CircRNA_001569 promotes cell proliferation through absorbing miR-145 in gastric cancer

Emerging roles of miR-145 in gastrointestinal cancers: A new paradigm

Gastrointestinal (GI) carcinomas are a group of cancers affecting the GI tract and digestive organs, such as the gastric, liver, bile ducts, pancreas, small intestine, esophagus, colon, and rectum. MicroRNAs (miRNAs) are small functional non-coding RNAs (ncRNAs) which are involved in regulating the expression of multiple target genes; mainly at the post-transcriptional level, via complementary binding to their 3'-untranslated region (3'-UTR). Increasing evidence has shown that miRNAs have critical roles in modulating of various physiological and pathological cellular processes and regulating the occurrence and development of human malignancies. Among them, miR-145 is recognized for its anti-oncogenic properties in various cancers, including GI cancers. MiR-145 has been implicated in diverse biological processes of cancers through the regulation of target genes or signaling, including, proliferation, differentiation, tumorigenesis, angiogenesis, apoptosis, metastasis, and therapy resistance. In this review, we have summarized the role of miR-145 in selected GI cancers and also its downstream molecules and cellular processes targets, which could lead to a better understanding of the miR-145 in these cancers. In conclusion, we reveal the potential diagnostic, prognostic, and therapeutic value of miR-145 in GI cancer, and hope to provide new ideas for its application as a biomarker as well as a therapeutic target for the treatment of these cancer.

Circular RNAs: novel actors of Wnt signaling pathway in lung cancer progression

Circular RNAs (CircRNAs) are a class of regulatory RNA transcripts, which are ubiquitously expressed in eukaryotes. CircRNA dysregulation has been shown to disrupt the interaction of the Wnt/β-catenin pathway, which regulates several biological processes involved in tumorigenesis, thereby contributing to the development and progression of cancer. Interactions of tumor-derived circRNAs with the Wnt/β-catenin signaling pathway provide both clinical diagnostic biomarkers and promising therapeutic targets. In this review, we outlined current evidence on the roles of circRNAs associated with the Wnt/β-catenin pathway in regulating lung cancer formation and development. We believe that our findings will assist in the advancement or establishment of circRNA-based lung cancer therapeutic approaches.

Circular RNA circPGD contributes to gastric cancer progression via the sponging miR-16-5p/ABL2 axis and encodes a novel PGD-219aa protein

CircRNAs have critical effects on tumor development and progression. However, circPGD effect on gastric cancer (GC) is still elusive. Nuclear and cytoplasmic RNA fractionation, and RNA-FISH assay examined the localization of circPGD in MGC-803 cells. qRT-PCR was conducted to detect the expression and prognostic significance of circPGD, miR-16-5p, and ABL2 within GC tissues. Meanwhile, qRT-PCR, luciferase reporter assays, rescue, and western blotting assays confirmed the interactions between circPGD, miR-16-5p, and ABL2. Transwell, wound healing, and colony-formation assays, as well as CCK-8 and cell apoptosis assays, analyzed the functions of circPGD, miR-16-5p, ABL2, as well as PGD-219aa within GC cells. Western blotting and cell immunofluorescence experiments detected the differences in the expression of the related proteins. Finally, xenograft and metastatic mouse models were used to investigate circPGD function in vivo. Mass spectrometry was used to detect the existence of PGD-219aa in MGC-803 cells. CircPGD was localized in the cytoplasm and nucleus of MGC-803 cells. Compared with the control, circPGD and ABL2 expression increased within GC tissues and cells, and the miR-16-5p level was decreased. Functionally, circPGD promoted cell proliferation, migration and suppressed apoptosis in vitro. Mechanistically, circPGD sponged miR-16-5p for relieving miR-16-5p suppression on the corresponding target ABL2 via the SMAD2/3 and YAP signaling pathways. In addition, circPGD encodes a novel PGD-219aa protein that can enhance the growth and migration of GC cells, while inhibiting GC cells apoptosis via the SMAD2/3 and YAP signaling pathways. Furthermore, circPGD overexpression enhanced tumor aggressiveness, while circPGD knockdown inhibited tumor growth. Overall, circPGD has a novel oncogenic effect on GC cells, indicating the potential of circPGD as the tumorigenic factor and a promising diagnostic marker for GC.

CircRNA-ABCB10 promotes gastric cancer progression by sponging miR-1915-3p to upregulate RaC1

BACKGROUND

Gastric cancer (GC) is a common malignant tumor of the digestive system. Increasing reports have demonstrated the crucial roles of circRNAs in tumorigenesis and progression of GC.

METHODS

The relative expression of circ-ABCB10 in GC tissues and cell lines was detected by qRT-PCR. A series of in vitro assays and a xenograft model in vivo were applied to explore the function of circ-ABCB10 in GC cells.

RESULTS

Circ-ABCB10 expression was upregulated in GC tissues and cell lines and positively correlated with poor survival of GC patients. Circ-ABCB10 downregulation decreased cell viability, inhibited cell growth, invasion, and migration, while promoted cell apoptosis of GC cell lines SGC-7901 and MKN-48. Circ-ABCB10 could upregulate Rac1 expression by directly sponging miR-1915-3p. Rescue experiments revealed that miR-1915-3p inhibitor obviously reversed the inhibitory effect of si-circ-ABCB10, and Rac1 overexpression obviously reversed the inhibitory effect of miR-1915-3p mimics on cell growth, invasion, migration, apoptosis, and cell cycle progression. Moreover, si-circ-ABCB10 effectively inhibited tumor growth in a xenograft model.

CONCLUSIONS

Our study revealed that circ-ABCB10 promoted GC progression via targeting the miR-1915-3p/Rac1 axis, and circ-ABCB10 might be a potential target for GC diagnosis and treatment.

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.

Astragaloside IV exhibits anti-tumor function in gastric cancer via targeting circRNA dihydrolipoamide S-succinyltransferase (circDLST)/miR-489-3p/ eukaryotic translation initiation factor 4A1(EIF4A1) pathway

Astragaloside IV (AS-IV) is an inartificial saponin separated from astragalus membranaceus, which has exhibited key anti-tumor regulation in some cancers. Circular RNAs (circRNAs) are important regulators in malignant development of gastric cancer (GC). Herein, we focused on the molecular mechanism of AS-IV with circRNA dihydrolipoamide S-succinyltransferase (circDLST) in GC. CircDLST, microRNA-489-3p (miR-489-3p), and eukaryotic translation initiation factor 4A1 (EIF4A1) levels were detected by quantitative real-time polymerase-chain reaction and western blot. Cell functions were assessed by cell counting kit-8 assay, ethynyl-2’-deoxyuridine assay, colony formation assay, and transwell assay. The interaction between miR-489-3p and circDLST or EIF4A1 was analyzed by dual-luciferase reporter assay. Xenograft tumor assay was adopted to check the role of circDLST and AS-IV in vivo. CircDLST and EIF4A1 were upregulated but miR-489-3p was downregulated in GC cells. AS-IV restrained cell proliferation and metastasis in GC cells by downregulating circDLST. CircDLST served as a miR-489-3p sponge, and miR-489-3p inhibition reversed anti-tumor function of AS-IV. EIF4A1 was a target for miR-489-3p and circDLST sponged miR-489-3p to regulate EIF4A1. AS-IV suppressed GC cell progression via circDLST-mediated downregulation of EIF4A1. Also, AS-IV recued tumor growth in vivo via targeting circDLST to regulate miR-489-3p/EIF4A1 axis. AS-IV inhibited the development of GC through circDLST/miR-489-3p/EIF4A1 axis.

