Androgen receptor (AR) promotes clear cell renal cell carcinoma (ccRCC) migration and invasion via altering the circHIAT1/miR-195-5p/29a-3p/29c-3p/CDC42 signals

Circulating microRNAs from the Molecular Mechanisms to Clinical Biomarkers: A Focus on the Clear Cell Renal Cell Carcinoma

microRNAs (miRNAs) are emerging as relevant molecules in cancer development and progression. MiRNAs add a post-transcriptional level of control to the regulation of gene expression. The deregulation of miRNA expression results in changing the molecular circuitry in which miRNAs are involved, leading to alterations of cell fate determination. In this review, we describe the miRNAs that are emerging as innovative molecular biomarkers from liquid biopsies, not only for diagnosis, but also for post-surgery management in cancer. We focus our attention on renal cell carcinoma, in particular highlighting the crucial role of circulating miRNAs in clear cell renal cell carcinoma (ccRCC) management. In addition, the functional deregulation of miRNA expression in ccRCC is also discussed, to underline the contribution of miRNAs to ccRCC development and progression, which may be relevant for the identification and design of innovative clinical strategies against this tumor.

The power and the promise of circRNAs for cancer precision medicine with functional diagnostics and prognostic prediction

Circular RNA (circRNA) is a large class of covalently closed circular RNA. As a member of competitive endogenous RNA (ceRNA), it participates in the regulation of circRNA-miRNA-mRNA network and plays an important role in the regulation of physiology and pathology. CircRNA is produced by the reverse splicing of exon, intron or both, forming exon or intron circRNA. Studies have shown that circRNA is a ubiquitous molecule, which exceeds the linear mRNA distributed in human cells. Because of its covalent closed-loop structure, circRNA is resistant to RNase R, which is more stable than linear mRNA; circRNA is highly conserved in different species. It was found that circRNA competitively adsorbs miRNA, as a miRNA sponge, to involve in the expression regulation of a variety of genes and plays an important role in tumor development, invasion, metastasis and other processes. These molecules offer new potential opportunities for therapeutic intervention and serve as biomarkers for diagnosis. In this paper, the origin, characteristics and functions of circRNA and its role in tumor development, invasion and metastasis, diagnosis and prognosis are reviewed.

Study on HOXBs of Clear Cell Renal Cell Carcinoma and Detection of New Molecular Target

Our study examined the transcriptional and survival data of HOXBs in patients with clear cell renal cell carcinoma (ccRCC) from the ONCOMINE database, Human Protein Atlas, and STRING website. We discovered that the expression levels of HOXB3/5/6/8/9 were significantly lower in ccRCC than in normal nephritic tissues. In ccRCC, patients with a high expression of HOXB2/5/6/7/8/9 mRNA have a higher overall survival (OS) than patients with low expression. Further analysis by the GSCALite website revealed that the methylation of HOXB3/5/6/8 in ccRCC was significantly negatively correlated to gene expression, while HOXB5/9 was positively correlated to the CCT036477 drug target. As DNA abnormal methylation is one of the mechanisms of tumorigenesis, we hypothesized that HOXB5/6/8/9 are potential therapeutic targets for patients with ccRCC. We analyzed the function of enrichment data of HOXBs in patients with ccRCC from the Kyoto Encyclopedia of Genes and Genomes pathway enrichment and the PANTHER pathway. The results of the analysis show that the function of HOXBs might be associated with the Wnt pathway and that HOXB5/6/8/9 was coexpressed with multiple Wnt pathway classical genes and proteins, such as MYC, CTNNB, Cyclin D1 (CCND1), and tumor protein P53 (TP53), which further confirms that HOXBs inhibit the growth of renal carcinoma cells through the Wnt signaling pathway. In conclusion, our analysis of the family of HOXBs and their molecular mechanism may provide a theoretical basis for further research.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

Deep learning with a convolutional neural network model to differentiate renal parenchymal tumors: a preliminary study

PURPOSE

With advancements in medical imaging, more renal tumors are detected early, but it remains a challenge for radiologists to accurately distinguish subtypes of renal parenchymal tumors. We aimed to establish a novel deep convolutional neural network (CNN) model and investigate its effect on identifying subtypes of renal parenchymal tumors in T2-weighted fat saturation sequence magnetic resonance (MR) images.

METHODS

This retrospective study included 199 patients with pathologically confirmed renal parenchymal tumors, including 77, 46, 34, and 42 patients with clear cell renal cell carcinoma (ccRCC), chromophobe renal cell carcinoma (chRCC), angiomyolipoma (AML), and papillary renal cell carcinoma (pRCC), respectively. All enrolled patients underwent kidney MR scans with the field strength of 1.5 Tesla (T) or 3.0 T before surgery. We selected T2-weighted fat saturation sequence images of all patients and built a deep learning model to determine the type of renal tumors. Receiver operating characteristic (ROC) curve was depicted to estimate the performance of the CNN model; the accuracy, precision, sensitivity, specificity, F₁-score, and area under the curve (AUC) were calculated. One-way analysis of variance and χ² tests of independent samples were used to analyze the variables.

RESULTS

The experimental results demonstrated that the model had a 60.4% overall accuracy, a 61.7% average accuracy, and a macro-average AUC of 0.82. The AUCs for ccRCC, chRCC, AML, and pRCC were 0.94, 0.78, 0.80, and 0.76, respectively.

CONCLUSION

Deep CNN model based on T2-weighted fat saturation sequence MR images was useful to classify the subtypes of renal parenchymal tumors with a relatively high diagnostic accuracy.

ZEB1 represses biogenesis of circ-DOCK5 to facilitate metastasis in esophageal squamous cell carcinoma via a positive feedback loop with TGF-β

ZEB1 is an important transcription factor that plays a critical role in TGF-β-induced epithelial-mesenchymal transition (EMT) and tumor metastasis. However, the mechanisms by which ZEB1 regulates metastasis in esophageal squamous cell carcinoma (ESCC) remain largely unknown. Here, we identified a novel circular RNA, circ-DOCK5, the biogenesis of which is directly regulated by ZEB1 and ZEB1-repressed RNA-binding protein eIF4A3. Tissue microarray analysis identified circ-DOCK5 to be downregulated in ESCC tissues, and its downregulation correlated with poor prognosis. Moreover, circ-DOCK5 increased the stability of miR-627-3p by functioning as a "reservoir" for miR-627-3p to partially reverse the ZEB1-enhanced migration and invasion in ESCC. MiR-627-3p inhibited the expression of TGFB2 and the secretion of TGF-β, which further resulted in downregulation of ZEB1 and suppression of TGF-β-induced EMT. In vivo experiments showed that ZEB1 promoted metastasis in ESCC by regulating expression of circ-DOCK5. Therefore, the present study revealed that ZEB1-mediated downregulation of circ-DOCK5 facilitates metastasis in ESCC by forming a positive feedback loop with TGF-β by altering the miR-627-3p/TGFB2 signaling. Targeting this signaling pathway may help suppress progression in ESCC.

CircUBAP2 Inhibits Proliferation and Metastasis of Clear Cell Renal Cell Carcinoma via Targeting miR-148a-3p/FOXK2 Pathway

Clear cell renal cell carcinoma (ccRCC) is the prominent histological subtype of renal cell carcinoma (RCC) with high incidence of local recurrence and distant metastasis. It has been documented that circular ribonucleic acids (circRNAs) play crucial roles in the development of cancers; however, study on exploring the role of circRNAs in ccRCC still remains limited. In the present study, we aimed to evaluate the biological function of a novel circRNA UBAP2 (circUBAP2) in ccRCC and the underlying mechanism. Our results showed that circUBAP2 expression was significantly down-regulated in ccRCC tissues and cell lines. Overexpression of circUBAP2 significantly inhibited the proliferation, migration, and invasion of ccRCC cells. MiR-148a-3p was a target miRNA of circUBAP2 in ccRCC cells, and its expression levels in ccRCC tissues and cell lines were negatively correlated with circUBAP2 levels. Moreover, miR-148a-3p reversed the inhibitory effects of circUBAP2 on cell proliferation, migration, and invasion in ccRCC cells. Additionally, forkhead box K2 (FOXK2) was found to be a target gene of miR-148a-3p and regulated by miR-148a-3p in ccRCC cells. Furthermore, knockdown of FOXK2 reversed the inhibitory effects of miR-148a-3p inhibitor on ccRCC cells. In conclusion, these findings indicated that circUBAP2 functioned as a novel tumor suppressor in ccRCC through regulating the miR-148a-3p/FOXK2 axis. Therefore, circUBAP2 might serve as a potential therapeutic target for the treatment of ccRCC.

