circFAM120B functions as a tumor suppressor in esophageal squamous cell carcinoma via the miR-661/PPM1L axis and the PKR/p38 MAPK/EMT pathway

Non‑coding RNA: A promising diagnostic biomarker and therapeutic target for esophageal squamous cell carcinoma (Review)

Esophageal cancer (EC) is a common form of malignant tumor in the digestive system that is classified into two types: Esophageal squamous cell carcinomas (ESCC) and esophageal adenocarcinoma. ESCC is known for its early onset of symptoms, which can be difficult to identify, as well as its rapid progression and tendency to develop drug resistance to chemotherapy and radiotherapy. These factors contribute to the high incidence of disease and low cure rate. Therefore, a diagnostic biomarker and therapeutic target need to be identified for ESCC. Non-coding RNAs (ncRNAs) are a class of molecules that are transcribed from DNA but do not encode proteins. Initially, ncRNAs were considered to be non-functional segments generated during transcription. However, with advancements in high-throughput sequencing technologies in recent years, ncRNAs have been associated with poor prognosis, drug resistance and progression of ESCC. The present study provides a comprehensive overview of the biogenesis, characteristics and functions of ncRNAs, particularly focusing on microRNA, long ncRNAs and circular RNAs. Furthermore, the ncRNAs that could potentially be used as diagnostic biomarkers and therapeutic targets for ESCC are summarized to highlight their application value and prospects in ESCC.

Biological functions of circRNA in regulating the hallmarks of gastrointestinal cancer (Review)

Circular RNA (circRNA) was first observed in the cytoplasm of eukaryotic cells in 1979, but it was not characterized in detail until 2012, when high‑throughput sequencing technology was more advanced and available. Consequently, the mechanism of circRNA formation and its biological function have been progressively elucidated by researchers. circRNA is abundant in eukaryotic cells and exhibits a certain degree of organization, timing and disease‑specificity. Additionally, it is poorly degradable, meeting the characteristics of an ideal clinical biomarker. In the present review, the recent research progress of circRNAs in digestive tract malignant tumors was primarily discussed. This included the roles, biological functions and clinical significance of circRNA, providing references for its research value and clinical potential in gastrointestinal cancer.

Circular RNAs as biomarkers and therapeutic targets for gastrointestinal cancers

Circular RNAs are a class of noncoding RNAs with covalently linked 5' and 3' ends that arise from backsplicing events. The absence of a 5' cap and a 3' poly(A) tail makes circular RNAs relatively more stable than their linear counterparts. They are evolutionary conserved and tissue-specific, and some show disease-specific expression patterns. Although their biological functions remain largely unknown, circular RNAs have been shown to play regulatory roles by acting as microRNA sponges, regulators of RNA-binding proteins, alternative splicing, and parental gene expression, and they could even encode proteins. Over the past few decades, circular RNAs have attracted wide attention in oncology owing to their implications in various tumors. Many circular RNAs have been characterized as key players in gastrointestinal cancers and influence cancer growth, progression, metastasis, and therapeutic resistance. Accumulating evidence reveals that their unique characteristics, coupled with their critical roles in tumorigenesis, make circular RNAs promising non-invasive clinical biomarkers for gastrointestinal cancers. In the present review, we summarized the biological roles of the emerging circular RNAs and their potential as biomarkers and therapeutic targets, which may help better understand their clinical significance in the management of gastrointestinal cancers.

Suppressing MTERF3 inhibits proliferation of human hepatocellular carcinoma via ROS-mediated p38 MAPK activation

Mitochondrial transcription termination factor 3 (MTERF3) negatively regulates mitochondrial DNA transcription. However, its role in hepatocellular carcinoma (HCC) progression remains elusive. Here, we investigate the expression and function of MTERF3 in HCC. MTERF3 is overexpressed in HCC tumor tissues and higher expression of MTERF3 positively correlates with poor overall survival of HCC patients. Knockdown of MTERF3 induces mitochondrial dysfunction, S-G2/M cell cycle arrest and apoptosis, resulting in cell proliferation inhibition. In contrast, overexpression of MTERF3 promotes cell cycle progression and cell proliferation. Mechanistically, mitochondrial dysfunction induced by MTERF3 knockdown promotes ROS accumulation, activating p38 MAPK signaling pathway to suppress HCC cell proliferation. In conclusion, ROS accumulation induced by MTERF3 knockdown inhibits HCC cell proliferation via p38 MAPK signaling pathway suggesting a promising target in HCC patients.

