Circular RNA circCRIM1 inhibits invasion and metastasis in lung adenocarcinoma through the microRNA (miR)-182/miR-93-leukemia inhibitory factor receptor pathway

Circular RNAs in lung cancer: implications for preventing therapeutic resistance

LC is one of the most common malignant tumours that often presents with no distinct symptoms in the early stages, leading to late diagnoses when patients are at an advanced stage and no longer suitable for surgical treatment. Although adjuvant treatments are available, patients frequently develop tolerance to these treatments over time, resulting in poor prognoses for patients with advanced LC. Recently, circular RNAs (circRNAs), a type of non-coding RNA, have gained significant attention in LC research. Owing to their unique circular structure, circRNAs are highly stable within cells. This review systematically summarises the expression, characteristics, biological functions, and molecular regulatory mechanisms of circRNAs involved in therapy resistance as well as the potential applications in early diagnosis and gene targeting therapy in LC.

The role of circular RNAs (circRNAs) as a prognostic factor in lung cancer: a meta-analysis

BACKGROUND

Lung cancer is a leading cause of cancer-related death worldwide. Among various histological types of lung cancer, majority are non-small cell lung cancer (NSCLC) which account for > 80%. Circular RNAs (circRNAs) are widely expressed in various cancers including lung cancer and implicated in tumourigenesis and cancer progression. This study aimed to systematically evaluate the prognostic values of circRNAs in lung cancer.

METHODS

A systematic literature search was done in PubMed, Embase, and MEDLINE databases to select the eligible studies which reported the association between the expression of circRNAs and overall survival (OS) or disease-free survival (DFS) in histopathologically diagnosed lung cancer patients. The pooled hazard ratio (HR) and 95% confidence interval (CI) were assessed to determine the prognostic significance of circRNAs.

RESULTS

A total of 43 studies were eligible for this meta-analysis (MA). 39 different types of circRNAs were reported: 28 showing upregulating and 11 showing downregulating action in lung cancer. High expression of circRNAs with upregulating action in lung cancer was associated with worse prognosis and poor OS (HR 1.93, 95% CI [1.61-2.33], p < 0.00001). High expression of circRNAs with downregulating action in lung cancer was associated with favorable OS and prognosis (HR 0.73, 95% CI [0.58-0.94], p = 0.01). However, there was no statistically significant association between high and low expression of both upregulating and downregulating circRNAs and DFS (HR 1.44, 95% CI [0.92-2.24], p = 0.11).

CONCLUSIONS

This MA confirmed the pivotal role of circRNAs as important prognostic biomarkers for lung cancer, especially NSCLC. High expression of upregulating circRNAs is associated with poor prognosis; however, high expression of downregulating circRNAs is associated with favorable prognosis. Therefore, downregulatory action of circRNAs should be considered a promising treatment in the management of lung cancer, especially NSCLC.

Identification of Hypoxia and Mitochondrial-related Gene Signature and Prediction of Prognostic Model in Lung Adenocarcinoma

Background: The correlation between hypoxia and tumor development is widely acknowledged. Meanwhile, the foremost organelle affected by hypoxia is mitochondria. This study aims to determine whether they possess prognostic characteristics in lung adenocarcinoma (LUAD). For this purpose, a bioinformatics analysis was conducted to assess hypoxia and mitochondrial scores related genes, resulting in the successful establishment of a prognostic model. Methods: Using the single sample Gene Set Enrichment Analysis algorithm, the hypoxia and mitochondrial scores were computed. Differential expression analysis and weighted correlation network analysis were employed to identify genes associated with hypoxia and mitochondrial scores. Prognosis-related genes were obtained through univariate Cox regression, followed by the establishment of a prognostic model using least absolute shrinkage and selection operator Cox regression. Two independent validation datasets were utilized to verify the accuracy of the prognostic model using receiver operating characteristic and calibration curves. Additionally, a nomogram was employed to illustrate the clinical significance of this study. Results: 318 differentially expressed genes associated with hypoxia and mitochondrial scores were identified for the construction of a prognostic model. The prognostic model based on 16 genes, including PKM, S100A16, RRAS, TUBA4A, PKP3, KCTD12, LPGAT1, ITPRID2, MZT2A, LIFR, PTPRM, LATS2, PDIK1L, GORAB, PCDH7, and CPED1, demonstrates good predictive accuracy for LUAD prognosis. Furthermore, tumor microenvironments analysis and drug sensitivity analysis indicate an association between risk scores and certain immune cells, and a higher risk scores suggesting improved chemotherapy efficacy. Conclusion: The research established a prognostic model consisting of 16 genes, and a nomogram was developed to accurately predict the prognosis of LUAD patients. These findings may contribute to guiding clinical decision-making and treatment selection for patients with LUAD, ultimately leading to improved treatment outcomes.

Extracellular Vesicles in Lung Cancer: Implementation in Diagnosis and Therapeutic Perspectives

Lung cancer represents the leading cause of cancer-related mortality worldwide, with around 1.8 million deaths in 2020. For this reason, there is an enormous interest in finding early diagnostic tools and novel therapeutic approaches, one of which is extracellular vesicles (EVs). EVs are nanoscale membranous particles that can carry proteins, lipids, and nucleic acids (DNA and RNA), mediating various biological processes, especially in cell-cell communication. As such, they represent an interesting biomarker for diagnostic analysis that can be performed easily by liquid biopsy. Moreover, their growing dataset shows promising results as drug delivery cargo. The aim of our work is to summarize the recent advances in and possible implications of EVs for early diagnosis and innovative therapies for lung cancer.

The functional significance of circRNA/miRNA/mRNA interactions as a regulatory network in lung cancer biology

Lung cancer, the leading cause of cancer-related deaths, presents significant challenges to patients due to its poor prognosis. Recent research has increasingly implicated circular RNAs in the development and progression of lung cancer. These circular RNAs have been found to impact various aspects of tumor behavior, including proliferation, metastasis, cell cycle regulation, apoptosis, cancer stem cells, therapy response, and the tumor microenvironment. One of the key mechanisms by which circular RNAs exert their influence is through their ability to act as miRNA sponges, sequestering microRNAs and preventing them from targeting other RNA molecules. Accumulating evidence suggests that circular RNAs can function as competing endogenous RNAs, affecting the expression of target mRNAs by sequestering microRNAs. Dysregulation of competing endogenous RNAs networks involving circular RNAs, microRNAs, and mRNAs leads to the aberrant expression of oncogenes and tumor suppressors involved in lung cancer pathogenesis. Understanding the dynamic interplay and molecular mechanisms among circular RNAs, microRNAs, and mRNAs holds great promise for advancing early diagnosis, personalized therapeutic interventions, and improved patient outcomes in lung cancer. Therefore, this study aims to provide an in-depth exploration of the executive roles of circular RNAs/microRNAs/ mRNAs interactions in lung cancer pathogenesis and their potential utility for diagnosing lung cancer, predicting patient prognosis, and guiding targeted therapies. By offering a comprehensive overview of the dysregulation of the axes as driving factors in lung cancer, we aim to pave the way for their translation into clinical practice in the future.

