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

circRNA-miRNA-mRNA regulatory network in human lung cancer: an update

Circular RNAs, as hopeful diagnosis markers and therapeutic molecules, have been studied, probed and applied into several diseases, such as cardiovascular diseases, systemic lupus erythematosus, leukemia, pulmonary tuberculosis, and cancer especially. Recently, mounting evidence has supported that circRNAs play a key role in the tumorigenesis, progress, invasion and metastasis in lung cancer. Its special structure—3′–5′ covalent loop—allow it to execute several special functions in both normal eukaryotic cells and cancer cells. Our review summaries the latest studies on characteristics and biogenesis of circRNAs, and highlight the regulatory functions about miRNA sponge of lung-cancer-related circRNAs. In addition, the interaction of the circRNA-miRNA-mRNA regulatory network will also be elaborated in detail in this review. Therefore, this review can provide a new idea or strategy for further development and application in clinical setting in terms of early-diagnosis and better treatment.

Overexpression of hsa_circ_0136666 predicts poor prognosis and initiates osteosarcoma tumorigenesis through miR-593-3p/ZEB2 pathway

Background: Osteosarcoma (OS) is a type of malignant bone tumor with a growing incidence. Increasing studies indicate circular RNA (circRNA) has a vital function in tumorigenesis. Yet, how circRNA regulates OS development is not clear. In the present work, we aimed to investigate the roles of hsa_circ_0136666 in OS progression.

Results: hsa_circ_0136666 was shown to be upregulated in OS and correlated with advanced stage and poor prognosis. Functional investigation using CCK8, colony formation assay and Transwell assay demonstrated that hsa_circ_0136666 promoted OS proliferation, migration and invasion, but inhibited cell death. Additionally, we identified hsa_circ_0136666 was a molecular sponge for miR-593-3p to facilitate ZEB2 expression. MiR-593-3p and ZEB2 were inversely expressed in OS tissues. And hsa_circ_0136666 exerts oncogenic roles in OS relying on miR-593-3p and ZEB2.

Conclusion: Our results demonstrate the involvement of hsa_circ_0136666 in regulating OS tumorigenesis and it may be a therapeutic target.

Methods: The expression of hsa_circ_0136666 was analyzed by qRT-PCR in OS tissues and cell lines. Proliferation was measured via CCK8 and colony formation assays. Migration and invasion were determined through Transwell assay. Luciferase reporter assay was utilized to determine the interaction between hsa_circ_0136666 and miR-593-3p or between miR-593-3p and ZEB2. Animal experiment was performed to investigate the role of hsa_circ_0136666 in vivo.

Dysregulation of CircRNA_0001946 Contributes to the Proliferation and Metastasis of Colorectal Cancer Cells by Targeting MicroRNA-135a-5p

This study was aimed to evaluate the potential function of circ-0001946 in the progression of colorectal cancer (CRC) and the related regulatory mechanism. First, the expression levels of circRNA_0001946 and microRNA-135a-5p (miR-135a-5p) in normal and CRC tissues were measured by quantitative real-time polymerase chain reaction (RT-qPCR). In addition, cell proliferation was assessed by the Cell Counting Kit-8 (CCK-8) assay, cell migration and invasion were evaluated by Transwell assays, and the cell cycle patterns were determined by flow cytometry. The relationship between the expression levels of circ_0001946 and miR-135a-5p was determined by dual-luciferase reporter assays. Our data showed that the expression of circ_0001946 was upregulated in CRC tissues, which was negatively correlated with tumor size, histologic grade, lymphatic metastasis, and TMN stage, and patients with circ_0001946 overexpression were more likely to have a poor prognosis. In addition, in vitro experiments showed that silencing circ_0001946 inhibited the epithelial–mesenchymal transition (EMT) pathway and markedly suppressed CRC cell growth, migration, and invasion. Furthermore, we discovered that the transfection of miR-135a-5p mimics could reverse the antitumor effects of circRNA_0001946 downregulation. To summarize, this study revealed that circRNA_0001946 might act as a tumor promoter by activating the miR-135a-5p/EMT axis and may be a promising treatment target for CRC.

Hsa_circ_0043265 Suppresses Proliferation, Metastasis, EMT and Promotes Apoptosis in Non-Small Cell Lung Cancer Through miR-25-3p/FOXP2 Pathway

Purpose

Non-small cell lung cancer (NSCLC) is the largest type of lung cancer (LC) with a higher mortality rate. Circular RNAs (circRNAs) have been shown to play an important role in cancer progression. Therefore, this study was to explore the function of hsa_circ_0043265 in NSCLC.

Methods

The expression levels of hsa_circ_0043265, microRNA-25-3p (miR-25-3p) and forkhead box P2 (FOXP2) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Ribonuclease R (RNase R) and Actinomycin D (ActD) were used to verify the authenticity and stability of hsa_circ_0043265. Cell counting kit-8 (CCK-8), flow cytometry and transwell assays were used to evaluate the abilities of proliferation, apoptosis, migration and invasion of NSCLC cells. Also, Western blot (WB) analysis was performed to assess the levels of apoptosis, epithelial–mesenchymal transition (EMT) and proliferation-related proteins and FOXP2 protein. RNA immunoprecipitation (RIP) and dual-luciferase reporter assays were used to verify the interaction between miR-25-3p and hsa_circ_0043265 or FOXP2. Besides, mice xenograft models were constructed to confirm the effect of hsa_circ_0043265 on NSCLC tumor growth in vivo.

Results

Hsa_circ_0043265 was lowly expressed in NSCLC tissues and cells, and its overexpression inhibited the proliferation, migration, invasion and EMT process, while improved the apoptosis of NSCLC cells. MiR-25-3p could be sponged by hsa_circ_0043265, and its overexpression could invert the suppression effect of overexpressed-hsa_circ_0043265 on NSCLC progression. Moreover, FOXP2 was a target of miR-25-3p, and its silencing also could reverse the inhibition effect of overexpressed-hsa_circ_0043265 on NSCLC progression. In addition, hsa_circ_0043265 overexpression reduced the tumor growth of NSCLC in vivo.

Conclusion

Hsa_circ_0043265 could sponge miR-25-3p to improve FOXP2 expression, thereby inhibiting NSCLC progression. This study showed that hsa_circ_0043265 could be a potential biomarker for early diagnosis of NSCLC.

The β-catenin/TCF-4-LINC01278-miR-1258-Smad2/3 axis promotes hepatocellular carcinoma metastasis

Hepatocellular carcinoma (HCC) metastasis is largely responsible for HCC-associated recurrence and mortality. We aimed to identify metastasis-related long non-coding RNAs (lncRNAs) to understand the molecular mechanism of HCC metastasis. We first identified that miR-1258 was downregulated in HCC tissues both in The Cancer Genome Atlas (TCGA) and Sun Yat-sen University Cancer Center (SYSUCC) dataset. MiR-1258 expression negatively correlated with recurrence-free survival and overall survival of HCC patients. MiR-1258 overexpression inhibited migration and invasion of HCC cells both in vitro and in vivo, whereas miR-1258 downregulation promoted cell metastasis. Luciferase assays verified direct binding of miR-1258 to Smad2 and Smad3, thereby attenuating TGF-β/Smad signaling. We further established that lncRNA LINC01278 was a negative regulator of miR-1258. In vivo and in vitro assays demonstrated that LINC01278-mediated HCC metastasis was dependent on miR-1258 expression. Furthermore, miR-1258 downregulation in turn increased LINC01278 expression. We also observed that TCF-4 could bind to the LINC01278 promoter site. In addition, LINC01278 downregulation decreased migration and invasion of HCC cells induced by β-catenin and TGF-β1 both in vitro and in vivo. We uncovered a novel mechanism for β-catenin/TCF-4-LINC01278-miR-1258-Smad2/3 feedback loop activation in HCC metastasis, and the study indicated that LINC01278 could serve as a therapeutic target for HCC metastasis.

