Circular RNA-100290 promotes cell proliferation and inhibits apoptosis in acute myeloid leukemia cells via sponging miR-203

The Role of Circular RNA in the Pathogenesis of Chemotherapy-Induced Cardiotoxicity in Cancer Patients: Focus on the Pathogenesis and Future Perspective

Cardiotoxicity is a serious challenge cancer patients face today. Various factors are involved in cardiotoxicity. Circular RNAs (circRNAs) are one of the effective factors in the occurrence and prevention of cardiotoxicity. circRNAs can lead to increased proliferation, apoptosis, and regeneration of cardiomyocytes by regulating the molecular pathways, as well as increasing or decreasing gene expression; some circRNAs have a dual role in cardiomyocyte regeneration or death. Identifying each of the pathways related to these processes can be effective on managing patients and preventing cardiotoxicity. In this study, an overview of the molecular pathways involved in cardiotoxicity by circRNAs and their effects on the downstream factors have been discussed.

Role of circRNAs in regulating cell death in cancer: a comprehensive review

Despite multiple diagnostic and therapeutic advances, including surgery, radiation therapy, and chemotherapy, cancer preserved its spot as a global health concern. Prompt cancer diagnosis, treatment, and prognosis depend on the discovery of new biomarkers and therapeutic strategies. Circular RNAs (circRNAs) are considered as a stable, conserved, abundant, and varied group of RNA molecules that perform multiple roles such as gene regulation. There is evidence that circRNAs interact with RNA-binding proteins, especially capturing miRNAs. An extensive amount of research has presented the substantial contribution of circRNAs in various types of cancer. To fully understand the linkage between circRNAs and cancer growth as a consequence of various cell death processes, including autophagy, ferroptosis, and apoptosis, more research is necessary. The expression of circRNAs could be controlled to limit the occurrence and growth of cancer, providing a more encouraging method of cancer treatment. Consequently, it is critical to understand how circRNAs affect various forms of cancer cell death and evaluate whether circRNAs could be used as targets to induce tumor death and increase the efficacy of chemotherapy. The current study aims to review and comprehend the effects that circular RNAs exert on cell apoptosis, autophagy, and ferroptosis in cancer to investigate potential cancer treatment targets.

A novel protein encoded by circLARP1B promotes the proliferation and migration of vascular smooth muscle cells by suppressing cAMP signaling

BACKGROUND AND AIMS

Circular RNA (circRNA) is closely related to atherosclerosis (AS) incidence and progression, but its regulatory mechanism in AS needs further elucidation. AS development is significantly influenced by abnormal vascular smooth muscle cells (VSMCs) growth and migration. This study explored the potential protein role of circLARP1B in VSMC proliferation and migration.

METHODS

We performed whole-transcriptome sequencing in human normal arterial intima and advanced atherosclerotic plaques to screen for differentially expressed circRNAs. The sequencing results were combined with database analysis to screen for circRNAs with coding ability. Real-time quantitative polymerase chain reaction was utilized to assess circLARP1B expression levels in atherosclerotic plaque tissues and cells. circLARP1B-243aa function and pathway in VSMCs growth and migration were studied by scratch, transwell, 5-ethynyl-2'-deoxyuridine, cell counting kit-8, and Western blot experiments.

RESULTS

We found that circLARP1B was downregulated in atherosclerotic plaque tissue and promoted the proliferation and migration of VSMCs. circLARP1B encodes a novel protein with a length of 243 amino acids. Through functional experiments, we confirmed the role of circLARP1B-243aa in enhancing VSMCs migration and proliferation. Mechanistically, circLARP1B-243aa promotes VSMCs migration and growth by upregulating phosphodiesterase 4C to inhibit the cyclic adenosine monophosphate signaling pathway.

CONCLUSIONS

Our results suggested that circLARP1B could promote VSMCs growth and migration through the encoded protein circLARP1B-243aa. Therefore, it could be a treatment target and biomarker for AS.

miR-557 inhibits hepatocellular carcinoma progression through Wnt/β-catenin signaling pathway by targeting RAB10

Accumulating evidence suggests that aberrant miRNAs participate in carcinogenesis and progression of hepatocellular carcinoma (HCC). Abnormal miR-557 expression is reported to interfere with the progression of several human cancers. However, the potential roles of miR-557 in HCC remain largely unknown. In the current study, we found that miR-557 was down-regulated in HCC tissues and cell lines, and was closely related to recurrence and metastasis of HCC. Notably, overexpression of miR-557 inhibited proliferation, migration, invasion, epithelial-to-mesenchymal transition (EMT) progression, blocked cells in G0/G1 phase of MHCC-97H cells in vitro, and suppressed tumor growth in vivo. However, loss of miR-557 facilitated these parameters in Huh7 cells both in vitro and in vivo. Moreover, RAB10 was identified as a direct downstream target of miR-557 through its 3'-UTR. Furthermore, RAB10 re-expression or knockdown partially abolished the effects of miR-557 on proliferation, migration, invasion, and EMT progression of HCC cells. Mechanistically, overexpression of miR-557 suppressed Wnt/β-catenin signaling by inhibiting GSK-3β phosphorylation, increasing β-catenin phosphorylation, and decreasing β-catenin transport to the nucleus, while knockdown of miR-557 activated Wnt/β-catenin signaling. Moreover, the TOP/FOP-Flash reporter assays showed that miR-557 overexpression or knockdown significantly suppressed or activated Wnt signaling activity, respectively. Additionally, low expression of miR-557 and high expression of RAB10 in HCC tissues was closely associated with tumor size, degree of differentiation, TNM stage and poor prognosis in HCC patients. Taken together, these results demonstrate that miR-557 blocks the progression of HCC via the Wnt/β-catenin pathway by targeting RAB10.

Circ_0058058 Knockdown Inhibits Acute Myeloid Leukemia Progression by Sponging miR-4319 to Regulate EIF5A2 Expression

Background: Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Circular RNAs (circRNAs) participate in the deterioration of many hominine cancers, including AML. In this study, the authors investigated the role and potential mechanism of circ_0058058 in AML progression. Methods: The expression of circ_0058058, microRNA-4319 (miR-4319), and eukaryotic initiation factor 5A2 (EIF5A2) was determined by quantitative real-time polymerase chain reaction. Cell proliferation, apoptosis, migration, and invasion were evaluated by cell counting kit-8 (CCK-8), cell colony formation, flow cytometry, and transwell assay, respectively. Levels of the relative proteins were detected by Western blot. The connection among circ_0058058, miR-4319, and EIF5A2 was verified by dual-luciferase reporter assay. Results: Circ_0058058 and EIF5A2 were enhanced, whereas miR-4319 was declined in AML. Circ_0058058 knockdown inhibited cell proliferation, migration, and invasion, and facilitated cell apoptosis by targeting miR-4319 in AML cells. Moreover, as a target of miR-4319, EIF5A2 overexpression overturned the inhibitory effects of miR-4319 upregulation on AML progression. Besides, circ_0058058 sponged miR-4319 to upregulate EIF5A2 expression in AML cells. Conclusion: Circ_0058058 knockdown inhibited cell proliferation, migration, and invasion, but accelerated cell apoptosis by reducing EIF5A2 expression by targeting miR-4319, suggesting that circ_0058058 could be a therapeutic target for the treatment of AML.

