Functional role of circular RNAs in cancer development and progression

CRAFT: a bioinformatics software for custom prediction of circular RNA functions

Circular RNAs (circRNAs), transcripts generated by backsplicing, are particularly stable and pleiotropic molecules, whose dysregulation drives human diseases and cancer by modulating gene expression and signaling pathways. CircRNAs can regulate cellular processes by different mechanisms, including interaction with microRNAs (miRNAs) and RNA-binding proteins (RBP), and encoding specific peptides. The prediction of circRNA functions is instrumental to interpret their impact in diseases, and to prioritize circRNAs for functional investigation. Currently, circRNA functional predictions are provided by web databases that do not allow custom analyses, while self-standing circRNA prediction tools are mostly limited to predict only one type of function, mainly focusing on the miRNA sponge activity of circRNAs. To solve these issues, we developed CRAFT (CircRNA Function prediction Tool), a freely available computational pipeline that predicts circRNA sequence and molecular interactions with miRNAs and RBP, along with their coding potential. Analysis of a set of circRNAs with known functions has been used to appraise CRAFT predictions and to optimize its setting. CRAFT provides a comprehensive graphical visualization of the results, links to several knowledge databases, and extensive functional enrichment analysis. Moreover, it originally combines the predictions for different circRNAs. CRAFT is a useful tool to help the user explore the potential regulatory networks involving the circRNAs of interest and generate hypotheses about the cooperation of circRNAs into the modulation of biological processes.

CircVPS13C promotes pituitary adenoma growth by decreasing the stability of IFITM1 mRNA via interacting with RRBP1

CircRNAs play important roles in a variety of biological processes by acting as microRNA sponges and protein scaffolds or by encoding functional proteins. However, their functions and underlying mechanisms remain largely unknown. Distinctive circRNA patterns were explored by comparing nonfunctioning pituitary adenomas (NFPAs) and normal pituitary tissues with a circRNA array. The biological functions of selected circRNAs were determined in vitro and in vivo. RNA-seq and circRNA pulldown assays were applied to investigate the underlying mechanisms. The circRNA profile of NFPAs is tremendously different from that of normal pituitary tissues. CircVPS13C is significantly upregulated in NFPA samples and cell lines. Gain- and loss-of-function experiments demonstrate that silencing circVPS13C inhibits the proliferation of pituitary tumor cells in vitro and in vivo. Mechanistically, circVPS13C silencing increases the expression of IFITM1 and subsequently activates its downstream genes involved in MAPK- and apoptosis-associated signaling pathways. Rescue experiments show that IFITM1 overexpression partly reverses the biological effects of circVPS13C. Further studies reveal that circVPS13C inhibits IFITM1 expression through a novel mechanism mainly by competitively interacting with RRBP1, a ribosome-binding protein of the endoplasmic reticulum membrane, and thereby alleviating the stability of IFITM1 mRNA. Clinically, circVPS13C expression is markedly higher in high-risk NFPA samples and is downregulated in patient serum 7 days post-transsphenoidal adenoma resection. Our findings suggest that circVPS13C is a critical regulator in the proliferation and development of NFPAs through a novel mechanism, whereby regulating mRNA stability via interacting with ribosome-binding proteins on the endoplasmic reticulum membrane.

The circROBO1/KLF5/FUS feedback loop regulates the liver metastasis of breast cancer by inhibiting the selective autophagy of afadin

BACKGROUND

Metastasis causes the majority of cancer-related deaths worldwide. Increasing studies have revealed that circRNAs are associated with the carcinogenesis and metastasis of many cancers. Nevertheless, the biological mechanisms of circRNAs in breast cancer (BC) liver metastasis remain extremely ambiguous.

METHODS

In this study, we identified circROBO1 from three pairs of primary BC and metastatic liver sites by RNA sequencing. FISH assays and RT-qPCR were conducted to validate the existence and expression of circROBO1. The oncogenic role of circROBO1 was demonstrated both in vitro and in vivo. Western blot, ChIP, RIP, RNA pull-down, and dual-luciferase reporter assays were used to confirm the interaction of the feedback loop among circROBO1, miR-217-5p, KLF5, and FUS. Meanwhile, the regulation of selective autophagy was investigated by immunofluorescence, CoIP, and western blot.

RESULTS

In this study, upregulated expression of circROBO1 was found in BC-derived liver metastases and was correlated with poor prognosis. Knockdown of circROBO1 strikingly inhibited the proliferation, migration, and invasion of BC cells, whereas overexpression of circROBO1 showed the opposite effects. Moreover, overexpression of circROBO1 promoted tumor growth and liver metastasis in vivo. Further research revealed that circROBO1 could upregulate KLF5 by sponging miR-217-5p, allowing KLF5 to activate the transcription of FUS, which would promote the back splicing of circROBO1. Therefore, a positive feedback loop comprising circROBO1/KLF5/FUS was formed. More importantly, we found that circROBO1 inhibited selective autophagy of afadin by upregulating KLF5.

CONCLUSIONS

Our results demonstrated that circROBO1 facilitates the carcinogenesis and liver metastasis of BC through the circROBO1/KLF5/FUS feedback loop, which inhibits the selective autophagy of afadin by suppressing the transcription of BECN1. Therefore, circROBO1 could be used not only as a potential prognostic marker but also as a therapeutic target in BC.

The involvement of the circFOXM1-miR-432-Gα12 axis in glioma cell proliferation and aggressiveness

Accumulating evidence indicates that circFOXM1 (Hsa_circ_0025033) is highly expressed in several cancers; however, the function of circFOXM1 in glioma and the molecular mechanism have not been well explored. In the present study, we found that expression of circFOXM1 was upregulated in both glioma tissues and cell lines. In addition, circFOXM1 knockdown suppressed glioma-cell proliferation, activated apoptosis in vitro, and repressed tumour growth in vivo. Moreover, we clarified that circFOXM1 binds with miR-432, which was downregulated in glioma cells. Furthermore, we indicated that Gα12, a direct target of miR-432, was highly expressed in glioma cells, and Gα12 silencing might limit the progression of glioma. Rescue assays indicated that Gα12 reversed the inhibitory effect of circFOXM1 silencing on glioma-cell tumorigenesis. In conclusion, circFOXM1 acts as a sponge of miR-432 to promote the proliferation and aggressiveness of glioma cells through the Gα12 signalling pathway.

CircTMC5 promotes gastric cancer progression and metastasis by targeting miR-361-3p/RABL6

BACKGROUND

Gastric cancer (GC) is common in East Asia, yet its molecular and pathogenic mechanisms remain unclear. Circular RNAs (circRNAs) are differentially expressed in GC and may be promising biomarkers. Here, we investigated the role and regulatory mechanism of circTMC5 in GC.

METHODS

CircTMC5 expression was detected in human GC and adjacent tissues using microarray assays and qRT-PCR, while the clinicopathological characteristics of patients with GC were used to assess its diagnostic and prognostic value. The circTMC5/miR-361-3p/RABL6 axis was examined in vitro and vivo, and the immune roles of RABL6 were evaluated using bioinformatics analyses and immunohistochemistry (IHC).

RESULTS

CircTMC5 was highly expressed in GC tissues, plasma, and cell lines, and was closely related to histological grade, pathological stage, and T classification in patients with GC. CircTMC5 expression was also an independent prognostic factor for GC and its combined detection with carcinoembryonic antigen may improve GC diagnosis. Low circTMC5 expression correlated with good prognosis, inhibited GC cell proliferation, and promoted apoptosis. Mechanistically, circTMC5 overexpression promoted GC cell proliferation, invasion, and metastasis but inhibited apoptosis by sponging miR-361-3p and up-regulating RABL6 in vitro and vivo, whereas miR-361-3p up-regulation had the opposite effects. RABL6 was highly expressed in GC and was involved in immune regulation and infiltration in GC.

CONCLUSIONS

CircTMC5 promotes GC and sponges miR-361-3p to up-regulate RABL6 expression, thus may have diagnostic and prognostic value in GC. RABL6 also displays therapeutic promise due to its role in the immune regulation of GC.

circHUWE1 Exerts an Oncogenic Role in Inducing DDP-Resistant NSCLC Progression Depending on the Regulation of miR-34a-5p/TNFAIP8

Background

Circular RNAs (circRNAs) are reported as competing endogenous RNAs (ceRNAs) and play key roles in non-small-cell lung cancer (NSCLC) progression. Thus, this study was aimed at clarifying underlying molecular mechanisms of circHUWE1 in NSCLC.

Methods

The quantitative real-time polymerase chain reaction (RT-qPCR) and western blot analyses were used for examining circHUWE1, microRNA-34a-5p (miR-34a-5p), and tumor necrosis factor alpha-induced protein 8 (TNFAIP8). IC₅₀ of cisplatin (DDP) in A549/DDP and H1299/DDP cells and cell viability were analyzed by the Cell Counting Kit 8 (CCK-8) assay. Colony forming assay was performed to assess colony forming ability. Cell apoptosis and cell cycle distribution were determined by flow cytometry. Migrated and invaded cell numbers were examined by transwell assay. The association among circHUWE1, miR-34a-5p, and TNFAIP8 was analyzed by dual-luciferase reporter and RNA immunoprecipitation assays. A xenograft experiment was applied to clarify the functional role of circHUWE1 in vivo.

