Circular RNA hsa_circ_0008305 (circPTK2) inhibits TGF-β-induced epithelial-mesenchymal transition and metastasis by controlling TIF1γ in non-small cell lung cancer

Roles of circular RNA in breast cancer: present and future

Breast cancer is one of the most common cancers with the highest morbidity and mortality among women despite the treatment approaches have advanced including surgery, endocrine therapy and targeted therapy. Novel biomarkers are warranted to be discovered for the early detection, treatment and prognosis for breast cancer. CircRNA is a class of covalently closed single-stranded circular RNA molecules without free 5' or 3' end which makes them well expressed and more stable than their linear counterparts. In this review, we mainly discuss the oncogenic or anti-oncogenic roles of circRNAs can be utilized in the treatment and prognosis of breast cancer. A large number of circRNAs have shown great potential to function in carcinogenesis, metastasis or chemoresistance of breast cancer through transcriptional regulation of RNAs including miRNA and mRNA, in addition to their promise as stable biomarkers that can be used for monitoring breast cancer progression. However, the translation phenomenon of circRNAs in breast cancer and the diagnostic value of circRNAs in breast cancer requires further investigation for which the detection of circRNAs in plasma exosomes could be worthy of a try. Above all, engineered exosomes preloaded with engineered anti-oncogenic circRNAs are likely to provide a novel direction in the personal medicine of breast cancer.

circGFRA1 Promotes Ovarian Cancer Progression By Sponging miR-449a

Backgroud: Increasing studies show that circular RNAs (circRNAs) play important roles in tumor progression. However, the function of circRNAs in ovarian cancer is mostly unclear. Methods: We detected the expression of circGFRA1 by quantitative real-time PCR (qRT-PCR) in 50 pairs of ovarian cancer tissues and adjacent normal tissues. Then, we explored the function of circGFRA1 in ovarian cancer progression, such as cell proliferation, apoptosis and invasion. Moreover, we performed luciferase reporter and RNA immunoprecipitation (RIP) assay to study the competing endogenous RNA (ceRNA) function of circGFRA1 in ovarian cancer progression. Results: qRT-PCR showed that circGFRA1 was overexpressed in ovarian cancer tissues. Inhibition of circGFRA1 suppressed cell proliferation and invasion, but induced cell apoptosis in ovarian cancer. Luciferase reporter and RIP assay revealed that circGFRA1 could regulate the expression of GFRA1 by sponging miR-449a. Conclusions: In summary, circGFRA1 regulated GFRA1 expression and ovarian cancer progression by sponging miR-449a. circGFRA1 could be a potential diagnostic biomarker and therapeutic target for ovarian cancer.

circ-PKD2 inhibits carcinogenesis via the miR-204-3p/APC2 axis in oral squamous cell carcinoma

Recent findings have shown that dysregulation of circular RNAs (circRNAs) is implicated in various cancers. However, the contribution of circRNAs in oral squamous cell carcinoma (OSCC) remains largely unexplored. We screened circRNA expression profiles using a circRNA microarray in paired OSCC and normal tissues and explored the clinical significance of a downregulated circRNA, circ-PKD2. Moreover, the biological function of circ-PKD2 in OSCC was investigated both in vitro and in vivo. We found that downregulation of circ-PKD2 in OSCC correlated significantly with aggressive characteristics. Further analysis revealed that overexpression of circ-PKD2 inhibited OSCC cell proliferation, migration and invasion, induced apoptosis and cell cycle arrest, which were promoted by knockdown of circ-PKD2. In addition, circ-PKD2 was identified as a sponge for miR-204-3p and upregulated the expression of adenomatous polyposis coli 2 (APC2), which was the functional target of miR-204-3p. Moreover, circ-PKD2 attenuated the oncogenic effects of miR-204-3p-mediated APC2 on OSCC progression via multiple signaling pathways. These results demonstrate that the circ-PKD2/miR-204-3p/APC2 axis represents a novel pathway involved in the pathogenesis of OSCC and may serve as a novel therapeutic target of OSCC.

