CircRNA circ_0026344 as a prognostic biomarker suppresses colorectal cancer progression via microRNA-21 and microRNA-31

Advanced approaches of the use of circRNAs as a replacement for cancer therapy

Cancer is a broad name for a group of diseases in which abnormal cells grow out of control and are characterized by their complexity and recurrence. Although there has been progress in cancer therapy with the entry of precision medicine and immunotherapy, cancer incidence rates have increased globally. Non-coding RNAs in the form of circular RNAs (circRNAs) play crucial roles in the pathogenesis, clinical diagnosis, and therapy of different diseases, including cancer. According to recent studies, circRNAs appear to serve as accurate indicators and therapeutic targets for cancer treatment. However, circRNAs are promising candidates for cutting-edge cancer therapy because of their distinctive circular structure, stability, and wide range of capabilities; many challenges persist that decrease the applications of circRNA-based cancer therapeutics. Here, we explore the roles of circRNAs as a replacement for cancer therapy, highlight the main challenges facing circRNA-based cancer therapies, and discuss the key strategies to overcome these challenges to improve advanced innovative therapies based on circRNAs with long-term health effects.

Advanced strategies of targeting circular RNAs as therapeutic approaches in colorectal cancer drug resistance

Colorectal cancer (CRC) stands second in terms of mortality and third among the highest prevalent kinds of cancer globally. CRC prevalence is rising in moderately and poorly developed regions and is greater in economically advanced regions. Despite breakthroughs in targeted therapy, resistance to chemotherapeutics remains a significant challenge in the long-term management of CRC. Circular RNAs (circRNAs) have been involved in growing cancer therapy resistance, particularly in CRC, according to an increasing number of studies in recent years. CircRNAs are one of the novel subclasses of non-coding RNAs, previously thought of as viroid. According to studies, circRNAs have been recommended as biological markers for therapeutic targets and diagnostic and prognostic purposes. That is particularly notable given that the expression of circRNAs has been linked to the hallmarks of CRC since they are responsible for drug resistance in CRC patients; thereby, circRNAs are significant for chemotherapy failure. Moreover, knowledge concerning circRNAs remains relatively unclear despite using all these advanced techniques. Here, in this study, we will go over the most recent published work to highlight the critical roles of circRNAs in CRC development and drug resistance and highlight the main strategies to overcome drug resistance to improve clinical outcomes.

Insights into the molecular mechanisms and signalling pathways of epithelial to mesenchymal transition (EMT) in colorectal cancer: A systematic review and bioinformatic analysis of gene expression

Colorectal cancer (CRC) is ranked as the second leading cause of mortality worldwide, mainly due to metastasis. Epithelial to mesenchymal transition (EMT) is a complex cellular process that drives CRC metastasis, regulated by changes in EMT-associated gene expression. However, while numerous genes have been identified as EMT regulators through various in vivo and in vitro studies, little is known about the genes that are differentially expressed in CRC tumour tissue and their signalling pathway in regulating EMT. Using an integration of systematic search and bioinformatic analysis, gene expression profiles of CRC tumour tissues were compared to non-tumour adjacent tissues to identify differentially expressed genes (DEGs), followed by performing systematic review on common identified DEGs. Fifty-eight common DEGs were identified from the analysis of 82 tumour tissue samples obtained from four gene expression datasets (NCBI GEO). These DEGS were then systematically searched for their roles in modulating EMT in CRC based on previously published studies. Following this, 10 common DEGs (CXCL1, CXCL8, MMP1, MMP3, MMP7, TACSTD2, VIP, HPGD, ABCG2, CLCA4) were included in this study and subsequently subjected to further bioinformatic analysis. Their roles and functions in modulating EMT in CRC were discussed in this review. This study enhances our understanding of the molecular mechanisms underlying EMT and uncovers potential candidate genes and pathways that could be targeted in CRC.

Non-coding RNAs as Biomarkers for Survival in Colorectal Cancer Patients

Colorectal cancer (CRC) has a high incidence and fatality rate worldwide. It ranks second concerning death worldwide. Cancer patients are diagnosed with the disease at a later stage due to the absence of early diagnostic methods, which leads to increased death. With the help of recent advancements in the fields of diagnosis and therapy, the development of novel methods using new targets could be helpful for the long-term survival of CRC patients when CRC is detected early. However, the prognosis for the advanced stage of CRC is abysmal. New biomarkers are emerging as promising alternatives since they can be utilized for early detection of CRC, are simple to use, and non-invasive. Non-coding RNAs (ncRNAs) have been seen to have an aberrant expression in the development of many malignancies, including CRC. In the past two decades, much research has been done on non-coding RNAs, which may be valuable as biomarkers and targets for antitumor therapy. Non-coding RNAs can be employed in detecting and treating CRC. Non-coding RNAs play an essential role in regulating gene expression. This article reviews ncRNAs and their expression levels in CRC patients that could be used as potential biomarkers. Various ncRNAs have been associated with CRC, such as microRNAs, long non-coding RNAs, circular RNAs, etc. The expression of these non-coding RNAs may provide insights into the stages of cancer and the prognosis of cancer patients and therefore proper precautionary measures can be taken to decrease cancer-related deaths.

Circ_0005615 Regulates the Progression of Colorectal Cancer Through the miR-873-5p/FOSL2 Signaling Pathway

To determine the effects of circ_0005615 in CRC development and underneath mechanism. The expression levels of circ_0005615, microRNA-873-5p (miR-873-5p) and FOS-like antigen 2 (FOSL2) mRNA were determined by quantitative real-time polymerase chain reaction (qRT-PCR). The protein levels of exosome makers, proliferation-related makers and FOSL2 were detected by western blot or immunohistochemistry assay. Cell proliferation was evaluated by cell counting kit-8 (CCK-8) and cell colony formation assays. Cell migration and invasion were demonstrated by a transwell assay. Cell apoptosis was investigated by flow cytometry analysis. The binding relationship between miR-873-5p and circ_0005615 or FOSL2 was predicted by circular RNA interactome and targetscan online databases, respectively, and identified by dual-luciferase reporter assay. The impacts of circ_0005615 silencing on tumor formation were determined by in vivo tumor formation assay. Circ_0005615 expression was dramatically upregulated in serum exosomes of CRC patients compared with the control group. The CRC patients with a high circ_0005615 expression had a poor survival rate. Circ_0005615 and FOSL2 expressions were apparently increased, while miR-873-5p was decreased in CRC tissues or cells relative to control groups. Circ_0005615 knockdown inhibited cell proliferation, migration, and invasion, whereas promoted cell apoptosis in CRC; however, miR-873-5p inhibitor attenuated these impacts. Additionally, circ_0005615 acted as a sponge of miR-873-5p and miR-873-5p bound to FOSL2. FOSL2 overexpression restrained the effects of miR-873-5p mimic on CRC progression. Furthermore, circ_0005615 knockdown suppressed tumor growth in vivo. Circ_0005615 modulated CRC malignant progression by controlling FOSL2 expression through sponging miR-873-5p. This finding lays a foundation for the study on circRNA-mediated CRC therapy.

Characterization of cell-type specific circular RNAs associated with colorectal cancer metastasis

Colorectal cancer (CRC) is the most common gastrointestinal malignancy and a leading cause of cancer deaths in the United States. More than half of CRC patients develop metastatic disease (mCRC) with an average 5-year survival rate of 13%. Circular RNAs (circRNAs) have recently emerged as important tumorigenesis regulators; however, their role in mCRC progression remains poorly characterized. Further, little is known about their cell-type specificity to elucidate their functions in the tumor microenvironment (TME). To address this, we performed total RNA sequencing (RNA-seq) on 30 matched normal, primary and metastatic samples from 14 mCRC patients. Additionally, five CRC cell lines were sequenced to construct a circRNA catalog in CRC. We detected 47 869 circRNAs, with 51% previously unannotated in CRC and 14% novel candidates when compared to existing circRNA databases. We identified 362 circRNAs differentially expressed in primary and/or metastatic tissues, termed circular RNAs associated with metastasis (CRAMS). We performed cell-type deconvolution using published single-cell RNA-seq datasets and applied a non-negative least squares statistical model to estimate cell-type specific circRNA expression. This predicted 667 circRNAs as exclusively expressed in a single cell type. Collectively, this serves as a valuable resource, TMECircDB (accessible at https://www.maherlab.com/tmecircdb-overview), for functional characterization of circRNAs in mCRC, specifically in the TME.