CircINTS4 Facilitates Chemoresistance of TNBC by Competitively Binding miR-129-5p/POM121 Axis

Objectives. To detect the expression of circular RNA (circRNA) circINTS4 in triple-negative breast cancer (TNBC) and to analyze the relationship between the expression of circRNA circINTS4 and the clinicopathological characteristics and chemotherapy resistance of patients with TNBC. Methods. Bioinformatics was used to predict that circINTS4 and POM121 could bind to miR-129-5p, and dual luciferase reporter genes proved that circINTS4 could bind to miR-129-5p and miR-129-5p could bind to POM121. RNA immunoprecipitation (RIP) and RNA pull-down experiments confirmed that circINTS4 binds to miR-129-5p. The correlation among circINTS4, miR-129-5p, and POM121 was detected by qRT-PCR. Results. In ADR-resistant TNB cells, circINTS4 was significantly up-regulated, miR-129-5p was down-regulated, and POM121 protein expression was significantly up-regulated. Experimental results showed that circINTS4 knockdown inhibited proliferation, migration, invasion, and autophagy. Knocking down miR-129-5p or overexpression of POM121 reversed the inhibitory effect of sh-circints4 on the development of ADR-resistant TNBC cells. In addition, CIRCINTS4 regulates POM121 expression by sponge-adsorbed miR-129-5p. CIRCINTS4 knockdown prevents ADR-resistant tumor growth by regulating the miR-129-5p/POM121 axis in vivo. Conclusions. CircRNA circINTS4 may act as the ceRNA of miR-129-5p to regulate the expression of target gene POM121, thereby promoting the progress of TNBC molecular mechanism and providing scientific basis for circINTS4 as a new molecular target for clinical diagnosis and drug resistance therapy of TNBC.

Hsa_circ_0008434 regulates USP9X expression by sponging miR-6838-5p to promote gastric cancer growth, migration and invasion

BACKGROUND

The role of circular RNAs (circRNAs) in the occurrence and development of gastric cancer (GC) has recently attracted increasing interest. The following study investigates the role of a newly discovered hsa_circ_0008434, which has been confirmed to be highly expressed in GC tissues, in regulating GC biological behaviour.

METHODS

High-throughput RNA sequencing was used to identify differentially expressed genes between normal gastric tissues and GC tissues; actinomycin D and RNase R assays were used to determine the stability and loop structure of hsa_circ_0008434; and the miRanda database was used to predict the target genes of hsa_circ_0008434. The role of hsa_circ_0008434 in cell proliferation, migration, and invasion was examined using CCK-8, wound healing, Transwell and colony formation assays. The regulatory relationships among hsa_circ_0008434, microRNA-6838 (miR-6838), and ubiquitin-specific peptidase 9X (USP9X) were determined by dual-luciferase activity assays. The expression of hsa_circ_0008434 and miR-6838 was measured by qPCR; the expression of USP9X was detected by immunohistochemistry and Western blotting. The effects of hsa_circ_0008434 on in vivo tumour growth were assessed in xenograft models.

RESULTS

We found that hsa_circ_0008434 was one of the most upregulated circRNAs in GC tissue versus normal tissue. Further in vitro testing indicated that by acting as a miRNA sponge for miR-6838-5p, hsa_circ_0008434 promotes the expression of USP9X and further increases the proliferation, migration, and invasion of GC cells. In addition, animal studies indicated that hsa_circ_0008434 could promote tumour growth in vivo.

CONCLUSIONS

Hsa_circ_0008434 may promote GC proliferation, invasion and migration by regulating the expression of miR-6838 and USP9X.

One stomach, two subtypes of carcinoma-the differences between distal and proximal gastric cancer

Gastric cancer (GC) is one of the most common malignant tumors of the digestive tract, posing a significant risk to human health. Over the past 10 years, the pathological characteristics and the prognosis of GC have been determined based on the locations of the tumors that were then classified into two types-proximal and distal GC. This review focuses on the differences in epidemiology, etiology, cell source, pathological characteristics, gene expression, molecular markers, manifestations, treatment, prognosis, and prevention between proximal and distal GC to provide guidance and a basis for clinical diagnosis and treatment.

Contribution of circRNAs in gastric cancer

Gastric cancer (GC) is one of the most commonly diagnosed neoplasms in the world. A number of environmental and lifestyle factors, particularly chronic infection with Helicobacter pylori, have been found to partake in the pathogenesis of GC. The advent of high-throughput genome and transcriptome analysis has enhanced the knowledge about molecular mechanisms of the pathogenesis of GC. However, data regarding the expression of several circRNAs, such as circLMTK2, are not consistent. We explain the role of circRNAs in the development of GC. We searched databases for the newest publications using the terms gastric cancer and circRNA. Each circRNA alteration, downstream targets, its impacts on cancer cells, and the prognostic and diagnostic roles of these circRNAs have been discussed. Taken together, circRNAs can be putative biomarkers in GC and potential targets for the treatment of this cancer. Yet, this field is still in its infancy and needs further experiments for reaching the clinical application. As these transcripts are stable in circulation, they can be used in non-invasive methods of cancer detection and patients' follow-up.

Circular RNAs and their role in renal cell carcinoma: a current perspective

Circular RNAs (circRNAs) are a new class of long non-coding RNAs, that results from a special type of alternative splicing referred to as back-splicing. They are widely distributed in eukaryotic cells and demonstrate tissue-specific expression patterns in humans. CircRNAs actively participate in various important biological activities like gene transcription, pre-mRNA splicing, translation, sponging miRNA and proteins, etc. With such diverse biological functions, circRNAs not only play a crucial role in normal human physiology, as well as in multiple diseases, including cancer. In this review, we summarized our current understanding of circRNAs and their role in renal cell carcinoma (RCC), the most common cancer of kidneys. Studies have shown that the expression level of several circRNAs are considerably varied in RCC samples and RCC cell lines suggesting the potential role of these circRNAs in RCC progression. Several circRNAs promote RCC development and progression mostly via the miRNA/target gene axis making them ideal candidates for novel anti-cancer therapy. Apart from these, there are a few circRNAs that are significantly downregulated in RCC and overexpression of these circRNAs leads to suppression of RCC growth. Differential expression patterns and novel functions of circRNAs in RCC suggest that circRNAs can be utilized as potential biomarkers and therapeutic targets for RCC therapy. However, our current understanding of the role of circRNA in RCC is still in its infancy and much comprehensive research is needed to achieve clinical translation of circRNAs as biomarkers and therapeutic targets in developing effective treatment options for RCC.

Comparative Analysis of Clavien-Dindo Grade and Risk Factors of Complications after Dual-Port Laparoscopic Distal Gastrectomy and Hand-Assisted Laparoscopic Gastrectomy

Objective

To compare the Clavien–Dindo grade and risk factors of complications after dual-port laparoscopic distal gastrectomy (DPLDG) and hand-assisted laparoscopic gastrectomy (HALG).

Methods

The clinical data of 775 patients who underwent DPLDG or HALG in our hospital from May 2016 to May 2019 were retrospectively reviewed, and the patients were divided into the DPLDG group (n = 386) and HALG group (n = 389) according to the surgical method to explore the risk factors of postoperative complications by grading their postoperative complications according to the Clavien–Dindo classification system and single-factor and multivariate analysis of the association between variables in clinical data and complications.

