Circular RNA hsa_circ_0001982 Promotes Breast Cancer Cell Carcinogenesis Through Decreasing miR-143

Ferroptosis contributes to the progression of female-specific neoplasms, from breast cancer to gynecological malignancies in a manner regulated by non-coding RNAs: Mechanistic implications

Ferroptosis, a recently identified type of non-apoptotic cell death, triggers the elimination of cells in the presence of lipid peroxidation and in an iron-dependent manner. Indeed, ferroptosis-stimulating factors have the ability of suppressing antioxidant capacity, leading to the accumulation of reactive oxygen species (ROS) and the subsequent oxidative death of the cells. Ferroptosis is involved in the pathophysiological basis of different maladies, such as multiple cancers, among which female-oriented malignancies have attracted much attention in recent years. In this context, it has also been unveiled that non-coding RNA transcripts, including microRNAs, long non-coding RNAs, and circular RNAs have regulatory interconnections with the ferroptotic flux, which controls the pathogenic development of diseases. Furthermore, the potential of employing these RNA transcripts as therapeutic targets during the onset of female-specific neoplasms to modulate ferroptosis has become a research hotspot; however, the molecular mechanisms and functional alterations of ferroptosis still require further investigation. The current review comprehensively highlights ferroptosis and its association with non-coding RNAs with a focus on how this crosstalk affects the pathogenesis of female-oriented malignancies, from breast cancer to ovarian, cervical, and endometrial neoplasms, suggesting novel therapeutic targets to decelerate and even block the expansion and development of these tumors.

Role of circRNAs in regulating cell death in cancer: a comprehensive review

Despite multiple diagnostic and therapeutic advances, including surgery, radiation therapy, and chemotherapy, cancer preserved its spot as a global health concern. Prompt cancer diagnosis, treatment, and prognosis depend on the discovery of new biomarkers and therapeutic strategies. Circular RNAs (circRNAs) are considered as a stable, conserved, abundant, and varied group of RNA molecules that perform multiple roles such as gene regulation. There is evidence that circRNAs interact with RNA-binding proteins, especially capturing miRNAs. An extensive amount of research has presented the substantial contribution of circRNAs in various types of cancer. To fully understand the linkage between circRNAs and cancer growth as a consequence of various cell death processes, including autophagy, ferroptosis, and apoptosis, more research is necessary. The expression of circRNAs could be controlled to limit the occurrence and growth of cancer, providing a more encouraging method of cancer treatment. Consequently, it is critical to understand how circRNAs affect various forms of cancer cell death and evaluate whether circRNAs could be used as targets to induce tumor death and increase the efficacy of chemotherapy. The current study aims to review and comprehend the effects that circular RNAs exert on cell apoptosis, autophagy, and ferroptosis in cancer to investigate potential cancer treatment targets.

Circular RNAs as a novel molecular mechanism in diagnosis, prognosis, therapeutic target, and inhibiting chemoresistance in breast cancer

Breast cancer (BC) is the most common cancer among women, characterized by significant heterogeneity. Diagnosis of the disease in the early stages and appropriate treatment plays a crucial role for these patients. Despite the available treatments, many patients due to drug resistance do not receive proper treatments. Recently, circular RNAs (circRNAs), a type of non-coding RNAs (ncRNAs), have been discovered to be involved in the progression and resistance to drugs in BC. CircRNAs can promote or inhibit malignant cells by their function. Numerous circRNAs have been discovered to be involved in the proliferation, invasion, and migration of tumor cells, as well as the progression, pathogenesis, tumor metastasis, and drug resistance of BC. Circular RNAs can also serve as a biomarker for diagnosing, predicting prognosis, and targeting therapy. In this review, we present an outline of the variations in circRNAs expression in various BCs, the functional pathways, their impact on the condition, and their uses in clinical applications.

Circ_0001982 aggravates breast cancer development through the circ_0001982-miR-144-3p-GSE1 axis

This study was designed to explore the role of circ_0001982 in breast cancer (BC) development. Quantitative real-time polymerase chain reaction and western blot analysis assays were used to determine circ_0001982, miR-144-3p, and gse1 coiled-coil protein (GSE1) expression. Functional assays were performed to evaluate cell proliferation, apoptosis, migration, and invasion. The glycolysis was analyzed with commercial kits. Dual-luciferase reporter assay and RNA immunoprecipitation assays were conducted to analyze the relationships among circ_0001982, miR-144-3p, and GSE1. A murine xenograft model assay was performed to determine circ_0001982-induced effects on BC cell tumor properties in vivo. Circ_0001982 expression was upregulated, but miR-144-3p was reduced in BC tissues and cells in comparison with normal breast tissues and normal human mammary epithelial cells. Circ_0001982 knockdown or miR-144-3p overexpression inhibited BC cell proliferation, glycolysis, migration and invasion, and promoted apoptosis. Circ_0001982 sponged miR-144-3p and negatively regulated miR-144-3p expression in BC cells. In addition, GSE1 was identified as a target mRNA of miR-144-3p. Ectopic GSE1 expression relieved circ_0001982 depletion-induced effects on BC cell tumor properties. Furthermore, circ_0001982 absence suppressed BC cell tumor properties in vivo. Circ_0001982 contributed to the BC cell tumor properties by regulating the miR-144-3p-GSE1 axis.

