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

Circular RNAs in coronary heart disease: From molecular mechanism to promising clinical application (Review)

Coronary heart disease (CHD) remains a leading cause of morbidity and mortality worldwide, posing a substantial public health burden. Despite advancements in treatment, the complex etiology of CHD necessitates ongoing exploration of novel diagnostic markers and therapeutic targets. Circular RNAs (circRNAs), a distinct class of non‑coding RNAs with a covalently closed loop structure, have emerged as significant regulators in various diseases, including CHD. Their high stability, tissue‑specific expression and evolutionary conservation underscore their potential as biomarkers and therapeutic agents in CHD. This review discusses the current knowledge on circRNAs in the context of CHD and explores the molecular mechanisms by which circRNAs influence the pathophysiology of CHD, including cardiomyocyte death, endothelial injury, vascular dysfunction and inflammation. It also summarizes the emerging evidence highlighting the differential expression of circRNAs in patients with CHD and their potential utilities as non‑invasive diagnostic and prognostic biomarkers and therapeutic targets for this disease.

CircRNAs and miRNAs: Key Player Duo in Breast Cancer Dynamics and Biomarkers for Breast Cancer Early Detection and Prevention

Breast cancer (BC) remains a significant global health issue, necessitating advanced molecular approaches for early detection and prevention. This review delves into the roles of microRNAs (miRNAs) and circular RNAs (circRNAs) in BC, highlighting their potential as non-invasive biomarkers. Utilizing in silico tools and databases, we propose a novel methodology to establish mRNA/circRNA/miRNA axes possibly indicative of early detection and possible prevention. We propose that during early tumor initiation, some changes in oncogene or tumor suppressor gene expression (mRNA) are mirrored by alterations in corresponding circRNAs and reciprocal changes in sponged miRNAs affecting tumorigenesis pathways. We used two Gene Expression Omnibus (GEO) datasets and identified five mRNA/circRNA/miRNA axes as early possible tumor initiation biomarkers. We further validated the proposed axes through a Kaplan-Meier (KM) plot and enrichment analysis of miRNA expression using patient data. Evaluating coupled differential expression of circRNAs and miRNAs in body fluids or exosomes provides greater confidence than assessing either, with more axes providing even greater confidence. The proposed methodology not only improves early BC detection reliability but also has applications for other cancers, enhancing preventive measures.

Non-Coding RNAs as Key Regulators in Lung Cancer

For several decades, most lung cancer investigations have focused on the search for mutations in candidate genes; however, in the last decade, due to the fact that most of the human genome is occupied by sequences that do not code for proteins, much attention has been paid to non-coding RNAs (ncRNAs) that perform regulatory functions. In this review, we principally focused on recent studies of the function, regulatory mechanisms, and therapeutic potential of ncRNAs including microRNA (miRNA), long ncRNA (lncRNA), and circular RNA (circRNA) in different types of lung cancer.

Emerging functions and significance of circCDYL in human disorders

Circular RNAs (circRNAs) are a group of non-coding transcripts in which a loop structure is shaped via a back splicing procedure. They have central roles in the regulation of gene expression. hsa_circ_0008285, alternatively named as circCDYL, is a circular RNA originated from the exon 4 of CDYL gene. It is produced by a back-splice incident and is mainly located in the cytoplasm. It has no internal ribosome entry site, open reading frame and intronic sequences. CircCDYL dysregulation has been reported in the malignant conditions including multiple myeloma, mantle cell lymphoma, breast cancer, non-small cell lung cancer, Wilms tumor, bladder cancer, colon cancer, and hepatocellular carcinoma. It also has an emerging role in the pathophysiology of non-malignant conditions including myocardial infarction, gestational diabetes mellitus, membranous nephropathy, and abdominal aortic aneurysm. In the current study, we summarize the emerging roles of circCDYL in malignant and non-malignant conditions.