MiR-409-3p regulates the proliferation and apoptosis of THP-1 through targeting Rab10

Acute myeloid leukemia cytogenetics and molecular subtypes are connected with microRNAs, although it is unclear how miRNAs affect AML pathogenesis. miR-409-3p expression is downregulated in bone marrows, as we have previously demonstrated in our team. Nevertheless, the tumor-suppressing activities and molecular mechanisms of miR-409-3p remain unknown. Hence, in this study, we investigate at the functional significance of miR-409-3p in the development of AML. We found that a significant decrease in miR-409-3p expression was observed in THP-1 cell. The expression of miR-409-3p was altered in THP-1 by transfecting with agomiR-409-3p and agomiR-409-3p NC. A series of experiments showed that overexpression of miR-409-3p expression significantly suppressed proliferation and increased the apoptosis of THP-1. Moreover, Rab10 was confirmed as a direct target gene of miR-409-3p and was negatively modulated by miR-409-3p. Rab10 downregulation imitated the suppressed proliferation and increased the apoptosis of THP-1. Furthermore, miR-409-3p overexpression or Rab10 knockdown obviously down-regulated the expression levels of Bcl-2, but up-regulated Bax expression. In a xenograft mouse model, miR-409-3p-overexpressed THP-1 cells resulted in much less tumor weight and size in the mice bearing the cells as compared to the mock-transfected mice. Collectively, our findings demonstrated that miR-409-3p exerted tumor suppressor gene effects in AML by directly targeting Rab10, which might provide a promising therapeutic target for AML.

The non-coding competing endogenous RNAs in acute myeloid leukemia: biological and clinical implications

Acute myeloid leukemia (AML) is a hematologic carcinoma that has seen a considerable improvement in patient prognosis because of genetic diagnostics and molecularly-targeted therapies. Nevertheless, recurrence and drug resistance remain significant obstacles to leukemia treatment. It is critical to investigate the underlying molecular mechanisms and find solutions. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), circular RNAs, long non-coding RNAs, and pseudogenes, have been found to be crucial components in driving cancer. The competing endogenous RNA (ceRNA) mechanism has expanded the complexity of miRNA-mediated gene regulation. A great deal of literature has shown that ncRNAs are essential to the biological functions of the ceRNA network (ceRNET). NcRNAs can compete for the same miRNA response elements to influence miRNA-target RNA interactions. Recent evidence suggests that ceRNA might be a potential biomarker and therapeutic strategy. So far, however, there have been no comprehensive studies on ceRNET about AML. What is not yet clear is the clinical application of ceRNA in AML. This study attempts to summarize the development of research on the related ceRNAs in AML and the roles of ncRNAs in ceRNET. We also briefly describe the mechanisms of ceRNA and ceRNET. What's more significant is that we explore the clinical value of ceRNAs to provide accurate diagnostic and prognostic biomarkers as well as therapeutic targets. Finally, limitations and prospects are considered.

Circular RNA Expression Signatures Provide Promising Diagnostic and Therapeutic Biomarkers for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a known hematologic malignancy associated with a growing incidence and post-treatment relapse. Hence, finding a reliable diagnostic biomarker for CLL is crucial. Circular RNAs (circRNAs) represent a new class of RNA involved in many biological processes and diseases. This study aimed to define a circRNA-based panel for the early diagnosis of CLL. To this point, the list of the most deregulated circRNAs in CLL cell models was retrieved using bioinformatic algorithms and applied to the verified CLL patients' online datasets as the training cohort (n = 100). The diagnostic performance of potential biomarkers represented in individual and discriminating panels, was then analyzed between CLL Binet stages and validated in individual sample sets I (n = 220) and II (n = 251). We also estimated the 5-year overall survival (OS), introduced the cancer-related signaling pathways regulated by the announced circRNAs, and provided a list of possible therapeutic compounds to control the CLL. These findings show that the detected circRNA biomarkers exhibit better predictive performance compared to current validated clinical risk scales, and are applicable for the early detection and treatment of CLL.

Hsa_circ_0001944 regulates apoptosis by regulating the binding of PARP1 and HuR in leukemia and malignant transformed cells induced by hydroquinone

Hydroquinone (HQ) is one of the major metabolites of benzene and can cause abnormal gene expression. It is a known carcinogen that alters cell cycle disruption and cell proliferation. However, its chemical mechanism remain a mystery. Circular RNAs (circRNAs) are a subtype of noncoding RNAs (ncRNAs) that play a variety of roles in biological processes. Hsa_circ_001944 expression was upregulated in 30 leukemia patients and HQ-induced malignant transformed TK6 cells. Hsa_circ_001944 silencing inhibited the growth of HQ-TK6 cells and halted the cell cycle. The silencing of hsa_circ_0001944 led to increased cell accumulation in G1 versus S phase, increased apoptosis in the sh1944 versus the shNC group, and increased levels of DNA damage (γ-H2AX), leading to cell cycle arrest. In summary, inhibition of hsa_circ_001944 restricted cell growth by inhibiting cell cycle arrest and induced growth of HQ-TK6 cells by modulating PARP1 expression. Hsa_circ_0001944 targeted HuR, which is a kind of RNA-binding protein, to control PARP1 expression via RNAinter, RBPmap, and RBPdb. Fluorescence in situ hybridization combined with immunofluorescent labeling and western blotting experiments showed that hsa_circ_001944 was able to dissociate HuR and PARP1 binding in HQ-TK6 cells, control PARP1 production, and ultimately alter the PARP1/H-Ras pathway.

Circ_0035381 Regulates Acute Myeloid Leukemia Development by Modulating YWHAZ Expression via Adsorbing miR-582-3p

Acute myeloid leukemia (AML) is a common hematopoietic disorder. Many circular RNAs (circRNAs) are abnormally expressed in AML, including hsa_circ_0035381 (circ_0035381). Nevertheless, the function and mechanism of circ_0035381 in AML remain mostly unclear. Expression of circ_0035381 was determined by qRT-PCR. The impacts of circ_0035381 on AML cell proliferation, apoptosis, and mitochondrial damage were validated via performing loss-of-function experiments. Targeting relationship was predicted by bioinformatics analysis and verified via dual-luciferase reporter and RNA immunoprecipitation assays. Circ_0035381 was upregulated in AML bone marrow samples and cells. Circ_0035381 downregulation decreased AML cell growth in nude mice and restrained AML cell proliferation and contributed to AML apoptosis and mitochondrial damage in vitro. Circ_0035381 acted as a miR-582-3p sponge, and miR-582-3p downregulation mitigated the impacts of circ_0035381 interference on AML cell proliferation, apoptosis, and mitochondrial damage. MiR-582-3p targeted Tyrosine3-monooxygenase/tryptophan5-monooxygenase activation protein zeta (YWHAZ), and it restrained AML cell proliferation and facilitated AML cell apoptosis and mitochondrial damage by decreasing YWHAZ expression. Notably, circ_0035381 regulated YWHAZ expression via miR-582-3p. Circ_0035381 knockdown repressed cell proliferation and promoted cell apoptosis and mitochondrial damage via regulating the miR-582-3p/YWHAZ axis in AML.

