CircACC1 Regulates Assembly and Activation of AMPK Complex under Metabolic Stress

CircLIFR synergizes with MSH2 to attenuate chemoresistance via MutSα/ATM-p73 axis in bladder cancer

Background

Cisplatin (CDDP) has become a standard-of-care treatment for muscle-invasive bladder cancer (MIBC), while chemoresistance remains a major challenge. Accumulating evidence indicates that circular RNAs (circRNAs) are discrete functional entities. However, the regulatory functions as well as complexities of circRNAs in modulating CDDP-based chemotherapy in bladder cancer are yet to be well revealed.

Methods

Through analyzing the expression profile of circRNAs in bladder cancer tissues, RNA FISH, circRNA pull-down assay, mass spectrometry analysis and RIP, circLIFR was identified and its interaction with MSH2 was confirmed. The effects of circLIFR and MSH2 on CDDP-based chemotherapy were explored by flow cytometry and rescue experiments. Co-IP and Western blot were used to investigate the molecular mechanisms underlying the functions of circLIFR and MSH2. Biological implications of circLIFR and MSH2 in bladder cancer were implemented in tumor xenograft models and PDX models.

Results

CircLIFR was downregulated in bladder cancer and expression was positively correlated with favorable prognosis. Moreover, circLIFR synergizing with MSH2, which was a mediator of CDDP sensitivity in bladder cancer cells, positively modulated sensitivity to CDDP in vitro and in vivo. Mechanistically, circLIFR augmented the interaction between MutSα and ATM, ultimately contributing to stabilize p73, which triggered to apoptosis. Importantly, MIBC with high expression of circLIFR and MSH2 was more sensitive to CDDP-based chemotherapy in tumor xenograft models and PDX models.

Conclusions

CircLIFR could interact with MSH2 to positively modulate CDDP-sensitivity through MutSα/ATM-p73 axis in bladder cancer. CircLIFR and MSH2 might be act as promising therapeutic targets for CDDP-resistant bladder cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01360-4.

The circACC1/miR-29c-3p/FOXP1 network plays a key role in gastric cancer by regulating cell proliferation

Although substantial progress has been made in early detection and treatment of GC, this disease remains a major burden worldwide. CircRNAs have potential as prognostic and diagnostic biomarkers in tumorigenesis. Therefore, we aimed to clarify the role and mechanism of circACC1 in GC cell proliferation. The expression levels of circACC1, miR-29c-3p and FOXP1 were validated in GC tissue samples and adjacent tissue samples. The impact of circACC1 and miR-29c-3p on overall survival was evaluated in GC specimens. A functional study was performed on MKN-45 and BGC823 cells transfected with different vectors. Cell proliferation was assayed by CCK-8 and colony formation assays. The interactions among circACC1, miR-29c-3p and FOXP1 were tested by RNA immunoprecipitation and luciferase reporter assays. This study demonstrated that circACC1 is upregulated in GC tissues, and its upregulation predicts poorer OS in GC patients. Upregulation of circACC1 promoted GC cell proliferation, as indicated by CCK-8 and colony formation assays. A mechanistic study revealed that the pro-oncogenic effect of circACC1 was mainly caused by binding to miR-29c-3p, thus regulating expression of its downstream target FOXP1. The circACC1/miR-29c-3p/FOXP1 network plays a key role in gastric cancer by regulating cell proliferation.

The Involvement of Long Non-Coding RNAs in Bone

A harmonious balance between osteoblast and osteoclast activity guarantees optimal bone formation and resorption, pathological conditions affecting the bone may arise. In recent years, emerging evidence has shown that epigenetic mechanisms play an important role during osteoblastogenesis and osteoclastogenesis processes, including long non-coding RNAs (lncRNAs). These molecules are a class of ncRNAs with lengths exceeding 200 nucleotides not translated into protein, that have attracted the attention of the scientific community as potential biomarkers to use for the future development of novel diagnostic and therapeutic approaches for several pathologies, including bone diseases. This review aims to provide an overview of the lncRNAs and their possible molecular mechanisms in the osteoblastogenesis and osteoclastogenesis processes. The deregulation of their expression profiles in common diseases associated with an altered bone turnover is also described. In perspective, lncRNAs could be considered potential innovative molecular biomarkers to help with earlier diagnosis of bone metabolism-related disorders and for the development of new therapeutic strategies.

A tumor-suppressive circular RNA mediates uncanonical integrin degradation by the proteasome in liver cancer

Circular RNAs (circRNAs) have emerged as important regulators of various cellular processes and have been implicated in cancer. Previously, we reported the discovery of several dysregulated circRNAs including circPABPC1 (polyadenylate-binding protein 1) in human hepatocellular carcinoma (HCC), although their roles in HCC development remained unclear. Here, we show that circPABPC1 is preferentially lost in tumor cells from clinical samples and inhibits both intrahepatic and distant metastases in a mouse xenograft model. This tumor-suppressive function of circPABPC1 can be attributed to its inhibition of cell adhesion and migration through down-regulating a key member of the integrin family, ITGB1 (β₁ integrin). Mass spectrometry and biochemical evidence demonstrate that circPABPC1 directly links ITGB1 to the 26S proteasome for degradation in a ubiquitination-independent manner. Our data have revealed an uncanonical route for integrin turnover and a previously unidentified mode of action for circRNAs in HCC that can be harnessed for anticancer treatment.

Downregulation of circ-RANBP9 in laryngeal cancer and its clinical significance

Background

Laryngeal cancer (LC) is a common malignant tumor of the head and neck. As circular RNAs (circRNAs) and other non-coding RNAs are involved in various malignant processes, we analyzed circRNAs to better understand LC and explored specific tumor markers.

Methods

High-throughput sequence was performed to analyze the differential circular RNAs in four coupled laryngeal cancers and para-cancerous tissues. The differential expression of selected circ-RANBP9 in laryngeal cancer tissues and cells was verified by RT-qPCR assay. CCK8, EDU, Transwell and wound healing assays were used to confirm the biological function of circ-RANBP9 in laryngeal cancer. Western blot assay was performed to identify the effects of circ-RANBP9 having on the epithelial to mesenchymal transition process. One-way AN0VA was used to analyze the correlation between the expression of circ-RANBP9 and clinicopathological parameters of the included patients. Kaplan-Meier analysis was used to investigate whether the expression level of circ-RANBP9 correlated with survival in LC patients. Bioinformatic analyses were also conducted to predict the functions and possible signaling pathways of the targeted mRNAs of circ-RANBP9 via co-expression and competing endogenous RNA network.

Results

We found a transcript from RNA sequence data, termed hsa_circ_0001578, which is a circRNA spliced from RANBP9. Circ-RANBP9 was downregulated in the LC cell lines tissues, relating to a better prognosis. Circ-RANBP9 was found to inhibit the proliferation, migration, and invasion ability of LC, exerting a suppressive role in the epithelial to mesenchymal transition process as well. For the diagnostic value of circ-RANBP9, the sensitivity and the specificity were 0.979 and 0.553, respectively. Circ-RANBP9 downregulation was significantly correlated with differentiation (P=0.031), T-stage (P=0.018), lymphatic metastasis (P=0.046), and clinical stage (P=0.003). Circ-RANBP9 was involved in insulin-like growth factor receptor binding, cell polarity, focal adhesion, and MAPK signaling pathways. CeRNA analysis identified the possible involvement of circ-RANBP9 in the ECM-receptor interaction, cAMP, calcium, and Wnt signaling pathways by harboring miRNA genes.