Androgen Receptor-Related Non-coding RNAs in Prostate Cancer

Prostate cancer (PCa) is the second leading cause of cancer-related death among men in the United States. Androgen receptor (AR) signaling is the dominant oncogenic pathway in PCa and the main strategy of PCa treatment is to control the AR activity. A large number of patients acquire resistance to Androgen deprivation therapy (ADT) due to AR aberrant activation, resulting in castration-resistant prostate cancer (CRPC). Understanding the molecular mechanisms underlying AR signaling in the PCa is critical to identify new therapeutic targets for PCa patients. The recent advances in high-throughput RNA sequencing (RNA-seq) techniques identified an increasing number of non-coding RNAs (ncRNAs) that play critical roles through various mechanisms in different diseases. Some ncRNAs have shown great potentials as biomarkers and therapeutic targets. Many ncRNAs have been investigated to regulate PCa through direct association with AR. In this review, we aim to comprehensively summarize recent findings of the functional roles and molecular mechanisms of AR-related ncRNAs as AR regulators or targets in the progression of PCa.

Identification of a Novel Protein-Based Signature to Improve Prognosis Prediction in Renal Clear Cell Carcinoma

Background

Clear cell renal cell carcinoma (ccRCC) is one of the most common types of malignant adult kidney cancer, and its incidence and mortality are not optimistic. It is well known that tumor-related protein markers play an important role in cancer detection, prognosis prediction, or treatment selection, such as carcinoembryonic antigen (CEA), programmed cell death 1 (PD-1), programmed cell death 1 ligand 1 (PD-L1), and cytotoxic T lymphocyte antigen 4 (CTLA-4), so a comprehensive analysis was performed in this study to explore the prognostic value of protein expression in patients with ccRCC.

Materials and Methods

Protein expression data were obtained from The Cancer Proteome Atlas (TCPA), and clinical information were downloaded from The Cancer Genome Atlas (TCGA). We selected 445 patients with complete information and then separated them into a training set and testing set. We performed univariate, least absolute shrinkage and selection operator (LASSO) Cox analyses to find prognosis-related proteins (PRPs) and constructed a protein signature. Then, we used stratified analysis to fully verify the prognostic significance of the prognostic-related protein signature score (PRPscore). Besides, we also explored the differences in immunotherapy response and immune cell infiltration level in high and low score groups. The consensus clustering analysis was also performed to identify potential cancer subgroups.

Results

From the training set, a total of 233 PRPs were selected, and a seven-protein signature was constructed, including ACC1, AR, MAPK, PDK1, PEA15, SYK, and BRAF. Based on the PRPscore, patients could be divided into two groups with significantly different overall survival rates. Univariate and multivariate Cox regression analyses proved that this signature was an independent prognostic factor for patients (P < 0.001). Moreover, the signature showed a high ability to distinguish prognostic outcomes among subgroups, and the low score group had a better prognosis (P < 0.001) and better immunotherapy response (P = 0.003) than the high score group.

Conclusion

We constructed a novel protein signature with robust predictive power and high clinical value. This will help to guide the disease management and individualized treatment of ccRCC patients.

Role of Circular RNA in Kidney-Related Diseases

The kidney is vital in maintaining fluid, electrolyte, and acid–base balance. Kidney-related diseases, which are an increasing public health issue, can happen to people of any age and at any time. Circular RNAs (circRNAs) are endogenous RNA that are produced by selective RNA splicing and are involved in progression of various diseases. Studies have shown that various kidney diseases, including renal cell carcinoma, acute kidney injury, and chronic kidney disease, are linked to circRNAs. This review outlines the characteristics and biological functions of circRNAs and discusses specific studies that provide insights into the function and potential of circRNAs for application in the diagnosis and treatment of kidney-related diseases.

circ‑0000212 promotes cell proliferation of colorectal cancer by sponging miR‑491 and modulating FOXP4 expression

Colorectal cancer (CRC) is a lethal and common malignancy worldwide. Non-coding (nc)RNAs have been shown to modulate tumor progression in several types of cancer. The present study aimed to investigate the role of hsa_circ_0000212 in CRC, as a sponge of microRNA (miR)-491. The expression levels of miR-491 and forkhead box P4 (FOXP4) were analyzed using data from The Cancer Genome Atlas. The association between miR-491 and FOXP4 and the clinicopathological characteristics were also analyzed. A novel circular (circ)RNA, hsa_circ_0000212, was found to sponge miR-491 based on bioinformatics analysis. The potential binding site between miR-491 and FOXP4 or circ-0000212 was validated using luciferase and RNA immunoprecipitation assays. The expression levels and distribution of circ-0000212 was also determined. Cell Counting Kit-8 and colony formation assays were performed to determine the role of miR-491 or circ-0000212 on the proliferation of the CRC cells. Decreased miR-491 or increased FOXP4 expression levels were associated with the pathological stage in patients with CRC. In addition, miR-491 inhibited cell proliferation by targeting FOXP4. circ-0000212 was increased in CRC tissues and was predominantly localized in the cytoplasm. Furthermore, circ-0000212 augmented viability of the CRC cells by sponging miR-491 and modulating FOXP4. In conclusion, circ-0000212 may serve as a novel tumor-promoter and drug target in CRC.

Androgen receptor decreases renal cell carcinoma bone metastases via suppressing the osteolytic formation through altering a novel circEXOC7 regulatory axis

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) has gender differences, with the androgen receptor (AR) linked positively with metastasis to the lung. Its linkage to ccRCC bone metastases (RBMs), however, remains unclear.

METHODS

In the current study, five human RCC and five RCC bone metastasis tissues were deeply sequenced using Arraystar human circRNA V2.0 microarray. We conducted gain-of-function screening in vitro and in vivo to elucidate the AR's role in the RBM. Loss/gain-of-function was also implemented to verify the roles of related non-coding RNAs and proteins.

RESULTS

We uncovered that RBM also has a gender difference showing higher AR expression may be linked to fewer RBMs, which might involve suppressing osteolytic formation. Mechanism dissection indicates that AR can decrease the circular RNA EXOC7 (circEXOC7), expression via enhancing transcription of DHX9, a regulatory protein in circRNA biogenesis. The circEXOC7 can sponge/suppress miR-149-3p resulting in suppressing the CSF1 expression by directly binding to the 3'UTR region of CSF1 mRNA. Results from clinical epidemiological surveys also found that AR has a positive correlation with miR-149-3p and a negative correlation with CSF1 in AR-positive ccRCC tissues. Preclinical studies with Balb/c nude mouse model also validated that targeting this newly verified AR/DHX9/circEXOC7/miR-149-3p/CSF1 signaling via altering circEXOC7 or AR could lead to suppressing the RBM progression.

CONCLUSIONS

These data showed that AR/DHX9/circEXOC7/miR-149-3p/CSF1 signaling acts as a valuable feature in the bone metastasis of renal cancer, which may benefit in suppressing the RBM progression.

Baicalein Represses Cervical Cancer Cell Growth, Cell Cycle Progression and Promotes Apoptosis via Blocking AKT/mTOR Pathway by the Regulation of circHIAT1/miR-19a-3p Axis

Background

Baicalein has a significant anti-cancerous function in the treatment of cervical cancer (CC). Its functional mechanism regarding circular RNA (circRNA) hippocampus abundant transcript 1 (circHIAT1) and microRNA-19a-3p (miR-19a-3p) was explored in this research.

Methods

CC cell viability and colony formation were determined using Cell Counting Kit-8 (CCK-8) and colony formation assay. Cell cycle progression and apoptosis were analyzed via flow cytometry. Protein markers of cell cycle, apoptosis and protein kinase B/mammalian target of rapamycin (AKT/mTOR) pathway were detected by Western blot. CircHIAT1 and miR-19a-3p levels were assayed through the quantitative real-time polymerase chain reaction (qRT-PCR). The interaction between circHIAT1 and miR-19a-3p was validated by dual-luciferase reporter and RNA pull-down assays. In vivo experiment was performed by xenograft model.