The Promising Role of Non-Coding RNAs as Biomarkers and Therapeutic Targets for Leukemia

Early-stage leukemia identification is crucial for effective disease management and leads to an improvement in the survival of leukemia patients. Approaches based on cutting-edge biomarkers with excellent accuracy in body liquids provide patients with the possibility of early diagnosis with high sensitivity and specificity. Non-coding RNAs have recently received a great deal of interest as possible biomarkers in leukemia due to their participation in crucial oncogenic processes such as proliferation, differentiation, invasion, apoptosis, and their availability in body fluids. Recent studies have revealed a strong correlation between leukemia and the deregulated non-coding RNAs. On this basis, these RNAs are also great therapeutic targets. Based on these advantages, we tried to review the role of non-coding RNAs in leukemia. Here, the significance of several non-coding RNA types in leukemia is highlighted, and their potential roles as diagnostic, prognostic, and therapeutic targets are covered.

Circular RNAs: pivotal role in the leukemogenesis and novel indicators for the diagnosis and prognosis of acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematological malignancy and affected patients have poor overall survival (OS) rates. Circular RNAs (circRNAs) are a novel class of non-coding RNAs (ncRNAs) with a unique loop structure. In recent years, with the development of high-throughput RNA sequencing, many circRNAs have been identified exhibiting either up-regulation or down-regulation in AML patients compared with healthy controls. Recent studies have reported that circRNAs regulate leukemia cell proliferation, stemness, and apoptosis, both positively and negatively. Additionally, circRNAs could be promising biomarkers and therapeutic targets in AML. In this study, we present a comprehensive review of the regulatory roles and potentials of a number of dysregulated circRNAs in AML.

Hsa_circ_0015278 Regulates FLT3-ITD AML Progression via Ferroptosis-Related Genes

AML with the FLT3-ITD mutation seriously threatens human health. The mechanism by which circRNAs regulate the pathogenesis of FLT3-ITD mutant-type AML through ferroptosis-related genes (FerRGs) remains unclear. Differentially expressed circRNAs and mRNAs were identified from multiple integrated data sources. The target miRNAs and mRNAs of the circRNAs were predicted using various databases. The PPI network, ceRNA regulatory network, GO, and KEGG enrichment analyses were performed. The "survival" and the "pROC" R packages were used for K-M and ROC analysis, respectively. GSEA, immune infiltration analysis, and clinical subgroup analysis were performed. Finally, circRNAs were validated by Sanger sequencing and qRT-PCR. In our study, 77 DECircs-1 and 690 DECircs-2 were identified. Subsequently, 11 co-up-regulated DECircs were obtained by intersecting DECircs-1 and DECircs-2. The target miRNAs of the circRNAs were screened by CircInteractome, circbank, and circAtlas. Utilizing TargetScan, ENCORI, and miRWalk, the target mRNAs of the miRNAs were uncovered. Ultimately, 73 FerRGs were obtained, and the ceRNA regulatory network was constructed. Furthermore, MAPK3 and CD44 were significantly associated with prognosis. qRT-PCR results confirmed that has_circ_0015278 was significantly overexpressed in FLT3-ITD mutant-type AML. In summary, we constructed the hsa_circ_0015278/miRNAs/FerRGs signaling axis, which provides new insight into the pathogenesis and therapeutic targets of AML with FLT3-ITD mutation.

Functions and clinical significance of circular RNAs in acute myeloid leukemia

Circular RNAs (circRNAs) are a class of covalently closed single-stranded RNA molecules. Four types of circRNAs have been reported in animal cells, and they have typical characteristics in their biogenesis, nuclear export and degradation. Advances in our understanding of the molecular functions of circRNAs in sponging microRNAs, modulating transcription, regulating RNA-binding proteins, as well as encoding proteins have been made very recently. Dysregulated circRNAs are associated with human diseases such as acute myeloid leukemia (AML). In this review, we focus on the recently described mechanisms, role and clinical significance of circRNAs in AML. Although great progress of circRNAs in AML has been achieved, substantial efforts are still required to explore whether circRNAs exert their biological function by other mechanisms such as regulation of gene transcription or serving as translation template in AML. It is also urgent that researchers study the machineries regulating circRNAs fate, the downstream effectors of circRNAs modulatory networks, and the clinical application of circRNAs in AML.

Rapamycin inhibits the progression of human acute myeloid leukemia by regulating circ_0094100/miR-217/ATP1B1 axis

Rapamycin has been reported to inhibit the progression of diverse tumor cells. However, the functions of rapamycin in acute myeloid leukemia (AML) are little known. Cell Counting Kit-8 (CCK-8) assay was conducted to evaluate cell viability. Flow cytometry analysis was employed to analyze cell apoptosis and cell cycle process. Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed to determine the levels of circRNA_0094100 (circ_0094100) and microRNA-217 (miR-217). Western blot assay was carried out to measure the protein levels of proliferating cell nuclear antigen (PCNA), cyclin D1, B-cell lymphoma-2 (Bcl-2) and ATPase Na+/K+ transporting subunit beta 1 (ATP1B1). Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted to verify the relationship between miR-217 and circ_0094100 or ATP1B1. Rapamycin treatment suppressed AML cell viability and promoted apoptosis in a dose-dependent way. Circ_0094100 was elevated in AML tissues and cells. Moreover, the circ_0094100 level was reduced in AML cells treated with rapamycin. Circ_0094100 knockdown further inhibited rapamycin-mediated AML cell viability, and cell cycle, and promoted cell apoptosis. Circ_0094100 silencing reduced the protein levels of PCNA, cyclin D1, and Bcl-2 in rapamycin-treated AML cells. For mechanism analysis, circ_0094100 acted as the sponge for miR-217 and miR-217 inhibition reversed circ_0094100 knockdown-mediated malignant behaviors of rapamycin-treated AML cells. Furthermore, miR-217 overexpression suppressed cell viability and cell cycle and facilitated apoptosis in rapamycin-exposed AML cells, which were abolished by increasing ATP1B1. Rapamycin inhibited AML cell viability and cell cycle process and induced apoptosis through regulating circ_0094100/miR-217/ATP1B1 axis.

Circular RNAs Activity in the Leukemic Bone Marrow Microenvironment

Acute myeloid leukemia (AML) is a hematological malignancy originating from defective hematopoietic stem cells in the bone marrow. In spite of the recent approval of several molecular targeted therapies for AML treatment, disease recurrence remains an issue. Interestingly, increasing evidence has pointed out the relevance of bone marrow (BM) niche remodeling during leukemia onset and progression. Complex crosstalk between AML cells and microenvironment components shapes the leukemic BM niche, consequently affecting therapy responsiveness. Notably, circular RNAs are a new class of RNAs found to be relevant in AML progression and chemoresistance. In this review, we provided an overview of AML-driven niche remodeling. In particular, we analyzed the role of circRNAs and their possible contribution to cell-cell communication within the leukemic BM microenvironment. Understanding these mechanisms will help develop a more effective treatment for AML.

