Emerging Roles of Circular RNAs in Osteosarcoma

circ_0002060 Enhances Doxorubicin Resistance in Osteosarcoma by Regulating the miR-198/ABCB1 Axis

Background: Osteosarcoma (OS) is a common, aggressive primary sarcoma of bone. Drug resistance is a huge obstacle to chemotherapy for cancer. This study aimed to investigate the role and mechanism of circ_0002060 in OS resistance to doxorubicin (DOX). Methods: The levels of circ_0002060, miR-198, and ATP-binding cassette subfamily B member 1 (ABCB1) in OS tissues and DOX-resistant OS cells were measured by quantitative real-time polymerase chain reaction or Western blot assay. Kaplan-Meier analysis was performed to determine the relationship between circ_0002060 expression in OS tissues and overall survival of OS patients. The half-inhibitory concentration (IC50) of DOX was calculated using the Cell Counting Kit-8 (CCK-8) assay. Proliferation and apoptosis of DOX-resistant OS cells were assessed by colony formation assay and flow cytometry. The levels of apoptosis-related proteins in DOX-resistant OS cells were measured by Western blot assay. Xenograft assay was utilized to analyze the effect of circ_0002060 on DOX resistance in vivo. The interactions among circ_0002060, miR-198, and ABCB1 in DOX-resistant OS cells were confirmed by dual-luciferase reporter assay, RNA immunoprecipitation assay, or RNA pull-down assay. Results: circ_0002060 and ABCB1 were upregulated, while miR-198 was downregulated in OS tissues and DOX-resistant OS cells. circ_0002060 silencing reduced DOX resistance in vitro and in vivo. Moreover, circ_0002060 enhanced DOX resistance by sponging miR-198. Besides, miR-198 decreased DOX resistance by binding to ABCB1. In addition, circ_0002060 sponged miR-198 to upregulate ABCB1 expression. Conclusions: circ_0002060 promoted DOX resistance and OS progression by regulating the miR-198/ABCB1 axis, suggesting that circ_0002060 might be a promising biomarker for OS therapy.

Advancements in Understanding the Role of Circular RNA in Osteosarcoma

Osteosarcoma, the most prevalent primary malignant bone tumor and the third most frequent cancer in children and adolescents worldwide, still poses a significant therapeutic challenge. Even though combined chemotherapy and surgical resection have improved survival rates up to 60%, the prognosis for most patients with metastatic osteosarcoma continues to be dismal. The specific pathogenesis and key regulators of tumor invasion and metastasis remain largely elusive. Circular RNAs (circRNAs), novel endogenous non-coding RNA molecules that form covalently closed continuous loops through splicing, play a crucial role in the development, progression, clinical diagnosis, and treatment of various diseases. Recently, an escalating number of circular structures have been identified in osteosarcoma. Understanding their role in osteosarcoma is advantageous for early detection, diagnosis, and treatment of this disease. The primary function of circRNA involves its unique ability to bind specifically to miRNA, although their biological functions also extend to interacting with proteins, regulating gene transcription, and serving as translation templates. In this review, we explore the mechanisms and clinical applications of circRNAs in the pathogenesis and progression of osteosarcoma, with a particular emphasis on the regulatory mechanisms and functions of circRNAs as miRNA sponges in osteosarcoma development.

Cinobufacini injection suppresses the proliferation of human osteosarcoma cells by inhibiting PIN1-YAP/TAZ signaling pathway

Cinobufacini injection (CI), an aqueous extract of Cutis Bufonis, is clinically used for cancer therapy in China, but its molecular mechanism for the treatment of osteosarcoma (OS) remains unclear. We constructed U2OS ectopic subcutaneous tumor model to verify the anti-OS effect of CI in vivo. Meanwhile, cell proliferation of U2OS and MG63 cells was monitored in vitro using the CCK-8 assay, colony formation and morphological changes. Cell cycle arrest and apoptosis were detected by flow cytometry and western blot, which showed that CI significantly inhibited proliferation, induced cell cycle arrest and apoptosis in human OS cells. The further RNA-seq results identified that the Hippo signaling pathway was involved in the anti-OS effect of CI. YAP/TAZ are two major components of the Hippo pathway in breast cancer and are positively regulated by prolyl isomerase PIN1, we assessed their role in OS using both clinicopathological sections and western blots. CI also inhibited PIN1 enzyme activity in a dose-dependent manner, which resulted in impaired PIN1, YAP, and TAZ expression in vitro and in vivo. Additionally, 15 potential compounds of CI were found to occupy the PIN1 kinase domain and inhibit its activity. In summary, CI plays an anti-OS role by down-regulating the PIN1-YAP/TAZ pathway.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

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

The roles and mechanisms of circular RNAs related to mTOR in cancers

BACKGROUND

Circular RNAs (circRNAs) are stable molecules with covalently closed structures that have an irreplaceable role in the occurrence, progression, and even treatment of plenty of cancers. Mammalian/mechanistic target of rapamycin (mTOR) is a key regulator in cancers and plays several biological functions, such as proliferation, migration, invasion, autophagy, and apoptosis.

METHODS

All data were collected through PubMed and CNKI, using terms including "circRNA," "mTOR," "caner," "signaling pathway," "biomarker," "diagnosis," "treatment." Articles published in Chinese and English were included.