Results

circHUWE1 was upregulated in NSCLC tissues and cells, especially in DDP-resistant groups. circHUWE1 downregulation inhibited DDP resistance, proliferation, migration, and invasion while it induced apoptosis and cell cycle arrest of DDP-resistant NSCLC cells, which was overturned by silencing of miR-34a-5p. TNFAIP8 was a functional gene of miR-34a-5p, and the suppressive effects of miR-34a-5p overexpression on DDP-resistant NSCLC progression were dependent on the suppression of TNFAIP8. circHUWE1 inhibition also delayed tumor growth of DDP-resistant NSCLC cells.

Conclusion

circHUWE1 functioned as a promoter in DDP-resistant NSCLC by interaction with miR-34a-5p-TNFAIP8 networks, providing novel insight into DDP-resistant NSCLC diagnosis and treatment.

hsa_circ_0068631 promotes breast cancer progression through c-Myc by binding to EIF4A3

Breast cancer (BC) is one of the most common malignancies among women worldwide with a high incidence of recurrence and metastasis. In this study, we demonstrate that hsa_circ_0068631, a circRNA generated from the transferrin receptor (TFRC), is upregulated in BC tissues and cell lines. Knockdown of hsa_circ_0068631 inhibited the proliferation and migration of BC cells in vitro and in vivo. Mechanistically, an RNA pull-down assay and RNA immunoprecipitation assay revealed that eukaryotic translation initiation factor 4A3 (EIF4A3) could bind to hsa_circ_0068631 and c-Myc mRNA. Additionally, the expression of hsa_circ_0068631 was positively correlated with c-Myc, and the upregulation of hsa_circ_0068631 was a crucial factor for the dysregulation of c-Myc. Through an actinomycin D assay, we confirmed that the mRNA stability of c-Myc was influenced by hsa_circ_0068631 and EIF4A3. Furthermore, hsa_circ_0068631 could recruit EIF4A3 to increase c-Myc mRNA stability. Rescue assays manifesting depletion of c-Myc rescued the promotive effect of hsa_circ_0068631 overexpression on biological activities in BC. In conclusion, to our knowledge, this study is the first to unveil the role of hsa_circ_0068631 and the hsa_circ_0068631/EIF4A3/c-Myc axis in BC, providing a new target for BC treatment.

circNUDT21 promotes bladder cancer progression by modulating the miR-16-1-3p/MDM2/p53 axis

Bladder cancer (BC) is a common genitourinary malignancy. This study investigated the regulatory effects of an exonic circRNA, circNUDT21, in the progression of BC. The circNUDT21 level was overexpressed in BC tissues and cell lines as compared to normal controls. Overexpression and silencing of circNUDT21 promoted and inhibited, respectively, the proliferative and invasive abilities of BC cells. Mechanistical analysis showed that circNUDT21 acted as a miR-16-1-3p sponge and that MDM2 was a potential downstream target of miR-16-1-3p. We further verified that overexpression of circNUDT21 was associated with elevated MDM2 and reduced p53 expression. CircNUDT21 promoted BC progression by acting as a sponge of miR-16-1-3p to activate the miR-16-1-3p/MDM2/p53 axis. These findings suggest that circNUDT21 functions as an oncogenic circRNA and may be a potential therapy target for BC.

Hsa-circ_0058106 induces EMT and metastasis in laryngeal cancer via sponging miR-153 and inducing Twist1 nuclear translocation

PURPOSE

A new circular RNA (hsa-circ_0058106) has been found to be upregulated in laryngeal cancer, but its function remains unknown. Here, we explored its role in the metastasis of laryngeal cancer.

METHODS

The level of hsa-circ_0058106 in laryngeal cancer was detected by qRT-PCR. The effect of hsa-circ_0058106 silencing on the metastasis of laryngeal cancer was assessed using scratch wound healing and transwell assays, as well as nude mouse lung metastasis models. Fluorescence in situ hybridization was employed to analyze the cellular localization of hsa-circ_0058106. A luciferase activity assay was used to assess binding between hsa-circ_0058106 and miR-153. Interaction between hsa-circ_0058106 and Twist1 was confirmed using RNA pull-down and RNA immunoprecipitation assays.

RESULTS

A high level of hsa-circ_0058106 was found to be associated with lymph node metastasis and advanced clinical stages. Stable knockdown of hsa-circ_0058106 inhibited the migration and invasion of laryngeal cancer cells in vitro and in vivo. Moreover, we found that downregulation of hsa-circ_0058106 suppressed epithelial-mesenchymal transition (EMT), which was underscored by the observation that hsa-circ_0058106 silencing led to decreases in the expression of N-cadherin and Vimentin, and an increase in the expression of E-cadherin. Mechanistically, we found that hsa-circ_0058106 can specifically bind to miR-153 and regulate Snail1 expression by acting as a miR-153 sponge. In addition, we found that knockdown of hsa-circ_0058106 blocked the nuclear translocation of Twist1.

CONCLUSIONS

Our results indicate that hsa-circ_0058106 induces EMT and metastasis in laryngeal cancer by sponging miR-153 and inducing Twist1 nuclear translocation. These observations provide new insights into the regulatory effects of circRNAs in laryngeal cancer metastasis.

Circ_0003204 knockdown protects endothelial cells against oxidized low-density lipoprotein-induced injuries by targeting the miR-491-5p-ICAM1 pathway

Emerging evidence indicates that circular RNA (circRNA) is implicated in the development of atherosclerosis (AS). This study investigated the effect of circ_0003204 on endothelial cell function and explored the functional mechanism of circ_0003204 in AS progression. AS cell models were constructed by treating human umbilical vein endothelial cells (HUVEC) with oxidized low-density lipoprotein (ox-LDL). The expression of circ_0003204 was detected by quantitative real-time PCR (qPCR). The releases of pro-inflammatory factors were determined by ELISA. Cell viability was checked by CCK-8 assay. Cell apoptosis was monitored by flow cytometry assay. The ability of angiogenesis was assessed by tube formation assay. The protein levels of cell development- and apoptosis-related markers were measured by western blot. The binding relationship between miR-491-5p and circ_0003204 or intercellular adhesion molecule 1 (ICAM1) was verified by dual-luciferase reporter assay or RIP assay. The expression of circ_0003204 was strengthened in ox-LDL-treated HUVECs. Circ_0003204 knockdown inhibited ox-LDL-induced inflammation and cell apoptosis, and promoted ox-LDL-depleted cell viability and tube formation ability in HUVECs. MiR-491-5p was a target of circ_0003204, and miR-491-5p directly bound to ICAM1 3'UTR. Accordingly, circ_0003204 positively regulated ICAM1 expression by targeting miR-491-5p. Rescue experiments presented that miR-491-5p inhibition reversed the effects of circ_0003204 knockdown, and ICAM1 overexpression abolished the effects of miR-491-5p restoration. Circ_0003204 knockdown protects HUVECs against ox-LDL-induced injuries by targeting the miR-491-5p-ICAM1 pathway, hinting that circ_0003204 inhibition might prevent AS development.

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

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

Circular RNA hsa_circ_0103552 Promotes Proliferation, Migration, and Invasion of Breast Cancer Cells through Upregulating Cysteine-Rich Angiogenic Inducer 61 (CYR61) Expression via Sponging MicroRNA-515-5p

Circular RNAs (circRNAs) exert a significant regulatory function on tumor progression. This work intends to probe into the biological function and regulatory mechanism of circRNA_0103552 (circ_0103552) in breast cancer carcinogenesis. In this study, circ_0103552, microRNA-515-5p (miR-515-5p), and cysteine-rich angiogenic inducer 61 (CYR61) mRNA expressions in breast cancer cells and tissues were determined by quantitative real-time polymerase chain reaction, followed by cell counting kit 8 and Transwell experiments to examine the multiplication, migration, and invasion of breast cancer cells. Circular RNA Interactome database and StarBase database were searched, and dual-luciferase reporter gene experiments were applied to verify the targeting relationship between circ_0103552 and miR-515-5p, and between miR-515-5p and CYR61, and Western blot was adopted to the regulatory function of circ_0103552 and miR-515-5p on CYR61 protein expression. Circ_0103552 expression was found to be remarkably up-modulated in breast cancer tissues and cells, and circ_0103552 overexpression facilitated the multiplication, migration, and invasion of breast cancer cells, while knocking down circ_0103552 induced the opposite effects. Mechanistically, circ_0103552 could sponge miR-515-5p and restrained its expression in breast cancer cells. MiR-515-5p could counteract the functions of circ_0103552 in breast cancer cells. Additionally, CYR61 was revealed to be a downstream target of miR-515-5p in breast cancer cells. In summary, this study shows that circ_0103552 up-modulates CYR61 expression by targeting miR-515-5p and thus facilitates the multiplication, migration, and invasion of breast cancer cells.

circ_0038718 promotes colon cancer cell malignant progression via the miR-195-5p/Axin2 signaling axis and also effect Wnt/β-catenin signal pathway

OBJECTIVE

Colon cancer (CC) is one of the most common cancers whose progression is regulated by a number of factors, including circular RNAs (circRNAs). Nonetheless, circ_0038718 is a novel circRNA, and its regulatory mechanism in CC remains unclear.

METHODS

Real-time quantitative PCR (qRT-PCR) was performed to detect the expression of circ_0038718, miR-195-5p and Axin2. Western blot was conducted to determine the protein expression of Axin2 and the key proteins on Wnt/β-catenin signaling pathway. Oligo (dT) ₁₈ primers and RNase R were employed to identify the circular features of circ_0038718, and the location of circ_0038718 in cells was detected via nucleocytoplasmic separation. Dual-luciferase reporter assay and RNA binding protein immunoprecipitation experiment were carried out to investigate the molecular mechanism of circ_0038718/miR-195-5p/Axin2. Additionally, MTT assay was conducted to assess cell proliferation; Transwell assay was performed to evaluate cell migration and invasion, respectively. The effect of circ_0038718 on CC tumor growth was tested through tumor formation in nude mice.

