Circular RNA circ-TSPAN4 promotes lung adenocarcinoma metastasis by upregulating ZEB1 via sponging miR-665

Circ_100549 promotes tumor progression in lung adenocarcinoma through upregulation of BIRC6

Lung adenocarcinoma (LUAD) is a subtype of lung cancer with high incidence and mortality globally. Emerging evidence suggests that circular RNAs (circRNAs) exert critical functions in human cancers, including LUAD. CircRNA_100549 (circ_100549) has been reported to be significantly upregulated in non-small cell lung cancer (NSCLC) samples, while its role in modulating LUAD progression remains to be explored. The current study aims at investigating the functional roles of circ_100549 in LUAD and its downstream molecular mechanism. First, we found that the expression of circ_100549 was higher in LUAD cell lines. Loss-of-function assays verified that depletion of circ_100549 repressed LUAD cell proliferation but accelerated cell apoptosis. Furthermore, in vivo experiments demonstrated that silencing of circ_100549 suppressed tumor growth. Subsequently, based on database analysis, we carried out a series of experiments to explore the mechanisms and effects of circ_100549 underlying LUAD progression, including RNA-binding protein immunoprecipitation (RIP), RNA/DNA pull-down, luciferase reporter, and chromatin immunoprecipitation (ChIP) assays. The results indicated that circ_100549 serves as a ceRNA by sponging miR-95-5p to upregulate BPTF expression, thus upregulating BIRC6 expression at a transcriptional level in LUAD. In summary, our study demonstrated that circ_100549 facilitates LUAD progression by upregulating BIRC6 expression.

Novel insights into the roles of migrasome in cancer

Cell migration, a hallmark of cancer malignancy, plays a critical role in cancers. Improperly initiated or misdirected cell migration can lead to invasive metastatic cancer. Migrasomes are newly discovered vesicular cellular organelles produced by migrating cells and depending on cell migration. Four marker proteins [NDST1 (bifunctionalheparan sulfate N-deacetylase/N-sulfotransferase 1), EOGT (Epidermal growth factor domains pecific O-linked N-acetylglucosaminetransferase), CPQ (carboxypeptidase Q), and PIGK (phosphatidylinositol glycan anchor biosynthesis, class K)] of migrasomes were successfully identified. There are three marker proteins (NDST1, PIGK, and EOGT) of migrasome expressed in cancer. In this review, we will discuss the process of migrasome discovery, the formation of migrasome, the possible functions of migrasome, and the differences between migrasomes and exosomes, especially, the biological functions of migrasome marker proteins in cancer, and discuss some possible roles of migrasomes in cancer. We speculate that migrasomes and migracytosis can play key roles in regulating the development of cancer.

Silencing of circ_0088036 inhibits growth and invasion of lung adenocarcinoma through miR-203/SP1 axis

Lung cancer is the leading cause of cancer-related deaths worldwide. Circular RNA (circRNA) circ_0088036 is a recently discovered circRNA known for its roles in rheumatoid arthritis. The study aimed to study the function of circ_0088036 in lung adenocarcinoma (LUAD). Circ_0088036 expressions were analyzed in the Gene Expression Omnibus (GEO) database. The relationship between circ_0088036 expressions and clinicopathological data of LUAD was assessed. The messenger RNA and protein levels were analyzed by quantitative real-time polymerase chain reaction and Western blot. Cell viability, apoptosis, and invasion were tested by Cell Counting Kit-8, flow cytometry, and transwell assay. The direct interaction between microRNA-203 (miR-203) and circ_0088036 or specificity protein 1 (SP1) was confirmed by dual-luciferase reporter assay, RNA pull-down, and RNA immunoprecipitation assays. Circ_0088036 was overexpressed in LUAD from the analysis of the GEO database. The poor prognosis was found in the patients with high expressions of circ_0088036. The level of Circ_0088036 was increased in LUAD tissues and cells. In terms of function, the deletion of circ_0088036 inhibited LUAD tumorigenesis in vitro by repressing cell growth, invasion, and epithelial-mesenchymal transition (EMT). In mechanism, circ_0088036 could competitively sponge miR-203, thereby affecting the expressions of the target gene SP1. In addition, lessening of miR-203 and enlarging of SP1 could eliminate the anticancer effect of short hairpin RNA-circ_0088036 on LUAD cells. Besides, the knockout of circ_0088036 hindered the growth of xenografted tumors in vivo. Circ_0088036 promoted the LUAD cell growth, invasion, and EMT via modulating the miR-203/SP1 axis in LUAD.

CircAGFG1 Promotes Ovarian Cancer Progression Through the miR-409-3 p/ZEB1 Axis

OBJECTIVES

Circular RNAs (circRNAs) serve a crucial regulatory role in ovarian cancer (OC). Circular RNA ArfGAP with FG repeats 1 (circAGFG1) has been shown to be involved in promoting the progression of several cancers, containing triple-negative breast cancer, esophageal cancer and colorectal cancer. However, the function of circAGFG1 in OC is unclear.

METHODS

Quantitative real-time reverse transcription PCR (RT-qPCR) was conducted to determine the expression levels of circAGFG1 and miR-409-3p. The proliferation and metastasis of cells were determined by colony formation assays, EdU assays, transwell assays and wound healing assays. In addition, a dual-luciferase reporter assay was performed to validate the mechanism between circAGFG1, miR-409-3p, and ZEB1.

RESULTS

Our data suggested that circAGFG1 was significantly overexpressed in OC tissues compared to normal ovarian epithelial tissues. Overexpression of circAGFG1 was correlated with intraperitoneal metastasis, tumor recurrence and advanced stage. Additionally, circAGFG1 overexpression revealed a poor prognosis in OC patients. Knockdown of circAGFG1 suppressed the proliferation, invasion and migration of OC cells. Mechanistically, circAGFG1 acted as a sponge of miR-409-3p to enhance the expression level of zinc finger E-box binding homeobox 1 (ZEB1), thereby conferring OC cell proliferation, invasion and migration. Importantly, re-expression of ZEB1 effectively reversed the effects of circAGFG1 knockdown on OC cells.

CONCLUSIONS

In summary, our study indicated that circAGFG1 may act as a prognostic biomarker and potential therapeutic target for patients with OC.