RESULTS

In this review, the expression, function, and mechanism of circRNA-associated mTOR in cancers were described. CircRNA-associated-mTOR can regulate the progression and therapy of a variety of cancers in multiple signaling pathways, such as phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mTOR, mitogen-activated protein kinase (MAPK)/mTOR, and AMP-activated protein kinase (AMPK)/mTOR axis. These cancers including esophageal carcinoma (circLPAR3, ciRS-7), gastric cancer (circNRIP1, hsa_circ_0010882, hsa_circ_0000117, hsa_circ_0072309, and circST3GAL6), colorectal cancer (hsa_circ_0000392, hsa_circ_0084927, hsa_circ_0104631, and circFBXW7), liver cancer (circC16orf62, hsa_circ_100338, hsa_circ_0004001, hsa_circ_0004123, hsa_circ_0075792, hsa_circ_0079299, and hsa_circ_0002130), pancreatic cancer (circ-IARS and circRHOBTB3), renal carcinoma (ciRS-7), bladder cancer (circUBE2K), prostate cancer (circMBOAT2 and circ-ITCH), ovarian cancer (circEEF2, circRAB11FIP1, circMYLK, and circTPCN), endometrial cancer (hsa_circ_0002577 and circWHSC1), lung cancer (circHIPK3, hsa_circ_0001666), thyroid cancer (hsa_circ_0007694 and hsa_circ_0008274), glioma (circGFRA1, circ-MAPK4, circPCMTD1, and hsa_circ_0037251), osteosarcoma (circTCF25), leukemia (circ-PRKDC), and breast cancer (hsa_circ_0000199, circUBAP2, and circWHSC1).

Modulation of immunosuppressive cells and noncoding RNAs as immunotherapy in osteosarcoma

The most common bone cancer is osteosarcoma (OS), which mostly affects children and teenagers. Early surgical resection combined with chemotherapy significantly improves the prognosis of patients with OS. Existing chemotherapies have poor efficacy in individuals with distant metastases or inoperable resection, and these patients may respond better to novel immunotherapies. Immune escape, which is mediated by immunosuppressive cells in the tumour microenvironment (TME), is a major cause of poor OS prognosis and a primary target of immunotherapy. Myeloid-derived suppressor cells, regulatory T cells, and tumour-associated macrophages are the main immunosuppressor cells, which can regulate tumorigenesis and growth on a variety of levels through the interaction in the TME. The proliferation, migration, invasion, and epithelial-mesenchymal transition of OS cells can all be impacted by the expression of non-coding RNAs (ncRNAs), which can also influence how immunosuppressive cells work and support immune suppression in TME. Interferon, checkpoint inhibitors, cancer vaccines, and engineered chimeric antigen receptor (CAR-T) T cells for OS have all been developed using information from studies on the metabolic properties of immunosuppressive cells in TME and ncRNAs in OS cells. This review summarizes the regulatory effect of ncRNAs on OS cells as well as the metabolic heterogeneity of immunosuppressive cells in the context of OS immunotherapies.

Circular RNA ROCK1, a novel circRNA, suppresses osteosarcoma proliferation and migration via altering the miR-532-5p/PTEN axis

As the most prevalent bone tumor in children and adolescents, the pathogenesis and metastasis of osteosarcoma (OS) remain largely unclear. Here, we investigated the expression and function of a novel circular RNA (circRNA), circROCK1-E3/E4, which is back-spliced from exons 3 and 4 of Rho-associated coiled-coil containing protein kinase 1 (ROCK1) in OS. We found that circROCK1-E3/E4, regulated by the well-known RNA-binding protein quaking (QKI), was downregulated in OS and correlated with unfavorable clinical features of patients with OS. Functional proliferation and cell motility assays indicated that circROCK1-E3/E4 serves as a tumor suppressor in OS cells. Mechanistically, circROCK1-E3/E4 suppressed proliferation and migration by upregulating phosphatase and tensin homolog (PTEN) through microRNA-532-5p (miR-532-5p) sponging. In the constructed nude mouse model, circROCK1-E3/E4 inhibited tumor growth and lung metastasis in vivo. This study demonstrates the functions and molecular mechanisms of circROCK1-E3/E4 in the progression of OS. These findings may identify novel targets for the molecular therapy of OS.

Understanding the role of a circular RNA molecule in bone cancer may provide a foundation for potential therapies. The factors underlying the development and progression of osteosarcoma, an aggressive bone cancer most common in young people, remain unclear. Circular RNAs (circRNAs), derived from RNA splicing events, have multiple functions in diseases such as cancer. Yong Wang at Zhejiang University, China, and co-workers had already demonstrated that the ROCK1 gene plays critical roles in osteosarcoma progression. Now, they have identified a novel circRNA called circROCK1-E3/E4 derived from ROCK1, which acts as a tumor suppressor in osteosarcoma. In experiments on human cell lines and mouse models, they found that circROCK1-E3/E4 regulates a key pathway that suppresses the proliferation and migration of cancer cells. Poor prognosis is linked to downregulated levels of this circRNA.

miR-29a-3p mitigates the development of osteosarcoma through modulating IGF1 mediated PI3k/Akt/FOXO3 pathway by activating autophagy