Results

Compared with the HALG group, the DPLDG group had significantly shorter surgical time, less intraoperative blood loss, and better postoperative exhaust time (p < 0.05), with no significant difference in other clinical indicators between the two groups (p > 0.05); the postoperative complication incidence rate of DPLDG group was significantly lower than that of the HALG group; it was shown in the single-factor analysis that the age, tumor length, intraoperative blood loss, pathological stages, and surgical method were related to the postoperative complications, and the results of multivariate analysis indicated that DPLDG was the protective factor for reducing postoperative complications, while age no less than 60 years old and intraoperative blood loss no less than 180 ml were the independent risk factors leading to complications; after surgery, the PNI level values at T1, T2, and T3 of DPLDG group were significantly higher than those of the HALG group (p < 0.05); and at 1 month after surgery, both groups obtained significantly higher GLQI scores than before, and the GLQI score of the DPLDG group was significantly higher in the between-group comparison (p < 0.05).

Conclusion

The DPLDG has lower postoperative complication incidence rate than the HALG, but age no less than 60 years old and intraoperative blood loss not less than 180 ml are the independent risk factors for postoperative complications, so advanced prevention measures shall be taken to lower the incidence of complications.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

Knockdown of Circ_0000144 Suppresses Cell Proliferation, Migration and Invasion in Gastric Cancer Via Sponging MiR-217

Previous studies have uncovered the role of circ_0000144 in various tumors. Here, we investigated the function and mechanism of circ_0000144 in gastric cancer (GC) progression. The expression of circ_0000144 in GC tissues and cells was detected through quantitative real-time polymerase chain reaction (qRT-PCR) method. Gain- and loss-of-function experiments including colony formation, wound healing and transwell assays were performed to examine the role of circ_0000144 in GC cells. Furthermore, western blot was conducted to determine the expressions of epithelial mesenchymal transition (EMT)-related proteins. The interaction between circ_0000144 and miR-217 was analyzed by bioinformatic analysis and luciferase reporter assays. The circ_0000144 expression was obviously upregulated in GC tissues and cells. Silencing of circ_0000144 inhibited cell proliferation, migration and invasion of GC cells, but ectopic expression of circ_0000144 showed the opposite results. Moreover, circ_0000144 sponged miR-217, and rescue assays revealed that silencing miR-217 expression reversed the inhibitory effect of circ_0000144 knockdown on the progress of GC. Our findings reveal that circ_0000144 inhibition suppresses GC cell proliferation, migration and invasion via absorbing miR-217, providing a new biomarker and potential therapeutic target for treatment of GC.

CircCSNK1G1 Contributes to the Tumorigenesis of Gastric Cancer by Sponging miR-758 and Regulating ZNF217 Expression

Background

Increasing evidence indicates that circular RNAs (circRNAs) act as vital regulators in various cancers. Nevertheless, the effect of circCSNK1G1 on gastric cancer (GC) is still unknown.

Methods

The mRNA levels of circCSNK1G1, miR-758, and ZNF217 were measured by RT-qPCR. The protein levels of ZNF217 were evaluated by Western blotting. Cell migration, invasion, proliferation, and apoptosis were detected by Transwell, CCK-8, and flow cytometry assays. The association between miR-758 and circCSNK1G1/ZNF217 was confirmed by RIP and luciferase reporter assays. Xenograft assay was employed for in vivo experiment.

Results

In the current study, it was demonstrated that the expression levels of circCSNK1G1 and ZNF217 were upregulated in GC tissues and cells, while the level of miR-758 was declined. Furthermore, functional assays indicated that circCSNK1G1 depletion suppressed GC progression in vitro and in vivo. In addition, circCSNK1G1 directly interacted with miR-758, and the supplementation of miR-758 suppressed the development of GC, which was abolished following pcDNA3.1-circCSNK1G1 transfection. Then, we explored the downstream mechanism of miR-758 and found that miR-758 could target the 3'UTR of ZNF217 mRNA. The overexpression of miR-758 neutralized the ZNF217-mediated effects on facilitating the progression of GC. Finally, we revealed that circCSNK1G1 could upregulate ZNF217 expression by sponging miR-758 in GC cells.

Conclusion

Our study revealed that circCSNK1G1 accelerated GC progression via the miR-758/ZNF217 axis, suggesting that circCSNK1G1 might be a potential biomarker for GC diagnosis and treatment.

CircRNA_100290 promotes GC cell proliferation and invasion via the miR-29b-3p/ITGA11 axis and is regulated by EIF4A3

Background

Circular RNAs (circRNAs) have been reported to be important regulators of the development and progression of various carcinomas. However, the role of circRNA_100290 in gastric cancer (GC) is still unclear. This study aimed to investigate the role of circRNA_100290 in GC invasion and metastasis and the possible underlying mechanism.

Methods

The expression of circRNA_100290 in GC cells and tissues was examined using quantitative real-time polymerase chain reaction (qRT-PCR). The role of circRNA_100290 in cell proliferation, migration, and invasion was evaluated in the AGS and HGC-27 cell lines in vitro. Bioinformatics tools, dual-luciferase reporter assays, Western blot assays and qRT-PCR were used to explore the pathways downstream of circRNA_100290. The mechanism underlying the regulation of circRNA_100290 expression was explored using RNA immunoprecipitation, qRT-PCR, and Western blot assays.

Results

The expression of circRNA_100290 was significantly upregulated in GC cells and 102 GC tissues, and high circRNA_100290 expression in GC was closely related to Borrmann’s type, lymph node metastasis and tumour-node-metastasis stage. In vitro, knockdown of circRNA_100290 in AGS and HGC-27 cells significantly inhibited cell proliferation, migration, and invasion. Mechanistically, a dual-luciferase reporter assay confirmed the direct interaction between circRNA_100290 and miR-29b-3p, which targets ITGA11, an oncogene that is closely related to epithelial–mesenchymal transition (EMT). In addition, EIF4A3, an RNA-binding protein (RBP), could inhibit the formation of circRNA_100290 by binding to the flanking sites of circRNA_100290. Low EIF4A3 expression in GC was related to a poor prognosis.

Conclusions

Elevated circRNA_100290 expression in GC promotes cell proliferation, invasion and EMT via the miR-29b-3p/ITGA11 axis and might be regulated by EIF4A3. CircRNA_100290 might be a promising biomarker and target for GC therapy.

Graphical abstract

Circular RNA PTK2 Accelerates Cell Proliferation and Inhibits Cell Apoptosis in Gastric Carcinoma via miR-139-3p

BACKGROUND

Gastric carcinoma (GC) is one of the most common malignant tumors. Although increasing studies have indicated that circular RNAs function as ideal biomarkers for multiple cancers, only a few researches elucidated the correlation between circular RNA PTK2 (circPTK2) and human cancers.

AIM

To further explore the expression status, biological function, and regulatory mechanism of circPTK2 in GC.

METHODS

Bioinformatics analysis and function or mechanism experiments including RT-qPCR, flow cytometry, Western blot, luciferase reporter assay, and xenografts assays were applied to investigate the function of circPTK2 and miR-139-3p.

RESULTS

High expression of circPTK2 was presented in GC tissues and cells. The circPTK2 knockdown notably suppressed cell proliferation and promoted cell apoptosis in GC. In mechanism, circPTK2 served as a sponge of miR-139-3p. Inhibition of miR-139-3p could reverse circPTK2 silence-mediated effects on GC cell proliferation and apoptosis. Furthermore, the xenograft tumor model was established to investigate the role of circPTK2 in GC tumor growth. Experimental results delineated that the reduction in tumor growth in response to circPTK2 knockdown was partly recovered by miR-139-3p inhibitor.

CONCLUSIONS

CircPTK2 promotes GC development by sponging miR-139-3p, which may function as an effective gene target for managing GC.

Depletion of hsa_circ_0000144 Suppresses Oxaliplatin Resistance of Gastric Cancer Cells by Regulating miR-502-5p/ADAM9 Axis

Background

Circular RNAs (circRNAs) have been disclosed to exert important roles in human cancers, including gastric cancer (GC). CircRNA hsa_circ_0000144 was identified as an oncogene in GC development. The aim of our study was to explore the role of hsa_circ_0000144 in oxaliplatin (OXA) resistance of GC.