Non-coding RNA-based therapeutics in cancer therapy: An emphasis on Wnt/β-catenin control

Non-coding RNA transcripts are RNA molecules that have mainly regulatory functions and they do not encode proteins. microRNAs (miRNAs), lncRNAs and circRNAs are major types of this family and these epigenetic factors participate in disease pathogenesis, especially cancer that their abnormal expression may lead to cancer progression. miRNAs and lncRNAs possess a linear structure, whereas circRNAs possess ring structures and high stability. Wnt/β-catenin is an important factor in cancer with oncogenic function and it can increase growth, invasion and therapy resistance in tumors. Wnt upregulation occurs upon transfer of β-catenin to nucleus. Interaction of ncRNAs with Wnt/β-catenin signaling can determine tumorigenesis. Wnt upregulation is observed in cancers and miRNAs are able to bind to 3'-UTR of Wnt to reduce its level. LncRNAs can directly/indirectly regulate Wnt and in indirect manner, lncRNAs sponge miRNAs. CircRNAs are new emerging regulators of Wnt and by its stimulation, they increase tumor progression. CircRNA/miRNA axis can affect Wnt and carcinogenesis. Overall, interaction of ncRNAs with Wnt can determine proliferation rate, migration ability and therapy response of cancers. Furthermore, ncRNA/Wnt/β-catenin axis can be utilized as biomarker in cancer and for prognostic applications in patients.

Colon cancer transcriptome

Over the last four decades, methodological innovations have continuously changed transcriptome profiling. It is now feasible to sequence and quantify the transcriptional outputs of individual cells or thousands of samples using RNA sequencing (RNA-seq). These transcriptomes serve as a connection between cellular behaviors and their underlying molecular mechanisms, such as mutations. This relationship, in the context of cancer, provides a chance to unravel tumor complexity and heterogeneity and uncover novel biomarkers or treatment options. Since colon cancer is one of the most frequent malignancies, its prognosis and diagnosis seem to be critical. The transcriptome technology is developing for an earlier and more accurate diagnosis of cancer which can provide better protectivity and prognostic utility to medical teams and patients. A transcriptome is a whole set of expressed coding and non-coding RNAs in an individual or cell population. The cancer transcriptome includes RNA-based changes. The combined genome and transcriptome of a patient may provide a comprehensive picture of their cancer, and this information is beginning to affect treatment decision-making in real-time. A full assessment of the transcriptome of colon (colorectal) cancer has been assessed in this review paper based on risk factors such as age, obesity, gender, alcohol use, race, and also different stages of cancer, as well as non-coding RNAs like circRNAs, miRNAs, lncRNAs, and siRNAs. Similarly, they have been examined independently in the transcriptome study of colon cancer.

Clinical Value of Circulating miRNA in Diagnosis, Prognosis, Screening and Monitoring Therapy of Pancreatic Ductal Adenocarcinoma-A Review of the Literature

Pancreatic cancer (PC) is considered to be the seventh most common cause of cancer-related deaths. The number of deaths caused by PC is estimated to increase in the future. An early diagnosis of PC is crucial for improving treatment outcomes. The most common histopathological subtype of PC is pancreatic ductal adenocarcinoma (PDAC). MicroRNAs (miRNAs)-which are endogenous non-coding RNAs involved in the posttranscriptional regulation of multiple gene expression-constitute useful diagnostic and prognostic biomarkers in various neoplasms, including PDAC. Circulating miRNAs detected in a patient's serum or plasma are drawing more and more attention. Hence, this review aims at evaluating the clinical value of circulating miRNA in the screening, diagnosis, prognosis and monitoring of pancreatic ductal adenocarcinoma therapy.

Biological functions, mechanisms, and clinical significance of circular RNA in colorectal cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide due to the lack of effective diagnosis and prognosis biomarkers and therapeutic targets, resulting in poor patient survival rates. Circular RNA (circRNA) is a type of endogenous non-coding RNA (ncRNA) with a closed-loop structure that plays a crucial role in physiological processes and pathological diseases. Recent studies indicate that circRNAs are involved in the diagnosis, prognosis, drug resistance, and development of tumors, particularly in CRC. Therefore, circRNA could be a potential new target for improving CRC diagnosis, prognosis, and treatment. This review focuses on the origin and biological functions of circRNA, summarizes recent research on circRNA's role in CRC, and discusses the potential use of circRNAs as clinical biomarkers for cancer diagnosis and prognosis, as well as therapeutic targets for CRC treatment.

Identifying potential microRNA biomarkers for colon cancer and colorectal cancer through bound nuclear norm regularization

Colon cancer and colorectal cancer are two common cancer-related deaths worldwide. Identification of potential biomarkers for the two cancers can help us to evaluate their initiation, progression and therapeutic response. In this study, we propose a new microRNA-disease association identification method, BNNRMDA, to discover potential microRNA biomarkers for the two cancers. BNNRMDA better combines disease semantic similarity and Gaussian Association Profile Kernel (GAPK) similarity, microRNA function similarity and GAPK similarity, and the bound nuclear norm regularization model. Compared to other five classical microRNA-disease association identification methods (MIDPE, MIDP, RLSMDA, GRNMF, AND LPLNS), BNNRMDA obtains the highest AUC of 0.9071, demonstrating its strong microRNA-disease association identification performance. BNNRMDA is applied to discover possible microRNA biomarkers for colon cancer and colorectal cancer. The results show that all 73 known microRNAs associated with colon cancer in the HMDD database have the highest association scores with colon cancer and are ranked as top 73. Among 137 known microRNAs associated with colorectal cancer in the HMDD database, 129 microRNAs have the highest association scores with colorectal cancer and are ranked as top 129. In addition, we predict that hsa-miR-103a could be a potential biomarker of colon cancer and hsa-mir-193b and hsa-mir-7days could be potential biomarkers of colorectal cancer.

Prognostic significance of hsa_circ_0048122 to predict liver metastasis in early‐stage colorectal cancer

Background

Liver metastasis is the primary cause of lethal colorectal cancer (CRC). The predominant risk of poor patient prognosis in early‐stage CRC emerges as metachronous liver metastasis. This necessitates the search for potential biomarkers for this metastasis to assess treatment outcomes and provide targeted therapy.

Methods

The role of hsa_circ_0048122 in predicting liver metastasis in CRC was probed in this work. This retrospective and multi‐center investigation entailed exploration and identification stages with 158 and 176 patients. While RT‐qPCR was employed to scrutinize hsa_circ_0048122 expression, Kaplan–Meier survival, and multivariate analyses were used to probe its prognostic impact in early‐stage CRC and stage IV CRC cases, respectively.

Results

A strong correlation between liver metastases and hsa_circ_0048122 expression in stage IV CRC patients with a high hsa_circ_0048122 profile indicated a poor overall survival. Likewise, a high expression level of hsa_circ_0048122 appears as a potential predictor of liver metastases in patients' initial stages.

Conclusions

Predicting liver metastasis can be plausibly facilitated using Hsa_circ_0048122 as a biomarker in early‐stage CRC cases.

Quercetin Inhibits Tumorigenesis of Colorectal Cancer Through Downregulation of hsa_circ_0006990

Quercetin can significantly inhibit the progression of colorectal cancer (CRC). However, its specific mechanism remains largely unclear. In this study, we aimed to explore the correlation among quercetin, tumour-associated macrophages (TAMs) and circular RNAs (circRNAs) in the progression of CRC and to present a novel strategy for the treatment of CRC. In this study, we revealed that quercetin could suppress the autophagy of M2-TAMs and induced their differentiation into M1-TAMs, by which quercetin significantly reversed the inhibition of M2-TAMS on CRC cell apoptosis and the promotion of M2-TAMS on CRC cell proliferation. Moreover, quercetin could promote the expression of downregulated hsa_circ_0006990 in CRC cells co-cultured with M2-TAMs, and the overexpression of hsa_circ_0006990 significantly reversed the anti-tumour effect of quercetin on CRC. Furthermore, we found quercetin can notably suppress the progression of CRC via mediation of the hsa_circ_0006990/miR-132-3p/MUC13 axis. In conclusion, our results suggested that quercetin inhibits the tumorigenesis of CRC via inhibiting the polarisation of M2 macrophages and downregulating hsa_circ_0006990. Our study provides useful insights for those exploring new methods of treating CRC.