Results

CC cell growth and cell cycle progression were repressed while apoptosis was enhanced by baicalein. MiR-19a-3p was downregulated in baicalein-treated CC cells and miR-19a-3p overexpression lightened the baicalein-induced CC progression inhibition. Moreover, circHIAT1 was found to be a sponge of miR-19a-3p in CC cells. Baicalein-induced cell growth inhibition, cell cycle arrest and apoptosis promotion were neutralized by knockdown of circHIAT1 via targeting miR-19a-3p. Baicalein acted on the circHIAT1/miR-19a-3p to inactivate AKT/mTOR pathway. Baicalein also reduced CC tumor growth in vivo via regulating the levels of circHIAT1 and miR-19a-3p.

Conclusion

These findings demonstrated that the inhibitory function of baicalein in CC progression was dependent on the repression of AKT/mTOR pathway by upregulating circHIAT1 to sponge miR-19a-3p, showing a specific mechanism for baicalein in CC.

HOTAIR and androgen receptor synergistically increase GLI2 transcription to promote tumor angiogenesis and cancer stemness in renal cell carcinoma

Tumor angiogenesis is a major characteristic of renal cell carcinoma (RCC). Herein, we report a novel mechanism of how lncRNA and androgen receptor (AR) drive the Hedgehog pathway to promote tumor angiogenesis in RCC. We found that the high expression of lncRNA HOTAIR in RCC is associated with poor prognosis. Moreover, HOTAIR and AR form a feedback loop to promote the expression of each other. Interestingly, we also found that in RCC, HOTAIR is associated with the Hedgehog pathway, especially GLI2, via bioinformatics analysis. Furthermore, HOTAIR promotes GLI2 expression in the presence of AR. Mechanistically, HOTAIR interacts with AR and they cooperatively bind to GLI2 promoter and increase its transcription activity. We further confirmed how HOTAIR-AR axis regulates GLI2 expression by analyzing its function in RCC cells and found that HOTAIR and AR synergistically enhanced the expression of GLI2 downstream genes, such as VEGFA, PDGFA, and cancer stem cell transcription factors, and promoted tumor angiogenesis and cancer stemness in RCC cells both in vitro and in tumor xenografts. Overall, these findings suggest that HOTAIR and GLI2 could be novel therapeutic targets against RCC.

Novel biomarkers for the diagnosis and prognosis of gallbladder cancer

Gallbladder cancer (GBC) is the most common form of biliary tract malignancy with a dismal prognosis. A poor outcome in patients with GBC is related to the aggressive nature of the tumor, delayed diagnosis, and a lack of reliable biomarkers and effective treatment. Therefore, early diagnosis and accurate disease assessment are crucial to prolonging the patient survival. Identification of novel prognostic and diagnostic biomarkers may help improve the early diagnostic rate and develop specific targeted treatments for patients with GBC. We herein review the novel biomarkers that may be associated with the diagnosis and prognosis in GBC and their potential clinical significance in the management of GBC.

Review on circular RNAs and new insights into their roles in cancer

Circular RNAs (circRNAs) are a very interesting class of conserved single-stranded RNA molecules derived from exonic or intronic sequences by precursor mRNA back-splicing. Unlike canonical linear RNAs, circRNAs form covalently closed, continuous stable loops without a 5'end cap and 3'end poly(A) tail, and therefore are resistant to exonuclease digestion. The majority of circRNAs are highly abundant, and conserved across different species with a tissue or developmental-stage-specific expression. circRNAs have been shown to play important roles as microRNA sponges, regulators of gene splicing and transcription, RNA-binding protein sponges and protein/peptide translators. Emerging evidence reveals that circRNAs function in various human diseases, particularly cancers, and may function as better predictive biomarkers and therapeutic targets for cancer treatment. In consideration of their potential clinical relevance, circRNAs have become a new research hotspot in the field of tumor pathology. In the present study, the current understanding of the biogenesis, characteristics, databases, research methods, biological functions subcellular distribution, epigenetic regulation, extracellular transport and degradation of circRNAs was discussed. In particular, the multiple databases and methods involved in circRNA research were first summarized, and the recent advances in determining the potential roles of circRNAs in tumor growth, migration and invasion, which render circRNAs better predictive biomarkers, were described. Furthermore, future perspectives for the clinical application of circRNAs in the management of patients with cancer were proposed, which could provide new insights into circRNAs in the future.

Updated review on green tea polyphenol epigallocatechin-3-gallate as a cancer epigenetic regulator

In-depth insights in cancer biology over the past decades have highlighted the important roles of epigenetic mechanisms in the initiation and progression of tumorigenesis. The cancer epigenome usually experiences multiple alternations, including genome-wide DNA hypomethylation and site-specific DNA hypermethylation, various histone posttranslational modifications, and dysregulation of non-coding RNAs (ncRNAs). These epigenetic changes are plastic and reversible, and could potentially occur in the early stage of carcinogenesis preceding genetic mutation, offering unique opportunities for intervention therapies. Therefore, targeting the cancer epigenome or cancer epigenetic dysregulation with some selected agents (called epi-drugs) represents an evolving and promising strategy for cancer chemoprevention and therapy. Phytochemicals, as a class of pleiotropic molecules, have manifested great potential in modulating different cancer processes through epigenetic machinery, of which green tea polyphenol epigallocatechin-3-gallate (EGCG) is one of the most extensively studied. In this review, we first summarize epigenetic events involved in the pathogenesis of cancer, including DNA/RNA methylations, histone modifications and ncRNAs' dysregulations. We then focus on the recently discovered roles of phytochemicals, with a special emphasis on EGCG, in modulating different cancer processes through regulating epigenetic machinery. We finally discuss limitations of EGCG as an epigenetic modulator for cancer chemoprevention and treatment and offer potential strategies to overcome the shortcomings.

Hsa_circ_0123190 acts as a competitive endogenous RNA to regulate APLNR expression by sponging hsa-miR-483-3p in lupus nephritis

Background

Lupus nephritis (LN) is one of the most severe complications of systemic lupus erythematosus (SLE). Circular RNAs (circRNAs) can act as competitive endogenous RNAs (ceRNAs) to regulate gene transcription, which is involved in mechanism of many diseases. However, the role of circRNA in lupus nephritis has been rarely reported. In this study, we aim to investigate the clinical value of circRNAs and explore the mechanism of circRNA involvement in the pathogenesis of LN.

Methods

Renal tissues from three untreated LN patients and three normal controls (NCs) were used to identify differently expressed circRNAs by next-generation sequencing (NGS). Validated assays were used by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The interactions between circRNA and miRNA, or miRNA and mRNA were further determined by luciferase reporter assay. The extent of renal fibrosis between the two groups was assessed by Masson-trichome staining and immunohistochemistry (IHC) staining.

Results

159 circRNAs were significantly dysregulated in LN patients compared with NCs. The expression of hsa_circ_0123190 was significantly decreased in the renal tissues of patients with LN (P = 0.014). Bio-informatics analysis and luciferase reporter assay illustrated that hsa_circ_0123190 can act as a sponge for hsa-miR-483-3p, which was also validated to interact with APLNR. APLNR mRNA expression was related with chronicity index (CI) of LN (P = 0.033, R² = 0.452). Moreover, the fibrotic-related protein, transforming growth factor-β1 (TGF-β1), which was regulated by APLNR, was more pronounced in the LN group (P = 0.018).

Conclusion

Hsa_circ_0123190 may function as a ceRNA to regulate APLNR expression by sponging hsa-miR-483-3p in LN.

Circular RNAs as biomarkers and therapeutic targets in cancer

Circular RNAs (circRNAs) are a class of single-stranded closed non-coding RNA molecules (ncRNAs), which are formed as a result of reverse splicing of mRNAs. Despite their relative abundance, an interest in understanding their regulatory importance is rather recent. High stability, abundance and evolutionary conservation among species underline some of their important traits. CircRNAs perform a variety of cellular functions ranging from miRNA and proteins sponges to transcriptional modulation and splicing. Additionally, most circRNAs are expressed aberrantly in pathological conditions suggesting their possible exploitation as diagnostic biomarkers. Their covalent closed cyclic structure resulting in resistance to RNases further makes them suitable as cancer biomarkers. Studies involving human tumors have verified differences in the expression profiles of circRNAs, indicating a regulatory role in cancer pathogenesis and metastasis. As endogenous competitive RNA, circRNAs can regulate tumor proliferation and invasion. Further, some circRNAs located in the nucleus can regulate transcription of genes by binding to RNA polymerase II. In this review, we elaborate the characteristics, functions and mechanisms of action of circRNAs in cancer. We also discuss the possibility of using circRNAs as potential therapeutic targets and biomarkers for cancer.