Circular RNA cESRP1 sensitises small cell lung cancer cells to chemotherapy by sponging miR-93-5p to inhibit TGF-β signalling

Circular RNAs (circRNAs) are novel RNA molecules that play important roles in chemoresistance in different cancers, including breast and gastric cancers. However, whether circRNAs are involved in the response to chemotherapy in small cell lung cancer (SCLC) remains largely unknown. In this study, we observed that cESRP1 (circular RNA epithelial splicing regulatory protein-1) expression was significantly downregulated in the chemoresistant cells compared with the parental chemosensitive cells. cESRP1 enhanced drug sensitivity by repressing miR-93-5p in SCLC. Cytoplasmic cESRP1 could directly bind to miR-93-5p and inhibit the posttranscriptional repression mediated by miR-93-5p, thereby upregulating the expression of the miR-93-5p downstream targets Smad7/p21(CDKN1A) and forming a negative feedback loop to regulate transforming growth factor-β (TGF-β) mediated epithelial-mesenchymal transition. Furthermore, cESRP1 overexpression and TGF-β pathway inhibition both altered tumour responsiveness to chemotherapy in an acquired chemoresistant patient-derived xenograft model. Importantly, cESRP1 expression was downregulated in SCLC patient tissues and was associated with survival. Our findings reveal, for the first time, that cESRP1 plays crucial a role in SCLC chemosensitivity by sponging miR-93-5p to inhibit the TGF-β pathway, suggesting that cESRP1 may serve as a valuable prognostic biomarker and a potential therapeutic target in SCLC patients.

Inhibiting of self-renewal, migration and invasion of ovarian cancer stem cells by blocking TGF-β pathway

OBJECTIVE

To investigate the effect and mechanism of SB525334 on self-renewal, migration and invasion of ovarian cancer stem cells.

METHODS

ALDHhigh-expressing cancer stem cells (CSCs) were isolated from human ovarian cancer cell line SKOV-3 by flow cytometry and treated with 2μg/mL SB525334 for 6h. The sphere forming assay was used to detect the ability of self-renewal of CSCs and the colony formation assay was used to detect the tumorigenicity in vitro. Transwell migration and invasion assay were used to detect the migration and invasion ability of CSCs. To further explore the mechanism, real-time quantitative PCR and flow cytometry were used to detect the mRNA and protein expression of TGF-β, Smad2, Smad3, phosphorylated Smad2, phosphorylated Smad3 and Smad4, respectively. Expressions of epithelial-mesenchymal transition (EMT)-related genes E-cadherin, Snail, Vimentin were also assessed.

RESULTS

The self-renewal ability, tumorigenicity in vitro, migration and invasion ability of CSCs were significantly attenuated after SB525334 treatment. The expressions of TGF-β, phosphorylated Smad2, phosphorylated Smad3, Snail, and Vimentin were decreased, while Smad4 and E-cadherin expressions were increased.

CONCLUSION

SB525334 may inhibit the self-renewal, invasion and migration of ovarian CSCs by blocking the TGF-β/Smad/EMT pathway.

Critical function of circular RNAs in lung cancer

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

CircMRPS35 suppresses gastric cancer progression via recruiting KAT7 to govern histone modification

Background

Aberrant expression of circular RNAs contributes to the initiation and progression of cancers, but the underlying mechanism remains elusive.

Methods

RNA-seq and qRT-PCR were performed to screen differential expressed circRNAs between gastric cancer tissues and adjacent normal tissues. Candidate circRNA (circMRPS35) was screened out and validated by qRT-PCR. Cell proliferation and invasion ability were determined by CCK-8 and cell invasion assays. RNA-seq, GO-pathway, RNA pull-down and ChIRP were further applied to search for detailed mechanism.

Results

Here, a novel circRNA named circMRPS35, was screened out by RNA-seq in gastric cancer tissues, whose expression is related to clinicopathological characteristics and prognosis in gastric cancer patients. Biologically, circMRPS35 suppresses the proliferation and invasion of gastric cancer cells in vitro and in vivo. Mechanistically, circMRPS35 acts as a modular scaffold to recruit histone acetyltransferase KAT7 to the promoters of FOXO1 and FOXO3a genes, which elicits acetylation of H4K5 in their promoters. Particularly, circMRPS35 specifically binds to FOXO1/3a promoter regions directly. Thus, it dramatically activates the transcription of FOXO1/3a and triggers subsequent response of their downstream target genes expression, including p21, p27, Twist1 and E-cadherin, resulting in the inhibition of cell proliferation and invasion. Moreover, circMRPS35 expression positively correlates with that of FOXO1/3a in gastric cancer tissues.

Conclusions

Our findings not only reveal the pivotal roles of circMRPS35 in governing histone modification in anticancer treatment, but also advocate for triggering circMRPS35/KAT7/FOXO1/3a pathway to combat gastric cancer.

Insights into the regulatory role of circRNA in angiogenesis and clinical implications

Angiogenesis is the physiological process of new blood vessel formation from existing capillary vessels or posterior capillary veins. Its dysfunction could result in a number of diseases, such as cardiovascular diseases and cancer, contributing to death and disability worldwide. Circular RNAs (circRNAs) are a class of novel identified RNA molecules with a special covalent loop structure without a 5' cap and 3' tail, which can lead to novel back-splicing or skipping events from precursor mRNAs. Accumulating evidence suggests that circRNA play critical roles in diseases; in particular, they are abundantly and abnormally expressed in angiogenesis-related diseases. In this review, we describe the role of circRNA under pathological conditions, discuss the association between circRNA and angiogenesis, classify the regulatory mechanisms and suggest that circRNA can be used as potential therapeutic targets for angiogenesis-related diseases under clinical evaluation.

Circular RNAs in Cancer: Biogenesis, Function, and Clinical Significance

Circular RNA (circRNA) is a class of single-stranded molecules with tissue/development-specific expression patterns. Unlike linear RNA, circRNA forms a covalently closed loop produced from 'back-splicing' of primary transcripts, conferring on them inherent resistance to exonucleolytic RNA decay. Increasing evidence demonstrates that many circRNAs exert important biological functions by acting as miRNA inhibitors ('sponges'), protein 'decoys', or by encoding small peptides. Importantly, circRNAs are aberrantly expressed in cancer and play indispensable oncogenic or tumor suppressive roles during tumor development and progression. In this review, we summarize the biogenesis, turnover, and involvements of circRNAs in cancer and also discuss their potential as diagnostic biomarkers or therapeutic targets.

Circular RNA CRIM1 functions as a ceRNA to promote nasopharyngeal carcinoma metastasis and docetaxel chemoresistance through upregulating FOXQ1

Background

Circular RNAs (circRNAs), a new type of noncoding RNA (ncRNA), have been identified as significant gene expression regulators and are involved in cancer progression. However, the roles of circRNAs in nasopharyngeal carcinoma (NPC) remain largely unknown.

Methods

Here, the expression profile of circRNAs in a pair of NPC cell lines with different metastatic abilities (S18 and S26 cells) was analyzed by RNA-sequencing. Quantitative reverse transcription PCR was used to detect the expression level of circCRIM1 in NPC cells and tissues. Then, function experiments in vitro and in vivo were performed to evaluate the effects of circCRIM1 on NPC metastasis and EMT. Mechanistically, RNA immunoprecipitation, luciferase reporter assay, pull-down assay with biotinylated miRNA, fluorescent in situ hybridization were performed to confirm the interaction between circCRIM1 and miR-422a in NPC. The clinical value of circCRIM1 was evaluated in NPC metastasis and chemosensitivity.