Advances in the Study of circRNAs in Hematological Malignancies

Circular RNAs (circRNAs) are non–protein-coding RNAs that have a circular structure and do not possess a 5` cap or 3` poly-A tail. Their structure is more stable than that of linear RNAs, and they are difficult to deform via hydrolysis. Advancements in measurement technology such as RNA sequencing have enabled the detection of circRNAs in various eukaryotes in both in vitro and in vivo studies. The main function of circRNAs involves sponging of microRNAs (MiRNAs) and interaction with proteins associated with physiological and pathological processes, while some circRNAs are involved in translation. circRNAs act as tumor suppressors or oncogenes during the development of many tumors and are emerging as new diagnostic and prognostic biomarkers. They also affect resistance to certain chemotherapy drugs such as imatinib. The objective of this review is to investigate the expression and clinical significance of circRNAs in hematological malignancies. We will also explore the effect of circRNAs on proliferation and apoptosis in hematological malignancy cells and their possible use as biomarkers or targets to determine prognoses. The current literature indicates that circRNAs may provide new therapeutic strategies for patients with hematologic malignancies.

LncRNA136131 suppresses apoptosis of renal tubular epithelial cells in acute kidney injury by targeting the miR-378a-3p/Rab10 axis

The pathogenesis of acute kidney injury (AKI) is not fully understood. To date, the exact role and regulatory mechanism of long non-coding RNA (lncRNA)136131 in AKI remains unclear. Here, we demonstrate that lncRNA136131 in BUMPT cells is induced by antimycin A. Furthermore, after incubating BUMPT cells in antimycin for two hours, lncRNA136131 prevented BUMPT cell apoptosis and cleaved caspase-3 expression. Mechanistically, lncRNA136131 sponged miR-378a-3p and then increased the expression of Rab10 to suppress apoptosis. Finally, I/R-induced decline of renal function, tubular damage, renal tubular cells apoptosis, and the upregulation of cleaved caspase-3 were aggravated by lncRNA136131 siRNA. In contrast, this effect was attenuated by the overexpression of lncRNA136131. In conclusion, lncRNA136131 protected against I/R-induced AKI progression by targeting miR-378a-3p/Rab10 and may be utilized as a novel target for AKI therapeutics.

Circ_KCNQ5 participates in the progression of childhood acute myeloid leukemia by enhancing the expression of RAB10 via binding to miR-622

BACKGROUND

: Acute myeloid leukemia (AML) is regarded as a haematological malignancy and seriously threatens the public's health. Circular RNA (circRNA) is gradually confirmed to be involved in the development of AML. The purpose of this study was to disclose the role of circRNA Potassium Voltage-Gated Channel Subfamily Q Member 5 (circ_KCNQ5) in AML.

METHODS

: Quantitative real-time PCR (qPCR) and western blot were used for expression analysis. Colony formation assay, EdU assay and MTT assay were performed to determine cell proliferation. Flow cytometry assay was conducted to determine cell apoptosis. The predicted binding relationship between miR-622 and circ_KCNQ5 or RAS oncogene family member 10 (RAB10) was verified by dual-luciferase reporter assay.

RESULTS

: The expression of circ_KCNQ5 was increased in bone marrow samples of childhood AML patients and AML cell lines. The knockdown of circ_KCNQ5 largely suppressed AML cell proliferation and promoted cell apoptosis. Circ_KCNQ5 directly bound to miR-622 and inhibited miR-622 expression. The cotransfection of miR-622 inhibitor reversed the effects of circ_KCNQ5 knockdown and thus recovered cell proliferation and depleted cell apoptosis. RAB10 was a target of miR-622, and circ_KCNQ5 bound to miR-622 to increase the expression of RAB10. MiR-622 restoration inhibited AML cell proliferation and induced cell apoptosis, while RAB10 overexpression abolished these effects.

CONCLUSION

: Circ_KCNQ5 high expression was associated with childhood AML malignant development, and circ_KCNQ5 participated in AML progression by regulating the miR-622/RAB10 pathway.

Homo sapiens circular RNA 0003602 (Hsa_circ_0003602) accelerates the tumorigenicity of acute myeloid leukemia by modulating miR-502-5p/IGF1R axis

Acute myeloid leukemia (AML) has become a worldwide malignant cancer. We intended to investigate the critical roles and mechanism underlying homo sapiens circular RNA 0003602 (hsa_circ_0003602) in AML progression, especially in tumor cell proliferation, migration, invasion, and apoptosis. Real-time PCR was applied to identify the differential expression of hsa_circ_0003602 and miR-502-5p in AML bone marrow tissues and cell lines. In addition, western blot analysis was employed to determine the levels insulin-like growth factor 1 receptor (IGF1R) protein. The biological behaviors were assessed by CCK-8 cell viability assay, flow cytometry assay for apoptosis detection, and Transwell migration and invasion assay. The relationships between target miRNA and downstream mRNA were investigated by bioinformatics, luciferase reporter assay, and biotin-labeled RNA pull-down assay. Hsa_circ_0003602 was upregulated and predicted poor survival in AML. Knockdown of hsa_circ_0003602 in AML cell lines induced the inhibition of proliferation, migration, and invasion and caused apoptosis. Hsa_circ_0003602 sequestered miR-502-5p by functioning as a competitive endogenous RNA (ceRNA), thereby regulating IGF1R expression. Hsa_circ_0003602 acted as a tumor promoter in AML via miR-502-5p/IGF1R axis. Our study provides evidence that hsa_circ_0003602, miR-502-5p, and IGF1R might form a regulatory axis to affect the carcinogenicity of AML cells and provide potential targets for the treatment of AML.

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.

Epigenetic modifications in acute myeloid leukemia: The emerging role of circular RNAs (Review)

Canonical epigenetic modifications, which include histone modification, chromatin remodeling and DNA methylation, play key roles in numerous cellular processes. Epigenetics underlies how cells that posses DNA with similar sequences develop into different cell types with different functions in an organism. Earlier epigenetic research has primarily been focused at the chromatin level. However, the number of studies on epigenetic modifications of RNA, such as N1‑methyladenosine, 2'‑O‑ribosemethylation, inosine, 5‑methylcytidine, N6‑methyladenosine (m6A) and pseudouridine, has seen an increase. Circular RNAs (circRNAs), a type of RNA species that lacks a 5' cap or 3' poly(A) tail, are abundantly expressed in acute myeloid leukemia (AML) and may regulate disease progression. circRNAs possess various functions, including microRNA sponging, gene transcription regulation and RNA‑binding protein interaction. Furthermore, circRNAs are m6A methylated in other types of cancer, such as colorectal and hypopharyngeal squamous cell cancers. Therefore, the critical roles of circRNA epigenetic modifications, particularly m6A, and their possible involvement in AML are discussed in the present review. Epigenetic modification of circRNAs may become a diagnostic and therapeutic target for AML in the future.

Circular RNAs in acute myeloid leukemia

Although mechanistic studies clarifying the molecular underpinnings of AML have facilitated the development of several novel targeted therapeutics, most AML patients still relapse. Thus, overcoming the inherent and acquired resistance to current therapies remains an unsolved clinical problem. While current diagnostic modalities are primarily defined by gross morphology, cytogenetics, and to an extent, by deep targeted gene sequencing, there is an ongoing demand to identify newer diagnostic, therapeutic and prognostic biomarkers for AML. Recent interest in exploring the role of circular RNA (circRNA) in elucidating AML biology and therapy resistance has been promising. This review discerns the circular RNAs’ evolving role on the same scientific premise and attempts to identify its potential in managing AML.