Targeting the circBMPR2/miR-553/USP4 Axis as a Potent Therapeutic Approach for Breast Cancer

Emerging evidence suggests that circular RNAs (circRNAs) have crucial roles in various processes, including cancer development and progression. However, the functional roles of circRNAs in breast cancer remain to be elucidated. In this study, we identified a novel circRNA (named circBMPR2) whose expression was lower in breast cancer tissues with metastasis. Moreover, circBMPR2 expression was negatively associated with the motility of breast cancer cells and significantly downregulated in human breast cancer tissues. Functionally, we found that circBMPR2 knockdown effectively enhanced cell proliferation, migration, and invasion. Moreover, circBMPR2 knockdown promoted tamoxifen resistance of breast cancer cells through inhibiting tamoxifen-induced apoptosis, whereas circBMPR2 overexpression led to decreased tamoxifen resistance. Mechanistically, we demonstrated that circBMPR2 could abundantly sponge miR-553 and that miR-553 overexpression could attenuate the inhibitory effects caused by circBMPR2 overexpression. We also found that ubiquitin-specific protease 4 (USP4) was a direct target of miR-553, which functions as a tumor suppressor in breast cancer. Our findings demonstrated that circBMPR2 might function as a miR-553 sponge and then relieve the suppression of USP4 to inhibit the progression and tamoxifen resistance of breast cancer. Targeting this newly identified circRNA may help us to develop potential novel therapies for breast cancer patients.

Circular RNA ABCB10 promotes tumor progression and correlates with pejorative prognosis in clear cell renal cell carcinoma

OBJECTIVE

Our study aimed to evaluate the effect of circular RNA ABCB10 (circ-ABCB10) on proliferation and apoptosis of clear cell renal cell carcinoma (ccRCC) cells, and its prognostic value in patients with ccRCC.

METHODS

Circ-ABCB10 expression in five ccRCC cell lines and normal kidney epithelial cell line was measured by quantitative polymerase chain reaction (qPCR). Empty overexpression, circ-ABCB10 overexpression, empty shRNA, and circ-ABCB10 shRNA plasmids were transfected into A498 cells as negative control for circ-ABCB10 over expression {NC (+)}, Circ-ABCB10(+), negative control (-){NC(-)}, and Circ-ABCB10(-) groups, then cell proliferation and apoptosis were evaluated by Cell Counting Kit-8 and annexin V/propidium iodide. Meanwhile, apoptotic markers were measured by western blot. Subsequently, circ-ABCB10 expression in tumor tissues and paired adjacent tissues from 120 ccRCC patients was measured by qPCR.

RESULTS

Circ-ABCB10 expression was elevated in all the ccRCC cell lines compared with the normal kidney cells line. A498 cell proliferation was enhanced in the Circ-ABCB10(+) group compared with the NC(+) group, while it was inhibited in the Circ-ABCB10(-) group compared with the NC (-) group; and A498 cell apoptosis was repressed in the Circ-ABCB10(+) group than the NC(+) group, but was promoted in the Circ-ABCB10(-) group compared with the NC(-) group. In addition, circ-ABCB10 was up-regulated in tumor tissues compared with paired adjacent tissues, and its high expression correlated with the advanced pathological grade and the tumor node metastasis stage as well as independently predicting worse overall survival in ccRCC patients.

CONCLUSION

Circ-ABCB10 promotes tumor progression and correlates with pejorative prognosis in ccRCC.

Circular RNAs and RNA Splice Variants as Biomarkers for Prognosis and Therapeutic Response in the Liquid Biopsies of Lung Cancer Patients

Lung cancer, including non-small cell lung carcinoma (NSCLC), is the most frequently diagnosed cancer. It is also the leading cause of cancer-related mortality worldwide because of its late diagnosis and its resistance to therapies. Therefore, the identification of biomarkers for early diagnosis, prognosis, and monitoring of therapeutic response is urgently needed. Liquid biopsies, especially blood, are considered as promising tools to detect and quantify circulating cancer biomarkers. Cell-free circulating tumor DNA has been extensively studied. Recently, the possibility to detect and quantify RNAs in tumor biopsies, notably circulating cell-free RNAs, has gained great attention. RNA alternative splicing contributes to the proteome diversity through the biogenesis of several mRNA splice variants from the same pre-mRNA. Circular RNA (circRNA) is a new class of RNAs resulting from pre-mRNA back splicing. Owing to the development of high-throughput transcriptomic analyses, numerous RNA splice variants and, more recently, circRNAs have been identified and found to be differentially expressed in tumor patients compared to healthy controls. The contribution of some of these RNA splice variants and circRNAs to tumor progression, dissemination, or drug response has been clearly demonstrated in preclinical models. In this review, we discuss the potential of circRNAs and mRNA splice variants as candidate biomarkers for the prognosis and the therapeutic response of NSCLC in liquid biopsies.