Role of circular RNAs in lung cancer

Lung cancer remains a global public health concern with significant research focus on developing better diagnosis/prognosis biomarkers and therapeutical targets. Circular RNAs (circRNAs) are a type of single-stranded RNA molecules that covalently closed and have ubiquitous expression. These molecules have been implicated in a variety of disease mechanisms, including lung cancer, as they exhibit oncogenic or tumor suppressor characteristics. Recent research has shown an important role that circRNAs play at different stages of lung cancer, particularly in lung adenocarcinoma. In this review, we summarize the latest research on circRNAs and their roles within lung cancer diagnosis, as well as on disease mechanisms. We also discuss the knowledge gaps on these topics and possible future research directions.

Non-Coding RNAs as Key Regulators in Lung Cancer

For several decades, most lung cancer investigations have focused on the search for mutations in candidate genes; however, in the last decade, due to the fact that most of the human genome is occupied by sequences that do not code for proteins, much attention has been paid to non-coding RNAs (ncRNAs) that perform regulatory functions. In this review, we principally focused on recent studies of the function, regulatory mechanisms, and therapeutic potential of ncRNAs including microRNA (miRNA), long ncRNA (lncRNA), and circular RNA (circRNA) in different types of lung cancer.

Emerging roles of circular RNAs in the invasion and metastasis of head and neck cancer: Possible functions and mechanisms

Head and neck cancer (HNC) is the seventh most prevalent malignancy worldwide in 2020. Cancer metastasis is the main cause of poor prognosis in HNC patients. Recently, circular RNAs (circRNAs), initially thought to have no biological function, are attracting increasing attention, and their crucial roles in mediating HNC metastasis are being extensively investigated. Existing studies have shown that circRNAs primarily function through miRNA sponges, transcriptional regulation, interacting with RNA-binding proteins (RBPs) and as translation templates. Among these functions, the function of miRNA sponge is the most prominent. In this review, we summarized the reported circRNAs involved in HNC metastasis, aiming to elucidate the regulatory relationship between circRNAs and HNC metastasis. Furthermore, we summarized the latest advances in the epidemiological information of HNC metastasis and the tumor metastasis theories, the biogenesis, characterization and functional mechanisms of circRNAs, and their potential clinical applications. Although the research on circRNAs is still in its infancy, circRNAs are expected to serve as prognostic markers and effective therapeutic targets to inhibit HNC metastasis and significantly improve the prognosis of HNC patients.

CircRNAs and lung cancer: Insight into their roles in metastasis

Lung cancer is the leading cause of cancer-related mortality worldwide. A major contributing factor to the poor survival rates in lung cancer is the high prevalence of metastasis at the time of diagnosis. To address this critical issue, it is imperative to investigate the mechanisms underlying lung cancer metastasis. Circular RNAs (circRNAs), a distinct type of ribonucleic acid characterized by their unique circular structure, have been implicated in the progression of various diseases. Recent studies have highlighted the close association between circRNAs and the occurrence and development of lung cancer, particularly in relation to metastasis. In this review, we provide a concise overview of the expression patterns and prognostic significance of circRNAs in lung cancer. Additionally, we summarized the current understanding of the clinical relevance of circRNAs in lung cancer metastasis. Furthermore, we systematically focused on the roles of circRNAs in each step of lung cancer metastasis, reflecting the sequential progression of this process. Notably, circRNAs exhibit dual functionality in lung cancer metastasis, acting both as facilitators and inhibitors of metastatic processes. Given their potential, circRNAs hold promise as novel biomarkers and therapeutic targets for lung cancer metastasis, warranting further investigation.

CircCRIM1 suppresses osteosarcoma progression via sponging miR146a-5p and targeting NUMB

CircCRIM1 (hsa_circ_0002346) is a circular RNA derived from gene CRIM1 (the cysteine rich transmembrane BMP regulator 1 circRNAs) by back-splicing. Recent studies have suggested the diverse function of CircCRIM1 in the tumorigenesis of multiple malignancies, including osteosarcoma (OS). Here, we investigated the role and mechanism of circCRIM1 during OS progression. Differentially expressed circRNAs (including circCRIM1) in OS and human osteoblast (hFOB1.19) cell lines were selected by searching the circRNA expression microarray dataset of GSE96964. The expression levels of circCRIM1 and its sponging miRNAs and target genes were examined by RT-qPCR. The effects of circCRIM1 on the proliferation, migration, and invasion of OS cells were investigated by in vitro gain of function experiments. The in vivo function of circCRIM1 on OS was evaluated by measuring the subcutaneous and in situ tumor growth in nude mice. In addition, dual-luciferase reporter assay and in situ hybridization (FISH) were performed to explore the underlying mechanisms of circCRIM1 and its sponging miRNAs and target genes in OS. CircCRIM1 is downregulated in human OS cell lines and predominantly presents in the cytoplasm as demonstrated by RT-qPCR and FISH assays. Overexpression of circCRIM1 suppressed the migration, invasion, proliferation of OS cells in vitro and OS tumor growth in vivo. Mechanistically, we identified miR146a-5p as a sponge miRNA of circCRIM1 through bioinformatic prediction and confirmed their interaction and colocalization via reporter gene assay and FISH analysis. This interaction leads to increase expression of the downstream target gene NUMB, which will cause inhibition of the Notch signal pathway. We further demonstrated that miR146a-5p overexpression could reverse the antitumor effect induced by circCRIM1 in OS cells. Our results support that circCRIM1 acts as a tumor suppressor in OS by sponging miR146a-5p and its downstream target NUMB.

The emerging roles of circRNAs in traits associated with livestock breeding

Many indicators can be used to evaluate the productivity and quality of livestock, such as meat and milk production as well as fat deposition. Meat and milk production are measures of livestock performance, while fat deposition affects the taste and flavor of the meat. The circRNAs, are non-coding RNAs, that are involved in the regulation of all these three traits. We review the functions and mechanisms of circRNAs in muscle and fat development as well as lactation to provide a theoretical basis for circRNA research in animal husbandry. Various phenotypic changes presented in livestock may be produced by different circRNAs. Our current concern is how to use the roles played by circRNAs to our advantage to produce the best possible livestock. Hence, we describe the advantages and disadvantages of knockout techniques for circRNAs. In addition, we also put forward our thoughts regarding the mechanism and network of circRNAs to provide researchers with novel ideas of how molecular biology can help us advance our goals in animal farming. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

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_0001058 represses the progression of lung adenocarcinoma through governing of the miR-486-5p/TEK signaling axis

The most common type of lung cancer is lung adenocarcinoma. Emerging views believe that circular RNA (circRNA) participates in its pathogenesis. The objective of this study is to find out the potential functions and mechanisms of circ_0001058 in lung adenocarcinoma pathogenesis. To detect circ_0001058, miR-486-5p and TEK tyrosine kinase (TEK) receptor tyrosine kinase expressions, real-time quantitative PCR (RT-qPCR) and western blotting were performed. Cell functions, including proliferation, apoptosis and invasion, were then evaluated using cell counting kit-8, caspase-3 activity and transwell assays, respectively. To establish the role of circ_0001058 in tumorigenesis, nude mice were utilized as in-vivo models. The predicted binding relationships of miR-486-5p to circ_0001058 or TEK were further verified by performing a dual-luciferase assay and ribonucleoprotein immunoprecipitation (RIP) analysis. Decreased circ_0001058 expression was observed in lung adenocarcinoma cells and tissue specimens. Circ_0001058 was predominantly situated in the cytoplasm and was greatly resistant to RNase R digestion. Circ_0001058 overexpression restrained A549 and PC9 cells' abilities to proliferate, survive and invade, and it also repressed tumorigenesis in the animal models. Circ_0001058 directly targeted miR-486-5p and depleted its expression. Restoring miR-486-5p could invert the inhibitory effects of circ_0001058 in the cancer cell phenotypes. Furthermore, miR-486-5p targeted TEK, so the inhibitory effects of TEK overexpression on the malignant behaviors of A549 and PC9 cells could also be abolished by miR-486-5p restoration. Circ_0001058 overexpression blocked the malignant development of lung adenocarcinoma via modulation of the miR-486-5p/TEK pathway. These results contribute new insights on the pathogenesis of lung adenocarcinoma.