From circRNAs to fusion circRNAs in hematological malignancies

Circular RNAs (circRNAs) represent a type of endogenous noncoding RNA generated by back-splicing events. Unlike the majority of RNAs, circRNAs are covalently closed, without a 5' end or a 3' poly(A) tail. A few circRNAs can be associated with polysomes, suggesting a protein-coding potential. CircRNAs are not degraded by RNA exonucleases or ribonuclease R and are enriched in exosomes. Recent developments in experimental methods coupled with evolving bioinformatic approaches have accelerated functional investigation of circRNAs, which exhibit a stable structure, a long half-life, and tumor specificity and can be extracted from body fluids and used as potential biological markers for tumors. Moreover, circRNAs may regulate the occurrence and development of cancers and contribute to drug resistance through a variety of molecular mechanisms. Despite the identification of a growing number of circRNAs, their effects in hematological cancers remain largely unknown. Recent studies indicate that circRNAs could also originate from fusion genes (fusion circRNAs, f-circRNAs) next to chromosomal translocations, which are considered the primary cause of various cancers, notably hematological malignancies. This Review will focus on circRNAs and f-circRNAs in hematological cancers.

Circ_0009910 sponges miR-491-5p to promote acute myeloid leukemia progression through modulating B4GALT5 expression and PI3K/AKT signaling pathway

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias with an overall poor prognosis. Circular RNAs (circRNAs) have been verified to play important regulatory roles in AML progression. However, the role and molecular mechanism of circ_0009910 in AML development have not be completely clarified.

METHODS

The expression levels of circ_0009910, microRNA-491-5p (miR-491-5p), and β-1, 4-galactosyltransferase 5 (B4GALT5) were measured by quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot. Cell proliferation and self-renewal ability were assessed via Cell Counting Kit-8 (CCK-8) and sphere formation assay. Cell cycle distribution and cell apoptosis were evaluated by flow cytometry. Caspase-3 activity was tested by Caspase-3 Activity Assay Kit. Western blot was used to examine the protein levels of autophagy-related markers and PI3K/AKT pathway-related markers. The interaction between miR-491-5p and circ_0009910 or B4GALT5 was confirmed by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, or RNA pull-down assay.

RESULTS

Circ_0009910 was highly expressed in AML tissues and cells. Silenced circ_0009910 could significantly inhibit the proliferation, sphere formation, and autophagy and promoted the apoptosis of AML cells. Circ_0009910 bound to miR-491-5p in AML cells, and circ_0009910 promoted AML progression partly through sponging miR-491-5p in vitro. B4GALT5 was a target of miR-491-5p, and miR-491-5p overexpression-mediated influences in AML cells were effectually overturned by the addition of B4GALT5 overexpression plasmid. Furthermore, circ_0009910 could regulate the expression of B4GALT5 by downregulating miR-491-5p in AML cells. Additionally, circ_0009910 could activate the PI3K/AKT signaling pathway by sponging miR-491-5p.

CONCLUSION

Circ_0009910 could suppress the proliferation, sphere formation, and autophagy and accelerated apoptosis by modulating B4GALT5 expression and activating the PI3K/AKT signaling pathway via sponging miR-491-5p in AML cells, suggesting that circ_0009910 might be a potential biomarker for the treatment of AML.

Exosomal circ_0004136 enhances the progression of pediatric acute myeloid leukemia depending on the regulation of miR-570-3p/TSPAN3 axis

Circular RNAs (circRNAs) have been implicated in the progression of pediatric acute myeloid leukemia (AML). Although circ_0004136 has been found to play a crucial role in AML, our understanding of its molecular mechanism remains very limited. The levels of circ_0004136, miR-570-3p and tetraspanin 3 (TSPAN3) were determined by quantitative real-time PCR or western blot. Cell viability, migration, invasion, cell cycle and apoptosis were detected using the Cell Counting Kit-8, transwell and flow cytometry assays. Targeted relationships among circ_0004136, miR-570-3p and TSPAN3 were validated by dual-luciferase reporter and RNA immunoprecipitation assays. Our data showed that circ_0004136 could be transmitted by exosomes, and exosomal circ_0004136 was highly expressed in AML serum and cells. Circ_0004136 was unusually stable and mainly localized in the cytoplasm. Circ_0004136 knockdown mediated by exosomes hampered AML cell viability, cell cycle progression, migration and invasion, and promoted cell apoptosis. Moreover, circ_0004136 worked as a sponge of miR-570-3p and TSPAN3 was a functional target of miR-370-3p in AML cells. The suppression of circ_0004136 knockdown mediated by exosomes on AML cell malignant progression was reversed by miR-570-3p downregulation, and the increased miR-570-3p expression hindered the progression of aggressive AML by downregulating TSPAN3. Furthermore, circ_0004136 worked as a miR-570-3p sponge to modulate TSPAN3 expression. Our findings identified a novel regulatory mechanism in which exosome-mediated circ_0004136 knockdown restrained AML cell malignant progression at least partly through targeting the miR-570-3p/TSPAN3 axis, highlighting a novel therapeutic strategy for AML management.

Long noncoding RNA CYTOR triggers gastric cancer progression by targeting miR-103/RAB10

Growing evidence has indicated that the long noncoding RNA (lncRNA) CYTOR is involved in the initiation and progression of malignancies, including gastric cancer. Nevertheless, the mechanisms of CYTOR in gastric cancer development are not fully understood. In the present study, we aimed to clarify the association of CYTOR, miR-103, and RAB10 in gastric cancer progression. We found that CYTOR expression was increased in metastatic gastric cancer biopsies compared with that in primary samples. CYTOR expression was significantly positively correlated with the invasiveness, lymph node metastasis, and advanced stages of gastric cancer. In addition, downregulation of CYTOR expression hampered cell proliferation and migration but induced cell apoptosis. Furthermore, CYTOR sponged miR-103 and diminished miR-103 expression, thus rescuing oncogene RAB10 expression. Knockdown of CYTOR suppressed tumor growth in human BGC823 mouse models. These findings suggest that the CYTOR/miR-103/RAB10 axis is a novel signaling pathway that facilitates gastric cancer progression. CYTOR-targeted interventions provide a rationale to improve therapies targeting gastric cancer progression.

Silencing of circTASP1 inhibits proliferation and induces apoptosis of acute myeloid leukaemia cells through modulating miR-515-5p/HMGA2 axis

Acute myeloid leukaemia (AML) is a common hematopoietic disease that is harmful to the lives of children and adults. CircRNAs are aberrantly expressed in the haematologic malignancy cells. However, the expression of circTASP1 and its function in AML remain unclear. In this study, we showed that circTASP1 was significantly up‐regulated in AML peripheral blood samples and cells. Knockdown of circTASP1 inhibited proliferation and promoted apoptosis of HL60 and THP‐1 cells in vitro. Bioinformatics prediction and luciferase reporter assay proved that circTASP1 sponged miR‐515‐5p and negatively regulated miR‐515‐5p expression in HL60 and THP‐1 cells. High mobility group A2 (HMGA2) was proved to be a downstream target of miR‐515‐5p. The rescue experiments confirmed that knockdown of circTASP1 inhibited proliferation and induced apoptosis by modulating miR‐515‐5p/HMGA2 pathway. Moreover, the in vivo experiment indicated that knockdown of circTASP1 suppressed tumour growth. In conclusion, circTASP1 acts as a sponge for miR‐515‐5p to regulate HMGA2, thereby promoting proliferation and inhibiting apoptosis during AML progression. Thus, circTASP1 has the potential to be explored as a therapeutic target for AML treatment.

