Hsa_circ_0020397 regulates colorectal cancer cell viability, apoptosis and invasion by promoting the expression of the miR-138 targets TERT and PD-L1

Circular RNAs perspective: exploring the direction of immunotherapy for colorectal cancer

Circular RNAs (circRNAs) are multifaceted molecules that play a pivotal role in regulating gene expression at both transcriptional and post-transcriptional levels. Their expression is highly tissue-specific and developmentally regulated, making them critical players in various physiological processes and diseases, particularly cancer. In colorectal cancer, circRNAs exhibit significantly dysregulated expression patterns and profoundly influence disease progression through diverse molecular mechanisms. Unraveling the complex roles of circRNAs in modulating colorectal cancer immunotherapy outcomes highlights their potential as both promising biomarkers and therapeutic targets. Moving forward, advancements in circRNA-based therapeutic strategies and delivery systems are poised to transform precision medicine, enabling early colorectal cancer diagnosis and improving patient prognosis.

Circular RNAs as key regulators in cancer hallmarks: New progress and therapeutic opportunities

Circular RNAs (circRNAs) have emerged as critical regulators in cancer biology, contributing to various cancer hallmarks, including cell proliferation, apoptosis, metastasis, and drug resistance. Defined by their covalently closed loop structure, circRNAs possess unique characteristics like high stability, abundance, and tissue-specific expression. These non-coding RNAs function through mechanisms such as miRNA sponging, interactions with RNA-binding proteins (RBPs), and modulating transcription and splicing. Advances in RNA sequencing and bioinformatics tools have enabled the identification and functional annotation of circRNAs across different cancer types. Clinically, circRNAs demonstrate high specificity and sensitivity in samples, offering potential as diagnostic and prognostic biomarkers. Additionally, therapeutic strategies involving circRNA mimics, inhibitors, and delivery systems are under investigation. However, their precise mechanisms remain unclear, and more clinical evidence is needed regarding their roles in cancer hallmarks. Understanding circRNAs will pave the way for novel diagnostic and therapeutic approaches, potentially improving patient outcomes.

Circular RNAs in cancer

Circular RNA (circRNA), a subtype of noncoding RNA, has emerged as a significant focus in RNA research due to its distinctive covalently closed loop structure. CircRNAs play pivotal roles in diverse physiological and pathological processes, functioning through mechanisms such as miRNAs or proteins sponging, regulation of splicing and gene expression, and serving as translation templates, particularly in the context of various cancers. The hallmarks of cancer comprise functional capabilities acquired during carcinogenesis and tumor progression, providing a conceptual framework that elucidates the nature of the malignant transformation. Although numerous studies have elucidated the role of circRNAs in the hallmarks of cancers, their functions in the development of chemoradiotherapy resistance remain unexplored and the clinical applications of circRNA-based translational therapeutics are still in their infancy. This review provides a comprehensive overview of circRNAs, covering their biogenesis, unique characteristics, functions, and turnover mechanisms. We also summarize the involvement of circRNAs in cancer hallmarks and their clinical relevance as biomarkers and therapeutic targets, especially in thyroid cancer (TC). Considering the potential of circRNAs as biomarkers and the fascination of circRNA-based therapeutics, the "Ying-Yang" dynamic regulations of circRNAs in TC warrant vastly dedicated investigations.

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

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

Molecular functions of microRNAs in colorectal cancer: recent roles in proliferation, angiogenesis, apoptosis, and chemoresistance

MiRNAs (microRNAs) constitute a group of diminutive molecules of non-coding RNA intricately involved in regulating gene expression. This regulation is primarily accomplished through the binding of miRNAs to complementary sequences situated in the 3'-UTR of the messenger RNA (mRNA) target; as a result, they are degraded or repressed. The multifaceted biogenesis of miRNAs is characterized by a meticulously orchestrated sequence of events encompassing transcription, processing, transportation, and decay. Colorectal cancer stands as a pervasive and formidable ailment, afflicting millions across the globe. Colorectal cancer is not well diagnosed early, and metastasis rates are high, which results in low survival rates in advanced stages. The genesis and progression of colorectal cancer are subject to the influence of genetic and epigenetic factors, among which miRNAs play a pivotal role. When it comes to colorectal cancer, miRNAs have a dual character, depending on the genes they target, functioning as either tumor suppressors or oncogenes and the prevailing cellular milieu. Their impact extends to modulating critical facets of colorectal cancer pathogenesis, including proliferation, angiogenesis, apoptosis, chemoresistance, and radiotherapy response. The discernible potential of miRNAs which are used as biomarkers to diagnose colorectal cancer, prognosis, and treatment response has come to the forefront. Notably, miRNAs are easily found and detected readily in a variety of biological fluids, including saliva, blood, urine, and feces. This prominence is attributed to the inherent advantages of miRNAs over conventional biomarkers, including heightened stability, specificity, sensitivity, and accessibility. Various investigations have pinpointed miRNA signatures or panels capable of differentiating colorectal cancer patients from their healthy counterparts, predicting colorectal cancer stage and survival, and monitoring colorectal cancer recurrence and therapy response. Although there has been research on miRNAs in various diseases, there has been less research on miRNAs in cancer. Moreover, updated results of preclinical and clinical studies on miRNA biomarkers and drugs are required. Nevertheless, the integration of miRNAs as biomarkers for colorectal cancer is not devoid of challenges and limitations. These encompass the heterogeneity prevalent among colorectal cancer subtypes and stages, the variability in miRNA expression across different tissues and individuals, the absence of standardized methodologies for miRNA detection and quantification, and the imperative for validation through extensive clinical trials. Consequently, further research is imperative to conclusively establish the clinical utility and reliability of miRNAs as colorectal cancer biomarkers. MiR-21 demonstrates carcinogenic characteristics by targeting several tumor suppressor genes, which encourages cell division, invasion, and metastasis. On the other hand, by controlling the Wnt/β-catenin pathway, the tumor suppressor miRNA miR-34a prevents CRC cell proliferation, migration, and invasion. Furthermore, in colorectal cancer, the miR-200 family increases chemotherapy sensitivity while suppressing epithelial-mesenchymal transition (EMT). As an oncogene, the miR-17-92 cluster targets elements of the TGF-β signaling pathway to encourage the growth of CRC cells. Finally, miR-143/145, which is downregulated in CRC, influences apoptosis and the progression of the cell cycle. These miRNAs affect pathways like Wnt, TGF-β, PI3K-AKT, MAPK, and EMT, making them potential clinical biomarkers and therapeutic targets. This review summarizes recent research related to miRNAs, their role in tumor progression and metastasis, and their potential as biomarkers and therapeutic targets in colorectal cancer. In addition, we combined miRNAs' roles in tumorigenesis and development with the therapy of CRC patients, leading to novel perspectives on colorectal cancer diagnosis and treatment.

Non-coding RNAs as therapeutic targets in cancer and its clinical application

Cancer genomics has led to the discovery of numerous oncogenes and tumor suppressor genes that play critical roles in cancer development and progression. Oncogenes promote cell growth and proliferation, whereas tumor suppressor genes inhibit cell growth and division. The dysregulation of these genes can lead to the development of cancer. Recent studies have focused on non-coding RNAs (ncRNAs), including circular RNA (circRNA), long non-coding RNA (lncRNA), and microRNA (miRNA), as therapeutic targets for cancer. In this article, we discuss the oncogenes and tumor suppressor genes of ncRNAs associated with different types of cancer and their potential as therapeutic targets. Here, we highlight the mechanisms of action of these genes and their clinical applications in cancer treatment. Understanding the molecular mechanisms underlying cancer development and identifying specific therapeutic targets are essential steps towards the development of effective cancer treatments.