Downregulated circular RNA hsa_circ_0067301 regulates epithelial-mesenchymal transition in endometriosis via the miR-141/Notch signaling pathway

Endometriosis is a common gynecologic disorder with enigmatic etiopathogenesis and is characterized by tumor-like biological behaviors. Epithelial-mesenchymal transition (EMT) has been recognized as a core mechanism of endometriosis. Recently, circular RNAs (circRNAs) have attracted considerable attention because they play an important role in the progression of cancer. However, little is known about the function of circRNAs in endometriosis. This study is intended to investigate the involvement of circRNAs and microRNAs in the process of EMT in ovarian endometriosis in vitro. We found that relative RNA levels of hsa_circ_0067301 and miR-141-5p were significantly reduced in ectopic endometrium when compared to control endometrium. Hsa_circ_0067301 knockdown could promote the proliferation and migration in Ishikawa and End1/E6E7 cells, concomitant with increased the relative protein expression against Notch-1, Hes-1, N-cadherin, and vimentin but reduced expression of E-cadherin. After co-transfection with the miR-141-5p inhibitor, the miR-141-5p that competes for binding to hsa_circ_0067301 was reduced, reversed EMT and partially restored the expression of Notch-1 and Hes-1. Results demonstrate the hsa_circ_0067301/miR-141-5p/Notch-1 axis plays an important regulatory role in the process of EMT in endometriosis. The study highlighted the importance of circRNAs in ovarian endometriosis and provided unique insights into the molecular basis concerning the pathogenesis of endometriosis.

Circular RNAs in Cancer: emerging functions in hallmarks, stemness, resistance and roles as potential biomarkers

Circular RNAs (circRNAs) are a class of RNA molecules with closed loops and high stability. CircRNAs are abundantly expressed in eukaryotic organisms and exhibit both location- and step-specificity. In recent years, circRNAs are attracting considerable research attention attributed to their possible contributions to gene regulation through a variety of actions, including sponging microRNAs, interacting with RNA-binding proteins, regulating transcription and splicing, and protein translation. Growing evidence has revealed that circRNAs play critical roles in the development and progression of diseases, especially in cancers. Without doubt, expanding our understanding of circRNAs will enrich knowledge of cancer and provide new opportunities for cancer therapy. In this review, we provide an overview of the characteristics, functions and functional mechanisms of circRNAs. In particular, we summarize current knowledge regarding the functions of circRNAs in the hallmarks, stemness, resistance of cancer, as well as the possibility of circRNAs as biomarkers in cancer.

Upregulated circ RNA hsa_circ_0000337 promotes cell proliferation, migration, and invasion of esophageal squamous cell carcinoma

Background

As a new class of endogenous ncRNAs, circRNAs have been recently verified to be involved in the carcinogenesis and progression of human cancers. In the current study, we attempted to explore the potential function of a candidate circRNA (hsa_circ_0000337) in esophageal squamous cell carcinoma (ESCC).

Patients and methods

The altered expression of hsa_circ_0000337 was validated in clinical samples from 48 patients with ESCC. The human esophageal carcinoma cell lines KYSE-150 and TE-1, and the normal human esophageal epithelial cell line (HET-1A) were applied for functional analysis of hsa_circ_0000337. Cell proliferation was measured using the Cell Counting Kit-8 assay and the colony formation assay. Cell invasion and migration were detected by Transwell and wound healing assays, respectively. We further performed bioinformatic analysis and luciferase reporter assays to explore the role of hsa_circ_0000337 as a miRNA sponge.

Results

hsa_circ_0000337 was significantly upregulated in ESCC tissues compared to adjacent normal-appearing tissues (P<0.0001). In our in vitro experiment, the expression of hsa_circ_0000337 was higher in TE-1 compared to the normal human esophageal epithelial cell line HET-1A (P<0.001), but was not significantly different in KYSE-150 (P>0.05). Knockdown of hsa_circ_0000337 significantly inhibited cell proliferation, migration, and invasion in TE-1 and KYSE-150 cell lines. Bioinformatics predicted and luciferase reporter assay verified that hsa_circ_0000337 could bind to miR-670-5p, a ncRNA involved in carcinogenesis. It is estimated that 21 genes are regulated by miR-670-5p.