Osteosarcoma (OS), occurring in mesenchymal tissues and with a high degree of malignancy, is most common in children and adolescents. At present, we intend to figure out the expression and functions of miR-29a-3p in OS development. Reverse transcription-polymerase chain reaction (RT-PCR) was adopted to monitor the expression of miR-29a-3p and IGF1 in OS tissues and adjacent non-tumor tissues. Then, the 3- (4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT) assay, colony formation experiment, western blot and Transwell assay were conducted to validate OS cell proliferation, colony formation ability, apoptosis, migration and invasion. Next, the association between miR-29a-3p and IGF1 was corroborated by the dual-luciferase reporter assay and the Pearson correlation analysis. Finally, WB was implemented to test the levels of autophagy-related proteins LC3-I/LC3-II, Beclin-1, p62, and the IGF-1R/PI3k/Akt/FOXO3 axis in OS cells. As a result, miR-29a-3p was down-regulated in OS tissues (versus adjacent non-tumor tissues) and OS cell lines. Overexpressing miR-29a-3p aggravated apoptosis, dampened cell proliferation, colony formation, migration and invasion, and promoted autophagy of OS cells. IGF1 was identified as a target of miR-29a-3p. IGF1 induced oncogenic effects in OS by activating IGF-1R/ PI3k/Akt pathway, and it dampened the tumor-suppressive effect of miR-29a-3p on OS. Taken together, miR-29a-3p repressed the OS evolvement through inducing autophagy and inhibiting IGF1 mediated PI3k/Akt/FOXO3 pathway.

CircRNA PVT1 promotes proliferation and chemoresistance of osteosarcoma cells via the miR-24-3p/KLF8 axis

OBJECTIVE

To investigate the regulatory effect and mechanism of circular RNA PVT1 (circPVT1) in proliferation and chemoresistance of osteosarcoma (OS) cells.

METHODS

The expression of circPVT1 in human OS and adjacent normal tissues was detected. The correlation between circPVT1 expression and clinical features of OS was analyzed. The expressions of circPVT1 and miR-24-3p in OS cells resistant to cisplatin, doxorubicin or methotrexate and parental OS cells were detected after cell transfection. CCK-8 and colony formation assay assessed the viability and proliferative ability of OS cells. qRT-PCR and Western blotting measured the expression of KLF8. Dual-luciferase reporter and RNA pull-down assays verified the targeting relationships of circPVT1/miR-24-3p and miR-24-3p/KLF8.

RESULTS

CircPVT1 was over-expressed in OS tissues and cells, and correlated with clinical features of OS. Over-expressed circPVT1 reduced the survival of OS patients. CircPVT1 was up-regulated in chemoresistant OS cells compared to their parental cells. CircPVT1 inhibition suppressed the proliferation and chemoresistance of OS cells. MiR-24-3p was under-expressed in OS cells and further down-regulated in chemoresistant cells. CircPVT1 could bind and down-regulate miR-24-3p. MiR-24-3p overexpression inhibited the proliferation and chemoresistance of OS cells. KLF8 was over-expressed in OS cells and further up-regulated in chemoresistant cells. MiR-24-3p negatively regulated the expression of KLF8.

CONCLUSION

CircPVT1 mediates proliferation and chemoresistance of OS cells via the miR-24-3p/KLF8 axis. The findings may provide guidance for clinical treatment of OS.

Circle RNA circCSPP1 promotes human osteosarcoma cell proliferation and increases glucose metabolism by suppressing miR-200c maturation

INTRODUCTION

MiR-200c plays a central role in glucose metabolism in cancer cells. However, its upstream regulators in this process are unknown. CircRNA CSPP1 (circCSPP1) was predicted to bind to premature miR-200c, an oncogenic miRNA. Therefore, we explored their interaction in osteosarcoma (OS).

METHODS

Differential circCSPP1 and miR-200c expression in OS was analyzed using RT-qPCR. Glucose metabolism was analyzed by glucose uptake assay. Subcellular circCSPP1 location in OS cells was detected using cellular fractionation assay. The direct interaction between circCSPP1 and miR-200c was explored using RNA-RNA pull-down assay. The role of circCSPP1 in miR-200c maturation was investigated by analyzing both mature and premature miR-200c levels in OS cells with circCSPP1 overexpression.

RESULTS

CircCSPP1 and premature miR-200c levels were increased while mature miR-200c level was decreased in OS. CircCSPP1 was detected in both the nuclear and cytoplasm fractions of OS cells. CircCSPP1 directly interacted with premature miR-200c. CircCSPP1 overexpression increased premature miR-200c level, glucose uptake, and cell proliferation, but decreased mature miR-200c level. MiR-200c overexpression suppressed the role of circCSPP1 in OS cells.

CONCLUSIONS

CircCSPP1 promotes OS cell proliferation and increases glucose metabolism by suppressing miR-200c maturation.

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.

The circular RNA circCRIM1 inhibits osteosarcoma progression through sponging miR-513

Numerous studies have suggested that the abnormal expression of circular RNAs plays an essential role in the pathological progression of numerous tumors. Nonetheless, the functions and underlying mechanisms of the circular RNA circCRIM1 in osteosarcoma (OS) are still not fully understood. In this study, 47 classes of OS tissues and adjoining normal tissues were obtained from patients. Real-time PCR was employed to measure circCRIM1 expression levels in both OS tissues and cell lines. The proliferation, migration, and invasion ability in OS cell lines were measured by MTT assays, EDU assays, transwell migration experiments, and transwell invasion assays. The results demonstrated that the expression of circCRIM1 was notably decreased both in OS tissues and cell lines. Depressed circCRIM1 expression was correlated with lymph node metastasis, advanced FIGO stage, and low overall survival of OS patients. In addition, the results indicated that circCRIM1 could decrease the migration, invasion, and growth of OS cells. Further mechanistic studies indicated that circCRIM1 served as a competing endogenous RNA (ceRNA) of miR-513, leading to decreases in the proliferation, migration, and invasion of OS cells. Taken together, our data uncovered a significant role of the circCRIM1/miR-513 pathway in the proliferation, migration, and invasion of OS cell lines and suggested that circCRIM1 may serve as a possible therapeutic target for OS treatment.