The role of circular RNAs in regulating resistance to cancer immunotherapy: mechanisms and implications

Cancer immunotherapy has rapidly transformed cancer treatment, yet resistance remains a significant hurdle, limiting its efficacy in many patients. Circular RNAs (circRNAs), a novel class of non-coding RNAs, have emerged as pivotal regulators of gene expression and cellular processes. Increasing evidence indicates their involvement in modulating resistance to cancer immunotherapy. Notably, certain circRNAs function as miRNA sponges or interact with proteins, influencing the expression of immune-related genes, including crucial immune checkpoint molecules. This, in turn, shapes the tumor microenvironment and significantly impacts the response to immunotherapy. In this comprehensive review, we explore the evolving role of circRNAs in orchestrating resistance to cancer immunotherapy, with a specific focus on their mechanisms in influencing immune checkpoint gene expression. Additionally, we underscore the potential of circRNAs as promising therapeutic targets to augment the effectiveness of cancer immunotherapy. Understanding the role of circRNAs in cancer immunotherapy resistance could contribute to the development of new therapeutic strategies to overcome resistance and improve patient outcomes.

Emerging roles of circular RNAs in regulating the hallmarks of thyroid cancer

Thyroid cancer is a prevalent endocrine malignancy with increasing incidence in recent years. Although most thyroid cancers grow slowly, they can become refractory, leading to a high mortality rate once they exhibit recurrence, metastasis, resistance to radioiodine therapy, or a lack of differentiation. However, the mechanisms underlying these malignant characteristics remain unclear. Circular RNAs, a type of closed-loop non-coding RNAs, play multiple roles in cancer. Several studies have demonstrated that circular RNAs significantly influence the development of thyroid cancers. In this review, we summarize the circular RNAs identified in thyroid cancers over the past decade according to the hallmarks of cancer. We found that eight of the 14 hallmarks of thyroid cancers are regulated by circular RNAs, whereas the other six have not been reported to be correlated with circular RNAs. This review is expected to help us better understand the roles of circular RNAs in thyroid cancers and accelerate research on the mechanisms and cure strategies for thyroid cancers.

Mutant KRAS-activated circATXN7 fosters tumor immunoescape by sensitizing tumor-specific T cells to activation-induced cell death

Mutant KRAS (KRASMUT) is often exploited by cancers to shape tumor immunity, but the underlying mechanisms are not fully understood. Here we report that tumor-specific cytotoxic T lymphocytes (CTLs) from KRASMUT cancers are sensitive to activation-induced cell death (AICD). circATXN7, an NF-κB-interacting circular RNA, governs T cell sensitivity to AICD by inactivating NF-κB. Mechanistically, histone lactylation derived from KRASMUT tumor cell-produced lactic acid directly activates transcription of circATXN7, which binds to NF-κB p65 subunit and masks the p65 nuclear localization signal motif, thereby sequestering it in the cytoplasm. Clinically, circATXN7 upregulation in tumor-specific CTLs correlates with adverse clinical outcomes and immunotherapeutic resistance. Genetic ablation of circAtxn7 in CD8+ T cells leads to mutant-selective tumor inhibition, while also increases anti-PD1 efficacy in multiple tumor models in female mice. Furthermore, targeting circATXN7 in adoptively transferred tumor-reactive CTLs improves their antitumor activities. These findings provide insight into how lymphocyte-expressed circRNAs contribute to T-cell fate decisions and anticancer immunotherapies.

Mechanisms of immune checkpoint inhibitors: insights into the regulation of circular RNAS involved in cancer hallmarks

Current treatment strategies for cancer, especially advanced cancer, are limited and unsatisfactory. One of the most substantial advances in cancer therapy, in the last decades, was the discovery of a new layer of immunotherapy approach, immune checkpoint inhibitors (ICIs), which can specifically activate immune cells by targeting immune checkpoints. Immune checkpoints are a type of immunosuppressive molecules expressed on immune cells, which can regulate the degree of immune activation and avoid autoimmune responses. ICIs, such as anti-PD-1/PD-L1 drugs, has shown inspiring efficacy and broad applicability across various cancers. Unfortunately, not all cancer patients benefit remarkably from ICIs, and the overall response rates to ICIs remain relatively low for most cancer types. Moreover, the primary and acquired resistance to ICIs pose serious challenges to the clinical application of cancer immunotherapy. Thus, a deeper understanding of the molecular biological properties and regulatory mechanisms of immune checkpoints is urgently needed to improve clinical options for current therapies. Recently, circular RNAs (circRNAs) have attracted increasing attention, not only due to their involvement in various aspects of cancer hallmarks, but also for their impact on immune checkpoints in shaping the tumor immune microenvironment. In this review, we systematically summarize the current status of immune checkpoints in cancer and the existing regulatory roles of circRNAs on immune checkpoints. Meanwhile, we also aim to settle the issue in an evidence-oriented manner that circRNAs involved in cancer hallmarks regulate the effects and resistance of ICIs by targeting immune checkpoints.

Hsa_circ_0003596 enhances the development of cell renal clear cell carcinoma through the miR-502-5p/IGF1/PI3K/AKT axis

Accumulating research findings have shown that circular RNAs (circRNAs) play an indispensable role in tumorigenesis and tumor progression. The current study aimed to explore the role and modulatory mechanism of hsa_circ_0003596 in clear cell renal cell carcinoma (ccRCC). Quantitative real-time polymerase chain reaction was adopted to detect the expression of hsa_circ_0003596 in ccRCC tissue and cell lines. 5-Ethynyl-2'-deoxyuridine, cell counting kit 8 and the colony formation assay were utilized to assess the proliferation potential of the ccRCC cells. Transwell along with wound healing assays were adopted to quantify infiltration coupled with the migration potential of the cells. The current research study found that the circRNA hsa_circ_0003596 was overexpressed in ccRCC tissue and cell lines. Further, result showed that hsa_circ_0003596 was associated with distant metastasis of renal cancer. Notably, the knockdown of hsa_circ_0003596 can lower the proliferation, infiltration and migration potential of ccRCC cells. The results of in vivo experiments found that the reduction of hsa_circ_0003596 significantly hampered the growth of tumors in mice. In addition, it was evident that hsa_circ_0003596 acts as a "molecular sponge" for miR-502-5p to upregulate the expression of the microRNA-502-5p (miR-502-5p) target insulin-like growth factor 1 (IGF1R). Furthermore, it was found that the phosphatidylinositol 3-kinase (PI3K)/AKT signaling was the downstream cascade of hsa_circ_0003596/miR-502-5p/IGF1R cascade, which is partly responsible for the cancer-promoting effect. Overall, the results of the present study showed that hsa_circ_0003596 facilitated the proliferation, infiltration and migration of ccRCC through the miR-502-5p/IGF1R/PI3K/AKT axis. Therefore, it was evident that hsa_circ_0003596 can serve as a possible biomarker and therapeutic target against ccRCC.

Non-coding RNAs in cancer immunotherapy: Predictive biomarkers and targets

BACKGROUND

To date, standardising clinical predictive biomarkers for assessing the response to immunotherapy remains challenging due to variations in personal genetic signatures, tumour microenvironment complexities and epigenetic onco-mechanisms.

MAIN BODY

Early monitoring of key non-coding RNA (ncRNA) biomarkers may help in predicting the clinical efficacy of cancer immunotherapy and come up with standard predictive ncRNA biomarkers. For instance, reduced miR-125b-5p level in the plasma of non-small cell lung cancer patients treated with anti-PD-1 predicts a positive outcome. The level of miR-153 in the plasma of colorectal cancer patients treated with chimeric antigen receptor T lymphocyte (CAR-T) cell therapy may indicate the activation of T-cell killing activity. miR-148a-3p and miR-375 levels may forecast favourable responses to CAR-T-cell therapy in B-cell acute lymphoblastic leukaemia. In cancer patients treated with the GPC3 peptide vaccine, serum levels of miR-1228-5p, miR-193a-5p and miR-375-3p were reported as predictive biomarkers of good response and improved overall survival. Therefore, there is a critical need for further studies to elaborate on the key ncRNA biomarkers that have the potential to predict early clinical responses to immunotherapy.