Circ-NUP98 Promotes Lung Adenocarcinoma Development Through Regulating CBX1 by miR-188-3p

Lung cancer has a high morbidity and mortality among malignant tumors, and lung adenocarcinoma (LUAD) is the main type of lung cancer. In recent years, circular RNAs (circRNAs) have been confirmed to play an important role in the generation and development of human cancer. However, the specific role and mechanism of circ-NUP98 in LUAD are still unclear and need to be further investigated. Circ-NUP98, microRNA-188-3p (miR-188-3p), and chromobox homolog 1 (CBX1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell-counting Kit-8 (CCK-8), 5-Ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry, wound healing, and transwell assay were used to observe LUAD cell proliferation, apoptosis, migration, invasion, and cell-cycle progression. Malondialdehyde (MDA) and superoxide dismutase (SOD) levels were examined using special assay kits. CyclinD1, Bcl-2-related X protein (Bax), matrix metalloproteinase 9 (MMP9) protein, and CBX1 protein levels were determined using Western blot. The interaction between miR-188-3p and circ-NUP98 or CBX1 was identified by dual-luciferase reporter and RNA immunoprecipitation (RIP) assay. In vivo efficacy of circ-NUP98 was evaluated in a xenograft tumor model. Besides, the expression of CBX1 and KI67 in the tumors was detected by immunohistochemical (IHC) assay. Circ-NUP98 and CBX1 expressions were upregulated in LUAD tissues and cells, and miR-188-3p was decreased. Downregulation of circ-NUP98 could inhibit the proliferation, migration, invasion, and oxidative stress, and promote apoptosis of LUAD cells. Mechanism experiments showed that circ-NUP98 acted as a sponge for miR-188-3p to increase CBX1 expression. Knockdown of circ-NUP98 could inhibit the growth of LUAD tumors in vivo. Circ-NUP98 might promote the malignant development of LUAD via the miR-188-3p/CBX1 axis, which might provide a potential new marker for early diagnosis of LUAD.

Circ_0004140 promotes lung adenocarcinoma progression by upregulating NOVA2 via sponging miR-330-5p

BACKGROUND

Circular RNAs (circRNAs) play a significant role in the tumorigenesis and progression of diverse human cancers, including lung adenocarcinoma. A previous study suggested that circ_0004140 expression was increased in lung adenocarcinoma cells. However, the molecular mechanism of circRNA circ_0004140 involved in lung adenocarcinoma is poorly defined.

METHODS

Circ_0004140, microRNA-330-5p (miR-330-5p), and NOVA alternative splicing regulator 2 (NOVA2) expression were determined by real-time quantitative polymerase chain reaction (RT-qPCR). Cell proliferation, apoptosis, migration, invasion, and angiogenesis ability were assessed using 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, wound healing, transwell, and capillary-like network formation assays. Proliferating cell nuclear antigen (PCNA), cyclin D1, and NOVA2 protein levels were detected using Western blot assay. The interaction between miR-330-5p and circ_0004140 or NOVA2 was verified by dual-luciferase reporter assay. Xenograft tumor model was utilized to assess the role of circ_0004140 in tumor growth in vivo.

RESULTS

Circ_0004140 was upregulated in lung adenocarcinoma tissues and cell lines. Circ_0004140 silencing suppressed cell proliferation, migration, invasion and tube formation ability, and triggered the apoptosis of lung adenocarcinoma cells. Circ_0004140 acted as a molecular sponge for miR-330-5p, and miR-330-5p silencing largely reversed circ_0004140 knockdown-induced effects in lung adenocarcinoma cells. NOVA2 was a target of miR-330-5p, and NOVA2 overexpression might largely overturn miR-330-5p overexpression-induced influences in lung adenocarcinoma cells. Circ_0004140 upregulated NOVA2 expression via sponging miR-330-5p in lung adenocarcinoma cells. Circ_0004140 silencing restrained xenograft tumor growth in vivo.

CONCLUSION

Circ_0004140 knockdown might suppress the malignant biological behaviors of lung adenocarcinoma cells via miR-330-5p-dependent regulation of NOVA2.

Hsa_circ_0129047 sponges miR-665 to attenuate lung adenocarcinoma progression by upregulating protein tyrosine phosphatase receptor type B

Compelling evidence has demonstrated the critical role of circular RNAs (circRNAs) during lung adenocarcinoma (LUAD) progression. Herein, we explored a novel circRNA, circ_0129047, and detailed its mechanism of action. The expression of circ 0129047, microRNA-665 (miR-665), and protein tyrosine phosphatase receptor type B (PTPRB) in LUAD tissues and cells was determined using reverse transcription quantitative polymerase chain reaction and Western blotting. Cell Counting Kit-8 and colony formation assays were conducted to detect LUAD cell proliferation, and western blotting was performed to quantify apoptosis-related proteins (Bcl-2 and Bax). Luciferase reporter and RNA immunoprecipitation assays were used to validate the predicted interaction between miR-665 and circ_0129047 or PTPRB. A xenograft assay was used for the in vivo experiments. Circ_0129047 and PTPRB were downregulated in LUAD tissues and cells, whereas miR-665 expression was upregulated. Overexpression of circ_0129047 suppresses LUAD growth in vivo and in vitro. Circ_0129047 is the target of miR-665, and the miR-665 mimic ablated the antiproliferative and pro-apoptotic phenotypes of LUAD cells by circ_0129047 augmentation. MiR-665 targets the 3'UTR of PTPRB and downregulates PTPRB expression. PTPRB overexpression offsets the pro-proliferative potential of miR-665 in LUAD cells. Circ_0129047 sequestered miR-665 and upregulated PTPRB expression, thereby reducing LUAD progression, suggesting a promising approach for preventing LUAD.