Hsa_circ_0032463 acts as the tumor promoter in osteosarcoma by regulating the miR‑330‑3p/PNN axis

Osteosarcoma (OS), also known as bone cancer, is a threat to the lives of millions of adolescents worldwide. Although dedicated efforts have been invested in reducing the mortality rate of this bone cancer, the research community is yet to find the exact causes of OS. Thus, the present research aimed to study the association between circular RNA circ_0032463 and OS progression. The impact of circ_0032463 on cells with OS was first evaluated using reverse transcription-quantitative PCR. This evaluation was followed by the assessment of cell proliferation, viability, apoptosis, invasion and adhesion using BrdU, Cell Counting Kit-8, flow cytometry, Transwell and cell adhesion assays, respectively. RNA pull-down, RNA immunoprecipitation chip and dual-luciferase reporter systems were utilized to investigate the relationship between circ_0032463, microRNA (miR)-330-3p and Pinin desmosome associated protein (PNN) in OS. The findings indicated that circ_0032463 and PNN were highly expressed in OS tissues and OS cell lines, and that they facilitated cell proliferation, viability, invasion and adhesion, but attenuated cell apoptosis in OS cells. The low expression of miR-330-3p suppressed OS development. It was also noted that circ_0032463 inhibited miR-330-3p to upregulate PNN expression. In conclusion, this study confirmed that by regulating the miR-330-3p/PNN axis, circular RNA circ_0032463 could function as a tumor enhancer in cells with OS.

CircORC2 is involved in the pathogenesis of slow transit constipation via modulating the signalling of miR-19a and neurotensin/motilin

In this study, we aimed to investigate the role of circORC2 in modulating miR‐19a and its downstream signalling during the pathogenesis of STC. In this study, three groups of patients, that is healthy control (HC) group, normal transit constipation (NTC) group (N = 42) and slow transit constipation (STC) group, were, respectively, recruited. RT‐PCR and Western blot analysis were exploited to investigate the changes in the expression levels of miR‐19a and circORC2 in these patients, so as to establish a circORC2/miR‐19a signalling pathway. The basic information of the patients showed no significant differences among different patient groups. Compared with the HC group, concentrations of neurotensin (NST) and motilin (MLN) were both significantly reduced in the NTC and STC groups, especially in the STC group. Also, miR‐19a level was highest, whereas circORC2 level was lowest in the STC group. Furthermore, circORC2 was validated to sponge the expression of miR‐19a, and the transfection of circORC2 reduced the expression of miR‐19a. Meanwhile, MLN and NST mRNAs were both targeted by miR‐19a, and the transfection of circORC2 dramatically up‐regulated the expression of MLN and NST. On the contrary, the transfection of circORC2 siRNA into SMCs and VSMCs exhibited the opposite effect of circORC2. Collectively, the results of this study established a regulatory relationship among circORC2, miR‐19a and neurotensin/motilin, which indicated that the overexpression of circORC2 could up‐regulate the levels of neurotensin and motilin, thus exerting a beneficial effect during the treatment of STC.

Circular RNA circ_0002137 regulated the progression of osteosarcoma through regulating miR-433-3p/ IGF1R axis

Current clinical treatment targeting osteosarcoma (OS) are limited for OS patients with pulmonary metastasis or relapse, which led to high mortality (70%‐85%) for advanced osteosarcoma patients. Although ongoing efforts have been made to illustrate the mechanisms of tumorigenesis and progression in OS; however, it was far for us to learn a comprehensive molecular mechanism implies in OS development. In our study, we implicated a circRNA hsa_circ_0002137, which was higher expressed in osteosarcoma tumours compared with paracancerous tissue. The dysregulated expression pattern was also found in osteosarcoma cell lines. The role of circ_0002137 was explored via down‐ or up‐regulated experiments. It was proved that down‐regulation of circ_0002137 suppressed the progress of OS, including cell invasion, cell cycle and cell apoptosis. Furthermore, the correlation between circ_0002137 and miR‐433‐3p was predicted using bioinformatic tools and verified utilizing RNA pull‐down assay and luciferase reporter assay. Interestingly, we found that the inhibitory effect of circ_0002137 on OS was dependent of insulin‐like growth factor‐1 receptor (IGF1R). In conclusion, it was demonstrated that circ_0002137 could restrain the progression of OS through regulating miR‐433‐3p/IGF1R axis, providing a comprehensive landscape of circ_0002137 in the generation and development of OS.

Circ_0056285 Regulates Proliferation, Apoptosis and Glycolysis of Osteosarcoma Cells via miR-1244/TRIM44 Axis

Background

Osteosarcoma (OS) is a common malignant bone cancer that occurs in adolescents and children. Circular RNAs (circRNAs) are important regulators of tumorigenesis and development. This study aimed to explore the role and molecular basis of circ_0056285 in OS.