Results

We identified that circCRIM1 was upregulated in highly metastatic NPC cells. CircCRIM1 was also overexpressed in NPC tissues with distant metastasis, and its overexpression promoted NPC cell metastasis and EMT. Mechanistically, circCRIM1 competitively bound to miR-422a and prevented the suppressive effects of miR-422a on its target gene FOXQ1, which finally led to NPC metastasis, EMT and docetaxel chemoresistance. Furthermore, high circCRIM1 expression was associated with unfavorable survival in NPC patients. We established a prognostic model based on circCRIM1 expression and N stage that effectively predicted the risk of distant metastasis and treatment response to docetaxel-containing induction chemotherapy in NPC patients.

Conclusions

Our findings reveal the critical role of circCRIM1 specifically in promoting NPC metastasis and chemoresistance via a ceRNA mechanism and provide an exploitable biomarker and therapeutic target for prognosis and treatment resistance in NPC patients.

Circular RNA hsa_circ_0014130 Inhibits Apoptosis in Non-Small Cell Lung Cancer by Sponging miR-136-5p and Upregulating BCL2

Previous studies indicated that circular RNAs (circRNA) played vital roles in the development of non-small cell lung cancer (NSCLC). Although hsa_circ_0014130 might be a potential NSCLC biomarker, its function in NSCLC remains unknown. Thus, this study aimed to investigate the role of hsa_circ_0014130 in the progression of NSCLC. The levels of hsa_circ_0014130 in NSCLC tissues and adjacent normal tissues were determined by qRT-PCR. In addition, the expressions of Bcl-2 and cleaved caspase-3 in A549 cells were detected with Western blot analysis. Meanwhile, the dual luciferase reporter system assay was used to determine the interaction of hsa_circ_0014130 and miR-136-5p or Bcl-2 and miR-136-5p in NSCLC, respectively. The level of hsa_circ_0014130 was significantly upregulated in NSCLC tissues. Downregulation of hsa_circ_0014130 markedly inhibited the proliferation and invasion of A549 cells via inducing apoptosis. In addition, downregulation of hsa_circ_0014130 inhibited the tumorigenesis of subcutaneous A549 xenograft in mice in vivo. Meanwhile, mechanistic analysis indicated that downregulation of hsa_circ_0014130 decreased the expression of miR-136-5p-targeted gene Bcl-2 via acting as a competitive "sponge" of miR-136-5p. In this study, we found that hsa_circ_0014130 was upregulated in NSCLC tissues. In addition, hsa_circ_0014130 functions as a tumor promoter in NSCLC to promote tumor growth through upregulating Bcl-2 partially via "sponging" miR-136-5p. IMPLICATIONS: In conclusion, hsa_circ_0014130 might function as a prognostic factor for patients with NSCLC and might be a therapeutic target for the treatment of NSCLC in future.

Hsa_circ_0011385 accelerates the progression of thyroid cancer by targeting miR-361-3p

Background

Thyroid cancer is an endocrine malignancy that is growing in incidence worldwide. Despite progress in diagnostics and treatment of thyroid cancer, prognosis remains poor. Emerging research has shown that circular RNAs (circRNAs) have crucial regulatory roles in cancers. However, the possible functions and mechanisms of hsa_circ_0011385 remain undetermined.

Materials and methods

Expression levels of hsa_circ_0011385 and miR-361-3p were evaluated by qRT-PCR assay. The interaction between hsa_circ_0011385 and miR-361-3p was verified by dual-luciferase reporter assay. Effects of hsa_circ_0011385 or miR-361-3p on cell viability, proliferation, cell cycle, apoptosis, migration and invasion were confirmed by cell counting kit-8 (CCK-8), carboxyfluoresceinsuccinimidyl ester (CFSE), flow cytometry, and Transwell assays in vitro. The effect of hsa_circ_0011385 on thyroid cancer progression was also determined by in vivo tumor formation assay. Target genes of miR-361-3p were predicted by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and the expression of apoptosis- and metastasis-related proteins were assessed by Western blot assay.

Results

Hsa_circ_0011385 upregulated in thyroid cancer; hsa_circ_0011385 knockdown inhibited thyroid cancer cell proliferation, migration and invasion, and promoted cell cycle arrest and apoptosis. In addition, hsa_circ_0011385 could negatively regulate miR-361-3p by functioning as a sponge. Hsa_circ_0011385 promoted thyroid cancer cell proliferation, migration and invasion and suppressed cell cycle arrest and apoptosis by targeting miR-361-3p in vitro. We also found that hsa_circ_0011385 knockdown dramatically inhibited thyroid cancer growth in vivo. Furthermore, hsa_circ_0011385 regulated expression of apoptosis and metastasis-related proteins in thyroid cancer.

Conclusions

Hsa_circ_0011385facilitated thyroid cancer cell proliferation, invasion and migration, and inhibited thyroid cancer cell cycle arrest and apoptosis by targeting miR-361-3p, suggesting that the hsa_circ_0011385/miR-361-3p axis might be a promising therapeutic target for thyroid cancer.

MiRNAs and LncRNAs: Dual Roles in TGF-β Signaling-Regulated Metastasis in Lung Cancer

Lung cancer is one of the most malignant cancers around the world, with high morbidity and mortality. Metastasis is the leading cause of lung cancer deaths and treatment failure. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs), two groups of small non-coding RNAs (nc-RNAs), are confirmed to be lung cancer oncogenes or suppressors. Transforming growth factor-β (TGF-β) critically regulates lung cancer metastasis. In this review, we summarize the dual roles of miRNAs and lncRNAs in TGF-β signaling-regulated lung cancer epithelial-mesenchymal transition (EMT), invasion, migration, stemness, and metastasis. In addition, lncRNAs, competing endogenous RNAs (ceRNAs), and circular RNAs (circRNAs) can act as miRNA sponges to suppress miRNAs, thereby mediating TGF-β signaling-regulated lung cancer invasion, migration, and metastasis. Through this review, we hope to cast light on the regulatory mechanisms of miRNAs and lncRNAs in TGF-β signaling-regulated lung cancer metastasis and provide new insights for lung cancer treatment.

MYOCD and SMAD3/SMAD4 form a positive feedback loop and drive TGF-β-induced epithelial-mesenchymal transition in non-small cell lung cancer

Myocardin (MYOCD) promotes Smad3-mediated transforming growth factor-β (TGF-β) signaling in mouse fibroblast cells. Our previous studies show that TGF-β/SMADs signaling activation enhances epithelial-mesenchymal transition (EMT) in human non-small cell lung cancer (NSCLC) cells. However, whether and how MYOCD contributes to TGF-β-induced EMT of NSCLC cells are poorly elucidated. Here, we found that TGF-β-induced EMT was accompanied by increased MYOCD expression. Interestingly, MYOCD overexpression augmented EMT and invasion of NSCLC cells induced by TGF-β, whereas knockdown of MYOCD expression attenuated these effects. Overexpression and knockdown of MYOCD resulted in the upregulation and downregulation of TGF-β-induced Snail mRNA, respectively. Moreover, MYOCD overexpression promoted TGF-β-stimulated NSCLC cell metastasis in vivo. MYOCD was highly expressed and positively correlated with Snail in metastatic NSCLC tissues. Mechanistically, MYOCD directly interacted with SMAD3 and sustained the formation of TGF-β-induced nuclear SMAD3/SMAD4 complex, facilitating TGF-β/SMAD3-induced transactivation of Snail. Importantly, MYOCD was transcriptionally activated by TGF-β-induced SMAD3/SMAD4 complex and CRISPR/Cas9-mediated silencing of SMAD3/SMAD4 led to a reduction in MYOCD mRNA expression. Taken together, our findings indicate that MYOCD promotes TGF-β-induced EMT and metastasis of NSCLC and identify a positive feedback loop between MYOCD and SMAD3/SMAD4 driving TGF-β-induced EMT.