Research Progress and Direction of Novel Organelle-Migrasomes

Migrasomes are organelles that are similar in structure to pomegranates, up to 3 μm in diameter, and contain small vesicles with a diameter of 50-100 nm. These membranous organelles grow at the intersections or tips of retracting fibers at the back of migrating cells. The process by which cells release migrasomes and their contents outside the cell is called migracytosis. The signal molecules are packaged in the migrasomes and released to the designated location by migrasomes to activate the surrounding cells. Finally, the migrasomes complete the entire process of information transmission. In this sense, migrasomes integrate time, space, and specific chemical information, which are essential for regulating physiological processes such as embryonic development and tumor invasion and migration. In this review, the current research progress of migrasomes, including the discovery of migrasomes and migracytosis, the structure of migrasomes, and the distribution and functions of migrasomes is discussed. The migratory marker protein TSPAN4 is highly expressed in various cancers and is associated with cancer invasion and migration. Therefore, there is still much research space for the pathogenesis of migratory bodies and cancer. This review also makes bold predictions and prospects for the research directions of the combination of migrasomes and clinical applications.

Landscape of circular RNAs in different types of lung cancer and an emerging role in therapeutic resistance (Review)

Lung cancer is one of the most common malignant tumor types and the leading cause of cancer‑associated death worldwide. Different types of lung cancer exhibit differences in terms of pathophysiology and pathogenesis, and also treatment and prognosis. Accumulating evidence has indicated that circular RNAs (circRNAs) are abnormally expressed among different types of lung cancer and confer important biological functions in progression and prognosis. However, studies comparing different circRNAs in lung cancer subtypes are scarce. Furthermore, circRNAs have an important role in drug resistance and are related to clinicopathological features in lung cancer. Summaries of the association of circRNAs with drug resistance are also scarce in the literature. The present study outlined the biological functions of circRNAs and focused on discriminating differential circRNA patterns and mechanisms in three different types of lung cancer. The emerging roles of circRNAs in the resistance to chemotherapy, targeted therapy, radiotherapy and immunotherapy were also highlighted. Understanding these aspects of circRNAs sheds light on novel physiological and pathophysiological processes of lung cancer and suggests the application of circRNAs as biomarkers for diagnosis and prognosis, as well as therapeutic resistance.

Circ_0044556 Promotes the Progression of Colorectal Cancer via the miR-665-Dependent Expression Regulation of Diaphanous Homolog 1

BACKGROUND

Cancer progression can be regulated by noncoding circular RNAs. A recent study has indicated that circ_0044556 facilitated the progression of colorectal cancer.

AIM

This research was performed to explore the regulatory mechanism of circ_0044556 in CRC.

METHODS

Circ_0044556, miR-665 and Diaphanous Homolog 1 levels were detected by the quantitative real-time polymerase chain reaction. Cell proliferation analysis was performed by cell counting kit-8 assay and Edu assay. Cell cycle progression was assessed using flow cytometry. The protein examination was conducted using western blot. Transwell assay was used to analyze cell migration and invasion. Dual-luciferase reporter assay was performed to validate the interaction between targets. In vivo research was implemented by xenograft tumor assay.

RESULTS

Circ_0044556 was upregulated in colorectal cancer samples and cells. Silencing circ_0044556 inhibited cell proliferation, cell cycle progression, migration, invasion, and epithelial-mesenchymal transition in CRC cells. Circ_0044556 could directly target miR-665 and the function of circ_0044556 was associated with the regulation of miR-665. In addition, Diaphanous Homolog 1 was a target gene for miR-665 and the anti-tumor role of miR-665 in colorectal cancer was dependent on the downregulation of Diaphanous Homolog 1. Diaphanous Homolog 1 level was regulated by circ_0044556 via sponging miR-665 in CRC cells. In vivo assay suggested that circ_0044556 promoted CRC tumor growth by regulating the miR-665 and Diaphanous Homolog 1 levels.

CONCLUSION

Our findings manifested that circ_0044556 functioned as an oncogenic circRNA in colorectal cancer by mediating the miR-665/Diaphanous Homolog 1 axis, elucidating the molecular mechanism of circ_0044556 in CRC progression.

Circular RNA Eps15-homology domain-containing protein 2 induce resistance of renal cell carcinoma to sunitinib via microRNA-4731-5p/ABCF2 axis

Circular RNAs (circRNAs) are linked with the occurrence and progression of renal cell carcinoma (RCC). However, circRNAs’ mechanism in developing resistance to RCC has not been clarified. This research assessed the role and mechanism of circular RNA circ Eps15-homology domain-containing protein 2 (EHD2) in the resistance of sunitinib (SU) to RCC. ACHN, 786-O, 769P, and HEK-293 T cells and RCC tissue samples were used for the investigations. The circEHD2 expression in RCC cells and tissues was determined through RT-qPCR. Association of circEHD2 with RCC histological grade of RCC was done through Chi-square. MiR-4731-5p, ABCF2, and circEHD2 were transfected into RCC cell lines. A dual-luciferase reporter assay was used to determine the interaction between miR-4731-5p, circEHD2, and ABCF2. MTT assay was used to analyze cell viability, while apoptosis was studied using flow cytometry. Colony-formation and transwell experiments were used to assess migration and invasion. The ATP Binding Cassette Subfamily F Member 2 (ABCF2) expression was analyzed through western blot. The results showed increased circEHD2 in SU-resistant RCC tissues and cell lines and implicated in RCC histological grade and SU resistance. Knock-down of circEHD2 down-regulated the resistance of RCC to SU in vitro and vivo; circEHD2 bound to miR-4731-5p to mediate ABCF2 in RCC; ABCF2 rescued the inhibitory effect of circEHD2 knock-down on SU resistance of RCC. In conclusion, circEHD2 enhances RCC resistance to SU via acting as a miR-4731-5p sponge to mediate ABCF2. MiR-4731-5p can target circEHD2 and ABCF2, thus providing a novel and effective therapeutic against renal cell carcinoma.