Conclusions

Circ-RANBP9 was confirmed to play important roles in inhibiting laryngeal cancers. Circ-RANBP9 was also validated to be associated with the clinicopathological parameters and diagnostic value, suggesting that circ-RANBP9 is a promising biomarker for LC prognosis and early diagnosis.

LncRNA GIRGL drives CAPRIN1-mediated phase separation to suppress glutaminase-1 translation under glutamine deprivation

Glutamine constitutes an essential source of both carbon and nitrogen for numerous biosynthetic processes. The first and rate-limiting step of glutaminolysis involves the generation of glutamate from glutamine, catalyzed by glutaminase-1 (GLS1). Shortages of glutamine result in reductions in GLS1, but the underlying mechanisms are not fully known. Here, we characterize a long noncoding RNA, GIRGL (glutamine insufficiency regulator of glutaminase lncRNA), that is induced upon glutamine starvation. Manipulating GIRGL revealed a relationship between its expression and the translational suppression of GLS1. Cellular GIRGL levels are balanced by a combination of transactivation by c-JUN together with negative stability regulation via HuR/Ago2. Increased levels of GIRGL in the absence of glutamine drive formation of a complex between dimers of CAPRIN1 and GLS1 mRNA, serving to promote liquid-liquid phase separation of CAPRIN1 and inducing stress granule formation. Suppressing GLS1 mRNA translation enables cancer cells to survive under prolonged glutamine deprivation stress.

Insights Into the Involvement of Circular RNAs in Autoimmune Diseases

Circular RNAs (circRNAs) are single-stranded, endogenous, non-coding RNA (ncRNA) molecules formed by the backsplicing of messenger RNA (mRNA) precursors and have covalently closed circular structures without 5′-end caps and 3′-end polyadenylation [poly(A)] tails. CircRNAs are characterized by abundant species, stable structures, conserved sequences, cell- or tissue-specific expression, and widespread and stable presence in many organisms. Therefore, circRNAs can be used as biomarkers for the prediction, diagnosis, and treatment of a variety of diseases. Autoimmune diseases (AIDs) are caused by defects in immune tolerance or abnormal immune regulation, which leads to damage to host organs. Due to the complexity of the pathophysiological processes of AIDs, clinical therapeutics have been suboptimal. The emergence of circRNAs sheds new light on the treatment of AIDs. In particular, circRNAs mainly participate in the occurrence and development of AIDs by sponging targets. This review systematically explains the formation, function, mechanism, and characteristics of circRNAs in the context of AIDs. With a deeper understanding of the pathophysiological functions of circRNAs in the pathogenesis of AIDs, circRNAs may become reasonable, accurate, and effective biomarkers for the diagnosis and treatment of AIDs in the future.

The Latest Overview of circRNA in the Progression, Diagnosis, Prognosis, Treatment, and Drug Resistance of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the main causes of tumor-related deaths worldwide. Due to the lack of obvious early symptoms and the lack of sensitive screening indicators in the early stage of HCC, the vast majority of patients are diagnosed with advanced or metastatic HCC, resulting in dissatisfactory treatment result. Therefore, it is urgent to determine effective and sensitive diagnostic and prognostic indicators and to determine new therapeutic targets. Circular RNA (circRNA) is a type of non-coding RNA that has been neglected for a long time. In recent years, it has been proved to play an important role in the development of many human diseases. Increasing evidence shows that change in circRNA expression has an extensive effect on the biological behavior of HCC. In this study, we comprehensively tracked the latest progress of circRNA in the pathogenesis of HCC, and reviewed its role as a biomarker for diagnosis and prognosis prediction in patients with HCC. In addition, we also summarized the potential of circRNA as therapeutic target in HCC and its relationship with HCC drug resistance, providing clues for the clinical development of circRNA-based therapeutic strategies.

Comprehensive landscape and future perspectives of circular RNAs in colorectal cancer

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

The circular RNA circZFR phosphorylates Rb promoting cervical cancer progression by regulating the SSBP1/CDK2/cyclin E1 complex

Background

As a novel type of non-coding RNA, circular RNAs (circRNAs) play a critical role in the initiation and development of various diseases, including cancer. However, the exact function of circRNAs in human cervical cancer remains largely unknown.

Methods

We identified the circRNA signature of upregulated circRNAs between cervical cancer and paired adjacent normal tissues. Using two different cohorts and GEO database, a total of six upregulated circRNAs were identified with a fold change > 2, and P < 0.05. Among these six circRNAs, hsa_circ_0072088 (circZFR) was the only exonic circRNA significantly overexpressed in cervical cancer. Functional experiments were performed to investigate the biological function of circZFR. CircRNA pull-down, circRNA immunoprecipitation (circRIP) and Co-immunoprecipitation (Co-IP) assays were executed to investigate the molecular mechanism underlying the function of circZFR.

Results

Functionally, circZFR knockdown represses the proliferation, invasion, and tumor growth. Furthermore, circRNA pull-down experiments combined with mass spectrometry unveil the interactions of circZFR with Single-Stranded DNA Binding Protein 1 (SSBP1). Mechanistically, circZFR bound with SSBP1, thereby promoting the assembly of CDK2/cyclin E1 complexes. The activation of CDK2/cyclin E1 complexes induced p-Rb phosphorylation, thus releasing activated E2F1 leading to cell cycle progression and cell proliferation.

Conclusion

Our findings provide the first evidence that circZFR is a novel onco-circRNA and might be a potential biomarker and therapeutic target for cervical cancer patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01849-2.

circNDUFB2 inhibits non-small cell lung cancer progression via destabilizing IGF2BPs and activating anti-tumor immunity

Circular RNAs (circRNA) are a class of covalently closed single-stranded RNAs that have been implicated in cancer progression. Here we identify circNDUFB2 to be downregulated in non-small cell lung cancer (NSCLC) tissues, and to negatively correlate with NSCLC malignant features. Elevated circNDUFB2 inhibits growth and metastasis of NSCLC cells. Mechanistically, circNDUFB2 functions as a scaffold to enhance the interaction between TRIM25 and IGF2BPs, a positive regulator of tumor progression and metastasis. This TRIM25/circNDUFB2/IGF2BPs ternary complex facilitates ubiquitination and degradation of IGF2BPs, with this effect enhanced by N6-methyladenosine (m6A) modification of circNDUFB2. Moreover, circNDUFB2 is also recognized by RIG-I to activate RIG-I-MAVS signaling cascades and recruit immune cells into the tumor microenvironment (TME). Our data thus provide evidences that circNDUFB2 participates in the degradation of IGF2BPs and activation of anti-tumor immunity during NSCLC progression via the modulation of both protein ubiquitination and degradation, as well as cellular immune responses.