CircRNF111 Contributes to Adipocyte Differentiation by Elevating PPARγ Expression via miR-27a-3p

The content and distribution of adipocytes is an important factor that affects meat quality. Previous studies showed that circRNAs are involved in various physiological processes. Nevertheless, more research is needed to investigate the function of circRNAs in adipogenesis. The present study examines the effects of circRNF111 on adipogenesis of bovine preadipocyte and aims to elucidate the underlying molecular mechanisms. In our study, the sequence signature of circRNF111 was identified using bioinformatics, RNA-FISH, and sequencing. Mechanistically, knockdown or exogenous expression of circRNF111 in preadipocytes was done to prove the functional significance of circRNF111. Combined with bioinformatics, a dual fluorescein reporter system, and immunoprecipitation, the interaction between circRNF111, miR-27a-3p, and the target gene PPARγ was verified. The results reveal that circRNF111 is positively correlated with adipocyte differentiation. The newly identified bovine circRNF111 functions as a miR-27a-3p sponge to rescue the inhibitory effect of miR-27a-3p on the PPARγ gene, thereby promoting adipogenesis.

Induction of perineural invasion in salivary adenoid cystic carcinoma by circular RNA RNF111

OBJECTIVE

Local recurrence, distant metastasis, and perineural invasion (PNI) viciously occur in salivary adenoid cystic carcinoma (SACC), resulting in a poor prognosis. This study aimed to explore the mechanism by which circular RNA RNF111 (circ-RNF111) regulates PNI in SACC by targeting the miR-361-5p/high mobility group box 2 (HMGB2) axis.

METHOD

Circ-RNF111 and HMGB2 were highly expressed in SACC specimens, while miR-361-5p was underexpressed. Functional experiments showed that ablating circ-RNF111 or promoting miR-361-5p hindered the biological functions and PNI of SACC-LM cells.

RESULTS

HMGB2 overexpression induced the reversal of SACC-LM cell biological functions and PNI caused by circ-RNF111 knockout. Furthermore, reduction of circ-RNF111 suppressed PNI in a SACC xenograft model. Circ-RNF111 regulated HMGB2 expression through targeted modulation of miR-361-5p.

CONCLUSION

Taken together, circ-RNF111 stimulates PNI in SACC by miR-361-5p/HMGB2 axis and may serve as a potential therapeutic target for SACC.

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

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

Knockdown of circADAM9 inhibits cell progression and glycolysis by targeting the miR-1236-3p/FGF7 axis in breast cancer

BACKGROUND

Circular RNAs (circRNAs) are closely associated with the development of breast cancer (BC). In this study, we aimed to clarify how differentially expressed circRNAs affect the development of BC.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression of circADAM9, miR-1236-3p and fibroblast growth factor 7 (FGF7). Colony formation, 5-ethynyl-2'-deoxyuridine (EdU), wound healing, transwell, and flow cytometry were used to assess cell proliferation, migration, invasion, and apoptosis. Glucose consumption, lactic acid production and ATP levels were assessed using glycolysis metabolism analysis. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were carried out to verify the relationship between miR-1236-3p and circADAM9 or FGF7. The roles of cirADAM9 on tumor growth were analyzed using a xenograft tumor model. Ki-67 and FGF7 expression was measured via immunohistochemistry (IHC) assay. Apoptosis-related proteins and exosome markers were detected by western blot.

RESULTS

CircADAM9 was highly expressed in BC cells, and circADAM9 silencing inhibited BC cell proliferation, migration, invasion, and glycolysis, and promoted cell apoptosis. Furthermore, miR-1236-3p inhibition could overturn circADAM9 knockdown-mediated BC inhibition. Moreover, the negative influences of miR-1236-3p overexpression on BC progression were restrained via FGF7 overexpression. CircADAM9 silence also inhibited BC tumor growth in vivo.

CONCLUSION

CircADAM9 promoted BC development partly by the miR-1236-3p/FGF7 axis, highlighting a potential prognostic biomarker and therapeutic target for BC patients.

Therapeutic and diagnostic applications of exosomal circRNAs in breast cancer

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

Identification and Characterization of circRNAs in Non-Lactating Dairy Goat Mammary Glands Reveal Their Regulatory Role in Mammary Cell Involution and Remodeling

This study conducted transcriptome sequencing of goat-mammary-gland tissue at the late lactation (LL), dry period (DP), and late gestation (LG) stages to reveal the expression characteristics and molecular functions of circRNAs during mammary involution. A total of 11,756 circRNAs were identified in this study, of which 2528 circRNAs were expressed in all three stages. The number of exonic circRNAs was the largest, and the least identified circRNAs were antisense circRNAs. circRNA source gene analysis found that 9282 circRNAs were derived from 3889 genes, and 127 circRNAs' source genes were unknown. Gene Ontology (GO) terms, such as histone modification, regulation of GTPase activity, and establishment or maintenance of cell polarity, were significantly enriched (FDR < 0.05), which indicates the functional diversity of circRNAs' source genes. A total of 218 differentially expressed circRNAs were identified during the non-lactation period. The number of specifically expressed circRNAs was the highest in the DP and the lowest in LL stages. These indicated temporal specificity of circRNA expression in mammary gland tissues at different developmental stages. In addition, this study also constructed circRNA-miRNA-mRNA competitive endogenous RNA (ceRNA) regulatory networks related to mammary development, immunity, substance metabolism, and apoptosis. These findings help understand the regulatory role of circRNAs in mammary cell involution and remodeling.