Non-coding RNAs' function in cancer development, diagnosis and therapy

While previous research on cancer biology has focused on genes that code for proteins, in recent years it has been discovered that non-coding RNAs (ncRNAs)play key regulatory roles in cell biological functions. NcRNAs account for more than 95% of human transcripts and are an important entry point for the study of the mechanism of cancer development. An increasing number of studies have demonstrated that ncRNAs can act as tumor suppressor genes or oncogenes to regulate tumor development at the epigenetic level, transcriptional level, as well as post-transcriptional level. Because of the importance of ncRNAs in cancer, most clinical trials have focused on ncRNAs to explore whether ncRNAs can be used as new biomarkers or therapies. In this review, we focus on recent studies of ncRNAs including microRNAs (miRNAs), long ncRNAs (lncRNAs), circle RNAs (circRNAs), PIWI interacting RNAs (piRNAs), and tRNA in different types of cancer and explore the application of these ncRNAs in the development of cancer and the identification of relevant therapeutic targets and tumor biomarkers. Graphical abstract drawn by Fidraw.

Eukaryotic translation initiation factor 2α kinase 2 in pancreatic cancer: An approach towards managing clinical prognosis and molecular immunological characterization

Most patients with pancreatic cancer are already in the late stages of the disease when they are diagnosed, and pancreatic cancer is a deadly disease with a poor prognosis. With the advancement of research, immunotherapy has become a new focus in the treatment of tumors. To the best of our knowledge, there is currently no reliable diagnostic or prognostic marker for pancreatic cancer; therefore, the present study investigated the potential of eukaryotic translation initiation factor 2α kinase 2 (EIF2AK2) as a predictive and diagnostic marker for pancreatic cancer. Immunohistochemical staining of clinical samples independently verified that EIF2AK2 expression was significantly higher in clinically operated pancreatic cancer tissues than in adjacent pancreatic tissues., and EIF2AK2 expression and differentially expressed genes (DEGs) were identified using downloadable RNA sequencing data from The Cancer Genome Atlas and Genomic Tumor Expression Atlas. In addition, Gene Ontology/Kyoto Encyclopedia of Genes and Genomes analyses and immune cell infiltration were used for functional enrichment analysis of EIF2AK2-associated DEGs. The clinical importance of EIF2AK2 was also determined using Kaplan-Meier survival, Cox regression and time-dependent survival receiver operating characteristic curve analyses, and a predictive nomogram model was generated. Finally, the functional role of EIF2AK2 was assessed in PANC-1 cells using a short hairpin RNA-EIF2AK2 knockdown approach, including CCK-8, wound healing assay, cell cycle and apoptosis assays. The findings suggested that EIF2AK2 may have potential as a diagnostic and prognostic biomarker for patients with pancreatic cancer. Furthermore, EIF2AK2 may provide a new therapeutic target for patients with pancreatic cancer.

Hsa_circ_0043603 promotes the progression of esophageal squamous cell carcinoma by sponging miR-1178-3p and regulating AADAC expression

This study aims to investigate the regulatory impact of hsa_circ_0043,603, a circular RNA, on the progression of esophageal squamous cell carcinoma (ESCC), which ranks as the sixth leading cause of global mortality. We evaluated the expression, origin, and localization of hsa_circ_0043,603 in ESCC tumors using qRT-PCR, bioinformatics, and FISH analysis. Functional studies were conducted by manipulating the hsa_circ_0043,603 expression in Eca109 cells through overexpression and silencing plasmids. Additionally, xenografts derived from circ_0043,603-overexpressing Eca109 cells enabled us to investigate tumor growth, proliferation, and apoptosis. Through Starbase analysis, we identified miR-1178-3p as a target of circ_0043,603, which was validated using RIP and luciferase assays. Furthermore, we predicted arylacetamide deacetylase (AADAC) as a target of miR-1178-3p and examined its expression in ESCC tissues using Western blot. Lastly, we performed AADAC silencing and overexpression in Eca109 cells to study their impact on cellular phenotypic features, apoptosis, and their interaction with miR-1178-3p mimics and inhibitors. The low expression of hsa_circ_0043,603 in ESCC tissue was associated with poor prognosis. Overexpression of hsa_circ_0043,603 inhibited ESCC growth, invasion, migration, and proliferation, while promoting apoptosis in vitro and suppressing tumor growth in vivo. hsa_circ_0043,603 achieved these effects by targeting the oncogenic miR-1178-3p. Furthermore, AADAC was identified as a target of miR-1178-3p, and its reduced expression was confirmed in ESCC tissues. Overexpression of AADAC in Eca109 cells resulted in suppressed cell growth, proliferation, migration, and invasion by regulating miR-1178-3p. hsa_circ_0043,603 acts as a sponge for miR-1178-3p, leading to the regulation of AADAC expression and inhibition of ESCC development. These results suggest the potential of hsa_circ_0043,603 as a therapeutic and diagnostic target for ESCC.