CircRNA ciRS-7: a Novel Oncogene in Multiple Cancers

circular RNA ciRS-7 (ciRS-7) is a type of endogenous circular RNA (circRNA) with a closed circular structure. Since Hansen first demonstrated that ciRS-7 could serve as a microRNA sponge in 2013, researchers have paid increased attention to this circRNA. ciRS-7 plays a crucial role in regulating RNA transcription, downstream gene expression, and protein production. Moreover, ciRS-7 acts as an oncogene and promotes tumor progression through competitively inhibiting miR-7 in various types of cancers. ciRS-7 has been identified to be closely associated with breast cancer, nasopharyngeal carcinoma, lung cancer, hepatocellular carcinoma, cervical cancer, osteosarcoma, melanoma, colorectal cancer, esophageal squamous cell carcinoma, gastric cancer, pancreatic cancer, laryngeal squamous cell carcinoma, and cholangiocarcinoma. In this review, we summarize the biological characteristics, molecular mechanisms, and future challenges of ciRS-7 in multiple tumors.

Circ_101341 Deteriorates the Progression of Clear Cell Renal Cell Carcinoma Through the miR- 411/EGLN3 Axis

Background

Clear cell renal cell carcinoma (ccRCC) is one of the main subtypes of renal cell carcinoma, with intense aggressiveness. The involvement of circular RNAs (circRNAs) in human cancers attracts much concern. The intention of this study was to investigate the expression of circ_101341 and explore its function in ccRCC.

Materials and Methods

The expression of circ_101341, miR-411 and Egl nine homolog 3 (EGLN3) was measured using quantitative real-time polymerase chain reaction (qRT-PCR). Cell proliferation was assessed by cell counting kit-8 (CCK-8) assay and colony formation assay. Cell migration and invasion were monitored by transwell assay. Xenograft model was established to explore the role of circ_101341 in vivo. The protein levels of E-cadherin (E-cad), N-cadherin (N-cad), matrix metalloprotein-9 (MMP9) and EGLN3 were detected by Western blot. Bioinformatic analysis was conducted using Circinteractome and starBase. The targeted relationship was verified using dual-luciferase reporter assay, RNA-binding protein immunoprecipitation (RIP) assay and RNA pull-down assay.

Results

The expression of circ_101341 was elevated in ccRCC tissues and cells. Functionally, circ_101341 knockdown depleted proliferation, migration and invasion of ccRCC cells in vitro and restricted tumor growth in vivo. Circ_101341 directly targeted miR-411, and miR-411 inhibition revised the inhibitory effects of circ_101341 knockdown on proliferation, migration and invasion in ccRCC cells. Moreover, miR-411 directly bound to EGLN3, and EGLN3 overexpression also rescued the effects of circ_101341 knockdown.

Conclusion

Circ_101341 functioned as a tumor promoter to strengthen proliferation, migration and invasion by regulating EGLN3 via sponging miR-411, indicating that circ_101341 was a potential diagnostic and therapeutic biomarker of ccRCC.

Circ-ZDHHC5 Accelerates Esophageal Squamous Cell Carcinoma Progression in vitro via miR-217/ZEB1 Axis

Circular RNA (circRNA) exhibits a covalently closed circular conformation and is structurally stable. Nevertheless, the precise effects exerted by circRNA in esophageal squamous cell carcinoma (ESCC) remains uncertain. circRNA was ascertained by a human circRNA array study and was confirmed by the quantification of reverse transcriptase polymerase reactions. A luciferase reporter, fluorescence in situ hybridization experiment was exploited to explore the interaction between circ-ZDHHC5 and miR-217. The function of circ-ZDHHC5 was determined by siRNA-mediated knockout of circ-ZDHHC5 in in vitro proliferation, migration, and invasion. circ-ZDHHC5, rather than linear ZDHHC5 mRNA, rose in the tissues of patients with ESCC, plasma, and ESCC cell lines in comparison with normal controls. Knockdown of circ-ZDHHC5 inhibited tumorigenesis in ESCC cells, and the co-transfection of si-circ-ZDHHC5 and miR-217 mimics further enhanced the above effect. Noticeably, the present study showed that circ-ZDHHC5 was an miR-217 sponge that modulated the expression of zinc finger E-box binding homeobox 1 (ZEB1), further facilitating ESCC tumorigenesis. As revealed by this study, circ-ZDHHC5 can act as a new potential circular biomarker for detecting ESCC. It provides a novel perceptivity for the treatment of ESCC suggesting that circ-ZDHHC5 could impact on ESCC progression by sponging miR-217 with ZEB1.

Identification of prognostic chromatin-remodeling genes in clear cell renal cell carcinoma

The aim of this study was to investigate the effects of chromatin-remodeling genes on the prognosis of patients with clear cell renal cell carcinoma (ccRCC). In TCGA-KIRC patients, two subgroups based on 86 chromatin-remodeling genes were established. The random forest algorithm was used for feature selection to identify BPTF, SIN3A and CNOT1 as characterized chromatin remodelers in ccRCC with good prognostic value. YY1 was indicated to be a transcription factor of genes highly related to BPTF, SIN3A and CNOT1. Functional annotations indicated that BPTF, SIN3A, CNOT1 and YY1 are all involved in the ubiquitin-mediated proteolysis process and that high expression of any of the five associated E3 ubiquitin ligases found in the pathway suggests a good prognosis. Protein network analysis indicated that BPTF has a targeted regulatory effect on YY1. Another independent dataset from International Cancer Genome Consortium (ICGC) showed a strong consistency with results in TCGA. In conclusion, we demonstrate that BPTF, SIN3A and CNOT1 are novel prognostic factors that predict good survival in ccRCC. We predicted that the good prognostic value of chromatin-remodeling genes BPTF and SIN3A is related to the regulation of YY1 and that YY1 regulates E3 ubiquitin ligases for further degradation of oncoproteins in ccRCC.

Upregulated circPDK1 Promotes RCC Cell Migration and Invasion by Regulating the miR-377-3P-NOTCH1 Axis in Renal Cell Carcinoma

Background

Circular RNAs (circRNAs) are novel clusters of endogenous noncoding RNAs (ncRNAs) that are involved in the regulation of multiple biological processes in diverse types of cancers. However, the roles and precise mechanisms of circRNAs in renal cell carcinoma (RCC) occurrence and progression have not been clearly elucidated.

Methods

We identified the aberrantly expressed circRNAs in RCC by high-throughput RNA-seq assay and used qRT-PCR to test the expression level of circRNAs in RCC tissues. Loss-of-function experiments were executed to detect the biological roles of circPDK1 in the RCC cells both in vivo and in vitro. RNA Fish, luciferase reporter assays and Western blotting were used to explore the molecular mechanism of circPDK1 function. All data were expressed as the means ± standard error of the mean (SEM). Student’s t-test, one-way ANOVA, Cox regression, an LSD-t-test, Pearson’s chi-squared test, a Log-rank test, and linear regression analyses were used to evaluate the group differences. P < 0.05 was considered significant.

Results

CircPDK1 was overexpressed in RCC tissues and positively associated with patient tumor metastasis and renal cell invasion. The in vivo functional assays also revealed that circPDK1 drove RCC xenograft metastasis. CircPDK1 was mainly located in the cytoplasm, serving as a sponge of miR-377-3P to regulate RCC invasion and metastasis through NOTCH1 (Notch Homolog 1). Ectopic express of NOTCH1 in RCC cell lines will block the metastasis inhibition effect after circPDK1 knockdown.

Conclusion

CircPDK1 is aberrantly expressed in RCC and promotes the metastasis of RCC cells mainly through sponging miR-377-3P and reducing its negative regulation of NOTCH1. Thus, circPDK1 may act as a therapeutic target and biomarker for RCC.

Liquid Biopsies in Renal Cell Carcinoma-Recent Advances and Promising New Technologies for the Early Detection of Metastatic Disease

Clear cell renal cell carcinoma (ccRCC) displays a highly varying clinical progression, from slow growing localized tumors to very aggressive metastatic disease (mRCC). Almost a third of all patients with ccRCC show metastatic dissemination at presentation while another third develop metastasis during the course of the disease. Survival rates of mRCC patients remain low despite the development of novel targeted treatment regimens. Biomarkers indicating disease progression could help to define its aggressive potential and thus guide patient management. However, molecular markers that can reliably assess metastatic dissemination and disease recurrence in ccRCC have not been recommended for clinical practice to date. Liquid biopsies could provide an attractive and non-invasive method to determine the risk of recurrence or metastatic dissemination during follow-up and thus assist the search for surveillance biomarkers in ccRCC tumors. A wide spectrum of circulating molecules have already shown considerable potential for ccRCC diagnosis and prognostication. In this review, we outline state of the art of the key circulating analytes such as cfDNA, cfRNA, proteins, and exosomes that may serve as biomarkers for the longitudinal monitoring of ccRCC progression to metastasis. Moreover, we address some of the prevailing limitations in the past approaches and present promising adoptable technologies that could help to pursue the implementation of liquid biopsies as a prognostic tool for mRCC.

