Circular RNA circFAT1(e2) Promotes Osteosarcoma Progression and Metastasis by Sponging miR-181b and Regulating HK2 Expression

Osteosarcoma in a ceRNET perspective

Osteosarcoma (OS) is the most prevalent and fatal type of bone tumor. It is characterized by great heterogeneity of genomic aberrations, mutated genes, and cell types contribution, making therapy and patients management particularly challenging. A unifying picture of molecular mechanisms underlying the disease could help to transform those challenges into opportunities.This review deeply explores the occurrence in OS of large-scale RNA regulatory networks, denominated "competing endogenous RNA network" (ceRNET), wherein different RNA biotypes, such as long non-coding RNAs, circular RNAs and mRNAs can functionally interact each other by competitively binding to shared microRNAs. Here, we discuss how the unbalancing of any network component can derail the entire circuit, driving OS onset and progression by impacting on cell proliferation, migration, invasion, tumor growth and metastasis, and even chemotherapeutic resistance, as distilled from many studies. Intriguingly, the aberrant expression of the networks components in OS cells can be triggered also by the surroundings, through cytokines and vesicles, with their bioactive cargo of proteins and non-coding RNAs, highlighting the relevance of tumor microenvironment. A comprehensive picture of RNA regulatory networks underlying OS could pave the way for the development of innovative RNA-targeted and RNA-based therapies and new diagnostic tools, also in the perspective of precision oncology.

Reprogramming of glucose metabolism: Metabolic alterations in the progression of osteosarcoma

Metabolic reprogramming is an adaptive response of tumour cells under hypoxia and low nutrition conditions. There is increasing evidence that glucose metabolism reprogramming can regulate the growth and metastasis of osteosarcoma (OS). Reprogramming in the progress of OS can bring opportunities for early diagnosis and treatment of OS. Previous research mainly focused on the glycolytic pathway of glucose metabolism, often neglecting the tricarboxylic acid cycle and pentose phosphate pathway. However, the tricarboxylic acid cycle and pentose phosphate pathway of glucose metabolism are also involved in the progression of OS and are closely related to this disease. The research on glucose metabolism in OS has not yet been summarized. In this review, we discuss the abnormal expression of key molecules related to glucose metabolism in OS and summarize the glucose metabolism related signaling pathways involved in the occurrence and development of OS. In addition, we discuss some of the targeted drugs that regulate glucose metabolism pathways, which can lead to effective strategies for targeted treatment of OS.

The roles of glycolysis in osteosarcoma

Metabolic reprogramming is of great significance in the progression of various cancers and is critical for cancer progression, diagnosis, and treatment. Cellular metabolic pathways mainly include glycolysis, fat metabolism, glutamine decomposition, and oxidative phosphorylation. In cancer cells, reprogramming metabolic pathways is used to meet the massive energy requirement for tumorigenesis and development. Metabolisms are also altered in malignant osteosarcoma (OS) cells. Among reprogrammed metabolisms, alterations in aerobic glycolysis are key to the massive biosynthesis and energy demands of OS cells to sustain their growth and metastasis. Numerous studies have demonstrated that compared to normal cells, glycolysis in OS cells under aerobic conditions is substantially enhanced to promote malignant behaviors such as proliferation, invasion, metastasis, and drug resistance of OS. Glycolysis in OS is closely related to various oncogenes and tumor suppressor genes, and numerous signaling pathways have been reported to be involved in the regulation of glycolysis. In recent years, a vast number of inhibitors and natural products have been discovered to inhibit OS progression by targeting glycolysis-related proteins. These potential inhibitors and natural products may be ideal candidates for the treatment of osteosarcoma following hundreds of preclinical and clinical trials. In this article, we explore key pathways, glycolysis enzymes, non-coding RNAs, inhibitors, and natural products regulating aerobic glycolysis in OS cells to gain a deeper understanding of the relationship between glycolysis and the progression of OS and discover novel therapeutic approaches targeting glycolytic metabolism in OS.

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

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

circRNA: A New Biomarker and Therapeutic Target for Esophageal Cancer

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

CircPVT1 promotes the tumorigenesis and metastasis of osteosarcoma via mediation of miR-26b-5p/CCNB1 axis

INTRODUCTION

Osteosarcoma (OS) is the most aggressive malignancy among the bone tumors in the world. Circular RNAs (circRNAs) have been reported to be participated in multiple cancers, including OS. Meanwhile, circPVT1 has been proved to be upregulated in OS. However, the mechanism by which circPVT1 mediates the tumorigenesis of OS remains to be further explored.