Identification of Pan-Cancer Biomarkers Based on the Gene Expression Profiles of Cancer Cell Lines

There are many types of cancers. Although they share some hallmarks, such as proliferation and metastasis, they are still very different from many perspectives. They grow on different organ or tissues. Does each cancer have a unique gene expression pattern that makes it different from other cancer types? After the Cancer Genome Atlas (TCGA) project, there are more and more pan-cancer studies. Researchers want to get robust gene expression signature from pan-cancer patients. But there is large variance in cancer patients due to heterogeneity. To get robust results, the sample size will be too large to recruit. In this study, we tried another approach to get robust pan-cancer biomarkers by using the cell line data to reduce the variance. We applied several advanced computational methods to analyze the Cancer Cell Line Encyclopedia (CCLE) gene expression profiles which included 988 cell lines from 20 cancer types. Two feature selection methods, including Boruta, and max-relevance and min-redundancy methods, were applied to the cell line gene expression data one by one, generating a feature list. Such list was fed into incremental feature selection method, incorporating one classification algorithm, to extract biomarkers, construct optimal classifiers and decision rules. The optimal classifiers provided good performance, which can be useful tools to identify cell lines from different cancer types, whereas the biomarkers (e.g. NCKAP1, TNFRSF12A, LAMB2, FKBP9, PFN2, TOM1L1) and rules identified in this work may provide a meaningful and precise reference for differentiating multiple types of cancer and contribute to the personalized treatment of tumors.

CircRNAs in lung adenocarcinoma: diagnosis and therapy

Lung adenocarcinoma (LUAD) is the common histological subtype of non-small-cell lung carcinoma (NSCLC). Circular RNAs (circRNAs) represent a new class of non-coding RNAs (ncRNAs) involved in the development of cancer. Accumulating evidence indicated that a large number of circular RNAs were found to be involved in many biological processes, including tumor initiation, proliferation and progression. These circRNAs present great potentials as new biomarkers and vital targets for disease diagnosis and prognosis. In this review, we mainly focus on the differentially expressed circRNAs and their functions in the pathogenesis of LUAD, which makes it possible for the utility of circRNAs as novel biomarkers for early diagnosis and therapy. Especially, it is helpful to develop circRNAs as crucial therapeutic targets, thus providing a promising biomedical application in the field of cancer gene therapy.

Hsa_circ_0001361 facilitates the progress of lung adenocarcinoma cells via targeting miR-525-5p/VMA21 axis

Background

Lung adenocarcinoma (LUAD) is a common subtype of lung cancer with high recurrence rate and fatality. Circ_0001361 has been recognized as key regulators in various malignancies, but its roles in LUAD remain ambiguous.

Methods

Circ_0001361, miR-525-5p, and VMA21 levels were assessed by RT-qPCR. The growth and metastasis of LUAD cells were detected by MTT, colony formation, wound scratch, and transwell assays, respectively. The interaction between circ_0001361/VMA21 and miR-525-5p was detected by dual luciferase, RNA immunoprecipitation, and RNA pull-down assays. VMA21 protein level was detected by Western blotting. Nude mouse xenograft model was established to determine the role of circ_0001361 in tumor growth in vivo.

Results

Circ_0001361 was up-regulated, while miR-525-5p was down-regulated in LUAD tissues and cells. Functional experiments demonstrated that circ_0001361 drove LUAD cell growth and metastasis. Mechanistically, circ_0001361 functioned as a sponge of miR-525-5p to up-regulate downstream target VMA21 level. MiR-525-5p/VMA21 axis was involved in circ_0001361-mediated malignant phenotypes of LUAD cells. Finally, inhibition of circ_0001361 restrained in vivo xenograft tumor growth via regulating miR-525-5p/VMA21 axis.

Conclusion

Our findings elucidate that circ_0001361 facilitates the tumorigenesis and development of LUAD through miR-525-5p/VMA21 axis, providing evidence for circ_0001361 as a potential prognosis biomarker and therapeutic target for clinical treatment of LUAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03045-4.

Construction and comprehensive analysis of a ceRNA network to reveal potential prognostic biomarkers for lung adenocarcinoma

Background

More and more studies have proven that circular RNAs (circRNAs) play vital roles in cancer development via sponging miRNAs. However, the expression pattern of competing endogenous RNA (ceRNA) in lung adenocarcinoma (LUAD) remains largely unclear. The current study explored functional roles and the regulatory mechanisms of circRNA as ceRNAs in LUAD and their potential impact on LUAD patient prognosis.

Methods

In this study, we systematically screened differential expression circRNAs (DEcircRNAs), miRNAs (DEmiRNAs) and mRNAs (DEGs) associated with LUAD. Then, DEcircRNAs, DEmiRNAs and DEGs were selected to construct a circRNA–miRNA–mRNA prognosis-related regulatory network based on interaction information from the ENCORI database. Subsequently, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed on the genes in the network to predict the potential underlying mechanisms and functions of circRNAs in LUAD. In addition, Kaplan–Meier survival analysis was performed to evaluate clinical outcomes of LUAD patients, and drug sensitivity analysis was used to screen potential biomarkers for drug treatment of patients with LUAD.

Results

As a result, 10 circRNAs were aberrantly expressed in LUAD tissues. The ceRNA network was built, which included 3 DEcircRNAs, 6 DEmiRNAs and 157 DEGs. The DEGs in the ceRNA network of hsa_circ_0049271 enriched in biological processes of cell proliferation and the Jak-STAT signaling pathway. We also detected 7 mRNAs in the ceRNA network of hsa_circ_0049271 that were significantly associated with the overall survival of LUAD patients (P < 0.05). Importantly, four genes (PDGFB, CCND2, CTF1, IL7R) identified were strongly associated with STAT3 activation and drugs sensitivity in GDSC.

Conclusions

In summary, a ceRNA network of hsa_circ_0049271 was successfully constructed, which including one circRNA, two miRNAs, and seven mRNAs. Seven mRNAs (PDGFB, TNFRSF19, CCND2, CTF1, IL11RA, IL7R and MAOA) were remarkably associated with the prognosis of LUAD patients. Among seven mRNA species, four genes (PDGFB, CCND2, CTF1, and IL7R) could be considered as drug targets in LUAD. Our research will provide new insights into the prognosis-related ceRNA network in LUAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08462-8.