A Novel circ_0104345/miR-876-3p/ZBTB20 Axis Regulates the Proliferation, Migration, Invasion, and Apoptosis of Breast Cancer Cells

Breast cancer (BC) is one of the most common malignant tumors in women. CircRNA/miRNA/mRNA regulatory axes have been shown to be involved in the pathogenesis of BC. Here, we sought to analyze the functional mechanism of circ_0104345 in BC. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the levels of circ_0104345, miR-876-3p and zinc finger and BTB domain containing 20 (ZBTB20) mRNA. Cell Counting Kit-8 (CCK8) and 5-ethynyl-2'-deoxyuridine (EdU) assays were used to test cell viability and proliferation, respectively. Cell migration was tested by wound healing assay, and cell invasion was examined by transwell assay. Tube formation ability was tested by angiogenesis assay. Flow cytometry was applied for cell apoptosis. Western blot assay was utilized to measure the protein expression. The relationship between miR-876-3p and circ_0104345 or ZBTB20 was identified by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Xenografts in mice were conducted to analyze the effect of sh-circ_0104345 on tumor growth in vivo. Circ_0104345 and ZBTB20 were upregulated and miR-876-3p expression was decreased in BC. Circ_0104345 knockdown inhibited cell proliferation, migration, invasion, and enhanced cell apoptosis. MiR-876-3p was targeted by circ_0104345. MiR-876-3p depletion reversed the effects of circ_0104345 downregulation on the progression of BC cells. ZBTB20 was regulated by circ_0104345 through miR-876-3p. The effects of miR-876-3p on BC cell behaviors were restored by ZBTB20 increase. The results of in vivo experiments indicated that silencing of circ_0104345 blocked the growth of xenograft tumors. In this study, we demonstrated, for the first time, the crucial regulation of the new circ_0104345/miR-876-3p/ZBTB20 axis in the biological phenotypes of BC cells.

Circ-DTL sponges miR-758-3p to accelerate cervical cancer malignant progression by regulating DCUN1D1 expression

Circular RNAs (circRNAs) play important roles in regulating various cancer progression. However, the function and clinical significance of circ-denticleless E3 ubiquitin proteinligase homolog (DTL) in cervical cancer (CC) have not been studied. The present work explored the function and mechanism of circ-DTL in CC development. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to examine the expression of circ-DTL, miR-758-3p, and DCUN1D1. Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) assays were used to detect cell proliferation. Cell cycle and cell apoptosis were investigated by flow cytometry. Wound-healing assay and transwell assay were conducted to assess cell migration and cell invasion. Western blot assay was carried out to determine protein expression. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were used to identify the relationship between miR-758-3p and circ-DTL or DCUN1D1. Xenograft mouse model assay was conducted to explore the role of circ-DTL in CC progression in vivo. Circ-DTL and DCUN1D1 expression were upregulated in CC tissues and CC cells, but miR-758-3p expression was downregulated. Knockdown of circ-DTL inhibited CC cell growth, migration, and invasion and promoted cell cycle arrest and cell apoptosis. Circ-DTL could sponge miR-758-3p to modulate CC cell progression. Moreover, miR-758-3p inhibited CC malignant development by suppressing DCUN1D1 expression. In addition, circ-DTL knockdown repressed CC cell tumor properties in vivo. Circ-DTL acted as a tumor promoter in CC development by regulating the miR-758-3p/DCUN1D1 pathway.

The oncogenic potential of Rab-like protein 1A (RBEL1A) GTPase: The first review of RBEL1A research with future research directions and challenges

Research on Rab-like protein 1A (RBEL1A) in the past two decades highlighted the oncogenic properties of this gene. Despite the emerging evidence, its importance in cancer biology was underrated. This is the first RBEL1A critical review covering its discovery, biochemistry, physiological functions, and clinical insights. RBEL1A expression at the appropriate levels appears essential in normal cells and tissues to maintain chromosomal stability; however, its overexpression is linked to tumorigenesis. Furthermore, the upstream and downstream targets of the RBEL1A signaling pathways will be discussed. Mechanistically, RBEL1A promotes cell proliferation signals by enhancing the Erk1/2, Akt, c-Myc, and CDK pathways while blunting the apoptotic signals via inhibitions on p53, Rb, and caspase pathways. More importantly, this review covers the clinical relevance of RBEL1A in the cancer field, such as drug resistance and poor overall survival rate. Also, this review points out the bottle-necks of the RBEL1A research and its future research directions. It is becoming clear that RBEL1A could potentially serve as a valuable target of anticancer therapy. Genetic and pharmacological researches are expected to facilitate the identification and development of RBEL1A inhibitors as cancer therapeutics in the future, which could undoubtedly improve the management of human malignancy.

hsa_circ_0000264 promotes tumor progression via the hsa-let-7b-5p/HMGA2 axis in head and neck squamous cell carcinoma

OBJECTIVE

Circular RNAs (CircRNAs) are involved in various tumors. However, their role in head and neck squamous cell carcinoma (HNSCC) is unknown. CircRNA sequencing data showed that hsa_circ_0000264 is significantly upregulated in HNSCC tissues. In this study, we aimed to investigate the role of hsa_circ_0000264 in HNSCC and elucidate its underlying regulation mechanism.