Hsa_circ_0006732 regulates colorectal cancer cell proliferation, invasion and EMT by miR-127-5p/RAB3D axis

Colorectal cancer (CRC) remains a malignancy tumor with high metastasis and poor prognosis. We aimed to explore the effect of circular RNA (circRNA) hsa_circ_0006732 in the progression of CRC. Hsa_circ_0006732 expression in CRC tissues and cell lines were detected using qRT-PCR. The relationship between hsa_circ_0006732 expression and clinicopathologic characteristics of patients with CRC was analyzed. Loss-of-function assay was conducted to determine the regulatory effect of hsa_circ_0006732 on CRC cell proliferation, migration and invasion by using the CCK-8, wound-healing assay and transwell assays. Protein expression changes on epithelial mesenchymal transition (EMT)-related factors were detected by western blotting. The downstream signaling pathway was investigated by bioinformatics, dual-luciferase reporter assay. Rescue assay was further examined for prediction validation. It was found that hsa_circ_0006732 was highly expressed in CRC tissues and cell lines. Downregulation of hsa_circ_0006732 suppressed the proliferation, migration, invasion and EMT of CRC cells. Further mechanistic investigations proved that hsa_circ_0006732 functioned as a competitive endogenous RNA (ceRNA) by directly sponging of miR-127-3p, which further affected the expression of Ras-related protein Rab-3D (Rab3D). Taken together, these findings indicated that hsa_circ_0006732 might be an oncogene in CRC through the regulation of the miR-127-5p/RAB3D axis. Thus, hsa_circ_0006732 might serve as a potential therapeutic target for the treatment of CRC.

Circular RNAs as Diagnostic and Prognostic Indicators of Colorectal Cancer: A Pooled Analysis of Individual Studies

Background: Circular RNAs (circRNAs) have proven as a special subset of endogenous RNAs that are implicated in the tumorigenesis of various cancers. This study sought to evaluate the role of circRNAs in the diagnosis and prognosis of colorectal cancer (CRC).

Methods: The online databases were searched for collecting relevant studies on circRNAs as diagnostic and prognostic biomarkers of CRC. Two researchers independently screened literature, extracted data, and evaluated the bias and risks of included studies. The diagnostic and prognostic indicators were merged and analyzed using STATA 12.0 software, and sources of heterogeneity were traced by the sensitivity analysis and the meta-regression test.

Results: A total of 29 articles representing 2639 CRC patients were included. The pooled sensitivity, specificity, and area under the curve (AUC) of circRNAs in differentiating CRC from non-tumor control were 0.75 (95% CI: 0.69–0.80) and 0.74 (95% CI: 0.69–0.78) and 0.81, respectively. The survival analysis showed that up-regulations of up-regulated circRNAs were significantly related to dismal survival in CRC patients (HR = 2.38, p < 0.001). A stratified analysis showed that the comprehensive diagnostic value of up-regualted circRNAs in CRC was higher than that of down-regualted circRNAs (AUC: 0.83 vs. 0.77; Z test, p < 0.05). The efficacy of tissue-derived circRNAs in the diagnosis of CRC was equal to that of plasma/serum-derived ones (AUC: 0.81 vs. 0.82; Z test, p > 0.05).

Conclusion: Abnormally expressed circRNAs as auxiliary biomarkers present underlying value in the diagnosis and prognosis prediction of CRC.

Expression and clinical significance of circular RNA hsa_circ_0003416 in pediatric pulmonary arterial hypertension associated with congenital heart disease

Background

Circular RNAs (circRNAs) have been found to be involved in the development of pulmonary arterial hypertension (PAH). However, their diagnostic value in pediatric PAH remains unclear. This study aimed to examine the characteristic expression of the circRNA hsa_circ_0003416 in the plasma of children with PAH caused by congenital heart disease (CHD); the potential of hsa_circ_0003416 as a diagnostic biomarker was also investigated.

Methods

The plasma expression levels of hsa_circ_0003416 were determined via quantitative reverse transcription–polymerase chain reaction in 50 CHD patients, 50 PAH patients, and 20 healthy subjects; the associations between hsa_circ_0003416 levels and clinical data were analyzed thereafter. Receiver operating characteristic curves were employed to determine the diagnostic capacity of this circRNA.

Results

Expression levels of hsa_circ_0003416 in plasma were lower in the PAH‐CHD group than in the CHD and healthy control groups (p = 0.009 vs. healthy control group, p = 0.026 vs. CHD group). Moreover, hsa_circ_0003416 was found to be negatively associated with B‐type natriuretic peptide (r = −0.342, p = 0.013). In addition, the area under the curve of hsa_circ_0003416 levels in plasma was 0.721 (95% confidence intervals = 0.585–0.857, p = 0.004), suggesting that it has a promising diagnostic value.

Conclusions

Overall, hsa_circ_0003416 was found to be significantly downregulated in children with PAH‐CHD and to be potent as a biomarker for PAH‐CHD diagnosis.

Non-coding RNAs and glioblastoma: Insight into their roles in metastasis

Glioma, also known as glioblastoma multiforme (GBM), is the most prevalent and most lethal primary brain tumor in adults. Gliomas are highly invasive tumors with the highest death rate among all primary brain malignancies. Metastasis occurs as the tumor cells spread from the site of origin to another site in the brain. Metastasis is a multifactorial process, which depends on alterations in metabolism, genetic mutations, and the cancer microenvironment. During recent years, the scientific study of non-coding RNAs (ncRNAs) has led to new insight into the molecular mechanisms involved in glioma. Many studies have reported that ncRNAs play major roles in many biological procedures connected with the development and progression of glioma. Long ncRNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are all types of ncRNAs, which are commonly dysregulated in GBM. Dysregulation of ncRNAs can facilitate the invasion and metastasis of glioma. The present review highlights some ncRNAs that have been associated with metastasis in GBM. miRNAs, circRNAs, and lncRNAs are discussed in detail with respect to their relevant signaling pathways involved in metastasis.

Non-Coding RNAs in Colorectal Cancer: Their Functions and Mechanisms

Colorectal cancer (CRC) is a common malignancy with high mortality. However, the molecular mechanisms underlying CRC remain unclear. Controversies over the exact functions of non-coding RNAs (ncRNAs) in the progression of CRC have been prevailing for multiple years. Recently, accumulating evidence has demonstrated the regulatory roles of ncRNAs in various human cancers, including CRC. The intracellular signaling pathways by which ncRNAs act on tumor cells have been explored, and in CRC, various studies have identified numerous dysregulated ncRNAs that serve as oncogenes or tumor suppressors in the process of tumorigenesis through diverse mechanisms. In this review, we have summarized the functions and mechanisms of ncRNAs (mainly lncRNAs, miRNAs, and circRNAs) in the tumorigenesis of CRC. We also discuss the potential applications of ncRNAs as diagnostic and prognostic tools, as well as therapeutic targets in CRC. This review details strategies that trigger the recognition of CRC-related ncRNAs, as well as the methodologies and challenges of studying these molecules, and the forthcoming clinical applications of these findings.

MicroRNAs and 'Sponging' Competitive Endogenous RNAs Dysregulated in Colorectal Cancer: Potential as Noninvasive Biomarkers and Therapeutic Targets

The gastrointestinal (GI) tract in mammals is comprised of dozens of cell types with varied functions, structures, and histological locations that respond in a myriad of ways to epigenetic and genetic factors, environmental cues, diet, and microbiota. The homeostatic functioning of these cells contained within this complex organ system has been shown to be highly regulated by the effect of microRNAs (miRNA). Multiple efforts have uncovered that these miRNAs are often tightly influential in either the suppression or overexpression of inflammatory, apoptotic, and differentiation-related genes and proteins in a variety of cell types in colorectal cancer (CRC). The early detection of CRC and other GI cancers can be difficult, attributable to the invasive nature of prophylactic colonoscopies. Additionally, the levels of miRNAs associated with CRC in biofluids can be contradictory and, therefore, must be considered in the context of other inhibiting competitive endogenous RNAs (ceRNA) such as lncRNAs and circRNAs. There is now a high demand for disease treatments and noninvasive screenings such as testing for bloodborne or fecal miRNAs and their inhibitors/targets. The breadth of this review encompasses current literature on well-established CRC-related miRNAs and the possibilities for their use as biomarkers in the diagnoses of this potentially fatal GI cancer.