Circular RNAs in Lung Cancer: Recent Advances and Future Perspectives

Globally, lung cancer is the most commonly diagnosed cancer and carries with it the greatest mortality rate, with 5-year survival rates varying from 4–17% depending on stage and geographical differences. For decades, researchers have studied disease mechanisms, occurrence rates and disease development, however, the mechanisms underlying disease progression are not yet fully elucidated, thus an increased understanding of disease pathogenesis is key to developing new strategies towards specific disease diagnoses and targeted treatments. Circular RNAs (circRNAs) are a class of non-coding RNA widely expressed in eukaryotic cells, and participate in various biological processes implicated in human disease. Recent studies have indicated that circRNAs both positively and negatively regulate lung cancer cell proliferation, migration, invasion and apoptosis. Additionally, circRNAs could be promising biomarkers and targets for lung cancer therapies. This review systematically highlights recent advances in circRNA regulatory roles in lung cancer, and sheds light on their use as potential biomarkers and treatment targets for this disease.

Circ_0030586 inhibits cell proliferation and stemness in bladder cancer by inactivating the ERK signaling via miR-665/NR4A3 axis

Increasing evidence reveals that circular RNAs (circRNAs) serve as oncogenes or tumor suppressors in the development of various tumors including bladder cancer (BCa). In this study, we explored the function and mechanism of circ_0030586 (also named circABCC4, ATP binding cassette subfamily C member 4) in BCa. The expression of circ_0030586 was significantly decreased in BCa tissues and cells, as suggested by RT-qPCR. The circular characteristics of circ_0030586 were verified by agarose gel electrophoresis and RNase R treatment. Colony formation, 5-Ethynyl-2'-deoxyuridine and sphere formation assays revealed that overexpression of circ_0030586 suppressed BCa cell proliferation and stemness in vitro. According to xenograft experiment, circ_0030586 overexpression suppressed tumor growth in vivo. Mechanistically, RNA pulldown and luciferase reporter assays were carried out to explore the interaction between genes. Circ_0030586 served as a competing endogenous RNA (ceRNA) for hsa-miR-665 to upregulate the expression of nuclear receptor subfamily 4 group A member 3 (NR4A3) which is a downstream target gene of miR-665 in BCa. MiR-665 exhibited high expression in BCa tissues and cells while NR4A3 expression was downregulated in BCa. MiR-665 overexpression or NR4A3 silencing reversed the suppressive effect of circ_0030586 overexpression on BCa cell proliferation and stemness. Moreover, western blot analysis revealed that circ_0030586 inactivated the extracellular signal-regulated kinase (ERK) pathway by upregulating NR4A3 expression. In conclusion, circ_0030586 inhibits BCa cell proliferation and stemness by serving as a ceRNA for miR-665 to upregulate NR4A3 expression and thus inactivate the ERK signaling.

hsa_circ_0008234 inhibits the progression of lung adenocarcinoma by sponging miR-574-5p

circRNAs are a novel type of noncoding RNA (ncRNA) that have been identified as an important regulator of gene expression and play a part in the progression of various diseases. However, the function of circ_0008234 in lung adenocarcinoma (LUAC) remains unknown. Through the GEO (Gene Expression Omnibus) database, circ_0008234 was first found to be downregulated in LUAC tissues. It could inhibit cell growth and accelerate apoptosis in vitro and in vivo. In terms of its possible mechanism, circ_0008234 mainly was present in the cytoplasm and competed with miR-574-5p to regulate RND3 (Rho family GTPase 3). Our results revealed that circ_0008234 inhibited the progression of LUAC through a competing endogenous RNA (ceRNA)-based mechanism and provided potential biomarkers and therapeutic targets for LUAC treatment.

CircMYBL2 regulates the resistance of cervical cancer cells to paclitaxel via miR-665-dependent regulation of EGFR

Circular RNAs are considered to be associated with cancer resistance. This study aims to investigate the function and mechanism of circMYBL2 in paclitaxel (PTX) resistance of cervical cancer (CC). The expression of circMYBL2, miR-665 and epidermal growth factor receptor (EGFR) was investigated using quantitative real-time polymerase chain reaction assay. Cell viability, cell colony number, cell proliferation, apoptosis and lactate dehydrogenase (LDH) were detected by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, colony formation, 5-ethynyl-2'-deoxyuridine incorporation, flow cytometry and LDH release assays, respectively. The interaction between miR-665 and circMYBL2 or EGFR was confirmed by dual-luciferase reporter assay. The protein expression levels were quantified by western blot or immunohistochemistry assay. Mice xenograft models were constructed to investigate the effect of circMYBL2 on CC tumor growth. CircMYBL2 was upregulated in CC tissues and cells, especially in PTX-resistant CC tissues and cells, and it was a stable circRNA mainly distributed in the cytoplasm. CircMYBL2 could enhance the PTX resistance of CC cells in vitro and promote CC tumor growth in vivo. Mechanistically, circMYBL2 could inhibit the PTX sensitivity and promote cell malignant behaviors in PTX-sensitive and PTX-resistant CC cells via upregulating EGFR mediated by miR-665. CircMYBL2 played a positive role in the PTX resistance and malignant activities of PTX-sensitive and PTX-resistant CC cells by regulating the miR-665/EGFR network, providing a novel therapeutic strategy for the treatment of CC patients resistant to PTX.

Epigenome-wide scan identifies differentially methylated regions for lung cancer using pre-diagnostic peripheral blood

BACKGROUND

DNA methylation markers have been associated with lung cancer risk and may identify aetiologically relevant genomic regions, or alternatively, be markers of disease risk factors or biological processes associated with disease development.

METHODS

In a nested case-control study, we measured blood leukocyte DNA methylation levels in pre-diagnostic samples collected from 430 participants (208 cases; 222 controls) in the 1989 CLUE II cohort. We compared DNA methylation levels with case/control status to identify novel genomic regions, both single CpG sites and differentially methylated regions (DMRs), while controlling for known DNA methylation changes associated with smoking using a previously described pack-years-based smoking methylation score. Stratification analyses were conducted over time from blood draw to diagnosis, histology, and smoking status.

RESULTS

We identified 16 single CpG sites and 40 DMRs significantly associated with lung cancer risk (q < 0.05). The identified genomic regions were associated with genes including H19, HOXA3/HOXA4, RUNX3, BRICD5, PLXNB2, and RP13. For the single CpG sites, the strongest association was noted for cg09736286 in the DIABLO gene (OR [for 1 SD] = 2.99, 95% CI: 1.95-4.59, P-value = 4.81 × 10-7). We found that CpG sites in the HOXA3/HOXA4 region were hypermethylated in cases compared to controls.