Hsa_circ_0002483 regulates miR-758-3p/MYC axis to promote acute myeloid leukemia progression

Circular RNAs are relevant to progression of acute myeloid leukemia (AML). Nevertheless, how and whether hsa_circ_0002483 (circ_0002483) participates in AML progression are largely uncertain. The bone marrow samples were harvested from 31 AML patients or 31 normal subjects. Circ_0002483, microRNA (miR)-758-3p and myelocytomatosis oncogene (MYC) abundances were examined via quantitative reverse transcription polymerase chain reaction and Western blot. Cell proliferation, cycle process and apoptosis were analyzed via Cell Counting Kit-8, flow cytometry, caspase 3 activity and related protein levels. Target relationship was investigated by dual-luciferase reporter assay and RNA immunoprecipitation. Circ_0002483 expression was elevated in AML patients and cells. Circ_0002483 silence constrained AML cell proliferation and facilitated cell cycle arrest and apoptosis. miR-758-3p was reduced in AML and decreased via circ_0002483. miR-758-3p down-regulation mitigated the inhibitive influence of circ_0002483 interference on AML progression. MYC was decreased by miR-758-3p, and circ_0002483 could regulate MYC expression by miR-758-3p. miR-758-3p overexpression restrained cell proliferation and promoted cycle arrest and apoptosis via decreasing MYC. Circ_0002483 knockdown repressed AML cell proliferation and promoted cycle arrest and apoptosis via controlling miR-758-3p/MYC axis.

CircRNA_104889 promotes lung adenocarcinoma cell invasion via sponging miR4458

Background

Lung adenocarcinoma is metastatic cancer with a high mortality rate. Circular RNAs (circRNAs) are a type of noncoding RNA and play a vital role in cancer progression. However, the expression and function of circRNAs in lung adenocarcinoma are still mostly unknown.

Methods

In this study, we screened the differential expression of circRNAs in human bronchial epithelial cells (HBE) and A549 human lung adenocarcinoma cell line (A549) by human circRNA microarray and RT-qPCR. The role of overexpressed circRNA_104889 in A549 cell proliferation, apoptosis, migration, and invasion was studied extensively. Intracellular localization of circRNA_104889 was visualized by FISH assay. MiRNA sponging, ERK1/2 signaling, and caspase-3 expression were analyzed in siRNA-mediated circRNA_104889 knockdowned A549 cells.

Results

CircRNA microarray showed overexpression of circRNA_104889 (> 13-fold) in A459 cells compared to HBE. This finding was further corroborated by the RT-qPCR result. CircRNA_104889 was mainly localized in the cytoplasm of A549 cells. The knockdown of circRNA_104889 in A549 cells by si-RNA mediated RNA interference did not affect cell proliferation and apoptosis but significantly inhibited cell migration and invasion in vitro. Furthermore, knockdown of circRNA_104889 led to an increase of miR4458 expression. Overexpression of miR4458 inhibited A549 cell migration. Both the knockdown of circRNA_104889 and overexpression of miR4458 inhibited the caspase-3 expression and ERK1/2 phosphorylation in A549 cells.

Conclusions

CircRNA_104889 promotes lung adenocarcinoma cell migration and invasion by sponging miR4458 and targeting ERK1/2 signaling and caspase-3 expression.

CircRAD18 Accelerates the Progression of Acute Myeloid Leukemia by Modulation of miR-206/PRKACB Axis

Background

Circular RNAs (circRNAs) play a crucial role in tumorigenesis. However, the effects of circRNAs on acute myeloid leukemia (AML) remain largely unexplored. We explored the function of circRAD18 in AML development.

Methods

QRT-PCR was performed for the levels of circRAD18, RAD18, microRNA-206 (miR-206) and protein kinase CAMP-activated catalytic subunit beta (PRKACB). Cell Counting Kit-8 (CCK-8) assay and colony formation assay were utilized for cell proliferation. Flow cytometry analysis was carried out to analyze cell apoptosis and cell cycle process. Transwell assay was manipulated for cell migration and invasion. Western blot assay was conducted for protein levels. Dual-luciferase reporter assay was adopted to verify the interaction between miR-206 and circRAD18 or PRKACB.

Results

CircRAD18 level was increased in AML patients’ blood specimens and AML cell lines compared to normal controls. CircRAD18 knockdown impeded the proliferation, migration and invasion and facilitated the apoptosis and cell cycle arrest in AML cells. Moreover, circRAD18 was identified as a sponge for miR-206, and circRAD18 knockdown-mediated effect on AML cell progression was reversed by miR-206 suppression. Additionally, PRKACB was the target gene of miR-206. MiR-206 overexpression suppressed the malignant behaviors of AML cells, while PRKACB elevation restored the effects.

Conclusion

CircRAD18 aggravated the malignancy of AML cells through reducing miR-206 expression and elevating PRKACB expression, indicating circRAD18 might be a therapeutic target for AML.

The functions and clinical significance of circRNAs in hematological malignancies

With covalently closed circular structures, circular RNAs (circRNAs) were once misinterpreted as by-products of mRNA splicing. Being abundant, stable, highly conserved, and tissue-specific, circRNAs are recently identified as a type of regulatory RNAs. CircRNAs bind to certain miRNAs or proteins to participate in gene transcription and translation. Emerging evidence has indicated that the dysregulation of circRNAs is closely linked to the tumorigenesis and treatment response of hematological malignancies. CircRNAs play critical roles in various biological processes, including tumorigenesis, drug resistance, tumor metabolism, autophagy, pyroptosis, and ferroptosis. The N6-methyladenosine modification of circRNAs and discovery of fusion-circRNAs provide novel insights into the functions of circRNAs. Targeting circRNAs in hematological malignancies will be an attractive treatment strategy. In this review, we systematically summarize recent advances toward the novel functions and molecular mechanisms of circRNAs in hematological malignancies, and highlight the potential clinical applications of circRNAs as novel biomarkers and therapeutic targets for future exploration.

Circ-PTK2 promotes the proliferation and suppressed the apoptosis of acute myeloid leukemia cells through targeting miR-330-5p/FOXM1 axis

BACKGROUND

Acute myeloid leukemia (AML) is characterized by malignant clonal disorder of blood cells with high relapse rate and low survival rate. Circular RNAs (circRNAs) have shown their important regulatory roles in AML progression. Here, we intended to disclose the role of circular RNA protein tyrosine kinase 2 (circ-PTK2) in the progression of AML and illustrate the potential working mechanisms.

METHODS

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and colony formation assay were conducted to analyze cell proliferation ability, and the apoptosis rate was assessed by flow cytometry. Dual-luciferase reporter assay was used to validate the direct interaction between microRNA-330-5p (miR-330-5p) and circ-PTK2 or forkhead box M1 (FOXM1).