Methods

Expression levels of hsa_circ_0000144, microRNA-502-5p (miR-502-5p) and A disintegrin and metalloproteinase 9 (ADAM9) were examined by quantitative real-time PCR (RT-qPCR) or Western blot assay. The OXA resistance of GC cells was evaluated by Cell Counting Kit-8 (CCK-8) assay. Colony formation assay was performed to assess the colony formation capacity. Cell apoptosis was determined by flow cytometry and caspase 3 activity. And cell migration and invasion were detected by Transwell assay. Target association between miR-502-5p and hsa_circ_0000144 or ADAM9 was demonstrated by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Moreover, role of hsa_circ_0000144 in vivo was analyzed by xenograft tumor assay.

Results

Hsa_circ_0000144 and ADAM9 were highly expressed, while miR-502-5p was downregulated in OXA-resistant GC tissues and cells. Depletion of hsa_circ_0000144 could inhibit OXA resistance, proliferation and metastasis in OXA-resistant GC cells, which was attenuated by miR-502-5p inhibition. Hsa_circ_0000144 sponged miR-502-5p to positively regulate ADAM9 expression. MiR-502-5p suppressed OXA resistance, proliferation and metastasis in OXA-resistant GC cells by targeting ADAM9. Hsa_circ_0000144 knockdown could hamper tumor growth in vivo.

Conclusion

Hsa_circ_0000144 exerted inhibitory effects on OXA resistance, proliferation and metastasis of OXA-resistant GC cells by regulating miR-502-5p/ADAM9 axis, at least in part.

Circular RNAs as important players in human gastric cancer

As one of the most prevalent gastrointestinal diseases, gastric cancer (GC) is the second leading cause of cancer-related deaths worldwide. Since GC has no clinical manifestations in the early stage of the disease, most patients are detected in the later phases of disease and have an unfortunately lower chance of recovery. Circular RNAs (circRNAs), a novel category of non-coding RNAs (ncRNAs), are mainly engaged in the regulation of gene expression at the transcriptional and post-transcriptional levels. Numerous evidences have revealed that circRNAs play key roles in GC as they are involved in cell proliferation, growth, and apoptosis via modulating the expression of some target genes, miRNAs, and proteins. Many studies have addressed the impact of circRNA dysregulation on GC initiation, progression, and invasion via binding to miRNAs or RNA binding proteins. Moreover, changes in circRNA expression are associated with pathological and clinical features of GC highlighting their potentials as diagnostic or prognostic biomarkers in GC. In the current study, the recent findings on the significance of circRNAs in the development and progression of GC are reviewed. We focus on the implications of circRNAs as potential diagnostic or prognostic biomarkers in this malignancy.

hsa_circ_001653 up-regulates NR6A1 expression and elicits gastric cancer progression by binding to microRNA-377

NEW FINDINGS

What is the central question of this study? Does hsa_circ_001653 influence the development of gastric cancer (GC) and if so how? What is the main finding and its importance? Bioinformatics analysis revealed the presence of differentially expressed hsa_circ_001653 in GC and adjacent normal tissues, and this was strongly related to the pathology of patients with GC. Knockdown of hsa_circ_001653 suppressed the proliferation, invasion and migration of GC cells, while inducing cell apoptosis via miR-377-mediated NR6A1 inhibition. The effect of hsa_circ_001653 and miR-377 on tumour growth in GC was further confirmed in vivo.

ABSTRACT

Gastric cancer (GC) is one of the leading causes of human mortality through malignant tumours. Circular RNAs (circRNAs) have been identified as binding to microRNAs (miRNAs) to modulate the progression of tumours. This study explores the role of hsa_circ_001653, a newly identified circRNA, in the development of GC. hsa_circ_001653 expression was measured in 86 paired normal and tumour tissues surgically resected from GC patients. Cross-talk between hsa_circ_001653 and microRNA-377 (miR-377)/nuclear receptor subfamily 6, group A, member 1 (NR6A1) was assessed using bioinformatics analysis, dual-luciferase reporter assay, Ago2 immunoprecipitation and western blot analysis. A series of functional experiments were carried out to elucidate the role of hsa_circ_001653 in GC cell proliferation, invasion, migration and apoptosis, and its underlying molecular mechanisms. Nude mice were inoculated with GC cells for in vivo analysis. hsa_circ_001653 was found to be an up-regulated circRNA in GC tissues and cells. Down-regulation of hsa_circ_001653 inhibited GC cell proliferation, migration and invasion, while stimulating cell apoptosis. hsa_circ_001653 was found to bind to miR-377, which targeted NR6A1 and repressed its expression. Inhibition of miR-377 and overexpression of NR6A1 restored the proliferation, migration and invasion in GC cells lacking hsa_circ_001653. Furthermore, inhibition of hsa_circ_001653 attenuated tumour growth in nude mice inoculated with GC cells. Collectively, the demonstration that hsa_circ_001653 exerts its anticancer effects by regulating the miR-377-NR6A1 axis increases our understanding of gastric cancer pathophysiology. The findings uncover new potential therapeutic targets for GC.

circEYA1 Functions as a Sponge of miR-582-3p to Suppress Cervical Adenocarcinoma Tumorigenesis via Upregulating CXCL14

Circular RNAs (circRNAs) function as efficient microRNA (miRNA) sponges that regulate gene expression in the pathogenesis of many human malignancies. However, their roles in cervical adenocarcinoma remain largely unknown. In this study, we aimed to seek novel circRNAs that regulate cervical adenocarcinoma carcinogenesis and to explore their regulatory mechanisms as well as clinical significance. We identified that 24 circRNAs were differentially expressed in cervical adenocarcinoma tissues by RNA sequencing. Among them, circEYA1 was the most significantly downregulated circRNA in cervical adenocarcinoma. In cervical adenocarcinoma cells, circEYA1 overexpression led to suppression of cell viability and colony formation, promotion of apoptosis, and a decrease of the xenograft tumor growth. The mechanism underlying these observations is that circEYA1 functioned as a sponge of miR-582-3p and abrogated its suppression of CXCL14 expression. Consistently, miR-582-3p inhibition phenocopied the biological effects of circEYA1 overexpression in cervical adenocarcinoma cells. Moreover, miR-582-3p overexpression reversed the suppressive behaviors of circEYA1 in vitro and in vivo. In addition, the expression, correlation, and clinical diagnostic value of circEYA1/miR-582-3p/CXCL14 were confirmed in 198 clinical cervical tissue samples. In summary, our findings highlight a novel tumor suppressive role of circEYA1 in cervical adenocarcinoma tumorigenesis and may provide a potential diagnostic marker and therapeutic target for patients with cervical adenocarcinoma.

Overexpression of circRNA circUCK2 Attenuates Cell Apoptosis in Cerebral Ischemia-Reperfusion Injury via miR-125b-5p/GDF11 Signaling

Circular RNAs (circRNAs) are expressed at high levels in the brain and are involved in various central nervous system diseases. However, the potential role of circRNAs in ischemic stroke-associated neuronal injury remains largely unknown. Herein, we uncovered the function and underlying mechanism of the circRNA UCK2 (circUCK2) in ischemia stroke. The oxygen-glucose deprivation model in HT-22 cells was used to mimic ischemia stroke in vitro. Neuronal viability and apoptosis were determined by Cell Counting Kit-8 (CCK-8) assays and TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling) staining, respectively. Middle cerebral artery occlusion was conducted to evaluate the function of circUCK2 in mice. The levels of circUCK2 were significantly decreased in brain tissues from a mouse model of focal cerebral ischemia and reperfusion. Upregulated circUCK2 levels significantly decreased infarct volumes, attenuated neuronal injury, and improved neurological deficits. circUCK2 reduced oxygen glucose deprivation (OGD)-induced cell apoptosis by regulating transforming growth factor β (TGF-β)/mothers against decapentaplegic homolog 3 (Smad3) signaling. Furthermore, circUCK2 functioned as an endogenous miR-125b-5p sponge to inhibit miR-125b-5p activity, resulting in an increase in growth differentiation factor 11 (GDF11) expression and a subsequent amelioration of neuronal injury. Consequently, these findings showed that the circUCK2/miR-125b-5p/GDF11 axis is an essential signaling pathway during ischemia stroke. Thus, the circRNA circUCK2 may serve as a potential target for novel treatment in patients with ischemic stroke.