Hypoxia-circular RNA crosstalk to promote breast cancer

The expression of hypoxia-inducible factors (HIFs), particularly HIF-1, plays a major role in the adaptation of solid tumors to hypoxic conditions. The activation of the HIF pathway results in an expression of genes involved in the promotion of cell growth, proliferation, vascularization, metastasis, and therapeutic resistance. Circular RNA (CircRNA) is considered as a major regulator of gene expression. CircRNAs could regulate the HIF-1 pathway in cancer cells. In addition, they might be regulated by the HIF-1 pathway to promote cancer progression. Therefore, the crosstalk between hypoxia and circRNA might be involved in the pathogenesis of cancers, including breast cancer. In this review, we discussed the function of HIF-related circRNAs in the progression, angiogenesis, metabolic reprogramming, and stemness maintenance of breast cancer. In addition, the correlation between HIF-related circRNAs and clinical features of breast cancer is reviewed.

Circ_0001982 Up-regulates the Expression of E2F1 by Adsorbing miR-1205 to Facilitate the Progression of Glioma

This study was aimed at probing into the regulatory effects of circular RNA (circRNA)_0001982 on glioma cell proliferation, migration, invasion, and cell cycle, and its underlying mechanism. CircRNA expression profile of glioma tissues/normal brain tissues was downloaded from the Gene Expression Omnibus (GEO) database and analyzed. Circ_0001982, microRNA (miRNA, miR)-1205, and E2F transcription factor 1 (E2F1) expressions in glioma tissues and cell lines were quantified using quantitative real-time polymerase chain reaction (qRT-PCR) and/or Western blot. Glioma cell proliferation, migration, invasion, and cell cycle were detected employing cell counting kit-8 (CCK-8), 5-Ethynyl-2'-deoxyuridine (EdU), scratch-healing, Transwell, and flow cytometry assays, respectively. The targeting relationships between miR-1205 and circ_0001982, and miR-1205 and E2F1 3'UTR were verified using bioinformatics, dual-luciferase reporter experiments, and RNA immunoprecipitation (RIP) assay. Pearson's correlation analysis was applied to detect the correlations among circ_0001982, miR-1205, and E2F1 expression levels. Circ_0001982 expression level was increased in glioma tissues and correlated with larger tumor size. Circ_0001982 overexpression enhanced glioma cell proliferation, migration, and invasion, and accelerated cell cycle progression while knocking down circ_0001982 exerted opposite effects. Circ_0001982 directly targeted miR-1205, and miR-1205 directly targeted E2F1. Besides, circ_0001982 could up-regulate E2F1 expression via repressing miR-1205 expression. Circ_0001982 accelerates glioma progression by modulating the miR-1205/E2F1 axis.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

Advances in high-throughput sequencing techniques and bioinformatic analysis have refuted the "junk" RNA hypothesis that was claimed against non-coding RNAs (ncRNAs). Circular RNAs (circRNAs); a class of single-stranded covalently closed loop RNA molecules have recently emerged as stable epigenetic regulators. Although the exact regulatory role of circRNAs is still to be clarified, it has been proven that circRNAs could exert their functions by interacting with other ncRNAs or proteins in their own physiologically authentic environment, regulating multiple cellular signaling pathways and other classes of ncRNAs. CircRNAs have also been reported to exhibit a tissue-specific expression and have been associated with the malignant transformation process of several hematological and solid malignancies. Along this line of reasoning, this review aims to highlight the importance of circRNAs in Breast Cancer (BC), which is ranked as the most prevalent malignancy among females. Notwithstanding the substantial efforts to develop a suitable anticancer therapeutic regimen against the heterogenous BC, inter- and intra-tumoral heterogeneity have resulted in an arduous challenge for drug development research, which in turn necessitates the investigation of other markers to be therapeutically targeted. Herein, the potential of circRNAs as possible diagnostic and prognostic biomarkers have been highlighted together with their possible application as novel therapeutic targets.

hsa-mir-133a-2 promotes the proliferation and invasion of cervical cancer cells by targeting the LAMB3-mediated PI3K/ATK pathway

OBJECTIVE

Cervical cancer, one of the common types of malignant tumors progressed in women, is on the rise in developing countries. Numerous previous studies have demonstrated that hsa-mir-133a-2 miRNA is abnormally expressed in cervical cancer cells. However, its fundamental mechanism in cervical cancer needs to be further clarified. Our study set out to investigate the effect of hsa-mir-133a-2 on the phenotypes of cervical cancer cells as well as any potential molecular processes involved in the proliferation and invasion of cervical cancer cells.

