Comprehensive profile of differentially expressed circular RNAs reveals that hsa_circ_0000069 is upregulated and promotes cell proliferation, migration, and invasion in colorectal cancer

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.

Circ_0000069 promotes the development of hepatocellular carcinoma by regulating CCL25

BACKGROUND

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths globally, influenced by aberrant circRNA expression. Investigating circRNA-miRNA-mRNA interactions can unveil underlying mechanisms of HCC and identify potential therapeutic targets.

METHODS

In this study, we conducted differential analyses of mRNAs, miRNAs, and circRNAs, and established their relationships using various databases such as miRanda, miRDB, and miTarBase. Additionally, functional enrichment and immune infiltration analyses were performed to evaluate the roles of key genes. We also conducted qPCR assays and western blotting (WB) to examine the expression levels of circRNA, CCL25, and MAP2K1 in both HCC cells and clinical samples. Furthermore, we utilized overexpression and knockdown techniques for circ_0000069 and conducted wound healing, transwell invasion assays, and a tumorigenesis experiment to assess the migratory and invasive abilities of HCC cells.

RESULTS

Our findings revealed significant differential expression of 612 upregulated genes and 1173 downregulated genes in HCC samples compared to normal liver tissue. Additionally, 429 upregulated circRNAs and 453 downregulated circRNAs were identified. Significantly, circ_0000069 exhibited upregulation in HCC tissues and cell lines. The overexpression of circ_0000069 notably increased the invasion and migration capacity of Huh7 cells, whereas the downregulation of circ_0000069 reduced this capability in HepG2 cells. Furthermore, this effect was counteracted by CCL25 silencing or overexpression, separately. Animal studies further confirmed that the overexpression of hsa_circ_0000069 facilitated tumor growth in xenografted nude mice, while the inhibition of CCL25 attenuated this effect.

CONCLUSION

Circ_0000069 appears to promote HCC progression by regulating CCL25, suggesting that both circ_0000069 and CCL25 can serve as potential therapeutic targets.

COL: a pipeline for identifying putatively functional back-splicing

Circular RNAs (circRNAs) are a class of generally non-coding RNAs produced by back- splicing. Although the vast majority of circRNAs are likely to be products of splicing error and thereby confer no benefits to organisms, a small number of circRNAs have been found to be functional. Identifying other functional circRNAs from the sea of mostly non-functional circRNAs is an important but difficult task. Because available experimental methods for this purpose are of low throughput or versality and existing computational methods have limited reliability or applicability, new methods are needed. We hypothesize that functional back- splicing events that generate functional circRNAs (i) exhibit substantially higher back-splicing rates than expected from the total splicing amounts, (ii) have conserved splicing motifs, and (iii) show unusually high back-splicing levels. We confirm these features in back-splicing shared among human, macaque, and mouse, which should enrich functional back-splicing. Integrating the three features, we design a computational pipeline named COL for identifying putatively functional back-splicing. Different from the methods that require multiple samples, COL can predict functional back-splicing using a single sample. Under the same data requirement, COL has a lower false positive rate than that of the commonly used method that is based on the back- splicing level alone. We conclude that COL is an efficient and versatile method for rapid identification of putatively functional back-splicing and circRNAs that can be experimentally validated. COL is available at https://github.com/XuLabSJTU/COL .

Hsa_circ_0000069 Accelerates Cervical Cancer Progression by Sponging miR-1270 to Facilitate CPEB4 Expression

The critical importance of circular RNAs (circRNAs) in human cancers, including cervical cancer (CC), has been discovered in recent years. However, the function and mechanism of hsa_circ_0000069 (circ_0000069) in CC have been fully understood. The expression levels of circ_0000069, microRNAs (miR-1270, miR-1276 and miR-620) and cytoplasmic polyadenylation element binding protein 4 (CPEB4) mRNA were detected by quantitative real time polymerase chain reaction (qRT-PCR). Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, wound healing, transwell and tube formation assays were used to clarify the effects of circ_0000069 on the functional behaviors of CC cells. The binding relationships among miR-1270, circ_0000069 and CPEB4 were detected by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. A xenograft tumor model was established to explore the effect of circ_0000069 on tumor growth in vivo. Circ_0000069 was upregulated in CC clinical samples and cell lines, and its expression was associated with the clinical stage of CC patients. Circ_0000069 knockdown significantly decreased cell proliferation, invasion, migration, and tube formation and increased cell apoptosis in vitro. Moreover, miR-1270 was a direct target of circ_0000069, and CPEB4 was the downstream target of miR-1270. Knockdown of miR-1270 reversed the inhibitory effect of circ_0000069 knockdown on CC progression, and CPEB4 overexpression overturned the effect of miR-1270 on CC progression. In xenograft experiments, the oncogenic effect of circ_0000069 on tumor growth was verified. Altogether, circ_0000069 adsorbed miR-1270 to upregulate CPEB4 expression, thereby promoting the malignant phenotypes of CC cells. Circ_0000069 might be a potential target for treatment of CC.

CircUSP1 as a novel marker promotes gastric cancer progression via stabilizing HuR to upregulate USP1 and Vimentin

Circular RNAs (circRNAs) play a crucial role in regulating various tumors. However, their biological functions and mechanisms in gastric cancer (GC) have not been well understood. Here, we discovered a stable cytoplasmic circRNA named circUSP1 (hsa_circ_000613) in GC. CircUSP1 upregulation in GC tissues was correlated with tumor size and differentiation. We observed that circUSP1 promoted GC growth and metastasis. Mechanistically, circUSP1 mainly interacted with the RRM1 domain of an RNA-binding protein (RBP) called HuR, stabilizing its protein level by inhibiting β-TrCP-mediated ubiquitination degradation. The oncogenic properties of HuR mediated promotive effects of circUSP1 in GC progression. Moreover, we identified USP1 and Vimentin as downstream targets of HuR in post-transcriptional regulation, mediating the effects of circUSP1. The parent gene USP1 also enhanced the viability and mobility of GC cells. Additionally, tissue-derived circUSP1 could serve as an independent prognostic factor for GC, while plasma-derived circUSP1 showed promise as a diagnostic biomarker, outperforming conventional markers including serum alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA) and carbohydrate antigen 199 (CA19-9). Our study highlights that circUSP1 promotes GC progression by binding to and stabilizing oncogenic HuR, thereby facilitating the upregulation of USP1 and Vimentin at the post-transcriptional level. These findings suggest that circUSP1 could be a potential therapeutic target and a diagnostic and prognostic biomarker for GC.

The Role of Circular RNAs in Male Infertility and Reproductive Cancers: A Narrative Review

Infertility is a global health problem affecting about 15% of all couples, of which 50% are due to male infertility. Although the etiology of infertility is known in most infertile men, idiopathic male infertility remains a challenge. Therefore, there is a need for novel diagnostic methods to detect the underlying mechanisms and develop appropriate therapies. Recent studies have focused on the role of non-coding RNAs (ncRNAs) in male infertility. Circular RNAs (CircRNAs), a type of ncRNAs, are found to play a key role in the development of some pathological conditions, including cardiovascular diseases, diabetes, cancers, autoimmune diseases, etc. Several studies have reported the presence of CircRNAs and their target genes in the human reproductive system. In addition, their expression in testicular tissues, sperm cells, and seminal fluid has been identified. Abnormal expression of CircRNAs has been associated with azoospermia and asthenozoospermia in infertile men. The present narrative review provides a brief description of the role of CircRNAs in spermatogenic cells, male infertility, and reproductive cancers. In addition, some CircRNAs have been identified as potential biomarkers for disease detection and treatment.