CONCLUSION

This review summarises important predictive ncRNA biomarkers that were reported in cancer patients treated with different immunotherapeutic modalities, including monoclonal antibodies, small molecule inhibitors, cancer vaccines and CAR-T cells. In addition, a concise discussion on forthcoming perspectives is provided, outlining technical approaches for the optimal utilisation of immunomodulatory ncRNA biomarkers as predictive tools and therapeutic targets.

Highlighting functions of apoptosis and circular RNAs in colorectal cancer

Colorectal cancer (CRC) is known as one of the global problems that endangers the lives of thousands of people every year. Various treatments have been used to deal with this disease, but in some cases, they are not effective. Circular RNAs, as a novel class of noncoding RNAs, have different expression levels and various functions in cancer cells, such as gene regulation through microRNA sponging. They play an important role in various cellular processes, including differentiation, proliferation, invasion, and apoptosis. Changes in the process of apoptosis are closely related to the progression or inhibition of various malignancies. Induction of apoptosis in cancer cells is a promising target for tumor therapy. In this study, circRNAs were investigated as being central to the induction or inhibition of apoptosis in CRC. It is hoped that through targeted changes in the function of these biomolecules, better outcomes will be achieved in cancer treatment. Perhaps better outcomes for cancer treatment can be achieved by using new methods and modifying the expression of these nucleic acids. However, using this method may come with challenges and limitations.

Exosomes-delivered PD-L1 siRNA and CTLA-4 siRNA protect against growth and tumor immune escape in colorectal cancer

OBJECTIVE

This study aims to dissect impacts of exosomes-delivered PD-L1 and CTLA-4 siRNAs on colorectal cancer (CRC) progression and immune responses.

METHODS

Exosomes containing PD-L1 siRNA and CTLA-4 siRNA were prepared and utilized to treat CRC cells to evaluate their effects. A tumor-bearing mouse model was established for verification.

RESULTS

Exosomes containing PD-L1 siRNA and CTLA-4 siRNA repressed malignant features of CRC cells and restrained tumor growth and activated tumor immune responses in vivo. Co-culture of CRC cells treated with exosomes containing PD-L1 siRNA and CTLA-4 siRNA with human CD8+ T cells increased the percentage of CD8+ T cells, decreased the apoptotic rate of CD8+ T cells, elevated IL-2, IFN-γ, and TNF-α expression in cell supernatants, reduced adherent density of CRC cells, augmented the positive rate of CRC cells, and subdued tumor immune escape.

CONCLUSION

Exosomes containing PD-L1 siRNA and CTLA-4 siRNA suppressed CRC progression and enhanced tumor immune responses.

Different Roles of Apoptosis and Autophagy in the Development of Human Colorectal Cancer

Colorectal cancer (CRC) remains a major life-threatening malignancy, despite numerous therapeutic and screening attempts. Apoptosis and autophagy are two processes that share common signaling pathways, are linked by functional relationships and have similar protein components. During the development of cancer, the two processes can trigger simultaneously in the same cell, causing, in some cases, an inhibition of autophagy by apoptosis or apoptosis by autophagy. Malignant cells that have accumulated genetic alterations can take advantage of any alterations in the apoptotic process and as a result, progress easily in the cancerous transformation. Autophagy often plays a suppressive role during the initial stages of carcinogenicity, while in the later stages of cancer development it can play a promoting role. It is extremely important to determine the regulation of this duality of autophagy in the development of CRC and to identify the molecules involved, as well as the signals and the mechanisms behind it. All the reported experimental results indicate that, while the antagonistic effects of autophagy and apoptosis occur in an adverse environment characterized by deprivation of oxygen and nutrients, leading to the formation and development of CRC, the effects of promotion and collaboration usually involve an auxiliary role of autophagy compared to apoptosis. In this review, we elucidate the different roles of autophagy and apoptosis in human CRC development.

CircRNAs regulate the crosstalk between inflammation and tumorigenesis: The bilateral association and molecular mechanisms

Inflammation, a hallmark of cancer, has been associated with tumor progression, transition into malignant phenotype and efficacy of the chemotherapeutic agents in cancer. Chronic inflammation provides a favorable environment for tumorigenesis by inducing immunosuppression, whereas acute inflammation prompts tumor suppression by generating anti-tumor immune responses. Inflammatory factors derived from interstitial cells or tumor cells can stimulate cell proliferation and survival by modulating oncogenes and/or tumor suppressors. Recently, a new class of RNAs, i.e., circular RNAs (circRNAs), has been implicated in inflammatory diseases. Although there are reports on circRNAs imparting functions in inflammatory insults, whether these circularized transcripts hold the potential to regulate inflammation-induced cancer or tumor-related inflammation, and modulate the interactions between tumor microenvironment (TME) and the inflammatory stromal/immune cells, awaits further elucidation. Contextually, the current review describes the molecular association between inflammation and cancer, and spotlights the regulatory mechanisms by which circRNAs can moderate TME in response to inflammatory signals/triggers. We also present comprehensive information about the immune cell(s)-specific expression and functions of the circRNAs in TME, modulation of inflammatory signaling pathways to drive tumorigenesis, and their plausible roles in inflammasomes and tumor development. Moreover, the therapeutic potential of these circRNAs in harnessing inflammatory responses in cancer is also discussed.

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.

Identification of CircRNA signature associated with tumor immune infiltration to predict therapeutic efficacy of immunotherapy

Circular RNAs (circRNAs) play important roles in the regulation of cancer. However, the clinical implications and regulatory networks of circRNAs in cancer patients receiving immune checkpoint blockades (ICB) have not been fully elucidated. Here, we characterize circRNA expression profiles in two independent cohorts of 157 ICB-treated advanced melanoma patients and reveal overall overexpression of circRNAs in ICB non-responders in both pre-treatment and early during therapy. Then, we construct circRNA-miRNA-mRNA regulatory networks to reveal circRNA-related signaling pathways in the context of ICB treatment. Further, we construct an ICB-related circRNA signature (ICBcircSig) score model based on progression-free survival-related circRNAs to predict immunotherapy efficacy. Mechanistically, the overexpression of ICBcircSig circTMTC3 and circFAM117B could increase PD-L1 expression via the miR-142-5p/PD-L1 axis, thus reducing T cell activity and leading to immune escape. Overall, our study characterizes circRNA profiles and regulatory networks in ICB-treated patients, and highlights the clinical utility of circRNAs as predictive biomarkers of immunotherapy.

CircRNAs in tumor immunity and immunotherapy: Perspectives from innate and adaptive immunity

Tumor immunotherapy is a new therapeutic approach that has been evolving in the last decade and has dramatically changed the treatment options for cancer. Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) with high stability, tissue-specific and cell-specific expression. There is growing evidence that circRNAs are involved in the regulation of both adaptive and innate immunity. They play important roles in tumor immunotherapy by affecting macrophage, NK and T cell function. The high stability and tissue specificity make them ideal candidate biomarkers for therapeutic effects. CircRNAs also represent one of promising targets or adjuvant for immunotherapy. Investigations in this field progress rapidly and provide essential support for the diagnosis, prognosis and treatment guidance of cancers in the future. In this review, we summarize the role of circRNAs on tumor immunity from the viewpoint of innate and adaptive immunity, and explore the role of circRNAs in tumor immunotherapy.

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.