RESULTS

circ_0038718 was highly expressed in CC and could sponge miR-195-5p in cytoplasm. Silencing circ_0038718 suppressed the proliferative, migratory and invasive abilities of CC cells, while the promoting effect of high circ_0038718 expression on CC cells was reversed upon miR-195-5p over-expression. Axin2 was a downstream target of miR-195-5p and could regulate the Wnt/β-catenin signaling pathway. Axin2 expression was modulated by circ_0038718/miR-195-5p. Knockdown of Axin2 could also attenuate the promoting effect of high circ_0038718 expression on CC cell malignant progression, thus inhibiting tumor growth.

CONCLUSION

circ_0038718 is able to facilitate CC cell malignant progression via the miR-195-5p/Axin2 axis, which will provide a new idea for finding a novel targeted treatment of CC.

Circular RNA hsa_circ_0001306 Functions as a Competing Endogenous RNA to Regulate FBXW7 Expression by Sponging miR-527 in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of cancer worldwide. Circular RNAs (circRNAs) have been reported to regulate many types of cancers, including HCC. The purpose of this study was to investigate the potential roles of hsa_circ_0001306 in HCC. Firstly, the downregulation of hsa_circ_0001306 was identified by high‑throughput RNA sequencing and further verified by qRT-PCR. Secondly, we evaluated the effects of hsa_circ_0001306 on HCC cell proliferation, invasion, cell cycle. Finally, we used an animal model to validate the in vitro experimental results. The expression of hsa_circ_0001306 was closely related to tumor size. Knockdown of hsa_circ_0001306 could downregulate F-box and WD repeat domain containing 7(FBXW7), a target of miR-527, thereby promoting HCC cell proliferation and invasion. Furthermore, hsa_circ_0001306 siRNA increased the multiplication rate of HCC tumors. Mechanistic studies indicated that hsa_circ_0001306 acts as a ceRNA for miR-527, which resulted in the reduction of its endogenous target, FBXW7. Hsa_circ_001306 is significantly downregulated in HCC, and the hsa_circ_0001306/miR-527/FBXW7 axis plays an important role in HCC progression.

Plasma circRNAs as Biomarkers in Cancer

The incidence and mortality of cancer are increasing each year. At present, the sensitivity and specificity of the blood biomarkers that were used in clinical practice are low, which make the detection rate of cancer decrease. With advances in bioinformatics and technology, some non-coding RNA as biomarkers can be easily detected through some traditional and new technologies. Circular RNAs (circRNAs) are non-coding RNAs, that is, they do not encode proteins, and have important regulatory functions. CircRNAs can remain stable in bodily fluids, such as in saliva, blood, urine, and especially plasma. The difference in the expression of plasma circRNAs between cancer patients and normal people may suggest that plasma circRNAs may play an important role in the occurrence and development of cancer. In this review, we summarized the clinical effect of plasma circRNAs in several high-incidence cancers. CircRNAs may be effective biomarkers for tumour diagnosis, treatment selection and prognosis evaluation.

circFLNA promotes glioblastoma proliferation and invasion by negatively regulating miR‑199‑3p expression

Glioblastoma (GBM) is one of the most common and malignant types of primary cancer in the central nervous system; however, the clinical outcomes of patients with GBM remain poor. Circular RNAs (circRNAs) have been revealed to serve important roles in diverse biological processes, such as regulating cell proliferation, epithelial-mesenchymal transition and tumor development. However, the underlying biological function of circRNA filamin A (circFLNA) and its potential role in GBM remain to be determined. The present study aimed to identify differentially expressed circRNAs in GBM. Reverse transcription-quantitative PCR was used to analyze the expression levels of circFLNA. The results demonstrated that the expression levels of circFLNA were significantly upregulated in clinical GBM samples and GBM cells compared with adjacent healthy brain tissues and normal human astrocytes, respectively. The results of the Cell Counting Kit-8 and Transwell assays revealed that circFLNA knockdown significantly inhibited the proliferative and invasive abilities of GBM cell lines. Moreover, high circFLNA expression levels were associated with a worse prognosis in GBM. MicroRNA (miR)-199-3p was subsequently predicted to be target of circFLNA. The inhibitory effect of miR-199-3p on cell proliferation and invasion was partially reversed following circFLNA knockdown. In conclusion, the findings of the present study identified novel roles for circFLNA in GBM and indicated that the circFLNA/miR-199-3p signaling axis may serve an important role in GBM progression. Therefore, circFLNA may represent a novel target for the diagnosis and treatment of GBM.

Paeoniflorin Suppresses Rheumatoid Arthritis Development via Modulating the Circ-FAM120A/miR-671-5p/MDM4 Axis

Paeoniflorin is an active ingredient derived from Paeonia, which has an anti-inflammatory effect. However, the potential role and basis of paeoniflorin in rheumatoid arthritis (RA) are indistinct. Cell viability, cycle distribution, migration, and invasion were evaluated via Cell Counting Kit-8 (CCK-8), flow cytometry, and transwell assays. The contents of inflammatory cytokines were examined using enzyme-linked immunosorbent assay (ELISA). RNA expression levels were determined via qRT-PCR and western blot. The targeting relationship between miR-671-5p and circ-FAM120A (hsa_circ_0003972) or murine double minute 4 (MDM4) was validated via dual-luciferase reporter assay. Paeoniflorin restrained proliferation, migration, invasion, and inflammation and accelerated cell cycle arrest in RA fibroblast-like synoviocytes (RA-FLSs). Circ-FAM120A was boosted in RA synovial tissues and RA-FLSs. Circ-FAM120A upregulation, miR-671-5p knockdown, or MDM4 augmentation reversed the repressive effect of paeoniflorin on RA-FLS progression. Moreover, paeoniflorin attenuated RA-FLS progression by regulating the circ-FAM120A/miR-671-5p/MDM4 axis. Paeoniflorin inhibited RA-FLS proliferation, mobility, and inflammation and triggered cell cycle arrest via mediating the circ-FAM120A/miR-671-5p/MDM4 pathway.

Hsa_circ_0004674 promotes osteosarcoma doxorubicin resistance by regulating the miR-342-3p/FBN1 axis

Background

The occurrence of chemoresistance is a common problem in tumor treatment. Circular RNA (circRNA) has been confirmed to be related to tumor chemoresistance. However, the role and the underlying molecular mechanism of hsa_circ_0004674 in the chemoresistance of osteosarcoma (OS) are still unclear.

Methods

The expression of hsa_circ_0004674, miR-342-3p, and fibrillin-1 (FBN1) was determined by qRT-PCR. Cell counting kit 8 assay was used to evaluate the doxorubicin (DXR) resistance of cells. The proliferation and apoptosis of cells were measured using colony formation assay and flow cytometry. Western blot analysis was utilized to examine the protein levels of resistance markers, Wnt/β-catenin pathway markers and FBN1. The interaction between miR-342-3p and hsa_circ_0004674 or FBN1 was confirmed by dual-luciferase reporter assay and RNA pull-down assay. Moreover, animal experiments were performed to assess the effect of hsa_circ_0004674 silencing on the DXR sensitive of OS in vivo.

Results

The upregulated hsa_circ_0004674 was found in DXR-resistant OS tissues and cells. Knockdown of hsa_circ_0004674 could inhibit the DXR resistance of OS cells in vitro and promote the DXR sensitive of OS tumors in vivo. In addition, we discovered that hsa_circ_0004674 could sponge miR-342-3p, and miR-342-3p could target FBN1. MiR-342-3p inhibitor could reverse the inhibition effect of hsa_circ_0004674 knockdown on the DXR resistance of OS cells. Similarly, the suppressive effect of miR-342-3p on the DXR resistance of OS cells also could be reversed by FBN1 overexpression. Furthermore, we revealed that hsa_circ_0004674 silencing inhibited the activity of Wnt/β-catenin pathway by the miR-342-3p/FBN1 axis.

Conclusion

Hsa_circ_0004674 facilitated the DXR resistance of OS through Wnt/β-catenin pathway via regulating the miR-342-3p/FBN1 axis, suggesting that hsa_circ_0004674 was a promising target for the chemoresistance of OS.

Circular RNA hsa_circ_0081343 promotes trophoblast cell migration and invasion and inhibits trophoblast apoptosis by regulating miR-210-5p/DLX3 axis

BACKGROUND

Various circular RNAs (circRNAs) are dysregulated in the placenta of fetal growth restriction (FGR) fetuses, but their roles and regulatory mechanisms have not been fully elucidated. Herein, we aimed to elucidate the role of hsa_circ_0081343 in regulating the migration, invasion, and apoptosis of human extravillous trophoblast HTR-8 cells.

METHODS

CircRNA and miRNA levels were examined by quantitative reverse transcription PCR (qRT-PCR). Overexpression plasmid constructs and siRNAs were used to overexpress and knockdown hsa_circ_0081343, respectively. Transwell assays and flow cytometry analyses were performed to evaluate the effects of hsa_circ_0081343 or miR-210-5p on migration, invasion, and apoptosis. Protein levels were analyzed by western blotting. Dual luciferase activity and anti-AGO2 RNA immunoprecipitation (RIP) assays were performed to identify the relationship between miR-210-5p and hsa_circ_0081343.