Circular RNA circ_0000039 enhances gastric cancer progression through miR-1292-5p/DEK axis

BACKGROUND

Circular RNA (circRNA) is a class of non-coding RNA that is vital for regulating gene expression and biological functions. Mounting studies demonstrate that circRNA is crucial for human cancer development. However, the role of circ_0000039 in gastric cancer (GC) remains uncertain.

METHODS

Normal human gastric tissues and GC tissue samples were collected, and quantitative real-time polymerase chain reaction (qRT-PCR) was employed to detect the expression levels of circ_0000039, miR-1292-5p, and DEK. GC cell lines with overexpression and low expression of circ_0000039 were constructed. Cell counting kit-8 (CCK-8), scratch healing and Transwell experiments were used to assess the function of circ_0000039 on the proliferation, migration and invasion of GC cells. Bioinformatics analysis and dual-luciferase reporter assays were employed to detect the targeting relationship between circ_0000039 and miR-1292-5p.

RESULTS

Circ_0000039 expression was up-regulated in GC tissues and cell lines, and it was significantly related with poor differentiation of tumor tissues. In addition, circ_0000039 overexpression enhanced the proliferation, migration and invasion of GC cells, while circ_0000039 depletion inhibited these malignant biological behaviors. In terms of mechanism, it was found that circ_0000039 promoted the proliferation and progression of GC cells by adsorbing miR-1292-5p and up-regulating the expression of DEK.

CONCLUSION

Circ_0000039 is a new oncogenic circRNA in GC, which regulates the miR-1292-5p/DEK axis to modulate the malignant biological behaviors of GC.

Circular RNAs in renal cell carcinoma: implications for tumorigenesis, diagnosis, and therapy

Renal cell carcinoma (RCC) is the most common malignant kidney tumor and has a high incidence rate. Circular RNAs (circRNAs) are noncoding RNAs with widespread distribution and diverse cellular functions. They are highly stable and have organ- and tissue-specific expression patterns. CircRNAs have essential functions as microRNA sponges, RNA-binding protein- and transcriptional regulators, and protein translation templates. Recent reports have shown that circRNAs are abnormally expressed in RCC and act as important regulators of RCC carcinogenesis and progression. Moreover, circRNAs have emerged as potential biomarkers for RCC diagnosis and prognosis and targets for developing new treatments. However, further studies are needed to better understand the functions of circRNAs in RCC. In this review, we summarize and discuss the recent research progress on RCC-associated circRNAs, with a focus on their potential for RCC diagnosis and targeted therapy.

Prognostic Role of Circular RNAs Expression in Bladder Carcinoma: A Meta-Analysis

Background: Circular RNAs (circRNAs), a type of noncoding RNA, are associated with the occurrence and development of cancers. In recent years, their potential as biomarkers for bladder cancer (BC) has attracted increased attention. Aims: To reveal the value of circRNAs in the prognosis of BC. Methods: Relevant studies were collected to extract the clinicopathological data and overall survival (OS) of patients with BC. We then evaluated their tumor-related clinicopathological indicators using pooled odds ratio (OR) and 95% confidence interval (CI). Hazard ratio (HR) and 95% CI were used to estimate the OS of BC patients who expressed abnormal circRNAs. Results: The results indicate that seven circRNAs (circMYLK, circASXL1, hsa_circ_0000144, circ-VANGL1, circGprc5a, circZFR, and circ-cTFRC) whose expression was upregulated in tumor tissues, are associated with poor clinicopathological features (tumor/node/metastasis [TNM] stage: OR = 4.86, 95% CI: 2.53-9.34; histological grade: OR = 3.71, 95% CI: 2.37-5.79; lymph node metastasis: OR = 3.23; 95% CI: 2.15-4.88; recurrence: OR = 5.33; 95% CI: 2.27-12.52) and poor prognoses (OS: HR = 1.69; 95% CI: 1.17-2.44). We also found that seven circRNAs (circMTO1, circ-ITCH, circUBXN7, circFNDC3B, circ-ZKSCAN1, circPICALM, and circACVR2A) that were downregulated in tumors were associated with better clinicopathological indicators (TNM stage: OR = 0.23, 95% CI: 0.14-0.38; histological grade: OR = 0.21, 95% CI: 0.13-0.33; lymph node metastasis: OR = 0.26; 95% CI: 0.15-0.47) and better prognoses (OS: HR = 0.42; 95% CI: 0.30-0.58). Conclusion: Our results suggest that certain circRNAs are related to the clinicopathological characteristics and prognosis of BC patients, and may potentially be used as biomarkers.

The crosstalk between circular RNAs and the tumor microenvironment in cancer metastasis

Background

Carcinomas are highly heterogeneous with regard to various cancer cells within a tumor microenvironment (TME), which is composed of stromal cells, blood vessels, immunocytes, and modified extracellular matrix.

Focus of the study

Circular RNAs (circRNAs) are non-coding RNAs that are expressed in cancer and stromal cells. They are closely associated with cancer metastasis as their expression in tumor cells directs the latter to migrate to different organs. circRNAs packaged in exosomes might be involved in this process. This is particularly important as the TME acts in tandem with cancer cells to enhance their proliferation and metastatic capability. In this review, we focus on recent studies on the crosstalk between circRNAs and the TME during cancer metastasis.

Conclusion

We particularly emphasize the roles of the interaction between circRNAs and the TME in anoikis resistance, vessel co-option, and local circRNA expression in directing homing of exosome.

Circular RNA Sequencing Identifies CircASAP1 as a Key Regulator in Hepatocellular Carcinoma Metastasis

BACKGROUND AND AIMS

There is growing evidence that single-stranded, circular RNA (circRNA) plays a key role in the development of certain cancers, including hepatocellular carcinoma (HCC). It is less clear, however, what role circRNA plays in HCC metastasis.

APPROACH AND RESULTS

In this study, through circRNA sequencing, we identified a circRNA: circASAP1 (a circRNA derived from exons 2 and 3 of the ASAP1 gene, hsa_circ_0085616), which is associated with pulmonary metastasis after curative resection in patients with HCC. CircASAP1 was overexpressed in HCC cell lines with high metastatic potential and in metastatic HCCs. In vitro, circASAP1 promoted cell proliferation, colony formation, migration, and invasion, and in vivo, it enhanced tumor growth and pulmonary metastasis. Mechanism studies showed that circASAP1 acts as a competing endogenous RNA for microRNA 326 (miR-326) and microRNA 532-5p (miR-532-5p), both of which are tumor suppressors in HCC. We found that mitogen-activated protein kinase (MAPK) 1 and colony stimulating factor (CSF)-1 were direct common targets for microRNA 326 (miR-326) and microRNA 532-5p (miR-532-5p), which were regulated by circASAP1. CircASAP1 promotes HCC cell proliferation and invasion by regulating miR-326/miR-532-5p-MAPK1 signaling and, furthermore, mediates tumor-associated macrophage infiltration by regulating the miR-326/miR-532-5p-CSF-1 pathway. Clinical HCC samples exhibited a positive correlation between circASAP1 expression and levels of CSF-1, MAPK1, and CD68+ tumor-associated macrophages, all of which were predictive of patient outcomes.

CONCLUSION

We identified circASAP1 as a key regulator of HCC metastasis that acts on miR-326/miR-532-5p-MAPK1/CSF-1 signaling and serves as a prognostic predictor in patients with HCC.