Circular RNA ACACA negatively regulated p53-modulated mevalonate pathway to promote colorectal tumorigenesis via regulating miR-193a/b-3p/HDAC3 axis

This study aimed to explore the biological functions and underlying mechanism of circRNA acetyl-CoA carboxylase alpha (circACACA) in colorectal cancer (CRC). The RNA and protein levels were detected by qRT-PCR and western blot assays. The malignant capacities of CRC cells were analyzed by cell counting kit-8 (CCK-8), colony formation, flow cytometry, and transwell assays. The target relationship between miR-193a/b-3p and circACACA/histone deacetylase 3 (HDAC3) was determined by luciferase reporter assay and RNA immunoprecipitation. The binding of HDAC3 to the p53 promoter was validated by chromatin immunoprecipitation (ChIP). CRC cell growth and lung metastasis were evaluated in nude mice in vivo. High expression of circACACA was found in CRC tissues and cells, which was closely associated with the advanced tumor, lymph node, metastasis (TNM) stage, metastasis, and low overall survival rate. circACACA downregulation effectively delayed CRC cell proliferation and metastasis, but triggered apoptosis via inactivating the mevalonic acid (MVA) pathway. However, circACACA overexpression resulted in the opposite effects. Mechanistically, circACACA enhanced HDAC3 expression through sponging miR-193a/b-3p, which activated the MVA pathway via inhibiting the acetylation and transcription of p53. Moreover, rescue experiments confirmed that miR-193a/b-3p inhibition reversed the inhibitory effect of circACACA deficiency on CRC growth and metastasis. Moreover, circACACA overexpression-mediated malignant phenotypes of CRC cells were abrogated by HDAC3 knockdown. circACACA promoted CRC progression via regulating the miR-193a/b-3p/HDAC3/p53 axis to activate the MVA pathway, providing evidence for circACACA as a promising therapeutic target for CRC.

Role of circular RNA and its delivery strategies to cancer - An overview

With the passage of years and the progress of research on ribonucleic acids, the range of forms in which these molecules have been observed grows. One of them, discovered relatively recently, is circular RNA - covalently closed circles (circRNA). In recent years, there has been a huge increase in the interest of researchers in this group of molecules. It entailed a significant increase in the state of knowledge about them, which in turn caused a dramatic change in their perception. Rather than seeing circular RNAs as curiosities that represent a minor information noise in a cell or a result of RNA misprocessing, they came to be regarded as a common, essential, and potentially extremely useful group of molecules. Nevertheless, the current state of the art of circRNA is full of white cards. A lot of valuable information has been obtained from high-throughput methods to study whole transcriptomes, but many issues related to circular RNAs still need to be clarified. Presumably, each answer obtained will raise several new questions. However, circRNAs have a wealth of potential applications, including therapeutic applications.

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

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

Review of novel functions and implications of circular RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent malignancies, with high incidence and mortality. As the majority of HCC patients are diagnosed at an advanced stage and die of recurrence and metastasis, its pathology and new biomarkers are needed. Circular RNAs (circRNAs) are a large subclass of long non-coding RNAs (lncRNAs) with covalently closed loop structures and abundant, conserved, stable, tissue-specific expression in mammalian cells. CircRNAs exert multiple functions in HCC initiation, growth and progression, serving as promising biomarkers for diagnosis, prognosis and therapeutic targets for this disease. This review briefly describes the biogenesis and biological functions of circRNAs and elucidates the roles of circRNAs in the development and progression of HCC, especially regarding epithelial-mesenchymal transition (EMT), drug resistance and interactions with epigenetic modifications. In addition, this review highlights the implications of circRNAs as potential biomarkers and therapeutic targets for HCC. We hope to provide novel insight into the roles of circRNAs in HCC.

Expression analysis of hsa_circ_0020397, hsa_circ_0005986, hsa_circ_0003028, and hsa_circ_0006990 in renal cell carcinoma

Renal cell carcinoma (RCC) is a prevalent heterogeneous kidney cancer. So far, different genes have been reported for RCC development. However, its particular molecular mechanism remains unclear. Circular RNAs (circRNAs), a class of non-coding RNAs, are involved in numerous biological processes in different malignancies such as RCC. This study aims to assess the expression and underlying mechanism of four circRNAs (hsa_circ_0020397, hsa_circ_0005986, hsa_circ_0003028, hsa_circ_0006990) with possible new roles in RCC. In the experimental step, we investigated the expression of these four circRNAs in our RCC samples using quantitative real-time polymerase chain reaction. In the bioinformatics step, the differential expressed mRNAs (DEmRNAs), and miRNAs (DEmiRNAs) were obtained from the GEO datasets using the GEO2R tool. A protein-protein interaction network was constructed using the STRING database, and hub genes were identified by Cytoscape. Molecular pathways associated with hub genes were detected using KEGG pathway enrichment analysis. Then, we utilized the ToppGene database to detect the relationships between DEmiRNAs and hub genes. Furthermore, interactions between circRNAs and DEmiRNAs were predicted by the StarBase and circinteractome databases. Finally, a circRNA-DEmiRNA-hub gene triple network was constructed. Our results revealed that the expression of hsa_circ_0020397, hsa_circ_0005986, and hsa_circ_0006990 was downregulated in RCC tissues. Moreover, these circRNAs had a significantly lower expression in patients with a history of kidney disease. Furthermore, hsa_circ_0003028 and hsa_circ_0006990 showed higher expression in the tumor of participants with Lymphovascular/perineural invasion and oncocytoma type, respectively. Based on bioinformatic results, 15 circRNA-DEmiRNA-hub gene ceRNA regulatory axes were predicted, which included three hub genes, five miRNAs, and four selected circRNAs. In conclusion, the current work is the first to emphasize the expression of the hsa_circ_0020397, hsa_circ_0005986, hsa_circ_0003028, and hsa_circ_0006990 in RCC patients presents a novel perspective on the molecular processes underlying the pathogenic mechanisms of RCC.

Targets of Immune Escape Mechanisms in Cancer: Basis for Development and Evolution of Cancer Immune Checkpoint Inhibitors

Immune checkpoint blockade (ICB) has emerged as a novel therapeutic tool for cancer therapy in the last decade. Unfortunately, a small number of patients benefit from approved immune checkpoint inhibitors (ICIs). Therefore, multiple studies are being conducted to find new ICIs and combination strategies to improve the current ICIs. In this review, we discuss some approved immune checkpoints, such as PD-L1, PD-1, and CTLA-4, and also highlight newer emerging ICIs. For instance, HLA-E, overexpressed by tumor cells, represents an immune-suppressive feature by binding CD94/NKG2A, on NK and T cells. NKG2A blockade recruits CD8+ T cells and activates NK cells to decrease the tumor burden. NKG2D acts as an NK cell activating receptor that can also be a potential ICI. The adenosine A2A and A2B receptors, CD47-SIRPα, TIM-3, LAG-3, TIGIT, and VISTA are targets that also contribute to cancer immunoresistance and have been considered for clinical trials. Their antitumor immunosuppressive functions can be used to develop blocking antibodies. PARPs, mARTs, and B7-H3 are also other potential targets for immunosuppression. Additionally, miRNA, mRNA, and CRISPR-Cas9-mediated immunotherapeutic approaches are being investigated with great interest. Pre-clinical and clinical studies project these targets as potential immunotherapeutic candidates in different cancer types for their robust antitumor modulation.

Long Non-Coding RNAs as Epigenetic Regulators of Immune Checkpoints in Cancer Immunity

In recent years, cancer treatment has undergone significant changes, predominantly in the shift towards immunotherapeutic strategies using immune checkpoint inhibitors. Despite the clinical efficacy of many of these inhibitors, the overall response rate remains modest, and immunotherapies for many cancers have proved ineffective, highlighting the importance of knowing the tumor microenvironment and heterogeneity of each malignancy in patients. Long non-coding RNAs (lncRNAs) have attracted increasing attention for their ability to control various biological processes by targeting different molecular pathways. Some lncRNAs have a regulatory role in immune checkpoints, suggesting they might be utilized as a target for immune checkpoint treatment. The focus of this review is to describe relevant lncRNAs and their targets and functions to understand key regulatory mechanisms that may contribute in regulating immune checkpoints. We also provide the state of the art on super-enhancers lncRNAs (selncRNAs) and circular RNAs (circRNAs), which have recently been reported as modulators of immune checkpoint molecules within the framework of human cancer. Other feasible mechanisms of interaction between lncRNAs and immune checkpoints are also reported, along with the use of miRNAs and circRNAs, in generating new tumor immune microenvironments, which can further help avoid tumor evasion.