METHODS

The Cancer Genome Atlas-cervical squamous cell carcinoma and endocervical adenocarcinoma(TCGA-CESC) was adopted in order to verify the expression of hsa-mir-133a-2 in cervical cancer tissues and to identify its potential targets. The interaction between Laminin subunit beta-3(LAMB3) and hsa-mir-133a-2 was verified by TargetScan database as well as Luciferase reporter assay. The Cell Counting Kit-8 (CCK8) and transwell methods were utilized to assess the influence of hsa-mir-133a-2 on the proliferation and invasion characteristics of cervical cancer cells. We studied the role that hsa-mir-133a-2 plays in cervical cancer progression through Kyoto Encyclopedia of Genes and Genomes(KEGG) analysis as well as Western Blot (WB) experiment.

RESULTS

Down-regulation of hsa-mir-133a-2 was detected in cervical cancer tissues. It directly targeted LAMB3 and negatively regulated LAMB3 expression. The overexpression of hsa-mir-133a-2 has a significant inhibiting effect on cervical cancer cell proliferation and invasion. The overexpression of hsa-mir-133a-2 significantly inhibits the proliferation and invasion of cervical cancer cells. Moreover, the LAMB3 was able to up-regulate the phosphorylation levels of AKT and phosphatidylinositol 3-kinase (PI3K) protein in cervical cancer cells. hsa-mir-133a-2 could also modulate the PI3K/AKT signaling pathway by targeting LAMB3.

CONCLUSION

hsa-mir-133a-2 inhibits cervical cancer cell proliferation and invasion by indirectly regulating the PI3K/AKT signaling pathway, providing us with a new clinical treatment strategy for cervical cancer.

Exosomal circular RNAs: New player in breast cancer progression and therapeutic targets

Breast cancer is the most prevalent type of malignancy among women. Exosomes are extracellular vesicles of cell membrane origin that are released via exocytosis. Their cargo contains lipids, proteins, DNA, and different forms of RNA, including circular RNAs. Circular RNAs are new class of non-coding RNAs with a closed-loop shape involved in several types of cancer, including breast cancer. Exosomes contained a lot of circRNAs which are called exosomal circRNAs. By interfering with several biological pathways, exosomal circRNAs can have either a proliferative or suppressive role in cancer. The involvement of exosomal circRNAs in breast cancer has been studied with consideration to tumor development and progression as well as its effects on therapeutic resistance. However, its exact mechanism is still unclear, and there have not been available clinical implications of exo-circRNAs in breast cancer. Here, we highlight the role of exosomal circRNAs in breast cancer progression and to highlight the most recent development and potential of circRNAas therapeutic targets and diagnostics for breast cancer.

circKLHL24 Blocks Breast Cancer Development by Regulating the miR-1204/ALX4 Network

Background: Breast cancer is a major challenge affecting women's survival. Circular RNAs have been demonstrated to be vital regulators in the pathogenesis of human cancers. The authors' objective was to determine the functional role and mechanism of circKLHL24 in breast cancer development. Materials and Methods: The expression of circKLHL24, miR-1204, and aristaless-like 4 (ALX4) mRNA was measured using quantitative real-time polymerase chain reaction. The effects on cell viability, proliferation, migration/invasion, and glycolysis were identified using the Cell Counting Kit-8 (CCK-8) assay, colony formation assay, Transwell assay, and glycolysis stress test, respectively. For glycolysis progression analysis, glucose consumption and lactate production were assessed using corresponding kits, and the expression of glycolysis-related proteins was detected by Western blot. The putative interactions between miR-1204 and circKLHL24 or ALX4 were validated by dual-luciferase reporter assay or RNA pull-down assay. The expression of ALX4 at the protein level was detected by Western blot. Animal study was performed to clarify the role of circKLHL24 in vivo. Results: circKLHL24 and ALX4 were downregulated, while miR-1204 was upregulated in breast cancer tissues and cells. circKLHL24 overexpression blocked cell viability, colony formation, migration/invasion, and glycolysis progression. circKLHL24 competitively targeted miR-1204, and miR-1204 reintroduction reversed the effects of circKLHL24 restoration. miR-1204 bound to ALX4, and circKLHL24 sponged miR-1204 to upregulate ALX4. Cell viability, colony formation, migration/invasion, and glycolysis progression suppressed by miR-1204 deficiency were recovered by ALX4 knockdown. Besides, circKLHL24 blocked tumor growth in vivo by regulating miR-1204 and ALX4. Conclusions: circKLHL24 blocked the progression of breast cancer by activating ALX4 through targeting miR-1204, which might be a novel perspective to understand the pathogenesis of breast cancer.

CircPDSS1 promotes the proliferation, invasion, migration, and EMT of breast cancer cell via regulating miR-320c/CKAP5 axis

Background

Breast cancer (BC) poses serious threats to women’s health. A large number of reports have proved that circular RNAs (circRNAs) exert vital functions in human cancers, including BC.