Circular RNAs as biomarkers and therapeutic targets in cancer

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

Non-coding RNAs rewire cancer metabolism networks

Non-coding RNAs (ncRNAs) are functional RNAs with limited or no protein-coding ability. These interact with their target molecules and participate in the precise regulation of disease development. Metabolic reprogramming is a hallmark in cancer, and is considered essential in meeting increased macromolecular biosynthesis and energy generation of tumors. Recent studies have revealed the involvement of ncRNAs in several metabolic regulations of cancer through direct modulation of metabolic enzyme activities or participation of metabolism-related signaling pathways. Elucidation of how ncRNAs regulate metabolic reprogramming of cancers has opened up a novel intention to understand the mechanism of metabolic rewiring and also the opportunities of utilizing ncRNA-based therapeutics for targeting the metabolism in cancer treatment.

Estrogen-induced circRNA, circPGR, functions as a ceRNA to promote estrogen receptor-positive breast cancer cell growth by regulating cell cycle-related genes

Estrogen and estrogen receptor (ER)-regulated gene transcriptional events have been well known to be involved in ER-positive breast carcinogenesis. Meanwhile, circular RNAs (circRNAs) are emerging as a new family of functional non-coding RNAs (ncRNAs) with implications in a variety of pathological processes, such as cancer. However, the estrogen-regulated circRNA program and the function of such program remain uncharacterized. Methods: CircRNA sequencing (circRNA-seq) was performed to identify circRNAs induced by estrogen, and cell proliferation, colony formation, wound healing, transwell and tumor xenograft experiments were applied to examine the function of estrogen-induced circRNA, circPGR. RNA sequencing (RNA-seq) and ceRNA network analysis wereperformed to identify circPGR's target genes and the microRNA (miRNA) bound to circPGR. Anti-sense oligonucleotide (ASO) was used to assess circPGR's effects on ER-positive breast cancer cell growth. Results: Genome-wide circRNA profiling by circRNA sequencing (circRNA-seq) revealed that a large number of circRNAs were induced by estrogen, and further functional screening for the several circRNAs originated from PGR revealed that one of them, which we named as circPGR, was required for ER-positive breast cancer cell growth and tumorigenesis. CircPGR was found to be localized in the cytosol of cells and functioned as a competing endogenous RNA (ceRNA) to sponge miR-301a-5p to regulate the expression of multiple cell cycle genes. The clinical relevance of circPGR was underscored by its high and specific expression in ER-positive breast cancer cell lines and clinical breast cancer tissue samples. Accordingly, anti-sense oligonucleotide (ASO) targeting circPGR was proven to be effective in suppressing ER-positive breast cancer cell growth. Conclusions: These findings reveled that, besides the well-known messenger RNA (mRNA), microRNA (miRNA), long non-coding RNA (lncRNA) and enhancer RNA (eRNA) programs, estrogen also induced a circRNA program, and exemplified by circPGR, these estrogen-induced circRNAs were required for ER-positive breast cancer cell growth, providing a new class of therapeutic targets for ER-positive breast cancer.

RNA in cancer

While the processing of mRNA is essential for gene expression, recent findings have highlighted that RNA processing is systematically altered in cancer. Mutations in RNA splicing factor genes and the shortening of 3' untranslated regions are widely observed. Moreover, evidence is accumulating that other types of RNAs, including circular RNAs, can contribute to tumorigenesis. In this Review, we highlight how altered processing or activity of coding and non-coding RNAs contributes to cancer. We introduce the regulation of gene expression by coding and non-coding RNA and discuss both established roles (microRNAs and long non-coding RNAs) and emerging roles (selective mRNA processing and circular RNAs) for RNAs, highlighting the potential mechanisms by which these RNA subtypes contribute to cancer. The widespread alteration of coding and non-coding RNA demonstrates that altered RNA biogenesis contributes to multiple hallmarks of cancer.

Circular RNA: metabolism, functions and interactions with proteins

Circular RNAs (CircRNAs) are single-stranded, covalently closed RNA molecules that are ubiquitous across species ranging from viruses to mammals. Important advances have been made in the biogenesis, regulation, localization, degradation and modification of circRNAs. CircRNAs exert biological functions by acting as transcriptional regulators, microRNA (miR) sponges and protein templates. Moreover, emerging evidence has revealed that a group of circRNAs can serve as protein decoys, scaffolds and recruiters. However, the existing research on circRNA-protein interactions is quite limited. Hence, in this review, we briefly summarize recent progress in the metabolism and functions of circRNAs and elaborately discuss the patterns of circRNA-protein interactions, including altering interactions between proteins, tethering or sequestering proteins, recruiting proteins to chromatin, forming circRNA-protein-mRNA ternary complexes and translocating or redistributing proteins. Many discoveries have revealed that circRNAs have unique expression signatures and play crucial roles in a variety of diseases, enabling them to potentially act as diagnostic biomarkers and therapeutic targets. This review systematically evaluates the roles and mechanisms of circRNAs, with the hope of advancing translational medicine involving circRNAs.

CircCDKN2B-AS1 interacts with IMP3 to stabilize hexokinase 2 mRNA and facilitate cervical squamous cell carcinoma aerobic glycolysis progression

Background

Circular RNAs (circRNAs) have been reported to play key roles in the development of various cancers. However, the biological functions and clinical significance of most circRNAs are still elusive. The purpose of this study was to explore the function and mechanism of a certain circRNA named circCDKN2B-AS1 in cervical cancer development and its potential value in the clinic.

Methods

qRT-PCR was used to verify the expression level of circCDKN2B-AS1. CCK-8, Transwell, and flow cytometry (FCM) assays were performed to detect cellular proliferation, migration, and apoptosis, respectively. A Seahorse XFe96 Analyzer was used to measure glycolysis metabolism level. RNA pull-down, RNA immunoprecipitation (RIP), actinomycin-D addition assays and Western blotting were used to screen and elucidate the potential mechanisms involved. BALB/c nude mice and zebrafish embryos (AB, WT) were used as animal models to investigate tumorigenesis capability. ¹⁸FDG-microPET/CT imaging and lactic acid (LA) and pyruvic acid (PA) content detection assays were used to detect the level of glucose metabolism in subcutaneous tumors from nude mice.

Results

CircCDKN2B-AS1, a circular isoform of the long noncoding RNA (lncRNA) CDKN2B-AS1, was upregulated in cervical cancer and precancerous tissues. We found that circCDKN2B-AS1 associated with the IMP3 protein depending on a specific binding site and regulated the stability of Hexokinase 2 (HK2) mRNA, the rate-limiting enzyme of the aerobic glycolysis pathway. The expression level of circCDKN2B-AS1 fated the binding of IMP3 to the 3′ untranslated region (UTR) of HK2 mRNA, consequently affecting the malignant cell phenotype and aerobic glycolysis in cervical cancer in vitro and in vivo. Mutant circCDKN2B-AS1, lacking the IMP3 binding site, did not have such effects. Utilization of an inhibitory peptide to block the interaction between circCDKN2B-AS1 and the IMP3 protein impeded the binding of IMP3 to the 3’UTR of HK2 mRNA and suppressed aerobic glycolysis in cervical cancer cells.