Knockdown of circRAD23B Exerts Antitumor Response in Colorectal Cancer via the Regulation of miR-1205/TRIM44 axis

BACKGROUND

Colorectal cancer (CRC) is a common cancer with high metastatic property. Circular RNAs (circRNAs) have important involvement in cancer processes. This study focused on the regulation of circRNA RAD23 homologue B (circRAD23B) in CRC.

METHODS

The levels of circRAD23B, microRNA-1205 (miR-1205), and tripartite motif-44 (TRIM44) were examined by quantitative real-time polymerase chain reaction (qRT-PCR). Functional analyses were performed by Cell Counting Kit-8 (CCK-8) for cell proliferation, flow cytometry for cell cycle or cell apoptosis, and transwell assay for cell migration and invasion. Western blot was administrated for protein detection. The interaction of targets was analyzed by dual-luciferase reporter and RNA pull-down assays. The in vivo experiment was conducted via xenograft tumor in mice.

RESULTS

We identified that circRAD23B was overexpressed in CRC tissues and cells. CRC cell proliferation, cell cycle progression, and cell metastasis were inhibited, while apoptosis was promoted by downregulating circRAD23B. Target analysis indicated that circRAD23B-targeted miR-1205 and TRIM44 were downstream genes of miR-1205. Moreover, the antitumor response of circRAD23B downregulation and miR-1205 overexpression was, respectively, achieved by increasing miR-1205 and decreasing TRIM44. CircRAD23B could regulate TRIM44 level by sponging miR-1205. In vivo, circRAD23B knockdown also reduced CRC tumorigenesis via the miR-1205/TRIM44 axis.

CONCLUSION

These results suggested that the inhibition of circRAD23B retarded the progression of CRC via acting on the miR-1205/TRIM44 axis. CircRAD23B might be a novel target in CRC treatment.

Establishment of a novel prognostic signature based on an identified expression profile of integrin superfamily to predict overall survival of patients with colorectal adenocarcinoma

The abnormal expression of integrin superfamily members commonly related to kinds of malignancies. However, the role of integrins in predicting the prognosis of cancers is still little known, especially for colorectal cancer that is one of the leading causes of cancer-related death. RNA-seq data and clinical features of colorectal adenocarcinoma (COAD) patients were derived from The Cancer Genome Atlas (TCGA), used to analyze the expression pattern and genomic alterations of integrin genes in the COAD cohort. Unsupervised hierarchical clustering divided COAD patients into two clusters (clusters 1 & 2), and we observed that patients in cluster 2 with high expressions of most integrin genes had worse clinical features and shorter overall survival (a median OS: 67.25 months vs 99.93 months, p = 0.012), compared to those in cluster 1. Combined with univariate Cox regression analysis, Pearson Correlation Coefficients (PCC), and Principal Component Analysis (PCA), an integrin-related signature was established, including ITGA1, ITGA5, ITGA7, ITGA11, ITGAX, ITGAM, ITGB1, and ITGB5. And the AUC values for OS at 1, 3, and 5 years was 0.61, 0.59, and 0.56, further demonstrating the predicting capacity of our signature. Furthermore, overexpression of which also significantly correlated with poorer prognosis of colon cancer patients in a separate validation cohort, GSE17536 (p < 0.05). Meanwhile, the AUC values for OS in the validation cohort at 1, 3, and 5 years was 0.62, 0.59, and 0.59. Additionally, enrichment analysis indicated significant differences between cluster 1 and cluster 2 in the biological processes of cell adhesion, signal transduction, extracellular matrix, immune system, and in tumor microenvironment (TME), which were crucial to the progression of tumor. The findings supplied compelling evidence that our signature could be a novel prognostic biomarker for COAD patients, and these genes had the potential to be therapeutic targets.

The circ-PITX1 promotes non-small cell lung cancer development via the miR-30e-5p/ITGA6 axis

Non-small cell lung cancer (NSCLC) is one of the most prevalent tumors with high incidence and mortality across the globe. Recently, increasing studies have demonstrated that circular RNAs (circRNAs) exert outstanding functions in NSCLC progression. Notwithstanding, we are still in the dark about the function and exact mechanism of circ-PITX1, a newly discovered circRNA. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) confirmed the profile of circ-PITX1 in NSCLC tissues and adjacent normal tissues. Gain- and loss- of function assay verified the impact of circ-PITX1 and miR-30e-5p on the proliferation, invasion, and migration of NSCLC cells (H1975 and A549). Bioinformatics analysis corroborated the downstream mechanisms of circ-PITX1. Dual-luciferase reporter gene assay and RNA immunoprecipitation (RIP) examined the interactions between circ-PITX1 and miR-30e-5p, miR-30e-5p and ITGA6. The protein levels of ITGA6, PI3K, AKT were determined by Western blot. circ-PITX1 was substantially up-regulated in NSCLC tissues and cells, and circ-PITX1 up-regulation was correlated with NSCLC patients’ poor survival. Functionally, circ-PITX1 overexpression or miR-30e-5p inhibition markedly facilitated proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), reduced apoptosis, and enhanced ITGA6/PI3K/AKT expression in NSCLC cells, whereas circ-PITX1 knockdown or miR-30e-5p up-regulation resulted in the opposite results. Mechanistically, circ-PITX1 acted as a sponge of miR-30e-5p, which targeted the 3ʹuntranslated region (UTR) of ITGA6. Knockdown of circ-PITX1 or overexpressing miR-30e-5p reduced ITGA6/PI3K/AKT axis. circ-PITX1 modulates the miR-30e-5p/ITGA6 axis to boost NSCLC progression, hence functioning as an oncogene.

Circ-ACAP2 facilitates the progression of colorectal cancer through mediating miR-143-3p/FZD4 axis

BACKGROUND

Circular RNAs (circRNAs) play crucial roles in multiple cancers, including colorectal cancer (CRC). Here, we explored the role of circRNA ArfGAP with coiled-coil, ankyrin repeat and PH domains 2 (circ-ACAP2) in the progression and radioresistance of CRC.

METHODS

Quantitative real-time polymerase chain reaction (qPCR) and Western blot assay were used to detect RNA and protein expression, respectively. The proliferation, apoptosis, migration, invasion and radioresistance of CRC cells were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, transwell migration assay, transwell invasion assay and colony formation assay. The target interaction between microRNA-143-3p (miR-143-3p) and circ-ACAP2 or frizzled class receptor 4 (FZD4) was verified by dual-luciferase reporter assay. Murine xenograft model was established to explore the role of circ-ACAP2 in vivo.

RESULTS

The expression of circ-ACAP2 was prominently enhanced in CRC tissues and cell lines. Circ-ACAP2 facilitated the proliferation, migration, invasion and radioresistance whereas inhibited the apoptosis of CRC cells. MiR-143-3p was a direct target of circ-ACAP2 in CRC cells. Circ-ACAP2 promoted the progression and radioresistance of CRC partly by sponging miR-143-3p. MiR-143-3p interacted with the 3' untranslated region (3'UTR) of FZD4 in CRC cells, and FZD4 overexpression partly reversed miR-143-3p-mediated effects in CRC cells. Wnt/β-catenin signalling was modulated by circ-ACAP2/miR-143-3p/FZD4 axis in CRC cells.

CONCLUSION

Circ-ACAP2 contributed to the development and radioresistance of CRC partly through targeting miR-143-3p/FZD4 axis, which provided novel potential diagnostic and therapeutic targets for CRC.