RESULTS

Hsa_circ_0081343 expression was significantly downregulated in 37 FGR placental tissues compared to healthy placental control tissues. Hsa_circ_0081343 overexpression may inhibit apoptosis by downregulating the expression of cleaved caspase 3 and caspase 9 and alleviating the migration and invasion of HTR-8 cells by inducing the expression of MMP2 and MMP9. The dual luciferase activity and anti-AGO2 RIP assay results showed that hsa_circ_0081343 binds to miR-210-5p. miR-210-5p overexpression eliminated the effect of hsa_circ_0081343 overexpression in HTR-8 cells. Finally, DLX3 was identified as a direct target of miR-210-5p.

CONCLUSIONS

hsa_circ_0081343 expression levels are significantly downregulated in FGR placental tissues. Hsa_circ_0081343 regulates the migration, invasion, and apoptosis of HTR-8 cells via the hsa-miR-210-5p/DLX3 axis.

CircFBXL5 promotes the 5-FU resistance of breast cancer via modulating miR-216b/HMGA2 axis

Background

Circular RNAs (circRNAs) have been confirmed to be relevant to the 5-fluorouracil (5-FU) resistance of breast cancer. Nevertheless, how and whether circRNA F-box and leucine-rich repeat protein 5 (circFBXL5) regulates the 5-FU resistance of breast cancer is uncertain. This study aims to explore the function and mechanism of circFBXL5 in the 5-FU resistance of breast cancer.

Methods

Thirty nine paired breast cancer and normal tissues were harvested. circFBXL5, microRNA-216b (miR-216b) and high-mobility group AT-hook 2 (HMGA2) abundances were examined via quantitative reverse transcription polymerase chain reaction or western blot. Cell viability, 5-FU resistance, migration, invasion, and apoptosis were tested via cell counting kit-8 assay, wound healing analysis, transwell analysis, and flow cytometry. The relationship of miR-216b and circFBXL5 or HMGA2 was tested via dual-luciferase reporter analysis and RNA pull-down assay. The impact of circFBXL5 on breast cancer tumor growth in vivo was analyzed via xenograft model.

Results

circFBXL5 was highly expressed in breast cancer tissues and cells, and was more upregulated in 5-FU-resistant breast cancer cells. Function experiments showed that circFBXL5 knockdown inhibited the 5-FU resistance of breast cancer by inhibiting cell migration, invasion and promoting apoptosis. In the terms of mechanism, miR-216b could be sponged by circFBXL5, and its inhibitor could also reverse the influence of circFBXL5 silencing on the 5-FU resistance of breast cancer cells. In addition, HMGA2 was a target of miR-216b, and its overexpression also reversed the regulation of miR-216b overexpression on the 5-FU resistance of breast cancer. Furthermore, circFBXL5 interference declined breast cancer tumor growth in xenograft model.

Conclusion

Our data showed that circFBXL5 could promote the 5-FU resistance of breast cancer by regulating miR-216b/HMGA2 axis.

Upregulation of circular and linear METTL3 and USP3 in colorectal cancer

Several screening methods are currently used to detect colorectal cancer (CRC). However, these are either under-utilized due to their invasive nature or are limited in terms of their diagnostic ability. Numerous reports have investigated messenger and circular RNA as non-invasive biomarkers, but the majority of gene expression studies using RT-qPCR involve critical errors that often lead to irreproducible findings. In the present study, several of these issues were addressed. To the best of our knowledge, this study reports for the first time the upregulation of both the circular and the linear isoform of USP3 and METTL3 in leukocytes from patients with CRC. The linear transcripts of USP3 and METTL3 exhibited 2.3- and 2-fold increases on average in CRC samples (n=42 CRC) compared with the respective healthy controls (n=32), whereas their circular isoforms showed 1.6- and 1.7-fold increases, respectively. Moreover, a strong positive correlation was observed between the circular and linear isoforms of USP3 in the CRC cohort (P<0.0001), but not in the control group (P>0.05). In addition, the linear USP3 assay had excellent sensitivity (79%), specificity (75%), positive predictive value (81%), negative predictive value (73%) and area under the curve (AUC, 0.8534; P-value <0.0001). The circular (AUC, 0.6946; P-value =0.0043) and linear (AUC, 0.7202; P-value =0.0012) METTL3 assays also showed potential; however, this was not the case for the circular USP3 assay (P-value >0.05). Taken together, this stringent RT-qPCR approach provides evidence for the viability of using circular and linear RNA molecules as disease biomarkers and may help shed light on the regulatory pathways of CRC.

Hsa_circ_0006404 and hsa_circ_0000735 Regulated Ovarian Cancer Response to Docetaxel Treatment via Regulating p-GP Expression

Several microRNAs (miRNAs) and circular RNAs (circRNAs) were reported to be involved in the Docetaxel (DTX) chemoresistance of cancer treatment, but the underlying mechanisms remain to be explored. In this study, we established cellular and animal models respectively to study the effect and underlying molecular mechanisms of the dysregulation of circRNA_0006404 and circRNA_0000735 in tumor response to DTX treatment. Quantitative real-time PCR was performed to measure the expression of circRNA_0006404, miR-346, circRNA_0000735, miR-526b, Dickkopf-related protein 3 (DKK3), and Dickkopf-related protein 4 (DKK4) mRNA. The expression of circRNA_0006404 and circRNA_0000735 was remarkably suppressed and activated in DTX-treated SKOV3-R cell lines, respectively. As revealed by luciferase assays, circRNA_0006404 and circRNA_0000735 was found to be respectively targeted by miR-346 and miR-526b, while DKK3 and DKK4 were respectively targeted by miR-346 and miR-526b. Moreover, the expression of DKK3 and DKK4, which were targets of miR-346 and miR-526b, respectively, was significantly altered along with the expression of p-GP. Furthermore, circ_0006404 shRNA and circRNA_0000735 shRNA showed remarkable efficiency in stimulating the expression of circRNA_0006404, miR-346, DKK3, circRNA_0000735, miR-526b, DKK4, and p-GP in cellular and animal models. Accordingly, the cell apoptosis and proliferation were apparently changed by circ_0006404 shRNA and circRNA_0000735 shRNA in both cellular and animal models. In summary, our study found the involvement of the circRNA_0006404/miR-346/DKK3/p-GP and circRNA_0000735/miR-546b/DKK4/p-GP axis in the tumor response to DTX. Both the up-regulation of circRNA_0006404 and down-regulation of circRNA_0000735 could inhibit the expression of p-GP in vivo and ex vivo, leading to the suppressed tumor response to DTX treatment.

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.

Circular RNA hsa_circ_0000277 sequesters miR-4766-5p to upregulate LAMA1 and promote esophageal carcinoma progression

Growing evidence has indicated that circular RNAs (circRNAs) play a pivotal role as functional RNAs in diverse cancers. However, most circRNAs involved in esophageal squamous cell carcinoma (ESCC) remain undefined, and the underlying molecular mechanisms mediated by circRNAs are largely unclear. Here, we screened human circRNA expression profiles in ESCC tissues and found significantly increased expression of hsa_circ_0000277 (termed circPDE3B) in ESCC tissues and cell lines compared to the normal controls. Moreover, higher circPDE3B expression in patients with ESCC was correlated with advanced tumor-node-metastasis (TNM) stage and dismal prognosis. Functional experiments demonstrated that circPDE3B promoted the tumorigenesis and metastasis of ESCC cells in vitro and in vivo. Mechanistically, bioinformatics analysis, a dual-luciferase reporter assay, and anti-AGO2 RNA immunoprecipitation showed that circPDE3B could act as a competing endogenous RNA (ceRNA) by harboring miR-4766-5p to eliminate the inhibitory effect on the target gene laminin α1 (LAMA1). In addition, LAMA1 was significantly upregulated in ESCC tissues and was positively associated with the aggressive oncogenic phenotype. More importantly, rescue experiments revealed that the oncogenic role of circPDE3B in ESCC is partly dependent on the miR-4766-5p/LAMA1 axis. Furthermore, bioinformatics analysis combined with validation experiments showed that epithelial-mesenchymal transition (EMT) activation was involved in the oncogenic functions of the circPDE3B-miR-4766-5p/LAMA1 axis in ESCC. Taken together, we demonstrate for the first time that the circPDE3B/miR-4766-5p/LAMA1 axis functions as an oncogenic factor in promoting ESCC cell proliferation, migration, and invasion by inducing EMT, implying its potential prognostic and therapeutic significance in ESCC.

Chemoresistance and Metastasis in Breast Cancer Molecular Mechanisms and Novel Clinical Strategies

Breast cancer is the most common malignant tumor in females worldwide. Chemotherapy is the standard breast cancer treatment; however, chemoresistance is often seen in patients with metastatic breast cancer. Owing to high heterogeneity, the mechanisms of breast cancer chemoresistance and metastasis have not been fully investigated. The possible molecular mechanisms of chemoresistance in breast cancer include efflux transporters, signaling pathways, non-coding RNAs, and cancer stem cells. However, to overcome this hurdle, the use of novel clinical strategies such as drug carriers, immunotherapy, and autophagy regulation, are being investigated. The goal of this review is to summarize the current data about the molecular mechanisms of breast cancer chemoresistance and the novel clinical strategies; thus, providing a useful clinical tool to explore optimal treatment for breast cancer.