CONCLUSION

The single CpG sites and DMRs that we identified represented significant measurable differences in lung cancer risk, providing potential biomarkers for lung cancer risk stratification. Future studies will need to examine whether these regions are causally related to lung cancer.

Chinese Herbal Prescription Fu-Zheng-Qu-Xie Prevents Recurrence and Metastasis of Postoperative Early-Stage Lung Adenocarcinoma: A Prospective Cohort Study Followed with Potential Mechanism Exploration

Chinese herbal Fu-Zheng-Qu-Xie (FZQX) prescription has been found to improve the immune function and survival of patients with early-stage lung cancer. However, the therapeutic efficacy needs to be evaluated objectively, and the precise mechanism remains unclear. In the present study, a double-center, prospective cohort study was carried out to assess the clinical efficacy of the FZQX prescription in preventing the recurrence and metastasis of postoperative early-stage lung adenocarcinoma. Our results indicated that the FZQX prescription could significantly reduce the 3-year postoperative recurrence rate and improve the life quality. Moreover, the peripheral blood indices showed that the positive immune index (CD4 +T/CD8 +T) increased and the negative immune indices (CD8 +T, Myeloid-derived suppressor cells (MDSCs), Treg) decreased after treatment with the FZQX prescription. Since the positive regulatory effect of the FZQX prescription on immune function, a series of experiments were conducted to verify the tumor-suppressive effect and elucidate the underlying mechanisms. Through the MDSC clearance xenograft model, we confirmed that the FZQX prescription could effectively suppress tumor growth with lesser side effects in vivo, and MDSCs may be involved in the biological process of the FZQX prescription's intervention in lung cancer progression. By establishing the coculture system of MDSCs/LLC to simulate the immune microenvironment of lung cancer, the tumor suppression effect of the FZQX prescription was further validated by in vitro experiments. Besides, it was confirmed that the FZQX prescription could regulate MDSCs to remodel the immunosuppressive tumor microenvironment, thus exerting its preventive effect on relapse of lung cancer. Finally, the pathway activator and inhibitor were further used to explore the potential molecular mechanism. Results demonstrated that the IL-1β/NF-κB signaling pathway was one of the critical signaling pathways of FZQX prescription regulating MDSCs to prevent the recurrence and metastasis of lung adenocarcinoma.

Clinicopathological and prognostic significance of circRNAs in lung cancer: A systematic review and meta-analysis

BACKGROUND

Circular RNAs (circRNAs) regulate multiple pathways during lung cancer pathogenesis. Apart from functional significance, many circRNAs have been shown to be associated with clinicopathological characteristics and predict lung cancer prognosis. Our aim is to summarize the expanding knowledge of clinical roles of circRNAs in lung cancer.

METHODS

A thorough search of literature was conducted to identify articles about the correlation between circRNA expression and its prognostic and clinicopathological values. Biological mechanisms were summarized.

RESULTS

This study included 35 original articles and 32 circRNAs with prognostic roles for lung cancer. Increased expression of 25 circRNAs and decreased expression of 7 circRNAs predicted poor prognosis. For non-small cell lung cancer, changes of circRNAs were correlated with tumor size, lymph node metastasis, distant metastasis, tumor node metastasis (TNM) stage, and differentiation, indicating the major function of circRNAs is to promote lung cancer invasion and migration. Particularly, meta-analysis of ciRS-7, hsa_circ_0020123, hsa_circ_0067934 showed increase of the 3 circRNAs was associated with positive lymph node metastasis. Increase of ciRS-7 and hsa_circ_0067934 was also related with advanced TNM stage. The biological effects depend on the general function of circRNA as microRNA sponge.

CONCLUSIONS

CircRNAs have the potential to function as prognostic markers and are associated with lung cancer progression and metastasis.

Circ-HMGA2 (hsa_circ_0027446) promotes the metastasis and epithelial-mesenchymal transition of lung adenocarcinoma cells through the miR-1236-3p/ZEB1 axis

Lung adenocarcinoma (LUAD) has high incidence and mortality rates worldwide; however, its detailed molecular pathology remains unclear. Although circRNAs have gradually been identified as molecules that are differentially expressed in tumors and play key roles in tumor progression, their role in LUAD is poorly understood. Through microarray analysis, we obtained the circRNA expression profile of LUAD and found that circ-HMGA2 (hsa_circ_0027446), a novel RNA, is highly expressed in LUAD. The high expression of circ-HMGA2 was further verified in 36 paired LUAD and adjacent normal tissues. Functionally, circ-HMGA2 promoted LUAD cell metastasis in vitro and in vivo. The luciferase reporter assay and FISH results showed that circ-HMGA2 interacts with miR-1236-3p and that miR-1236-3p interacts with ZEB1. In addition, miR-1236-3p was expressed at low levels in LUAD, inhibited LUAD cell metastasis, and suppressed the function of circ-HMGA2. ZEB1 is an EMT-promoting transcription factor. The PCR and WB analysis results showed that circ-HMGA2 promotes both ZEB1 expression and EMT. MiR-1236-3p had the opposite effect, reversing the promotive effect of circ-HMGA2 on EMT. In summary, circ-HMGA2 promotes LUAD cell metastasis through the miR-1236-3p/EMT axis, indicating that it could be a therapeutic target in LUAD.

CircRNAs as promising biomarker in diagnostic and prognostic of lung cancer: An updated meta-analysis

BACKGROUND

As a class of endogenous non-coding RNAs with closed-loop structure, circular RNAs (circRNAs) are receiving more and more attention. CircRNAs have been reported to be widely expressed in various human cancers and are implicated in tumorigenesis and progression. The present study aimed to systematically evaluate the clinicopathological, diagnostic and prognostic values of circRNAs in lung cancer.

METHODS

We searched literature from PubMed, Web of science, Cochrane Library, EMBASE and Ovid online databases up to May 29, 2020. Statistical analyses were undertaken based on Stata 11.0, Meta-DiSc 1.4, and RevMan 5.3 software.