Develop a circular RNA-related regulatory network associated with prognosis of gastric cancer

Background

In gastric cancer (GC), circular RNAs (circRNAs) mainly play an important role in miRNA sponge, which not only indicate long‐term survival and prognosis but also increase resistance to the apoptosis. The purpose of the study is to explore new circRNAs and their underlying mechanisms in GC.

Method

Through rigorous retrieval strategies, we used the sva package to analyze and identify differentially expressed circRNAs (DECs) from three Gene Expression Omnibus microarray datasets (GSE83521, GSE89143, and GSE78092). Online website CSCD and CircInteractome were used to reveal the binding sites between miRNAs and DECs. The possible target miRNAs of the DECs identified based on miRNAs, and Cytoscape was used to create a regulatory network of circRNA‐miRNA‐mRNA and identified the hub genes which were further validated using The Cancer Genome Atlas database and Human Protein Atlas.

Results

Twenty‐eight DECs were obtained using the sva package. A regulatory network of circRNA‐miRNA‐mRNA (competing endogenous RNA) containing 15 circRNAs, 24 miRNAs, and 158 genes was identified. A protein‐protein interaction network based on the 158 genes was established, and further determined that 10 hub genes (SKA1, ANLN, CHEK1, SKA3, TOP2A, BIRC5, RRM2, NCAPG2, FANCI, and RAD51) were associated with some cancer‐related pathways based on the functional enrichment analysis. Finally, six hub genes (BIRC5, TOP2A, FANCI, NCAPG2, RAD51, and RRM2) were proven to influence the overall survival of GC.

Conclusion

Our study established a circRNA‐miRNA‐mRNA regulatory network and defined six circRNA‐related hub genes in GC, which could serve as potential therapeutic targets or prognostic biomarker for GC treatment.

Current Status of Research on the Role of Circular RNAs in Hepatocellular Carcinoma and Clinical Implications

The latest statistics show that rates of morbidity and mortality for hepatocellular carcinoma are gradually increasing over time. Accumulating evidence indicates that circular RNAs (circRNAs) participate in the regulation of gene transcription and translation and exert a crucial role in endogenous RNA network. circRNAs are implicated in the pathogenesis of numerous tumors including hepatocellular carcinoma (HCC), gastric carcinoma and bladder cancer. Of note, the effect of circRNAs in HCC has drawn increasing public attention. Previous studies revealed that the function of circRNAs mainly consists of sponges of miRNA and RNA-binding proteins, alternative splicing of pre-mRNAs, transcriptional and translational regulators, and potential to encode proteins. In addition, recent research data indicate that the expression level of circRNAs is closely correlated with metastasis, invasion, and occurrence of HCC in patients. These findings imply that circRNAs may be useful as biomarkers for diagnosis and prediction of prognosis of HCC. In this review, we have systemically summarized current viewpoints regarding the role of circRNAs expression in HCC to provide an important reference illustrating the underlying mechanism of HCC.

Circulating Tumour DNAs and Non-Coding RNAs as Liquid Biopsies for the Management of Colorectal Cancer Patients

Circulating tumour DNAs and non-coding RNAs present in body fluids have been under investigation as tools for cancer diagnosis, disease monitoring, and prognosis for many years. These so-called liquid biopsies offer the opportunity to obtain information about the molecular make-up of a cancer in a minimal invasive way and offer the possibility to implement theranostics for precision oncology. Furthermore, liquid biopsies could overcome the limitations of tissue biopsies in capturing the complexity of tumour heterogeneity within the primary cancer and among different metastatic sites. Liquid biopsies may also be implemented to detect early tumour formation or to monitor cancer relapse of response to therapy with greater sensitivity compared with the currently available protein-based blood biomarkers. Most colorectal cancers are often diagnosed at late stages and have a high mortality rate. Hence, biomolecules as nucleic acids present in liquid biopsies might have prognostic potential and could serve as predictive biomarkers for chemotherapeutic regimens. This review will focus on the role of circulating tumour DNAs and non-coding RNAs as diagnostic, prognostic, and predictive biomarkers in the context of colorectal cancer.

Circular RNAs in Gastric Cancer: Potential Biomarkers and Therapeutic Targets

Circular RNAs (circRNAs), as a recently established group of endogenous noncoding RNAs, have been involved in the occurrence and development of different malignancies. Gastric cancer (GC) remains a globally significant contributor to death in cancer patients due to insufficient early diagnosis, limited treatment measures, and poor prognosis. An increasing number of studies have found that many circRNAs are dysregulated in GC and are closely associated with its tumorigenesis and metastasis. Thus, circRNAs have the potential to serve as diagnostic and prognostic biomarkers and even therapeutic targets. This review comprehensively summarizes the most recent findings on how circRNAs influence GC progression and their clinical value. In addition, we present several methological deficiencies in the studies and provide some promising ideas for future research.

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

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

Circular RNA-hsa-circ-0000670 promotes gastric cancer progression through the microRNA-384/SIX4 axis

Circular RNAs (circRNAs), a special type of non-coding RNA molecules, have been addressed to be implicated in gastric cancer progression. The GSE93541 and GSE83521 microarrays found hsa-circRNA-000670 (hsa-circ-0000670) as an up-regulated circRNAin gastric cancer. We mainly investigated the function and molecular mechanisms of hsa-circ-0000670 involved in gastric cancer. The expression of hsa-circ-0000670 was determined by RT-qPCR to be highly expressed in gastric cancer tissues relative to corresponding adjacent normal tissues, as well as in gastric cancer cell lines relative to normal gastric mucosal epithelial cell line. By conducting EdU, scratch test and Transwell assays, hsa-circ-000670 was found to be a tumor promoter by potentiating the proliferative, invasive and migrating capabilities of gastric cancer cells. Consistently, a tumor-promotive role of hsa-circ-000670 was validated in vivo. Dual-luciferase reporter gene and RIP assays identified the binding of hsa-circ-0000670 to microRNA-384 (miR-384) and the binding of miR-384 to sine oculis-related homeobox 4 (SIX4). The oncogenic potential of hsa-circ-0000670 in gastric cancer cells were inhibited by overexpressed miR-384. Mechanistically, SIX4 was targeted by miR-384 and was upregulated in gastric cancer. High SIX4 expression was suggested to correlate with the poor prognosis of gastric cancer patients. Additionally, silencing of SIX4 delayed tumor growth and progression, which were reversed by overexpression of hsa-circ-0000670. Taken together, hsa-circ-0000670 acts as a tumor promotor in gastric cancer progression and might be a potential target for gastric cancer treatment.