Conclusion

hsa_circ_0000337 was found to be an upregulated circRNA that is related to ESCC and promotes the progression of disease by regulating cell proliferation, migration, and invasion. These findings suggest that this circRNA could be a promising diagnostic biomarker and potential therapeutic target.

A two-circular RNA signature as a noninvasive diagnostic biomarker for lung adenocarcinoma

BACKGROUND

Recently, circular RNAs (circRNAs) have been reported to be microRNA sponges and play essential roles in cancer development. This study aimed to evaluate whether circulating circRNAs could be used as diagnostic biomarkers for lung adenocarcinoma (LUAD).

METHODS

The Gene Expression Omnibus (GEO) dataset was used to investigate differentially expressed circRNAs (DEcircRNAs) in paired LUAD tissues and adjacent nontumor tissues. The expression levels of the host genes were analyzed in The Cancer Genome Atlas (TCGA)-LUAD dataset, and the prognostic value was assessed using the Kaplan-Meier plotter. Quantitative real-time PCR (qRT-PCR) was performed to validate the expression of candidate circRNAs in the LUAD plasma and cells. The CCK8 assay was used to measure the function of circRNAs in cell proliferation. Competing endogenous RNA (ceRNA) network, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to predict the possible mechanisms and functions of circRNAs in LUAD.

RESULTS

Two upregulated and two downregulated circRNAs were identified as candidate circRNAs using bioinformatics analysis. qRT-PCR demonstrated that hsa_circ_0005962 was upregulated in LUAD plasma and cells, whereas hsa_circ_0086414 was downregulated. Receiver operating characteristic (ROC) curve analysis confirmed that a signature comprising the two circRNAs had good diagnostic potential, with an area under the ROC curve (AUC) of 0.81 (P < 0.0001). In addition, we observed that overexpression of plasma hsa_circ_0086414 was related to EGFR mutations (P = 0.001). Plasma hsa_circ_0005962 displayed significantly different expression before and after surgery in patients with LUAD (P < 0.0001). In vitro experiments suggested that hsa_circ_0005962 promoted LUAD cell proliferation. For future studies, we predicted the circRNA-miRNA-mRNA network for hsa_circ_0005962. Bioinformatics analysis revealed that hsa_circ_0005962 might be involved in LUAD development.

CONCLUSION

A circRNA signature was identified as a potential noninvasive biomarker for LUAD diagnosis.

Circular RNA circPTK2 regulates oxygen-glucose deprivation-activated microglia-induced hippocampal neuronal apoptosis via miR-29b-SOCS-1-JAK2/STAT3-IL-1β signaling

Oxygen-glucose deprivation (OGD)-activated microglia contribute to neuronal apoptosis via releasing pro-inflammatory cytokines, and some miRNAs have been reported to be involved in this process. Circular RNAs (circRNAs) have been reported to function as miRNA sponges, but it remains unknown whether and how circRNAs contribute to OGD-activated microglia-induced neuronal apoptosis. Here, we investigated the function and relationship of miR-29b and circPTK2 in OGD-activated microglia-induced neuronal apoptosis. We found upregulation of TNF-α and IL-1β, and downregulation of miR-29b in OGD-activated microglia. miR-29b inhibited OGD-activated microglia-induced neuronal apoptosis. Meanwhile, miR-29b promoted SOCS-1 expression, and suppressed JAK2/STAT3 signaling. In addition, inhibition of JAK2/STAT3 signaling downregulated IL-1β expression, while upregulation of miR-29b or SOCS-1 also inhibited IL-1β production. IL-1β was confirmed to be an apoptosis inducer of hippocampal neurons. Moreover, either SOCS-1 upregulation or blockade of JAK2/STAT3 signaling suppressed OGD-activated microglia-induced neuronal apoptosis. These data suggest that miR-29b inhibits OGD-activated microglia-induced neuronal apoptosis via inducing SOCS-1 expression, blocking JNK2/STAT3 signaling, and inhibiting IL-1β production. circPTK2 was confirmed to inhibit miR-29b expression in OGD model by directly binding to miR-29b. Function assay showed that circPTK2 regulated microglia-induced neuronal apoptosis via sponging miR-29b. Collectively, these findings suggest that circPTK2 regulates OGD-activated microglia-induced neuronal apoptosis via miR-29b-SOCS-1-JAK2/STAT3-IL-1β signaling.