Conclusions

Our findings demonstrate that circCDKN2B-AS1 facilitates aerobic glycolysis by sponging the IMP3 protein to stabilize HK2 mRNA, consequently promoting the malignant phenotype in cervical cancer, which may provide a potential approach for cervical cancer therapeutics.

Circular RNA in cancer development and immune regulation

Circular RNAs (circRNAs) are a class of single‐stranded RNAs with closed loop structures formed by covalent bonds of head and tail. Exploration of circRNAs is continually increasing; however, their functional relevance largely remains to be elucidated. In general, they are stable, abundant, conserved and expressed in tissue‐specific manner. These distinct properties and their diverse cellular actions indicate that circRNAs modulate transcription and translation, and may even function as translation templates. Growing evidence reveals that circRNAs contribute to various physiological and pathological processes, including the initiation and progression of cancer. In this review, we present the current knowledge about circRNAs in cancer development, as well as their potential for use as biomarkers and even therapeutic targets. CircRNA’s role in immune regulation and antitumour immunotherapy is also discussed. In addition, possible challenges in antitumour therapy are raised, and current progress and future perspectives are provided.

The Role of Mitochondrial Fat Oxidation in Cancer Cell Proliferation and Survival

Tumors remodel their metabolism to support anabolic processes needed for replication, as well as to survive nutrient scarcity and oxidative stress imposed by their changing environment. In most healthy tissues, the shift from anabolism to catabolism results in decreased glycolysis and elevated fatty acid oxidation (FAO). This change in the nutrient selected for oxidation is regulated by the glucose-fatty acid cycle, also known as the Randle cycle. Briefly, this cycle consists of a decrease in glycolysis caused by increased mitochondrial FAO in muscle as a result of elevated extracellular fatty acid availability. Closing the cycle, increased glycolysis in response to elevated extracellular glucose availability causes a decrease in mitochondrial FAO. This competition between glycolysis and FAO and its relationship with anabolism and catabolism is conserved in some cancers. Accordingly, decreasing glycolysis to lactate, even by diverting pyruvate to mitochondria, can stop proliferation. Moreover, colorectal cancer cells can effectively shift to FAO to survive both glucose restriction and increases in oxidative stress at the expense of decreasing anabolism. However, a subset of B-cell lymphomas and other cancers require a concurrent increase in mitochondrial FAO and glycolysis to support anabolism and proliferation, thus escaping the competing nature of the Randle cycle. How mitochondria are remodeled in these FAO-dependent lymphomas to preferably oxidize fat, while concurrently sustaining high glycolysis and increasing de novo fatty acid synthesis is unclear. Here, we review studies focusing on the role of mitochondrial FAO and mitochondrial-driven lipid synthesis in cancer proliferation and survival, specifically in colorectal cancer and lymphomas. We conclude that a specific metabolic liability of these FAO-dependent cancers could be a unique remodeling of mitochondrial function that licenses elevated FAO concurrent to high glycolysis and fatty acid synthesis. In addition, blocking this mitochondrial remodeling could selectively stop growth of tumors that shifted to mitochondrial FAO to survive oxidative stress and nutrient scarcity.

Circular RNAs: Rising stars in lipid metabolism and lipid disorders

The underlying mechanisms of circular RNAs (circRNAs) in lipid metabolism regulation and the pathogenesis of lipid disorder diseases are clarified in this review. circRNAs are produced from host genes by back splicing and are mainly degraded by RNase L. circRNAs act as molecular sponges or scaffolds that bind with microRNAs or proteins and thus affect the intracorporeal processes of lipid metabolism. CircRNA_11897 and circSAMD4A facilitated adipogenesis while circH19 and circRNA_26852 accelerated adipolysis in adipose tissue. CircSAMD4A promoted the differentiation of preadipocytes, but circH19 and circFUT10 inhibited this differentiation. CircFUT10 also promoted the proliferation of preadipocytes. CiRS-133 fostered the browning of white adipose tissue. CircACC1, circRNA_021412, circRNA_0046366, and circRNA_0046367 promoted the mitochondrial β-oxidation of fatty acids in hepatocytes. CircRNA_021412 suppressed the synthesis of triglycerides in hepatocytes. CircScd1 inhibited hepatic lipid droplet formation. circ_0092317, circ_0003546, circ_0028198, circ_0092317, and circACC1 probably reduced cholesterol efflux from macrophages. circ_0037251 likely promoted lipid accumulation and inhibited lipophagy in macrophages. circRNAs participate in lipid metabolism regulation and affect the development of lipid disorder diseases.

Regulation of bone marrow mesenchymal stem cell fate by long non-coding RNA

Bone mesenchymal stem cells (BMSCs) are progenitor cells isolated from bone marrow, which keep potential to differentiate into several kinds of cells including osteoblasts and adipocytes. A dynamic mutual regulation exists between osteogenesis and adipogenesis processes. Long non-coding RNA (lncRNA) performs diverse functions in biological activities including regulation of BMSCs commitment. Evidence has shown that lncRNA regulates key signaling pathways including TGFβ/BMP, Wnt and Notch pathways, and several transcription factors in BMSCs differention. Dysregulation of lncRNA in BMSCs leads to disruption of osteo-adipogenesis difffrentiation and results in impairment of bone homeostasis. In this review, we focus on the role of lncRNA in several critical signaling pathways that involved in regulation of osteo-adipogenesis of BMSC and prospects the potential clinical application of lncRNA.

Comprehensive analysis of circular RNAs from steatotic livers after ischemia and reperfusion injury by next-generation RNA sequencing

Global organ shortage has led to the acceptance of steatotic livers for transplantation, taking the risk of graft dysfunction associated with the higher sensitivity of steatotic livers to ischemia and reperfusion injury (IRI). Data about circular RNAs (circRNAs) in steatotic livers following IRI are practically nonexistent. In our study, a high-fat diet-fed mouse model of hepatic steatosis was generated, and RNA sequencing was performed both on IRI and on sham liver tissues of these mice to screen for circRNAs with significant differential expression. To further validate our bioinformatics data, one upregulated circRNA and four downregulated circRNAs were examined. The circularity of these circRNAs was demonstrated using RNaseR digestion and Sanger sequencing. The expression of four stable circRNAs undigested by RNaseR was further validated by quantitative PCR. In summary, this study unearths several circRNAs as novel and potentially effective targets involved in the more severe damage of steatotic livers following IRI.

Emerging Roles of Exosomal Circular RNAs in Cancer

Circular RNA (circRNA) is a type of non-coding RNA that forms a covalently closed continuous loop. The expression pattern of circRNA varies among cell types and tissues, and many circRNAs are aberrantly expressed in various cancers. Aberrantly expressed circRNAs have been shown to play crucial roles in carcinogenesis, functioning as microRNA sponges or new templates for protein translation. Recent research has shown that circRNAs are enriched in exosomes. Exosomes are secretory vesicles that mediate intercellular communication through the delivery of cargo, including proteins, lipids, DNA, and RNA. Exosome-mediated crosstalk between cancer cells and the tumor microenvironment promotes the epithelial-mesenchymal transition, angiogenesis, and immune escape, and thus may contribute to cancer invasion and metastasis. In this review, we discuss the biological functions of exosomal circRNAs and their significance in cancer progression. Additionally, we discuss the potential clinical applications of exosomal circRNAs as biomarkers and in cancer therapy.