Methods

The function of circPDSS1 in BC cells was tested by CCK-8, colony formation, TUNEL, transwell-invasion, wound healing, and IF assays. RNA pull down, luciferase reporter and RIP assays were employed to verify the relationship among circPDSS1, miR-320c and CKAP5.

Results

CircPDSS1 was upregulated in BC cells, and circPDSS1 knockdown repressed BC cell malignant behaviors. Further, circPDSS1 was found to bind to miR-320c in BC cells, and miR-320c overexpression suppressed malignant processes of BC cells. MiR-320c could also bind to CKAP5. Moreover, miR-320c inhibition increased the level of CKAP5, but circPDSS1 downregulation decreased the level of CKAP5. Finally, rescue experiments indicated that CKAP5 knockdown countervailed the promoting effect of miR-320c inhibition on the malignant behaviors of circPDSS1-depleted BC cells.

Conclusions

CircPDSS1 promotes proliferation, invasion, migration as well as EMT of BC cells by modulating miR-320c/CKAP5 axis. Our finding may be useful for researchers to find new potential therapeutic or diagnostic targets for BC.

Hsa_circ_0001982 promotes the proliferation, invasion, and multidrug resistance of osteosarcoma cells

Background

Osteosarcoma (OS) is the most common bone cancer mostly seen in people aged 10–25 years. This research aims to clarify the function of hsa_circ_0001982 in osteosarcoma (OS) and its effect on drug resistance, preliminarily exploring its mechanism.

Methods

The expression of hsa_circ_0001982 and miR‐143 in OS clinical tissues and cells was detected by real‐time fluorescence quantitative polymerase chain reaction (qRT‐PCR), MTT, colony formation assay, and transwell assay assessed cell proliferation, colony formation, migration, and invasion, respectively. The targeted relationship of hsa_circ_0001982 and miR‐143 was verified by a dual‐luciferase reporter assay.

Result

The expression of hsa_circ_0001982 was significantly increased in OS tissues and cells (MG63), as in well as chemoresistant OS tissues and cells (MG63/Dox). Overexpression of hsa_circ_0001982 promoted proliferation, colony formation, migration, invasion, and multidrug resistance in MG63 cells. By contrast, knockdown of hsa_circ_0001982 markedly reduced the resistance of MG63/Dox cells to doxorubicin (IC50 evidently reduced). Bioinformatic prediction showed that miR‐143 was a target miRNA of hsa_circ_0001982, and a dual‐luciferase reporter assay proved this. Further experiments revealed that miR‐143 expression was notably downregulated in OS tissues, chemoresistant OS tissues, and MG63/Dox cells. Moreover, miR‐143 was negatively correlated with hsa_circ_0001982 in OS cells and tissues.

Conclusion

The regulation of malignant behaviors such as proliferation, invasion, migration, and multidrug resistance of OS cells by hsa_circ_0001982 may be achieved by targeting miR‐143. Moreover, hsa_circ_0001982 is a potential target for early diagnosis and targeted therapy of OS.

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

CircRNA_0044556 diminishes the sensitivity of triple‑negative breast cancer cells to adriamycin by sponging miR‑145 and regulating NRAS

CircRNAs are associated with adriamycin (ADM) resistance in triple‑negative breast cancer (TNBC), but the mechanism is unknown. Reverse transcription‑quantitative PCR was applied to quantify circular RNA (circRNA)_0044556, microRNA (miR)‑145 and NRAS proto‑oncogene, GTPase (NRAS) in TNBC tissues and cells with or without ADM treatment. Following ADM treatment, the effects of circRNA_0044556 on the viability, ADM resistance, apoptosis and migration of TNBC cells were investigated by cell function experiments (Cell Counting Kit‑8, flow cytometry and Transwell assays). The targeting relationship between circRNA_0044556 and miR‑145 was investigated via bioinformatics analysis, dual‑luciferase reporter assay and RNA immunoprecipitation. The effects of the circRNA_0044556/miR‑145 axis on the TNBC cells were revealed by rescue experiments. Correlations among circRNA_0044556, miR‑145 and NRAS were analyzed by Pearson's correlation test. CircRNA_0044556 was highly expressed in TNBC tissues and cells with or without ADM‑resistance. The overexpression of circRNA_0044556 promoted cell viability, ADM‑resistance and migration, while inhibiting the apoptosis by sponging miR‑145. Upregulation of miR‑145 reversed the effects of circRNA_0044556 on the TNBC cells. CircRNA_0044556 was negatively correlated with miR‑145 yet positively correlated with NRAS, the target gene of miR‑145, in addition to the discovery suggesting the negative regulatory effects of circRNA_0044556 on miR‑145. CircRNA_0044556 diminished the sensitivity of TNBC cells to ADM via the miR‑145/NRAS axis.