RESULTS

Finally, a total of 63 eligible articles were included in our meta-analysis, including 18 studies for diagnosis, 22 studies for prognosis and 57 studies for clinicopathological features. In terms of diagnostic values, circRNAs could discriminate between lung cancer patients and the normal individuals with a relatively high pooled area under the curve (AUC) of 0.83 (95%CI, 0.80-0.86). For the prognostic values, we found that elevated expression of oncogenic circRNAs could predict poor survival outcomes based on multivariate analysis (HR = 2.430, 95%CI = 2.003-2.948, P < 0.001 for OS; HR = 2.228, 95%CI = 1.289-3.853, P = 0.004 for DFS) while tumor-suppressor circRNAs was correlated with better OS in univariate analysis (HR = 0.627, 95%CI = 0.519-0.757, P < 0.001). The pooled results suggested that elevated expression of carcinogenic circRNAs was associated with tumor size (OR = 1.676, 95%CI = 1.209-2.323, P = 0.002), smoking statue (OR = 1.260, 95%CI = 1.062-1.494, P = 0.008), TNM stage (OR = 2.345, 95%CI = 1.617-3.399, P < 0.001), differentiation grade (OR = 1.843, 95%CI = 1.228-2.765, P = 0.003), and lymphatic metastasis (OR = 2.097, 95%CI = 1.482-2.967, P < 0.001). Moreover, the expression of tumor-suppressor circRNAs was related to the improved clinicopathological features (lymphatic metastasis: OR = 0.536, 95%CI = 0.311-0.926, P = 0.025).

CONCLUSIONS

Our meta-analysis demonstrated that circRNAs could be used as feasible and important biomarkers for diagnosis, prognosis and clinicopathological features in lung cancer.

Circular RNA circ-CCAC1 Facilitates Adrenocortical Carcinoma Cell Proliferation, Migration, and Invasion through Regulating the miR-514a-5p/C22orf46 Axis

Adrenocortical carcinoma (ACC) is a rare but clinically aggressive endocrine malignancy. Circular RNAs (circRNAs) were found to play key roles in tumorigenesis. In the current study, we aimed to investigate the functions and mechanisms of a novel circRNA, circ-CCAC1, in ACC cells. circ-CCAC1 expression levels in ACC tissue specimens and cell lines were evaluated by RT-qPCR. Kaplan-Meier analysis was applied to explore the relationship between circ-CCAC1 and patients' prognosis. Cell counting kit-8 (CCK-8), colony formation, acridine orange/ethidium bromide (AO/EB) double fluorescence staining, and Transwell assays were performed to evaluate the functions of circ-CCAC1 in ACC cells. Bioinformatics analysis and a dual-luciferase reporter assay were utilized to explore the mechanisms of circ-CCAC1. As a result, circ-CCAC1 was overexpressed in ACC tissue samples and cell lines and correlated with poor prognosis. Gain- and loss-of-function tests demonstrated that circ-CCAC1 acted as an oncogene in ACC. What is more, circ-CCAC1 enhanced C22orf46 expression by sponging miR-514a-5p in ACC cells. A rescue assay illustrated that circ-CCAC1 facilitated ACC progression through miR-514a-5p/C22orf46 signaling. To sum up, we identified a novel circRNA, circ-CCAC1, which may be used as a potential therapeutic target for ACC.

Circular RNA Signature in Lung Adenocarcinoma: A MiOncoCirc Database-Based Study and Literature Review

Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs (ncRNAs) with a structure of covalently closed continuous loops, which can regulate gene expression by acting as a microRNA sponge or through other mechanisms. Recent studies have identified that the expression of candidate circRNAs are dysregulated in various tumors and hence are considered as promising diagnostic or therapeutic targets across cancer types. However, the expression and function of circRNAs in lung adenocarcinoma (LUAD) remains unclear. In this article, we investigated the expression of circRNAs in LUAD via MiOncoCirc, which is the first and comprehensive database characterizing circRNAs across >2,000 cancer samples using an exome capture RNA sequencing. We identified seven abnormally expressed circRNAs in LUAD, including circCDR1-AS, circHIPK3, circFNDC3B, circPCMTD1, circRHOBTB3, circFAM13B, and circMAN1A2, as well as conducted a literature review about the function and features of these circRNAs. Previous studies have demonstrated that circCDR1-AS, circMAN1A2, and circHIPK3 were upregulated and significantly correlated with a poor survival, or promoted the tumor progression in lung cancer, whereas other circRNAs have not been fully explored. Besides, we reviewed all the publications regarding circRNAs and LUAD, and noticed that the dysregulation of these circRNAs impacts the development of LUAD through a variety of regulatory mechanisms. In conclusion, the underlying mechanisms of aberrant expression and functions of circRNAs in LUAD are worthy of being further investigated.

CircRNA Circ_0001721 Promotes the Progression of Osteosarcoma Through miR-372-3p/MAPK7 Axis

Background

Osteosarcoma (OS) is the most common bone tumor. Many studies have reported that circular RNAs (circRNAs) play an important role in the development of a variety of human cancers. However, the underlying mechanism of circ_0001721 in regulating osteosarcoma progression remains unknown.

Materials and Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the levels of circ_0001721, miR-372-3p, and mitogen-activated protein kinase 7 (MAPK7) in osteosarcoma tissues and cells. Besides, glycolysis was investigated by glucose consumption, lactate production and hexokinase II (HK2) protein level. Cell proliferation and apoptosis were determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and flow cytometry, separately. Cell migration and invasion were determined by transwell assay. Moreover, the protein levels of HK2 and epithelial-to-mesenchymal transition (EMT) markers were determined by Western blot analysis. The relationship between miR-372-3p and circ_0001721 or MAPK7 was predicated by starbase v3.0 and confirmed by dual-luciferase reporter assay or RNA binding protein immunoprecipitation (RIP) assay. Murine xenograft model was established to investigate the role of circ_0001721 in vivo.

Results

The levels of circ_0001721 and MAPK7 were upregulated in osteosarcoma tissues and cells, while miR-372-3p was downregulated. Knockdown of circ_0001721 inhibited glycolysis, cell proliferation, cell migration, invasion and epithelial-to-mesenchymal transition (EMT), and promoted apoptosis. Circ_0001721 was validated as a sponge of miR-372-3p and mediated glycolysis, cell proliferation, apoptosis, migration, invasion, and EMT of osteosarcoma cells through miR-372-3p. MAPK7 was a target of miR-372-3p and overexpression of MAPK7 attenuated anti-cancer role of miR-372-3p in OS cells. Further studies revealed that circ_0001721 regulates MAPK7 expression via sponging miR-372-3-p. Finally, knockdown of circ_0001721 inhibited tumor progression in vivo.