CircBACH1 (hsa_circ_0061395) promotes hepatocellular carcinoma growth by regulating p27 repression via HuR

In recent years, an increasing number of circular RNAs (circRNAs) have been discovered in hepatocellular carcinoma (HCC). However, the functions of most circRNAs require further investigation. Here, we found that circBACH1 was significantly upregulated in HCC tissues and that high circBACH1 levels were closely associated with poor prognosis. In addition, circBACH1 could promote HCC growth by accelerating cell cycle progression in vitro and in vivo. We next investigated the cellular and molecular mechanisms and discovered that circBACH1 inhibited p27 translation, which influenced cell cycle progression. Moreover, we revealed that circBACH1 could combine directly with HuR using RNA immunoprecipitation assays, pull-down assays, and electrophoretic mobility shift assays. The combination of these molecules facilitated HuR translocation from the nucleus to the cytoplasm according to the fluorescence in situ hybridization and immunofluorescence results. Finally, silencing HuR abrogated circBACH1's inhibition of p27 translation and abolished the circBACH1-induced effect on HCC proliferation. In sum, circBACH1 plays a significant role as an oncogene through the circBACH1/HuR/p27 axis in HCC development.

CircPTK2 (hsa_circ_0005273) as a novel therapeutic target for metastatic colorectal cancer

BACKGROUND

As a novel class of noncoding RNAs, circRNAs have been recently identified to regulate tumorigenesis and aggressiveness. However, the function of circRNAs in colorectal cancer (CRC) metastasis remains unclear. We aimed to identify circRNAs that are upregulated in CRC tissues from patients and study their function in CRC metastasis.

METHODS

We compared six pairs of CRC tissues and their matched adjacent non-tumor tissues by using circRNA microarray. We first evaluated the expression of circPTK2 (hsa_circ_0005273) in fresh tissues from CRC tumors and corresponding adjacent tissues by qPCR analysis. CircPTK2 expression levels in the tissue microarray with 5 years of survival information were determined by RNA-ISH analysis. Meanwhile, the expression levels of circulating circPTK2 were further analyzed according to the patients' clinical features. We analyzed cell apoptosis, colony formation, migration, and invasion in CRC cells. To further elucidate the effect of circPTK2 in CRC metastasis, we also conducted a colon cancer hepatic and pulmonary metastasis experiment. We used RNA biotin-labeled pull down and mass spectrometry to identify the target of circPTK2. We established a PDTX model to evaluate the effect of shRNA specifically targeting circPTK2 on tumor metastasis.

RESULTS

We identified a novel circRNA, circPTK2, which is back-spliced of three exons (exons 27, 28 and 29) of PTK2 by using circRNA microarray, bioinformatics and functional studies. CircPTK2 was elevated in CRC tissues and positively associated with tumor growth and metastasis. CRC patients with increased circPTK2 expression were positively correlated with poorer survival rates. Furthermore, our studies showed that circPTK2 could promote EMT of CRC cells in vitro and in vivo by binding to vimentin protein on sites Ser38, Ser55 and Ser82. We further demonstrated the interaction of circPTK2 and vimentin mediated the regulation of CRC by knockdown or overexpression of vimentin. In addition, we revealed that tail vein injection of shRNA specifically targeting circPTK2 blunt tumor metastasis in a patient-derived CRC xenograft model.

CONCLUSIONS

Collectively, these results demonstrate that circPTK2 exerts critical roles in CRC growth and metastasis and may serve as a potential therapeutic target for CRC metastasis, and also a promising biomarker for early diagnosis of metastasis.

Circular RNA FAM114A2 suppresses progression of bladder cancer via regulating ∆NP63 by sponging miR-762

Numerous evidences have shown that circular RNAs (circRNAs) play a key role in regulating the pathogenesis of cancer. However, the mechanism of circRNAs in urothelial carcinoma of bladder (UCB) remains largely unclear. In this study, we found circFAM114A2 was significantly downregulated both in UCB tissue specimens and cell lines, and the expression level was highly correlated with pathological TNM stage and grade. Functionally, overexpression of circFAM114A2 dramatically inhibited the migration, invasion and proliferation of UCB cells in vitro, and suppressed tumor growth in vivo. Mechanistically, we confirmed miR-762 was copiously pulled down by circFAM114A2 in 5637 and T24 cells. Fluorescence in situ hybridization (FISH) further indicated the cytoplasmic interactions between circFAM114A2 and miR-762. By using luciferase reporter assay, we found that miR-762 could directly target TP63. Subsequently, we found that circFAM114A2 might increase the expression of ∆NP63 (main isoform of TP63 in UCB) by sponging miR-762. Taken together, our results demonstrated that circFAM114A2 might serve as a competing endogenous RNA (ceRNA) of miR-762 in regulating the expression of ∆NP63, thus suppressed UCB progression through circFAM114A2/miR-762/∆NP63 axis.

Profiling and integrated analysis of differentially expressed circRNAs as novel biomarkers for breast cancer

Breast cancer (BC) is a globally common cancer with the highest and increasing morbidity and mortality among females. Novel biomarkers are warranted to be discovered for the early detection, treatment, and prognosis of BC. In this study, we investigated the profiles of differentially expressed (DE) circular RNAs (circRNAs) by competing endogenous RNAs (ceRNA) microarray to construct a genome-wide circRNA profile. Then, we performed Gene Ontology (GO) analysis and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway analysis of the host genes (HGs) of circRNAs. A total of 4,370 DE circRNAs were detected and GO and KEGG analysis showed that they were significantly associated with cell cycle, DNA replication, BC, and familial BC. We validated the differential circRNAs and relevant HGs through quantitative real-time polymerase chain reaction and constructed a putative circRNA-microRNA-messenger RNA regulatory network. Eight circRNAs, including hsa_circ_0069094, hsa_circ_0062558, hsa_circ_0074026, hsa_circ_0079876, hsa_circ_0017536, hsa_circ_0023302, hsa_circ_0017650, and hsa_circ_0017545, were validated significantly DE in BC tissue and associated with TNM staging, lymph node infiltration, and Ki67. Hsa_circ_0069094, hsa_circ_0079876, hsa_circ_0017650, and hsa_circ_0017526 were upregulated in plasma. This study revealed the general expression characteristics of specific DE circRNAs in BC and hsa_circ_0069094, hsa_circ_0079876, hsa_circ_0017650, and hsa_circ_0017526 might be promising candidate targets.

Interplay among SNAIL Transcription Factor, MicroRNAs, Long Non-Coding RNAs, and Circular RNAs in the Regulation of Tumor Growth and Metastasis

SNAIL (SNAI1) is a zinc finger transcription factor that binds to E-box sequences and regulates the expression of genes. It usually acts as a gene repressor, but it may also activate the expression of genes. SNAIL plays a key role in the regulation of epithelial to mesenchymal transition, which is the main mechanism responsible for the progression and metastasis of epithelial tumors. Nevertheless, it also regulates different processes that are responsible for tumor growth, such as the activity of cancer stem cells, the control of cell metabolism, and the regulation of differentiation. Different proteins and microRNAs may regulate the SNAIL level, and SNAIL may be an important regulator of microRNA expression as well. The interplay among SNAIL, microRNAs, long non-coding RNAs, and circular RNAs is a key event in the regulation of tumor growth and metastasis. This review for the first time discusses different types of regulation between SNAIL and non-coding RNAs with a focus on feedback loops and the role of competitive RNA. Understanding these mechanisms may help develop novel therapeutic strategies against cancer based on microRNAs.