MATERIALS AND METHODS

Protein and gene expressions in OS cells were measured by western blot and RT-qPCR, respectively. Cell growth was assessed by flow cytometry and colony formation, respectively. In addition, cell migration was assessed by wound healing, and invasion was evaluated by Transwell assay. Meanwhile, the correlation among circPVT1, miR-26b-5p and CCNB1 was explored by RNA pull-down and dual luciferase assay. Finally, in vivo model was established to explore the role of circPVT1 in OS in vivo.

RESULTS

CircPVT1 and CCNB1 were significantly upregulated in OS cells, while miR-26b-5p was downregulated. Knockdown of circPVT1 notably inhibited proliferation and induced apoptosis of OS cells. CircPVT1 shRNA significantly suppressed the OS cell invasion and migration. Meanwhile, circPVT1 sponged miR-26b-5p and CCNB1 was found to be the direct target of miR-26b-5p. Furthermore, silencing of circPVT1 inhibited the growth and metastasis of OS in vivo.

CONCLUSION

Silencing of circPVT1 notably suppressed the tumorigenesis and metastasis of OS via miR-26b-5p/CCNB1 axis. Therefore, circPVT1 might be used as a target for OS treatment.

Role of hsa_circ_0066966 in proliferation and migration of hepatitis B virus-related liver cancer cells

A large proportion of liver cancer cases is caused by hepatitis B virus (HBV) infection. In recent years, an increasing number of reports have indicated that circular RNAs (circRNAs) exert regulatory effects in cancer development, whereas the role of circRNAs in HBV-positive liver cancer requires further investigation. In the present study, abnormally expressed circRNAs were identified in HBV-positive liver cancer cells through microarray analysis. A total of 1,493 differentially expressed circRNAs [absolute fold-change (FC) ≥2] in HBV-positive liver cancer cells were detected, of which 171 were upregulated and 1,322 were downregulated. Subsequently, Gene Ontology enrichment analysis indicated that the genes of dysregulated circRNAs were mainly involved in regulating Sertoli cell differentiation and development, as well as telomeric DNA binding. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that most of these genes were enriched in cancer-related signaling pathways, including the MAPK and Hippo signaling pathways. Next, the expression levels of the top-10 dysregulated circRNAs were verified in HBV-positive liver cancer cells through reverse transcription-quantitative PCR. Among them, hsa_circ_0066966 had the highest absolute Log₂FC value and was abnormally increased in HBV-positive liver cancer cells. Functional experiments further verified that knockdown of hsa_circ_0066966 had a significant inhibitory effect on the proliferation and migration of HBV-positive liver cancer cells. By contrast, overexpression of hsa_circ_0066966 in HBV-negative liver cancer cells resulted in the opposite effect. In conclusion, in the present study, comprehensive circRNA profiling in HBV-positive liver cancer cells indicated that hsa_circ_0066966 may regulate the progression of HBV-positive liver cancer.

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

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

Overexpression of circRNA circFAT1 in Endometrial Cancer Cells Increases Their Stemness by Upregulating miR-21 Through Methylation

Background: Circular (Circ)RNA circFAT1 play tumor-suppressive or oncogenic roles in different cancers. Microarray analysis observed altered expression of circFAT1 in endometrial cancer (EC) and its inverse correlation with miR-21. Materials and Methods: Expression of circFAT1 and miR-21 in EC and paired nontumor tissues collected from 62 EC patients was analyzed by quantitative reverse transcription PCR (RT-qPCR). An experiment was conducted to evaluate the expression and interaction between circFAT1 and miR-21, followed by RT-qPCR and methylation-specific PCR. The role of circFAT1 and miR-21 in regulating the stemness was assessed by cell stemness assay. Heml 1.0 software was used to show differential gene expression. ANOVA Tukey's test and Pearson's correlation coefficient was used. Results: CircFAT1 was upregulated in EC and positively correlated with miR-21 across EC tissues. In RL95-2 and HEC-1-A cells, overexpression of circFAT1 increased the expression levels of miR-21 and decreased the methylation of miR-21 gene, whereas overexpression of miR-21 did not alter the expression of circFAT1. Cell stemness analysis showed that overexpression of circFAT1 and miR-21 increased cell stemness, and miR-21 inhibition decreased cell stemness. Moreover, inhibitor of miR-21 suppressed the role of circFAT1. Conclusions: In conclusion, circFAT1 is upregulated in EC and it may increase cancer cell stemness by upregulating miR-21.