Hsa_circ_0031787 promotes cell proliferation and invasion in colorectal cancer

OBJECTIVE

Circular RNA (circRNA) has been found to be involved in regulating tumor development. However, the roles and underlying mechanisms of circRNA in colorectal cancer (CRC) development remain unclear. In this study, we investigated the effects of hsa_circ_0031787 on CRC.a METHODS: Aberrant circRNA expression was explored by the Gene Expression Omnibus (GEO) database, and hsa_circ_0031787 was selected for further study. Hsa_circ_0031787 expression was determined in CRC tissues and cell lines by qRT-PCR. Cell proliferation was measured by Edu and colony formation assays. Cell invasion was tested by Transwell assays.

RESULTS

Hsa_circ_0031787 expression levels in CRC were significantly increased and correlated with advanced TNM stage and lymph node metastasis in CRC patients. Functional assays showed that hsa_circ_0031787 suppression reduced CRC cell proliferation and invasion in vitro and reduced tumor growth in vivo. Furthermore, hsa_circ_0031787 suppression reduced activation of the Wnt/β-catenin axis in CRC.

CONCLUSIONS

Our results showed that hsa_circ_0031787 may function as an oncogenic circRNA in CRC progression, thus providing a new potential therapeutic target.

Circ_0044516 Regulates miR-136/MAT2A Pathway to Facilitate Lung Cancer Development

Circular RNA (circRNA) is a type of noncoding RNA that can interact with miRNAs to regulate gene expression. However, little is known concerning circRNA, which is crucial in the pathogenesis of lung cancer. To date, limited studies have explored the role of circ_0044516 in lung cancer progression. Recently, we observed that circ_0044516 expression levels were obviously elevated in lung cancer tissues and cells. A549 and SPCA1 cells were transfected with circ_0044516 siRNA. We observed that knockdown of circ_0044516 dramatically repressed cell proliferation, increased cell apoptosis, and repressed the cell cycle. Moreover, A549 and SPCA1 cell migration and invasion abilities were greatly repressed by circ_0044516 siRNA. Due to accumulating evidence demonstrating the vital role of cancer stem cells, their mechanism of involvement has drawn increasing attention in tumor progression and metastasis research. We also found that cancer stem cell properties were restrained by silencing circ_0044516 in A549 and SPC-A1 cells. Moreover, in vivo xenograft experiments showed that circ_0044516 downregulation reduced tumor growth. Mechanistically, in lung cancer and using bioinformatics, we demonstrated that circ_0044516 sponges miR-136 targeting MAT2A. Furthermore, rescue assays were carried out to identify that circ_0044516 modulates cell proliferation, invasion, and stemness by regulating miR-136 and MAT2A in lung cancer. In summary, our study revealed that the circ_0044516/miR-136/MAT2A axis is involved in lung cancer progression. Our findings may provide novel targets for diagnosis and therapeutic intervention in lung cancer patients.

Exosomal circRNA as a novel potential therapeutic target for multiple myeloma-related myocardial damage

Introduction

Myocardial damage is a mostly incurable complication of multiple myeloma (MM) that seriously affects the treatment outcome and quality of life of patients. Exosomal circular RNAs (exo-circRNAs) play an important role in tumor occurrence and development and are considered key factors in MM pathogenesis. However, the role and mechanism of action of exo-circRNAs in MM-related myocardial damage are still unclear. This study aimed to investigate correlations between exo-circRNAs and MM and to preliminarily explore the role of exo-circRNAs in MM-related myocardial damage.

Methods

Six MM patients and five healthy controls (HCs) were included in the study. High-throughput sequencing and qRT-PCR verification were used to obtain a profile of abnormally expressed exo-circRNAs. GO, KEGG, miRanda, TargetScan and Metascape were used for bioinformatics analyses. H9C2 cells treated with exosomes from U266 cells were used in cell experiments. CCK-8, PCR, immunofluorescence and western blotting assays were used to detect cell proliferation and expression of autophagy-related indicators. Electron microscopy was used to observe the number of autophagic vesicles.

Results

Bioinformatics analysis showed that circRNAs with upregulated expression had the potential to promote MM-related myocardial damage. In addition, PCR results confirmed that circ-G042080 was abundantly expressed in the serum exosomes of 20 MM patients. Correlation analysis showed that the expression level of circ-G042080 was positively correlated with the clinical level of MM and MM-related myocardial damage and that circ-G042080 might interfere with MM-related myocardial damage through a downstream miRNA/TLR4 axis. Cell experiments demonstrated that the circ-G042080/hsa-miR-4268/TLR4 axis might exist in H9C2 cells incubated with exosomes and cause abnormal autophagy.

Conclusion

Abnormal expression of serum exo-circRNAs was found to be associated with MM-related myocardial damage, suggesting that exo-circRNAs might become a new diagnostic marker of MM-related myocardial damage and a therapeutic target.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02011-w.

Circ_0013359 facilitates the tumorigenicity of melanoma by regulating miR-136-5p/RAB9A axis

Background

Circular RNAs play crucial roles in tumor occurrence and progression. This research aimed to explore the role and potential mechanism of hsa_circ_0013359 (circ_0013359) in melanoma.

Methods

The levels of circ_0013359, microRNA-136-5p (miR-136-5p), and member RAS oncogene family (RAB9A) in melanoma tissues and cells were detected using quantitative reverse transcriptase-polymerase chain reaction or western blot. Cell proliferation, apoptosis, cell cycle, cell migration, and invasion were evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay, colony formation assay, flow cytometry, and transwell assay. Glycolysis was determined by detecting glucose consumption, lactate production, and extracellular acidification rate. The levels of hexokinase 2 and lactate dehydrogenase A were examined by western blot. The targeting relationship between miR-136-5p and circ_0013359 or RAB9A was confirmed by dual-luciferase reporter assay. Xenograft experiments were used to analyze tumor growth in vivo.

Results

Circ_0013359 and RAB9A levels were increased, while the miR-136-5p level was reduced in melanoma tissues and cells. Circ_0013359 knockdown inhibited proliferation, migration, invasion, and glycolysis and promoted apoptosis and cycle arrest in A875 and SK-MEL-1 cells. Circ_0013359 sponged miR-136-5p to regulate melanoma progression. In addition, miR-136-5p suppressed melanoma progression by targeting RAB9A. Besides, circ_0013359 silencing inhibited tumor growth in vivo.

Conclusion

Depletion of circ_0013359 hindered melanoma progression by regulating miR-136-5p/RAB9A axis.

CircTET1 Inhibits Retinoblastoma Progression via Targeting miR-492 and miR-494-3p through Wnt/β-catenin Signaling Pathway

Purpose: Retinoblastoma (RB) is a frequent intraocular malignancy in children. Circular RNA (circRNA) plays an essential role in regulating the occurrence and development of tumors. This study aimed at investigating the function and molecular basis of hsa_circ_0093996 (circTET1) in RB.Methods: The expression of circTET1, miR-492 and miR-494-3p was examined using quantitative real-time polymerase chain reaction. Cell proliferation, cycle arrest, apoptosis, migration and invasion of RB cells were detected using Cell Counting Kit-8 (CCK-8), colony formation assay, flow cytometry, scratch assay and transwell analysis, respectively. The levels of matrix metalloproteinase (MMP) 2, MMP9 and Wnt/β-catenin pathway-related proteins were measured via western blot assay. The association between circTET1 and miR-492/miR-494-3p was validated via dual-luciferase reporter assay and RNA pull-down assay. Xenograft assay was employed to analyze tumor growth in vivo.Results: CircTET1 level was reduced, while miR-492 and miR-494-3p levels were increased in RB tissues and cells. Overexpression of circTET1 inhibited proliferation, migration and invasion, and promoted apoptosis and cell cycle arrest in Y79 and WERI-Rb1 cells. Moreover, circTET1 impeded RB cell progression by sponging miR-492/miR-494-3p. Also, up-regulation of circTET1 restrained Wnt/β-catenin pathway via regulating miR-492 and miR-494-3p. Furthermore, circTET1 suppressed tumor growth in xenograft models.Conclusion: CircTET1 inhibited RB progression by sponging miR-492/miR-494-3p and inactivating the Wnt/β-catenin pathway, which provided new insights for RB treatment.

Circular RNA PTK2 Accelerates Cell Proliferation and Inhibits Cell Apoptosis in Gastric Carcinoma via miR-139-3p

BACKGROUND

Gastric carcinoma (GC) is one of the most common malignant tumors. Although increasing studies have indicated that circular RNAs function as ideal biomarkers for multiple cancers, only a few researches elucidated the correlation between circular RNA PTK2 (circPTK2) and human cancers.

AIM

To further explore the expression status, biological function, and regulatory mechanism of circPTK2 in GC.

METHODS

Bioinformatics analysis and function or mechanism experiments including RT-qPCR, flow cytometry, Western blot, luciferase reporter assay, and xenografts assays were applied to investigate the function of circPTK2 and miR-139-3p.

RESULTS

High expression of circPTK2 was presented in GC tissues and cells. The circPTK2 knockdown notably suppressed cell proliferation and promoted cell apoptosis in GC. In mechanism, circPTK2 served as a sponge of miR-139-3p. Inhibition of miR-139-3p could reverse circPTK2 silence-mediated effects on GC cell proliferation and apoptosis. Furthermore, the xenograft tumor model was established to investigate the role of circPTK2 in GC tumor growth. Experimental results delineated that the reduction in tumor growth in response to circPTK2 knockdown was partly recovered by miR-139-3p inhibitor.