NADPH homeostasis in cancer: functions, mechanisms and therapeutic implications

Nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all organisms, and provides the reducing power for anabolic reactions and redox balance. NADPH homeostasis is regulated by varied signaling pathways and several metabolic enzymes that undergo adaptive alteration in cancer cells. The metabolic reprogramming of NADPH renders cancer cells both highly dependent on this metabolic network for antioxidant capacity and more susceptible to oxidative stress. Modulating the unique NADPH homeostasis of cancer cells might be an effective strategy to eliminate these cells. In this review, we summarize the current existing literatures on NADPH homeostasis, including its biological functions, regulatory mechanisms and the corresponding therapeutic interventions in human cancers, providing insights into therapeutic implications of targeting NADPH metabolism and the associated mechanism for cancer therapy.

Circular RNAs in cancer: limitations in functional studies and diagnostic potential

Circular RNAs (circRNAs) are a large class of noncoding RNAs, generated from a process called back-splicing, that possess critical regulatory functions in many cellular events. A large body of literature has reported various circRNA functions and their underlying mechanisms, including sponging miRNA, exerting transcriptional and translational regulation, interacting with proteins, and translating into peptides and proteins. CircRNA dysregulation has been implicated in many cancers, including lung, breast, liver, gastric, colorectal, and ovarian cancer. They are detectable in bodily fluids and relatively stable, making them potential cancer biomarker candidates. Furthermore, targeting circRNA expression levels is a potential therapeutic approach for treating cancers. In this review, we describe the functional mechanisms of circRNAs and discuss limitations of current mechanism studies. Following this, we outline the potential of circRNAs to be effective biomarkers in various cancers and present circRNA-based therapeutic approaches. Finally, we discuss challenges in using circRNAs as diagnostic and therapeutic tools and propose future research directions.

circRNA CDR1as Promotes Pulmonary Artery Smooth Muscle Cell Calcification by Upregulating CAMK2D and CNN3 via Sponging miR-7-5p

Emerging evidence has suggested that circular RNAs (circRNAs) are involved in multiple physiological processes and participate in a variety of human diseases. However, the underlying biological function of circRNAs in pulmonary hypertension (PH) is still ambiguous. Herein, we investigated the implication and regulatory effect of a typical circRNA, CDR1as, in the pathological process of vascular calcification in PH. Human pulmonary artery smooth muscle cell (HPASMC) calcification was analyzed by western blotting, immunofluorescence, alizarin red S staining, alkaline phosphatase activity analysis, and calcium deposition quantification. CDR1as targets were identified by bioinformatics analysis and validated by dual-luciferase reporter and RNA antisense purification assays. We identified that CDR1as was upregulated in hypoxic conditions and promoted a phenotypic switch of HPASMCs from a contractile to an osteogenic phenotype. Moreover, microRNA (miR)-7-5p was shown to be a target of CDR1as, and calcium/calmodulin-dependent kinase II-delta (CAMK2D) and calponin 3 (CNN3) were suggested to be the putative target genes and regulated by CDR1as/miR-7-5p. The results showed that the CDR1as/miR-7-5p/CNN3 and CAMK2D regulatory axis mediates HPASMC osteoblastic differentiation and calcification induced by hypoxia. This evidence reveals an approach to the treatment of PH.

Targeting Mitochondria-Located circRNA SCAR Alleviates NASH via Reducing mROS Output

Mitochondria, which play central roles in immunometabolic diseases, have their own genome. However, the functions of mitochondria-located noncoding RNAs are largely unknown due to the absence of a specific delivery system. By circular RNA (circRNA) expression profile analysis of liver fibroblasts from patients with nonalcoholic steatohepatitis (NASH), we observe that mitochondrial circRNAs account for a considerable fraction of downregulated circRNAs in NASH fibroblasts. By constructing mitochondria-targeting nanoparticles, we observe that Steatohepatitis-associated circRNA ATP5B Regulator (SCAR), which is located in mitochondria, inhibits mitochondrial ROS (mROS) output and fibroblast activation. circRNA SCAR, mediated by PGC-1α, binds to ATP5B and shuts down mPTP by blocking CypD-mPTP interaction. Lipid overload inhibits PGC-1α by endoplasmic reticulum (ER) stress-induced CHOP. In vivo, targeting circRNA SCAR alleviates high fat diet-induced cirrhosis and insulin resistance. Clinically, circRNA SCAR is associated with steatosis-to-NASH progression. Collectively, we identify a mitochondrial circRNA that drives metaflammation and serves as a therapeutic target for NASH.

CircARHGAP12 promotes nasopharyngeal carcinoma migration and invasion via ezrin-mediated cytoskeletal remodeling

An increasing number of studies have shown that circular RNAs (circRNAs) play important roles in malignant tumor initiation and progression; however, many circRNAs are yet unidentified, and the role of circRNAs in nasopharyngeal carcinoma (NPC) is unclear. Using RNA sequencing, we discovered a novel circRNA, termed circARHGAP12, that was processed from the pre-mRNA of the ARHGAP12 gene. CircARHGAP12 was significantly upregulated in NPC tissues and cell lines and promoted NPC cell migration and invasion. Overexpression or knockdown experiments revealed that circARHGAP12 regulates the expression of cytoskeletal remodeling-related proteins EZR, TPM3, and RhoA. CircARHGAP12 was found to bind directly to the 3' UTR of EZR mRNA and promote its stability; moreover, EZR protein interacted with TPM3 and RhoA and formed a complex to promote NPC cell invasion and metastasis. This study identified the novel circRNA circARHGAP12, characterized its biological function and mechanism, and increased our understanding of circRNAs in NPC pathogenesis. In particular, circARHGAP12 was found to promote the malignant biological phenotype of NPC via cytoskeletal remodeling, thus providing a clue for targeted therapy of NPC.

Circular RNAs: A New Piece in the Colorectal Cancer Puzzle

Colorectal cancer (CRC) is the third most fatal type of malignancy, worldwide. Despite the advances accomplished in the elucidation of its molecular base and the existing CRC biomarkers introduced in the clinical practice, additional research is required. Circular RNAs (circRNAs) constitute a new RNA type, formed by back-splicing of primary transcripts. They have been discovered during the 1970s but were characterized as by-products of aberrant splicing. However, the modern high-throughput approaches uncovered their widespread expression; therefore, several questions were raised regarding their potential biological roles. During the last years, great progress has been achieved in the elucidation of their functions: circRNAs can act as microRNA sponges, transcription regulators, and interfere with splicing, as well. Furthermore, they are heavily involved in various human pathological states, including cancer, and could serve as diagnostic and prognostic biomarkers in several diseases. Particularly in CRC, aberrant expression of circRNAs has been observed. More specifically, these molecules either inhibit or promote colorectal carcinogenesis by regulating different molecules and signaling pathways. The present review discusses the characteristics and functions of circRNA, prior to analyzing the multifaceted role of these molecules in CRC and their potential value as biomarkers and therapeutic targets.

