level of chemoresistance-related genes. Moreover, circFAT1 knockdown remarkably facilitated apoptosis and decreased OX (half-maximal inhibitory concentration) IC₅₀ value, migration, and invasion in OX-resistant BC cells. It was identified that miR-525-5p directly targeted circFAT1 and SKA1. Besides, rescue assays exhibited that circFAT1 promoted OX resistance in BC cells via the miR-525-5p/SKA1 regulatory network. Furthermore, GSEA and western blotting identified that SKA1 activated the Notch and Wnt pathway in OX-resistant BC cells. In conclusion, our results demonstrated that circFAT1 conferred OX resistance in BC by regulating the miR-525-5p/SKA1 via the Notch and Wnt pathway, providing a potential therapeutic target for patients with OX-resistant BC.

Significance of Circular FAT1 as a Prognostic Factor and Tumor Suppressor for Esophageal Squamous Cell Carcinoma

Background

Circular RNA is a novel endogenous non-coding RNA with a stable loop structure, and theories for its biogenesis and usefulness as a biomarker in various cancers have been proposed. The present study investigated the significance of circular FAT1 (circFAT1) as a novel biomarker in esophageal squamous cell carcinoma (ESCC).

Method

CircFAT1 expression levels were measured in ESCC cell lines and the effects of downregulating circFAT1 on cell migration and invasion were examined using a transwell assay. The functions of miR-548g, which will be sponged by circFAT1, were assessed. Furthermore, the expression of circFAT1 was evaluated in 51 radically resected ESCC tissue samples using quantitative reverse transcription polymerase chain reaction (qRT-PCR). The relationships between circFAT1 expression, clinicopathological factors, and patient prognosis were analyzed.

Results

CircFAT1 expression levels were significantly lower in tumor tissue than in adjacent non-tumorous mucosal tissue (p = 0.01). The downregulation of circFAT1 expression promoted ESCC cell migration and invasive ability, but not proliferation. The expression of miR-548g was upregulated by the downregulation of circFAT1. The overexpression of miR-548g also promoted ESCC cell migration and invasion. Recurrence-free survival (p = 0.02) and cancer-specific survival (p = 0.04) rates were significantly higher in patients with elevated circFAT1 expression levels.

Conclusion

The expression level of circFAT1 is a novel prognostic marker in ESCC patients. New treatment strategies may be developed using the tumor suppressive functions of circFAT1.

Supplementary Information

The online version contains supplementary material available at 10.1245/s10434-021-10089-9.

Circular RNA circFAT1(e2) Promotes Colorectal Cancer Tumorigenesis via the miR-30e-5p/ITGA6 Axis

circRNAs (circular RNAs) are a family of noncoding RNAs and have diverse physiological and pathological functions. However, the functions and mechanisms of circRNAs in the development and progression of colorectal cancer (CRC) remain largely unknown. Here, we aimed to explore the functions and roles of circFAT1(e2) in CRC. qRT-PCR revealed that circFAT1(e2) in CRC tumor tissues was upregulated compared with that in adjacent normal tissues and was also upregulated in CRC cell lines. Small interfering RNAs (siRNAs) against circFAT1(e2) were used to decrease the expression of circFAT1(e2) in HCT116 and RKO cells in vitro. The roles of circFAT1(e2) in CRC cell metastasis and proliferation were then determined by transwell and CCK-8 assays. The results showed that circFAT1(e2) silencing markedly suppressed CRC growth. Moreover, we identified circFAT1(e2) as a promoter of CRC metastasis. Knockdown of circFAT1(e2) evidently reduced HCT116 and RKO cell migration and invasion. Furthermore, the regulatory relationship between circFAT1(e2) and its target miRNAs was verified by a luciferase reporter assay. We demonstrated that circFAT1(e2) could sponge miR-30e-5p, which regulated the expression level of integrin α6 (ITGA6), the downstream target gene of miR-30e-5p. Rescue assays demonstrated that knockdown of miR-30e-5p enhanced CRC proliferation and migration via ITGA6. Taken together, our results reveal the novel oncogenic roles of circFAT1(e2) in CRC through the miR-30e-5p/ITGA6 axis.

The emerging role of circular RNAs in common solid malignant tumors in children

Malignant tumors are one of the fatal diseases that threaten children’s physical and mental health and affect their development. Research has shown that the occurrence and development of malignant tumors are associated with the abnormal expression and regulation of genes. Circular RNAs (circRNAs) are noncoding RNAs that have a closed circular structure, with a relatively stable expression, and do not undergo exonuclease-mediated degradation readily. Recent studies have shown that circRNA plays an important role in the occurrence, metastasis, and invasion of solid malignant tumors (SMTs) in children. Thus, circRNA is being considered as a breakthrough in the treatment of SMTs in children. In this review, we describe the functions and mechanisms of circRNAs involved in SMTs in children oncogenesis, and summarize the roles of circRNAs in regulating cell proliferation, cell apoptotic death, the cell cycle, cell migrative and invasive ability, epithelial-mesenchymal transition (EMT), cancer stem cells and drug resistance in SMTs in children. In addition, we also discuss the role of circRNAs in the early diagnosis, pathological grading, targeted therapy, and prognosis evaluation of common SMTs in children. CircRNAs are likely to provide a novel direction in therapy in SMTs of children.

Role of noncoding RNA in drug resistance of prostate cancer

Prostate cancer is one of the most prevalent forms of cancer around the world. Androgen-deprivation treatment and chemotherapy are the curative approaches used to suppress prostate cancer progression. However, drug resistance is extensively and hard to overcome even though remarkable progress has been made in recent decades. Noncoding RNAs, such as miRNAs, lncRNAs, and circRNAs, are a group of cellular RNAs which participate in various cellular processes and diseases. Recently, accumulating evidence has highlighted the vital role of non-coding RNA in the development of drug resistance in prostate cancer. In this review, we summarize the important roles of these three classes of noncoding RNA in drug resistance and the potential therapeutic applications in this disease.