The Pleiotropic role, functions and targeted therapies of LIF/LIFR axis in cancer: Old spectacles with new insights

The dysregulation of leukemia inhibitory factor (LIF) and its cognate receptor (LIFR) has been associated with multiple cancer initiation, progression, and metastasis. LIF plays a significant tumor-promoting role in cancer, while LIFR functions as a tumor promoter and suppressor. Epithelial and stromal cells secrete LIF via autocrine and paracrine signaling mechanism(s) that bind with LIFR and subsequently with co-receptor glycoprotein 130 (gp130) to activate JAK/STAT1/3, PI3K/AKT, mTORC1/p70s6K, Hippo/YAP, and MAPK signaling pathways. Clinically, activating the LIF/LIFR axis is associated with poor survival and anti-cancer therapy resistance. This review article provides an overview of the structure and ligands of LIFR, LIF/LIFR signaling in developmental biology, stem cells, cancer stem cells, genetics and epigenetics of LIFR, LIFR regulation by long non-coding RNAs and miRNAs, and LIF/LIFR signaling in cancers. Finally, neutralizing antibodies and small molecule inhibitors preferentially blocking LIF interaction with LIFR and antagonists against LIFR under pre-clinical and early-phase pre-clinical trials were discussed.

CircRNAs in lung cancer- role and clinical application

Lung cancer holds the highest mortality rate among malignancies worldwide. Nevertheless, the potential molecular mechanisms of its tumorigenesis and evolution remain obscure. Circular RNAs (circRNAs), a broad category of covalently closed molecules, follow a malignancy-restricted expression pattern. Leading-edge studies have demonstrated the clinical application prospects of circRNAs in lung cancer. Herein, this review elucidates the biogenesis, biological functions, and pathophysiology of circRNAs. Furthermore, we underscore the forefront of the diagnostic, prognostic, and therapeutic potential of circRNAs in lung cancer as well as discuss the bottleneck that needs to be overcome to translate the basic advances of circRNAs into clinical practice.

circRNA CRIM1 regulates the migration and invasion of bladder cancer by targeting miR182/Foxo3a axis

PURPOSE

To explore the molecular mechanism of circRNA CRIM1 in the regulation of bladder cancer by targeting the miR182/Foxo3a axis.

METHODS

50 pairs of cancer tissues and para-cancerous tissues of patients with bladder cancer were collected. RT-PCR method was used to detect the expression of CRIM1 and miR-182. The association between circRNA CRIM1 and clinical data was analyzed. qPCR was used to measure the expression of circRNA CRIM1 and miR-182 in bladder cancer cell UMUC3 and endothelial cell line HUVEC. CRIM1 genes and miR-182 in UMUC3 cell lines were overexpressed and silenced, respectively, to investigate their effects on invasion and migration of bladder cancer, and to detect the changes of miR182/Foxo3a expression. The association between circRNA CRIM1 and miR182/Foxo3a was determined by bioinformatics analysis.

RESULTS

The results showed that there was a significant association between the expression of circRNA CRIM1 and distal migration. The expression of CRIM1 in adjacent tissues was significantly down-regulated and negatively correlated with distal migration. The overexpression of circRNA CRIM1 reduced migration and invasion processes in bladder cancer cells. After circRNA CRIM1 was overexpressed, the miR-182 was significantly down-regulated. The expression levels of Foxo3a mRNA and proteins were up-regulated after miR-182 silencing of bladder cancer cell line UMUC3. miR-182 silencing inhibited invasion and migration of cancer cells to some extent. In bladder cancer cells and tissues, CRIM1 and Foxo3a were significantly down-regulated, miR-182 was significantly up-regulated.

CONCLUSION

circRNA CRIM1 regulated the migration and invasion of bladder cancer by targeting the miR182/Foxo3a axis.

Circular RNA (circ)_0129047 upregulates bone morphogenetic protein receptor type 2 expression to inhibit lung adenocarcinoma progression by sponging microRNA (miR)-1206

Circular RNAs (circRNAs) play significant roles in the tumorigenesis and progression of various cancers, including lung adenocarcinoma (LAC). However, their underlying biological functions in LAC remain unclear. Here, we investigated the tumor suppressor role of the newly identified circRNA, circ_0129047, in LAC tumorigenesis and progression. The expression levels of circ_0129047, microRNA (miR)-1206, and bone morphogenetic protein receptor type 2 (BMPR2) mRNA in LAC cells and tissues were monitored using reverse transcription-quantitative polymerase chain reaction. Dual-luciferase reporter, RNA immunoprecipitation, and RNA pull-down assays were used to confirm the targeting relationships among circ_0129047, miR-1206, and BMPR2 mRNA. Functional experiments for A549 and PC9 cells were performed using cell counting kit-8, bromodeoxyuridine enzyme-linked immunosorbent, caspase-3 activity, cell adhesion, wound healing, and transwell assays. Circ_0129047 expression levels were reduced in LAC cells and tissues. Mechanistically, we discovered that circ_0129047 could sponge miR-1206, and miR-1206 could directly target BMPR2. In addition, circ_0129047 or BMPR2 knockdown facilitated the viability, proliferation, adhesion, migration, and invasion, while inhibiting the apoptosis of LAC cells. Furthermore, the inhibitory effects of circ_0129047 or BMPR2 overexpression on the malignant phenotype of LAC cells could be reversed by the overexpression of miR-1206. In conclusion, circ _0129047 was found to play a tumor suppressive role in LAC progression; it upregulated BMPR2 expression to inhibit LAC progression by sponging miR-1206.

Abbreviations: non-small cell lung cancer (NSCLC); small cell lung cancer (SCLC); lung adenocarcinoma (LAC); Circular RNA (circRNA); MicroRNA (miRNA); bone morphogenetic protein (BMP); squamous cell lung cancer (SCC); RNA immunoprecipitation (RIP)

CircMYC promotes proliferation, migration, invasion and inhibits apoptosis of small cell lung cancer by targeting miR-145/ Matrix Metallopeptidase 2 axis

Circular RNAs (circRNAs) are involved in the carcinogenesis of lung cancer. Human MYC gene is highly expressed in melanoma, multiple myeloma, and nasopharyngeal carcinoma. We aimed to investigate the role of circMYC in small cell lung cancer (SCLC). The expression of cirMYC in SCLC tissues and cells were examined. Functional studies were performed to evaluate the roles of circMYC in SCLC cells. Luciferase reporter gene assay, RNA pull-down assay, and rescue experiments were performed to evaluate the regulatory relationship between circMYC and miR-145, and MiR-145 and MMP2 mRNA. We found that CirMYC was highly expressed in SCLC tissues and cells. Knockdown of circMYC could inhibit cell proliferation, migration, invasion, and induce apoptosis. CircMYC targeted miR-145 and miR-145 targeted MMP2 (Matrix Metallopeptidase 2) mRNA. Our data indicated that circMYC upregulates the expression of MMP-2 by inhibiting miR-145, which functions to promote the proliferation, migration, and invasion and inhibit the apoptosis of SCLC. These findings suggest that targeting circMYC/miR-145/MMP-2 could serve as a potential therapeutic strategy for SCLC treatment.