CONCLUSIONS

CircPTK2 promotes GC development by sponging miR-139-3p, which may function as an effective gene target for managing GC.

The novel circular RNA circ-PGAP3 retards cervical cancer growth by regulating the miR-769-5p/p53 axis

Cervical cancer (CC) is still an intractable disease that seriously affects women's health. Elucidating its pathogenesis will bring new targets for clinical treatment. Circular RNA (circRNA) is an endogenous RNA that has recently been reported to be closely related to cancer progression and development. In the current study, by performing in silico analysis and qRT-PCR assay, we found a circRNA derived from PGAP3, referred as circ-PGAP3 (hsa_circ_0106800, chr17:37843549-37844086), which was significantly downregulated in CC tissues. Low circ-PGAP3 was closely linked to poor prognosis. And overexpression of circ-PGAP3 significantly reduced CC cell proliferation in vitro and tumor growth in vivo. In terms of mechanism, circ-PGAP3 was transcriptionally elevated by p53, a well-recognized tumor suppressor, and circ-PGAP3 was located in the cytoplasm where sponged miR-769-5p to increase the levels of p53 and its downstream targets. Importantly, the regulatory feedback loop of circ-PGAP3/p53 was also confirmed in vivo. Overall, our data clearly expounded the tumor-inhibiting role of circ-PGAP3 in CC, circ-PGAP3 repressed CC tumorigenesis via regulating the miR-769-5p/p53 axis. Therefore, restoration of circ-PGAP3 may be a promising therapeutic target for this thorny disease.

circTLK1 facilitates the proliferation and metastasis of renal cell carcinoma by regulating miR-495-3p/CBL axis

Renal cell carcinoma (RCC) is a common urological malignancy. Circular RNAs (circRNAs) have been confirmed to play an important regulatory role in various cancers. This study aimed to investigate the role and potential mechanism of circTLK1 (hsa_circ_0004442) in RCC. The levels of circTLK1, Cbl proto-oncogene (CBL), and microRNA-495-3p (miR-495-3p) were detected by quantitative reverse transcription polymerase chain reaction or western blot. Cell proliferation, cycle arrest and apoptosis, migration, and invasion were assessed by colony formation, flow cytometry, scratch, and transwell assays. The levels of E-cadherin and Vimentin were measured by western blot. The targeting relationship between miR-495-3p and miR-495-3p or CBL was verified by dual-luciferase reporter assay. Tumor growth in vivo was evaluated by xenograft assay. The results found that circTLK1 and CBL were up-regulated in RCC tissues and cells. Silencing of circTLK1 or CBL inhibited proliferation and metastasis and accelerated apoptosis in RCC cells. In addition, circTLK1 directly bound to miR-495-3p, and CBL was the target of miR-495-3p. circTLK1 sponged miR-495-3p to increase CBL expression. Moreover, knockdown of circTLK1 suppressed tumor growth in vivo. In conclusion, down-regulation of circTLK1 restrained proliferation and metastasis and promoted apoptosis in RCC cells by modulating miR-495-3p/CBL axis.

Circular RNA_0074027 participates in cell proliferation, apoptosis and metastasis of colorectal cancer cells through regulation of miR‑525‑3p

The present study aimed to elucidate the biological function of circular RNAs (circRNA) 0074027 in colorectal cancer (CRC). The expression of circRNA‑0074027 in CRC tissues and cells was determined by reverse transcription‑quantitative PCR. The in vitro experiments, including Cell Counting Kit‑8 (CCK‑8) assay, 5‑Ethynyl‑2'‑deoxyuridine assay, flow cytometry and Transwell assay, were applied to evaluate cell proliferation, apoptosis and metastasis ability respectively following downregulation of circRNA‑0074027. The correlation between circRNA‑0074027 and micro (mi)RNA‑525‑3p was determined via dual‑luciferase reporter assay. Finally, western blotting was used to explore the possible regulatory mechanism. CircRNA‑0074027 was upregulated in CRC tissues, while miR‑525‑3p expression was reduced. In addition, patients with CRC and circRNA‑0074027 overexpression were more likely to have low tumor differentiation, lymph node metastasis and advanced TMN stage. Deletion of circRNA‑0074027 could suppress cell proliferation and metastasis through up-regulating p53 expression and forbidding epithelial‑mesenchymal transition signaling pathway. The addition of miRNA‑525‑3p inhibitors could reverse the anti‑tumor effects induced by the deletion of circRNA‑0074027. The downregulation of cirRNA_0074027 inhibited tumor progression via sponging miR‑525‑3p, which could be a promising treatment bio‑marker for CRC.

Circ-VPS13C enhances cisplatin resistance in ovarian cancer via modulating the miR-106b-5p/YWHAZ axis

Introduction

Ovarian cancer (OC) is the malignant tumor with the highest mortality among gynecological cancers. Chemotherapy resistance is a major obstacle to OC therapy. Circular RNAs (circRNAs) play crucial roles in cancer development and chemoresistance. However, the role and potential mechanism of has-circ-001567 (circ-VPS13C) in chemoresistance of OC remain unknown.

Material and methods

The levels of circ-VPS13C, miR-106b-5p and 14-3-3 zeta (YWHAZ) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell Counting Kit-8 (CCK-8) assay was used to assess cell viability and calculate the half inhibition concentration (IC50) of cisplatin (DDP). The levels of autophagy-related markers were measured by western blot assay. Cell apoptosis and migration were evaluated by flow cytometry and transwell assay, respectively. The binding relationship between miR-106b-5p and circ-VPS13C or YWHAZ was confirmed by dual-luciferase reporter assay. Xenograft assay was performed to explore the role of circ-VPS13C in vivo.

Results

Circ-VPS13C and YWHAZ were up-regulated, while miR-106b-5p was down-regulated in DDP-resistant OC tissues and cells. Knockdown of circ-VPS13C enhanced DDP sensitivity by repressing autophagy in DDP-resistant cells. Circ-VPS13C increased DDP resistance via sponging miR-106b-5p. Moreover, miR-106b-5p directly targeted YWHAZ. Up-regulation of YWHAZ alleviated the decrease in DDP resistance caused by circ-VPS13C depletion. In addition, circ-VPS13C silencing decreased DDP resistance in vivo.

Conclusions

Circ-VPS13C knockdown enhanced DDP sensitivity of OC through modulation of autophagy via the miR-106b-5p/YWHAZ axis, providing a new biomarker for improving the efficacy of OC chemotherapy.

CircMETTL3, upregulated in a m6A-dependent manner, promotes breast cancer progression

Growing evidence indicates N6-methyladenosine (m6A) has biological function in oncogenesis. METTL3, the catalytic component, is the most important part of methyltransferase complex and plays a crucial role in cancers. However, the biological function of circRNAs derived from METTL3 in breast cancer and the underlying molecular mechanism remains unclear. Herein, we report circMETTL3, which has not been explored in breast cancer, and it is markedly upregulated in breast cancer. Moreover, we uncovered that circMETTL3 could facilitate cell proliferation, migration and invasion in breast cancer. Mechanism investigation showed that circMETTL3 might act as a competing endogenous RNA (ceRNA) of miR-31-5p and upregulate its target cyclin-dependent kinases (CDK1). Moreover, m6A modification of circMETTL3 might affect its expression. Taken together, our results elucidate that circMETTL3 promotes breast cancer progression through circMETTL3/miR-31-5p/CDK1 axis. Moreover, METTL3, the host gene of circMETTL3, may regulate circMETTL3 expression in an m6A-dependent manner, while circMETTL3 has no effect on METTL3 expression, providing a new relationship between the circRNA and the corresponding host gene. Thus, it may serve as a new therapeutic target for breast cancer.

LncRNA FAM83A-AS1 promotes lung adenocarcinoma progression by enhancing the pre-mRNA stability of FAM83A

Background

Lung cancer is the leading cause of cancer deaths worldwide. Long non‐coding RNAs (lncRNAs) affect a series of cellular biological processes, including oncogene function promotion. In this study, we explored the functions and mechanisms of FAM83A antisense RNA 1 (FAM83A‐AS1) in non‐small cell lung cancer (NSCLC) progression.

Methods

The expression of FAM83A‐AS1and FAM83A mRNA was analyzed using the Cancer Genome Atlas (TCGA) data. Proliferation, migration, invasion and Western blotting were measured after treatment with overexpressed or knockdown FAM83A‐AS1. To determine the relationship between FAM83A‐AS1 and FAM83A, RNase protection assay (RPA), amanitin treatment, RNA pulldown assay and RNA immunoprecipitation (RIP) assay were performed.

Results

High expression of FAM83A‐AS1 in lung adenocarcinoma (LUAD) was closely associated with low overall survival (OS) and progression‐free survival (PFS). Functionally, high FAM83A‐AS1 expression increased LUAD cell proliferation and metastasis, indicating that FAM83A‐AS1 exerted its oncogenic functions. Furthermore, FAM83A‐AS1 promoted NSCLC progression via ERK signaling pathways. Mechanistically, FAM83A‐AS1 post‐transcriptionally increased FAM83A expression by enhancing pre‐mRNA stability. FAM83A‐AS1 enhanced FAM83A mRNA stability not only by forming an RNA duplex but also by binding to FBL.

Conclusions

We determined that FAM83A‐AS1 increased FAM83A expression by enhancing FAM83A pre‐mRNA stability and promoted the tumorigenesis of LUAD.