Crosstalk between RNA m6A Modification and Non-coding RNA Contributes to Cancer Growth and Progression

N6-methyladenosine (m6A) is the most common RNA modification and has an important role in normal development and tumorigenesis. The abnormal expression of m6A regulators can lead to an imbalance in m6A levels in cancer cells, leading to the dysregulated expression of oncogenes and tumor suppressor genes that may contribute to cancer development, patient response to chemoradiotherapy, and clinical prognosis. Recent studies demonstrate that non-coding RNAs are involved in epigenetic modification of both DNA and RNA in tumor cells, and may also affect the development and progression of cancer by targeting m6A regulators. In this review, we describe the functional crosstalk between m6A and non-coding RNAs, particularly microRNA, long non-coding RNA, and circular RNA, and illustrate their roles in tumor regulation. Finally, we discuss the significance of non-coding RNA and m6A modification in the diagnosis, treatment, and prognosis of cancer patients, as well as potential future research directions.

Functions of Circular RNAs in Regulating Adipogenesis of Mesenchymal Stem Cells

The mesenchymal stem cells (MSCs) are known as highly plastic stem cells and can differentiate into specialized tissues such as adipose tissue, osseous tissue, muscle tissue, and nervous tissue. The differentiation of mesenchymal stem cells is very important in regenerative medicine. Their differentiation process is regulated by signaling pathways of epigenetic, transcriptional, and posttranscriptional levels. Circular RNA (circRNA), a class of noncoding RNAs generated from protein-coding genes, plays a pivotal regulatory role in many biological processes. Accumulated studies have demonstrated that several circRNAs participate in the cell differentiation process of mesenchymal stem cells in vitro and in vivo. In the current review, characteristics and functions of circRNAs in stem cell differentiation will be discussed. The mechanism and key role of circRNAs in regulating mesenchymal stem cell differentiation, especially adipogenesis, will be reviewed and discussed. Understanding the roles of these circRNAs will present us with a more comprehensive signal path network of modulating stem cell differentiation and help us discover potential biomarkers and therapeutic targets in clinic.

Non-coding RNAs, metabolic stress and adaptive mechanisms in cancer

Metabolic reprogramming in cancer describes the multifaceted alterations in metabolism that contribute to tumorigenesis. Major determinants of metabolic phenotypes are the changes in signalling pathways associated with oncogenic activation together with cues from the tumor microenvironment. Therein, depleted oxygen and nutrient levels elicit metabolic stress, requiring cancer cells to engage adaptive mechanisms. Non-coding RNAs (ncRNAs) act as regulatory elements within metabolic pathways and their widespread dysregulation in cancer contributes to altered metabolic phenotypes. Indeed, ncRNAs are the regulatory accomplices of many prominent effectors of metabolic reprogramming including c-MYC and HIFs that are activated by metabolic stress. By example, this review illustrates the range of ncRNAs mechanisms impacting these effectors throughout their DNA-RNA-protein lifecycle along with presenting the mechanistic roles of ncRNAs in adaptive responses to glucose, glutamine and lipid deprivation. We also discuss the facultative activation of metabolic enzymes by ncRNAs, a phenomenon which may reflect a broad but currently invisible level of metabolic regulation. Finally, the translational challenges associated with ncRNA discoveries are discussed, emphasizing the gaps in knowledge together with importance of understanding the molecular basis of ncRNA regulatory mechanisms.

CircCDK14 protects against Osteoarthritis by sponging miR-125a-5p and promoting the expression of Smad2

Rationale: Osteoarthritis (OA) is the most common joint disease worldwide. Previous studies have identified the imbalance between extracellular matrix (ECM) catabolism and anabolism in cartilage tissue as the main cause. To date, there is no cure for OA despite a few symptomatic treatments. This study aimed to investigate the role of CircCDK14, a novel circRNA factor, in the progression of OA, and to elucidate its underlying molecular mechanisms.

Methods: The function of CircCDK14 in OA, as well as the interaction between CircCDK14 and its downstream target (miR-125a-5p) and mRNA target (Smad2), was evaluated by western blot (WB), immunofluorescence (IF), RNA immunoprecipitation (RIP), quantitative RT-PCR, luciferase assay and fluorescence in situ hybridization (FISH). Rabbit models were introduced to examine the function and mechanism of CircCDK14 in OA in vivo.

Results: In our present study, we found that CircCDK14, while being down-regulated in the joint wearing position, regulated metabolism, inhibited apoptosis and promoted proliferation in the cartilage. Mechanically, the protective effect of CircCDK14 was mediated by miR-125a-5p sponging, which downregulated the Smad2 expression and led to the dysfunction of TGF-β signaling pathway. Intra-articular injection of adeno-associated virus-CircCDK14 also alleviated OA in the rabbit model.

Conclusion: Our study revealed an important role of CircCDK14/miR-125a-5p/Smad2 axis in OA progression and provided a potential molecular therapeutic strategy for the treatment of OA.

Hsa_circ_0003998 promotes epithelial to mesenchymal transition of hepatocellular carcinoma by sponging miR-143-3p and PCBP1

BACKGROUND

Circular RNAs (circRNAs) play a critical regulatory role in cancer progression. However, the underlying mechanisms of circRNAs in hepatocellular carcinoma (HCC) metastasis remain mostly unknown.

METHODS

Has_circ_0003998 (circ0003998) was identified by RNAs sequencing in HCC patients with /without portal vein tumor thrombus (PVTT) metastasis. The expression level of circ0003998 was further detected by in situ hybridization on tissues microarray (ISH-TMA) and qRT-PCR in 25 HCC patients with PVTT metastasis. Moreover, the 25 HCC patients with PVTT metastasis and 50 HCC patients without PVTT metastasis were recruited together to analyze the correlation between circ0003998 expression and HCC clinical characteristics. Transwell, migration and CCK8 assays, as well as nude mice model of lung or liver metastasis were used to evaluate the role of circ0003998 in epithelial to mesenchymal transition (EMT) in HCC. The regulatory mechanisms of circ0003998 in miR-143-3p and PCBP1 were determined by dual-luciferase reporter assay, nuclear-cytoplasmic fractionation, fluorescent in situ hybridization, RNA pull- down, microRNA sequence, western blot and RNA immunoprecipitation.

RESULTS

Compared with adjacent normal liver tissues (ANL), circ0003998 expression was significantly upregulated in PVTT tissues and HCC tissues, and its expression correlates with the aggressive characteristics of HCC patients. Further assays suggested that circ0003998 promoted EMT of HCC both in vitro and in vivo. Mechanistically, our data indicated that circ0003998 may act as a ceRNA (competing endogenous RNA) of microRNA-143-3p to relieve the repressive effect on EMT-related stimulator, FOSL2; meanwhile, circ0003998 could bind with PCBP1-poly(rC) binding protein 1 (PCBP1) to increase the expression level of EMT-related genes, CD44v6.

CONCLUSION

Circ0003998 promotes EMT of HCC by circ0003998/miR-143-3p/FOSL2 axis and circ0003998 /PCBP1/CD44v6 axis.