Hsa_circRNA_103124 Upregulation in Crohn's Disease Promotes Cell Proliferation and Inhibits Autophagy by Regulating the Hsa-miR-650/AKT2 Signaling Pathway

Circular RNAs (circRNAs) play important roles in the pathogenesis of Crohn's disease (CD). We discovered that hsa_circRNA_103124 was upregulated in CD patients in our previous study. Nonetheless, the function of hsa_circRNA_103124 is unclear. In this study, hsa_circRNA_103124 was predicted to interact with hsa-miR-650. Gene Ontology (GO) and pathway analyses identified AKT serine/threonine kinase 2 (AKT2) as the downstream target protein of hsa-miR-650. Activated AKT2 inhibits autophagy, but promotes cell proliferation. Recent studies suggest that the inhibition of autophagy is one of the mechanisms of CD pathogenesis. Therefore, we inferred that hsa_circRNA_103124 might regulate autophagy and proliferation by targeting AKT2 as a sponge for hsa-miR-650. Here, quantitative reverse transcription PCR (RT-QPCR) results revealed that upregulated hsa_circRNA_103124 expression in patients with CD was negatively correlated with hsa-miR-650 expression but positively correlated with the white blood cell count and calprotectin levels. TSC complex subunit 1 (TSC1), one of the proteins upstream of autophagy was downregulated in patients with CD. Consisting with the bioinformatics prediction, it was verified that hsa_circRNA_103124 targeted to hsa-miR650 by fluorescence in situ hybridization (FISH) and luciferase reporter assays. A hsa-miR-650 inhibitor reversed the promotion of rapamycin-induced autophagy and the inhibition of cell proliferation by the hsa_circRNA_103124 siRNA. However, hsa-miR-650 mimics reversed the inhibition of rapamycin-induced autophagy and the promotion of cell proliferation through hsa_circRNA_103124 overexpression. These results indicate that hsa_circRNA_103124 upregulation in patients with CD promotes cell proliferation and inhibits autophagy by regulating the hsa-miR-650/AKT2 signaling pathway.

The Dual Role of Circular RNAs as miRNA Sponges in Breast Cancer and Colon Cancer

Breast cancer (BC) and colon cancer (CRC) are the two most deadly cancers in the world. These cancers partly share the same genetic background and are partially regulated by the same genes. The outcomes of traditional chemoradiotherapy and surgery remain suboptimal, with high postoperative recurrence and a low survival rate. It is, therefore, urgent to innovate and improve the existing treatment measures. Many studies primarily reported that the microRNA (miRNA) sponge functions of circular RNA (circRNA) in BC and CRC have an indirect relationship between the circRNA–miRNA axis and malignant behaviors. With a covalent ring structure, circRNAs can regulate the expression of target genes in multiple ways, especially by acting as miRNA sponges. Therefore, this review mainly focuses on the roles of circRNAs as miRNA sponges in BC and CRC based on studies over the last three years, thus providing a theoretical reference for finding new therapeutic targets in the future.

Robust Glycogene-Based Prognostic Signature for Proficient Mismatch Repair Colorectal Adenocarcinoma

Background

Proficient mismatch repair (pMMR) colorectal adenocarcinoma (CRAC) metastasizes to a greater extent than MMR-deficient CRAC. Prognostic biomarkers are preferred in clinical practice. However, traditional biomarkers screened directly from sequencing are often not robust and thus cannot be confidently utilized.

Methods

To circumvent the drawbacks of blind screening, we established a new strategy to identify prognostic biomarkers in the conserved and specific oncogenic pathway and its regulatory RNA network. We performed RNA sequencing (RNA-seq) for messenger RNA (mRNA) and noncoding RNA in six pMMR CRAC patients and constructed a glycosylation-related RNA regulatory network. Biomarkers were selected based on the network and their correlation with the clinicopathologic information and were validated in multiple centers (n = 775).

Results

We constructed a competing endogenous RNA (ceRNA) regulatory network using RNA-seq. Genes associated with glycosylation pathways were embedded within this scale-free network. Moreover, we further developed and validated a seven-glycogene prognosis signature, GlycoSig (B3GNT6, GALNT3, GALNT8, ALG8, STT3B, SRD5A3, and ALG6) that prognosticate poor-prognostic subtype for pMMR CRAC patients. This biomarker set was validated in multicenter datasets, demonstrating its robustness and wide applicability. We constructed a simple-to-use nomogram that integrated the risk score of GlycoSig and clinicopathological features of pMMR CRAC patients.

Conclusions

The seven-glycogene signature served as a novel and robust prognostic biomarker set for pMMR CRAC, highlighting the role of a dysregulated glycosylation network in poor prognosis.

CircRNA_0026344 via exosomal miR-21 regulation of Smad7 is involved in aberrant cross-talk of epithelium-fibroblasts during cigarette smoke-induced pulmonary fibrosis

For smoking-induced pulmonary fibrosis (PF), a serious disease endangering human health, there is no effective clinical treatment. Aberrant epithelium-fibroblast cross-talk is involved in formation of the excessive extracellular matrix (ECM) that contributes to PF. Circular RNAs have been associated with various pulmonary diseases. However, the mechanisms of circRNAs in PF are not clear. Herein, our goals were to investigate the involvement of circRNA_0026344 in the aberrant epithelium-fibroblast cross-talk induced by cigarette smoke (CS) and to define its mechanism. Chronic exposure (16 weeks) of BALB/c mice to 500 mg/m3 CS induced lung injury and fibrosis in lung tissues. From HBE cells, circRNA_0026344 was selected by microarray analysis and verified as that with the most severe down-regulation caused by cigarette smoke extract (CSE). The regulatory relationship between circRNA_0026344 and miR-21 was assessed by use of bioinformatics, RNA pull-down assays, and qRT-PCR. We found that miR-21 binding sites were present in circRNA_0026344 and, in HBE cells, it could act as a sponge for miR-21. When pcDNA3.0-circRNA_0026344, a high expression plasmid of circRNA_0026344, was transfected into HBE cells, the CSE-induced up-regulation of miR-21 levels was reversed. In MRC-5 cells, HBE-secreted exosomal miR-21 decreased levels of Smad7 and activated the TGF-β1/Smad3 pathway. By using the Targetscan database, the presence of species-conserved miR-21 binding sites in the Smad7 3'UTR region were predicted. We verified, by use of a luciferase reporter gene, that miR-21 bound to the 3'UTR region of Smad7 mRNA to inhibit its transcription. In conclusion, the results reveal that, in CS-induced pulmonary fibrosis, circRNA_0026344, via exosomal miR-21 regulation of Smad7, is involved in aberrant cross-talk of epithelium-fibroblasts. These results will be useful for the discovery of early biomarkers and for providing therapeutic targets for smoking-induced pulmonary fibrosis.

Roles of circular RNAs in colorectal cancer

Colorectal cancer (CRC) is one of the most common types of malignant cancer worldwide and poses a significant burden on both the individual and healthcare systems. Despite advances in treatment options, advanced-stage CRC has a high mortality rate due to its heterogeneity, metastatic potential and/or delay in diagnosis. In recent years, an increasing number of studies have indicated that circular RNAs (circRNAs) serve important roles in several types of cancer, including CRC. Recent studies have revealed that circRNAs are aberrantly expressed in CRC tissues and function as oncogenic or tumor suppressive regulators of CRC carcinogenesis and development. Numerous circRNAs have been associated with the clinicopathological features of patients with CRC and have been considered as potential biomarkers for the diagnosis and prognosis of CRC, as well as targets for treatment. However, a deeper understanding of their potential function is required. In the present review, the current body of knowledge on the biogenesis and functions of CRC-associated circRNAs, and their potential value in clinical applications, such as in CRC diagnosis, prognosis and treatment, is discussed and summarized.

Circ_0007031 Silencing Inhibits Cell Proliferation and Induces Cell Apoptosis via Downregulating MELK at a miR-485-3p-Dependent Way in Colorectal Cancer

Colorectal cancer (CRC) is a malignant cancer with an increasing incidence. Circular RNA (circRNA) is recently found to participate in the regulation of CRC progression. However, the role of circ_0007031 in CRC malignant progression remains elusive. 50 CRC patients were implicated in this study. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the RNA expression of circ_0007031, microRNA-485-3p (miR-485-3p) and maternal embryonic leucine zipper kinase (MELK). Western blot analysis was conducted to determine protein expression. Cell viability and proliferation were demonstrated by cell counting kit-8 and 5-Ethynyl-29-deoxyuridine (EdU) assays, respectively. Cell cycle and apoptosis were investigated by flow cytometry analysis. The interaction among circ_0007031, miR-485-3p and MELK was predicted by online databases, and identified by dual-luciferase reporter assay. Mouse model assay was conducted to reveal the effect of circ_0007031 on tumor formation in vivo. Circ_0007031 and MELK expression were obviously increased, while miR-485-3p expression was decreased in CRC tissues and cells compared with normal colorectal tissues or cells. Circ_0007031 knockdown repressed proliferation, whereas induced cell arrest at G0/G1 phase and apoptosis. On the opposite, circ_0007031 overexpression promoted cell proliferation and induced cell arrest at S phase. Additionally, miR-485-3p inhibitors attenuated circ_0007031 silencing-mediated CRC cell malignancy. MiR-485-3p was unveiled to regulate CRC cell processes via targeting MELK. Circ_0007031 controlled MELK expression via interacting with miR-485-3p. Furthermore, circ_0007031 contributed to tumor formation in vivo. Circ_0007031 knockdown repressed CRC malignant progression by reducing MELK expression through associating with miR-485-3p, suggesting that circ_0007031 was a potential target for the therapy of CRC.