Overexpression of hsa_circ_0094742 inhibits IL-1β-induced decline in CHON-001 cell viability by targeting microRNA-127-5p

Osteoarthritis (OA) is a public health problem that affects 240 million people globally; however, the current treatment options for OA are not effective. Therefore, there is still an urgent need to identify novel strategies to reduce the incidence and progression of OA. The circular RNA hsa_circ_0094742 was reported to be downregulated in patients with OA. However, the underlying mechanism remains unclear. The levels of hsa_circ_0094742 in CHON-001 were detected by reverse transcription quantitative polymerase chain reaction. Moreover, Cell Counting Kit-8 assay and Ki67 staining were used to determine the cell viability. The protein expression of biomarkers was detected by western blot analysis. In addition, the putative downstream target of hsa_circ_0094742 was predicted using the Circinteractome and TargetScan online databases. The putative targeting relationship was verified by dual luciferase reporter assay and fluorescence in situ hybridization. Next, cell apoptosis was determined by Annexin V/PI staining. hsa_circ_0094742 overexpression (OE) inhibited interleukin (IL)-1β-induced decline in the viability of CHON-001 cells and primary human chondrocytes. Furthermore, IL-1β-induced alterations in aggrecan, matrix metallopeptidase 13, X-linked inhibitor of apoptosis protein (XIAP), Bax and active caspase 3 were reversed by hsa_circ_0094742 OE. Luciferase reporter assay indicated that miR-127-5p was the downstream target of hsa_circ_0094742, and latexin was the target of miR-127-5p. hsa_circ_0094742 OE inhibited IL-1β-induced decline in CHON-001 cell viability by targeting miRNA-127-5p. The findings of the present study revealed the biological rational of the use of hsa_circ_0094742 OE as an anti-IL-1β effector in human chondrocytes. These findings may prompt further research on hsa_circ_0094742 as a potent circRNA target for the treatment of OA.

Emerging roles of circular RNAs in systemic lupus erythematosus

Circular RNAs (circRNAs) are a class of non-coding RNAs with covalently closed single-stranded structures lacking 5'-3' polarity and a polyadenine tail. Over recent years, a growing body of studies have been conducted to explore the roles of circRNAs in human diseases. Systemic lupus erythematosus (SLE) is a severe autoimmune disorder characterized by the presence of autoantibodies and excessive inflammation, which impact multiple organs. Recent advances have begun to shed light on the roles of circRNAs in SLE, providing fresh insights into the pathogenesis of SLE and the latent capacity for translation into clinical applications. Here, we briefly introduce these "star molecules" and summarize their roles in SLE. In addition, we outline the limitations of the current studies and raise prospects for future research.

The regulation of protein translation and its implications for cancer

In addition to the deregulation of gene transcriptions and post-translational protein modifications, the aberrant translation from mRNAs to proteins plays an important role in the pathogenesis of various cancers. Targeting mRNA translation are expected to become potential approaches for anticancer treatments. Protein translation is affected by many factors including translation initiation factors and RNA-binding proteins. Recently, modifications of mRNAs mainly N6-methyladenine (m⁶A) modification and noncoding RNAs, such as microRNAs and long noncoding RNAs are involved. In this review, we generally summarized the recent advances on the regulation of protein translation by the interplay between mRNA modifications and ncRNAs. By doing so, we hope this review could offer some hints for the development of novel approaches in precision therapy of human cancers.

CircRNA ZNF609 Knockdown Represses the Development of Non-Small Cell Lung Cancer via miR-623/FOXM1 Axis

Background

The dysregulated circular RNAs (circRNAs) are relevant to the development of non-small cell lung cancer (NSCLC). Nevertheless, the function and mechanism of circRNA zinc finger protein 609 (circZNF609) in NSCLC development remain uncertain.

Methods

Sixty-two NSCLC patients were recruited. circZNF609, microRNA-623 (miR-623) and forkhead box M1 (FOXM1) abundances were measured via quantitative reverse transcription polymerase chain reaction or Western blot. Cell viability, apoptosis, migration and invasion were analyzed via cell counting kit-8 (CCK8), flow cytometry, caspase3 activity, transwell assay and Western blot. The interaction between miR-623 and circZNF609 or FOXM1 was analyzed via dual-luciferase reporter analysis, RNA immunoprecipitation and pull-down. The function of circZNF609 on cell growth in vivo was tested via xenograft model.

Results

circZNF609 abundance was enhanced in NSCLC tissues and cells. High expression of circZNF609 indicated the lower overall survival. circZNF609 interference restrained cell viability, migration and invasion and increased apoptosis. miR-623 was targeted via circZNF609. FOXM1 was targeted via miR-623 and regulated via circZNF609. miR-623 knockdown or FOXM1 overexpression mitigated the role of circZNF609 silence in NSCLC development. circZNF609 knockdown decreased NSCLC xenograft tumor growth.

Conclusion

circZNF609 knockdown repressed NSCLC development via regulating miR-623 and FOXM1.

Upregulated hsa_circ_0000129 expression promotes proliferation and migration of breast cancer cells

Circular RNAs (circRNAs) are considered potential biomarkers in the pathogenesis and detection of several types of cancer. The present study aimed to investigate the role of hsa_circ_0000129 in the pathogenesis and molecular mechanism underlying breast cancer. A total of 68 pairs of breast cancer and corresponding paracancerous tissue samples, three different breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and a normal human breast cell line (MCF-10A) were used to investigate the expression of hsa_circ_0000129. The effect of hsa_circ_0000129 on cell proliferation, migration and colony formation was assessed in MCF-7 and MDA-MB-468 cells, along with the expression of enhancer of zeste homolog 2 (EZH2). The results demonstrated that hsa_circ_0000129 expression was significantly higher in breast cancer tissues compared with normal tissues. In addition, high hsa_circ_0000129 expression was significantly associated with lymph node metastasis and a higher tumor-node-metastasis stage. Comparisons between the breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and MCF-10A cells indicated similar results. MCF-7 cells overexpressed with hsa_circ_0000129 significantly increased cell proliferation, migration and colony formation compared with the negative control group, the effects of which were reversed following hsa_circ_0000129 knockdown in MDA-MB-468 cells. Furthermore, EZH2 expression was positively associated with hsa_circ_0000129 expression. Taken together, the results of the present study suggest that hsa_circ_0000129 may represent a promising prognostic biomarker for breast cancer. In addition, the role of hsa_circ_0000129 in breast cancer cell lines indicates a mechanism for tumorigenesis, as well as a potent target for the treatment of malignant progression.

Propofol suppresses lung cancer tumorigenesis by modulating the circ-ERBB2/miR-7-5p/FOXM1 axis

BACKGROUND

Propofol is a commonly used anesthetic for cancer surgery. Previous studies have shown that propofol has an anticancer role in various cancers, including lung cancer. This study aimed to investigate the role of propofol in lung cancer and its underlying mechanism.

METHODS

Cell proliferation was determined by cell counting kit-8 (CCK-8) and colony formation assays. Flow cytometry and transwell assays were used to detect cell apoptosis and invasion, respectively. Glycolysis was evaluated by detecting glucose consumption, lactate production and ATP/ADP ratios. The levels of circular RNA erb-b2 receptor tyrosine kinase 2 (circ-ERBB2), microRNA-7-5p (miR-7-5p) and forkhead box M1 (FOXM1) were tested by quantitative real-time PCR and Western blot. The binding relationship between miR-7-5p and circ-ERBB2/FOXM1 was verified by dual-luciferase reporter assay. Moreover, in vivo experiments were performed by establishing a mouse xenograft model.

RESULTS

Propofol suppressed cell proliferation, invasion and glycolysis and expedited apoptosis in lung cancer cells. Circ-ERBB2 and FOXM1 were upregulated, while miR-7-5p was decreased in lung cancer tissues and cells. Propofol suppressed lung cancer cell progression by regulating circ-ERBB2. Additionally, miR-7-5p directly interacted with circ-ERBB2 and FOXM1. Also, propofol played an antitumor role in lung cancer via modulating miR-7-5p or FOXM1. Moreover, circ-ERBB2 knockdown enhanced the suppressive effect of propofol on tumor growth in vivo.

CONCLUSIONS

Propofol inhibited lung cancer progression via mediating circ-ERBB2/miR-7-5p/FOXM1 axis, which might provide an effective therapeutic target for lung cancer therapy.

Circ_0008305-mediated miR-660/BAG5 axis contributes to hepatocellular carcinoma tumorigenesis

Increasing circRNAs have attracted a lot of attention because of their significant biological effects in many diseases. It has been reported that circ_0008305 can modulate lung cancer progression. However, the association between circ_0008305 and hepatocellular carcinoma (HCC) needs to be well explored. In this current research, we studied the molecular function and potential mechanism of circ_0008305 in HCC progression. First, it was demonstrated that circ_0008305 was greatly increased in HCC tissues and cells. Moreover, we observed silencing circ_0008305 markedly repressed HCC cells in vitro growth and reduced tumor growth in vivo. Additionally, it was identified that circ_0008305 can act as a sponge of miR‐660 while miR‐660 targeted Bcl‐2‐associated athanogene 5 (BAG5). BAG5 belongs to a member of BAG family and it is involved in multiple diseases. We reported that circ_0008305 contributed to the inhibition of miR‐660, which resulted in an upregulated expression of BAG5 in HCC. Subsequently, rescue assays were conducted and it was indicated that loss of BAG5 reversed the effects of miR‐660 inhibitors on HCC partially. To sum up, it was illustrated by our study that circ_0008305‐mediated miR‐660‐5p/BAG5 axis triggered HCC progression, which could provide a novel insight on the underlying mechanism of HCC progression.