The SIRT2-mediated deacetylation of AKR1C1 is required for suppressing its pro-metastasis function in Non-Small Cell Lung Cancer

Aldo-keto reductase family 1 member C1 (AKR1C1) promotes malignancy of Non-Small Cell Lung Cancer (NSCLC) by activating Signal Transducer and Activator of Transcription 3 (STAT3) pathway. However, how the pro-metastatic functions of AKR1C1 are switched on/off remains unknown. Methods: Immunoprecipitation and LC-MS/MS analyses were performed to identify the acetylation on AKR1C1 protein, and the functional analyses (in vitro and in vivo) were performed to depict the contribution of acetylation to the pro-metastatic effects of AKR1C1. Results: Here we report that acetylated AKR1C1 on two lysine residues K185 & K201 is critical to its pro-metastatic role. The acetylation modification has no impact on the canonical enzymatic activity of AKR1C1, while it is required for the interaction between AKR1C1 to STAT3, which triggers the downstream transduction events, ultimately mobilizing cells. Importantly, the deacetylase Sirtuin 2 (SIRT2) is capable of deacetylating AKR1C1, inhibiting the transactivation of STAT3 target genes, thus suppressing the migration of cells. Conclusion: Acetylation on Lysines 185 and 201 of AKR1C1 dictates its pro-metastatic potential both in vitro and in vivo, and the reverting of acetylation by Sirtuin 2 provides potential therapeutic targets for treatment against metastatic NSCLC patients with high AKR1C1 expression.

Identification of circRNA-miRNA networks for exploring an underlying prognosis strategy for breast cancer

Aim: Circular RNAs (circRNAs) still have many potential functions in the process of tumor development that are not completely understood. The study aims to explore novel circRNAs and their mechanisms of action in breast cancer (BCa). Materials & methods: A combination strategy of RNA-sequencing (RNA-seq) technique, quantitative real-time PCR and bioinformatic analysis was employed to identify the potential mechanisms involving differentially expressed circRNAs in the serum exosomes and tissues of BCa patients. Results: The expression levels of hsa-circRNA-0005795 and hsa-circRNA-0088088 were significantly different both in serum exosomes and tissues and might function as competing endogenous RNAs and play vital roles in BCa development. Conclusion: We constructed two circRNA-miRNA networks and provided new insight into the prognosis and therapy of BCa using circRNAs from serum exosomes.

[Role of Circular RNA in Diagnosis, Development and Durg Resistance of Lung Cancer]

肺癌在全球范围内的致死率一直居高不下。近年来针对多种分子分型的靶向药物已成为中晚期肺癌治疗的新有效手段，但是肺癌在早期诊断以及长期有效的治疗上仍然面临着严峻的挑战。环状RNA（circular RNA, circRNA）是一类具有环形结构的独特RNA分子，具有优异的稳定性以及表达特异性。越来越多的研究发现circRNA在肿瘤中表达异常，这种异常表达不仅与肿瘤的恶性相关，同时可以参与调控肿瘤进展，为肿瘤的诊断与治疗提供了新的思路。因此，本文就circRNA在肺癌中的表达、诊断、预后价值以及发生发展机制展开综述，以期为肺癌的早期诊断与治疗寻找新的靶点。

Analysis of circular RNA-associated competing endogenous RNA network in breast cancer

As the most common type of cancer in female patients, the morbidity and mortality rates of breast cancer (BC) are high, and its incidence is gradually increasing worldwide. However, the underlying molecular and genetic mechanisms involved in the etiopathogenesis of BC remain unclear. Circular RNAs (circRNAs) are a novel type of non-coding RNAs that have been verified to serve a crucial role in tumorigenesis. However, the majority of functions and mechanisms of circRNAs remain unknown. The present study identified 47 differentially expressed circRNAs in a dataset from Gene Expression Omnibus. Using the cancer-specific circRNA database, the potential microRNA (miRNA) response elements, RNA-binding proteins and open reading frames of the candidate circRNAs were predicted. Combing the predictions of miRNAs and target mRNAs, a competing endogenous RNA network was constructed, which may serve as the theoretical basis for further research. Furthermore, the analyses conducted using Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways indicated that candidate circRNAs may serve a role in transcriptional regulation. Moreover, 20 BC tissue specimens and their paired adjacent normal tissue specimens were used to evaluate the expression levels of the screened circRNAs. Thus, the analyses of the raw microarray data conducted in the present study offer perspectives on the exploration of mechanisms associated with BC tumorigenesis with regard to the circRNA-miRNA-mRNA network.

Retracted Article: Circular RNA PTK2 modifies the progression and radiosensitivity in gastric cancer via miR-369-3p/ZEB1 axis

Gastric cancer (GC) is one of the common cancers worldwide. Emerging findings imply that aberrant expression of circular RNA_0003221 (circPTK2) is involved in GC. Nevertheless, the function of circPTK2 in GC needs more explanation. Profiles of circPTK2, microRNA (miR)-369-3p, and zinc finger E-box binding homeobox 1 (ZEB1) were determined by quantitative real-time polymerase chain reaction assay. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and transwell assays were employed to estimate cell proliferation, apoptosis, and mobility in GC cells, respectively. Meanwhile, levels of ZEB1 and other indicated proteins were tested using western blot. Survival fraction was assessed utilizing clonogenic assay. Additionally, the role of circPTK2 in tumorigenesis was investigated via a xenograft tumor model. Dual-luciferase reporter, RNA immunoprecipitation, and RNA pull-down assays were conducted to confirm the interrelation between miR-369-3p and circPTK2 or ZEB1. Levels of circPTK2 and ZEB1 were markedly augmented, but miR-369-3p was downregulated in GC tissues and cells. CircPTK2 depletion restrained cell growth, metastasis, and epithelial–mesenchymal transition, and promoted radiosensitivity in GC cells. And circPTK2 depletion reduced tumor growth and metastasis in vivo. Moreover, the effect of circPTK2 silencing on cellular phenotypes and radiosensitivity was regained by miR-369-3p inhibitor. Furthermore, upregulation of ZEB1 could overturn miR-369-3p mimic-induced effect on cell metastasis and radiosensitivity of GC cells. Mechanically, circPTK2 was a sponge of miR-369-3p to separate ZEB1. CircPTK2/miR-369-3p/ZEB1 axis modulated cell behaviors and radiosensitivity in GC; thus circPTK2 might serve as a promising target for GC therapy.

Circular RNA PTK2 regulates the cell proliferation, apoptosis, mobility and radiosensitivity via ZEB1 by sponging miR-369-3p in gastric cancer.

Krüppel-like factor 4 regulates stemness and mesenchymal properties of colorectal cancer stem cells through the TGF-β1/Smad/snail pathway

Krüppel-like factor 4 (KLF4) was closely associated with epithelial-mesenchymal transition and stemness in colorectal cancer stem cells (CSCs)-enriched spheroid cells. Nonetheless, the underlying molecular mechanism is unclear. This study showed that KLF4 overexpression was accompanied with stemness and mesenchymal features in Lgr5⁺ CD44⁺ EpCAM⁺ colorectal CSCs. KLF4 knockdown suppressed stemness, mesenchymal features and activation of the TGF-β1 pathway, whereas enforced KLF4 overexpression activated TGF-β1, phosphorylation of Smad 2/3 and Snail expression, and restored stemness and mesenchymal phenotypes. Furthermore, TGF-β1 pathway inhibition invalidated KLF4-facilitated stemness and mesenchymal features without affecting KLF4 expression. The data from the current study are the first to demonstrate that KLF4 maintains stemness and mesenchymal properties through the TGF-β1/Smad/Snail pathway in Lgr5⁺ CD44⁺ EpCAM⁺ colorectal CSCs.