The function and mechanism of circular RNAs in gastrointestinal tumours

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

Circular RNAs in gastric cancer: Biomarkers for early diagnosis

Circular RNAs (circRNAs) are highly conserved and stable closed-loop non-coding RNAs. They are involved in numerous biological functions, including regulating gene transcription or protein translation by interacting with proteins and regulating expression of microRNAs. The aberrant expression of circRNAs has been reported in many cancers, including gastric cancer. By regulating gene expression, circRNAs are able to affect the proliferation, invasion and metastasis of gastric cancer. The current review focused on the characteristics and biological functions of circRNAs, the carcinogenic potential and the possible implications of circRNAs on the diagnosis and treatment of gastric cancer. In conclusion, circRNAs may serve as potential biomarkers for diagnosis, as well as therapeutic targets.

High Expression of hsa_circRNA_001387 in Nasopharyngeal Carcinoma and the Effect on Efficacy of Radiotherapy

Background

Nasopharyngeal carcinoma (NPC) is one of the most difficult cancers to be detected and treated. Hunting for novel cancer-specific biomarkers for NPC patients is helpful for timely diagnosis and clinical treatment of NPC.

Methods

In this study, high-throughput circRNA sequencing was used to screen the circRNAs with expression variation in NPC patients. qRT-PCR was used to detect the expression level of hsa_circRNA_001387 in the cancer tissues from 100 surgical patients, the peripheral blood samples from 100 radiotherapy patients and NPC cell lines. Based on clinical data of the patients, the relationship between hsa_circRNA_001387 and radiotherapy as well as antibody to Epstein-Barr (EB) virus was investigated. The use of this circRNA as a biomarker for NPC was also discussed.

Results

Expression of hsa_circRNA_001387 was significantly increased in the tumor tissues of NPC surgical patients, in the peripheral blood samples of NPC radiotherapy patients and in the NPC cell lines (P<0.01). Expression of hsa_circRNA_001387 was significantly elevated in patients with well-differentiated tumors, lymph node metastasis and distant metastases, stage III-IV, positive EB virus, or family history of NPC. hsa_circRNA_001387 was closely associated with the prognosis of the patients. The overall survival and progression-free survival were shorter in patients with high expression. Through univariate and multivariate analyses, it was found that hsa_circRNA_001387 was considered as an independent factor for the prognosis of NPC patients.

Conclusion

This study reported for the first time that expression of hsa_circRNA_001387 is significantly upregulated, and it was also indicated that hsa_circRNA_001387 can be used as a novel biomarker for NPC.

Exosome-transmitted circ_MMP2 promotes hepatocellular carcinoma metastasis by upregulating MMP2

Exosomes released by tumor cells have been recently identified as important determinants of tumor progression. They often carry circular RNAs that are differentially expressed in tumors and may regulate tumorigenesis and metastasis. Here, we showed that supernatant of 97H hepatocellular carcinoma (HCC) cell line could promote metastasis in L02 human liver cells and HCC cell lines. Moreover, we determined that circ_MMP2 (has_circ_0039411) could be delivered by 97H‐ or LM3 cell‐derived exosomes to L02 and HepG2 cell cultures. High expression of circ_MMP2 led to the upregulation of its host gene matrix metallopeptidase 2 (MMP2) via the sponging of miR‐136‐5p. Rescue assays demonstrated that miR‐136‐5p and MMP2 were two essential participants in HCC metastasis. Finally, high level of circ_MMP2 or MMP2, as well as low level of miR‐136‐5p, was correlated with low overall survival of HCC patients. Our study highlights a novel molecular pathway in HCC cell‐derived exosomes.

CircRNA: a rising star in gastric cancer

In recent years, a large number of circRNAs have been identified in mammalian cells with high-throughput sequencing technologies and bioinformatics. The aberrant expression of circRNAs has been reported in many human diseases including gastric cancer (GC). The number of GC-related circRNAs with validated biological functions and mechanisms of action is growing. CircRNAs are critically involved in GC cell proliferation, apoptosis, migration, and invasion. CircRNAs have been shown to function as regulators of parental gene transcription and alternative splicing and miRNA sponges. Moreover, circRNAs have been suggested to interact with proteins to regulate their expression level and activities. Several circRNAs have been identified to encode functional proteins. Due to their great abundance, high stability, tissue- and developmental-stage-specific expression patterns, and wide distribution in various body fluids and exosomes, circRNAs exhibit a great potential to be utilized as biomarkers for GC. Herein, we briefly summarize their biogenesis, properties and biological functions and discuss about the current research progress of circRNAs in GC with a focus on the potential application for GC diagnosis and therapy.

Diagnostic value of circular RNAs in female reproductive system diseases: A PRISMA-compliant meta-analysis

Circular RNAs (circRNAs) are novel non-coding RNAs that have been reported to be involved in the progression of numerous diseases. However, the clinical diagnostic value of circRNAs in female reproductive system diseases remains unknown. The present study is a systemic review and meta-analysis of the available literature on circRNAs as novel biomarkers for female reproductive system diseases. Relevant studies were systematically searched using the PubMed, Embase, Web of Science and Cochrane Library databases. The data obtained from the included studies were analyzed by RevMan5.3 and STATA 14.2. A total of six studies involving 613 individuals across three types of disease examined the diagnostic capabilities of circRNAs. Within these publications, the pooled sensitivity of circRNAs was 0.70 (95% CI, 0.64-0.76), and the pooled specificity was 0.70 (95% CI, 0.64-0.75). The pooled positive likelihood ratio and negative likelihood ratio were 2.33 and 0.42, respectively. The diagnostic score was 1.70 and the pooled diagnostic odds ratio was 5.48. The area under the summary receiver operator characteristic curve was 0.76 (95% CI, 0.72-0.79), indicating that circRNAs exhibited a moderate diagnostic value for female reproductive system diseases and may function as potential diagnostic biomarkers. However, further studies are required to verify the clinical applications of circRNAs.

Observation of tumor-associated macrophages expression in gastric cancer and its clinical pathological relationship

The present study was designed to investigate the expression of tumor-associated macrophages (TAMs) in gastric cancer and its clinicopathological relationship. In addition, we also aimed to analyze the relationship between helicobacter pylori (HP) infection and TAMs in gastric cancer.The protein expression of CD16 and CD163 in 90 gastric cancer tissues and 30 margin tissues was detected by immunohistochemistry. HP infection was detected in 90 gastric cancer tissues and 30 margin tissues by gram staining and immunohistochemistry.There was no clear correlation between CD16 macrophages and gastric cancer. The density of CD163 macrophages was not correlated with the general condition of tumor patients, but with tumor size, tumor differentiation, lymphatic metastasis, depth of invasion and TNM stage. Additionally, the infection rate of HP in gastric cancer tissues was significantly higher.In summary, TAMs are associated with tumor size, degree of differentiation, depth of invasion, lymph node metastasis and TNM stage, suggesting their critical role in the invasion and metastasis of gastric cancer.

The Regulatory Functions of Circular RNAs in Digestive System Cancers

Circular ribonucleic acids (circRNAs), which are a type of covalently closed circular RNA, are receiving increasing attention. An increasing amount of evidence suggests that circRNAs are involved in the biogenesis and development of multiple diseases such as digestive system cancers. Dysregulated circRNAs have been found to act as oncogenes or tumour suppressors in digestive system cancers. Moreover, circRNAs are related to ageing and a wide variety of processes in tumour cells, such as cell apoptosis, invasion, migration, and proliferation. Moreover, circRNAs can perform a remarkable multitude of biological functions, such as regulating splicing or transcription, binding RNA-binding proteins to enable function, acting as microRNA (miRNA) sponges, and undergoing translated into proteins. However, in digestive system cancers, circRNAs function mainly as miRNA sponges. Herein, we summarise the latest research progress on biological functions of circRNAs in digestive system cancers. This review serves as a synopsis of potential therapeutic targets and biological markers for digestive system cancer.