Applications of engineered exosomes in drugging noncoding RNAs for cancer therapy

Noncoding RNAs (ncRNAs) are engaged in key cell biological and pathological events, and their expression alteration is connected to cancer progression both directly and indirectly. A huge number of studies have mentioned the significant role of ncRNAs in cancer prevention and therapy that make them an interesting subject for cancer therapy. However, there are several limitations, including delivery, uptake, and short half-life, in the application of ncRNAs in cancer treatment. Exosomes are introduced as promising options for the delivery of ncRNAs to the target cells. In this review, we will briefly discuss the application and barriers of ncRNAs. After that we will focus on exosome-based ncRNAs delivery and their advantages as well as the latest achievements in drugging ncRNAs with exosomes.

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.

CircRNA circSTIL inhibits ferroptosis in colorectal cancer via miR-431/SLC7A11 axis

Ferroptosis is an emerging programmed cell death and plays essential roles in tumorigenesis, including colorectal cancer (CRC). The present study intended to disclose the role of a novel oncogene circular RNA (circRNA) circSTIL in CRC phenotypes, especially ferroptosis. The expression of circSTIL was measured in CRC tissues and cells. Then, the impacts of circSTIL expression on the proliferation and ferroptosis of CRC cells were examined by loss-of-function assays in vitro. Bioinformatics, luciferase reporter assay and cell rescue assay were further performed to reveal the ceRNA-associated mechanism of circSTIL. CircSTIL was significantly upregulated in CRC. Cell proliferation was suppressed while ferroptosis was induced with the silencing of circSTIL in CRC cells. Interestingly, circSTIL competed with miR-431 for solute carrier family 7 member 11 (SLC7A11) binding. Additionally, miR-431 suppression or SLC7A11 overexpression overturned circSTIL silencing-mediated cell phenotypes in CRC cells. CircSTIL promotes CRC cell proliferation and suppresses ferroptosis in vitro via miR-431/SLC7A11 signaling, revealing the pathogenesis of CRC, and providing potential therapeutic targets of CRC.

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.

Circ_0000069 contributes to the growth, metastasis and glutamine metabolism in renal cell carcinoma (RCC) via regulating miR-125a-5p-dependent SLC1A5 expression

BACKGROUND

Circular RNAs (circRNAs) have emerged as critical mediators in various cancers, including renal cell carcinoma (RCC). In the present research, the functions of circ_0000069 in RCC were explored.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) assay, western blot assay and immunohistochemistry (IHC) assay were performed for the expression of circ_0000069, microRNA-125a-5p (miR-125a-5p) and solute carrier family 1 member 5 (SLC1A5). Cell Counting Kit-8 (CCK-8) assay and 5'-ethynyl-2'-deoxyuridine (EdU) assay were performed for cell proliferation. Flow cytometry assay was manipulated for cell apoptosis. Transwell assay and wound-healing assay were utilized for cell invasion and migration. Glutamine metabolism level was evaluated by examining glutamine consumption, α-ketoglutarate production and glutamate production. Dual-luciferase reporter assay was used to analyze the relationships of circ_0000069, miR-125a-5p and SLC1A5. Murine xenograft model assay was conducted to analyze the function of circ_0000069 in vivo.

RESULTS

Circ_0000069 level was abnormally upregulated in RCC tissues and cells. Knockdown of circ_0000069 inhibited the proliferation, invasion, migration and glutamine metabolism and promoted the apoptosis in RCC cells in vitro and restrained tumor growth in vivo. Circ_0000069 served as the sponge for miR-125a-5p. MiR-125a-5p inhibition ameliorated the effects of circ_0000069 knockdown on RCC cell malignant behaviors. SLC1A5 was identified as the target gene of miR-125a-5p. Moreover, miR-125a-5p overexpression repressed the progression of RCC cells, while SLC1A5 elevation abrogated the effect.

CONCLUSION

Circ_0000069 knockdown inhibited the carcinogenesis of RCC by regulating miR-125a-5p/SLC1A5 axis.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

Advances in high-throughput sequencing techniques and bioinformatic analysis have refuted the "junk" RNA hypothesis that was claimed against non-coding RNAs (ncRNAs). Circular RNAs (circRNAs); a class of single-stranded covalently closed loop RNA molecules have recently emerged as stable epigenetic regulators. Although the exact regulatory role of circRNAs is still to be clarified, it has been proven that circRNAs could exert their functions by interacting with other ncRNAs or proteins in their own physiologically authentic environment, regulating multiple cellular signaling pathways and other classes of ncRNAs. CircRNAs have also been reported to exhibit a tissue-specific expression and have been associated with the malignant transformation process of several hematological and solid malignancies. Along this line of reasoning, this review aims to highlight the importance of circRNAs in Breast Cancer (BC), which is ranked as the most prevalent malignancy among females. Notwithstanding the substantial efforts to develop a suitable anticancer therapeutic regimen against the heterogenous BC, inter- and intra-tumoral heterogeneity have resulted in an arduous challenge for drug development research, which in turn necessitates the investigation of other markers to be therapeutically targeted. Herein, the potential of circRNAs as possible diagnostic and prognostic biomarkers have been highlighted together with their possible application as novel therapeutic targets.

Circ_0000799 promotes proliferation and invasion in colorectal cancer and epithelial-mesenchymal transition

Background

The current study aimed to investigate the effect of circ_0000799 on the biological function of colorectal cancer (CRC) cells and its mechanism.

Methods

First, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was employed for detecting the expression of circ_0000799, miR-647, and miR-1243 in surgically resected specimens from hospitalized CRC patients, CRC-adjacent normal tissues (Normal group), human normal colon epithelial cells (FHC group), and CRC cell lines (HCT116, HT29, SW480, SW620). The cell proliferation, viability, and invasion were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), colony formation assay, transwell assay in HCT116 and SW480 cells with overexpression or inhibition of circ_0000799. The targeting relationship between circ_0000799 and miR-647 was verified by dual-luciferase reporter assay. The expression of epithelial-mesenchymal transition (EMT) proteins (E-cadherin, vimentin, and N-cadherin) was tested by western blot.

Results

The expression level of circ_0000799 was significantly increased in CRC tissues and cells. Overexpression of circ_0000799 significantly increased cell proliferation rate, viability, invasion, and the EMT process, whereas knockdown of circ_0000799 inhibited the biological performance of CRC cells. Bioinformatic analysis suggested that miR-647 was regulated by circ_0000799, and a dual-luciferase reporter assay further showed a targeting relationship between the two. In addition, circ_0000799 was negatively correlated with miR-647 expression in CRC.

Conclusions

Our findings suggest that circ_0000799 promotes proliferation and invasion in CRC and EMT. These effects of circ_0000799 may be achieved by negatively regulating miR-62.

Circular RNA circ_0065378 upregulates tumor suppressor candidate 1 by competitively binding with miR-4701-5p to alleviate colorectal cancer progression

BACKGROUND AND AIM

Colorectal cancer (CRC), the third most lethal human cancer worldwide, seriously threatens human health and life. Numerous circular RNAs (circRNAs) including circ_PLXNB1 (hsa_circ_0065378) have been confirmed to be dysregulated in CRC by RNA-seq analysis. We aimed to explore the functional role of circ_PLXNB1 in CRC malignant behaviors and clarify its potential molecular mechanism.

METHODS

Gene expression levels of circ_PLXNB1 and miR-4701-5p were determined by quantitative real-time polymerase chain reaction analysis. MTT and Transwell assays were conducted to measure cell proliferation, invasion, and migration. Protein expression of tumor suppressor candidate 1 (TUSC1), E-cadherin and N-cadherin was determined by western blot analysis. Mouse xenograft models were used to investigate the role of circ_PLXNB1 in tumor growth.