Circ-ZKSCAN1 regulates FAM83A expression and inactivates MAPK signaling by targeting miR-330-5p to promote non-small cell lung cancer progression

Background

Circular RNAs (circRNAs) belong to a new type of endogenous non-coding RNA and plays a key role in carcinogenesis. Circ-ZKSCAN1 (hsa_circ_0001727) has been proven to be a tumor-dependent circRNA. However, its role in non-small cell lung cancer (NSCLC) has been underreported.

Methods

The expression patterns of circ-ZKSCAN1 were determined using qRT-PCR in NSCLC samples and cell lines. Cell proliferation was examined utilizing the CCK-8 assay. Cell migration and invasion were evaluated using the Transwell assay. The combination of circ-ZKSCAN1 and miR-330-5p in NSCLC cells was analyzed by RNA pull-down and luciferase reporter assay. We used the bioinformatics software circbank, CircInteractome, TargetScan and Miranda to predict circRNA-miRNA and miRNA-mRNA interactions.

Results

Our results showed that circ-ZKSCAN1 was significantly up-regulated in NSCLC, closely related to malignant characteristics and poor prognosis, and clinically related to tumor size and clinical stage. Subsequent experiments showed that circ-ZKSCAN1 could inhibit the growth of NSCLC cells in vitro and in vivo. Importantly, circ-ZKSCAN1 can act as a sponge of carcinogenic miR-330-5p to increase the expression of FAM83A, resulting in the inhibition of MAPK signal transduction pathway, thus promoting the progress of NSCLC. Interestingly, the increase in FAM83A expression caused by circ-ZKSCAN1 overexpression could in turn promote the expression of circ-ZKSCAN1.

Conclusions

Circ-ZKSCAN1 is a key positive regulator of NSCLC, and clarifies the potential molecular mechanism of the new circ-ZKSCAN1/miR-330-5p/FAM83A feedback loop in promoting the progress of NSCLC.

Circular RNAs Regulate Cancer Onset and Progression via Wnt/β-Catenin Signaling Pathway

Cancer remains to be a major challenge for public health providers, and is the second leading cause of death worldwide. Therefore, it is imperative to explore the mechanisms underlying cancer initiation and development, and design novel diagnostics and therapeutics. Circular RNAs (circRNAs), which exhibit a covalently closed loop structure, are involved in a variety of diseases, including cancer. The aberrant expression of circRNAs contributes to the initiation and development of various cancers by disrupting the interplay of specific signaling pathways, including the Wnt/β-catenin pathway, which controls a plethora of cellular processes that drive cancer development. The interactions between circRNAs (specifically expressed in different cancer tissues) and Wnt/β-catenin signaling pathway presents potential diagnostic biomarkers and novel therapeutic targets. In this review, we have summarized research discoveries on the functions of Wnt/β-catenin pathway-related circRNAs in the modulation of oncogenesis and progression of different types of cancer. We anticipate that our findings will contribute to the improvement or development of circRNAs-based strategies for cancer treatment.

Circ_0000003 promotes the proliferation and metastasis of non-small cell lung cancer cells via miR-338-3p/insulin receptor substrate 2

Background: Circular RNAs (circRNAs) play a pivotal regulatory role in a variety of tumors.Nevertheless, the detailed function of circ_0000003 in non-small cell lung cancer (NSCLC) and its regulatory mechanism remain elusive.Methods: RT-PCR was carried out to detect the expressions of circ_0000003, miR-338-3p and insulin receptor substrate 2 (IRS2)in NSCLC tissues. Besides, western blot was done to monitor IRS2 expression in NSCLC cells. The correlation between circ_0000003 and clinicopathologic characteristics of NSCLC patients was analyzed as well.CCK8 and BrdUassays were used to monitor cell proliferation; flow cytometry was used to detect apoptosis; and transwell assay was conducted to detect its migration and invasion.Moreover, dual luciferase reporter gene assay was done to verify the targeting relationship between circ_0000003 and miR-338-3p.Additionally, the effect of circ_0000003 on the growth of NSCLC cells in vivo was evaluated by tumorigenesis assay in nude mice.Results: The expression of circ_0000003 was significantly high in NSCLC tissues and cell lines, and its high expression level was notably correlated with lymph node metastasis andTNM staging.In vitro experiments showed that overexpression of circ_0000003 facilitated the proliferation, migration, invasion and inhibited the apoptosis of NSCLC cells, while the knockdown of circ_0000003 had the opposite effect.In vivo experiments revealed that knockdown of circ_0000003 impeded tumor growth and metastasis. Further, the underlying mechanism showed that circ_0000003 functioned as endogenous competitive RNA and directly targeted miR-338-3p to positively regulated IRS2 expression.Conclusion: Circ_0000003 promotes the proliferation and metastasis of NSCLC cells via modulating miR-338-3p/IRS2 axis.

Downregulated Circular RNA hsa_circ_0000291 Suppresses Migration And Proliferation Of Gastric Cancer Via Targeting The miR-183/ITGB1 Axis

Background

Circular RNAs are implicated in a variety of cancers. This investigation found that hsa_circ_0000291 expression was upregulated in gastric cancer (GC) cell lines, yet its role in GC has not yet been reported.

Objective

To explore the effects of hsa_circ_0000291 on GC cell proliferation and invasion.

Materials and methods

In the current research, we used the gastric cancer cell lines MGC803 and MKN-28 to study hsa_circ_0000291 function. The relationship between hsa_circ_0000291, miR-183 and ITGB1 was analyzed by firefly luciferase analysis and Western blots, and qRT-PCR approaches were used for protein and gene expression analysis, respectively. Tumor growth and metastasis were determined in nude mice xenografts using MKN-28 cells, with or without hsa_circ_000r0291 downregulation.

Results

Our data showed that hsa_circ_0000291 was upregulated in GC cell lines, whereas hsa_circ_0000291 silencing suppressed cell metastasis and proliferation in in vivo and in vitro studies. Our results showed that the downregulation of hsa_circ_0000291 suppressed integrin beta 1 (ITGB1) expression via miR-183 “sponging,” which was validated by rescue experiments using the luciferase reporter assay. Our observations suggested that hsa_circ_0000291 silencing suppressed the aggressive, metastatic GC phenotype.

Conclusion

Taken together, hsa_circ_0000291 knockdown inhibited GC cell metastasis and growth by regulating the miR-183/ITGB1 axis. Importantly, this approach could provide a therapy target and potential biomarker for the diagnosis and treatment of GC.

Circ-AKT3 inhibits clear cell renal cell carcinoma metastasis via altering miR-296-3p/E-cadherin signals

BACKGROUND

Circular RNA (circRNA) is a type of circular endogenous RNA produced by special selective splicing and participates in progression of diverse diseases. However, the role of circRNA in clear cell renal cell carcinoma (ccRCC) is still rarely reported.

METHODS

We detected lower circ-AKT3 expression in ccRCC using the circular RNA microarray. Then, qPCR array was applied to verify the expression of circ-AKT3 in between 60 ccRCC tissues and adjacent normal tissues, as well as ccRCC cell lines and human normal kidney cell (HK-2). We investigated the function of circ-AKT3 in ccRCC in vitro and in vivo and detected underlying mechanisms by Western blotting, bioinformatic analysis, RNA pull-down assay and luciferase reporter assay.