MATERIALS AND METHODS

RNase R treatment was performed to confirm the loop structure of hsa_circ_0000264. Fluorescence in situ hybridization was performed to show the subcellular localization of hsa_circ_0000264. We then performed wound healing assay, Transwell assay, Western blot, and in vivo experiments to determine the effect of alterations in hsa_circ_0000264 expression. We performed RNA pull-down and dual luciferase reporter assay to identify and confirm the binding sites in RNAs.

RESULTS

hsa_circ_0000264 was upregulated in HNSCC tissues and cells, and its loop structure was confirmed. Knockdown of hsa_circ_0000264 inhibited the migration, invasion, and epithelial-to-mesenchymal transition of HNSCC cells in vivo and in vitro. Mechanistically, hsa_circ_000026 upregulation can upregulate the expression of high mobility group AT-hook 2 (HMGA2) by sponging hsa-let-7b-5p, which in turn promotes HNSCC progression.

CONCLUSION

Our results showed that hsa_circ_0000264 promotes HNSCC progression via the hsa-let-7b-5p/HMGA2 axis, and hsa_circ_0000264 can serve as a potential target for HNSCC treatment.

The emerging regulatory roles of non-coding RNAs associated with glucose metabolism in breast cancer

Altered energy metabolism is one of the hallmarks of tumorigenesis and essential for fulfilling the high demand for metabolic energy in a tumor through accelerating glycolysis and reprogramming the glycolysis metabolism through the Warburg effect. The dysregulated glucose metabolic pathways are coordinated not only by proteins coding genes but also by non-coding RNAs (ncRNAs) during the initiation and cancer progression. The ncRNAs are responsible for regulating numerous cellular processes under developmental and pathological conditions. Recent studies have shown that various ncRNAs such as microRNAs, circular RNAs, and long noncoding RNAs are extensively involved in rewriting glucose metabolism in human cancers. In this review, we demonstrated the role of ncRNAs in the progression of breast cancer with a focus on outlining the aberrant expression of glucose metabolic pathways. Moreover, we have discussed the existing and probable future applications of ncRNAs to regulate energy pathways along with their importance in the prognosis, diagnosis, and future therapeutics for human breast carcinoma.

Circ-MALAT1 accelerates cell proliferation and epithelial mesenchymal transformation of colorectal cancer through regulating miR-506-3p/KAT6B axis

Colorectal cancer (CRC) is a prevalent malignant tumor of the digestive tract. Circular RNAs may play important roles in the progression of CRC. In this study, we investigated the roles and mechanisms of action of circ-MALAT1 in CRC. Gene expression and protein abundance were determined using qRT-PCR and western blot, respectively. Cell proliferation and migration were assessed by MTT, clone formation, and wound-healing assays. The interactions among the long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (circ-MALAT1), miR-506-3p, and lysine acetyltransferase 6B (KAT6B) were predicted using the StarBase software and confirmed by the luciferase activity assay. Circ-MALAT1 and KAT6B were upregulated, while miR-506-3p was downregulated in CRC cells. We validated that knocking down of circ-MALAT1 suppressed proliferation, migration, and epithelial-mesenchymal transition (EMT) of CRC cells, and these effects were abolished by miR-506-3p downregulation or KAT6B sufficiency. Our study suggests that circ-MALAT1 could sponge miR-506-3p to regulate the expression of KAT6B. Moreover, KAT6B sufficiency could neutralize miR-506-3p-dependent growth arrest, migration, and EMT. Circ-MALAT1 promotes cell proliferation, migration, and EMT of CRC cells via the miR-506-3p/KAT6B axis, thereby acting as a novel potential therapeutic target for the treatment of colorectal cancer.

Identification of miR-106b-5p, miR-601, and miR-760 Expression and Their Clinical Values in Non-Small Cell Lung Cancer (NSCLC) Patients' Serum

AIM

to explore the relative quantitative determination of the serum level of three miRNAs (miR-601, 760, and 106b-5p) and determine their expression pattern in non-small cell lung cancer (NSCLC) patients in comparison to controls. Also, to reveal each miRNA's diagnostic and prognostic impact on NSCLC patients.

MATERIALS AND METHODS

Serum miR-106b-5p, 601, and 760 expression profiles were estimated by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) for 70 NSCLC patients, age-matched with 30 control subjects. The receiver operating characteristic (ROC) curve analysis estimated their diagnostic and prognostic potentials.