Methods

The levels of circ_0056285, miR-1244 and tripartite motif containing 44 (TRIM44) were determined by quantitative real-time polymerase chain reaction or Western blot assay. Cell proliferation was evaluated by Cell Counting Kit-8 (CCK-8) assay and colony formation assay. Cell apoptosis was assessed by flow cytometry and caspase 3and caspase 9 activity assay kits. Glucose uptake, lactate product and ATP level were examined using commercial kits. Hexokinase II (HK2) and lactate dehydrogenase A (LDHA) levels were measured by Western blot assay. The interaction among circ_0056285, miR-1244 and TRIM44 was confirmed by dual-luciferase reporter assay, RNA immunoprecipitation assay or RNA pull-down assay. Xenograft experiment was conducted to explore tumor growth in vivo. Exosomes were identified by transmission electron microscope (TEM), nanoparticle tracking analysis (NTA) and Western blot. The diagnostic value of exosomal circ_0056285 was evaluated by receiver operating characteristic (ROC) curve.

Results

Circ_0056285 and TRIM44 were up-regulated, and miR-1244 was down-regulated in OS tissues and cells. Circ_0056285 silencing inhibited proliferation and glycolysis and promoted apoptosis in OS cells. Also, circ_0056285 knockdown hindered proliferation and accelerated apoptosis in OS cells by regulating miR-1244/TRIM44 axis. Circ_0056285 depletion impeded tumor growth in vivo. Furthermore, ROC curve showed that circ_0056285 might be a diagnostic biomarker in OS.

Conclusion

Circ_0056285 facilitated OS progression by sponging miR-1244 and increasing TRIM44 expression, providing a promising therapeutic target for OS.

Down-regulation of circular RNA hsa_circ_0007534 suppresses cell growth by regulating miR-219a-5p/SOX5 axis in osteosarcoma

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The interaction between circ_0007534 and miR-219a-5p is confirmed for the first time.

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The interaction between miR-219a-5p and SOX5 is confirmed for the first time.

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Circ_0007534 knockdown inhibits the progression of osteosarcoma cells.

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Circ_0007534 regulates the growth of osteosarcoma cells through modulating miR-219a-5p/SOX5 axis.

Introduction

Circular RNA circ_0007534 and microRNA-219a (miR-219a-5p) were reported to be involved in osteosarcoma (OS) development. Osteosarcoma (OS) is one of the most common malignant bone tumors, which was more prone to occur in the metaphysis of long bones, including distal femur and proximal tibia. However, the detailed mechanisms were not fully clear. The purpose of this research was to reveal the functional mechanisms of circ_0007534 and miR-219a-5p in OS.

Methods

The levels of genes were determined by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell proliferation ability was detected by cell counting kit-8 (CCK-8) and colony formation assay. Cell migration and invasion abilities were measured using the transwell assay. Furthermore, the interaction between miR-219a-5p and circ_0007534 or SRY (sex-determining region Y)-box 5 (SOX5) was predicted by starbaseV3.0, and confirmed by the dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Besides, tumor xenograft experiment was performed to analyze the effect of circ_0007534 depletion on tumor growth in vivo.

Results

The levels of circ_0007534 and SOX5 were increased, while the miR-219a-5p level was decreased in OS tissues and cells. Circ_0007534 knockdown repressed the proliferation, colony formation, migration, and invasion in OS cells. Circ_0007534 targeted miR-219a-5p, and miR-219a-5p interacted with SOX5. Furthermore, circ_0007534 regulated the growth of OS cells through modulating the levels of miR-219a-5p and SOX5.

Conclusion

Our finding demonstrated that circ_0007534 knockdown suppressed the growth of OS cells via regulating miR-219a-5p/SOX5 axis, providing a potential target for OS treatment and diagnosis.

Cisplatin-resistant osteosarcoma cell-derived exosomes confer cisplatin resistance to recipient cells in an exosomal circ_103801-dependent manner

Studies have shown that exosomes can mediate the chemoresistance of drug-resistant cells by transmitting circular RNAs (circRNAs). However, the role of exosome-derived hsa_circ_103801 (exosomal hsa_circ_103801) in osteosarcoma (OS) remains unclear. The level of hsa_circ_103801 was upregulated in the serum exosomes from patients with OS, and OS patients with high hsa_circRNA_103801 expression had a shorter survival time relative to patients with low hsa_circ_103801 expression. The expression of hsa_circ_103801 was upregulated in cisplatin-resistant MG63 (MG63/CDDP) cells compared with that in MG63 cells. In addition, hsa_circ_103801 was highly enriched in exosomes derived from CDDP-resistant OS cells and could be delivered to MG63 and U2OS cells through exosomes. Exosomes derived from CDDP-resistant cells were shown to reduce the sensitivity of MG63 and U2OS cells to CDDP, inhibit apoptosis, and increase the expression of multidrug resistance-associated protein 1 and P-glycoprotein. Moreover, exosomal hsa_circ_103801 could strengthen the promotive effect of exosomes on the chemoresistance of MG63 and U2OS cells to CDDP. Hence, serum exosomal hsa_circ_103801 may serve as an effective prognostic biomarker for OS, and exosomal hsa_circ_103801 could be a potential target for overcoming OS chemoresistance.