Hsa_circ_0001666 promotes non-small cell lung cancer migration and invasion through miR-1184/miR-548I/AGO1 axis

Accumulating evidence has revealed that the dysregulation of circular RNAs (circRNAs) plays crucial roles in the occurrence and progression of cancers. However, the aberrant expression profile and dysfunction of circRNAs in non-small cell lung cancer (NSCLC) have not been fully explored. Herein, we discovered that a circRNA, hsa_circ_0001666 (circ0001666), was highly expressed in NSCLC tissues and cell lines, and it was positively correlated with NSCLC tumor pathological grade and lymph node metastasis. Moreover, Kaplan-Meier survival analysis implied that NSCLC patients with high circ0001666 expression were negatively correlated with favorable survival. Functionally, circ0001666 could promote migration and invasion of NSCLC cells in vitro and in vivo. Mechanistically, circ0001666 could act as a sponge to miR-1184/miR-548I and upregulate the expression of AGO1, thereby promoting the activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR signaling pathway in NSCLC cells. Collectively, these findings demonstrated that circ0001666 could serve as an oncogene to promote the migration and invasion of NSCLC via a novel miR-1184/miR-548I/AGO1 axis, which might be a promising therapeutic target for NSCLC treatment.

Identification of potential circular RNA biomarkers in lung adenocarcinoma: A bioinformatics analysis and retrospective clinical study

Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer-associated mortality. Lung adenocarcinoma (LAC) is the most prevalent pathological subtype of NSCLC and accounts for ~40% of all lung cancer mortalities. There remains an urgent demand for the identification of novel biomarkers for the diagnosis and development of therapeutic strategies for LAC. In the present study, the profiles of the differentially-expressed circular RNAs (circRNAs) in LAC tissues compared with those in their corresponding non-cancerous tissues were obtained after analyzing the circRNA microarray dataset GSE101586. The expression pattern of the indicated circRNAs in the LAC tissues were subsequently verified using reverse transcription-quantitative PCR (RT-qPCR). The potential prognostic significance of these circRNAs in patients with LAC were then analyzed in a retrospective clinical study. A circRNA-microRNA (miR or miRNA)-mRNA regulatory network in LAC was established by using Cytoscape. In addition, a protein-protein interaction (PPI) network was plotted using the Search Tool for the Retrieval of Interacting Genes/Proteins and visualized through Cytoscape. The prognostic value of the hub genes found was then analyzed based on the Gene Expression Profiling Interactive Analysis database. In total, four differentially-expressed circRNAs were obtained from the GSE101586 microarray dataset, three of which (hsa_circ_0006220, hsa_circ_0072088 and hsa_circ_0001666) were confirmed by RT-qPCR to be highly expressed in LAC tissues. This retrospective clinical study revealed that higher expression levels of these three circRNAs were associated with poorer prognoses in patients with LAC. In addition, siRNA-mediated knockdown of these circRNAs was found to inhibit cell proliferation, migration and invasion in LAC cells. Following analysis of the molecular mechanism underlying these circRNAs, eight miRNAs, namely miR-520f, miR-1261, miR-1270, miR-620, miR-188-3p, miR-516b, miR-940 and miR-661, were identified with potential binding sites for these three circRNAs. Subsequently, 232 overlapped genes from the 795 upregulated genes in the LAC samples from The Cancer Genome Atlas database and 7,829 predicted target genes of the list of eight aforementioned miRNAs were obtained. A circRNA-miRNA-mRNA network was then constructed. A PPI network was established, with six hub genes, namely kinesin family member (KIF) 2C, KIF18B, maternal embryonic leucine zipper kinase, baculoviral IAP repeat-containing 5, polo-like kinase 1 and cytoskeleton-associated protein 2-like, determined from this network. Higher expression levels of each of these hub genes were found to be associated with poorer prognoses of patients with LAC. To conclude, data from the present study suggested that circRNAs hsa_circ_0006220, hsa_circ_0072088 and hsa_circ_0001666 have the potential to be viable biomarkers and therapeutic targets for LAC.

CircCRIM1 Promotes Hepatocellular Carcinoma Proliferation and Angiogenesis by Sponging miR-378a-3p and Regulating SKP2 Expression

Mounting evidence has demonstrated that circular RNAs have an important function in tumorigenesis and cancer evolvement. CircCRIM1 has been shown to be a poor prognostic element in multiple human malignancies. However, the clinical significance and mechanism of circCRIM1 in hepatocellular carcinoma (HCC) is still unclear. The present study confirmed the expression level of circCRIM1 using quantitative real-time PCR. In addition, circCRIM1 siRNA and overexpression vectors were used for transfection into LM3 or Huh7 cells to down- or up-regulate the expression of circCRIM1. In vitro and in vivo experiments were performed to explore the function of circCRIM1 in HCC. RNA pull-down, RNA immunoprecipitation, fluorescent in situ hybridization, and luciferase reporter assays were conducted to confirm the relationship between miR-378a-3p and circCRIM1 or S-phase kinase-associated protein 2 (SKP2) in HCC. Then, circCRIM1 was up-regulated in HCC and its expression level was significantly associated with poor prognosis and clinicopathologic characteristics. CircCRIM1 enhanced the proliferation and angiogenesis of HCC cells in vitro and promoted xenograft growth in vivo. Moreover, circCRIM1 upregulated the expression of SKP2 by functioning as a sponge for miR-378a-3p. These findings suggest that circCRIM1 boosts the HCC progression via the miR-378-3p/SKP2 axis and may act as a crucial epigenetic therapeutic molecule target in HCC.

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.

Construction of circRNA-miRNA-mRNA network and identification of novel potential biomarkers for non-small cell lung cancer

Background

The underlying circular RNAs (circRNAs)-related competitive endogenous RNA (ceRNA) mechanisms of pathogenesis and prognosis in non-small cell lung cancer (NSCLC) remain unclear.

Methods

Differentially expressed circRNAs (DECs) in two Gene Expression Omnibus datasets (GSE101684 and GSE112214) were identified by utilizing R package (Limma). Circinteractome and StarBase databases were used to predict circRNA associated-miRNAs and mRNAs, respectively. Then, protein–protein interaction (PPI) network of hub genes and ceRNA network were constructed by STRING and Cytoscape. Also, analyses of functional enrichment, genomic mutation and diagnostic ROC were performed. TIMER database was used to analyze the association between immune infiltration and target genes. Kaplan–Meier analysis, cox regression and the nomogram prediction model were used to evaluate the prognostic value of target genes. Finally, the expression of potential circRNAs and target genes was validated in cell lines and tissues by quantitative real-time PCR (qRT-PCR) and Human Protein Atlas (HPA) database.