Circular RNA circ-FIRRE interacts with HNRNPC to promote esophageal squamous cell carcinoma progression by stabilizing GLI2 mRNA

Increasing evidence has shown that circular RNAs (circRNAs) interact with RNA-binding proteins (RBPs) and promote cancer progression. However, the function and mechanism of the circRNA/RBP complex in esophageal squamous cell carcinoma (ESCC) are still largely unknown. Herein, we first characterized a novel oncogenic circRNA, circ-FIRRE, by RNA sequencing (Ribo-free) profiling of ESCC samples. Furthermore, we observed marked circ-FIRRE overexpression in ESCC patients with high TNM stage and poor overall survival. Mechanistic studies indicated that circ-FIRRE, as a platform, interacts with the heterogeneous nuclear ribonucleoprotein C (HNRNPC) protein to stabilize GLI2 mRNA by directly binding to its 3'-UTR in the cytoplasm, thereby resulting in elevated GLI2 protein expression and subsequent transcription of its target genes MYC, CCNE1, and CCNE2, ultimately contributing to ESCC progression. Moreover, HNRNPC overexpression in circ-FIRRE knockdown cells notably abolished circ-FIRRE knockdown-mediated Hedgehog pathway inhibition and ESCC progression impairment in vitro and in vivo. Clinical specimen results showed that circ-FIRRE and HNRNPC expression was positively correlated with GLI2 expression, which reveals the clear significance of the circ-FIRRE/HNRNPC-GLI2 axis in ESCC. In summary, our results indicate that circ-FIRRE could serve as a valuable biomarker and potential therapeutic target for ESCC and highlight a novel mechanism of the circ-FIRRE/HNRNPC complex in ESCC progression regulation.

Roles of circRNA dysregulation in esophageal squamous cell carcinoma tumor microenvironment

Esophageal squamous cell carcinoma (ESCC) is the most prevalent histological esophageal cancer characterized by advanced diagnosis, metastasis, resistance to treatment, and frequent recurrence. In recent years, numerous human disorders such as ESCC, have been linked to abnormal expression of circular RNAs (circRNAs), suggesting that they are fundamental to the intricate system of gene regulation that governs ESCC formation. The tumor microenvironment (TME), referring to the area surrounding the tumor cells, is composed of multiple components, including stromal cells, immune cells, the vascular system, extracellular matrix (ECM), and numerous signaling molecules. In this review, we briefly described the biological purposes and mechanisms of aberrant circRNA expression in the TME of ESCC, including the immune microenvironment, angiogenesis, epithelial-to-mesenchymal transition, hypoxia, metabolism, and radiotherapy resistance. As in-depth research into the processes of circRNAs in the TME of ESCC continues, circRNAs are promising therapeutic targets or delivery systems for cancer therapy and diagnostic and prognostic indicators for ESCC.

Circular RNAs as the pivotal regulators of epithelial-mesenchymal transition in gastrointestinal tumor cells

Gastrointestinal (GI) cancers, as the most common human malignancies are always considered one of the most important health challenges in the world. Late diagnosis in advanced tumor stages is one of the main reasons for the high mortality rate and treatment failure in these patients. Therefore, investigating the molecular pathways involved in GI tumor progression is required to introduce the efficient markers for the early tumor diagnosis. Epithelial-mesenchymal transition (EMT) is one of the main cellular mechanisms involved in the GI tumor metastasis. Non-coding RNAs (ncRNAs) are one of the main regulatory factors in EMT process. Circular RNAs (circRNAs) are a group of covalently closed loop ncRNAs that have higher stability in body fluids compared with other ncRNAs. Considering the importance of circRNAs in regulation of EMT process, in the present review we discussed the role of circRNAs in EMT process during GI tumor invasion. It has been reported that circRNAs mainly affect the EMT process through the regulation of EMT-specific transcription factors and signaling pathways such as WNT, PI3K/AKT, TGF-β, and MAPK. This review can be an effective step in introducing a circRNA/EMT based diagnostic panel marker for the early tumor detection among GI cancer patients.