ZEB1-Mediated Transcriptional Upregulation of circWWC3 Promotes Breast Cancer Progression through Activating Ras Signaling Pathway

Zinc finger E-box binding homeobox 1 (ZEB1) has been widely recognized as an important driver of tumor growth and metastasis. However, nothing is known about ZEB1-regulated circular (circ)RNAs in cancer. In the current study, we evaluated the function of a novel ZEB1-regulated circRNA derived from the WWC3 gene locus, circWWC3 in breast cancer progression. We found that ZEB1 upregulated circWWC3 expression but not the linear WWC3 mRNA expression. circWWC3 is highly expressed in breast cancer tissues and is associated with the poor prognosis of breast cancer patients. Silencing of circWWC3 significantly suppresses the proliferation, migration, and invasion of breast cancer cells. Mechanically, circWWC3 upregulates multiple oncogenes' expression of the Ras signaling pathway through acting as the sponge of microRNA (miR)-26b-3p and miR-660-3p. Moreover, short hairpin (sh)RNA-mediated knockdown of circWWC3 partially antagonized ZEB1-mediated breast cancer growth and metastasis in vivo. Our findings reveal that ZEB1-mediated upregulation of circWWC3 promotes breast cancer progression through activating Ras signaling pathway, which provides a potential therapeutic target and prognostic biomarker for breast cancer.

Circular RNA DHX33 promotes malignant behavior in ccRCC by targeting miR-489-3p/MEK1 axis

Mounting evidence indicates that circular RNAs modulate the initiation of clear cell renal cell carcinoma (ccRCC). However, their specific roles in the malignancy of ccRCC is understudied. Here, we present a novel circular RNA, circDHX33, that is up-regulated in ccRCC cell lines and tissues. Upregulated circDHX33 in ccRCC patients significantly correlates with advanced TNM stage and metastasis. Suppressing circDHX33 expression inhibits the proliferation and invasion of cultured cells, and suppresses tumor growth in vivo. Mechanistically, we show that circDHX33 promotes ccRCC progression by sponging miR-489-3p and modulating MEK1 expression. In conclusion, our findings suggest that circDHX33 plays a role in promoting ccRCC via the miR-489-3p/MEK1 axis and may serve as a novel therapeutic target for the treatment of ccRCC patients

Coordinated AR and microRNA regulation in prostate cancer

The androgen receptor (AR) remains a key driver of prostate cancer (PCa) progression, even in the advanced castrate-resistant stage, where testicular androgens are absent. It is therefore of critical importance to understand the molecular mechanisms governing its activity and regulation during prostate tumourigenesis. MicroRNAs (miRs) are small ∼22 nt non-coding RNAs that regulate target gene, often through association with 3′ untranslated regions (3′UTRs) of transcripts. They display dysregulation during cancer progression, can function as oncogenes or tumour suppressors, and are increasingly recognised as targets or regulators of hormonal action. Thus, understanding factors which modulate miRs synthesis is essential. There is increasing evidence for complex and dynamic bi-directional cross-talk between the multi-step miR biogenesis cascade and the AR signalling axis in PCa. This review summarises the wealth of mechanisms by which miRs are regulated by AR, and conversely, how miRs impact AR's transcriptional activity, including that of AR splice variants. In addition, we assess the implications of the convergence of these pathways on the clinical employment of miRs as PCa biomarkers and therapeutic targets.

Multidrug resistance protein 4 (MRP4/ABCC4) is overexpressed in clear cell renal cell carcinoma (ccRCC) and is essential to regulate cell proliferation

Kidney cancer accounts for 2.5% of all cancers, with an annual global incidence of almost 300,000 cases leading to 111,000 deaths. Approximately 85% of kidney tumors are renal cell carcinoma (RCC) and their major histologic subtype is clear cell renal cell carcinoma (ccRCC). Although new therapeutic treatments are being designed and applied based on the combination of tyrosine kinase inhibitors and immunotherapy, no major impact on the mortality has been reported so far. MRP4 is a pump efflux that transporters multiple endogenous and exogenous substances. Recently it has been associated with tumoral persistence and cell proliferation in several types of cancer including pancreas, lung, ovary, colon, ostesarcoma, etc. Herein, we demonstrate for the first time, that MRP4 is overexpressed in ccRCC tumors, compared to control renal tissues. In addition, using cell culture models, we observed that MRP4 pharmacological inhibition produces an imbalance in cAMP metabolism, induces cell arrest, changes in lipid composition, increase in cytoplasmic lipid droplets and finally apoptosis. These data provide solid evidence for the future evaluation of MRP4 as a possible new therapeutic target in ccRCC.

MicroRNA profile in stage I clear cell renal cell carcinoma predicts progression to metastatic disease

OBJECTIVE

This study sought to identify microRNA (miRNA) profiles of small, pathologically confirmed stage 1 clear cell renal cell carcinoma (ccRCC) tumors that are associated with progression to metachronous metastatic disease.

MATERIALS AND METHODS

Fifty-five pathologic stage 1 ccRCC tumors ≤5cm, from 2 institutions, were examined in a miRNA screening, followed by a validation study. For the screening phase 752 miRNA were evaluated on each sample to identify those with differential expression between tumors that subsequently did (n = 10) or did not (n = 10) progress to metastatic disease. For the validation, 35 additional samples (20 nonprogressors and 15 with distant progression) were utilized to investigate 20 miRNA to determine if a miRNA panel could differentiate aggressive tumors: associations of miRNA expression with cancer specific survival was also investigated.

RESULTS

In the screening analysis, 35 miRNA were differentially expressed (P < 0.05, FDR < 0.1) between the groups. In the validation, 11 miRNA were confirmed to have differential expression. The miRNA -10a-5p, -23b-3p, and -26a-5p differentiated nonprogressive and distant progressive disease with a sensitivity of 73.3% and a specificity of 85% (AUC=0.893). In addition, levels of miR-30a-3p and -145-5p were identified as independent prognostic factors of cancer specific survival.

CONCLUSIONS

This investigation identified miRNA biomarkers that may differentiate between non-progressive ccRCC tumors and those that progress to metastatic disease in this group of stage I tumors. The miRNA profiles determined in this study have the potential to identify patients with small renal masses who are likely to have progressive ccRCC. Such information may be valuable to incorporate into predictive models.

CircTLK1 promotes the proliferation and metastasis of renal cell carcinoma by sponging miR-136-5p

BACKGROUND

Circular RNAs (circRNAs), a novel type of noncoding RNA (ncRNA), are covalently linked circular configurations that form via a loop structure. Accumulating evidence indicates that circRNAs are potential biomarkers and key regulators of tumor development and progression. However, the precise roles of circRNAs in renal cell carcinoma (RCC) remain unknown.

METHODS

Through circRNA high-throughput sequencing of RCC cell lines, we identified the circRNA TLK1 (circTLK1) as a novel candidate circRNA derived from the TLK1 gene. qRT-PCR detected the mRNA, circRNA and miRNA expression levels in RCC tissues and cells. Loss-of function experiments were executed to detect the biological roles of circTLK1 in the RCC cell phenotypes in vitro and in vivo. RNA-FISH, RNA pull-down, dual-luciferase reporter, western blot and immunohistochemistry assays were used to investigate the molecular mechanisms underlying the functions of circTLK1.

RESULTS

circTLK1 is overexpressed in RCC, and expression is positively correlated with distant metastasis and unfavorable prognosis. Silencing circTLK1 significantly inhibited RCC cell proliferation, migration and invasion in vitro and in vivo. circTLK1 was mainly distributed in the cytoplasm and positively regulated CBX4 expression by sponging miR-136-5p. Forced CBX4 expression reversed the circTLK1 suppression-induced phenotypic inhibition of RCC cells. Moreover, CBX4 expression was positively correlated with VEGFA expression in RCC tissues. CBX4 knockdown significantly inhibited VEGFA expression in RCC cells.

CONCLUSION

Collectively, our findings demonstrate that circTLK1 plays a critical role in RCC progression by sponging miR-136-5p to increase CBX4 expression. circTLK1 may act as a diagnostic biomarker and therapeutic target for RCC.

CTBP1‑AS2 inhibits proliferation and induces autophagy in ox‑LDL‑stimulated vascular smooth muscle cells by regulating miR‑195‑5p/ATG14

Atherosclerosis (AS) is a chronic progressive disease caused by injury and functional changes in vascular smooth muscle cells (VSMCs). Long non‑coding RNAs (lncRNAs) are pivotal regulators in AS development. The present study aimed to explore the roles and molecular mechanisms of lncRNA CTBP1‑AS2 in AS progression. A dual‑luciferase reporter assay confirmed that miR‑195‑5p is a downstream target miRNA of lncRNA CTBP1‑AS2 and miR‑195‑5p was increased in AS. The expression levels of miR‑195‑5p and CTBP1‑AS2 in the serums of patients with AS and human aorta vascular smooth muscle cells was increased or decreased, respectively, following treatment with oxidized low‑density lipoprotein (ox‑LDL). Functional experiments showed that the overexpression of lncRNA CTBP1‑AS2 inhibited the proliferation of HA‑VSMCs and promoted their autophagy following ox‑LDL treatment. This effect could be reversed by treatment with ROC‑325, the inhibitor of autophagy, or miR‑195‑5p mimics. Autophagy related 14 (ATG14) was identified to be a target of miR‑195‑5p, and lncRNA CTBP1‑AS2 promoted ATG14 expression by serving as a competing endogenous RNA of miR‑195‑5p. The present study revealed that lncRNA CTBP1‑AS2 may serve a role in AS by inhibiting the proliferation and promoting the autophagy of VSMCs through ATG14 modulation via miR‑195‑5p. These data may provide a novel therapeutic target for AS.