Circ-DONSON Knockdown Inhibits Cell Proliferation and Radioresistance of Breast Cancer Cells via Regulating SOX4

Background

Circular RNAs have been validated as critical regulators in the development of breast cancer (BC). Circ-DONSON is involved in the progression of glioma and gastric cancer. However, the biological role of circ-DONSON in BC remains unclear, and the aim of this study was to explore the biological role of circ-DONSON in BC.

Methods

Human tissue samples and BC cell lines were collected in this study. siRNAs against circ-DONSON were transfected into BC cell lines for silencing of circ-DONSON. Quantitative real-time PCR was used to test the circ-DONSON expression. Cell counting kit-8 (CCK-8), 5-bromo-2' deoxyuridine enzyme-linked immunosorbent assay (BrdU-ELISA), colony formation, and caspase-3 activity assays were used to assess cell proliferation, cell survival, and cell viability. Western blotting analysis was used to detect the protein expression levels.

Results

Our findings showed that circ-DONSON showed high expression in BC tissues and cell lines. CCK-8 and BrdU-ELISA assays showed that circ-DONSON knockdown inhibited BC cell proliferation. Moreover, cell survival, cell viability, and caspase-3 activity assays showed that circ-DONSON knockdown reduced the radioresistance of BC cells. Mechanistically, circ-DONSON regulated BC cell proliferation and radioresistance via SRY-box transcription factor 4 (SOX4). SOX4 overexpression significantly rescued the effect of circ-DONSON knockdown on BC cell proliferation and radioresistance. Moreover, circ-DONSON activated the Wnt/β-catenin pathway in BC cells via SOX4.

Conclusion

Our study concluded that circ-DONSON knockdown hindered cell proliferation and radioresistance through the SOX4/Wnt/β-catenin pathway in BC.

CircARL8B Contributes to the Development of Breast Cancer Via Regulating miR-653-5p/HMGA2 Axis

Circular RNAs (circRNAs) act as essential regulators in breast cancer (BC) progression. In this paper, we aimed to investigate the functions of circARL8B in BC. The levels of circARL8B, ADP Ribosylation Factor Like GTPase 8B (ARL8B), miR-653-5p and high-mobility group AT-hook 2 (HMGA2) mRNA were examined by qRT-PCR. The stability of circARL8B was determined by RNase R assay and Actinomycin D assay. Cell viability and metastasis were evaluated by Cell Counting Kit-8 (CCK-8) assay and transwell assay, respectively. The levels of cellular phospholipids and triglycerides were measured using relevant kits. Protein levels were measured by western blot analysis. The association between miR-653-5p and circARL8B or HMGA2 was verified by dual-luciferase reporter assay. A murine xenograft model was established to explore the function of circARL8B in vivo. CircARL8B was increased in BC tissues and cells. CircARL8B silencing inhibited cell viability, migration, invasion and fatty acid metabolism in BC cells in vitro and blocked tumor growth in vivo. MiR-653-5p was identified as the target of circARL8B and miR-653-5p was negatively modulated by circARL8B. The suppressive role of circARL8B silencing in BC cell progression was abolished by miR-653-5p downregulation. Moreover, HMGA2 was the target gene of miR-653-5p. HMGA2 overexpression abrogated the effect of miR-653-5p on BC cell development. In addition, circARL8B knockdown might block PGE2/PI3K/AKT/GSK-3β/Wnt/β-catenin pathway. Silencing of circARL8B inhibited cell viability, migration, invasion and fatty acid metabolism via miR-653-5p/HMGA2 axis in BC.

Circular RNAs and complex diseases: from experimental results to computational models

Circular RNAs (circRNAs) are a class of single-stranded, covalently closed RNA molecules with a variety of biological functions. Studies have shown that circRNAs are involved in a variety of biological processes and play an important role in the development of various complex diseases, so the identification of circRNA-disease associations would contribute to the diagnosis and treatment of diseases. In this review, we summarize the discovery, classifications and functions of circRNAs and introduce four important diseases associated with circRNAs. Then, we list some significant and publicly accessible databases containing comprehensive annotation resources of circRNAs and experimentally validated circRNA-disease associations. Next, we introduce some state-of-the-art computational models for predicting novel circRNA-disease associations and divide them into two categories, namely network algorithm-based and machine learning-based models. Subsequently, several evaluation methods of prediction performance of these computational models are summarized. Finally, we analyze the advantages and disadvantages of different types of computational models and provide some suggestions to promote the development of circRNA-disease association identification from the perspective of the construction of new computational models and the accumulation of circRNA-related data.

CircRNAs: Insights into Gastric Cancer

Background

Gastric cancer (GC) is recorded as the fifth most common cancer globally. The classic resemblance of early symptoms of chronic gastritis including nausea, dysphagia, and dyspepsia with GC is the current challenge limiting the early diagnosis of GC. The current diagnostic procedures of GC are limited due to their invasive nature. This directs the research question toward alternative approaches, specifically at the molecular level. Recent advances in molecular regulation of cancer suggest the prominence of circular RNAs (circRNAs) in the multistep process of tumourigenesis.