Altered Expression of hsa_circ_0001445 and hsa_circ_0020397 in Breast Cancer Representing Associations with BMI and Reproductive Factors

BACKGROUND

Circular RNAs (circRNAs), one of the recent subclasses of non-coding RNAs (ncRNAs), show pivotal functions in regulation of gene expression and have significant roles in malignancies including breast cancer (BC). This study was aimed to assess the hsa_circ_0001445 and hsa_circ_0020397 expression and role in BC, as well as the potential circRNA/miRNA/mRNA crosstalk in these contexts.

METHODS

The expression of hsa_circ_0001445 and hsa_circ_0020397 in 50 breast tumors and 50 normal tissues adjacent to the tumors was investigated using quantitative real-time polymerase chain reaction (qRT-PCR). Finally, bioinformatics analyses were used to uncover hsa_circ_0001445, hsa_circ_0020397-miRNA-mRNA potential regulatory networks.

RESULTS

The hsa_circ_0001445 expression was considerably downregulated in malignant tissues compared to their normal counterparts (P=0.020), while the hsa_circ_0020397 showed an upregulated pattern (P<0.001). Additionally, it was observed that the higher expression of hsa_circ_0001445 was associated with hair dye avoidance (P=0.034) and normal body mass index (BMI) (P=0.016) while hsa_circ_0020397 over-expression had an important association with a lack of vitamin D consumption (P=0.039). On the other hand, lower expression of hsa_circ_0001445 was significantly associated with age at menarche ˂14 years (P=0.027). Our study also revealed that the two circRNAs have potential ability to regulate key mRNAs and miRNAs in competing endogenous RNA (ceRNA) networks.

CONCLUSION

It is suggested that hsa_circ_0001445 and hsa_circ_0020397 with two opposite roles may be involved in BC development through sponging some miRNAs regulating ceRNA networks. However, their molecular interactions should be validated by further functional studies.

Dysregulation of global circular RNA abundance regulated by spliceosomes predicts prognosis in hepatocellular carcinoma

CircRNAs have been reported to play crucial roles in tumor progression and recurrence, showing potential as biomarkers in cancer. However, the global abundance of circRNA and their involvement in hepatocellular carcinoma (HCC) development have not been fully explored. Whole transcriptome sequencing was performed on tumor and peritumor from 60 patients with HCC to quantify the expression of circRNAs, and the global circRNA abundance was calculated by circRNA index (CRI). Gene-set enrichment analysis and weighted gene co-expression network analysis were used to reveal the biological signaling pathways associated with the global circRNA abundance. The correlation between the global circRNA abundance and the infiltration level of CD8+ T cells was explored by immunohistochemical assays. Small interfering RNA was used to knock down the pre-messenger RNA spliceosome in HCC cell lines to verify the regulation of spliceosome in global circRNA abundance. We found that dysregulation of global circRNA abundance in both tumor and peritumor could lead to worse prognosis. The immunohistochemical assay further revealed that the dysregulation of global circRNA abundance in both tumor and peritumor would obstruct the CD8+ T cells from invading into the tumor, which might explain its correlation with HCC prognosis. We also demonstrated that the spliceosome genes were the main factors to regulate the global circRNA abundance in HCC, and these results were also confirmed by knockdown experiments. Conclusion: This study revealed the association between the global circRNA abundance and patients' prognosis and its underlying mechanism.

Deregulated Expression of Circular RNAs Is Associated with Immune Evasion and Leukemia Relapse after Allogeneic Hematopoietic Stem Cell Transplantation

BACKGROUND

Circular RNAs (circRNAs) are a novel class of epigenetic regulators that participate in leukemogenesis. However, their roles in leukemia relapse after transplantation remain unclear.

METHODS

We defined the circRNAs profile of the bone-marrow-enriched CD34⁺ cells from ten acute myeloid leukemia (AML) patients after transplantation (five relapse [RE] and five continuous complete remission [CR]) and four healthy controls (HCs) by RNA-seq. Differentially expressed circRNAs were validated using real-time quantitative polymerase chain reaction (RT-qPCR) in an independent cohort of six AML patients with pairwise samples at diagnosis and at relapse and six controls.

RESULTS

The bioinformatics analysis revealed a distinct circRNAs profile in relapse patients compared with controls (CR or HCs), while there was no significant difference between CR and HCs. Functional enrichment analysis demonstrated that mRNAs co-expressed with identified circRNAs were primarily involved in immune-related pathways, including the T cell receptor signaling pathway and lymphocyte differentiation. Moreover, we performed a protein-protein interaction network based on the immune-related genes and annotated 20 hub genes. The abnormal expression of hub genes was responsible for impairing T cell co-stimulation and activation, thus contributing to the immune escape of relapse blasts. We further constructed competing endogenous RNAs (ceRNA) regulatory networks based on immune-related genes and identified 10 key circRNAs that are associated with immune evasion. Six candidate circRNAs and their associated miRNA/mRNAs in the ceRNA network were randomly selected to be validated in another set by RT-qPCR.

CONCLUSIONS

CircRNAs dysregulation may be involved in the immune evasion of relapse blasts and is associated with AML relapse. Our results identify several promising biomarkers and might provide novel insights into the biology of AML relapse post-transplantation.

Circ-FAT1 Up-Regulates FOSL2 Expression by Sponging miR-619-5p to Facilitate Colorectal Cancer Progression

Circular RNA FAT atypical cadherin 1 (circ-FAT1) has been reported to play roles in colorectal cancer (CRC) development. Here, the purpose of this study was to investigate the function and mechanism of circ-FAT1 in CRC tumorigenesis and its potential value in the clinic. Levels of genes and proteins were examined by quantitative real-time polymerase chain reaction and Western blot. In vitro assays were conducted using cell counting kit-8 assay, 5-Ethynyl-2'-deoxyuridine assay, flow cytometry, transwell assay, and tube formation assay, respectively. The target relationship between miR-619-5p and circ-FAT1 or FOS-like antigen 2 (FOSL2) was verified by dual-luciferase reporter and RNA immunoprecipitation assays. In vivo assay was performed using a mouse subcutaneous xenograft model. Circ-FAT1 and FOSL2 were highly expressed in CRC tissues and cells. Functionally, knockdown of circ-FAT1 or FOSL2 suppressed CRC cell apoptosis, migration, invasion, and angiogenesis, but induced cell apoptosis in vitro. Mechanistically, circ-FAT1 acted as a sponge for miR-619-5p to up-regulate the expression of FOSL2, which was confirmed to be a target of miR-619-5p. A series of rescue experiments demonstrated that miR-619-5p inhibition or FOSL2 overexpression reversed the inhibitory action of circ-FAT1 silencing on CRC cell malignant phenotypes mentioned above. Pre-clinically, lentivirus-mediated circ-FAT1 knockdown inhibited the tumorigenesis of CRC xenografts in nude mice via regulating miR-619-5p and FOSL2. Circ-FAT1 knockdown repressed FOSL2 expression by sponging miR-619-5p to suppress CRC tumorigenesis, providing a potential approach for CRC therapeutics.

Significance of circRNAs as biomarkers for systemic lupus erythematosus: a systematic review and meta-analysis

Objective

To comprehensively evaluate the significance of circular RNAs (circRNAs) as potential diagnostic biomarkers for systemic lupus erythematosus (SLE) via pooled analyses of data from published studies that focussed on the association between circRNAs and SLE.