Circular RNA in renal diseases

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

Emerging Role of Circular RNAs in Cancer

Circular RNAs (circRNAs), which are generated mainly from back-splicing of exons in precursor mRNAs (pre-mRNAs), are a novel class of endogenous covalently closed RNA molecules. Their functions as microRNA sponges, protein scaffolds, and modulators of transcription and splicing, as well as occasional templates for polypeptide production, are beginning to be recognized, though the investigation of circRNAs is in its infancy. circRNAs play critical roles in diverse cellular processes. Aberrant expression of circRNAs in malignancies sustains cellular growth and proliferation, promotes cellular invasiveness, and circumvents cellular senescence and death, suggesting their potential for exploitation as clinical biomarkers and therapeutic targets. In this review, we highlight recent progress in research on circRNAs in cancer, emphasizing the molecular mechanisms and potential clinical value of circRNAs.

The Biogenesis, Functions, and Roles of circRNAs in Bladder Cancer

Bladder cancer (BCa) is the 10th most prevalent malignancy worldwide and remains a crucial cause of cancer-related morbidity and mortality. Circular RNAs (circRNAs), a large class of endogenous non-coding RNAs, contain unique covalent closed structures and their biogenesis and turnover are regulated by multiple factors. Recently, multiple circRNAs have been found to serve as important factors in several biological processes such as tumorigenesis. An increasing amount of research discovered that circRNAs are dysregulated in multiple cancer tissues compared with matched normal tissues, especially in BCa, indicating that circRNAs can act as biomarkers for the diagnosis and prognosis of BCa. In this review, we focus on the biogenesis, properties, turnover, and functions of circRNAs, summarizing their potential functions and clinical implications in BCa.

Circular RNAs in nasopharyngeal carcinoma

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a geographical distributed epithelial tumor of head and neck, which is prevalent in east Africa and Asia, especially southern China. Moreover, NPC has an unfavorable clinical effect and is prone to metastasis at an advanced stage. Although the recovery rate of patients has been improved due to concurrent chemoradiotherapy, poor curative effects and low overall survival remain key issues. The precise mechanisms and pivotal regulators of NPC remain still unclear. To improve the therapeutic efficacy, we focused on related-NPC circular RNAs (circRNAs). CircRNAs are a unique type of endogenous non-coding RNAs (ncRNAs) with a covalent closed-loop structure. Their expression is rich, stable and conservative. Different circRNA have specific tissue and developmental stages and can be detected in body fluids. In addition, circRNAs are involved in multiple pathological processes, especially in cancers. In recent years, using high-throughput indicator technology and bioinformatics technology, a large number of circRNAs have been identified in NPC cells and verified to have biological functions and mechanisms of action. This article aims to provide a retrospective review of the latest research on the proliferation and migration of related-NPC circRNA. Specifically, we focused on the roles and mechanisms of circRNAs in the development and progression of NPC.

CONCLUSION

CircRNA can act as an oncogene or tumor suppressor gene and participate in NPC progression (e.g., proliferation, apoptosis, migration, and invasion). In short, circRNAs have potential as biomarkers for the diagnosis, prognosis and treatment of NPC.

The expanding regulatory mechanisms and cellular functions of circular RNAs

Many protein-coding genes in higher eukaryotes can produce circular RNAs (circRNAs) through back-splicing of exons. CircRNAs differ from mRNAs in their production, structure and turnover and thereby have unique cellular functions and potential biomedical applications. In this Review, I discuss recent progress in our understanding of the biogenesis of circRNAs and the regulation of their abundance and of their biological functions, including in transcription and splicing, sequestering or scaffolding of macromolecules to interfere with microRNA activities or signalling pathways, and serving as templates for translation. I further discuss the emerging roles of circRNAs in regulating immune responses and cell proliferation, and the possibilities of applying circRNA technologies in biomedical research.

Structure, Regulation, and Function of Linear and Circular Long Non-Coding RNAs

Long non-coding RNAs (lncRNAs), including linear lncRNAs and circular RNAs (circRNAs), exhibit a surprising range of structures. Linear lncRNAs and circRNAs are generated by different pathways. Linear lncRNAs perform functions that depend on their specific sequences, transcription, and DNA elements of their gene loci. In some cases, linear lncRNAs contain a short open reading frame encoding a peptide. circRNAs are covalently closed RNAs with tissue-specific and cell-specific expression patterns that have recently been extensively investigated. Pioneering work focusing on their biogenesis and functional characterization indicates that circRNAs regulate cell development via multiple mechanisms and play critical roles in the immune system. Furthermore, circRNAs in exosomes function on target cells. As with linear lncRNAs, specific circRNAs can also be translated. In this review, we summarize current understanding and highlight the diverse structure, regulation, and function of linear lncRNAs and circRNAs.

Circular RNAs in Cancer: Biogenesis, Function, and Clinical Significance

Circular RNA (circRNA) is a class of single-stranded molecules with tissue/development-specific expression patterns. Unlike linear RNA, circRNA forms a covalently closed loop produced from 'back-splicing' of primary transcripts, conferring on them inherent resistance to exonucleolytic RNA decay. Increasing evidence demonstrates that many circRNAs exert important biological functions by acting as miRNA inhibitors ('sponges'), protein 'decoys', or by encoding small peptides. Importantly, circRNAs are aberrantly expressed in cancer and play indispensable oncogenic or tumor suppressive roles during tumor development and progression. In this review, we summarize the biogenesis, turnover, and involvements of circRNAs in cancer and also discuss their potential as diagnostic biomarkers or therapeutic targets.

Spatial control of AMPK signaling at subcellular compartments

AMP-activated protein kinase (AMPK) is a master regulator of energy homeostasis that functions to restore the energy balance by phosphorylating its substrates during altered metabolic conditions. AMPK activity is tightly controlled by diverse regulators including its upstream kinases LKB1 and CaMKK2. Recent studies have also identified the localization of AMPK at different intracellular compartments as another key mechanism for regulating AMPK signaling in response to specific stimuli. This review discusses the AMPK signaling associated with different subcellular compartments, including lysosomes, endoplasmic reticulum, mitochondria, Golgi apparatus, nucleus, and cell junctions. Because altered AMPK signaling is associated with various pathologic conditions including cancer, targeting AMPK signaling in different subcellular compartments may present attractive therapeutic approaches for treatment of disease.

Circular RNA CRIM1 functions as a ceRNA to promote nasopharyngeal carcinoma metastasis and docetaxel chemoresistance through upregulating FOXQ1

Background

Circular RNAs (circRNAs), a new type of noncoding RNA (ncRNA), have been identified as significant gene expression regulators and are involved in cancer progression. However, the roles of circRNAs in nasopharyngeal carcinoma (NPC) remain largely unknown.

Methods

Here, the expression profile of circRNAs in a pair of NPC cell lines with different metastatic abilities (S18 and S26 cells) was analyzed by RNA-sequencing. Quantitative reverse transcription PCR was used to detect the expression level of circCRIM1 in NPC cells and tissues. Then, function experiments in vitro and in vivo were performed to evaluate the effects of circCRIM1 on NPC metastasis and EMT. Mechanistically, RNA immunoprecipitation, luciferase reporter assay, pull-down assay with biotinylated miRNA, fluorescent in situ hybridization were performed to confirm the interaction between circCRIM1 and miR-422a in NPC. The clinical value of circCRIM1 was evaluated in NPC metastasis and chemosensitivity.