Conclusion

Circ_0001721 promoted osteosarcoma development through the miR-372-3p/MAPK7 axis.

MicroRNAs and Their Influence on the ZEB Family: Mechanistic Aspects and Therapeutic Applications in Cancer Therapy

Molecular signaling pathways involved in cancer have been intensively studied due to their crucial role in cancer cell growth and dissemination. Among them, zinc finger E-box binding homeobox-1 (ZEB1) and -2 (ZEB2) are molecules that play vital roles in signaling pathways to ensure the survival of tumor cells, particularly through enhancing cell proliferation, promoting cell migration and invasion, and triggering drug resistance. Importantly, ZEB proteins are regulated by microRNAs (miRs). In this review, we demonstrate the impact that miRs have on cancer therapy, through their targeting of ZEB proteins. MiRs are able to act as onco-suppressor factors and inhibit the malignancy of tumor cells through ZEB1/2 down-regulation. This can lead to an inhibition of epithelial-mesenchymal transition (EMT) mechanism, therefore reducing metastasis. Additionally, miRs are able to inhibit ZEB1/2-mediated drug resistance and immunosuppression. Additionally, we explore the upstream modulators of miRs such as long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), as these regulators can influence the inhibitory effect of miRs on ZEB proteins and cancer progression.

Circular RNA circ_0001368 inhibited growth and invasion in renal cell carcinoma by sponging miR-492 and targeting LATS2

Circular RNAs (circRNAs) act as essential regulators in the tumorigenesis of renal cell carcinoma. Our study aims to investigate the underlying function and the molecular mechanisms of circ_0001368 in renal cell carcinoma. The qRT-PCR results indicate that the circ_0001368 expression level was downregulated in the carcinoma cells and tissues of the renal cell. circ_0001368 weakened cell proliferation and invasion in the ACHN and 786-O cells. The luciferase reporter assay showed that circ_0001368 functioned as an endogenous sponge for miR-492. The transwell and CCK8 assays showed that circ_0001368 suppressed cell proliferation and invasion in the ACHN and 786-O cells. Large tumor suppressor kinase 2 (LATS2) was confirmed by Targetscan as a target gene of miR-492. The overexpression of LATS2 repressed the growth and invasion of ACHN and 786-O cells. circ_0001368 upregulated the LATS2 expression and suppressed ACHN and 786-O cell growth and invasion by sponging miR-492. circ_0001368 suppressed the proliferation ability of 786-O in vivo. In conclusion, circ_0001368 was identified in this study as a novel anti-tumor RNA in renal cell carcinoma and can function as a potential therapeutic target for renal cell carcinoma treatment.

Critical function of circular RNAs in lung cancer

Lung cancer is one of the main causes of cancer-related death in the world, especially due to its frequency and ineffective therapeutically approaches in the late stages of the disease. Despite the recent advent of promising new targeted therapies, lung cancer diagnostic strategies still have difficulty in identifying the disease at an early stage. Therefore, the characterizations of more sensible and specific cancer biomarkers have become an important goal for clinicians. Circular RNAs (circRNAs), a type of RNA with covalently closed continuous loop structures that display high structural resistance and tissue specificity pointed toward a potential biomarker role. Current investigations have identified that circRNAs have a prominent function in the regulation of oncogenic pathways, by regulating gene expression both at transcriptional and post-transcriptional level. The aim of this review is to provide novel information regarding the implications of circRNAs in lung cancer, with an emphasis on the role in disease development and progression. Initially, we explored the potential utility of circRNAs as biomarkers, focusing on function, mechanisms, and correlation with disease progression in lung cancer. Further, we will describe the interaction between circRNAs and other non-coding species of RNA (particularly microRNA) and their biological significance in lung cancer. Describing the nature of these interactions and their therapeutic potential will provide additional insight regarding the altered molecular landscape of lung cancer and consolidate the potential clinical value of these circular transcripts. This article is categorized under: RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

Circular RNA circ-TSPAN4 promotes lung adenocarcinoma metastasis by upregulating ZEB1 via sponging miR-665

Background

Cancer metastasis is responsible for 90% of cancer‐related deaths. Recently, circular RNA (circRNA) is deemed to be an important regulator of cancer progression. However, little is known about the role of circRNA in the metastasis of lung adenocarcinoma (LUAD). Herein, we investigated the clinical implication and regulatory effect of circ‐TSPAN4 (hsa_circ_0020732) in LUAD.

Methods

Gene Expression Omnibus (GEO) database (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE104854) was used to identify the aberrantly expressed circRNAs in LUAD. The expression levels of circ‐TSPAN4, miR‐4731‐5p, miR‐665, and ZEB1 were determined by quantitative reverse transcription PCR (qRT‐PCR). The functional experiments were carried out with wound healing and transwell assays. And, the luciferase reporter and RNA pull‐down assays were employed to examine the crosstalk between circ‐TSPAN4, miR‐665, and ZEB1. In vivo metastasis experiment was tested by the lung metastasis model.

Results

Circ‐TSPAN4 was significantly upregulated in LUAD tissues and cell lines. The increased circ‐TSPAN4 was linked to advanced tumor‐node‐metastasis stage, lymph node and distant metastasis, and poor outcome. Lentivirus‐mediated stably circ‐TSPAN4 knockdown dramatically attenuated the metastatic ability of LUAD cells both in vitro and in vivo. Mechanistically, circ‐TSPAN4 directly interacted with miR‐665, but not miR‐4731‐5p, to increase the expression of ZEB1, which is a well‐known metastasis trigger. Importantly, the reduced metastatic capacity caused by circ‐TSPAN4 depletion was partially rescued by miR‐665 silencing or ZEB1 overexpression.

Conclusions

Circ‐TSPAN4 plays a pivotal metastasis‐promoting role in LUAD through acting as a sponge for miR‐665 and upregulating ZEB1.