RESULTS

The results showed that gene expression of circ_PLXNB1 in CRC tissues was significantly downregulated. Overexpression of circ_PLXNB1 inhibited the malignant behaviors of CRC cells, as manifested by the decrease in cell proliferation, cell invasion, migration, and EMT. Mechanistically, circ_PLXNB1 exerted its functional effects by binding with miR-4701-5p. Moreover, TUSC1 siRNA partially abolished the suppressive effect of the miR-4701-5p inhibitor or circ_PLXNB1 on CRC cell malignant behaviors.

CONCLUSIONS

Circ_PLXNB1 attenuated CRC progression by binding with miR-4701-5p to overexpress TUSC1, indicating that the circ_PLXNB1/miR-4701-5p/TUSC1 axis might be a potential novel molecular target in CRC diagnosis and therapy.

Circular RNA Circ-STIL Contributes to Cell Growth and Metastasis in Hepatocellular Carcinoma via Regulating miR-345-5p/AQP3 Axis

BACKGROUND

Circular RNAs (circRNAs) are implicated in the pathogenesis and development of hepatocellular carcinoma (HCC). However, the function and latent mechanism of circ-STIL in HCC have not been elucidated.

AIMS

This study was designed to explore the precise role and underlying molecular mechanism of circ-STIL in HCC advancement.

METHODS

The expression levels of circ-STIL, SCL/TAL1 interrupting locus (STIL), miR-345-5p and aquaporin-3 (AQP3) were measured by quantitative real-time polymerase chain reaction or western blot. Cell proliferation was assessed by 3-(4,5-dimethylthizol-2-yl)-2,5-diphenyltetrazolium bromide assay and colony formation assay. Cell apoptosis was analyzed by flow cytometry. Transwell assay was conducted to analyze cell migratory and invasive capacities. The interactions among circ-STIL, miR-345-5p and AQP3 were confirmed by dual-luciferase reporter and RNA immunoprecipitation assays. Xenograft tumor model was established to analyze the role of circ-STIL in HCC in vivo.

RESULTS

Circ-STIL was upregulated in HCC tissues and cells. Circ-STIL knockdown inhibited HCC cell progression by reducing cell proliferation, migration and invasion and promoting cell apoptosis. MiR-345-5p was a direct target of circ-STIL, and AQP3 was targeted by miR-345-5p in HCC. Circ-STIL knockdown or miR-345-5p overexpression impeded cell malignant behaviors in HCC cells, and the effects could be reversed by miR-345-5p silence or AQP3 enhancement, respectively. Meanwhile, circ-STIL regulated AQP3 expression by sponging miR-345-5p. Besides, circ-STIL downregulation retarded HCC tumor growth in vivo.

CONCLUSION

Circ-STIL knockdown suppressed HCC development by regulating miR-345-5p/AQP3 pathway, which might provide a promising target for HCC therapy.

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

hsa_circ_0000231 Promotes colorectal cancer cell growth through upregulation of CCND2 by IGF2BP3/miR-375 dual pathway

Background

Circular RNAs (circRNAs) have emerged as vital regulators of the initiation and progression of diverse kinds of human cancers. In this study, we explored the role of hsa_circ_0000231 and its downstream pathway in CRC.

Methods

The expression profile of circRNAs in 5 pairs of CRC tissues and adjacent normal tissues were analyzed by Microarray. Quantitative real-time PCR and in situ hybridization and Base Scope Assay were used to determine the level and prognostic values of hsa_circ_0000231. Then, functional experiments in vitro and in vivo were performed to investigate the effects of hsa_circ_0000231 on cell proliferation. Mechanistically, fluorescent in situ hybridization, dual luciferase reporter assay, RNA pull-down and RNA immunoprecipitation experiments were performed to confirm the interaction between hsa_circ_0000231 and IGF2BP3 or has_miR-375.

Results

We acquired data through circRNA microarray profiles, showing that the expression of hsa_circ_0000231 was upregulated in CRC primary tissues compared to adjacent normal tissues, which was indicated poor prognosis of patients with CRC. Functional analysis indicated that inhibition of hsa_circ_0000231 in CRC cell lines could suppress CRC cell proliferation as well as tumorigenesis in vitro and in vivo. The mechanistic analysis showed that hsa_circ_0000231 might, on the one hand, act as a competing endogenous RNA of miR-375 to promote cyclin D2 (CCND2) and, on the other hand, bind to the IGF2BP3 protein to prevent CCND2 degradation.

Conclusions

The findings suggested that hsa_circ_0000231 facilitated CRC progression by sponging miR-375 or binding to IGF2BP3 to modulate CCND2, implying that hsa_circ_0000231 might be a potential new diagnostic and therapeutic biomarker of CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02455-8.

Hsa_circ_0087302, a circular RNA, affects the progression of osteosarcoma via the Wnt/β-catenin signaling pathway

Osteosarcoma is the most common malignant tumor in adolescent bone malignancies. It has the characteristics of a high metastasis rate, high mortality and poor prognosis. As a subclass of endogenous noncoding RNAs, circRNAs have been identified to be related to the occurrence, development and prognosis of different kinds of cancers, but the mechanism of their effect on osteosarcoma is not clear. In the present study, we identified a novel circRNA, hsa_circ_0087302, by RNA-seq, and we found that it was expressed at low levels in osteosarcoma. Using RT-PCR, we confirmed that the expression of hsa_circ_0087302 in osteosarcoma cells was lower than that in osteoblasts. Functional validation experiments revealed that hsa_circ_0087302 overexpression inhibited proliferation, cell cycle, migration, and invasion in osteosarcoma cells. Furthermore, Western blotting experiments demonstrated that hsa_circ_0087302 affected the expression of cell cycle- and Wnt/β-catenin signaling pathway-related proteins. For the first time, we identified that hsa_circ_0087302 may affect the malignant biological behavior of osteosarcoma cells through the Wnt/β-catenin signaling pathway. In summary, hsa_circ_0087302 may provide a new direction for the diagnosis and treatment of osteosarcoma.

Integrated Analysis of Circular RNA-Associated ceRNA Network Reveals Potential circRNA Biomarkers in Human Breast Cancer

Circular RNA (circRNA) is closely related to tumorigenesis and cancer progression. Yet, the roles of cancer-specific circRNAs in the circRNA-related ceRNA network of breast cancer (BRCA) remain unclear. The aim of this study was to construct a ceRNA network associated with circRNA and to explore new therapeutic and prognostic targets and biomarkers for breast cancer. We downloaded the circRNA expression profile of BRCA from Gene Expression Omnibus (GEO) microarray datasets and downloaded the miRNA and mRNA expression profiles of BRCA from The Cancer Genome Atlas (TCGA) database. Differentially expressed mRNAs (DEmRNAs), differentially expressed miRNAs (DEmiRNAs), and differentially expressed circRNAs (DEcircRNAs) were identified, and a competitive endogenous RNA (ceRNA) regulatory network was constructed based on circRNA-miRNA pairs and miRNA-mRNA pairs. Gene ontology and pathway enrichment analyses were performed on mRNAs regulated by circRNAs in ceRNA networks. Survival analysis and correlation analysis of all mRNAs and miRNAs in the ceRNA network were performed. A total of 72 DEcircRNAs, 158 DEmiRNAs, and 2762 DE mRNAs were identified. The constructed ceRNA network contains 60 circRNA-miRNA pairs and 140 miRNA-mRNA pairs, including 40 circRNAs, 30 miRNAs, and 100 mRNAs. Functional enrichment indicated that DEmRNAs regulated by DEcircRNAs in ceRNA networks were significantly enriched in the PI3K-Akt signaling pathway, microRNAs in cancer, and proteoglycans in cancer. Survival analysis and correlation analysis of all mRNAs and miRNAs in the ceRNA network showed that 13 mRNAs and 6 miRNAs were significantly associated with overall survival, and 48 miRNA-mRNA interaction pairs had a significant negative correlation. A PPI network was established, and 21 hub genes were determined from the network. This study provides an effective bioinformatics basis for further understanding of the molecular mechanisms and predictions of breast cancer. A better understanding of the circRNA-related ceRNA network in BRCA will help identify potential biomarkers for diagnosis and prognosis.