Results

In this study, 15 DECs were identified between NSCLC tissues and adjacent-normal tissues in two GEO datasets. Following the qRT-PCR corroboration, 7 DECs (hsa_circ_0002017, hsa_circ_0069244, hsa_circ_026337, hsa_circ_0002346, hsa_circ_0007386, hsa_circ_0008234, hsa_circ_0006857) were dramatically downregulated in A549 and SK-MES-1 compared with HFL-1 cells. Then, 12 circRNA-sponged miRNAs were screened by Circinteractome and StarBase, especially, hsa-miR-767-3p and hsa-miR-767-5p were significantly up-regulated and relevant to the prognosis. Utilizing the miRDB and Cytoscape, 12 miRNA-target genes were found. Functional enrichment, genomic mutation and diagnostic analyses were also performed. Among them, FNBP1, AKT3, HERC1, COL4A1, TOLLIP, ARRB1, FZD4 and PIK3R1 were related to the immune infiltration via TIMER database. The expression of ARRB1, FNBP1, FZD4, and HERC1 was correlated with poor overall survival (OS) in NSCLC patients by cox regression and nomogram. Furthermore, the hub-mRNAs were validated in cell lines and tissues.

Conclusion

We constructed the circRNA-miRNA-mRNA network that might provide novel insights into the pathogenesis of NSCLC and reveal promising immune infiltration and prognostic biomarkers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02278-z.

circ_0002346 Suppresses Non-Small-Cell Lung Cancer Progression Depending on the Regulation of the miR-582-3p/STXBP6 Axis

Background

Accumulating articles have reported the pivotal regulatory roles of circular RNAs (circRNAs) in non-small-cell lung cancer (NSCLC) tumorigenesis. Here, our purpose was to explore the role of circ_0002346 in NSCLC progression and its associated mechanism.

Methods

Cell proliferation ability was assessed by a 5-ethynyl-2′-deoxyuridine (EDU) assay and a colony formation assay. Transwell assays were conducted to analyze cell migration and invasion abilities. Cell apoptosis was analyzed by flow cytometry and by using a caspase3 activity assay kit. The glycolysis of NSCLC cells was analyzed using a fluorescence-based glucose/lactate assay kit. A dual-luciferase reporter assay and an RNA pull-down assay were performed to verify the binding relationship between microRNA-582-3p (miR-582-3p) and circ_0002346 or syntaxin-binding protein 6 (STXBP6).

Results

circ_0002346 level was prominently downregulated in NSCLC tissues and cell lines. circ_0002346 overexpression significantly suppressed the proliferation, migration, invasion, and glycolysis and triggered the apoptosis of NSCLC cells. circ_0002346 directly interacted with miR-582-3p, and circ_0002346 overexpression-mediated antitumor effects in NSCLC cells were partly reversed by miR-582-3p overexpression. miR-582-3p directly interacted with the 3′ untranslated region (3′UTR) of STXBP6, and STXBP6 silencing partly counteracted circ_0002346 overexpression-mediated antitumor influences in NSCLC cells. circ_0002346 can upregulate the expression of STXBP6 by acting as a miR-582-3p sponge in NSCLC cells. circ_0002346 overexpression suppressed xenograft tumor growth in vivo.

Conclusion

circ_0002346 overexpression suppressed the malignant properties of NSCLC cells by binding to miR-582-3p to induce the expression of STXBP6.

Circular RNA hsa_circ_0002483 promotes growth and invasion of lung adenocarcinoma by sponging miR-125a-3p

Background

Increasing evidence indicates that the aberrant expression of circular RNAs (circRNAs) is involved in the pathogenesis and progression of lung adenocarcinoma (LUAC). However, the function and molecular mechanisms of hsa_circ_0002483 (circ_0002483) in LUAC remain unclear.

Methods

The association between circ_0002483 expression and clinicopathological characteristics and prognosis in patients with LUAC was analyzed by fluorescence in situ hybridization. The functional experiments such as CCK-8, colony formation and Transwell assays and a subcutaneous tumor model were conducted to determine the role of circ_0002483 in LUAC cells. The specific binding between circ_0002483 and miR-125a-3p was validated by RNA immunoprecipitation, luciferase gene report and qRT-PCR assays. The effects of circ_0002483 on miR-125a-3p-mediated C-C motif chemokine ligand 4 (CCL4)-CCR5 axis were assessed by Western blot analysis.

Results

We found that circ_0002483 was upregulated in LUAC tissue samples and associated with Tumor Node Metastasis (TNM) stage and poor survival in patients with LUAC. Knockdown of circ_0002483 inhibited proliferation, colony formation and invasion of A549 and PC9 cells in vitro, whereas overexpression of circ_0002483 harbored the opposite effects. Furthermore, circ_0002483 sponged miR-125a-3p and negatively regulated its expression. CCL4 was identified as a direct target of miR-125a-3p. The rescue experiments showed that miR-125a-3p mimics reversed the tumor-promoting effects of circ_0002483 by targeting CCL4-CCR5 axis in A549 and PC9 cells. In addition, the in vivo experiment further validated that knockdown of circ_0002483 repressed tumor growth.

Conclusions

Our findings demonstrated that circ_0002483 could act as a sponge of miR-125a-3p to upregulate CCL4-CCR5 axis, contributing to the tumorigenesis of LUAC, and represent a potential therapeutic target for LUAC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02241-y.

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.

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.

Knockdown of circ‑PVT1 inhibits the progression of lung adenocarcinoma and enhances the sensitivity to cisplatin via the miR‑429/FOXK1 signaling axis

Lung cancer is one of the most prevalent cancers in China, and its incidence and morbidity remain high due to various independent factors. Lung adenocarcinoma (ADC) is the most common type of non‑small cell lung carcinoma. Circular RNA plasmacytoma variant translocation 1 (circ‑PVT1) plays an oncogenic role in various types of cancer, but the specific role of circ‑PVT1 in lung ADC has not yet been reported. In the present study, circ‑PVT1 was knocked down in A549 cells and the cell viability, proliferation, migration and invasion were measured via MTT, colony formation, wound healing and Transwell assays, respectively. Then, the cell viability of A549 cells with circ‑PVT1‑knockdown or ‑overexpression was detected after exposure to cisplatin (DDP). After confirming the associations among circ‑PVT1, microRNA (miR)‑429 and forkhead box k1 (FOXK1) using various tools and assays, the cellular functions of A549 cells treated with combined short hairpin (sh)RNA‑circ‑PVT1 and miR‑429 inhibitor/pcDNA3.1‑FOXK1 were tested again. The expression of circ‑PVT1 was found to be increased in lung ADC cells, and shRNA‑circ‑PVT1 led to decreased cell viability, proliferation, migration and invasion. The expression of circ‑PVT1 was higher in A549/DDP cells than that in A549 cells, and the activity of caspase‑3 was also activated by DDP in A549/DDP cells transfected with shRNA‑circ‑PVT1, whereas it was inactivated by DDP in A549 cells transfected with circ‑PVT1 overexpression plasmid. Furthermore, the decreased cell viability, proliferation, invasion and migration induced by shRNA‑circ‑PVT1 could be abated by transfection with miR‑429 inhibitor and pcDNA3.1‑FOXK1. In conclusion, interference of circ‑PVT1 inhibits the progression of lung ADC and enhances its sensitivity to DDP via miR‑429/FOXK1, which may provide a theoretical basis for the use of novel targets in the treatment of lung ADC.