CircPIP5K1A activates KRT80 and PI3K/AKT pathway to promote gastric cancer development through sponging miR-671-5p

BACKGROUND

Gastric cancer (GC) has been regarded as a kind of the most common cancers in gastrointestinal malignant tumors. Circular RNA (circRNA) is a newly discovered category of non-coding RNAs and plays a significant role in the initiation or development of human cancers. Nevertheless, the role of circPIP5K1A in GC remains unclear.

METHODS

The relative expression level and the circular structure of circPIP5K1A were confirmedby RT-qPCR. The biological function of circPIP5K1A in GC was evaluated by colony formation, transwell and western blot assays. The binding capacity between miR-671-5p and circPIP5K1A (or KRT80) was assessed by luciferase reporter and Ago2-RIP assays. Protein levels of PI3K/AKT pathway were measured by western blot assay.

RESULTS

CircPIP5K1A was up-regulated in GC tissues and cells with a circular structure. Functionally, circPIP5K1A silence limited cell proliferation, invasion, migration and EMT process. Mechanistically, circPIP5K1A directly interacted with miR-671-5p to modulate KRT80 expression. Either miR-671-5p inhibitor or KRT80 overexpression could offset the inhibitory effect of circPIP5K1A depletion on GC development. Besides, circPIP5K1A played its oncogenic role in GC through regulating PI3K/AKT pathway. At last, circPIP5K1A promoted GC tumor growth in vivo.

CONCLUSIONS

CircPIP5K1A/miR-671-5p/KRT80 axis contributes to GC progression through PI3K/AKT pathway, implying this axis may be a potential therapeutic target for the treatment of GC patients.

circRNA-14723 promotes hepatocytes proliferation in rat liver regeneration by sponging rno-miR-16-5p

Circular RNA (circRNA) is a subclass of noncoding RNA (ncRNA) detected within mammalian tissues and cells. However, its regulatory role during the proliferation phase of rat liver regeneration (LR) remains unreported. This study was designed to explore their regulatory mechanisms in cell proliferation of LR. The circRNA expression profile was detected by high-throughput sequencing. It was indicated that 260 circRNAs were differentially expressed during the proliferation phase of rat LR. Among them, circ-14723 displayed a significantly differential expression. We further explored its regulatory mechanism in rat hepatocytes (BRL-3A cells). First, EdU, flow cytometry and western blot (WB) indicated that knocking down circ-14723 inhibited BRL-3A cells proliferation. Second, RNA-Pulldown and dual-luciferase report assay showed that circ-14723 could sponge rno-miR-16-5p. At last, WB showed that the reported target genes of rno-miR-16-5p, CCND1, and CCNE1 were downregulated after knocking down circ-14723. In conclusion, we found that circ-14723 exerted a critical role in G1/S arrest to promote cell proliferation via rno-miR-16-5p/CCND1 and CCNE1 axis in rat LR. This finding further revealed the regulatory mechanisms of circRNA on cell proliferation of LR, and might provide a potential target for clinical problems.

Circular RNAs and gastrointestinal cancers: Epigenetic regulators with a prognostic and therapeutic role

Both environmental and genetic factors are involved in the initiation and development of gastrointestinal cancer. Covalent closed circular RNAs (circRNAs) are produced by a mechanism called "back-splicing" from mRNAs. They are highly stable and show cell and tissue specific expression patterns. Although some functions such as "microRNA sponge" and "RNA binding protein sponge" have been reported for a small number of circRNAs, the function of thousands of other circRNAs is still unknown. Dysregulation of circRNAs has been reported in many GI cancers and are involved in metastasis and invasion. CircRNAs have been reported to be useful as prognostic markers and targets for developing new treatments. We first describe the properties and biogenesis of circRNAs. We then summarize recent reports about circRNA functions, expression status, and their potential to be used as biomarkers in GI cancers including, gastric cancer, colorectal cancer, esophageal cancer, hepatocellular carcinoma, gallbladder cancer and pancreatic cancer.

Current Understanding of Circular RNAs in Gastric Cancer

Gastric cancer (GC) is the third most common cause of cancer-related death worldwide. Advanced diagnosis and high rates of relapse and metastasis are associated with the poor prognosis of this disease. GC has a complex etiopathogenesis of which the underlying mechanisms remain to be explored. Studies on circular RNAs (circRNAs), noncoding RNAs that may be potential targets in GC, have made substantial progress over the past few years. CircRNAs exert important effects on the onset and progression of GC. Hence, this article aims to summarize the findings of recent studies of circRNAs related to GC and to describe the underlying mechanisms and potential applications. The findings indicate that circRNAs participate in GC regulation, proliferation, invasion, and metastasis through regulating microRNAs, proteins, genes, and signaling pathways. In addition, dysregulated circRNAs may be used as novel diagnostic and prognostic biomarkers or therapeutic targets. This review is expected to facilitate a better understanding of GC, and it suggests novel circRNA-based methods to inhibit or prevent GC.

Hsa_circ_001569 is an unfavorable prognostic factor and promotes cell proliferation and metastasis by modulating PI3K-AKT pathway in breast cancer

Circular RNAs (circRNAs) have gained attention for their involvement in carcinogenesis, but its functional effects in breast cancer (BC) remains largely unclear. In this study, we aimed to explore the expressing pattern, clinical significance and potential function of a newly identified circRNA, hsa_circ_001569, in BC. RT-PCR was performed to detect the expression of hsa_circ_001569 in both BC tissues and cell lines. The associations between hsa_circ_001569 expression and clinicopathological features and prognosis in BC patients were statistically analyzed. Next, we investigated the effects of hsa_circ_001569 on the proliferation, apoptosis, migration and invasion in BC cells lines. The effects of abnormal hsa_circ_001569 expression on EMT pathway and PI3K/AKT pathway were determined using Western blot. We found that hsa_circ_001569 expression was significantly up-regulated in both BC tissues and cell lines. Overexpression of hsa_circ_001569 was associated with Lymph node metastasis, advanced clinical stage and shorter overall survival. Multivariate assay confirmed that hsa_circ_001569 expression was an independent prognostic factor for 5-year overall survival. Furthermore, functional investigations revealed that knockdown of hsa_circ_001569 significantly suppressed the growth and metastatic potentials of BC cells. Besides, molecular mechanistic study revealed that depression of hsa_circ_001569 impeded the activation of PI3K-AKT signaling in BC cells. Our results indicated that hsa_circ_001569 upregulation was associated with BC lymph-node metastasis, clinical stage, and poor prognosis. Hsa_circ_001569 might contribute to progression of BC by modulating PI3K-AKT pathway.

circLMTK2 acts as a sponge of miR-150-5p and promotes proliferation and metastasis in gastric cancer

BACKGROUND

As a novel class of non-coding RNAs, circular RNAs (circRNAs) are key regulators of the development and progression of different cancers. However, little is known about the function and biological mechanism of circLMTK2, also named hsa_circ_0001725, in gastric cancer (GC) tumourigenesis.

METHODS

circLMTK2 was identified in ten paired cancer specimens and adjacent normal tissues by RNA sequencing and genome-wide bioinformatic analysis and verified by quantitative real-time PCR (qRT-PCR). Knockdown or exogenous expression of circLMTK2 combined with in vitro and in vivo assays were performed to prove the functional significance of circLMTK2. The molecular mechanism of circLMTK2 was demonstrated by searching the CircNet database and confirmed by RNA in vivo precipitation assays, western blotting, luciferase assays and rescue experiments.