Methods

The systematic review and meta-analysis protocol was registered in PROSPERO (registration No. CRD42021229383). Relevant studies published before 3 April 2022 were selected to verify the relationship between circRNA expression levels and SLE. Extracted data were analysed using a random-effects model with Meta-DiSc 1.4 and Stata 16 software. Transcription factors related to hsa_circ_0000479 and its parental gene were extracted from the TRCirc and hTFtarget databases, respectively.

Results

A total of 10 studies, involving 438 patients with SLE and 434 controls, were included in the meta-analysis. The pooled sensitivity, specificity, and diagnostic odds ratio of circRNAs in detecting SLE were 0.66 (95% confidence interval [CI] 0.63, 0.70), 0.79 (95% CI 0.76, 0.82), and 10.80 (95% CI 6.58, 17.73), respectively. The area under the summary receiver operating characteristic curve was 0.8366.

Conclusions

Meta-analysis of pooled data indicated a moderate accuracy of circRNAs in diagnosing SLE. The exact diagnostic value of circRNAs and the mechanisms of interaction between circRNAs and their parental genes should be confirmed in further studies.

Circular RNAs Acting as miRNAs’ Sponges and Their Roles in Stem Cells

Circular RNAs (circRNAs), a novel type of endogenous RNAs, have become a subject of intensive research. It has been found that circRNAs are important players in cell differentiation and tissue homeostasis, as well as disease development. Moreover, the expression of circRNAs is usually not correlated with their parental gene expression, indicating that they are not only a steady-state by-product of mRNA splicing but a product of variable splicing under novel regulation. Sequence conservation analysis has also demonstrated that circRNAs have important non-coding functions. CircRNAs exist as a covalently closed loop form in mammalian cells, where they regulate cellular transcription and translation processes. CircRNAs are built from pre-messenger RNAs, and their biogenesis involves back-splicing, which is catalyzed by spliceosomes. The splicing reaction gives rise to three different types of intronic, exotic and exon–intron circular RNAs. Due to higher nuclease stability and longer half lives in cells, circRNAs are more stable than linear RNAs and have enormous clinical advantage for use as diagnostic and therapeutic biomarkers for disease. In recent years, it has been reported that circRNAs in stem cells play a crucial role in stem cell function. In this article, we reviewed the general feature of circRNAs and the distinct roles of circRNAs in stem cell biology, including regulation of stem cell self-renewal and differentiation. CircRNAs have shown unique expression profiles during differentiation of stem cells and could serve as promising biomarkers of these cells. As circRNAs play pivotal roles in stem cell regulation as well as the development and progression of various diseases, we also discuss opportunities and challenges of circRNA-based treatment strategies in future effective therapies for promising clinical applications.

The functions, oncogenic roles, and clinical significance of circular RNAs in renal cell carcinoma

Renal cell carcinoma (RCC) is the most common form of malignancy affecting the kidneys. Circular RNAs (circRNAs) are non-coding RNAs that are derived from exonic or intronic sequences through a selective shearing process. There is growing evidence that these circRNAs can influence a range of biological pathways by serving as protein decoys, microRNA sponges, regulators of transcriptional activity, or templates for protein translation. The dysregulation of circRNA expression patterns is a hallmark of RCC and other cancer types, and there is strong evidence that these RNA species can play central roles in the onset and progression of RCC tumors. In the present review, we summarized recent findings on the functional roles and clinical impacts of circRNAs in RCC. Further, we discussed their potential utility as diagnostic biomarkers or targets for therapeutic intervention.

The circular RNA circHMGB2 drives immunosuppression and anti-PD-1 resistance in lung adenocarcinomas and squamous cell carcinomas via the miR-181a-5p/CARM1 axis

BACKGROUND

Previous studies have confirmed the oncogenic role of HMGB2 in various cancers, but the biological functions of HMGB2-derived circRNAs remain unknown. Thus, we intended to investigate the potential role of HMGB2-derived circRNAs in lung adenocarcinomas (LUAD) and squamous cell carcinomas (LUSC).

METHODS

The expression profiles of HMGB2-derived circRNAs in LUAD and LUSC tissues and matched normal tissues were assessed using qRT-PCR. The role of circHMGB2 in the progression of the LUAD and LUSC was determined in vitro by Transwell, CCK-8, flow cytometry and immunohistochemistry assays, as well as in vivo in an immunocompetent mouse model and a humanized mouse model. In addition, in vivo circRNA precipitation assays, luciferase reporter assays and RNA pulldown assays were performed to explore the underlying mechanism by which circHMGB2 promotes anti-PD-1 resistance in the LUAD and LUSC.

RESULTS

The expression of circHMGB2 (hsa_circ_0071452) was significantly upregulated in NSCLC tissues, and survival analysis identified circHMGB2 as an independent indicator of poor prognosis in the LUAD and LUSC patients. We found that circHMGB2 exerted a mild effect on the proliferation of the LUAD and LUSC cells, but circHMGB2 substantially reshaped the tumor microenvironment by contributing to the exhaustion of antitumor immunity in an immunocompetent mouse model and a humanized mouse model. Mechanistically, circHMGB2 relieves the inhibition of downstream CARM1 by sponging miR-181a-5p, thus inactivating the type 1 interferon response in the LUAD and LUSC. Moreover, we found that the upregulation of circHMGB2 expression decreased the efficacy of anti-PD-1 therapy, and we revealed that the combination of the CARM1 inhibitor EZM2302 and an anti-PD-1 antibody exerted promising synergistic effects in a preclinical model.

CONCLUSION

circHMGB2 overexpression promotes the LUAD and LUSC progression mainly by reshaping the tumor microenvironment and regulating anti-PD-1 resistance in the LUAD and LUSC patients. This study provides a new strategy for the LUAD and LUSC treatment.

Noncoding RNAs as novel immunotherapeutic tools against cancer

Immunotherapy is implemented as an important treatment strategy in various malignancies. In cancer, immunotherapy is employed for successful killing of tumor cells with high specificity and greater efficacy, with minimum side effects. Despite various available strategies, cellular immunotherapy including innate (NK cells, macrophages, dendritic cells) and adaptive (B cells and T cells) immune cells plays a critical role in tumor microenvironment. Since past few years, many drugs targeting immune checkpoint proteins including CTLA-4 and PD-1/PD-L1 have been investigated as immunotherapy approach against cancer but complete effectiveness still remains a question, as diverse mechanisms involved in tumorigenesis may result in the development of cancer cell resistance. Number of evidences have highlighted the significant role of non-coding RNAs (ncRNAs) in regulating multiple stages of cancer initiation, progression & immunity. ncRNAs comprises 98% human transcriptome and are basically considered as dark genome. Among ncRNAs, miRNAs and lncRNAs have been extensively studied in regulating diverse processes of cancer tumorigenesis. Upregulation of oncogenic and downregulation of tumor suppressive miRNAs/lncRNAs has been reported to facilitate the cancer progression and invasiveness. This chapter summarizes how an interplay between ncRNAs and immune cells in cancer pathogenesis can be therapeutically targeted to improve current treatment regimen. Strategies should be employed to improve the efficacy and reduce off-target effects of ncRNA based immunotherapy. Henceforth, combination of ncRNAs and available immunotherapy can be argued to enhance the efficacy of existing immunotherapeutic approaches against cancer to improve patient's survival.

Targeting non-coding RNAs to overcome cancer therapy resistance

It is now well known that non-coding RNAs (ncRNAs), rather than protein-coding transcripts, are the preponderant RNA transcripts. NcRNAs, particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), are widely appreciated as pervasive regulators of multiple cancer hallmarks such as proliferation, apoptosis, invasion, metastasis, and genomic instability. Despite recent discoveries in cancer therapy, resistance to chemotherapy, radiotherapy, targeted therapy, and immunotherapy continue to be a major setback. Recent studies have shown that ncRNAs also play a major role in resistance to different cancer therapies by rewiring essential signaling pathways. In this review, we present the intricate mechanisms through which dysregulated ncRNAs control resistance to the four major types of cancer therapies. We will focus on the current clinical implications of ncRNAs as biomarkers to predict treatment response (intrinsic resistance) and to detect resistance to therapy after the start of treatment (acquired resistance). Furthermore, we will present the potential of targeting ncRNA to overcome cancer treatment resistance, and we will discuss the challenges of ncRNA-targeted therapy—especially the development of delivery systems.