Results

We identified that circCRIM1 was upregulated in highly metastatic NPC cells. CircCRIM1 was also overexpressed in NPC tissues with distant metastasis, and its overexpression promoted NPC cell metastasis and EMT. Mechanistically, circCRIM1 competitively bound to miR-422a and prevented the suppressive effects of miR-422a on its target gene FOXQ1, which finally led to NPC metastasis, EMT and docetaxel chemoresistance. Furthermore, high circCRIM1 expression was associated with unfavorable survival in NPC patients. We established a prognostic model based on circCRIM1 expression and N stage that effectively predicted the risk of distant metastasis and treatment response to docetaxel-containing induction chemotherapy in NPC patients.

Conclusions

Our findings reveal the critical role of circCRIM1 specifically in promoting NPC metastasis and chemoresistance via a ceRNA mechanism and provide an exploitable biomarker and therapeutic target for prognosis and treatment resistance in NPC patients.

Circular RNAs: The crucial regulatory molecules in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Recent studies have shown that circular RNAs (circRNAs) play critical roles in the pathogenesis and progression of CRC. CircRNAs are a special class of endogenous non-coding RNAs (ncRNAs) that harbor covalently closed ring structure with high conservation and stability, which are expressed in a tissue- and developmental-stage-specific manner. A growing body of evidence suggests that circRNAs are abnormally expressed in CRC tissues, cell lines and plasma, and are closely linked with CRC clinical malignant features. CircRNAs participate in various biological processes of CRC cells, including cell proliferation, apoptosis, senescence, migration and invasion and so on, through acting as "microRNA (miRNA) sponges", binding to protein and even translating protein. In the present review, we systematically introduce the CRC-related circRNAs and their functional mechanisms, as well as the potential applications for CRC diagnosis and prognosis.

Do lncRNAs and circRNAs expression profiles influence discoid lupus erythematosus progression?-a comprehensive analysis

Background

Long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs)are involved in the progression of discoid lupus erythematosus (DLE), but an understanding of their underlying mechanisms remains elusive. To explore the expression profiles of lncRNAs and circRNAs in DLE, we surveyed the lncRNA/circRNA and mRNA expression profiles in the epithelia of oral DLE and adjacent normal tissues.

Methods

The lesional and non-lesional lower lips of three DLE patients were analysed by RNA-sequencing (RNA-seq). The principal functions of the significantly deregulated genes were identified using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. And the correlated expression networks (coding-noncoding co-expression and lncRNAs-transcription factor-mRNA) were evaluated as well.

Results

Hundreds of significantly changed lncRNAs and mRNAs and dozens of significantly changed circRNAs were identified. lncRNA lnc-MIPOL1-6 and IncRNA IncDDX47-3 expressions were correlated with immune response-related genes, including IL19, CXCL1, CXCL11, and TNFSF15. Up-regulated IncRNA-TF network consists of 8 TFs and 74 related lncRNAs. The lncRNA-TF-gene trans-regulation consisting of 204 lncRNAs,39 TFs, and correlated 3 genes.

Conclusions

These results demonstrate that lncRNAs and circRNAs can influence the progression of DLE. Certain mRNAs/lncRNAs/circRNAs may have substantial value in DLE diagnosis and therapy.

Therapeutic targeting of circ-CUX1/EWSR1/MAZ axis inhibits glycolysis and neuroblastoma progression

Aerobic glycolysis is a hallmark of metabolic reprogramming in tumor progression. However, the mechanisms regulating glycolytic gene expression remain elusive in neuroblastoma (NB), the most common extracranial malignancy in childhood. Herein, we identify that CUT‐like homeobox 1 (CUX1) and CUX1‐generated circular RNA (circ‐CUX1) contribute to aerobic glycolysis and NB progression. Mechanistically, p110 CUX1, a transcription factor generated by proteolytic processing of p200 CUX1, promotes the expression of enolase 1, glucose‐6‐phosphate isomerase, and phosphoglycerate kinase 1, while circ‐CUX1 binds to EWS RNA‐binding protein 1 (EWSR1) to facilitate its interaction with MYC‐associated zinc finger protein (MAZ), resulting in transactivation of MAZ and transcriptional alteration of CUX1 and other genes associated with tumor progression. Administration of an inhibitory peptide blocking circ‐CUX1‐EWSR1 interaction or lentivirus mediating circ‐CUX1 knockdown suppresses aerobic glycolysis, growth, and aggressiveness of NB cells. In clinical NB cases, CUX1 is an independent prognostic factor for unfavorable outcome, and patients with high circ‐CUX1 expression have lower survival probability. These results indicate circ‐CUX1/EWSR1/MAZ axis as a therapeutic target for aerobic glycolysis and NB progression.

Splicing factor derived circular RNA circUHRF1 accelerates oral squamous cell carcinoma tumorigenesis via feedback loop

Emerging evidences have suggested the vital roles of circular RNA (circRNA) in the human cancers. However, the underlying biological functions and biogenesis of circRNA in the oral squamous cell carcinoma (OSCC) is still ambiguous. Here, we investigate the oncogenic roles and biogenesis of the novel identified circRNA, circUHRF1 (hsa_circ_0002185), in the OSCC tumorigenesis. Results showed that circUHRF1 was markedly upregulated in the OSCC cells and tissue, besides, the overexpression was closely correlated with the poor prognosis of OSCC patients. Functionally, circUHRF1 promoted the proliferation, migration, invasion, and epithelial mesenchymal transformation (EMT) in vitro and the tumor growth in vivo. Mechanically, circUHRF1 acted as the sponge of miR-526b-5p, thereby positively regulating c-Myc. Transcription factor c-Myc could accelerate the transcription of TGF-β1 and ESRP1. Moreover, splicing factor ESRP1 promoted the circularization and biogenesis of circUHRF1 by targeting the flanking introns, forming the circUHRF1/miR-526b-5p/c-Myc/TGF-β1/ESRP1 feedback loop. In conclusion, our research identified the oncogenic roles of circUHRF1 in the OSCC tumorigenesis and EMT via circUHRF1/miR-526b-5p/c-Myc/TGF-β1/ESRP1 feedback loop, shedding light on the pathogenic mechanism of circUHRF1 for OSCC and providing the potential therapeutic target.

Circular RNAs: Biogenesis, Mechanism, and Function in Human Cancers

CircRNAs are a class of noncoding RNA species with a circular configuration that is formed by either typical spliceosome-mediated or lariat-type splicing. The expression of circRNAs is usually abnormal in many cancers. Several circRNAs have been demonstrated to play important roles in carcinogenesis. In this review, we will first provide an introduction of circRNAs biogenesis, especially the regulation of circRNA by RNA-binding proteins, then we will focus on the recent findings of circRNA molecular mechanisms and functions in cancer development. Finally, some open questions are also discussed.