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.

Upregulation of circular and linear METTL3 and USP3 in colorectal cancer

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

Sevoflurane inhibits malignant progression of colorectal cancer via hsa_circ_0000231-mediated miR-622

Background

Sevoflurane (Sev), a commonly used volatile anesthetic, has been reported to inhibit the process of colorectal cancer (CRC). Circular RNAs (circRNAs) are revealed to participate in the pathogenesis of CRC. This study aims to reveal the mechanism of hsa_circ_0000231 in Sev-mediated CRC progression.

Methods

The expression of hsa_circ_0000231 and microRNA-622 (miR-622) was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Protein level was determined by western blot analysis. Cell proliferation was investigated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), cell colony formation and DNA content quantitation assays. Cell apoptosis was detected by Annexin V-fluorescein isothiocyanate and propidium iodide double staining and caspase 3 activity assays. Cell migration and invasion were investigated by wound-healing and transwell invasion assays, respectively. The putative relationship between hsa_circ_0000231 and miR-622 was predicted by circular RNA Interactome online database, and identified by dual-luciferase reporter and RNA immunoprecipitation assays. The impacts of hsa_circ_0000231 on Sev-mediated tumor formation in vivo were presented by in vivo assay.

Results

Hsa_circ_0000231 expression was upregulated, while miR-622 was downregulated in CRC tissues and cells compared with control groups. Sev treatment decreased hsa_circ_0000231 expression, but increased miR-622 expression in CRC cells. Sev treatment suppressed cell proliferation, migration and invasion, and induced cell apoptosis. Hsa_circ_0000231 overexpression restored Sev-mediated CRC progression in vitro. Additionally, hsa_circ_0000231 acted as a sponge of miR-622, and miR-622 inhibitors reversed the impacts of hsa_circ_0000231 silencing on CRC process. Furthermore, Sev treatment inhibited tumor growth by regulating hsa_circ_0000231 in vivo.

Conclusion

Hsa_circ_0000231 attenuated Sev-aroused repression impacts on CRC development by sponging miR-622. This findings may provide an appropriate anesthetic protocol for CRC sufferers undergoing surgery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40709-021-00145-6.

Identification of circRNA circ-CSPP1 as a potent driver of colorectal cancer by directly targeting the miR-431/LASP1 axis

Colorectal cancer (CRC) is the third most common malignancy worldwide. Circular RNAs (circRNAs) have been implicated in cancer biology. The purpose of the current work is to investigate the precise parts of circRNA centrosome and spindle pole-associated protein 1 (circ-CSPP1) in the progression of CRC. Our data showed that circ-CSPP1 was significantly overexpressed in CRC tissues and cells. The knockdown of circ-CSPP1 attenuated cell proliferation, migration, invasion and promoted apoptosis in vitro and weakened tumor growth in vivo. circ-CSPP1 directly targeted miR-431, and circ-CSPP1 knockdown modulated CRC cell progression in vitro via upregulating miR-431. Moreover, LIM and SH3 protein 1 (LASP1) was a functional target of miR-431 in modulating CRC cell malignant progression. Furthermore, circ-CSPP1 in CRC cells functioned as a posttranscriptional regulator on LASP1 expression by targeting miR-431. Our present study identified the oncogenic role of circ-CSPP1 in CRC partially by the modulation of the miR-431/LASP1 axis, providing evidence for circ-CSPP1 as a promising biomarker for CRC management.

Exosomal circ_0088300 Derived From Cancer-Associated Fibroblasts Acts as a miR-1305 Sponge and Promotes Gastric Carcinoma Cell Tumorigenesis

Cancer-associated fibroblast (CAF)-derived exosomes play a major role in gastric carcinoma (GC) tumorigenesis. However, the mechanism behind the activity of circular RNAs in CAF-derived exosomes in GC remains unclear. In the present study, we identified differentially expressed circ_0088300 in GC tissues and plasma exosomes. We found that CAFs delivered functional circ_0088300 to GC tumor cells via exosomes and promoted the proliferation, migration and invasion abilities of GC cells. Furthermore, we demonstrated that circ_0088300 packaging into exosomes was driven by KHDRBS3. In addition, we verified that circ_0088300 served as a sponge that directly targeted miR-1305 and promoted GC cell proliferation, migration and invasion. Finally, the JAK/STAT signaling pathway was found to be involved in the circ_0088300/miR-1305 axis, which accelerates GC tumorigenesis. In conclusion, our results indicated a previously unknown regulatory pathway in which exosomal circ_0088300 derived from CAFs acts as a sponge of miR-1305 and promotes GC cell proliferation, migration and invasion; these data identify a potential biomarker and novel therapeutic target for GC in the future.

Propofol postpones colorectal cancer development through circ_0026344/miR-645/Akt/mTOR signal pathway

Colorectal cancer (CRC) is responsible for thousands of slow and painful annual deaths. Propofol, an anesthetic, is commonly used in CRC surgery. The role of circularRNA0026344 (circ_0026344) in propofol-treated CRC remains unclear, which was further explored in this study. Real-time polymerase chain reaction (qPCR) was used to detect the expression of circ_0026344 and microRNA645 (miR-645) in CRC cells and normal cells. Western blot was devoted to testing the protein expression of phospho-protein kinase B (p-AKT), AKT, phospho-mammalian target of rapamycin (p-mTOR), and mTOR in CRC cells. Moreover, cell counting kit-8 (CCK8), colony formation, flow cytometry, and transwell assays were employed to assess the proliferation, apoptosis, and metastasis in CRC cells. Circinteractome online tool was applied to predict the combination between circ_0026344 and miR-645, which was further verified by dual-luciferase reporter system. circ_0026344 was lowly expressed and miR-645 was abundantly expressed in CRC cells. The relative protein expression of p-AKT/AKT and p-mTOR/mTOR was strikingly elevated by si-circ#1, which could be reversed by anti-miR-645 in propofol-treated CRC cells. circ_0026344 overexpression inhibited the proliferation and metastasis and promoted apoptosis in CRC cells. Propofol treatment induced the restraint in proliferation and metastasis and stimulation in apoptosis, which were allayed by si-circ#1; meanwhile, this alleviation could further be abolished by anti-miR-645 in CRC cells. Furthermore, circ_0026344 sponged miR-645 to inhibited Akt/mTOR signal pathway in propofol-treated CRC cells. Propofol postponed CRC process by circ_0026344/miR-645/Akt/mTOR axis. This finding might provide a possibility to improve the therapy of CRC with propofol.

Circular RNA in colorectal cancer

Circular RNA (circRNA) is a highly abundant type of single-stranded non-coding RNA. Novel research has discovered many roles of circRNA in colorectal cancer (CRC) including proliferation, metastasis and apoptosis. Furthermore, circRNAs also play a role in the development of drug resistance and have unique associations with tumour size, staging and overall survival in CRC that lend circRNAs the potential to serve as diagnostic and prognostic biomarkers. Among cancers worldwide, CRC ranks second in mortality and third in incidence. In order to have a better understanding of the influence of circRNA on CRC development and progression, this review summarizes the role of specific circRNAs in CRC and evaluates their potential value as therapeutic targets and biomarkers for CRC. We aim to provide insight in the development of therapy and clinical decision-making.