Circular RNA hsa_circ_0032463 Acts as the Tumor Promoter in Osteosarcoma by Regulating the MicroRNA 498/LEF1 Axis

Several studies have examined the relationship between osteosarcoma (OS) and microRNAs (miRNAs). However, only a few researchers have investigated the underlying mechanism of circular RNAs (circRNAs) in OS development. Our paper aimed to assess how hsa_circ_0032463 (abbreviated “circ_0032463” here) initiates and regulates OS progression. We detected circ_0032463 expression in OS tissues and cell lines by using reverse transcription-quantitative PCR (RT-qPCR) analysis and then investigated the interaction between circ_0032463, miRNA 489 (miR-498), and LEF1 using RNA pulldown, RNA immunoprecipitation (RIP), and luciferase assays. The effect of the circ_0032463/miR-498/LEF1 axis on the migration, proliferation, and apoptosis levels of OS cells was explored using CCK-8, bromodeoxyuridine (BrdU), wound healing, and fluorescein isothiocyanate (FITC) assays. Our findings revealed that circ_0032463 expression was upregulated in OS tissues and cell lines. We also found that circ_0032463 interacted with miR-498, thereby reducing the expression of miR-498 in OS cells. Experimental results indicated that miR-498 could directly target LEF1 in OS cells and that circ_0032463 could abrogate the tumor-inhibitory effect of miR-498 by upregulating LEF1 in OS. More specifically, by binding to miR-498 and inhibiting LEF1 expression, circ_0032463 promoted the migration and proliferation abilities of OS cells and suppressed the apoptosis ability of OS cells. Overall, this research suggested that circ_0032463 could promote OS development by regulating the miR-498/LEF1 axis.

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

Background

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

Method

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

Results

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

Conclusion

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

Supplementary Information

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

CircFAT1 is Overexpressed in Colorectal Cancer and Suppresses Cancer Cell Proliferation, Invasion and Migration by Increasing the Maturation of miR-10a

Purpose

It has been reported that circFAT1 plays opposite roles in gastric cancer and osteosarcoma. This study aimed to explore the involvement of circFAT1 in colorectal cancer (CRC).

Patients and Methods

Paired CRC and non-tumor tissues from 64 CRC patients were subjected to RNA preparations and RT-qPCRs to determine the expression of circFAT1, premature miR-10a, and mature miR-10a. In CRC cells, the effects of circFAT1 overexpression on miR-10a maturation were analyzed by determining the expression of both premature miR-10a and mature miR-10a using RT-qPCRs. The role of circFAT1 and miR-10a in regulating the proliferation, invasion, and migration of CRC cells was analyzed by BrdU and Transwell assays, respectively.

Results

We found that circFAT1 was upregulated in CRC. Mature miR-10a, but not premature miR-10a, was overexpressed in CRC and positively correlated with circFAT1. CircFAT1 overexpression increased the expression of mature miR-10a, but not premature miR-10a. Overexpression of circFAT1 and miR-10a increased cell proliferation, invasion and migration, and miR-10a inhibitor suppressed cell behaviors and reversed the effects of circFAT1 overexpression.

Conclusion

circFAT1 is overexpressed in CRC and may suppress CRC cell proliferation, invasion and migration by increasing miR-10a maturation.

circRNA circFAT1(e2) Elevates the Development of Non-Small-Cell Lung Cancer by Regulating miR-30e-5p and USP22

Background

As a newly discovered regulatory RNA, circular RNA (circRNA) has become a hot spot in many tumor pieces of research. In recent years, it has been discovered that circRNAs have multiple biological effects in different stages of cancer. However, the expression pattern and mechanism of circFAT1(e2) in non-small-cell lung cancer (NSCLC) are still unclear.

Methods

The expressions of circFAT1(e2) in NSCLC tissues and cell lines were studied. Functionally, CCK-8 and transwell experiments were performed in A549 and H1299. In addition, we also performed a dual-luciferase report analysis to clarify the mechanism of action of circFAT1(e2).