Role of circular RNAs in gastrointestinal tumors and drug resistance

The incidence of gastrointestinal cancers has increased significantly over the past decade and gastrointestinal malignancies now rank among the leading causes of mortality globally. Although newer therapeutic strategies such as targeted therapies have greatly improved patient outcomes, their clinical success is limited by drug resistance, treatment failure and recurrence of metastatic disease. Therefore, there is an urgent need for further research identifying accurate and reliable biomarkers for precise treatment strategies. Circular RNAs (circRNAs) exhibit a covalently closed structure, high stability and biological conservation, and their expression is associated with the occurrence and development of gastrointestinal tumors. Moreover, circRNAs may significantly influence drug resistance of gastrointestinal cancers. In this article, we review the role of circRNAs in the occurrence and development of gastrointestinal cancer, their association with drug resistance, and potential application for early diagnosis, treatment and prognosis in gastrointestinal malignancies. Furthermore, we summarize characteristics of circRNA, including mechanism of formation and biological effects via mRNA sponging, chromatin replication, gene regulation, translational modification, signal transduction, and damage repair. Finally, we discuss whether circRNA-related noninvasive testing may be clinically provided in the future. This review provides new insights for the future development of diagnostics and therapeutics based on circRNAs in gastrointestinal tumors.

Small extracellular vesicle non-coding RNAs in pancreatic cancer: molecular mechanisms and clinical implications

Pancreatic cancer has the worst prognosis among common tumors which is attributed to its aggressive phenotype, diagnosis at advanced, inoperable stages, and resistance to systemic therapy. Non-coding RNAs (ncRNAs) such as microRNAs, long non-coding RNAs, and circular RNAs have been established as important regulators of gene expression and their deregulation has been implicated in multiple diseases and foremost cancer. In the tumor microenvironment, non-coding RNAs can be distributed among cancer cells, stromal cells, and immune cells via small extracellular vesicles (sEVs), thereby facilitating intercellular communication and influencing major cancer hallmarks such as angiogenesis, evasion of the immune system, and metastatic dissemination. Furthermore, sEV-ncRNAs have shown promising potential as liquid biopsies with diagnostic and prognostic significance. In this review, we summarize the role of sEVs as carriers of ncRNAs and underlying molecular mechanisms in pancreatic cancer. Moreover, we review the potential of sEV-ncRNAs as biomarkers and highlight the suitability of sEVs as delivery vehicles for ncRNA-based cancer therapy.

Circ_0000317/microRNA-520g/HOXD10 axis affects the biological characteristics of colorectal cancer

Circular RNAs (circRNAs) are a class of noncoding RNAs that are widely expressed in cancer tissues and play a pro- or anticancer role in modulating cancer progression. This work is aimed to probe the biological role of circ_0000317 in colorectal cancer (CRC) and its underlying mechanism. Circ_0000317 was selected from the circRNA microarray datasets (GSE121895). Quantitative real-time polymerase chain reaction was utilized to examine circ_0000317, microRNA (miR)-520g, and homeobox D10 (HOXD10) mRNA expression in CRC. Cell Counting Kit-8 and Transwell experiments were conducted to examine the effects of circ_0000317 on proliferation, migration, and invasion of CRC cells. Bioinformatic analysis and dual-luciferase reporter gene experiments were implemented to predict and validate the targeting relationship between circ_0000317 and miR-520g, miR-520g, and HOXD10. Western blot was employed to examine HOXD10 expression at protein level in CRC cells. Circ_0000317 and HOXD10 mRNA expression were unveiled to be down-modulated and miR-520g expression was up-modulated in CRC. Functionally, circ_0000317 overexpression repressed CRC cell proliferation, migration, and invasion. Mechanistically, miR-520g was a direct target of circ_0000317 and miR-520g specifically modulated HOXD10 expression. Furthermore, miR-520g mimics partially counteracted the suppressing effect of circ_0000317 on malignant phenotype of CRC cells. Circ_0000317 represses CRC progression by targeting miR-520g and modulating HOXD10 expression. Hence, circ_0000317 may be a promising diagnostic biomarker and a therapeutic target for CRC.

Oncogenic Functions and Clinical Significance of Circular RNAs in Colorectal Cancer

Colorectal cancer (CRC) is ranked as the second most commonly diagnosed disease in females and the third in males worldwide. Therefore, the finding of new more reliable biomarkers for early diagnosis, for prediction of metastasis, and resistance to conventional therapies is an important challenge in overcoming the disease. The current review presents circular RNAs (circRNAs) with their unique features as potential prognostic and diagnostic biomarkers in CRC. The review highlights the mechanism of action and the role of circRNAs with oncogenic functions in the CRC as well as the association between their expression and clinicopathological characteristics of CRC patients. The comprehension of the role of oncogenic circRNAs in CRC pathogenesis is growing rapidly and the next step is using them as suitable new drug targets in the personalized treatment of CRC patients.

Hsa_circRNA_002144 promotes growth and metastasis of colorectal cancer through regulating miR-615-5p/LARP1/mTOR pathway

CircRNAs (circular RNAs), recently identified as a critical regulator in tumorigenesis, participate in CRC (colorectal cancer) growth. However, the role of hsa_circRNA_002144 in CRC was poorly understood. Firstly, hsa_circRNA_002144 showed significantly elevation in both of CRC tissues and cell lines, and suggested closely associated with poor prognosis in patients. Secondly, data from functional assays revealed that silence of hsa_circRNA_002144 inhibited CRC progression with reduced cell viability, proliferation, migration and invasion, while enhanced cell apoptosis. In addition, in vivo CRC growth and metastasis were also suppressed by knockdown of hsa_circRNA_002144. However, CRC progression was promoted with over-expression of hsa_circRNA_002144. Thirdly, hsa_circRNA_002144 colocalized with miR-615-5p in the cytoplasm of CRC cells, and decreased miR-615-5p expression. Moreover, miR-615-5p could target LARP1 (La ribonucleoprotein 1, translational regulator). Lastly, the suppressive effects of hsa_circRNA_002144 knockdown on CRC progression were reversed by LARP1 over-expression. In conclusion, hsa_circRNA_002144 could sponge miR-615-5p to promote CRC progression through the regulation of LARP1, providing a therapeutic target for cancer intervention.

Role of Virally Encoded Circular RNAs in the Pathogenicity of Human Oncogenic Viruses

Human oncogenic viruses are a group of important pathogens that etiologically contribute to at least 12% of total cancer cases in the world. As an emerging class of non-linear regulatory RNA molecules, circular RNAs (circRNAs) have gained increasing attention as a crucial player in the regulation of signaling pathways involved in viral infection and oncogenesis. With the assistance of current circRNA enrichment and detection technologies, numerous novel virally-encoded circRNAs (vcircRNAs) have been identified in the human oncogenic viruses, initiating an exciting new era of vcircRNA research. In this review, we discuss the current understanding of the roles of vcircRNAs in the respective viral infection cycles and in virus-associated pathogenesis.