Advances in peptides encoded by non-coding RNAs: A cargo in exosome

The metastasis of malignant tumors determines patient prognosis. This is the main reason for the poor prognosis of patients with cancer and the most challenging aspect of treating malignant tumors. Therefore, it is important to identify early tumor markers and molecules that can predict patient prognosis. However, there are currently no molecular markers with good clinical accuracy and specificity. Many non-coding RNA (ncRNAs)have been identified, which can regulate the process of tumor development at multiple levels. Interestingly, some ncRNAs are translated to produce functional peptides. Exosomes act as signal carriers, are encapsulated in nucleic acids and proteins, and play a messenger role in cell-to-cell communication. Recent studies have identified exosome peptides with potential diagnostic roles. This review aims to provide a theoretical basis for ncRNA-encoded peptides or proteins transported by exosomes and ultimately to provide ideas for further development of new diagnostic and prognostic cancer markers.

circCYP24A1 facilitates esophageal squamous cell carcinoma progression through binding PKM2 to regulate NF-κB-induced CCL5 secretion

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a common gastrointestinal malignant tumor, while the molecular mechanisms have not been fully elucidated. Multiple circular RNAs have been reported to involve in the onset and progression of malignant tumors through various molecular mechanisms. However, the clinical significance and functional mechanism of most circRNAs involved in the progression of ESCC remains obscure.

METHODS

RNA-Seq was used to explore potential circRNAs in participated in 5 pairs of ESCC and their corresponding normal esophageal tissues. The up-regulated circCYP24A1 was selected. Fluorescence in situ hybridization was cunducted to verificated the expression and intracellular localization of circCYP24A1 by using the tissue microarray. The Kaplan-Meier method and Cox proportional hazards model was used to examine the potential prognostic value of circCYP24A1 on overall survival of ESCC patients. The biological function were confirmed by gain- and loss-of-function approaches in vivo. mRNA expression profile microarray was proformed to investigate the downstream signaling pathways involved in circCYP24A1. RNA pull-down assay and mass spectrometry were performed to identify the proteins associated with circCYP24A1. Rescue experiments were carried out to identified hypothetical regulatory role of circCYP24A1 on ESCC progression in vivo and in virto.

RESULTS

In this study, we identified circCYP24A1 in ESCC tissues by RNA sequencing, which is up-regulated in 114 cases of ESCC tissues and acts as a novel prognosis-related factor. Moreover, circCYP24A1 promoted the ability of proliferation, migration, invasion and clone formation in vitro, as well as tumor growth in vivo. Mechanistically, chemokine (C-Cmotif) ligand 5 (CCL5) is functional downstream mediator for circCYP24A1, which is screened by mRNA microarray. Moreover, circCYP24A1 physically interacts with M2 isoform of pyruvate kinase (PKM2). Rescue experiments showed that PKM2 knockdown partly reverses the promotional effects of circCYP24A1. It was revealed that circCYP24A1 increases secretion of CCL5 through the mechanism mainly by interacting with PKM2, an activator of NF-κB pathway, and thereby accelerate malignant progression of ESCC.

CONCLUSIONS

Up-regulated circCYP24A1 could activate NF-κB pathway by binding PKM2, which promotes the secretion of CCL5 and accelerate malignant progression of ESCC. Our fndings recommended a novel function for circCYP24A1 as a potential effective biomarker for judging prognosis and a therapeutic target in ESCC.

Circ_0007624 suppresses the development of esophageal squamous cell carcinoma via targeting miR-224-5p/CPEB3 to inactivate the EGFR/PI3K/AKT signaling