Anticancer effects and the mechanism underlying 2-methoxyestradiol in human osteosarcoma in vitro and in vivo

Osteosarcoma (OS) occurs in both children and adolescents and leads to a poor prognosis. 2-methoxyestradiol (2-ME) has a strong antitumor effect and is effective against numerous types of tumor. However, 2-ME has a low level of antitumor effects in OS. The present study investigated the effects of 2-ME on the proliferation and apoptosis of human MG63 OS cells. The potential biological mechanisms by which 2-ME exerts its biological effects were also investigated in the present study. The results of the present study demonstrated that 2-ME inhibited the proliferation of OS cells in a time- and dose-dependent manner, induced G₂/M phase cell cycle arrest and early apoptosis. The expression levels of vascular endothelial growth factor (VEGF), Bcl-2 and caspase-3 were measured via western blotting and reverse transcription-quantitative PCR. As the concentration of 2-ME increased, the RNA and protein expression levels of VEGF and Bcl-2 decreased gradually, whereas the expression of caspase-3 increased gradually. In addition, tumor growth in nude mice was suppressed by 2-ME with no toxic side effects observed in the liver or kidney. Immunohistochemistry demonstrated that the expression levels of Bcl-2 and VEGF were significantly lower, and those of caspase-3 were significantly higher in test mice compared with the control group. TUNEL staining of xenograft tumors revealed that with increased 2-ME concentration, the number of apoptotic cells also gradually increased. Thus, 2-ME effectively inhibited the proliferation and induced apoptosis of MG63 OS cells in vitro and in vivo with no obvious side effects. The mechanism of the anticancer effect of 2-ME may be associated with the actions of Bcl-2, VEGF and caspase-3.

A Novel CircRNA Circ_0095424 Regulates Proliferation, Metastasis, and Apoptosis of Osteosarcoma Cells Via the PI3K/AKT Signaling Pathway Through Targeting the miR-1238/HMGB1 Axis

Cancer Biotherapy and Radiopharmaceuticals is officially retracting the article entitled, A Novel CircRNA Circ_0095424 Regulates Proliferation, Metastasis, and Apoptosis of Osteosarcoma Cells Via the PI3K/AKT Signaling Pathway Through Targeting the miR-1238/HMGB1 Axis by Zhang et al., (Cancer Biother Radiopharm epub 19 Aug 2020; DOI: 10.1089/cbr.2020.3563), due to manipulated images appearing in the published paper. The Editor of the journal received an email on August 31, 2020 from the corresponding author of the article, Dr. Chuan Qin, indicating that, ''due to our negligence in organizing the pictures, the protein pictures are repeatedly placed in Figure 7G PI3K. For this, we express our sincerest apologies. We need to [issue] an [erratum] on this issue. We have replaced the protein picture of Figure 7G with the correct picture.'' However, one of the attachments submitted with the request appeared to be the original version of Figure 7 from the accepted manuscript. A second attachment appeared to be the data from three replicates to be used (by the journal) to construct a revised version of Figure 7. The Editor, in turn, informed the authors that it was not at the journal's discretion to create a new image for them, and asked the authors to create the revised figure and supply it to the publisher. Below is the response from Dr. Qin, dated September 2, 2020. "In fact, our team's Western blot experiment commissioned a third-party company for testing. At present, some peers have found that the company has forged experimental reports. We believe that the authenticity of the data provided by the company is problematic. After contacting the company, they were unable to provide the original images. In view of the problems in this manuscript, all the authors discussed and agreed to withdraw the manuscript." As the entirety of the situation is unacceptable, the Editor officially retracts the article based on the "forged experimental reports" and the questionable validity of the data provided. The Editor and Publisher of Cancer Biotherapy and Radiopharmaceuticals is dedicated to preserving the integrity of the scientific literature and the community it serves.

Hint1 Overexpression Inhibits the Cell Cycle and Induces Cell Apoptosis in Human Osteosarcoma Cells

Background

New evidence suggests that histidine triad nucleotide-binding protein 1 (Hint1) exerts a tumor suppressor effect in various human tumors, such as colorectal cancer and gastric cancer. However, it has not been reported whether Hint1 is involved in the occurrence and development of osteosarcoma (OS).

Materials and Methods

The present study investigated the role of Hint1 in human OS cells by using cell lines, including 143B, U2OS, KHOS-240S, Saos-2 and MG-63. Cell proliferation and apoptosis were detected by flow cytometry.

Results

The present result revealed that Hint1 is downregulated in these cell lines. The overexpression of Hint1 by adenovirus transfection in 143B and MG63 cell lines suppressed the proliferation and cell cycle, and increased the cell apoptosis. Mechanically, it was found that Hint1 downregulated the cyclin D1 expression via FOXO1 inhibition. Furthermore, FOXO1 overexpression in the 143B and MG63 cell lines significantly blurred the effects of Hint1 on cellular proliferation and apoptosis.

Conclusion

The present study indicates that Hint1 inhibits the development of OS by regulating FoxO1-cyclin D1, suggesting that Hint1 may be a new method for the treatment of OS.

Circ_0000885 Enhances Osteosarcoma Progression by Increasing FGFR1 Expression via Sponging MiR-1294

Background

As a malignant tumor, the progression of osteosarcoma (OS) is mediated by multiple regulators, including circular RNAs (circRNAs). However, the role of circ_0000885 in OS is unclear.

Materials and Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) was applied to detect the expression of circ_0000885, miR-1294 and fibroblast growth factor receptor 1 (FGFR1). Cell proliferation was evaluated using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay and colony formation assay. Flow cytometry and transwell assay were employed to determine the cell cycle distribution, cell migration and invasion, respectively. Moreover, the relationship between miR-1294 and circ_0000885 or FGFR1 was confirmed by dual-luciferase reporter assay. The protein level of FGFR1 was assessed via Western blot (WB) analysis. Animal experiments were used to verify the effect of circ_0000885 silencing on OS tumor growth in vivo.