Multi-Omics Integrative Bioinformatics Analyses Reveal Long Non-coding RNA Modulates Genomic Integrity via Competing Endogenous RNA Mechanism and Serves as Novel Biomarkers for Overall Survival in Lung Adenocarcinoma

Long non-coding RNA (lncRNA) plays a crucial role in modulating genome instability, immune characteristics, and cancer progression, within which genome instability was identified as a critical regulator in tumorigenesis and tumor progression. However, the existing accounts fail to detail the regulatory role of genome instability in lung adenocarcinoma (LUAD). We explored the clinical value of genome instability-related lncRNA in LUAD with multi-omics bioinformatics analysis. We extracted the key genome instability-related and LUAD-related gene modules using weighted gene co-expression network analysis (WGCNA) and established a competing endogenous RNA (ceRNA) network using four lncRNAs (LINC01224, LINC00346, TRPM2-AS, and CASC9) and seven target mRNAs (CCNF, PKMYT1, GCH1, TK1, PSAT1, ADAM33, and DDX11). We found that LINC01224 is primarily located in the cytoplasm and that LINC00346 and TRPM2-AS are primarily located in the nucleus (CASC9 unknown). We found that all 11 genes were positively related to tumor mutational burden and involve drug resistance, cancer stemness, and tumor microenvironment infiltration. Additionally, an eight-lncRNA genome instability-related lncRNA signature was established and validated, predicting the overall survival and immunotherapy outcomes in LUAD. To conclude, we discovered that sponging microRNA, genome instability-related lncRNA functions as ceRNA, modulating genomic integrity. This research provides clinical references for LUAD immunotherapy and prognosis and interprets a potential genome instability-related ceRNA regulatory network in which LINC01224-miR-485-5p/miR-29c-3p-CCNF-RRM2 and LINC01224-miR485-5p-PKMYT1-CDK1 axes were the most promising pathways. However, the potential mechanisms underlying our findings still need biological validation through in vitro and in vivo experiments.

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.

Identification of Prognostic Signature and Gliclazide as Candidate Drugs in Lung Adenocarcinoma

Background

Lung adenocarcinoma (LUAD) is the most common pathological type of lung cancer, with high incidence and mortality. To improve the curative effect and prolong the survival of patients, it is necessary to find new biomarkers to accurately predict the prognosis of patients and explore new strategy to treat high-risk LUAD.

Methods

A comprehensive genome-wide profiling analysis was conducted using a retrospective pool of LUAD patient data from the previous datasets of Gene Expression Omnibus (GEO) including GSE18842, GSE19188, GSE40791 and GSE50081 and The Cancer Genome Atlas (TCGA). Differential gene analysis and Cox proportional hazard model were used to identify differentially expressed genes with survival significance as candidate prognostic genes. The Kaplan–Meier with log-rank test was used to assess survival difference. A risk score model was developed and validated using TCGA-LUAD and GSE50081. Additionally, The Connectivity Map (CMAP) was used to predict drugs for the treatment of LUAD. The anti-cancer effect and mechanism of its candidate drugs were studied in LUAD cell lines.

Results

We identified a 5-gene signature (KIF20A, KLF4, KRT6A, LIFR and RGS13). Risk Score (RS) based on 5-gene signature was significantly associated with overall survival (OS). Nomogram combining RS with clinical pathology parameters could potently predict the prognosis of patients with LUAD. Moreover, gliclazide was identified as a candidate drug for the treatment of high-RS LUAD. Finally, gliclazide was shown to induce cell cycle arrest and apoptosis in LUAD cells possibly by targeting CCNB1, CCNB2, CDK1 and AURKA.

Conclusion

This study identified a 5-gene signature that can predict the prognosis of patients with LUAD, and Gliclazide as a potential therapeutic drug for LUAD. It provides a new direction for the prognosis and treatment of patients with LUAD.

Hsa_circ_0008234 facilitates proliferation of cutaneous squamous cell carcinoma through targeting miR-127-5p to regulate ADCY7

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin malignant tumor with 25-50% of 5-year survival. There exist urgent needs for the identification of novel biomarkers for the diagnostic and therapeutic strategies of cSCC. The differentially expressed circRNAs in cSCC tissues and non-lesional skin tissues were obtained through analyzing the circular RNAs (circRNAs) microarray dataset GSE74758. The expression pattern of the indicated circRNAs in cSCC tissues was confirmed by qRT-PCR. FISH analysis was used to detect the location of hsa_circ_0008234 in cells. RIP experiment was used to detect the interaction between hsa_circ_0008234 and miR-127-5p. CCK-8 analysis and colony formation assay were used to detect the proliferation of cSCC cells. qRT-PCR and western blot were adopted to detect the expression of ACDY7. Three differential expressed circRNAs were obtained from the microarray data (GSE74758), and hsa_circ_0008234 was confirmed to be highly expressed in cSCC tissues by qRT-PCR. Hsa_circ_0008234 was mainly located in cytoplasm and stable in cSCC cells. RIP experiment revealed that hsa_circ_0008234 directly interacts with miR-127-5p in cSCC cells. Hsa_circ_0008234 increased the cell viability and colony formation of cSCC cells through acting as the sponge of miR-127-5p. MiR-127-5p inhibited the expression of ADCY7 in cSCC cells through binding the 3'UTR of ADCY7. Hsa_circ_0008234 was positively associated with ADCY7 expression in cSCC tissues. Hsa_circ_0008234 facilitates the proliferation of cSCC through targeting miR-127-5p to regulate ADCY7 expression and has the potential to be a novel therapeutic target for cSCC.

Emerging role of circular RNAs in the pathobiology of lung cancer

Lung cancer is among the leading causes of cancer mortality and incidence in both sexes. Different classes of transcripts have been proposed as molecular markers in this type of cancer. Circular RNAs (circRNAs) are a group of transcripts with circular enclosed and stable configuration. These transcripts are stable in the blood, thus can be used as markers for detection of disorders. Moreover, dysregulation of circRNAs in the affected tissues of patients with different cancers shows their possible roles in the carcinogenesis. Several circRNAs including circPRKC1, circFGFR1, hsa-circ-0020123 and circTP63 have been found to be up-regulated in lung cancer samples. Meanwhile, cir-ITCH, hsa_circ_100395, hsa_circ_0033155, circRNF13, circNOL10, circ-UBR5, circPTK2 and circCRIM1 have been shown to be down-regulated in lung cancer tissues compared with noncancerous counterparts. Finally, prognostic values of circPRKC1, circFGFR1, has-circ-00120123, circTP63, circ_0067934, CDR1as, hsa_circRN_103809 and some other circRNAs have been appraised in lung cancer. In the current manuscript, we describe the impact and utility of circRNAs in the pathology of lung cancer.

Hsa_circ_0001073 targets miR-626/LIFR axis to inhibit lung cancer progression

Circular RNAs (circRNAs) are associated with lung cancer progression. However, it is unclear whether and how circRNA hsa_circ_0001073 (circ_0001073) are involved in lung cancer progression. circ_0001073, microRNA (miR)-626, and leukemia inhibitory factor receptor (LIFR) abundances were determined via quantitative reverse transcription polymerase chain reaction or western blot. Cell viability, invasion, and apoptosis were analyzed by cell counting kit-8, transwell analysis and flow cytometry, respectively. The target correlation was tested by dual-luciferase reporter analysis or RNA immunoprecipitation. Results showed that circ_0001073 abundance was down-regulated in lung cancer cells. circ_0001073 constrained cell viability and invasion and facilitated apoptosis in lung cancer cells. miR-626 was targeted via circ_0001073, and circ_0001073 inhibited lung cancer progression via reducing miR-626 expression. LIFR was targeted via miR-626, and miR-626 knockdown constrained cell viability and invasion and facilitated apoptosis in lung cancer cells via up-regulating LIFR. circ_0001073 increased LIFR expression via miR-626 in lung cancer cells. In conclusion, circ_0001073 represses lung cancer progression via miR-626/LIFR axis, indicating the potential value of circ_0001073 in lung cancer treatment.