Circular RNAs Involve in Immunity of Digestive Cancers From Bench to Bedside: A Review

The immune system plays a complex role in tumor formation and development. On the one hand, immune surveillance can inhibit the growth of tumors; on the other hand, immune evasion of tumors can create conditions conducive for tumor development and growth. CircRNAs are endogenous non-coding RNAs with a covalently closed loop structure that are abundantly expressed in eukaryotic organisms. They are characterized by stable structure, rich diversity, and high evolutionary conservation. In particular, circRNAs play a vital role in the occurrence, development, and treatment of tumors through their unique functions. Recently, the incidence and mortality of digestive cancers, especially those of gastric cancer, colorectal cancer, and liver cancer, have remained high. However, the functions of circRNAs in digestive cancers immunity are less known. The relationship between circRNAs and digestive tumor immunity is systematically discussed in our paper for the first time. CircRNA can influence the immune microenvironment of gastrointestinal tumors to promote their occurrence and development by acting as a miRNA molecular sponge, interacting with proteins, and regulating selective splicing. The circRNA vaccine even provides a new idea for tumor immunotherapy. Future studies should be focused on the location, transportation, and degradation mechanisms of circRNA in living cells and the relationship between circRNA and tumor immunity. This paper provides a new idea for the diagnosis and treatment of gastrointestinal tumors.

Hsa_circRNA_0017620 regulated cell progression of non-small-cell lung cancer via miR-520a-5p/KRT5 axis

Background

CircRNA is a very important functional RNA that plays an important role in the development and metabolism of cancer. However, the study of circRNA in NSCLC has not been fully elucidated.

Methods

The expression of hsa_circ_0017620, SFMBT2, miR‐520a‐5p, and KRT5 was determined using qRT‐PCR. KRT5, Twist1, E‐cadherin, and Ki67 protein expression were measured with western blot. The positive expression rates of Ki67 and Vimentin were determined by immunohistochemistry assay. 5‐Ethynyl‐2’‐deoxyuridine (EdU), colony formation, and MTT assays were used to assess cell proliferation. Transwell migration and invasion assay were applied to determine cell migration and invasion. Dual‐luciferase reporter and RNA immunoprecipitation assays were used to verify the relationship among hsa_circ_0017620, miR‐520a‐5p, and KRT5. The animal experiment was used to ensure the effects of hsa_circ_0017620 on tumor growth in vivo.

Results

Hsa_circ_0017620 was upregulated in NSCLC cells and tissues. MiR‐520a‐5p had been verified to be a target miRNA of hsa_circ_0017620 and KRT5 had been verified to be a target mRNA of miR‐520a‐5p in NSCLC cells. Knockdown of hsa_circ_0017620 inhibited cell proliferation, migration, and invasion in NSCLC cells, which was reversed by downregulating miR‐520a‐5p or upregulating KRT5 in NSCLC. Overexpression of hsa_circ_0017620 had opposite effects in NSCLC. Moreover, hsa_circ_0017620 silencing inhibited tumor growth in vivo of NSCLC.

Conclusion

In this study, we found that hsa_circ_0017620 played an important role in NSCLC progression. Hsa_circ_0017620 regulated cell proliferation, invasion, and migration through targeting miR‐520a‐5p/KRT5 axis in NSCLC, providing a potential new target for the treatment and diagnosis of NSCLC.

[Role of circular RNAs in immune-related diseases]

Objective Circular RNAs (circRNAs) are non-coding RNAs (ncRNA) circularized without a 3′ polyadenylation [poly-(A)] tail or a 5′ cap, resulting in a covalently closed loop structure. circRNAs were first discovered in RNA viruses in the 1970s, but only a small number of circRNAs were discovered at that time due to limitations in traditional polyadenylated transcriptome analyses. With the development of specific biochemical and computational methods, recent studies have shown the presence of abundant circRNAs in eukaryotic transcriptomes. circRNAs play vital roles in many physiological and pathological processes, such as acting as miRNA sponges, binding to RNA-binding proteins (RBPs), acting as transcriptional regulatory factors, and even serving as translation templates. Current evidence has shown that circRNAs can be potentially used as excellent biomarkers for diagnosis, therapeutic effect evaluation, and prognostic assessment of a variety of diseases, and they may also provide effective therapeutic targets due to their stability and tissue and development-stage specificity. This review focuses on the properties of circRNAs and their immune relationship to disease, and explores the role of circRNAs in immune-related diseases and the directions of future research.

Circular RNAs Modulate Cancer Hallmark and Molecular Pathways to Support Cancer Progression and Metastasis

Simple Summary

Circular RNAs (circRNA) are a type of RNA molecule of circular shape that are now being extensively studied due to the important roles they play in different biological processes. In addition, they were also shown to be implicated in disease such as cancer. Cancer is a complex process which is often defined by a combination of specific processes called cancer hallmarks. In this review, we summarize the literature on circRNAs in cancer and classify them as being implicated in specific cancer hallmarks.

Abstract

Circular RNAs (circRNAs) are noncoding products of backsplicing of pre-mRNAs which have been established to possess potent biological functions. Dysregulated circRNA expression has been linked to diseases including different types of cancer. Cancer progression is known to result from the dysregulation of several molecular mechanisms responsible for the maintenance of cellular and tissue homeostasis. The dysregulation of these processes is defined as cancer hallmarks, and the molecular pathways implicated in them are regarded as the targets of therapeutic interference. In this review, we summarize the literature on the investigation of circRNAs implicated in cancer hallmark molecular signaling. First, we present general information on the properties of circRNAs, such as their biogenesis and degradation mechanisms, as well as their basic molecular functions. Subsequently, we summarize the roles of circRNAs in the framework of each cancer hallmark and finally discuss the potential as therapeutic targets.

Telomerase in Cancer: Function, Regulation, and Clinical Translation

Simple Summary

Cells undergoing malignant transformation must circumvent replicative senescence and eventual cell death associated with progressive telomere shortening that occurs through successive cell division. To do so, malignant cells reactivate telomerase to extend their telomeres and achieve cellular immortality, which is a “Hallmark of Cancer”. Here we review the telomere-dependent and -independent functions of telomerase in cancer, as well as its potential as a biomarker and therapeutic target to diagnose and treat cancer patients.

Abstract

During the process of malignant transformation, cells undergo a series of genetic, epigenetic, and phenotypic alterations, including the acquisition and propagation of genomic aberrations that impart survival and proliferative advantages. These changes are mediated in part by the induction of replicative immortality that is accompanied by active telomere elongation. Indeed, telomeres undergo dynamic changes to their lengths and higher-order structures throughout tumor formation and progression, processes overseen in most cancers by telomerase. Telomerase is a multimeric enzyme whose function is exquisitely regulated through diverse transcriptional, post-transcriptional, and post-translational mechanisms to facilitate telomere extension. In turn, telomerase function depends not only on its core components, but also on a suite of binding partners, transcription factors, and intra- and extracellular signaling effectors. Additionally, telomerase exhibits telomere-independent regulation of cancer cell growth by participating directly in cellular metabolism, signal transduction, and the regulation of gene expression in ways that are critical for tumorigenesis. In this review, we summarize the complex mechanisms underlying telomere maintenance, with a particular focus on both the telomeric and extratelomeric functions of telomerase. We also explore the clinical utility of telomeres and telomerase in the diagnosis, prognosis, and development of targeted therapies for primary, metastatic, and recurrent cancers.