CircRNAs as promising biomarkers of inflammatory bowel disease and its associated-colorectal cancer

In recent years, research on the pathogenesis of inflammatory bowel disease (IBD) and its associated-colorectal cancer has been well documented to involve environmental, genetic, immune, and intestinal microbiota factors. Evidence indicates that, regardless of the current high global incidence of IBD with over 3.5 million cases in Europe and North America only, it continues to emerge in newly industrialized countries across Asia, Middle East, and South America. Individuals with IBD have significant increased risk of gastrointestinal and extra-intestinal malignancies, particularly, colorectal cancer (CRC) and lymphomas. Among the significant areas of exploration in IBD and its associated-CRC is the search for effective and reliable diagnostic and prognostic markers, and treatment targets. To this effect, the role of non-coding RNAs in IBD and its associated-CRC has attracted research attention, among which microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) get more detailed exploration while little is known about circular RNAs (circRNAs). This review focuses on the emerging role of circRNAs in the diagnosis, prognosis, and treatment of IBD and its associated-CRC. It introduces the biogenesis of circRNAs and brings an up-to-date report on those found within IBD and CRC environment, as well as their participation toward the promotion or suppression of the conditions, and their diagnostic potentials.

circ0000069 promotes cervical cancer cell proliferation and migration by inhibiting miR-4426

Circular RNAs (circRNAs) have been shown to be associated with the occurrence and development of cervical cancer (CC). In the present study, we aimed to investigate the tumor-promoting effect of hsa_circ_0000069 (circ0000069) on CC and the mechanisms underlying its effect. We found that circ0000069 was upregulated in CC cells and tissues, and that N6-methyladenosine (m6A) modification maintained circ0000069 stability. Gain- and loss-of-function assays revealed that circ0000069 promoted CC cell proliferation and migration. miR-4426 specifically binds circ0000069 and mediates its functions in CC development. In conclusion, circ0000069 was upregulated partially due to m6A modification, which promoted cell proliferation and migration via sponging miR-4426 in CC.

The Role of circRNAs in Human Papillomavirus (HPV)-Associated Cancers

Circular RNAs (circRNAs) are a new class of "non-coding RNAs" that originate from non-sequential back-splicing of exons and/or introns of precursor messenger RNAs (pre-mRNAs). These molecules are generally produced at low levels in a cell-type-specific manner in mammalian tissues, but due to their circular conformation they are unaffected by the cell mRNA decay machinery. circRNAs can sponge multiple microRNAs or RNA-binding proteins and play a crucial role in the regulation of gene expression and protein translation. Many circRNAs have been shown to be aberrantly expressed in several cancer types, and to sustain specific oncogenic processes. Particularly, in virus-associated malignancies such as human papillomavirus (HPV)-associated anogenital carcinoma and oropharyngeal and oral cancers, circRNAs have been shown to be involved in tumorigenesis and cancer progression, as well as in drug resistance, and some are useful diagnostic and prognostic markers. HPV-derived circRNAs, encompassing the HPV E7 oncogene, have been shown to be expressed and to serve as transcript for synthesis of the E7 oncoprotein, thus reinforcing the virus oncogenic activity in HPV-associated cancers. In this review, we summarize research advances in the biogenesis of cell and viral circRNAs, their features and functions in the pathophysiology of HPV-associated tumors, and their importance as diagnostic, prognostic, and therapeutic targets in anogenital and oropharyngeal and oral cancers.

Role of circular RNAs in colorectal tumor microenvironment

Circular RNAs (circRNAs) are a class of endogenous noncoding RNA, which were previously considered as a byproduct of RNA splicing error. Numerous studies have demonstrated the altered expression of circRNAs in organ tissues during pathological conditions and their involvements in disease pathogenesis and progression, including cancers. In colorectal cancer (CRC), multiple circRNAs have been identified and characterized as "oncogenic", given their involvements in the downregulation of tumor suppressor genes and induction of tumor initiation, progression, invasion, and metastasis. Additionally, other circRNAs have been identified in CRC and characterized as "tumor suppressive" based on their ability of inhibiting the expression of oncogenic genes and suppressing tumor growth and proliferation. circRNAs could serve as potential diagnostic and prognostic biomarkers, and therapeutic targets or vectors to be utilized in cancer therapies. This review briefly describes the dynamic changes of the tumor microenvironment inducing immunosuppression and tumorigenesis, and outlines the biogenesis and characteristics of circRNAs and recent findings indicating their roles and functions in the CRC tumor microenvironment. It also discusses strategies and technologies, which could be employed in the future to overcome current cancer therapy challenges associated with circRNAs.

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.

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.

Investigation of circRNA-miRNA-mRNA network in colorectal cancer using an integrative bioinformatics approach

AIM

The aim of this study was to integrate both coding and non-coding available microarray data in the development of colorectal cancer (CRC) with bioinformatics analyses to attain a more inclusive pathobiologic map of their molecular interactions and functions.

BACKGROUND

Identification of competing endogenous RNAs (ceRNAs), especially circRNAs, has become a new hotspot in cancer research, although their roles and underlying mechanisms in CRC development remain mostly unknown.

METHODS

Microarray data was retrieved from the Gene Expression Omnibus (GEO) database and analyzed. Several bioinformatics tools and databases were applied for further elucidation. Principal component analysis (PCA) was run separately for four datasets. The dysregulated circRNA-miRNA-mRNA, co-expression, and protein-protein interaction (PPI) networks were established.

RESULTS

PCA discloses colorectal tumors; normal tissue can be distinguished not only by mRNAs expression profile, but also by both circRNA and miRNA expression profiles. In this study, 14 DE mRNAs, 85 DE miRNAs, and 36 DE circRNAs were identified in CRC tissue and compared with normal tissue. Taking their potential interactions into account, a circRNA-miRNA-mRNA network was constructed. The results disclosed some DE circRNAs with potential oncogenic (circ_0014879) or tumor suppressive (circ_0001666 and circ_0000977) effects. Finally, the PPI network suggests pivotal roles for DOCK2 and PTPRC dysregulation in the progression of CRC, possibly by facilitating tumor escape from immune surveillance.

CONCLUSION

The current study proposes a novel regulatory network consisting of DE circRNAs, miRNAs, and mRNAs in CRC development that highlights the roles of DE circRNAs at the upstream of oncotranscriptomic cascade in CRC development, suggesting their potential to be utilized as both prognostic and therapeutic biomarkers.

CircBACH1/let-7a-5p axis enhances the proliferation and metastasis of colorectal cancer by upregulating CREB5 expression

Background

In this study, we investigated the influences of circBACH1 on the proliferation, metastasis, migration, and apoptosis of human colorectal cancer LoVo cells and explored the molecular mechanism of its effect to guide the clinical diagnosis, treatment, and follow-up of colorectal cancer.

Methods

The expression of circBACH1 in colorectal cancer cells was measured to determine the high expression of BACH1 in colorectal cancer (CRC). LoVo was selected for a follow-up experiment. Then, quantificational reverse transcription-polymerase chain reaction (qRT-PCR) and biotinylated let-7a-5p probes were used to confirm that the expression of let-7a-5p was lowered in colorectal cancer, and let-7a-5p was the downstream target of BACH1 in CRC. Cell counting Kit-8 (CCK-8), Transwell, and wound repair experiments confirmed that BACH1 augmented the proliferation, migration, and metastasis of CRC by regulating let-7a-5p. The apoptosis rate was measured by flow cytometry. It was concluded that BACH1 inhibited apoptosis by regulating let-7a-5p in CRC. The results of the bioinformatics analysis showed that CREB5 was overexpressed in CRC by qRT-PCR and Western blot. The results of qRT-PCR, CCK-8 assay, Transwell assay, and flow cytometry showed that let-7a-5p inhibited the proliferation, migration, and invasion of CRC cells through targeting CREB5 and augmented cell apoptosis. According to tumor growth and the determination of CREB5 by Western blot, BACH1 can affect the proliferation of CRC cells through CREB5.