Circular RNAs (circRNAs) have been confirmed to be involved in the regulation of esophageal squamous cell carcinoma (ESCC) progression. According to GEO datasets (GSE112496 and GSE150476), we identified that circ_0007624 was abnormally down-regulated in ESCC. However, there is still no reports regarding the function and mechanism of circ_0007624 in ESCC development. Here, we found that circ_0007624 was significantly underexpressed in ESCC tissues, and low expression of circ_0007624 was indicative of a poor prognosis. Overexpressing circ_0007624 or silencing miR-224-5p suppressed cell proliferation, metastasis, epithelial-mesenchymal transition (EMT), and promoted apoptosis in vitro. Also, circ_0007624 up-regulation slowed ESCC tumor growth in vivo. Mechanistically, circ_0007624 could serve as a competing endogenous RNA (ceRNA) by sponging miR-224-5p to antagonize its inhibitory effect on the target cytoplasmic polyadenylation element binding protein 3 (CPEB3). Rescue experiments showed that the anti-cancer properity role of circ_0007624 in ESCC is partly reversed by the restoration of miR-224-5p or down-regulation of CPEB3. Furthermore, EGFR/PI3K/AKT pathway was involved in the regulation of circ_0007624/miR-224-5p/CPEB3 axis in ESCC. Together, our findings demonstrate for the first time that circ_0007624/miR-224-5p/CPEB3 suppresses ESCC progression by inactivating EGFR/PI3K/AKT signaling, providing a basis for developing circ_0007624-targeted therapies for ESCC patients.

circRNA: A New Biomarker and Therapeutic Target for Esophageal Cancer

Circular RNAs (circRNAs) comprise a large class of endogenous non-coding RNA with covalently closed loops and have independent functions as linear transcripts transcribed from identical genes. circRNAs are generated by a “back-splicing” process regulated by regulatory elements in cis and associating proteins in trans. Many studies have shown that circRNAs play important roles in multiple processes, including splicing, transcription, chromatin modification, miRNA sponges, and protein decoys. circRNAs are highly stable because of their closed ring structure, which prevents them from degradation by exonucleases, and are more abundant in terminally differentiated cells, such as brains. Recently, it was demonstrated that numerous circRNAs are differentially expressed in cancer cells, and their dysfunction is involved in tumorigenesis and metastasis. However, the crucial functions of these circRNAs and the dysregulation of circRNAs in cancer are still unknown. In this review, we summarize the recent reports on the biogenesis and biology of circRNAs and then catalog the advances in using circRNAs as biomarkers and therapeutic targets for cancer therapy, particularly esophageal cancer.

Critical Roles of Circular RNA in Tumor Metastasis via Acting as a Sponge of miRNA/isomiR

Circular RNAs (circRNAs), a class of new endogenous non-coding RNAs (ncRNAs), are closely related to the carcinogenic process and play a critical role in tumor metastasis. CircRNAs can lay the foundation for tumor metastasis via promoting tumor angiogenesis, make tumor cells gain the ability of migration and invasion by regulating epithelial-mesenchymal transition (EMT), interact with immune cells, cytokines, chemokines, and other non-cellular components in the tumor microenvironment, damage the normal immune function or escape the immunosuppressive network, and further promote cell survival and metastasis. Herein, based on the characteristics and biological functions of circRNA, we elaborated on the effect of circRNA via circRNA-associated competing endogenous RNA (ceRNA) network by acting as miRNA/isomiR sponges on tumor angiogenesis, cancer cell migration and invasion, and interaction with the tumor microenvironment (TME), then explored the potential interactions across different RNAs, and finally discussed the potential clinical value and application as a promising biomarker. These results provide a theoretical basis for the further application of metastasis-related circRNAs in cancer treatment. In summary, we briefly summarize the diverse roles of a circRNA-associated ceRNA network in cancer metastasis and the potential clinical application, especially the interaction of circRNA and miRNA/isomiR, which may complicate the RNA regulatory network and which will contribute to a novel insight into circRNA in the future.

The roles of circRNA-miRNA-mRNA networks in the development and treatment of osteoporosis

Osteoporosis is a systemic metabolic disease, mainly characterized by reduced bone mineral density and destruction of bone tissue microstructure. However, the molecular mechanisms of osteoporosis need further investigation and exploration. Increasing studies have reported that circular RNAs (circRNAs), a novel type of RNA molecule, play crucial roles in various physiological and pathological processes and bone-related diseases. Based on an in-depth understanding of their roles in bone development, we summarized the multiple regulatory roles and underlying mechanisms of circRNA-miRNA-mRNA networks in the treatment of osteoporosis, associated with bone marrow mesenchymal stem cells (BMSCs), osteoblasts, and osteoclasts. Deeper insights into the vital roles of circRNA-miRNA-mRNA networks can provide new directions and insights for developing novel diagnostic biomarkers and therapeutic targets in the treatment of osteoporosis.