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.

Emerging roles of circular RNAs in non‑small cell lung cancer (Review)

Circular RNAs (circRNAs) are a class of novel endogenous transcripts with limited protein‑coding abilities. CircRNAs have been demonstrated to function as critical regulators of tumor development and distant metastasis through binding to microRNAs (miRNAs) and interacting with RNA‑binding proteins, thereby regulating transcription and translation. Emerging evidence has illustrated that certain circRNAs can serve as biomarkers for diagnosis and prognosis of cancer, and/or serve as potential therapeutic targets. Expression of functional circRNAs is commonly dysregulated in cancer and this is correlated with advanced Tumor‑Node‑Metastasis stage, lymph node status, distant metastasis, poor differentiation and shorter overall survival of cancer patients. Recently, an increasing number of studies have shown that circRNAs are closely associated with NSCLC. Functional experiments have revealed that circRNAs are intricately associated with the pathological progression of NSCLC. The present review provides an overview of the regulatory effect of circRNAs in the development and progression of NSCLC, taking into consideration various physiological and pathological processes, such as proliferation, apoptosis, invasion and migration, and their potential value as biomarkers and therapeutic targets.

Circular RNA CDR1as promotes tumor progression by regulating miR-432-5p/E2F3 axis in pancreatic cancer

BACKGROUND

Pancreatic cancer (PC), characterized with high growth rate and metastatic rate. It's urgently necessary to explore new mechanism of PC. Circular RNA/miRNA/mRNA network was widely reported to participate in the cancer progression.

METHODS

In this research, circular RNA CDR1as (circCDR1as) was identified by microarray analysis and detected in pancreatic cancer (PC) tissues and cells. Transwell, colony-forming assay, nude mouse tumorigenicity assay were used to determine the function of circCDR1as in PC. Western blot, dual luciferase reporting test were applied to investigate the mechanism.

RESULTS

We found that circCDR1as was highly expressed in PC tissues. The levels of circCDR1as in PC tissues and cells were higher than those in controls. CircCDR1as promoted the migration, invasion and proliferation of PC cells in vitro and tumor growth in vivo via mediating E2F3 expression by sponging miR-432-5p.

CONCLUSIONS

In conclusion, circCDR1as could promote the development of PC and might be a novel diagnostic target for PC.

Circular RNA in tumor metastasis

Circular RNAs (circRNAs) are a type of endogenous non-coding RNA that were discovered to regulate gene expression through multiple pathways. Metastasis remains one of the biggest obstacles in cancer treatment. In this review, we focus on circRNAs involved in cancer tumorigenesis and metastasis. We present recently identified tumor-related circRNAs and discuss their functioning in tumor progression and metastasis. These circRNAs are categorized into different functional mechanisms, including microRNA (miRNA) sponging, protein binding, regulation of host genes, translation of circRNAs, and exosomal circRNAs. Additionally, the indirect functions of circRNAs that regulate epithelial-mesenchymal transition and autophagy are also discussed.

[Research Progress of Circular RNA in Lung Cancer]

Lung cancer is the most common malignant tumor with the highest morbidity and mortality worldwide, and its imposes an insupportable burden on patients due to its poor prognosis. The diagnosis and treatment of lung cancer is under great pressure. Therefore, it is urgent to explore effective therapeutic targets and molecular markers. Circular RNA (circRNA) is a kind of covalently closed non-coding RNAs, which has attracted much attention due to its conservation, stability and tissue specificity. Many studies have found that circRNA participates in the regulation of lung cancer through various mechanisms such as sponging miRNA and plays a part vital role in the early diagnosis, treatment and prognosis evaluation. In recent years, there have been numerous studies on circRNA in lung cancer. This paper summarizes the current progress of circRNA in the diagnosis, treatment and prognosis of lung cancer.
.

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-03955 Promotes Epithelial-Mesenchymal Transition in Osteosarcoma by Regulating miR-3662/Metadherin Pathway

Osteosarcoma is the most common primary malignant tumor, especially in children and adolescents. Circular RNAs (circRNAs) are found to play roles in the progression of osteosarcoma. However, the exact functions of circRNAs in osteosarcoma development still need to be clarified. We obtained differentially expressed circRNAs and miRNAs from a GSE99671 data set (GEO database). The gene co-expression network of ceRNAs and osteosarcoma-related genes was analyzed using the STRING database. qRT-PCR was used to detect the expression of circ-03955 and miR-3662. Transwell assays and flow cytometry were performed to detect phenotypic changes in cell function. A xenograft tumor model was established using BALB/c nude mice. Dual luciferase activity and RNA immunoprecipitation assays were performed to assess the relationship between circ-03955, miR-3662, and metadherin (MTDH). Immunohistochemistry, immunofluorescence, and Western blotting were used to assess protein expression levels. Circ-03955 was significantly upregulated, and miR-3662 was downregulated in osteosarcoma. Circ-03955 silencing inhibited the growth and metastasis of osteosarcoma. Mechanism analysis revealed that circ-03955 could bind to miR-3662, and the latter could target MTDH, leading to its suppressed expression and facilitating epithelial-mesenchymal transition (EMT). All these findings demonstrate that the presence of circ-03955 promotes EMT in osteosarcoma by acting as miR-3662 sponge-mediated MTDH expression.

Circular RNAs and Their Linear Transcripts as Diagnostic and Prognostic Tissue Biomarkers in Prostate Cancer after Prostatectomy in Combination with Clinicopathological Factors

As new biomarkers, circular RNAs (circRNAs) have been largely unexplored in prostate cancer (PCa). Using an integrative approach, we aimed to evaluate the potential of circRNAs and their linear transcripts (linRNAs) to act as (i) diagnostic biomarkers for differentiation between normal and tumor tissue and (ii) prognostic biomarkers for the prediction of biochemical recurrence (BCR) after radical prostatectomy. In a first step, eight circRNAs (circATXN10, circCRIM1, circCSNK1G3, circGUCY1A2, circLPP, circNEAT1, circRHOBTB3, and circSTIL) were identified as differentially expressed via a genome-wide circRNA-based microarray analysis of six PCa samples. Additional bioinformatics and literature data were applied for this selection process. In total, 115 malignant PCa and 79 adjacent normal tissue samples were examined using robust RT-qPCR assays specifically established for the circRNAs and their linear counterparts. Their diagnostic and prognostic potential was evaluated using receiver operating characteristic curves, Cox regressions, decision curve analyses, and C-statistic calculations of prognostic indices. The combination of circATXN10 and linSTIL showed a high discriminative ability between malignant and adjacent normal tissue PCa. The combination of linGUCY1A2, linNEAT1, and linSTIL proved to be the best predictive RNA-signature for BCR. The combination of this RNA signature with five established reference models based on only clinicopathological factors resulted in an improved predictive accuracy for BCR in these models. This is an encouraging study for PCa to evaluate circRNAs and their linRNAs in an integrative approach, and the results showed their clinical potential in combination with standard clinicopathological variables.

circEYA1 Functions as a Sponge of miR-582-3p to Suppress Cervical Adenocarcinoma Tumorigenesis via Upregulating CXCL14