RESULTS

In comparison to the control, the miR-106b-5p expression pattern was upregulated (1.836 ± 0.254, p = 0.0012) while both miR-601 and miR-760 expression patterns were considerably downregulated (-0.586 ± 0.1906, p < 0.0001) and (-1.633 ± 0.152, p < 0.0001), respectively with predominant down-expression for miR-760 among cases. MiR-760 showed the highest diagnostic potential (AUC = 0.943 and 0.864 respectively), whereas miR-601 has a higher prognostic power (AUC = 0.771 and 0.682, respectively) for differentiating early stages (I/II) NSCLC patients from control subjects. Moreover, miR-760 presented the highest prognostic potential for differentiating NSCLC stages.

CONCLUSION

Both serum miR-760 and miR-601 may be used as potential biomarkers of NSCLC in Egyptian patients with a stronger staging and diagnostic potential for miR-760.

Interactions between circRNAs and miR-141 in Cancer: From Pathogenesis to Diagnosis and Therapy

The function of non-coding RNAs (ncRNAs) in the pathogenesis and development of cancer is indisputable. Molecular mechanisms underlying carcinogenesis involve the aberrant expression of ncRNAs, including circular RNAs (circRNAs), and microRNAs (miRNAs). CircRNAs are a class of single-stranded, covalently closed RNAs responsible for maintaining cellular homeostasis through their diverse functions. As a part of the competing endogenous RNA (ceRNAs) network, they play a central role in the regulation of accessibility of miRNAs to their mRNA targets. The interplay between these molecular players is based on the primary role of circRNAs that act as miRNAs sponges, and the circRNA/miRNA imbalance plays a central role in different pathologies including cancer. Herein, we present the latest state of knowledge about interactions between circRNAs and miR-141, a well-known member of the miR-200 family, in malignant transformation, with emphasis on the biological role of circRNA/miR-141/mRNA networks as a future target for novel anti-cancer therapies.

Therapeutic and diagnostic applications of exosomal circRNAs in breast cancer

Circular RNAs (circRNAs) are regulatory elements that are involved in orchestrating gene expression and protein functions and are implicated in various biological processes including cancer. Notably, breast cancer has a significant mortality rate and is one of the most common malignancies in women. CircRNAs have been demonstrated to contribute to the pathogenesis of breast cancer including its initiation, progression, metastasis, and resistance to drugs. By acting as miRNA sponges, circRNAs can indirectly influence gene expression by disrupting miRNA regulation of their target genes, ultimately altering the course of cancer development and progression. Additionally, circRNAs can interact with proteins and modulate their functions including signaling pathways involved in the initiation and development of cancer. Recently, circRNAs can encode peptides that play a role in the pathophysiology of breast cancer and other diseases and their potential as diagnostic biomarkers and therapeutic targets for various cancers including breast cancer. CircRNAs possess biomarkers that differentiate, such as stability, specificity, and sensitivity, and can be detected in several biological specimens such as blood, saliva, and urine. Moreover, circRNAs play an important role in various cellular processes including cell proliferation, differentiation, and apoptosis, all of which are integral factors in the development and progression of cancer. This review synthesizes the functions of circRNAs in breast cancer, scrutinizing their contributions to the onset and evolution of the disease through their interactions with exosomes and cancer-related intracellular pathways. It also delves into the potential use of circRNA as a biomarker and therapeutic target against breast cancer. It discusses various databases and online tools that offer crucial circRNA information and regulatory networks. Lastly, the challenges and prospects of utilizing circRNAs in clinical settings associated with breast cancer are explored.

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.

CircCCDC66: Emerging roles and potential clinical values in malignant tumors

Circular RNAs (circRNAs) are endogenous non-coding RNAs (ncRNAs) with a closed-loop structure. In recent years, circRNAs have become the focus of much research into RNA. CircCCDC66 has been identified as a novel oncogenic circRNA and is up-regulated in a variety of malignant tumors including thyroid cancer, non-small cell carcinoma, gastric cancer, colorectal cancer, renal cancer, cervical cancer, glioma, and osteosarcoma. It mediates cancer progression by regulating epigenetic modifications, variable splicing, transcription, and protein translation. The oncogenicity of circCCDC66 suppresses or promotes the expression of related genes mainly through direct or indirect pathways. This finding suggests that circCCDC66 is a biomarker for cancer diagnosis, prognosis assessment and treatment. However, there is no review on the relationship between circCCDC66 and cancers. Thus, the expression, biological functions, and regulatory mechanisms of circCCDC66 in malignant tumor and non-tumor diseases are summarized. The clinical value and prognostic significance of circCCDC66 are also evaluated, which can provide insights helpful to those exploring new strategies for the early diagnosis and targeted treatment of malignancies.