Results

Overall, our study confirmed that BACH1 and CREB5 increased, while the expression of let-7a-5p was lowered in colorectal cancer cells. These different expressions enhance the proliferation, metastasis, and migration of colorectal cancer cells and inhibit colorectal cancer cells' apoptosis.

Conclusions

Our study clearly illustrates the molecular mechanism of circBACH1 acting on colorectal cancer, which can be used as a therapeutic target to augment colorectal cancer treatment.

Plasma circular RNA panel acts as a novel diagnostic biomarker for colorectal cancer detection

Circular RNAs (circRNAs) can function as key regulators of oncogenic processes, making them ideal diagnostic biomarkers of many cancers. However, few studies to date have reported on plasma circRNA profiles associated with colorectal cancer (CRC). To that end, we herein employed microarray- and qRT-PCR-based approaches to evaluate circulating plasma circRNAs in CRC patients. Area under the receiver operating characteristic curve (AUC) values were then used to assess the diagnostic utility of these circRNAs. We ultimately determined that hsa_circ_0001900, hsa_circ_0001178, and hsa_circ_0005927 were upregulated in the plasma of CRC patients relative to healthy controls and were correlated with clinicopathological findings in these patients. We further established that a panel composed of these three circRNAs (CircPanel) was able to differentiate between patients with and without CRC more reliably than CEA (carcinoembryonic antigen) (AUC, 0.859 [95% confidence interval, CI: 0.805-0.903] vs. 0.698 [0.631-0.759], P=0.0003), enabling us to detect patients with CEA-negative CRC. In conclusion, our study reveals that CircPanel could serve as a promising potential biomarker for CRC diagnosis.

Expression profile and diagnostic value of circRNAs in peripheral blood from patients with systemic lupus erythematosus

Circular RNAs (circRNAs) have gained attention due to their performance in disease diagnosis. However, the characteristics of circRNAs in peripheral blood from patients with systemic lupus erythematosus (SLE) remain unknown. Therefore, the aim of the present study was to determine the expression profile and diagnostic potential of circRNAs in peripheral blood from patients with SLE. The global circRNA expression in the peripheral blood of patients with SLE and healthy controls (HCs) was detected using a circRNA microarray. Then, the expression levels of three upregulated circRNAs were selected for further validation by reverse transcription‑quantitative PCR (RT‑qPCR) in a training set. Moreover, the diagnostic value of these circRNAs was assessed by constructing a receiver operating characteristic curve, and then verified in a blind testing set. In total, 1,566 circRNAs were identified to be dysregulated between patients with SLE and HCs (≥2 fold change, P<0.05). Furthermore, the RT‑qPCR results were consistent with the microarray data, in that all three selected circRNAs, hsa_circ_0082688, hsa_circ_0082689 and hsa_circ_0008675, were significantly upregulated in patients with SLE (P<0.05). Results from the training set demonstrated that the combination of hsa_circ_0082688‑hsa_circ_0082689 may provide the most beneficial diagnostic potential. Moreover, the blind test results indicated that the combination model of hsa_circ_0082688‑hsa_circ_0082689 could effectively discriminate between patients with SLE from patients with rheumatoid arthritis and HCs, with a sensitivity of 91.30%, a specificity of 78.57% and an accuracy of 82.28%. Moreover, the combination model of hsa_circ_0082688‑hsa_circ_0082689 + anti‑dsDNA could more effectively discriminated the SLE group from the control groups, with a sensitivity of 95.65%, a specificity of 100.00% and an accuracy of 98.73%. In addition, correlation analysis results suggested that all three circRNAs in patients with SLE did not correlate with the SLE disease activity index. In conclusion, the expression levels of hsa_circ_0082688‑hsa_circ_0082689 may serve as potential biomarkers for SLE diagnosis.

Circ0106714 inhibits tumorigenesis of colorectal cancer by sponging miR-942-5p and releasing DLG2 via Hippo-YAP signaling

This study aimed to investigate the role of circ0106714-miR-942-5p-discs large homolog 2 (DLG2), a novel interactome, in colorectal cancer (CRC). Circ0106714 was found to be the most significantly downregulated circular RNA in CRC using a bioinformatics method, and we researched whether the ability of circ0106714 to sponge miR-942-5p and release DLG2 could affect CRC development via Hippo-YES-associated protein (YAP) signaling. We first employed qRT-PCR and immunoblotting to detect messenger RNA (mRNA) and protein expression, respectively. Live imaging of mice tumor xenografts was then conducted to study the effect of circ0106714 on tumor progression in vivo. Reporter gene assays were subsequently conducted to verify the predicted targeting relationship between circ0106714, miR-942-5p, and DLG2 mRNA in SW480 and HCT116 cell lines. As well as using flow cytometry for both apoptosis and cell cycle profile analyses, CCK-8 and clone foci formation assays were performed to assess cell survival. Wound healing assay and transwell invasion assay were later carried out to evaluate the migration and invasion of the cell lines. Findings revealed that circ0106714 and DLG2 were significantly downregulated, while miR-942-5p was significantly upregulated in human CRC tissues and cell lines. However, circ0106714 upregulation significantly suppressed tumor progression in vivo and inhibited the malignancy phenotypes of tumor cells in vitro by targeting miR-942-5p. Also discovered in this research was that miR-942-5p could directly target DLG2 mRNA, thus enhancing the malignancy phenotypes of CRC cells. We even found that DLG2 overexpression resulted in enhanced phosphorylation of YAP, a critical downstream effector of DLG2. This downstream effector was demonstrated to have a tumor-suppressive capacity in CRC cell lines. In sum, circ0106714 could suppress CRC by sponging miR-942-5p and releasing DLG2, thus promoting YAP phosphorylation.

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.

Hsa_circ_0026416 promotes proliferation and migration in colorectal cancer via miR-346/NFIB axis

Background

Colorectal cancer (CRC) is one of the most common cancers worldwide. Circular RNAs (circRNAs), a novel class of non-coding RNAs, have been confirmed to be key regulators of many diseases. With many scholars devoted to studying the biological function and mechanism of circRNAs, their mysterious veil is gradually being revealed. In our research, we explored a new circRNA, hsa_circ_0026416, which was identified as upregulated in CRC with the largest fold change (logFC = 3.70) of the evaluated circRNAs via analysing expression profiling data by high throughput sequencing of members of the GEO dataset (GSE77661) to explore the molecular mechanisms of CRC.

Methods

qRT-PCR and western blot analysis were utilized to assess the expression of hsa_circ_0026416, miR-346 and Nuclear Factor I/B (NFIB). CCK-8 and transwell assays were utilized to examine cell proliferation, migration and invasion in vitro, respectively. A luciferase reporter assay was used to verify the combination of hsa_circ_0026416, miR-346 and NFIB. A nude mouse xenograft model was also utilized to determine the role of hsa_circ_0026416 in CRC cell growth in vivo.

Results

Hsa_circ_0026416 was markedly upregulated in CRC patient tissues and plasma and was a poor prognosis in CRC patients. In addition, the area under the curve (AUC) of hsa_circ_0026416 (0.767) was greater than the AUC of CEA (0.670), CA19-9 (0.592) and CA72-4 (0.575). Functionally, hsa_circ_0026416 promotes cell proliferation, migration and invasion both in vitro and in vivo. Mechanistically, hsa_circ_0026416 may function as a ceRNA via competitively absorbing miR-346 to upregulate the expression of NFIB.

Conclusions

In summary, our findings demonstrate that hsa_circ_0026416 is an oncogene in CRC. Hsa_circ_0026416 promotes the progression of CRC via the miR-346/NFIB axis and may represent a potential biomarker for diagnosis and therapy in CRC.