RESULTS

Circ-AKT3 was verified significantly downregulated in ccRCC. Knockdown of circ-AKT3 promoted ccRCC migration and invasion, while overexpression of circ-AKT3 suppressed ccRCC metastasis. Further, circ-AKT3/miR-296-3p/E-cadherin axis was shown responsible for circ-AKT3 inhibiting ccRCC metastasis.

CONCLUSION

Circ-AKT3 suppresses ccRCC metastasis by enforcing E-cadherin expression through competitively binding miR-296-3p. Circ-AKT3 may therefore serve as a novel therapeutic to better suppress ccRCC metastasis.

Tumor-suppressive circular RNAs: Mechanisms underlying their suppression of tumor occurrence and use as therapeutic targets

Circular RNAs (circRNAs) have a covalently closed circular conformation and are structurally stable. Those circRNAs with tumor-suppressive properties play an important role in tumorigenesis and metastasis and thus may be used as therapeutic targets of cancers. Herein, we review the current understanding of the classification of circRNAs and summarize the functions and mechanisms of circRNAs that have tumor-suppressive roles in various cancers, including liver cancer (circARSP91, circADAMTS13, circADAMTS14, circMTO1, hsa_circ_0079299, and circC3P1), bladder cancer (circFNDC3B, circITCH, circHIPK3, circRNA-3, cdrlas, and circLPAR1), gastric cancer (circLARP4, circYAP1, hsa_cric_0000096, hsa_circ_0000993, and circPSMC3), breast cancer (circ_000911, hsa_circ_0072309, and circASS1), lung cancer (hsa_circ_0000977, circPTK2, circ_0001649, hsa_circ_100395, and circ_0006916), glioma (circ_0001946, circSHPRH, and circFBXW7), and colorectal cancer (circITGA7 and hsa_circ_0014717). Thanks to their structural stability, these tumor-suppressive circRNAs may be used as potential and potent therapeutic targets. Moreover, we propose a new method for the classification of circRNAs. Based on whether they can be translated, circRNAs can be divided into noncoding circRNAs and coding circRNAs.

A novel circular RNA, hsa-circ-0000211, promotes lung adenocarcinoma migration and invasion through sponging of hsa-miR-622 and modulating HIF1-α expression

Recently, several studies have evaluated the role of circular RNAs in the metastasis and development of multiple cancers. In our earlier microarray-based study, we had reported the aberrant expression of a novel circular RNA, hsa-circ-0000211 in lung adenocarcinoma (LAC) tissues. However, the roles of hsa-circ-0000211 in LAC have not been studied. Here hsa-circ-0000211 expression in the LAC tissues and cell lines was determined by quantitative real-time PCR (qRT-PCR). The function of hsa-circ-0000211 was evaluated by transwell assay and wound healing. Mechanisms of hsa-circ-0000211 was measured by luciferase reporter assay and western blot. Results revealed the expression of hsa-circ-0000211 in the human LAC tissues and LAC cell lines was higher than that in normal tissue and human lung normal epithelial cells, respectively. The knockdown of hsa-circ-0000211 could inhibit the migration and invasion properties of LAC. Furthermore, hsa-circ-0000211 promoted the migration and invasion of LAC by sponging miR-622. Moreover, hsa-circ-0000211 upregulated the HIF1-α expression by targeting miR-622. hsa-circ-0000211 promoted LAC cell migration and invasion by modulating the miR-622/HIF1-α network. Our study demonstrated that hsa-circ-0000211 can be a potential novel therapeutic target for LAC.

Suppression of non-small cell lung cancer migration and invasion by hsa-miR-486-5p via the TGF-β/SMAD2 signaling pathway

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide. SMAD family member 2 (SMAD2) is a key element downstream of the transforming growth factor beta (TGF-β) signaling pathway that regulates cancer metastasis by promoting the epithelial-mesenchyme transition (EMT). MicroRNA miR-486-5p is a tumor suppressor in NSCLC progression. However, it remains unclear whether miR-486-5p is implicated in TGF-β signaling and EMT in NSCLC. In the present study, high expression of SMAD2 mRNA was detected in NSCLC tissues and cell lines, and was associated with poor survival of patients with NSCLC. By contrast, miR-486-5p was downregulated in NSCLC tissues and cell lines. In silico prediction showed that SMAD2 was a potential target of miR-486-5p. The prediction was verified using a dual-luciferase reporter assay. Transwell assays showed that knockdown of SMAD2 inhibited TGF-β-induced EMT and migration and invasion in NSCLC cells. Similarly, miR-486-5p overexpression suppressed TGF-β-induced EMT and migration and invasion of NSCLC cells. The present study provides a new insight into the role of miR-486-5p in regulating TGF-β-mediated EMT and invasion in NSCLC.

The Roles of TIF1γ in Cancer

Transcriptional intermediary factor 1 γ (TIF1γ), also known as TRIM33, RFG7, PTC7, or Ectodermin, is an E3 ubiquitin-ligase family member with a ring-box-coiled-coil region. It can regulate TGF-β/Smad signaling in two different ways in different cellular contexts. On one hand, TIF1γ can monoubiquitinate Smad4 to inhibit the formation of Smad2/3/4 nuclear complexes. On the other hand, TIF1γ can function as a cofactor of phosphorylated (p)-Smad2/3, competing with Smad4 to inhibit the formation of the Smad2/3/4 complex. In addition, TIF1γ has been reported to play a role in transcription elongation, cellular differentiation, embryonic development, and mitosis. As transforming growth factor-β (TGF-β) superfamily signaling plays an important role in the occurrence and development of cancer, and TIF1γ was reported to be involved in the regulation of TGF-β superfamily signaling, studies on TIF1γ during the last decade have focused on its role in the development of cancer. However, TIF1γ can function either as a tumor suppressor or promoter in different cellular contexts, yet there are few reviews focusing on the roles of TIF1γ in cancer. Hence, in this paper we systematically review and discuss the roles of TIF1γ in cancer. Firstly, we review the biological features, the regulatory mechanisms and the related signaling pathways of TIF1γ. Next, we illustrate the roles of TIF1γ in different tumors. We then provide a tentative hypothesis that explains the dual roles of TIF1 γ in cancer. Finally, we provide our viewpoint regarding the future developments of cancer research focusing on TIF1γ, especially in relation to the effects of TIF1γ on tumoral immunity.

MicroRNA‑133b targets TGFβ receptor I to inhibit TGF‑β‑induced epithelial‑to‑mesenchymal transition and metastasis by suppressing the TGF‑β/SMAD pathway in breast cancer

Breast cancer (BC) is one of the most common types of cancer and the leading cause of cancer-associated mortality among women worldwide. Accumulating evidence indicates that microRNA (miR)-133b inhibits the proliferation and invasion of cancer cells. Considering that transforming growth factor (TGF)-β signaling plays a key role in cellular epithelial-to-mesenchymal transition (EMT) and cancer metastasis, it is crucial to explore the roles and underlying molecular mechanisms of miR-133b in regulating TGF-β-induced EMT during progression of BC. In the present study, an inverse correlation was observed between the expression of miR-133b and TGFβ receptor I (TGFβR1) mRNA in BC cells and tissues. Furthermore, miR-133b expression was found to be decreased in the BC tissues of patients with lymph node metastasis and advanced tumor-node-metastasis stage, while the expression of TGFβR1 was upregulated. Overexpression of miR-133b significantly decreased the expression of TGFβR1, an indispensable receptor of TGF-β/SMAD signaling, and suppressed TGF-β-induced EMT and BC cell invasion in vitro, whereas miR-133b knockdown exerted the opposite effects. Mechanistically, TGFβR1 was verified as a direct target of miR-133b as determined by bioinformatics analysis and a dual-luciferase reporter assay. In addition, small interfering RNA-mediated knockdown of TGFβR1 mimicked the phenotype of miR-133b overexpression in BC cells. Furthermore, miR-133b overexpression suppressed BC cell invasion in vivo. Collectively, the findings of the present study indicated that miR-133b acts as a tumor suppressor, inhibiting TGF-β-induced EMT and metastasis by directly targeting TGFβR1, and suppressing the TGF-β/SMAD pathway. Therefore, miR-133b may be of value as a diagnostic biomarker of BC.