Circular RNA CUL2 regulates the development of colorectal cancer by modulating apoptosis and autophagy via miR-208a-3p/PPP6C

Aim: To explore the function of circular RNA CUL2 (circCUL2) in colorectal cancer progression.

Method: RT-PCR was carried out to detect the expression of circCUL2 in colorectal cancer tissues and cell lines. Western blot and immunofluorescence were used to determine the level of autophagy. CCK-8, clone formation assay, and EdU staining were used to assess the proliferation ability. Luciferase assay verified the relationship between miR-208a-3p and circCUL2 /PPP6C. The xenograft mouse model was used to confirm the function of circCUL2 in vivo.

Results: The expression level of circCUL2 was down-regulated in colorectal cancer tissues and cell lines. Forcing expression of circCUL2 inhibited proliferation ability, induced apoptosis, and autophagy in colorectal cancer cells. Luciferase assay verified that miR-208a-3p could bind with circCUL2/PPP6C. Overexpression of circCUL2 could inhibit cancer progression via targeting the miR-208a-3p/PPP6C signal pathway.

Conclusion: CircCUL2 participates in progression via the miR-208a-3p/PPP6C axis in colorectal cancer. CircCUL2 would be an underlying target for the diagnosis and therapy of colorectal cancer.

Cancer Stem Cells: An Ever-Hiding Foe

Cancer stem cells are a population of cells enable to reproduce the original phenotype of the tumor and capable to self-renewal, which is crucial for tumor proliferation, differentiation, recurrence, and metastasis, as well as chemoresistance. Therefore, the cancer stem cells (CSCs) have become one of the main targets for anticancer therapy and many ongoing clinical trials test anti-CSCs efficacy of plenty of drugs. This chapter describes CSCs starting from general description of this cell population, through CSCs markers, signaling pathways, genetic and epigenetic regulation, role of epithelial-mesenchymal transition (EMT) transition and autophagy, cooperation with microenvironment (CSCs niche), and finally role of CSCs in escaping host immunosurveillance against cancer.

Circular RNA: A potential diagnostic, prognostic, and therapeutic biomarker for human triple-negative breast cancer

Triple-negative breast cancer (TNBC), which is the most malignant subtype of breast cancer (BC), accounts for 10%–20% of all BC cases. TNBC, which occurs more frequently in young women, is characterized by high rates of cell proliferation and metastasis and poor prognosis. Chemotherapy is the primary systemic therapeutic strategy for TNBC. However, chemotherapy is largely unsuccessful, and effective targeted therapies for TNBC have not been established. Therefore, it is a matter of great urgency to identify precise molecular targets for the promising prognosis of patients with TNBC. Circular RNAs (circRNAs), which are a type of non-coding RNAs (ncRNAs), are abundantly expressed in the eukaryotic cells and exhibit diverse cellular functions. The roles of circRNAs are to sponge microRNA or RNA-binding proteins, regulate gene expression, and serve as templates for translation. Here, we review the current findings on the potential of circRNAs as a diagnostic, prognostic, and therapeutic biomarker for TNBC. However, further studies are essential to elucidate the functions of circRNAs in TNBC. This review also discusses the current limitations and future directions of TNBC-associated circRNAs, which can facilitate the translation of experimental research into clinical application.

circCORO1C promotes the proliferation and metastasis of hepatocellular carcinoma by enhancing the expression of PD-L1 through NF-κB pathway

BACKGROUND

Circular RNA (circRNA) affects the occurrence and development of human cancers, but the specific mechanism of hepatocellular carcinoma (HCC) has not yet been fully understood.

METHODS

CircRNAs were determined by human circRNA array analysis and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Cell viability, migration, invasion, and other indicators were used for cell function analysis. Knockdown and overexpression techniques were used to explore the mechanism of circCORO1C in the occurrence and development of HCC by RNA sequencing, qRT-PCR, western blot, and other methods.

RESULTS

Among the thousands of circRNAs, 1238 circRNAs were significantly changed. As for the top 10 upregulated circRNAs, the expression of circRNAs, hsa_circ_0036412, hsa_circ_0036411, hsa_circ_0028071, hsa_circ_0036409, hsa_circ_0000437, hsa_circ_0021427, hsa_circ_0097182, hsa_circ_0028067, hsa_circ_0006852, and hsa_circ_0003620 were significantly increased. In regard to the top 10 downregulated circRNAs, the expression of hsa_circ_0123629, hsa_circ_0096121, hsa_circ_0038932, hsa-circRNA3310-44, hsa_circ_0045746, hsa_circ_0016836, hsa-circRNA10899-9, hsa_circ_0050116, hsa_circ_0035543, and hsa_circ_0092118 decreased significantly. About these circRNAs, the downregulation of hsa_circ_0006852 (circCORO1C) can inhibit the tumorigenesis of HCC cells in vivo and in vitro, and the overexpression of circCORO1C can enhance the proliferation and metastasis ability of HCC cells. Mechanistically, circCORO1C activated the NF-κB signaling pathway, increased P65 phosphorylation and upregulation of c-Myc and COX-2, leading to increased PD-L1 expression.

CONCLUSION

CircCORO1C upregulates c-Myc and COX-2 through NF-κB signaling pathway, leading to the upregulation of PD-L1, which jointly promotes the development of HCC, suggesting that circCORO1C is a promising biomarker and therapeutic target for HCC.

circRNAs: Insight Into Their Role in Tumor-Associated Macrophages

Currently, it is well known that the tumor microenvironment not only provides energy support for tumor growth but also regulates tumor signaling pathways and promotes the proliferation, invasion, metastasis, and drug resistance of tumor cells. The tumor microenvironment, especially the function and mechanism of tumor-associated macrophages (TAMs), has attracted great attention. TAMs are the most common immune cells in the tumor microenvironment and play a vital role in the occurrence and development of tumors. circular RNA (circRNA) is a unique, widespread, and stable form of non-coding RNA (ncRNA), but little is known about the role of circRNAs in TAMs or how TAMs affect circRNAs. In this review, we summarize the specific manifestations of circRNAs that affect the tumor-associated macrophages and play a significant role in tumor progression. This review helps improve our understanding of the association between circRNAs and TAMs, thereby promoting the development and progress of potential clinical targeted therapies.

MiR-138-5p Suppresses Cell Growth and Migration in Melanoma by Targeting Telomerase Reverse Transcriptase

Recent evidence suggests the existence of a miRNA regulatory network involving human telomerase reverse transcriptase gene (hTERT), with miR-138-5p playing a central role in many types of cancers. However, little is known about the regulation of hTERT expression by microRNA (miRNAs) in melanocytic tumors. Here, we investigated the effects of miR-138-5p in hTERT regulation in melanoma cells lines. In vitro studies demonstrated higher miR-138-5p and lower hTERT messenger RNA (mRNA) expression in human epidermal melanocytes, compared with melanoma cell lines (A2058, A375, SK-MEL-28) by quantitative polymerase chain reaction (qPCR) observing a negative correlation between them. A2058 melanoma cells were selected to be transfected with miR-138-5p mimic or inhibitor. Using luciferase assay, hTERT was identified as a direct target of this miRNA. Overexpression of miR-138-5p detected by Western blot revealed a decrease in hTERT protein expression (p = 0.012), and qPCR showed a reduction in telomerase activity (p < 0.001). Moreover, suppressions in cell growth (p = 0.035) and migration abilities (p = 0.015) were observed in A2058-transfected cells using thiazolyl blue tetrazolium bromide and flow cytometry, respectively. This study identifies miR-138-5p as a crucial tumor suppressor miRNA involved in telomerase regulation. Targeting it as a combination therapy with immunotherapy or targeted therapies could be used in advanced melanoma treatment; however, more preclinical studies are necessary.