Circular RNA circABCC4 acts as a ceRNA of miR-154-5p to improve cell viability, migration and invasion of breast cancer cells in vitro

Breast cancer is one of the dominant cancers of women-related death universal. This inquiry aims to disclose the probable role of circABCC4 in breast cancer. The level of circABCC4 was discovered through qRT-PCR. The reactions of circABCC4 and miR-154-5p on the cell viability, apoptosis, migration as well as invasion were, respectively, inspected by CCK-8, flow cytometry, and transwell assays. The association betwixt circABCC4 and miR-154-5p was investigated. The accumulation of NF-κB and Wnt/β-catenin pathway proteins was discovered through Western blot. The expression of circABCC4 was far great in tumor tissues than in normal tissues. Knockdown of circABCC4 could subdue cell viability, migration, invasion, and enhance apoptosis in breast cancer cell lines. CircABCC4 negatively regulated the manifestation of miR-154-5p and shared binding sites with the latter. Suppression of miR-154-5p expression partially conversed the repressive effect of circABCC4 knockdown on breast cancer cell viability, migration, invasion, and NF-κB and Wnt/β-catenin pathways. CircABCC4 knockdown repressed breast cancer cells viability, migration, and invasion by up-regulating miR-154-5p via inhibiting NF-κB and Wnt/β-catenin signal pathways.

MetaDE-Based Analysis of circRNA Expression Profiles Involved in Gastric Cancer

BACKGROUND

Circular RNAs (circRNAs) could play carcinogenic roles in gastric cancer (GC) and have potential to be biomarkers for GC early diagnosis, which needs to be further excavated and supported by more evidence.

AIMS

The study aims to identify more authentic circRNA expression profiles that could function as potential biomarkers in GC.

METHODS

circRNA expression data in three microarrays were downloaded from Gene Expression Omnibus datasets. A systematic meta-analysis based on an integrated dataset pre-processed from the three microarrays was conducted to identify a panel of differentially expressed circRNAs (DEcircs) by using the metaDE package. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes term enrichment were used to note the corresponding functions of DEcircs. Quantitative real-time polymerase chain reaction was applied to verify the DEcircs expression in cancer tissues and adjacent paracancerous tissues. A GC risk-related circRNAs-miRNAs-mRNAs network was further constructed and analyzed.

RESULTS

MetaDE analysis suggested 64 DEcircs between cancer tissues and adjacent normal tissues. GO and KEGG analysis showed that the parental genes of these DEcircs were mainly associated with histone methylation, Wnt signalosome and histone methylation activity. Hsa_circ_0005927 and hsa_circ_0067934 were verified in GC tissues, and a GC risk-related network was constructed.

CONCLUSION

MetaDE-based circRNA expression profiles revealed a series of potential biomarkers involved in GC. Two circRNAs, hsa_circ_0005927 and hsa_circ_0067934, could be more authentic biomarkers for GC screening. The GC risk-related network of hsa_circ_0005927/hsa_circ_0067934 and their downstream targets will provide new genetic insights for GC research.

CircTBL1XR1/miR-424 axis regulates Smad7 to promote the proliferation and metastasis of colorectal cancer

BACKGROUND

This study analyzed the effect of circular RNA (circRNA), TBL1XR1, on the malignant progression of colon cancer cells and explored its possible molecular mechanism.

METHODS

The expression levels of circTBL1XR1 in colorectal cancer and paracancerous tissues were detected by quantitative real-time polymerase chain (qRT-PCR). Changes in circTBL1XR1 expression in normal intestinal epithelial cells and colon cancer cell lines were detected at the cellular level. LoVo and SW620 cells with the highest circTBL1XR1 expression were transfected with circTBL1XR1, and the transfection efficiency was verified by qRT-PCR. The effects of circTBL1XR1 on the proliferation, migration, and invasion of colon cancer cells were detected by MTT, Transwell migration, and invasion assay, and a subcutaneous tumor model. Target genes of circTBL1XR1 were verified by luciferase reporter assay. Expression levels of circTBL1XR1 target genes were detected by qRT-PCR and Western blotting.

RESULTS

circTBL1XR1 was highly expressed in colon cancer patients. circTBL1XR1 expression in colon cancer cells was also higher than that in normal intestinal cells. In vivo and in vitro experimental results showed that overexpression of circTBL1XR1 enhanced the proliferation, migration, and invasion of colon cancer cells. After lowering circTBL1XR1, the ability of migration and invasion of colon cancer cells was significantly reduced. Bioinformatics retrieval and luciferase reporter gene assay confirmed that circTBL1XR1 can bind to microRNA-424 (miR-424) and that the Smad7 gene is the target gene of miR-424.

CONCLUSIONS

circTBL1XR1 was highly expressed in colon cancer, and miR-424 was poorly expressed in colon cancer cells. circTBL1XR1 regulates the expression of Smad7 through miR-424, thereby affecting the malignant progression of colorectal cancer.

circRAE1 promotes colorectal cancer cell migration and invasion by modulating miR-338-3p/TYRO3 axis

Background

Growing evidence has revealed the involvement of circular RNAs (circRNAs) in numerous carcinogenesis. However, the role of circRNAs in the cancer biology of colorectal cancer (CRC) remains vague.

Methods

Quantitative RT-PCR was used to detect the expression level of circRAE1 in CRC tissues and CRC cell lines. Cell proliferation, migration, and invasion were detected using CCK8 assay, Colony formation assay, wound-healing and Transwell assays. The interaction between circRAE1 and miR-338-3p and TRYO3 was confirmed using dual-luciferase reporter assays.

Results

We uncovered a novel circRNA Hsa_circ_0060967 (also known as circRAE1) that was remarkably increased in CRC tissues. The high circRAE1 level was positively associated with advanced tumor stage, lymph node metastasis, and tumor size. The loss-of-function assay showed that circRAE1 accelerated cell proliferation, migration, and invasion. Besides, miR-338-3p was lowly expressed in the CRC tissues and CRC cell lines. The dual-luciferase reporter assays showed that circRAE1 could sponge miR-338-3p, which targeted TRYO3 in CRC cells. Furthermore, the overexpression of circRAE1 could rescue the impaired migration and invasion triggered by miR-338-3p mimics or si-TYRO3 in CRC cells and vice versa.

Conclusion

We identified the network of circRAE1, miR-338-3p, and TYRO3 in CRC cells and determined that the increase in circRAE1 could serve as an oncogene by sponging miR-338-3p, which resulted in an upregulated TYRO3 expression. The finding suggests that circRAE1 is a potential therapeutic target and diagnostic marker for CRC treatment.

Comprehensive Analysis of circRNA-miRNA-mRNA Network in Cervical Squamous Cell Carcinoma by Integrated Analysis

Purpose

Cervical squamous cell carcinoma (CSCC) seriously affects women’s health worldwide, and it is of great significance to illuminate the specific role of circRNAs in CSCC.

Materials and Methods

Three mRNA datasets, two miRNA datasets and one circRNA dataset of CSCC, downloaded from GEO, were utilized in this study. Differentially expressed mRNAs (DEmRNAs), miRNAs (DEmiRNAs) and circRNAs (DEcircRNAs) were identified, and a ceRNA (DEcircRNA-DEmiRNA-DEmRNA) regulatory network was constructed. GO and pathway analyses of DEcircRNAs and DEmRNAs in the ceRNA regulatory network were performed. Quantitative real-time polymerase chain reaction (qRT-PCR) validation of the expression of the selected DEmRNAs, DEmiRNAs and DEcircRNAs was performed.