Circular RNAs (circRNAs) function as efficient microRNA (miRNA) sponges that regulate gene expression in the pathogenesis of many human malignancies. However, their roles in cervical adenocarcinoma remain largely unknown. In this study, we aimed to seek novel circRNAs that regulate cervical adenocarcinoma carcinogenesis and to explore their regulatory mechanisms as well as clinical significance. We identified that 24 circRNAs were differentially expressed in cervical adenocarcinoma tissues by RNA sequencing. Among them, circEYA1 was the most significantly downregulated circRNA in cervical adenocarcinoma. In cervical adenocarcinoma cells, circEYA1 overexpression led to suppression of cell viability and colony formation, promotion of apoptosis, and a decrease of the xenograft tumor growth. The mechanism underlying these observations is that circEYA1 functioned as a sponge of miR-582-3p and abrogated its suppression of CXCL14 expression. Consistently, miR-582-3p inhibition phenocopied the biological effects of circEYA1 overexpression in cervical adenocarcinoma cells. Moreover, miR-582-3p overexpression reversed the suppressive behaviors of circEYA1 in vitro and in vivo. In addition, the expression, correlation, and clinical diagnostic value of circEYA1/miR-582-3p/CXCL14 were confirmed in 198 clinical cervical tissue samples. In summary, our findings highlight a novel tumor suppressive role of circEYA1 in cervical adenocarcinoma tumorigenesis and may provide a potential diagnostic marker and therapeutic target for patients with cervical adenocarcinoma.

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.

circ_2858 Helps Blood-Brain Barrier Disruption by Increasing VEGFA via Sponging miR-93-5p during Escherichia coli Meningitis

Meningitic Escherichia coli invasion of the host brain can lead to increased blood-brain barrier (BBB) permeability. Circular RNAs (circRNAs) are non-coding RNAs, highly abundant in the brain, that are widely involved in the pathological processes of central nervous system (CNS) disorders; however, whether circRNAs participate in the regulation of BBB permeability during E. coli meningitis remains unknown. Here, we identified a novel circRNA, circ_2858, that was significantly upregulated in human brain microvascular endothelial cells (hBMECs) upon meningitic E. coli infection. We also found that circ_2858 regulated BBB permeability in hBMECs by competitively binding miR-93-5p, thereby inducing the upregulation of vascular endothelial growth factor A and finally resulting in downregulation as well as altered distribution of tight junction proteins such as ZO-1, Occludin, and Claudin-5. These findings provide novel insights into the influence of circ_2858 on BBB permeability during the pathogenic process of E. coli meningitis, suggesting potential nucleic acid targets for future prevention and therapy of CNS infection induced by meningitic E. coli.

Disease-Associated Circular RNAs: From Biology to Computational Identification

Circular RNAs (circRNAs) are endogenous RNAs with a covalently closed continuous loop, generated through various backsplicing events of pre-mRNA. An accumulating number of studies have shown that circRNAs are potential biomarkers for major human diseases such as cancer and Alzheimer's disease. Thus, identification and prediction of human disease-associated circRNAs are of significant importance. To this end, a computational analysis-assisted strategy is indispensable to detect, verify, and quantify circRNAs for downstream applications. In this review, we briefly introduce the biology of circRNAs, including the biogenesis, characteristics, and biological functions. In addition, we outline about 30 recent bioinformatic analysis tools that are publicly available for circRNA study. Principles for applying these computational strategies and considerations will be briefly discussed. Lastly, we give a complete survey on more than 20 key computational databases that are frequently used. To our knowledge, this is the most complete and updated summary on publicly available circRNA resources. In conclusion, this review summarizes key aspects of circRNA biology and outlines key computational strategies that will facilitate the genome-wide identification and prediction of circRNAs.

Chemotherapy and chemo-resistance in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is closely associated with Epstein-Barr virus (EBV) and occurs frequently in the south of China and Southeast Asian countries. Concurrent chemo-radiotherapy is one of the main treatments for NPC. Although, the combined treatment of chemo-radiotherapy produces a satisfying survival rate, the chemo-resistance arises as a big obstacle in curing recurrent NPC patients. The acquirement of chemo-resistance is usually along with a poor prognosis. So far, the mechanism of chemo-resistance in NPC has not been fully elucidated and there have not been a comprehensive review on this issue. Thus, it is of great significance to summarize the mechanisms involved in NPC chemo-resistance. In this review, the importance and limitations of chemotherapy and the mechanisms of chemo-resistances in NPC were discussed.

Circular RNA hsa_circ_0001588 promotes the malignant progression of lung adenocarcinoma by modulating miR-524-3p/NACC1 signaling

AIMS

Previous studies have demonstrated that circular RNAs play significant roles in several tumors, including lung adenocarcinoma; however, specific biological functions and molecular mechanisms underlying this process remain unclear.

MATERIALS AND METHODS

Here, we conducted real-time quantitative PCR (qRT-PCR) to measure hsa_circ_0001588 expression levels in 60 paired lung adenocarcinoma tissues and cell lines. Furthermore, the association between hsa_circ_0001588 and clinical features of lung adenocarcinoma was analyzed. Functional experiments were conducted to assess the influence of hsa_circ_0001588 on proliferation, migration, and invasion in lung adenocarcinoma cells. We detected possible downstream targets of hsa_circ_0001588 using bioinformatics analysis. Luciferase reporter assays, qRT-PCR, and western blotting assays were performed to verify the molecular mechanism underlying hsa_circ_0001588 functions.

KEY FINDINGS

We found that hsa_circ_0001588 was prominently upregulated in lung adenocarcinoma tissues and cell lines; elevated expression of hsa_circ_0001588 was positively correlated with poor clinicopathological features of lung adenocarcinoma. Functional experiments revealed that hsa_circ_0001588 acts as an oncogene to promote the proliferation, migration, and invasion of lung adenocarcinoma in vitro. Mechanistically, hsa_circ_0001588 promoted the proliferation, migration, and metastasis of lung adenocarcinoma by binding to miR-524-3p to promote nucleus accumbens-associated protein 1(NACC1) expression.

SIGNIFICANCE

Together, our results revealed that hsa_circ_0001588 upregulated the expression of NACC1 by combining with miR-524-3p to promote the proliferation, migration, and invasion of lung adenocarcinoma cells, suggesting that hsa_circ_0001588 may be an underlying therapeutic target for lung adenocarcinoma.

Circular RNAs: Regulatory functions in respiratory tract cancers

Circular RNAs (circRNAs) are a class of single-stranded RNAs having a covalently closed loop structure generated from back-splicing of pre-mRNA. These novel RNAs are characterized by high stability, abundance and conservation. Accumulating evidence has revealed that circRNAs are intimately associated with the pathogenesis, development and progression of multiple human diseases, including respiratory tract cancers. CircRNAs may serve as oncogenes or tumor suppressors to influence cell proliferation, differentiation, apoptosis, invasion and metastasis. CircRNAs may act as microRNA (miRNA) sponges, interact with RNA-binding proteins (RBPs), regulate gene transcription and/or translate into mini-peptides or proteins. In this review, we discuss recent progress in understanding the pathologic roles of circRNAs in respiratory tract cancers, such as nasopharyngeal carcinoma, laryngeal squamous cell carcinoma, and especially lung adenocarcinoma. We further discuss the diagnostic, therapeutic and prognostic roles as potential biomarkers in respiratory tract cancers, providing insight into the possibilities of applying circRNAs as therapeutic targets and biomarkers in precision oncology.