Circular RNA in renal diseases

Circular RNA (circRNA) is a newly described type of non-coding RNA. Active research is greatly enriching the current understanding of the expression and role of circRNA, and a large amount of evidence has implicated circRNA in the pathogenesis of certain renal diseases, such as renal cell carcinoma, acute kidney injury, diabetic nephropathy and lupus nephritis. Studies have found evidence that circRNAs regulate programmed cell death, invasion, and metastasis and serve as biomarkers in renal diseases. Recently, circRNAs were identified in exosomes secreted by the kidneys. Nevertheless, the function of circRNA in renal diseases remains ambiguous. Given that circRNAs are regulators of gene expression, they may be involved in the pathology of multiple renal diseases. Additionally, emerging evidence is showing that circulating circRNAs may serve as novel biomarkers for renal disease. In this review, we have summarized the identification, biogenesis, degradation, and functions of circRNA and have evaluated the roles of circRNA in renal diseases.

Circ-100290 Positively Regulates Angiogenesis Induced by Conditioned Medium of Human Amnion-Derived Mesenchymal Stem Cells Through miR-449a/eNOS and miR-449a/VEGFA Axes

The powerful pro-angiogenic capacity of human amnion-derived mesenchymal stem cells (hAMSCs) could be a valuable therapeutic angiogenesis strategy for bone regeneration. However, the molecular mechanisms underlying this process remain largely unknown. Herein, we report upregulated expression of circular RNA 100290 (circ-100290) and an enhanced angiogenic phenotype of human umbilical vein endothelial cells (HUVECs) incubated with conditioned medium from hAMSCs (hAMSC-CM), whereas downregulation of circ-100290 reversed the pro-angiogenic capacity of HUVECs induced by hAMSC-CM. Circ-100290/microRNA 449a (miR-449a)/endothelial nitric oxide synthase (eNOS) and circ-100290/miR-449a/vascular endothelial growth factor A (VEGFA) axes were predicted by a bioinformatics method and subsequently verified by luciferase reporter assays in vitro. Gain- or loss-of-function assays were then performed using small interfering RNAs (siRNAs) targeting circ-100290, or a plasmid overexpressing circ-100290. As expected, downregulation of circ-100290 in HUVECs led to weakened tube formation and migration of HUVECs following hAMSC-CM treatment, along with decreased expression of eNOS and VEGFA. In contrast, upregulation of circ-100290 led to enhanced tube formation and migration of HUVECs following hAMSC-CM treatment, along with increased expression of eNOS and VEGFA. Furthermore, a miR-449a inhibitor could largely rescue the effect of circ-100290 silencing on HUVECs, whereas a miR-449a mimic could significantly rescue the effect of overexpressing circ-100290 on HUVECs. Functional assays using eNOS or VEGF receptor inhibitors indicated eNOS and VEGFA may be important targets of miR-449a. Finally, a Matrigel plug assay revealed weakened angiogenesis when circ-100290 was silenced in HUVECs, but enhanced angiogenesis when circ-100290 was overexpressed in vivo. Our results suggest that circ-100290 might function via miR-449a/eNOS and miR-449a/VEGFA axes in the pro-angiogenic role of hAMSC-CM on HUVECs.

Long non-coding RNA PCAT1 drives clear cell renal cell carcinoma by upregulating YAP via sponging miR-656 and miR-539

Clear cell renal cell carcinoma (ccRCC) is the most common RCC subtype with high metastasis, poor prognosis and conventional chemotherapy resistance. Prostate cancer associated transcript 1 (PCAT1) is an important lncRNA that was reported to be involved in cell proliferation, migration and invasion of several types of cancer cells. However, its role in ccRCC is still undetermined. This study found that PCAT1 levels were elevated in ccRCC tumors as well as several ccRCC cells, and knockdown of PCAT1 with siRNA (si-PCAT1) alleviated cell proliferation, migration and invasion of Caki-2 and ACHN cells. With bioinformatics analysis, dual-luciferase reported assay, RNA pull-down assay and Spearman's correlation analysis, we demonstrated that PCAT1 acted as a sponge for miR-656 and miR-539. Moreover, we found dual competitive interaction of miR-656/539 with PCAT1 and yes-associated protein (YAP), resulting in the identification of PCAT1-miR-656/539-YAP axis in Caki-2 and ACHN cells. With CCK-8 assay and transwell assay, miR-656/539 inhibitor or YAP overexpression could alleviate the effects of si-PCAT1 on the proliferation, migration and invasion of Caki-2 and ACHN cells. Our data indicated that PCAT1 promotes proliferation, migration and invasion of ccRCC cells by upregulating YAP via sponging miR-656 and miR-539. Taken together, this study provided a novel therapeutic target for ccRCC treatment.

Profiling and bioinformatics analyses reveal chronic lymphocytic leukemia cells share a unique circular RNA expression pattern

Approximately 10% of the human transcriptome is composed of circular RNAs (circRNAs). These are non-coding RNA molecules in which a covalent bond between the 3' and 5' forms a stable circular loop. Herein, we profiled the expression of 13,368 cricRNAS in 21 patients with chronic lymphocytic leukemia (CLL). Regardless of clinical, genetic, or prognostic characteristics, CLL cells share a unique expression profile distinguishable from that of normal B cells. Specifically, 859 circRNAs from 592 genes were differentially expressed (fold change ≥2 and false discovery rate ≤0.05). Whether dysregulation of circRNAs contributes to the pathogenesis of CLL remains to be determined.

circPRRC2A promotes angiogenesis and metastasis through epithelial-mesenchymal transition and upregulates TRPM3 in renal cell carcinoma

Background: Circular RNAs (circRNAs) have been identified as essential regulators in a plethora of cancers. Nonetheless, the mechanistic functions of circRNAs in Renal Cell Carcinoma (RCC) remain largely unknown.

Methods: In this study, we aimed to identify novel circRNAs that regulate RCC epithelial-mesenchymal transition (EMT), and to subsequently determine their regulatory mechanisms and clinical significance.

Results: circPRRC2A was identified by circRNA microarray and validated by qRT-PCR. The role of circPRRC2A in RCC metastasis was evaluated both in vitro and in vivo. We found that increased expression of circPRRC2A is positively associated with advanced clinical stage and worse survivorship in RCC patients. Mechanistically, our results indicate that circPRRC2A prevents the degradation of TRPM3, a tissue-specific oncogene, mRNA by sponging miR-514a-5p and miR-6776-5p. Moreover, circPRRC2A promotes tumor EMT and aggressiveness in patients with RCC.

Conclusions: These findings infer the exciting possibility that circPRRC2A may be exploited as a therapeutic and prognostic target for RCC patients.

Progress of research into circular RNAs in urinary neoplasms

Circular RNAs (circRNAs) are a large class of endogenous RNA that form a covalently closed continuous loop without 5′ or 3′ tails and are diffusely expressed in mammalian cells. Through the development of high-throughput sequencing, microarray, and bioinformatics analyses, recent studies have shown that the expression of circRNAs is dysregulated in human tumor tissues and cells, as well as in the blood of patients, and closely correlates with the development of tumors. circRNAs can regulate the progression of tumors through various mechanisms. An increasing number of studies have shown that circRNAs may play critical roles in the early diagnosis, targeted therapy, and prognostic prediction of cancer as biomarkers or therapeutic targets. This review briefly describes the definitions and functions of circRNAs, and the main content includes the most recent progress in research into their function, regulation, and clinical relevance to bladder, renal, and prostate cancers. We also provide some novel ideas regarding the treatment of these diseases.