RESULTS

Circ-PTK2 was highly expressed in AML. Circ-PTK2 interference suppressed the proliferation and triggered the apoptosis of AML cells. Circ-PTK2 directly bound to miR-330-5p. Si-circ-PTK2-mediated inhibition on the malignant behaviors of AML cells was partly counteracted by the addition of anti-miR-330-5p. MiR-330-5p directly interacted with FOXM1 messenger RNA (mRNA), and FOXM1 overexpression partly reversed miR-330-5p-induced influence in AML cells. Circ-PTK2 up-regulated FOXM1 expression through sponging miR-330-5p in AML cells.

CONCLUSION

Circ-PTK2 promoted the proliferation and hampered the apoptosis of AML cells through targeting miR-330-5p/FOXM1 axis.

Circular RNAs: New players in thyroid cancer

The prevalence of thyroid cancer the most frequent endocrine malignancy, is rapidly increasing. Most of thyroid cancers are relatively indolent, however, some cases still possess a risk of developing into lethal types of thyroid cancer. Regarding its multistep tumorigenesis, the determination of the underlying mechanisms is a vital issue for thyroid cancer therapy. Circular RNAs (circRNAs) are a type of non-coding RNAs with a closed loop structure. Numerous circRNAs have been identified in cancerous tissues. Mounting data recommends that the biological activities of circRNAs, such as serving as microRNA or ceRNAs sponges, interacting with proteins, modulating gene translation and transcription, suggesting that circRNAs will be potential targets as well as agents for the prognosis and diagnosis of diseases, including cancer. Given that circular RNAs acts as oncogenes or tumor suppressors in the thyroid cancer. Several studies documented that circular RNAs via microRNA and protein sponges could regulate a sequences of cellular and molecular mechanisms e.g., apoptosis, angiogenesis, tumor growth, and invasion that are involved in thyroid cancer pathogenesis. Herein, we summarized the role of circular RNAs as therapeutic and diagnostic biomarkers in the thyroid cancer. Moreover, we highlighted the role of these molecules in the pathogenesis of various cancers.

Circular RNAs in Hematopoiesis with a Focus on Acute Myeloid Leukemia and Myelodysplastic Syndrome

Circular RNAs (circRNAs) constitute a recently recognized group of noncoding transcripts that function as posttranscriptional regulators of gene expression at a new level. Recent developments in experimental methods together with rapidly evolving bioinformatics approaches have accelerated the exploration of circRNAs. The differentiation of hematopoietic stem cells into a broad spectrum of specialized blood lineages is a tightly regulated process that depends on a multitude of factors, including circRNAs. However, despite the growing number of circRNAs described to date, the roles of the majority of them in hematopoiesis remain unknown. Given their stability and disease-specific expression, circRNAs have been acknowledged as novel promising biomarkers and therapeutic targets. In this paper, the biogenesis, characteristics, and roles of circRNAs are reviewed with an emphasis on their currently recognized or presumed involvement in hematopoiesis, especially in acute myeloid leukemia and myelodysplastic syndrome.

Circular RNAs in leukemia

In pace with the development of gene sequencing technology and transcriptome research, it has been found that 70 to 90% of the human genome is transcribed into RNAs, while only 2% of RNAs encode proteins. This implies that non-coding RNAs (ncRNAs) may exert vital biological functions and a full analysis of non-coding transcriptomes is needed. Over the past decade, the advance in high-throughput sequencing and transcriptome profiling has enabled the identification of circular RNAs (circRNAs) involved in many biological processes and the occurrence and development of diseases. Accumulating evidence has revealed that circRNAs may serve as new biomarkers for diagnosis as well as provide promising therapeutic approaches and novel drug screening strategies for leukemia. A comprehensive understanding of circRNAs in leukemia is a prerequisite for the development of clinical translational research. In this review, we will discuss the general information of circRNAs and focus on the current advances in understanding the association between dysregulated circRNAs and leukemia.

Circular RNAs in Blood Malignancies

Circular (circ)RNAs influence a wide range of biological processes at least in part by interacting with proteins and microRNAs. CircRNAs expressed in the hematopoietic compartment have been increasingly recognized as modulators of physiological and pathological features of hematopoetic stem cell (HSC)-derived populations. In particular, several circRNAs were found to enhance or suppress tumor progression in blood malignancies such as leukemias and lymphomas. Moreover, numerous circRNAs have been proposed to help confer resistance to the conventional treatments used in hematopoietic cancers. Here, we review the most important circRNAs described thus far in acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), lymphomas, and multiple myeloma (MM). We discuss the usefulness of circRNAs as diagnostic and prognostic markers and their potential value as therapeutic targets.

Circ-100290 Positively Regulates Angiogenesis Induced by Conditioned Medium of Human Amnion-Derived Mesenchymal Stem Cells Through miR-449a/eNOS and miR-449a/VEGFA Axes

The powerful pro-angiogenic capacity of human amnion-derived mesenchymal stem cells (hAMSCs) could be a valuable therapeutic angiogenesis strategy for bone regeneration. However, the molecular mechanisms underlying this process remain largely unknown. Herein, we report upregulated expression of circular RNA 100290 (circ-100290) and an enhanced angiogenic phenotype of human umbilical vein endothelial cells (HUVECs) incubated with conditioned medium from hAMSCs (hAMSC-CM), whereas downregulation of circ-100290 reversed the pro-angiogenic capacity of HUVECs induced by hAMSC-CM. Circ-100290/microRNA 449a (miR-449a)/endothelial nitric oxide synthase (eNOS) and circ-100290/miR-449a/vascular endothelial growth factor A (VEGFA) axes were predicted by a bioinformatics method and subsequently verified by luciferase reporter assays in vitro. Gain- or loss-of-function assays were then performed using small interfering RNAs (siRNAs) targeting circ-100290, or a plasmid overexpressing circ-100290. As expected, downregulation of circ-100290 in HUVECs led to weakened tube formation and migration of HUVECs following hAMSC-CM treatment, along with decreased expression of eNOS and VEGFA. In contrast, upregulation of circ-100290 led to enhanced tube formation and migration of HUVECs following hAMSC-CM treatment, along with increased expression of eNOS and VEGFA. Furthermore, a miR-449a inhibitor could largely rescue the effect of circ-100290 silencing on HUVECs, whereas a miR-449a mimic could significantly rescue the effect of overexpressing circ-100290 on HUVECs. Functional assays using eNOS or VEGF receptor inhibitors indicated eNOS and VEGFA may be important targets of miR-449a. Finally, a Matrigel plug assay revealed weakened angiogenesis when circ-100290 was silenced in HUVECs, but enhanced angiogenesis when circ-100290 was overexpressed in vivo. Our results suggest that circ-100290 might function via miR-449a/eNOS and miR-449a/VEGFA axes in the pro-angiogenic role of hAMSC-CM on HUVECs.