Results

circFAT1(e2) was significantly upregulated in NSCLC tissues and cell lines. circFAT1(e2) gene knockdown could significantly inhibit the proliferation, migration, and invasion of NSCLC cells. Loss of function testing found that circFAT1(e2) functioned as an oncogene in NSCLC cells. In addition, circFAT1(e2) acted as a ceRNA to spongy miR-30e-5p, which led to the increase in USP22 and promoted cell growth.

Conclusions

The circFAT1(e2)-miR-30e-5p-USP22 axis is a crucial part of the progression of NSCLC. This study suggests that circFAT1(e2) may be an important potential of prognostic prediction and treatment targets for NSCLC patients.

Circular RNA circ_0046264 Suppresses Osteosarcoma Progression via microRNA-940/Secreted Frizzled Related Protein 1 Axis

Circular RNAs (circRNAs) feature prominently in regulating tumor progression. The study aims to investigate the role and mechanism of circ_0046264 in osteosarcoma. In this study, dysregulated circRNAs in osteosarcoma tissues and adjacent tissues were screened out by analyzing circRNA microarray (GSE140256). The expressions of circ_0046264 in 58 osteosarcoma tissues and 4 osteosarcoma cell lines were detected by quantitative real-time polymerase chain reaction. Subsequently, the relationship of circ_0046264 expression level and clinical features were analyzed. Ethyldeoxyuridine assay and Transwell assay were employed to detect cell viability, migration and invasion. Dual-luciferase reporter assay was adopted to confirm the targeting relationships between circ_0046264 and microRNA-940 (miR-940), as well as miR-940 and secreted frizzled related protein 1 (SFRP1). SFRP1 expression was determined by western blot. Here, we demonstrated that circ_0046264 was greatly down-regulated in osteosarcoma and was inversely related to tumor size and Ki67 expression. Functional assays validated that circ_0046264 could restrain the proliferation, migration and invasion. Mechanistically, circ_0046264 could adsorb miR-940 and indirectly modulate SFRP1 expression. Furthermore, the transfection of miR-940 mimics or SFRP1 small interfering RNA could reverse the impact of circ_0046264 overexpression on the growth, migration and invasion of osteosarcoma cells. Taken together, circ_0046264 is a tumor suppressor to inhibit the osteosarcoma progression via modulating the miR-940 / SFRP1 axis.

Circ-ELF2 Acts as a Competing Endogenous RNA to Facilitate Glioma Cell Proliferation and Aggressiveness by Targeting MiR-510-5p/MUC15 Signaling

Objective

Glioma (GM) is a common type of malignant and aggressive tumor in brain with poor prognosis. Circular RNAs (circRNAs) are well-known regulators in cancer progression. However, its molecular basis in GM remains to be investigated.

Materials and Methods

CircRNA microarray was used to detect differentially expressed circRNAs in GM and matched noncancerous tissues. qRT-PCR was applied to detect the expression profile of circ-ELF2 in GM tissue specimens and cell lines. CCK-8, clone formation, AO/EB staining, flow cytometry, wound healing, and transwell assays were performed to identify the functions of circ-ELF2 in GM cells. The distribution of circ-ELF2 was analyzed by RNA-FISH and subcellular fractionation assay. Dual-luciferase reporter assay was applied to verify the predicted binding sites between miR-510-5p and circ-ELF2/MUC15 3ʹ-UTR. Rescue assay was finally conducted to explore whether the oncogenic role of circ-ELF2 was partially attributed to miR-510-5p/MUC15 signaling.

Results

We observed that circ-ELF2 was significantly upregulated in GM tissues, which was analyzed by circRNA microarray and qRT-PCR. Upregulation of circ-ELF2 was associated with poor prognosis and high recurrence rate for GM patients after surgery. The collapse of circ-ELF2 caused growth arrest and downregulation of cell migratory and invasive potential of GM cells and promoted cell apoptosis. In contrast, elevated expression of circ-ELF2 led to the opposite effect. Mechanistically, circ-ELF2 acted as a competing endogenous RNA (ceRNA) for miR-510-5p to positive modulate MUC15 expression at posttranscriptional level. Circ-ELF2 upregulated MUC15 by sponging miR-510-5p, thus promoting GM growth and aggressiveness.

Conclusion

This study indicates that circ-ELF2/miR-510-5p/MUC15 signaling plays a key role in promoting the occurrence and development of GM.