Results

Circ_0000885 level was increased in OS tissues and cells. Knockdown of circ_0000885 repressed the proliferation, migration, invasion and induced cell cycle arrest in OS cells. There was a binding relationship between miR-1294 and circ_0000885, and miR-1294 inhibitor could reverse the inhibitory effect of silenced circ_0000885 on OS progression. MiR-1294 could target FGFR1, and overexpressed FGFR1 could invert the suppression effect of miR-1294 mimic on OS progression. Silencing of circ_0000885 hindered FGFR1 expression, while this effect could be recovered by miR-1294 inhibitor. In addition, circ_0000885 knockdown reduced OS tumor growth via regulating the FGFR1 expression by sponging miR-1294 in vivo.

Conclusion

Circ_0000885 played an active role in OS progression, indicating that it might be a potential target for OS therapy.

Identification of Osteosarcoma Metastasis-Associated Gene Biomarkers and Potentially Targeted Drugs Based on Bioinformatic and Experimental Analysis

BACKGROUND

Metastasis is the leading cause of death for patients with osteosarcoma (OS). In the present study, we explore the biomarkers for metastatic OS and provide potential therapeutic approaches.

MATERIALS AND METHODS

RNA-Seq data and clinical follow-up information were downloaded from TARGET and GEO databases. A Cox regression model was used to analyze metastatic events. L1000FWD, DGIdb, and CMap databases were used to identify potential drugs related to metastasis. Invasion and migration transwell assays and an adhesion assay were used to identify biological functions of genes.

RESULTS

A total of 15 metastasis-related signatures (MRSs) were associated with the prognosis based on the TARGET or GSE21257 cohorts, among which IL10RA and TLR7 genes were especially significant. In the DGIdb drug-gene interaction database, TLR7 and IFNGR1 were found to have potential interactions with drugs. After inhibiting the expression of TLR7, the migration, invasion, and adhesion ability of OS cells were significantly enhanced, which further promoted metastasis.

CONCLUSION

We identified a set of MRS that may be related to OS metastases. Among them, TLR7 plays a vital role and may be a potential target for OS metastasis treatment.

Emerging landscape of circular RNAs as biomarkers and pivotal regulators in osteosarcoma

Osteosarcoma represents the most prevailing primary bone tumor and the third most common cancer in children and adolescents worldwide. Among noncoding RNAs, circular RNAs (circRNAs) refer to a unique class in the shape of a covalently closed continuous loop with neither 5' caps nor 3'-polyadenylated tails, which are generated through back-splicing. Recently, with the development of whole-genome and transcriptome sequencing technologies, a growing number of circRNAs have been found aberrantly expressed in multiple diseases, including osteosarcoma. circRNA are capable of various biological functions including miRNA sponge, mediating alternatives, regulating genes at posttranscriptional levels, and interacting with proteins, indicating a pivotal role of circRNA in cancer initiation, progression, chemoresistance, and immune response. Moreover, circRNAs have been thrust into the spotlight as potential biomarkers and therapeutic targets in osteosarcoma. Herein, we briefly summarize the origin and biogenesis of circRNA with current knowledge of circRNA in tumorigenesis of osteosarcoma, aiming to elucidate the specific role and clinical implication of circRNAs in osteosarcoma.

Therapeutic Potential of Circular RNAs in Osteosarcoma

Osteosarcoma is the most common malignant bone tumor in children and adolescents. Multiagent chemotherapy, together with surgical removal of all detectable lesions, has improved the long-term survival rate to 65-70% in patients with localized osteosarcoma and to 25-30% in patients with metastatic osteosarcoma since the 1970s. However, the conventional strategy has not improved in recent decades. With accumulating knowledge of the natural circular RNA (circRNA) pathogenesis of osteosarcoma, the diagnostic and therapeutic potential of some circRNAs has been explored. Meanwhile, artificial circular RNAs have been designed as onco-microRNA inhibitors to exert antitumor functions. Therefore, natural and artificial circular RNAs, like other RNA counterparts, are attractive new classes of therapeutic molecules for the treatment of osteosarcoma. This review summarizes the latest progress in the relationship between circRNAs and the malignant phenotype of osteosarcoma and sheds light on the therapeutic potential of the two types of circular RNA in the clinic.

Circular RNA PVT1 promotes metastasis via regulating of miR-526b/FOXC2 signals in OS cells

As a class of covalently closed non-coding RNAs, circular RNAs (circRNAs) are key regulators in various malignancies including osteosarcoma (OS). In the present study, we found that circular RNA PVT1 (circPVT1) was up-regulated in OS and correlated with poor prognosis of patients with OS. Functionally, we showed that knockdown of circPVT1 suppressed OS cells metastasis. In addition, we found that (forkhead box C2) FOXC2 was a downstream gene in circPVT1-mediated metastasis in OS cells. We demonstrated that circPVT1 promoted OS cells metastasis via post-transcriptionally regulating of FOXC2. Furthermore, we revealed that microRNA 526b (miR-526b) was a key bridge which connected circPVT1 and FOXC2. We showed that miR-526b was down-regulated in OS tissue and cell lines. Through a transwell assay, we found that miR-526b suppressed OS cells metastasis by targeting of FOXC2. We also showed that miR-526b targeted circPVT1 via similar mircoRNA response elements (MREs) as it did for FOXC2. Finally, we proved that circPVT1 decoyed miR-526b to promote FOXC2-mediated metastasis in OS cells. In brief, our current study demonstrated that circPVT1, functioning as an oncogene, promotes OS cells metastasis via regulation of FOXC2 by acting as a ceRNA of miR-526b. CircPVT1/miR-526b/FOXC2 axis might be a novel target in molecular treatment of OS.

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.