Functional and Clinical Impact of CircRNAs in Oral Cancer

The increasing number of recently published works regarding the role of circular RNAs (circRNAs) in oral cancer highlights the key contribution of this novel class of endogenous noncoding RNAs as regulators of critical signaling pathways and their clinical value as novel biomarkers. This review summarizes and puts into context the existing literature in order to clarify the relevance of circRNAs as novel mediators of oral cancer pathogenesis as well as their potential usefulness as predictors of clinical outcome and response to therapy in this disease.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

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

LncRNA TUG1 Regulates Cell Viability and Death by Regulating miR-193a-5p/Rab10 Axis in Acute Myeloid Leukemia

Background

Acute myeloid leukemia (AML) is a serious threat to human health. Long non-coding RNA (lncRNA) Taurine-Upregulated Gene1 (TUG1) has been reported to participate in the development and progression of several cancers, including AML. Herein, we aimed to investigate the pathognomonic role of TUG1 in AML cells and its potential mechanistic pathway.

Methods

Quantitative real-time PCR (qRT-PCR) assay was applied to detect the expression levels of lncRNA TUG1, miR-193a-5p and Rab10 in AML bone marrow and cell lines. The CCK-8 assay was conducted to assess the cell viability of AML HL-60 and NB4 cells and cell apoptotic assay was performed to assess the cell death. Dual-luciferase reporter assay was carried out to clarify the relationships among TUG1, miR-193a-5p and Rab10. Also, the protein level of Rab10 was examined by Western blot assay.

Results

LncRNA TUG1 was up-regulated in AML bone marrow and cells. Functional analysis showed that the silencing of TUG1 suppressed cell viability, while promoted cell death in AML HL-60 and NB4 cells. TUG1 targeted miR-193a-5p and negatively regulated miR-193a-5p expression. Overexpressed miR-193a-5p resulted in the decrease of cell viability and the increase in the cell death in AML cells. Restoration experiments proved that TUG1 regulated the cell viability and death of AML cells through regulating the miR-193a-5p/Rab10 axis. Rab10 was a direct target of miR-193a-5p and was inversely regulated by miR-193a-5p. TUG1 regulated the cell viability and death of AML cells through upregulating Rab10.

Conclusion

Silencing of lncRNA TUG1 induces a cytotoxic effect on AML cell lines through sponging miR-193a-5p and the suppression of Rab10.

Overexpression of circRNA_100290 promotes the progression of laryngeal squamous cell carcinoma through the miR-136-5p/RAP2C axis

Circular RNAs (circRNAs) exert critical functions in tumorigenesis and tumor development, but whether and how circRNAs contribute to laryngeal squamous cell carcinoma (LSCC) is unclear. In this study, we explored the function and mechanisms of circRNA_100290 in LSCC. Tissue samples were obtained from 40 patients with LSCC. The expression of circRNA_100290 and other targets was measured through quantitative reverse transcription-polymerase chain reaction and western blot analysis. Cell proliferation, colony-forming ability, and apoptosis were tested using CCK-8 assay and EdU assay, colony formation assay, and flow cytometry, respectively. Cell migration and invasion were detected by Transwell assay. Moreover, the interactions between circRNA_100290, miR-136-5p, and RAP2C were analyzed by bioinformatics, and verified by dual-luciferase reporter assays. Here, we found that circRNA_100290 expression was significantly upregulated in LSCC tissues and cell lines compared with the normal controls. Expression of circRNA_100290 positively correlated with advanced TNM stage and lymph node metastasis in LSCC patients. In cell culture, upregulation of circRNA_100290 promoted LSCC cell proliferation, migration, and invasion, while it inhibited cell apoptosis; downregulating circRNA_100290 exerted the opposite effects. In vivo, circRNA_100290 overexpression dramatically promoted tumor growth. Mechanistically, circRNA_100290 may act as a sponge of miR-136-5p, and inhibiting miR-136-5p in LSCC cells indeed reversed the effects of circRNA_100290 downregulation. The RAS oncogene RAP2C was predicted to be a target of miR-136-5p, and downregulating RAP2C in LSCC cells partially reversed the oncogenic effects of circRNA_100290 overexpression or miR-136-5p decrease. Our findings suggest that circRNA_100290 promotes LSCC progression by targeting the miR-136-5p/RAP2C axis, which may lead to the identification of potential therapeutic targets.

Recent Progress on Circular RNA Research in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a myeloid malignancy characterized by the proliferation of abnormal and immature myeloid blasts in the bone marrow. Circular RNA (circRNA) is a novel class of long non-coding RNA with a stable circular conformation that regulates various biological processes. The aberrant expression of circRNA and its impact on AML progression has been reported by a number of studies. Despite recent advances in circRNA research, our understanding of the leukemogenic mechanism of circRNA remains very limited, and translating the current circRNA-related research into clinical practice is challenging. This review provides an update on the functional roles of and research progress on circRNAs in AML with an emphasis on mechanistic insights. The challenges and opportunities associated with circRNA-based diagonostic and therapeutic development in AML are also outlined.

Circular RNA circCHFR Facilitates the Proliferation and Migration of Vascular Smooth Muscle via miR-370/FOXO1/Cyclin D1 Pathway

Circular RNA (circRNA) is a novel subgroup of noncoding RNA in the human transcriptome playing a vital role in the atherosclerosis of cerebrovascular disease. However, the in-depth mechanism by which circRNA regulates the vascular smooth muscle proliferation and migration is still elusive. Here, a novel identified circRNA, circCHFR, was validated to be aberrantly overexpressed in the ox-LDL-induced vascular smooth muscle cell (VSMCs). Functionally, the circCHFR silencing by oligonucleotide transfection suppressed the proliferation and migration ability of VSMCs. Mechanically, bioinformatics tools and luciferase reporter assay state that circCHFR acts as a sponge of miR-370, and miR-370 targets the 3' UTR of FOXO1. Furthermore, the transcription factor FOXO1 could bind with the promoter region of CCND1 mRNA and promote Cyclin D1 expression. In summary, this finding states the vital role of the circCHFR/miR-370/FOXO1/Cyclin D1 axis and provides a profound understanding about the circRNA in smooth muscle cells and atherosclerosis.

Role of microRNAs, circRNAs and long noncoding RNAs in acute myeloid leukemia

Acute myeloid leukemia (AML) is a malignant tumor of the immature myeloid hematopoietic cells in the bone marrow (BM). It is a highly heterogeneous disease, with rising morbidity and mortality in older patients. Although researches over the past decades have improved our understanding of AML, its pathogenesis has not yet been fully elucidated. Long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are three noncoding RNA (ncRNA) molecules that regulate DNA transcription and translation. With the development of RNA-Seq technology, more and more ncRNAs that are closely related to AML leukemogenesis have been discovered. Numerous studies have found that these ncRNAs play an important role in leukemia cell proliferation, differentiation, and apoptosis. Some may potentially be used as prognostic biomarkers. In this systematic review, we briefly described the characteristics and molecular functions of three groups of ncRNAs, including lncRNAs, miRNAs, and circRNAs, and discussed their relationships with AML in detail.

Long non-coding RNA DLX6-AS1/miR-141-3p axis regulates osteosarcoma proliferation, migration and invasion through regulating Rab10

Long non-coding RNA (lncRNAs) DLX6-AS1 plays significant roles in various types of malignant tumors, including osteosarcoma (OS), the most prevalent primary malignant bone tumor.