Circular RNA circHIAT1 inhibits proliferation and epithelial-mesenchymal transition of gastric cancer cell lines through downregulation of miR-21

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide. Circular RNA circHIAT1 has been proved to play an antitumor role. We aimed to explore the function and mechanism of circHIAT1 in GC. MKN28 and MKN45 cells were transfected with PLCDH-circHIAT1, miR-21 mimic, and relative control. Cell viability and apoptosis were examined through Cell Counting Kit-8 and flow cytometry, respectively. CircHIAT1 expression and other relative factors were tested through quantitative reverse transcription-polymerase chain reaction and Western blot analysis, respectively. Our findings demonstrated that circHIAT1 was lowly expressed in GC tissues. After transfection with PLCDH-circHIAT1 in MKN28 and MKN45 cells, cell viability was decreased, while the expression levels of p53 and p21 were raised, as well as apoptosis. Besides this, the epithelial-mesenchymal transition process was inhibited by PLCDH-circHIAT1 transfection. Mechanistically, miR-21 expression was upregulated in GC tissues and could be negatively regulated by circHIAT1. Further experiments showed that the addition of miR-21 mimic reversed the growth inhibition effects of circHIAT1 overexpression. Moreover, circHIAT1 inhibited the activation of phosphatase and tensin homolog/phosphatidylinositol 3 kinase/protein kinase B and extracellular signal-regulated kinase signal pathways via downregulating miR-21. CircHIAT1 functioned as a tumor inhibitor in GC cells through downregulating miR-21, and could be a novel target for GC treatment.

The circular RNA hsa-circ-0072309 plays anti-tumour roles by sponging miR-100 through the deactivation of PI3K/AKT and mTOR pathways in the renal carcinoma cell lines

Aims: To explore the roles and regulatory mechanisms of the circular RNA (circRNA)-hsa-circ-0072309 in CAKI-1 and ACHN cells. Methods: CAKI-1 and ACHN cells were transfected with hsa-circ-0072309 overproduction vector (circRNA) and microRNA-100 (miR-100) mimic or the corresponding controls. Cell viability was detected with the CCK-8. The protein expression levels of p53, c-Myc, cleaved-caspase-3/9, matrix metalloproteinase (MMP)-2/9, vimentin, AKT, PI3K and mTOR were individually determined through western blot. qRT-PCR was used to examine the expressions of hsa-circ-0072309 and miR-100. The apoptotic rate and the migration or invasion rates were separately determined by the annexin v-FITC/PI with a flow cytometer and modified two-chamber migration assay or millicell hanging cell culture. Results: The hsa-circ-0072309 was poorly expressed in tumor tissue. Abundant hsa-circ-0072309 induced the inhibitions of cell proliferation, migration and invasion, as well as the PI3K/AKT and the mTOR cascades but enhancement of apoptosis. circRNA stimulated the down-regulation of miR-100, which was low-expressed in tumour tissue and whose overproduction abolished the impacts of circRNA on these elements mentioned above. Conclusion: The hsa-circ-0072309 played anti-tumour roles by targeting miR-100 by blocking the PI3K/AKT and mTOR cascades in the CAKI-1 and ACHN cell lines.

CircPRMT5 circular RNA promotes proliferation of colorectal cancer through sponging miR-377 to induce E2F3 expression

CircPRTM5 is associated with cell proliferation and migration in many kinds of malignancies. However, the functions and mechanisms of CircPRTM5 in CRC progression remain unclear. We explored the role and the mechanisms of CircPRTM5 in the development of CRC. Tissues of CRC patients and matched adjacent non‐tumour tissues were collected to evaluate the expression of CircPRTM5. The expression of CircPRTM5 in CRC tissues was significantly higher than that in adjacent tissues. The biological functions of CircPRTM5 in CRC were determined by overexpression and down‐regulation of CircPRTM5 in CRC cells in vitro and in vivo. The results indicate that knockdown of CircPRTM5 can significantly inhibit the proliferation of CRC cells. The potential mechanisms of CircPRTM5 in CRC development were identified by RT‐qPCR, Western blotting analysis and luciferase reporter assay. CircPRTM5 competitively regulates the expression of E2F3 by capillary adsorption of miR‐377. CircPRMT5 regulates CRC proliferation by regulating the expression of E2F3, which affects the expression of the cell cycle‐associated proteins cyclinD1 and CDK2. CircPRTM5 exerts critical regulatory role in CRC progression by sponging miR‐377 to induce E2F3 expression.

Circular RNA hsa_circ_001895 serves as a sponge of microRNA-296-5p to promote clear cell renal cell carcinoma progression by regulating SOX12

There is an urgent need to find novel potential therapeutic targets for the diagnosis and treatment of clear cell renal cell carcinoma (ccRCC) due to its highly invasive ability as a common urological malignant tumor. Circular RNAs (circRNAs) have been indicated as potentially critical mediators in various types of tumor progression. We first used qRT-PCR analysis to find dysregulated circRNAs in ccRCC. A novel circRNA, hsa_circ_001895, was upregulated in ccRCC specimens and associated with metastatic properties of ccRCC. However, the tumorigenic mechanism of hsa_circ_001895 on ccRCC is yet to be found. We first indicated that hsa_circ_001895 predicted a poor prognosis in ccRCC patients. Additionally, overexpression of hsa_circ_001895 not only promoted cell proliferation, invasion and migration of ccRCC, but also inhibited cell apoptosis, whereas hsa_circ_001895 knockdown reversed the effect on ccRCC progression. In vivo s.c. xenotransplanted tumor model also showed that silencing hsa_circ_001895 could suppress in vivo ccRCC growth. Mechanistically, hsa_circ_001895 directly binds with microRNA (miR)-296-5p and inhibits its expression. Moreover, sex determining region Y (SRY)-box 12 (SOX12) was identified as a target of miR-296-5p, the expression of which was suppressed by miR-296-5p. Notably, the inhibitory effect of hsa_circ_001895 on ccRCC progression was reversed by miR-296-5p inhibitor. In general, our findings indicated that hsa_circ_001895 may sponge miR-296-5p and promote SOX12 expression, which is the underlying mechanism of hsa_circ_001895-induced ccRCC progression.

Roles of circRNAs in the tumour microenvironment

The tumour microenvironment (TME) constitutes the area surrounding the tumour during its development and has been demonstrated to play roles in cancer-related diseases through crosstalk with tumour cells. Circular RNAs (circRNAs) are a subpopulation of endogenous noncoding RNAs (ncRNAs) that are ubiquitously expressed in eukaryotes and have multiple biological functions in the regulation of cancer onset and progression. An increasing number of studies have shown that circRNAs participate in the multifaceted biological regulation of the TME. However, details on the mechanisms involved have remained elusive until now. In this review, we analyse the effects of circRNAs on the TME from various perspectives, including immune surveillance, angiogenesis, hypoxia, matrix remodelling, exo-circRNAs and chemoradiation resistance. Currently, the enormous potential for circRNA use in targeted therapy and as noninvasive biomarkers have drawn our attention. We emphasize the prospect of targeting circRNAs as an essential strategy to regulate TME, overcome cancer resistance and improve therapeutic outcomes.

Upregulation of Circular RNA circATRNL1 to Sensitize Oral Squamous Cell Carcinoma to Irradiation

Accumulating evidence has demonstrated that circular RNAs (circRNAs) play important roles in regulating gene expression involved in tumor development. However, the role of circRNAs in modulating the radiosensitivity of oral squamous cell carcinoma (OSCC) and its potential mechanisms have not been documented. We performed high-throughput RNA sequencing (RNA-seq) to investigate the circRNA expression profile in OSCC patients and discovered that the circATRNL1 expression was significantly downregulated and closely related to tumor progression. The circATRNL1 was structurally validated via Sanger sequencing, RNase R treatment, and specific convergent and divergent primer amplification. Importantly, the expression levels of circATRNL1 decreased after irradiation treatment, and upregulation of circATRNL1 enhanced the radiosensitivity of OSCC through suppressing proliferation and the colony survival fraction, inducing apoptosis and cell-cycle arrest. Moreover, we observed that circATRNL1 could directly bind to microRNA-23a-3p (miR-23a-3p) and relieve inhibition for the target gene PTEN. In addition, the tumor radiosensitivity-promoting effect of circATRNL1 overexpression was blocked by miR-23a-3p in OSCC. Further experiments also showed that PTEN can reverse the inhibitory effect of OSCC radiosensitivity triggered by miR-23a-3p. We concluded that circANTRL1 may function as the sponge of miR-23a-3p to promote PTEN expression and eventually contributes to OSCC radiosensitivity enhancement. This study indicates that circANTRL1 may be a novel therapeutic target to improve the efficiency of radiotherapy in OSCC.