Circular RNA circ_0000467 regulates colorectal cancer development via miR-382-5p/EN2 axis

Circular RNAs (CircRNAs), belonging to non-coding RNAs, exert a crucial modulatory role in cancer progression. In this study, circRNA microarray analysis was utilized to screen differentially expressed circRNA in colorectal cancer (CRC) and circ_0000467 was identified as one circRNA whose expression was significantly upregulated in CRC. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) indicated that circ_0000467 and engrailed-2 (EN2) expression levels were up-modulated, while the expression level of miR-382-5p was down-modulated in CRC tissues. The depletion of circ_0000467 expression was found to impede the multiplication, migration, invasion, and epithelial-mesenchymal transition (EMT) processes in CRC cells, which were examined by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and Transwell experiments. Dual-luciferase reporter assay was used to verify the targeting relationship between circ_0000467 and miR-382-5p. It was also revealed that circ_0000467 could up-regulate EN2 expression via repressing miR-382-5p in CRC cells. Furthermore, EN2 overexpression counteracted the suppressing effects of circ_0000467 knockdown on the malignant behaviors of CRC cells. To sum up, circ_0000467 facilitates CRC development by modulating the miR-382-5p/EN2 axis, and circ_0000467 is a promising target for CRC therapy.

CircABCC4 Regulates the Proliferation, Migration, and Invasion of Colorectal Cancer SW620 Cells by Targeting Micro RNA-216a-3p

This work investigates the effect of circABCC4 on the proliferation, migration, and invasion of colorectal cancer SW620 cells; circABCC4’s regulation of miR-216a-3p is also studied. qRT-PCR was used to measure the levels of circABCC4 and miR-216a-3p in colorectal cancer and adjacent tissues. The human colorectal cancer SW620 cells were transfected with different constructs of circABCC4 or miR-216a-3p or both to study their interactions and combined effects on cell behavior. A dual-luciferase reporter experiment tested the targeted relationship between circABCC4 to miR-216a-3p. Furthermore, the behaviors of SW620 cells, such as cell viability, migration, and invasion, were investigated. Also, the proteins related to cell behaviors were investigated with western blotting. Our results showed that colorectal cancer tissues had a higher level of circABCC4 but a lower level miR-216a-3p. The increased level of circABCC4 and the reduced level of miR-216a-3p had analogous influences on the behaviors of SW620 cells, resulting in reduced cell proliferation, migration, and invasion; the levels of related protein were also decreased. Moreover, we found that disrupting miR-548c-3p could reverse the influence of inhibiting circABCC4 on SW620 cells. In addition, the dual-luciferase reporter assay results confirmed the targeting of miR-216a-3p by circABCC4. These data demonstrate that the silencing of circABCC4 may inhibit the proliferation, migration, and invasion of colorectal cancer cells by upregulating miR-548c-3p.

CircRNAs: a new target for the diagnosis and treatment of digestive system neoplasms

A circRNA is a type of endogenous noncoding RNA that consists of a closed circular RNA molecule formed by reverse splicing; these RNAs are widely distributed in a variety of biological cells. In contrast to linear RNAs, circRNAs have no 5′ cap or 3′ poly(A) tail. They have a stable structure, a high degree of conservation, and high stability, and they are richly and specifically expressed in certain tissues and developmental stages. CircRNAs play a very important role in the occurrence and progression of malignant tumors. According to their origins, circRNAs can be divided into four types: exon-derived circRNAs (ecRNAs), intron-derived circRNAs (ciRNAs), circRNAs containing both exons and introns (EIciRNAs) and intergenic circRNAs. A large number of studies have shown that circRNAs have a variety of biological functions, participate in the regulation of gene expression and play an important role in the occurrence and progression of tumors. In this paper, the structure and function of circRNAs are reviewed, along with their biological role in malignant tumors of the digestive tract, in order to provide a reference for the diagnosis and treatment of digestive system neoplasms.

circAPLP2 promotes colorectal cancer progression by upregulating HELLS by targeting miR-335-5p

Background

Colorectal cancer (CRC) is one of the deadliest cancers in the world. Increasing evidence suggests that circular RNAs (circRNAs) are implicated in CRC pathogenesis. This study aimed to determine the role of circAPLP2 and explore a potential mechanism of circAPLP2 action in CRC.

Methods

The expression of circAPLP2, miR-335-5p and helicase lymphoid-specific (HELLS) mRNA in CRC tissues and cells was measured by quantitative real-time polymerase chain reaction (qPCR). The functional effects of circAPLP2 on cell cycle progression/cell apoptosis, colony formation, cell migration, invasion and glycolysis metabolism were investigated by flow cytometry assay, colony formation assay, wound healing assay, transwell assay and glycolysis stress test. Glycolysis metabolism was also assessed by the levels of glucose uptake and lactate production. The protein levels of HELLS and HK2 were detected by western blot. The interaction between circAPLP2 and miR-335-5p, or miR-335-5p and HELLS was verified by dual-luciferase reporter assay. The role of circAPLP2 on solid tumor growth in nude mice was investigated.

Results

circAPLP2 and HELLS were overexpressed, but miR-335-5p was downregulated in CRC tissues and cells. Functional analyses showed that circAPLP2 knockdown suppressed CRC cell cycle progression, colony formation, migration, invasion and glycolysis metabolism, induced cell apoptosis and blocked solid tumor growth in nude mice. Moreover, miR-335-5p was a target of circAPLP2, and miR-335-5p could also bind to HELLS. Rescue experiments presented that miR-335-5p inhibition reversed the effects of circAPLP2 knockdown, and HELLS overexpression abolished the role of miR-335-5p restoration. Importantly, circAPLP2 could positively regulate HELLS expression by mediating miR-335-5p.

Conclusion

circAPLP2 triggered CRC malignant development by increasing HELLS expression via targeting miR-335-5p, which might be a novel strategy to understand and treat CRC.

Comprehensive landscape and future perspectives of circular RNAs in colorectal cancer

Colorectal cancer (CRC) is a common hereditary tumor that is often fatal. Its pathogenesis involves multiple genes, including circular RNAs (circRNAs). Notably, circRNAs constitute a new class of noncoding RNAs (ncRNAs) with a covalently closed loop structure and have been characterized as stable, conserved molecules that are abundantly expressed in tissue/development-specific patterns in eukaryotes. Based on accumulating evidence, circRNAs are aberrantly expressed in CRC tissues, cells, exosomes, and blood from patients with CRC. Moreover, numerous circRNAs have been identified as either oncogenes or tumor suppressors that mediate tumorigenesis, metastasis and chemoradiation resistance in CRC. Although the regulatory mechanisms of circRNA biogenesis and functions remain fairly elusive, interesting results have been obtained in studies investigating CRC. In particular, the expression of circRNAs in CRC is comprehensively modulated by multiple factors, such as splicing factors, transcription factors, specific enzymes and cis-acting elements. More importantly, circRNAs exert pivotal effects on CRC through various mechanisms, including acting as miRNA sponges or decoys, interacting with RNA binding proteins, and even translating functional peptides. Finally, circRNAs may serve as promising diagnostic and prognostic biomarkers and potential therapeutic targets in the clinical practice of CRC. In this review, we discuss the dysregulation, functions and clinical significance of circRNAs in CRC and further discuss the molecular mechanisms by which circRNAs exert their functions and how their expression is regulated. Based on this review, we hope to reveal the functions of circRNAs in the initiation and progression of cancer and highlight the future perspectives on strategies targeting circRNAs in cancer research.

Downregulation of hsa_circ_0006220 and its correlation with clinicopathological factors in human breast cancer

Background

Circular ribonucleic acids (circRNAs) are highly stable and conserved forms of RNAs present in all eukaryotes. They can modulate the expression of genes by sponging specific micro RNAs (miRNAs), thereby affecting various disease processes. However, their expression pattern in human breast cancer has not been elucidated.

Methods

In this study, differentially expressed circRNAs in breast cancer tissues and paired noncancerous tissues were analyzed using an Arraystar Human circRNA Microarray, and hsa_circ_0006220 was selected for its 27-fold downregulation in breast cancer tissues. Its expression was also verified in 50 breast cancer and paired noncancerous tissues using real-time polymerase chain reaction (RT-PCR). An analysis of the expression of hsa_circ_0006220 and the clinicopathological factors in breast cancer was conducted. A receiver operating characteristic (ROC) curve of hsa_circ_0006220 was constructed. The interaction between hsa_circ_0006220 and five possible target miRNAs was predicted, and their expression were verified when overexpressing hsa_circ_0006220 by RT-PCR.