Identification of differentially expressed circular RNAs in keloid and normal skin tissue by high-throughput sequencing

Keloid is a kind of pathological skin scar with unclear molecular pathology. Circular RNAs (circRNAs) are involved in the occurrence and development of many diseases; however, their relationship with keloid is not well understood. To investigate the involvement of dysregulated circRNAs in keloid. Thirty-seven keloids and 37 normal skin tissues were collected, and the changes of circRNAs, microRNAs (miRNAs) and mRNAs in 3 keloids and 3 normal samples by high-throughput sequencing were detected first. Based on the circRNA-miRNA-mRNA interaction network construction, gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis combining several signaling pathways associated with keloid formation and progression, the circRNAs required further verification were screened out. The expression levels of the selected circRNAs were verified in 37 keloids and 37 normal skin tissues using quantitative real-time polymerase chain reaction (QPCR). The interaction of candidate circRNA and its predicted binding miRNA was tested by dual-luciferase reporter gene experiment. Compared with normal controls, there was an average of 120 and 12 circRNAs, 44 and 63 miRNAs, 656 and 156 mRNAs were upregulated and downregulated, respectively, in keloids. According to the analysis of bioinformation, six circRNAs were picked out. The QPCR validation results of two upregulated circRNAs (hsa_circ_0001320 and circCOL5A1) were consistent with previous sequencing results. The interaction between hsa_circ_0001320 and miR-574-5p was confirmed. This study makes it clear that the abnormal expression of circRNAs may be related to the pathological process of keloid.

Circ_0007444 Inhibits the Progression of Ovarian Cancer via Mediating the miR-570-3p/PTEN Axis

Purpose

Some circular RNAs have been found to be effective therapeutic targets for OC. However, the biological function of circ_0007444 in OC is still unknown. Thus, this study investigated the role of circ_0007444 in OC progression.

Methods

circ_0007444 expression was monitored in 87 OC patients and OC cells by quantitative real-time polymerase chain reaction. An in vitro study was performed to research the biological function of circ_0007444, including cell counting kit-8 assay, flow cytometry, wound healing assay, and transwell experiment. Luciferase reporter gene assay and RNA immunoprecipitation assay were used to reveal the interaction between circ_0007444, miR-570-3p, and PTEN. PTEN protein expression was determined by Western blot. In vivo study was performed using nude mice. Ki67, PTEN expression, and apoptosis in xenograft tumors was respectively researched by immunohistochemistry and Tunel assay.

Results

circ_0007444 was down-regulated in 87 OC patients, which was related to advanced tumor stage and grade, large tumor size, and low 60-month percent survival (P<0.05 or P<0.01). circ_0007444 inhibited proliferation, migration, and invasion, and promoted apoptosis of OC cells (P<0.01). circ_0007444 promoted PTEN expression via sponging miR-570-3p. miR-570-3p up-regulation and PTEN down-regulation reversed the inhibitory effect of circ_0007444 on OC cells malignant phenotype (P<0.01). circ_0007444 inhibited OC growth in vivo. In xenograft tumor, circ_0007444 decreased Ki67 expression but increased PTEN expression and apoptosis.

Conclusion

circ_0007444 is a tumor suppressor in OC, which inhibits OC progression by mediating the miR-570-3p/PTEN. circ_0007444 can be a potential candidate for targeted therapy of OC.

Circular RNA profiling facilitates the diagnosis and prognostic monitoring of breast cancer: A pair-wise meta-analysis

Background

As circular RNAs (circRNAs) have been found to significantly involve in the onset and progression of multiple malignant tumors including breast cancer (BC), this study aims at evaluating the diagnostic and prognostic values of circRNAs in this malady.

Methods

Available databases were thoroughly searched to collect studies on the diagnosis and/or prognosis of BC using circRNA profiling. The updated Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS‐2) tool and the Newcastle Ottawa Scale (NOS) were used to assess the underlying bias of included studies. Clinical characteristics of the studies were merged by the quantitative‐weighted integral method to obtain the combined effects.

Results

Sixteen studies were included, comprising 2438 BC cases and 271 noncancerous controls. The expression signature covered 24 circRNAs (down‐regulated: circ‐VRK1, hsa_circ_0068033, hsa_circ_103110, hsa_circ_104689, and hsa_circ_104821; up‐regulated: circAGFG1, hsa_circ_0001785, hsa_circ_0108942, hsa_circ_0001785, hsa_circ_006054, hsa_circ_100219, hsa_circ_406697, circEPSTI1, circANKS1B, circGFRA1, circ_0103552, CDR1‐AS, has_circ_001569, hsa_circ_001783, circFBXL5, circ_0005230, circAGFG1, circ‐UBAP2, and circ_0006528). The sensitivity and specificity of circRNAs in distinguishing BC patients from noncancerous controls were 0.65 and 0.68, and the corresponding area under the curve was 0.66. Survival analysis revealed that patients showing highly expressed oncogenic circRNAs were associated with increased mortality risks of BC in overall survival (univariate analysis: hazard ratio [HR] = 3.30, P = .000; multivariate analysis: HR = 3.07, P = .000), and disease‐free survival (HR = 8.26, P = .000). Stratified analysis based on circRNA expression status and control type also showed robust results.

Conclusions

Circular RNA profiling presents prominent diagnostic and prognostic values in BC, and can be rated as a promising tool facilitating its early diagnosis and survival.

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.

circ2GO: A Database Linking Circular RNAs to Gene Function

Simple Summary

Ribonucleic acids (RNAs) are generally linear chains of nucleotides which function in many cellular processes, best known in protein biosynthesis. In the last decade, circular RNAs have been discovered which are circularized after their synthesis and differ in important features from linear RNAs. These circular RNAs have meanwhile been implicated in important cellular processes in health and disease. Here, we present a comprehensive database, circ2GO, compiling and analyzing circular RNAs found in lung cancer cell lines providing the data in tables as well as visualizing it in transcript maps and in heatmaps. Importantly, we also provide easy-to-use online tools to find circular forms of genes associated with specific molecular functions, biological processes or cellular components or predict their targeted microRNAs. This resource will enable researchers to rapidly identify circular RNAs relevant for their specific research question.

Abstract

Circular RNAs (circRNAs) play critical roles in a broad spectrum of physiological and pathological processes, including cancer. Here, we provide a comprehensive database—circ2GO—systematically linking circRNAs to the functions and processes of their linear counterparts. circ2GO contains 148,811 circular human RNAs originating from 12,251 genes, which we derived from deep transcriptomics after rRNA depletion in a panel of 60 lung cancer and non-transformed cell lines. The broad circRNA expression dataset is mapped to all isoforms of the respective gene. The data are visualized in transcript maps and in heatmaps, to intuitively display a comprehensive portrait for the abundance of circRNAs across transcripts and cell lines. By integrating gene ontology (GO) information for all genes in our dataset, circ2GO builds a connection between circRNAs and their host genes’ biological functions and molecular mechanisms. Additionally, circ2GO offers target predictions for circRNA—microRNA (miRNA) pairs for 25,166 highly abundant circRNAs from 6578 genes and 897 high-confidence human miRNAs. Visualization, user-friendliness, intuitive and advanced forward and reverse search options, batch processing and download options make circ2GO a comprehensive source for circRNA information to build hypotheses on their function, processes, and miRNA targets.

CircCSNK1G1 Contributes to the Development of Colorectal Cancer by Increasing the Expression of MYO6 via Competitively Targeting miR-455-3p

Background

Numerous circular RNAs (circRNAs) are functionally investigated in various human cancers, including colorectal cancer (CRC). In this study, we explored the function of circCSNK1G1 and mechanism of action in CRC, aiming to provide evidence for circCSNK1G1 involving in CRC pathogenesis.

Methods

The expression of circCSNK1G1, miR-455-3p and Myosin VI (MYO6) were examined using quantitative real-time polymerase chain reaction (qRT-PCR). The functions of circCSNK1G1 on cell proliferation, apoptosis, cycle and migration/invasion were investigated using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, colony formation assay, flow cytometry assay and transwell assay, respectively. The targeted relationship between miR-455-3p and circCSNK1G1 or MYO6 predicted by bioinformatics analysis was validated using dual-luciferase reporter assay and RNA pull-down assay. The role of circCSNK1G1 was also explored in nude mice in vivo.

Results

The expression of circCSNK1G1 and MYO6 was elevated, while the expression of miR-455-3p was declined in CRC tissues and cells. Silencing circCSNK1G1 inhibited CRC cell proliferation, migration and invasion and induced cell apoptosis and cell cycle arrest. MiR-455-3p was a target of circCSNK1G1, and miR-455-3p could bind to MYO6. CircCSNK1G1 positively regulated MYO6 expression by targeting miR-455-3p. Inhibition of miR-455-3p reversed the effects of circCSNK1G1 silencing in CRC cells. Besides, miR-455-3p restoration blocked CRC cell growth and metastasis, which were abolished by MYO6 overexpression. Moreover, circCSNK1G1 regulated the miR-455-3p/MYO6 axis to block tumor growth in vivo.

Conclusion

CircCSNK1G1 participated in the progression of CRC partly by modulating the miR-455-3p/MYO6 network, which provided a theoretical basis for circCSNK1G1 involving in CRC pathogenesis, hinting that circCSNK1G1 might be a useful biomarker for CRC treatment.