RESULTS

circLMTK2 was frequently upregulated in GC tissues, and high circLMTK2 expression was associated with poor prognosis, lymph node metastasis and poor TNM stage in GC patients. Functionally, circLMTK2 overexpression promoted GC cell proliferation and tumourigenicity in vitro and in vivo. Furthermore, ectopic circLMTK2 expression enhanced GC cell migration and invasion in vitro and tumour metastasis in vivo. In addition, we demonstrated that circLMTK2 could sponge miR-150-5p, thus indirectly regulating the c-Myc expression and contributing to GC tumourigenesis.

CONCLUSION

Our findings demonstrate that circLMTK2 functions as a tumour promoter in GC through the miR-150-5p/c-Myc axis and could thus be a prognostic predictor and therapeutic target for GC.

circRNA circAF4 functions as an oncogene to regulate MLL-AF4 fusion protein expression and inhibit MLL leukemia progression

Background

Circular RNAs (circRNAs) represent a type of endogenous noncoding RNAs that are generated by back-splicing events and favor repetitive sequences. Recent studies have reported that cancer-associated chromosomal translocations could juxtapose distant complementary repetitive intronic sequences, resulting in the aberrant formation of circRNAs. However, among the reported fusion genes, only a small number of circRNAs were found to originate from fusion regions during gene translocation. We question if circRNAs could also originate from fusion partners during gene translocation.

Methods

Firstly, we designed divergent primers for qRT-PCR to identify a circRNA circAF4 in AF4 gene and investigated the expression pattern in different types of leukemia samples. Secondly, we designed two small interfering RNAs specially targeting the back-spliced junction point of circAF4 for functional studies. CCK8 cell proliferation and cell cycle assay were performed, and a NOD-SCID mouse model was used to investigate the contribution of circAF4 in leukemogenesis. Finally, luciferase reporter assay, AGO2 RNA immunoprecipitation (RIP), and RNA Fluorescent in Situ Hybridization (FISH) were performed to confirm the relationship of miR-128-3p, circAF4, and MLL-AF4 expression.

Results

We discovered a circRNA, named circAF4, originating from the AF4 gene, a partner of the MLL fusion gene in MLL-AF4 leukemia. We showed that circAF4 plays an oncogenic role in MLL-AF4 leukemia and promotes leukemogenesis in vitro and in vivo. More importantly, knockdown of circAF4 increases the leukemic cell apoptosis rate in MLL-AF4 leukemia cells, while no effect was observed in leukemia cells that do not carry the MLL-AF4 translocation. Mechanically, circAF4 can act as a miR-128-3p sponge, thereby releasing its inhibition on MLL-AF4 expression. We finally analyzed most of the MLL fusion genes loci and found that a number of circRNAs could originate from these partners, suggesting the potential roles of fusion gene partner-originating circRNAs (named as FP-circRNAs) in leukemia with chromosomal translocations.

Conclusion

Our findings demonstrate that the abnormal elevated expression of circAF4 regulates the cell growth via the circAF4/miR-128-3p/MLL-AF4 axis, which could contribute to leukemogenesis, suggesting that circAF4 may be a novel therapeutic target of MLL-AF4 leukemia.

Potential Role of circPVT1 as a proliferative factor and treatment target in esophageal carcinoma

Background

Many circRNAs have been reported to play important roles in cancer development and have the potential to serve as a novel class of biomarkers for clinical diagnosis. However, the role of circRNAs in esophageal carcinoma (EC) remains unclear. In the current study, we investigated the potential role of circPVT1 in esophageal carcinoma.

Methods

Quantitative real-time PCR was performed to detect circPVT1 levels. CircPVT1-specific siRNA or plasmids were used to knock down or overexpression the target RNA. Hoechst Staining was implemented to evaluate the ratio of cell apoptosis. Transwell migration assays were carried out to study the effects of circPVT1 on esophageal squamous cell carcinoma cell invasion. RegRNA 2.0 was used for bioinformatics analysis. The expression levels of Pax-4, Pax-6, PPARα and PPAR-γ were assessed using Western blot.

Results

In the present study, we demonstrated a significant up-regulation of circPVT1 levels in EC tissues and cancer cell lines. The levels of circPVT1 decreased significantly when the cells were maintained to over-confluence. These results suggested a potential role for circPVT1 in cell proliferation. In addition, overexpressing circPVT1 in TE-10 cell promoted invasive ability of cancer cell. In contrast, siRNA knockdown of circPVT1 inhibited this phenomenon, leading to increased apoptosis levels of TE-10 cell. What’s more, miR-4663 had the effect of inhibiting tumor growth by downregulated Paxs and upregulated PPARs. Whereas, after the addition of circPVT1, this effect no longer worked, suggesting that circPVT1 may affect the malignancy of the tumor by affecting miRNA and regulating the levels of Paxs and PPARs.

Conclusions

Collectively, our study reveals a critical role for circPVT1 in esophageal carcinoma, which may provide new insights of this circRNA as a biomarker for the diagnosis and treatment target of EC.

CircRNAs and its relationship with gastric cancer

Circular RNAs (circRNAs), as a type of tissue specific RNA with more stable structure than linear RNAs, was poorly understood on its correlation with gastric cancer (GC). In this review, we outline the synthesis and characteristics of circRNAs and generalize their categories and functions. Through comprehensive analysis of the reported results, we find that circRNAs not only participate in the regulation of gastric cancer (GC) cell biological behaviors, such as proliferation, invasion, migration and epithelial mesenchymal transition (EMT), but also are related to the clinicopathological features of GC such as tumor differentiation, TNM stage and metastasis, etc. According to the present screening and verification results, circRNAs are suggested to be used as biomarkers for the early diagnosis and prognosis prediction of GC, and those circRNAs involved in the genesis and development of GC have the potential as novel targets for the individualized treatment of GC.

circGFRA1 Promotes Ovarian Cancer Progression By Sponging miR-449a

Backgroud: Increasing studies show that circular RNAs (circRNAs) play important roles in tumor progression. However, the function of circRNAs in ovarian cancer is mostly unclear. Methods: We detected the expression of circGFRA1 by quantitative real-time PCR (qRT-PCR) in 50 pairs of ovarian cancer tissues and adjacent normal tissues. Then, we explored the function of circGFRA1 in ovarian cancer progression, such as cell proliferation, apoptosis and invasion. Moreover, we performed luciferase reporter and RNA immunoprecipitation (RIP) assay to study the competing endogenous RNA (ceRNA) function of circGFRA1 in ovarian cancer progression. Results: qRT-PCR showed that circGFRA1 was overexpressed in ovarian cancer tissues. Inhibition of circGFRA1 suppressed cell proliferation and invasion, but induced cell apoptosis in ovarian cancer. Luciferase reporter and RIP assay revealed that circGFRA1 could regulate the expression of GFRA1 by sponging miR-449a. Conclusions: In summary, circGFRA1 regulated GFRA1 expression and ovarian cancer progression by sponging miR-449a. circGFRA1 could be a potential diagnostic biomarker and therapeutic target for ovarian cancer.

Role of circular RNAs in gastric cancer: Recent advances and prospects

Circular RNA (circRNA) is a newly discovered non-coding RNA with special structure, which is widely expressed in eukaryotic organisms and mainly located in the cytoplasm. circRNAs participate in gene regulation by working as miRNA sponges that block the inhibitory effect of miRNA on its target genes. In addition, circRNAs can bind to RNA binding proteins to regulate gene expression. Based on characteristics of stability, expression specificity and participation in gene regulation, circRNAs are expected to be biomarkers for early diagnosis of cancer or potential targets for cancer therapy. With the help of bioinformatics analysis, circRNA microarray analysis and high-throughput sequencing technology, more circRNAs were discovered to participate in the progression of gastric cancer (GC) over the past three years. This article gives an overview of these recent research focusing on the roles of circRNAs in GC and highlights the advances.