circRAPGEF5 Contributes to Papillary Thyroid Proliferation and Metastatis by Regulation miR-198/FGFR1

The circular RNA RAPGEF5 (circRAPGEF5) is generated from five exons of the RAPGEF5 gene and abnormal expression in papillary thyroid cancer (PTC). However, whether circRAPGEF5 plays a role in PTC tumorigenesis remains unclear. The aim of the present study was to investigate the role of circRAPGEF5 in PTC. The results showed that circRAPGEF5 was upregulated in PTC tissues and cell lines. circRAPGEF5 knockdown inhibited cell proliferation, migration, and invasion in vitro; and circRAPGEF5 silencing downregulated fibroblast growth factor receptor 1 (FGFR1) expression by “sponging” miR-198, suppressing the aggressive biological behaviors of PTC. Luciferase reporter assays confirmed that circRAPGEF5 interacted with miR-198 and that miR-198 interacted with the 3′ UTR of FGFR1 to downregulate its expression. Xenograft experiments confirmed that circRAPGEF5 knockdown suppressed FGFR1-mediated tumor growth by promoting miR-198 expression. circRAPGEF5 acts as a tumor promoter via a novel circRAPGEF5/miR-198/FGFR1 axis, providing a potential biomarker and therapeutic target for the management of PTC.

Circular RNA PVT1 acts as a competing endogenous RNA for miR-497 in promoting non-small cell lung cancer progression

Circular RNAs (circRNAs) are a class of covalently closed non-coding RNAs and play crucial regulatory roles in human cancer biology. The purpose of the present study was to explore the expression pattern and biological role of circular RNA PVT1 (circPVT1) in non-small cell lung cancer (NSCLC). We firstly found that circPVT1 was overexpressed in clinical NSCLC tissues and cell lines. NSCLC patients with high expression of circPVT1 exhibited aggressive clinicopathological characteristics and poor prognosis. In vitro assays of the NSCLC cell lines (H1299 and A549 cells) demonstrated that knockdown of circPVT1 inhibited NSCLC cell proliferation and induced NSCLC cell apoptosis. We further found that circPVT1 served as a competing endogenous RNA of miR-497 and indirectly regulated Bcl-2 expression in NSCLC cells. Finally, inhibition of miR-497 abrogated the effects of circPVT1 knockdown in NSCLC cells. Taken together, the results from our study indicated circPVT1 acts as an oncogene in NSCLC, and may serve as a promising therapeutic target for NSCLC patients.

CircVRK1 regulates tumor progression and radioresistance in esophageal squamous cell carcinoma by regulating miR-624-3p/PTEN/PI3K/AKT signaling pathway

As a novel class of noncoding RNAs (ncRNAs), circular RNAs (circRNAs) have been verified to be potential biomarkers and therapeutic targets for human malignant tumors. However, the thorough understanding of circRNAs in the progression of esophageal squamous cell carcinoma (ESCC) still needs to be improved. This study focused on exploring the function and mechanism of circVRK1 in ESCC. At first, we examined the expression level of circVRK1 in ESCC tissues and cell lines with qRT-PCR. We found that circVRK1 was downregulated in ESCC tissues and cell lines. Kaplan-Meier method was used to analyze the correlation between circVRK1 expression and the overall survival of ESCC patients. Functionally, overexpression of circVRK1 suppressed the cell proliferation, migration and epithelial-mesenchymal transition (EMT) and reversed the radioresistance. Therefore, we identified the tumor suppressive role of circVRK1 in ESCC progression. Mechanistically, circVRK1 positively regulated PTEN by acting as a molecular sponge of miR-624-3p. Moreover, circVRK1 decreased the activity of PI3K/AKT signaling pathway by upregulating PTEN. Rescue assays were carried out to confirm the function of circVRK1-miR-624-3p-PTEN axis in ESCC progression. Our findings showed that circVRK1 suppressed ESCC progression by regulating miR-624-3p/PTEN axis and PI3K/AKT signaling pathway, suggesting the potential therapeutic value of circVRK1 for ESCC.