Summary

CircRNAs are a class of non-coding RNAs, abundant in eukaryotes, with key roles in regulating genes and miRNAs as well as the alteration of processes involved in pathological conditions. Research studies have demonstrated the participation of circRNAs in the initiation and progression of tumours. This review provides a comprehensive insight into the potential of circRNAs as disease biomarkers for the early detection and treatment of GC.

Key Messages

This study is an amalgamation of the implications and future prospects of circRNAs for the detection and potential treatment of GC.

circ_0000467 promotes the proliferation, metastasis, and angiogenesis in colorectal cancer cells through regulating KLF12 expression by sponging miR-4766-5p

Background

Circular RNAs have been identified as crucial players in the initiation and progression of cancers, including colorectal cancer (CRC). The Has_circ_0000467 (circ_0000467) expression has been found to be upregulated in CRC, but its function and mechanism remain unclear.

Methods

The expression levels of circ_0000467, microRNA-4766-5p (miR-4766-5p), and Krueppel-like factor 12 (KLF12) were examined using reverse transcription-quantitative polymerase chain reaction. Cell proliferation was analyzed by cell counting kit-8 assay and colony formation assay. The apoptosis was measured by flow cytometry. Transwell migration and invasion assays were applied to evaluate cell metastatic ability. Angiogenesis was detected using tube formation assay. All protein expressions were quantified by western blot assay. Dual-luciferase reporter assay was used to analyze intergenic binding. Xenograft models were constructed for the experiment of circ_0000467 in vivo.

Results

The expression of circ_0000467 was upregulated in CRC tissues and cells. Knockdown of circ_0000467 repressed cell proliferation, metastasis, and angiogenesis, but it induced apoptosis in CRC cells. circ_0000467 targeted miR-4766-5p and inhibited the expression of miR-4766-5p. Silencing of circ_0000467 inhibited CRC progression by upregulating miR-4766-5p. miR-4766-5p suppressed the expression of target gene KLF12 and KLF12 overexpression reversed the effects of miR-4766-5p on CRC cell behaviors. circ_0000467 positively regulated the expression of KLF12 by targeting miR-4766-5p. circ_0000467 downregulation in vivo reduced CRC tumorigenesis by regulating miR-4766-5p and KLF12.

Conclusion

circ_0000467 acted as an oncogene in CRC through regulating KLF12 expression by sponging miR-4766-5p. Therefore, circ_0000467 can be used as an effective target in CRC diagnosis and therapy.

Serum Circ-FAF1/Circ-ELP3: A novel potential biomarker for breast cancer diagnosis

Background

Recently, measurement of serum circular RNAs (circRNAs) as a non‐invasive tumor marker has been considered more. We designed the present study to investigate the diagnostic efficiency of serum Circ‐ELP3 and Circ‐FAF1, separately and simultaneously, for diagnosis of patients with breast cancer.

Methods

Seventy‐eight female patients diagnosed as primary breast cancer participated in this study. We measured the level of circRNAs in serum specimens of the studied subjects. A receiver operating characteristic (ROC) curve was plotted and the diagnostic efficiency for both circRNAs was determined.

Results

Compared to non‐cancerous controls, Circ‐ELP3 was upregulated in breast cancer patients (p‐value = 0.004). On the other hand, serum Circ‐FAF1 was seen to be decreased in breast cancer patients than controls (p‐value = 0.001). According to ROC curve results, the area under the curve (AUC) for Circ‐ELP3 and Circ‐FAF1 was 0.733 and 0.787, respectively. Furthermore, the calculated sensitivity and specificity for Circ‐ELP3 and Circ‐FAF1 were 65, 64% and 77, 74%, respectively. Merging both circRNAs increased the diagnostic efficiency, with a better AUC, sensitivity and specificity values of 0.891, 96 and 62%, respectively.

Conclusion

Briefly, our results revealed the high diagnostic value for combined circRNAs panel, including Circ‐ELP3 and Circ‐FAF1 as a non‐invasive marker, in detection of breast carcinomas.

Circ-RPPH1 knockdown retards breast cancer progression via miR-328-3p-mediated suppression of HMGA2

BACKGROUND

Circular RNA Ribonuclease P RNA Component H1 (circ-RPPH1) was confirmed to act as an oncogene in many cancers to promote cancer progression. However, the exact function and mechanism of circ-RPPH1 in breast cancer (BC) remain vague.

METHODS

The expression of circ-RPPH1, microRNA (miR)-328-3p and high-mobility group AT-hook 2 (HMGA2) was detected using quantitative real-time polymerase chain reaction and western blot. Cell viability, apoptosis, migration and invasion were determined using cell counting kit-8 assay, flow cytometry and transwell assay, respectively. Glucose metabolism was calculated by detecting glucose uptake and lactate production. The target correlations between miR-328-3p and circ-RPPH1 or HMGA2 were confirmed by dual-luciferase reporter assay. The murine xenograft model was established to conduct in vivo experiments.