Results

A total of 1356 DEmRNAs, 13 DEmiRNAs and 77 DEcircRNAs were obtained. The ceRNA network contained 3 circRNA-miRNA pairs and 158 miRNA-mRNA pairs, including 3 circRNAs, 3 miRNAs, and 138 mRNAs. Functional annotation of DEmRNAs in the ceRNA regulatory network revealed that these DEmRNAs were significantly enriched in cell cycle, p53 signalling pathway and DNA replication. The qRT-PCR results were generally consistent with those of our integrated analysis.

Conclusion

In conclusion, we speculate that the regulation of the hsa_circ_0000069/hsa-miR-125b-5p/CDKN2A and hsa_circ_0020594/hsa-let-7c-5p/CCNB2 axes may be involved in CSCC.

Circular noncoding RNA circMBOAT2 is a novel tumor marker and regulates proliferation/migration by sponging miR-519d-3p in colorectal cancer

Colorectal cancer (CRC) is a common malignant tumor with a poor prognosis. However, its pathogenesis has not been fully elucidated, accounting for poor overall survival. Circular RNA (circRNA) is a class of noncoding RNAs discovered many years ago. Only recently have they been re-evaluated for their important roles in the regulation of gene expression. Studies have confirmed that circRNAs have important biological functions in a variety of malignant tumors. This study aimed to characterize one circRNA derived from the MBOAT2 gene and termed it circMBOAT2, which has been reported to promote prostate cancer progression. CircMBOAT2 is highly expressed in both CRC tissues and serum samples, and has a correlation with tumor stage. The receiver-operating characteristic curves suggested that circMBOAT2 acted as a novel diagnostic tumor marker in CRC. Univariate and multivariate analyses showed that the levels of circMBOAT2 in tissues were independent prognostic markers of CRC. Further functional studies revealed that circMBOAT2 served as a microRNA (miRNA) sponge of miR-519d-3p and promoted the proliferation, migration, and invasion of CRC cells. Also, circMBOAT2 regulated cell proliferation and migration by competitively binding to miR-519d-3p and targeting troponin-associated protein (TROAP) in CRC cells. These results suggested that circMBOAT2 might be a novel potential biomarker of CRC.

circ_0136666 Facilitates the Progression of Colorectal Cancer via miR-383/CREB1 Axis

Background

The changes in dietary patterns cause an increased incidence of colorectal cancer (CRC) globally. We aimed to explore the mechanism behind circular RNA circ_0136666 in the progression of CRC.

Materials and Methods

The expression of circ_0136666, miR-383 and cAMP response element binding protein 1 (CREB1) was detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell proliferation, apoptosis and glycolysis were measured by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry and glucose or lactate detection kit, respectively. The combination between miR-383 and circ_0136666 or CREB1 in 293T cells was predicted by Circular RNA Interactome or Starbase software and confirmed by dual-luciferase reporter assay. Western blot assay was performed to detect the abundance of CREB1, hexokinase 2 (HK2) and lactate dehydrogenase A (LDHA) in CRC cells. Murine xenograft model was established to verify the function of circ_0136666 in vivo.

Results

circ_0136666 was aberrantly up-regulated in CRC tissues and cells, and it promoted the proliferation and glycolysis and inhibited the apoptosis of CRC cells. circ_0136666 accelerated the progression of CRC through directly targeting and down-regulating miR-383. CREB1 could bind to miR-383 in 293T cells. The overexpression of CREB1 reversed the inhibitory effects of miR-383 accumulation on the proliferation and glycolysis and the promoting impact on the apoptosis of CRC cells. The enrichment of CREB1 was modulated by circ_0136666/miR-383 signaling in CRC cells. The glycolysis-related proteins (HK2 and LDHA) were modulated by circ_0136666/miR-383/CREB1 axis in CRC cells. circ_0136666 accelerated the growth of CRC tumors via circ_0136666/miR-383/CREB1 axis in vivo.

Conclusion

circ_0136666 deteriorated CRC through miR-383/CREB1 axis. circ_0136666/miR-383/CREB1 axis might be an underlying therapeutic target for CRC therapy.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

RNA-Seq Profiling of Serum Exosomal Circular RNAs Reveals Circ-PNN as a Potential Biomarker for Human Colorectal Cancer

Circular RNAs (circRNAs) are emerging as cardinal areas of focus in the non-coding RNA field. Growing evidences have revealed exosomal circRNAs as potential biomarkers for detection of various cancers. However, the clinical importance of most serum exosomal circRNAs in colorectal cancer (CRC) have rarely been investigated. In this study, we examined the possible clinical application of serum exosomal circRNAs in the diagnosis of CRC. Firstly, we conducted RNA sequencing (RNA-seq) analysis using fifty CRC and fifty healthy control serum samples to identify CRC-related circRNAs. The sequencing data showed 122 differentially expressed circRNAs including 100 up-regulated and 22 down-regulated circRNA transcripts in CRC patients. Then, eight most dysregulated circRNAs were selected for validation by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assay. Validation analysis revealed that the serum exosomal circ-PNN (hsa_circ_0101802) levels were significantly up-regulated in CRC cases compared with those in the healthy control groups. Receiver operating characteristic curve (ROC) analysis suggested that circ-PNN had significant value in CRC diagnosis with areas under the ROC curve (AUC) of 0.855 and 0.826 in the training and validation sets, respectively. We also found that the AUC of serum exosomal circ-PNN for early-stage CRC was 0.854. Finally, a network map based on circ-PNN was constructed to determine its potential miRNA-mRNAs binding. We also demonstrated that the expression of hsa-miR-6833-3P, hsa-let-7i-3p and hsa-miR-1301-3P were negatively correlated with circ-PNN in CRC patients. Collectively, our findings indicated that serum exosomal circ-PNN might be a potential non-invasive biomarker for the detection of CRC and may play a crucial role in the pathogenesis of CRC.

CircAPLP2 regulates the proliferation and metastasis of colorectal cancer by targeting miR-101-3p to activate the Notch signalling pathway

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers, and it has a poor prognosis. Emerging evidence shows that circular RNAs (circRNAs) may act as good therapeutic targets for cancers due to their abundance and stability. However, their regulatory role in CRC needs further investigation. This study revealed that circAPLP2 was upregulated and miR-101-3p was downregulated in CRC tissues and cells compared to normal controls. Knockdown of circAPLP2 and overexpression of miR-101-3p inhibited the cell proliferation, migration and invasion and induced the apoptosis of CRC cells. circAPLP2 acted as a miR-101-3p sponge to upregulate its target gene Notch1, which activated cascades of proliferation- and metastasis-related proteins (c-Myc, cyclin D1, MMP-2 and MMP-9). Additionally, knockdown of circAPLP2 suppressed tumour growth and liver metastases of CRC in nude mice. Taken together, these results indicate that circAPLP2 promotes proliferation and metastasis by targeting miR-101-3p to activate the Notch signalling pathway in CRC, which provides new insights into the mechanisms underlying CRC malignancy and suggests a new therapeutic target.

The function and mechanism of circular RNAs in gastrointestinal tumours

Gastrointestinal tumours are tumours that originate in the digestive tract and have extremely high morbidity and mortality. The main categories include: oesophageal, gastric, and colorectal cancers. Circular RNAs are a new class of non‐coding RNAs with a covalent closed‐loop structure without a 5’ cap or a 3’ poly A tail, which can encode a small amount of polypeptide. Recent studies have shown that circRNAs are involved in multiple biological processes during the development of gastrointestinal tumours including proliferation, invasion and metastasis, radio‐ and chemoresistance, and inflammatory responses. Also, the clinical and pathological characteristics of the patient, such as staging and lymph node metastasis, are closely associated with the expression level of circRNAs. Further investigation of the function and the role of circRNAs in the development of gastrointestinal tumours will provide new directions for its clinical diagnosis and treatment.