Circ_0009910 promotes imatinib resistance through ULK1-induced autophagy by sponging miR-34a-5p in chronic myeloid leukemia

BACKGROUND

The occurrence in drug resistance of chronic myeloid leukemia (CML) was accompanied by autophagy activation. Abnormal circular RNAs (circRNAs) participated in this progression. This study attempted to investigate the potential role of circ_0009910 in imatinib resistance of CML cells.

METHODS

The expression of circ_0009910 and miR-34a-5p was measured by quantitative real-time polymerase chain reaction (qRT-PCR). The characterization of circ_0009910 was investigated using oligo (dT)18 primers, Actinomycin D and RNase R. Cell viability (IC₅₀ value) and apoptosis were assessed by Cell Counting Kit-8 (CCK8) assay and flow cytometry assay, respectively. The relative protein expression was quantified by western blot. The relationship among miR-34a-5p, circ_0009910 and ULK1 was predicted by online bioinformatics tool, and verified by dual-luciferase reporter assay and RNA immunoprecipitation (RIP).

RESULTS

The expression of circ_0009910 was up-regulated in the serum of imatinib-resistance CML patients and K562/R cells, and associated with unfavorable clinicopathologic features. Circ_0009910 in K562 and K562/R cells was mainly localized in the cytoplasm. Circ_0009910 knockdown inhibited cell proliferation and autophagy, but induced apoptosis in K562/R cells. Circ_0009910 targeted miR-34a-5p to regulate ULK1. MiR-34a-5p depression rescued the effects of circ_0009910 knockdown on apoptosis and autophagy in K562/R cells.

CONCLUSION

Circ_0009910 accelerated imatinib-resistance in CML cells by modulating ULK1-induced autophagy via targeting miR-34a-5p, providing a potential target in imatinib resistance of CML.

Biology and pathogenesis of human osteosarcoma

Osteosarcoma (OS) is a bone tumor of mesenchymal origin, most frequently occurring during the rapid growth phase of long bones, and usually located in the epiphyseal growth plates of the femur or the tibia. Its most common feature is genome disorganization, aneuploidy with chromosomal alterations, deregulation of tumor suppressor genes and of the cell cycle, and an absence of DNA repair. This suggests the involvement of surveillance failures, DNA repair or apoptosis control during osteogenesis, allowing the survival of cells which have undergone alterations during differentiation. Epigenetic events, including DNA methylation, histone modifications, nucleosome remodeling and expression of non-coding RNAs have been identified as possible risk factors for the tumor. It has been reported that p53 target genes or those genes that have their activity modulated by p53, in addition to other tumor suppressor genes, are silenced in OS-derived cell lines by hypermethylation of their promoters. In osteogenesis, osteoblasts are formed from pluripotent mesenchymal cells, with potential for self-renewal, proliferation and differentiation into various cell types. This involves complex signaling pathways and multiple factors. Any disturbance in this process can cause deregulation of the differentiation and proliferation of these cells, leading to the malignant phenotype. Therefore, the origin of OS seems to be multifactorial, involving the deregulation of differentiation of mesenchymal cells and tumor suppressor genes, activation of oncogenes, epigenetic events and the production of cytokines.

Upregulation Of circMMP9 Promotes Osteosarcoma Progression Via Targeting miR-1265/CHI3L1 Axis

Background

Osteosarcoma (OS) is a very aggressive cancer. Nevertheless, how circular RNA (circRNA) contributes to OS progression remains unclear. Here, we aimed to research the functions of circMMP9 in OS progression.

Methods

Gene expression was determined via qRT-PCR. siRNA was used to knock down circMMP9. Proliferation was analyzed using CCK8 and colony formation assays. Migration and invasion were measured using Transwell assay.

Results

circMMP9 was overexpressed in cancer tissues. Overexpressed circMMP9 was correlated with advanced tumor stage and predicted poor prognosis. circMMP9 knockdown exhibited a tumor-suppressive phenotype via suppressing proliferation, migration and invasion. Besides, decreased circMMP9 level promoted OS cellular apoptosis. Mechanistically, circMMP9 was shown to be located in the cytoplasm and sponge miR-1265. Furthermore, miR-1265 directly targeted CHI3L1. CHI3L1 levels were modulated by circMMP9/miR-1265 axis. Rescue experiments indicated that circMMP9 contributes to OS development through the miR-1265/CHI3L1 pathway.

Conclusion

Our findings provide a novel insight about how circRNA regulates OS progression.

Current Status of Functional Studies on Circular RNAs in Bladder Cancer and their Potential Role as Diagnostic and Prognostic Biomarkers: A Review

Worldwide, bladder cancer represents the ninth most common malignancy and is the 13^th cause of cancer-associated death. Although surgery combined with chemotherapy and radiotherapy has improved patient outcomes, the prognosis remains poor for most patients with muscle-invasive bladder cancer. The exact mechanisms and critical regulators of bladder cancer remain unknown. Circular RNAs (circRNAs) are a distinct type of endogenous non-coding RNA. Recent studies have shown that circRNAs participate in many processes, including proliferation, invasion, migration, and apoptosis in multiple types of malignancy, including bladder cancer. Some circRNAs are dysregulated in bladder cancer and play essential roles in cancer progression. Importantly, some circRNAs may serve as diagnostic and prognostic biomarkers for bladder cancer. This review aims to summarize the findings from recent studies that have focused on the roles of human circRNAs in bladder cancer and discusses the clinical roles for circRNAs, including their potential roles as diagnostic or prognostic biomarkers.