Functional roles of circular RNAs during epithelial-to-mesenchymal transition

Cancer has become a major health issue worldwide, contributing to a high mortality rate. Tumor metastasis is attributed to the death of most patients. Epithelial-to-mesenchymal transition (EMT) plays a vital role in inducing metastasis. During EMT, epithelial cells lose their characteristics, such as cell-to-cell adhesion and cell polarity, and cells gain motility, migratory potential, and invasive properties to become mesenchymal stem cells. Circular RNAs (circRNAs) are closely associated with tumor metastasis and patient prognosis, as revealed by increasing lines of evidence. CircRNA is a type of single-stranded RNA that forms a covalently closed continuous loop. CircRNAs are insensitive to ribonucleases and are widespread in body fluids. This work is the first review on EMT-related circRNAs. In this review, we briefly discuss the characteristics and functions of circRNAs. The correlation of circRNAs with EMT has been reported, and we discuss the ways circRNAs can regulate EMT progression through EMT transcription factors, EMT-related signaling pathways, and other mechanisms. This work summarizes current studies on EMT-related circRNAs in various cancers and provides a theoretical basis for the use of EMT-related circRNAs in targeted management and therapy.

Upregulated circRNA ARHGAP10 Predicts an Unfavorable Prognosis in NSCLC through Regulation of the miR-150-5p/GLUT-1 Axis

Non-small-cell lung cancer (NSCLC) is one of the deadliest cancers in the world. Circular RNA (circRNA) has been shown to participate in oncogenesis regulation, including lung cancer. Although the involvement of circRNAs in lung cancer has been reported, the regulatory mechanisms of circRNAs in NSCLC remain poorly understood. Thus, the present study aims at investigating the role of circARHGAP10 in NSCLC progression, which has been observed to be significantly upregulated in both NSCLC tissues and cell lines with profile analysis. A higher expression of circARHGAP10 also leads to a poor prognosis in NSCLC patients with fluorescence in situ hybridization (FISH). Both in vitro and in vivo experiments found that the downregulation of circARHGAP10 suppressed glycometabolism by decreasing GLUT1 expression. Silencing circARHGAP10 also suppressed proliferation and metastasis by targeting the miR-150-5p/GLUT1 axis in NSCLC, which was confirmed with a luciferase reporter assay. Overexpression of GLUT1 or downregulation miR-150-5p will recover NSCLC cell proliferation and metastasis after a knockdown of circARHGAP10. Taken together, these findings demonstrate that circARHGAP10 suppresses NSCLC progression by acting as a miR-150-5p sponge to promote GLUT1 expression. Thus, circARHGAP10 may be a potential target for NSCLC treatment.

Role of CircRNAs_100395 in Proliferation and Metastases of Liver Cancer

BACKGROUND Circular RNAs (circRNAs) are a kind of noncoding RNA with high cancer-specific expression, and great potential in regulating tumorigenesis. Among these, circRNA_100395 (circ_100395) has been reported to be downregulated in lung cancer, and participates in the process of tumor cell proliferation and metastasis. However, its expression and function in liver cancer remain unknown. MATERIAL AND METHODS Quantitative real-time polymerase chain reaction (RT-qPCR) was used to evaluate the expression level of circ_100395 and microRNAs-1228 (miR-1228) in liver cancer samples and the adjacent non-tumor tissues. Cell proliferation, apoptosis, invasion, migration, and epithelial-mesenchymal transition (EMT) pathway of circ_100395 upregulated cells were analyzed using a Cell Counting Kit-8 (CCK-8), flow cytometry, Transwell assay, and Western blot analysis. RESULTS We found that circ_100395 was downregulated in cancerous liver tissues relative to the adjacent normal tissues. The overexpression of circ_100395 was negatively associated with tumor differentiation, microvascular invasion, and portal vein tumor thrombosis. However, patients with higher circ_10039 expression tended to have better postoperative disease-free survival time. Moreover, upregulation of circ_100395 in liver cancer cells inhibited cell proliferation, induced apoptosis, then silenced the EMT pathway and reduced migration and invasion abilities, while this anti-tumor effect was significantly reversed by the downstream target, miR-1228. CONCLUSIONS circ_100395 appears to be a promising therapeutic target for liver cancer.

circKDM4C suppresses tumor progression and attenuates doxorubicin resistance by regulating miR-548p/PBLD axis in breast cancer

Increasing evidence has indicated that circular RNAs (circRNAs) play a critical role in cancer development. However, only a small number of circRNAs have been experimentally validated and functionally annotated. In this study, using a high-throughput microarray assay, we identified a novel circRNA, circKDM4C, which was downregulated in breast cancer tissues with metastasis. Furthermore, we analyzed a cohort of breast cancer patients and found that circKDM4C expression was decreased in breast cancer tissues, and lower circKDM4C expression was associated with poor prognosis and metastasis in breast cancer. Functionally, we demonstrated that circKDM4C significantly repressed breast cancer proliferation, metastasis, and doxorubicin resistance in vitro and in vivo. Mechanistically, using a dual-luciferase activity assay and AGO2 RNA immunoprecipitation, circKDM4C was identified as a miR-548p sponge. We also found that PBLD was a direct target of miR-548p, which functioned as a tumor suppressor in breast cancer. Moreover, miR-548p overexpression was able to reverse the circKDM4C-induced attenuation of malignant phenotypes and elevated expression of PBLD in breast cancer cells. Taken together, our data indicate that circKDM4C might have considerable potential as a prognostic biomarker in breast cancer, and support the notion that therapeutic targeting of circKDM4C/miR-548p/PBLD axis may be a promising treatment approach for breast cancer patients.

CircTRNC18 inhibits trophoblast cell migration and epithelial-mesenchymal transition by regulating miR-762/Grhl2 pathway in pre-eclampsia

Dysfunctions of epithelial-mesenchymal transition (EMT)-regulated cell migration and invasion have been involved in the pathogenesis of pre-eclampsia (PE). However, the role of circRNAs in EMT of PE has not been widely investigated. In this study, we identified that circTNRC18 was upregulated in PE placentas compared with normal pregnancy placentas. Moreover, circTNRC18 negatively regulated trophoblast cell migration and EMT. Overexpression of circTNRC18 reduced while depletion of circTNRC18 enhanced trophoblast cell migration and EMT. Mechanistically, circTNRC18 sponged miR-762 contributed to inhibit miR-762 activity and elevated EMT-related transcriptional factor Grhl2 protein level. miR-762 expression was lower in PE placentas and played a promoting role in trophoblast cell migration and EMT. In contrast, Grhl2 was highly expressed in PE placentas. Furthermore, we confirmed that upregulation of Grhl2 by circ-TNRC18-induced inhibition of miR-762 led to trophoblast cell migration and EMT. In conclusions, circTNRC18/miR-762/Grhl2 axis plays a key role in trophoblast cell migration and EMT. circTNRC18/miR-762/Grhl2 axis may be a potential therapeutic target in PE.

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.