The hsa_circ_0039857/miR-338-3p/RAB32 axis promotes the malignant progression of colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is a prevalent malignancy of the gastrointestinal. Circular RNAs (circRNAs) act as important roles in CRC malignant progression. However, the role of circ_0039857 in CRC is still unclear. Therefore, this study aimed to explore the function and mechanism of hsa_circ_0039857 in the CRC.

METHODS

The mRNA and protein expression were measured via RT-qPCR. RNase R assay and Actinomycin D were employed to evaluate the stability of circ_0039857. Functional experiments, such as proliferation and apoptosis, were applied to study the function of circ_0039857 in CRC cells. The underlying mechanisms of circ_0039857 were then analyzed by bioinformatics, dual-luciferase reporter gene assay, RNA pull-down and rescue experiments.

RESULTS

We revealed that circ_0039857 was significantly enhanced in CRC. Circ_0039857 was stabler than linear RNA in cells and valuable for the disease diagnosis. In addition, circ_0039857 knockdown inhibited proliferation and promoted apoptosis. Mechanistically, circ_0039857 positively regulated the expression of RAB32 via sponging miR-338-3p.

CONCLUSION

This study demonstrated that circ_0039857 knockdown suppressed CRC malignant progression through miR-338-3p/RAB32 axis. Most importantly, this will help us to better understand the circRNA network in CRC, and may find potential biomarkers and targets for CRC clinical treatment.

CircP50 functions through the phosphorylation- and acetylation-activated p53 pathway to mediate inorganic arsenic-induced apoptosis in A549 cells

As a class I carcinogen, arsenic has been reported to cause diseases accompanied by circRNAs regulating proliferation and apoptosis at the molecular level, but whether circP50 (circBase ID: hsa_circ_0008012) does the same has not been demonstrated. The aim of this study is to provide the basis for anti-lung cancer mechanism research, by studying the expression of circP50 under arsenic-induced conditions, and the effect and mechanism on the proliferation and apoptosis of A549 cells based on the circP50 knockdown models. To explore whether the circP50 is responsive to arsenic exposure, the qRT-PCR was applied to discover that the relative expression of circP50 in A549 cells increased only with increasing NaAsO₂ dose and independent of its metabolites. We further determined the mechanism of circP50 by establishing circP50 knockdown models. The results of cell viability and EdU assays indicated the proliferation of A549 cells. According to the western blotting, phosphorylation of p53 at Ser15, Ser376, and Ser392 and acetylation of p53 at Lys370 and Lys382 were inhibited, resulting in the deficiency of p53 expression. Subsequently, the expression of genes downstream of p53 was reduced, including p21, PUMA, Caspase3, and Bcl-xS. Furthermore, the expressions of IKB-α, p65, and p50 decreased, but C-myc expression did not change significantly, referring to the NF-κB pathway was not dominant. The results suggest that circP50 mainly functions through the p53 pathway to mediate apoptosis in response to arsenic exposure.

Promising Biomarkers in Head and Neck Cancer: The Most Clinically Important miRNAs

Head and neck cancers (HNCs) comprise a heterogeneous group of tumors that extend from the oral cavity to the upper gastrointestinal tract. The principal etiologic factors for oral tumors include tobacco smoking and alcohol consumption, while human papillomavirus (HPV) infections have been accused of a high incidence of pharyngeal tumors. Accordingly, HPV detection has been extensively used to categorize carcinomas of the head and neck. The diverse nature of HNC highlights the necessity for novel, sensitive, and precise biomarkers for the prompt diagnosis of the disease, its successful monitoring, and the timely prognosis of patient clinical outcomes. In this context, the identification of certain microRNAs (miRNAs) and/or the detection of alterations in their expression patterns, in a variety of somatic fluids and tissues, could serve as valuable biomarkers for precision oncology. In the present review, we summarize some of the most frequently studied miRNAs (including miR-21, -375, -99, -34a, -200, -31, -125a/b, -196a/b, -9, -181a, -155, -146a, -23a, -16, -29, and let-7), their role as biomarkers, and their implication in HNC pathogenesis. Moreover, we designate the potential of given miRNAs and miRNA signatures as novel diagnostic and prognostic tools for successful patient stratification. Finally, we discuss the currently ongoing clinical trials that aim to identify the diagnostic, prognostic, or therapeutic utility of miRNAs in HNC.