Results

Hsa_circ_0006220 was found to be significantly downregulated in breast cancer tissues compared to the paired noncancerous tissues by microarray and RT-PCR. The expression of hsa_circ_0006220 was significantly inversely correlated with histological type (P=0.0028) and lymph node metastasis (P=0.0341). The area under the ROC curve (AUC) was 0.706. Five miRNAs that might be sponged by hsa_circ_0006220 were predicted. MiR-197-5p was significantly downregulated after overexpression of hsa_circ_0006220.

Conclusions

Our results indicated that hsa_circ_0006220 may play a role in human breast cancer and might be a potential tumor marker for breast cancer screening.

Cancer-related circular RNA: diverse biological functions

Noncoding RNAs, including long noncoding RNAs (lncRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs), are involved in regulating biological functions. In recent decades, miRNAs and lncRNAs have both inspired a wave of research, but the study of circRNA functions is still in its infancy. Studies have found that circRNAs actively participate in the occurrence and development of various diseases, which emphasizes the importance of circRNAs. Here, we review the features and classification of circRNAs and summarize their functions. Then, we briefly describe how to analyze circRNAs by bioinformatics procedures. In addition, the relationship between circRNAs and cancers is discussed with an emphasis on proving whether circRNAs can be potential biomarkers for the prognosis and diagnosis of cancer.

Identification of Circ_001569 as a Potential Biomarker in the Diagnosis and Prognosis of Pancreatic Cancer

Emerging evidence has shown that circular RNAs (circRNAs) serve as a promising biomarker in different malignancies. Specifically, circ_001569 has been found to be upregulated in some types of human gastrointestinal cancer. In this study, we aimed to investigate clinical significances, diagnostic and prognostic values of circ_001569 in pancreatic cancer (PC), and identify its effects on the malignant behaviors of PC cells. The expression of circ_001569 was determined in 26 tissues samples and 97 plasma samples from PC patients by qRT-PCR. Relationship between circ_001569 expression and clinicopathological parameters was analyzed by Chi-square test. Diagnostic and prognostic values of circ_001569 were evaluated by ROC curves, Kaplan-Meier curves, and Cox regression analysis. The effects of circ_001569 on the proliferation, migration, invasion, and apoptosis of PC cells were assessed by MTT, wound healing, Transwell invasion assays, and flow cytometric analysis, respectively. Results showed that the expression of circ_001569 was upregulated in tissues and plasma of PC patients. High circ_001569 level was positively correlated with lymphatic metastasis, clinical stage, and venous invasion. Circ_001569 level was an independent prognostic indicator for overall survival rates of PC patients, and patients with high circ_001569 level had a poor prognosis. The AUC of circ_001569 was 0.716 (95% CI: 0.642-0.790) with a sensitivity and specificity of 62.76% and 74.29%, respectively. In vitro, circ_001569 silencing decreased cell proliferation, migration, and invasion, but promoted cell apoptosis of PC cells. Our data demonstrate that high circ_001569 level associates with tumor malignant behaviors, and may serve as a potential biomarker in the diagnosis and prognosis of PC.

Hsa_circ_0001696 modulates cell proliferation and migration in colorectal cancer

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNA molecules that are extensively expressed in a variety of species. Recently, increasing evidence suggests that circRNAs have vital functions indifferent types of human cancer, such as gastric cancer, papillary thyroid cancer and lung cancer. However, the roles of circRNAs in the development of colorectal cancer (CRC) remain unclear. The present study aimed to determine the molecular mechanism underlying hsa_circ_0001696 on the proliferation and migration of CRC cells. Reverse transcription-quantitative PCR analysis was performed to detect hsa_circ_0001696 expression in 18 paired CRC tissues and matched adjacent normal tissues. RNA interference was also performed to decrease hsa_circ_0001696 expression, and its biological effects were further assessed via flow cytometry, wound healing, colony formation and western blot assays. The results demonstrated that hsa_circ_0001696 expression was significantly lower in CRC tissues compared with adjacent normal tissues. Furthermore, hsa_circ_0001696 knockdown promoted cell proliferation and migration, and the number of cell colonies significantly increased. In addition, western blot analysis demonstrated that the protein expression levels of cyclin-dependent kinase 4 (CDK4), cyclin D, cyclin E and matrix metalloproteinase 9 (MMP9) increased. Taken together, the results of the present study demonstrated that hsa_circ_0001696 expression was downregulated in CRC tissues, and inhibition of hsa_circ_0001696 promoted cell proliferation and migration by regulating the levels of CDK4, cyclin D, cyclin E and MMP9.

hsa_circRNA_001587 upregulates SLC4A4 expression to inhibit migration, invasion, and angiogenesis of pancreatic cancer cells via binding to microRNA-223

Pancreatic cancer (PC) is a malignant tumor that is difficult to diagnose and treat. Circular RNAs (circRNAs) are biomarkers that may be used to diagnose certain cancers or act as targets for cancer treatment. We aimed to explore the functions of human circular RNA 001587 (hsa_circRNA_001587) on the progression of PC and the underlying mechanism. The expression pattern of hsa_circRNA_001587 and microRNA-223 (miR-223) in PC tissues and cells was determined by RT-qPCR. Dual-luciferase reporter gene assay, RNA-pulldown, Argonaute 2 (AGO2) immunoprecipitation assay, and Northern blot analysis were applied to verify the binding relationships among hsa_circRNA_001587, miR-223 and solute carrier family 4 member 4 (SLC4A4). Further analysis of their roles was performed in PC cell line PANC-1. Moreover, we either downregulated or upregulated the expression of hsa_circRNA_001587, miR-223, and SLC4A4 by transfection in vitro. A mouse xenograft model of PC cells was established to evaluate tumor growth in vivo. hsa_circRNA_001587 was poorly expressed, but miR-223 was highly expressed in PC tissues and cell lines. Upregulation of hsa_circRNA_001587 downregulated the expression of matrix metalloproteinase-2 and-9, minichromosome maintenance 2, and vascular endothelial growth factor, and decreased the proliferation, migration, invasion, angiogenic and tumorigenic abilities of PC cells. MiR-223, which can bind with hsa_circRNA_001587, reversed the effects of hsa_circRNA_001587 on PC cells. In addition, SLC4A4 was identified as a target of miR-223, and its knockdown could counteract the regulatory effects of overexpressed hsa_circRNA_001587 or inhibited miR-223 expression on PC cells. Therefore, hsa_circRNA_001587 inhibits PC cell migration, invasion, angiogenesis and tumorigenesis by impairing miR-223-mediated SLC4A4 inhibition.NEW & NOTEWORTHY Human circular (hsa_circ)RNA_001587 and solute carrier family 4 member 4 (SLC4A4) are poorly expressed but microRNA (miR)R-223 is overexpressed in pancreatic cancer (PC) cells. hsa_circRNA_001587 binds to miR-223. Overexpression of hsa_circRNA_001587 inhibits PC progression. Overexpression of miR-223 downregulates the expression of SLC4A4 and promotes PC cell growth. hsa_circRNA_001587 may be a potential target for PC treatment.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

Omics technologies for improved diagnosis and treatment of colorectal cancer: Technical advancement and major perspectives

Colorectal cancer (CRC) ranks third among the most commonly occurring cancers worldwide, and it causes half a million deaths annually. Alongside mechanistic study for CRC detection and treatment by conventional techniques, new technologies have been developed to study CRC. These technologies include genomics, transcriptomics, proteomics, and metabolomics which elucidate DNA markers, RNA transcripts, protein and, metabolites produced inside the colon and rectum part of the gut. All these approaches form the omics arena, which presents a remarkable opportunity for the discovery of novel prognostic, diagnostic and therapeutic biomarkers and also delineate the underlying mechanism of CRC causation, which may further help in devising treatment strategies. This review also mentions the latest developments in metagenomics and culturomics as emerging evidence suggests that metagenomics of gut microbiota has profound implications in the causation, prognosis, and treatment of CRC. A majority of bacteria cannot be studied as they remain unculturable, so culturomics has also been strengthened to develop culture conditions suitable for the growth of unculturable bacteria and identify unknown bacteria. The overall purpose of this review is to succinctly evaluate the application of omics technologies in colorectal cancer research for improving the diagnosis and treatment strategies.