RESULTS

Circ-RPPH1 expression was elevated and miR-328-3p was decreased in BC tissues and cells. Circ-RPPH1 knockdown or miR-328-3p re-expression suppressed cell proliferation, migration, invasion and glycolysis but induced apoptosis in BC in vitro. Circ-RPPH1 was a sponge of miR-328-3p, and silencing of miR-328-3p reversed the inhibitory effects of circ-RPPH1 knockdown on BC cell malignant phenotypes and glycolysis. MiR-328-3p directly targeted HMGA2, and HMGA2 overexpression abolished the action of miR-328-3p in BC cells. Besides, circ-RPPH1 could regulate HMGA2 expression by miR-328-3p in BC cells. Moreover, murine xenograft model analysis suggested circ-RPPH1 knockdown inhibited tumor growth in vivo.

CONCLUSION

Circ-RPPH1 knockdown retarded cell malignant phenotypes and glycolysis via miR-328-3p/HMGA2 axis in BC, providing a potential therapeutic target for BC treatment.

Circ-RNF111 aggravates the malignancy of gastric cancer through miR-876-3p-dependent regulation of KLF12

Background

The aberrant expression of circular RNAs (circRNAs) plays vital roles in the advancement of human cancers, including gastric cancer (GC). In this study, the functions of circRNA ring finger protein 111 (circ-RNF111) in GC were investigated.

Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed for the levels of circ-RNF111, microRNA-876-3p (miR-876-3p) and krueppel-like factor 12 (KLF12) mRNA. RNase R assay was conducted for the feature of circ-RNF111. Cell Counting Kit-8 (CCK-8) assay, colony formation assay, wound-healing assay, and transwell assay were applied for cell viability, colony formation, migration, and invasion, respectively. Flow cytometry analysis was used to analyze cell apoptosis and cell cycle process. The glycolysis level was examined using specific commercial kits. Western blot assay was carried out to measure the protein levels of hexokinase 2 (HK-2) and KLF12. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were employed to verify the combination between miR-876-3p and circ-RNF111 or KLF12. Murine xenograft model was constructed for the role of circ-RNF111 in vivo. Immunohistochemistry (IHC) was used for KLF12 level.

Results

Circ-RNF111 was higher expressed in GC tissues and cells than normal tissues and cells. Silencing of circ-RNF111 restrained cell viability, colony formation, migration, invasion, cell cycle process and glycolysis and induced apoptosis in GC cells in vitro. Circ-RNF111 positively regulated KLF12 expression via absorbing miR-876-3p. MiR-876-3p downregulation reversed the impacts of circ-RNF111 silencing on GC cell malignant phenotypes. MiR-876-3p overexpression repressed GC cell growth, metastasis and glycolysis, inhibited apoptosis and arrested cell cycle, while KLF12 elevation weakened the effects. Besides, circ-RNF111 knockdown inhibited tumor growth in vivo.

Conclusion

Circ-RNF111 knockdown relieved the development of GC by regulating miR-876-3p/KLF12 axis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12957-021-02373-5.

Characteristics of circRNA and its approach as diagnostic tool in melanoma

One of the most common types of cancer in the world is skin cancer, which has been divided into two groups: non-melanoma and melanoma skin cancer. Different external and internal agents are considered as risk factors for melanoma skin cancer pathogenesis but the exact mechanisms are not yet confirmed. Genetic and epigenetic changes, UV exposure, arsenic compounds, and chemical substances are contributory factors to the development of melanoma. A correlation has emerged between new therapies and the discovery of a basic molecular pattern for skin cancer patients. Circular RNAs (circRNAs) are described as a unique group of extensively expressed endogenous regulatory RNAs with closed-loop structure bonds connecting the 5' and 3' ends, which are commonly expressed in mammalian cells. In this review, we describe the biogenesis of circular RNAs and its function in cancerous conditions focusing on the crosstalk between different circRNAs and melanoma. Increasing evidence suggests that circRNAs appears to be relative to the origin and development of skin-related diseases like malignant melanoma. Different circular RNAs like hsa_circ_0025039, hsa_circRNA006612, circRNA005537, and circANRIL, by targeting different cellular and molecular targets (e.g., CDK4, DAB2IP, ZEB1, miR-889, and let-7 c-3p), can participate in melanoma cancer progression.

Knockdown circ_0040414 inhibits inflammation, apoptosis and promotes the proliferation of cardiomyocytes via miR-186-5p/PTEN/AKT axis in chronic heart failure

Previous studies have shown that circ_0040414 is highly expressed in the blood of patients with heart failure (HF), which suggests that circ_0040414 is associated with heart failure (HF). However, the functional involvement of circ_0040414 in HF and its potential mechanism remains unclear. Consistent with previous studies, our study showed that the expression of circ_0040414 in the peripheral blood of patients with chronic heart failure (CHF) was significantly higher than that of healthy control, which indicated that circ_0040414 could be used as a diagnostic biomarker in patients with CHF. In cardiomyocytes, circ_0040414 increased the level of proapoptotic proteins Bax, cleaved-caspase 3 and reduced the expression of antiapoptotic protein Bcl-2. It also promoted inflammatory factors IL-6, TNF-α, and IL-β, but inhibited cell proliferation. In terms of mechanism, circ_0040414 upregulated the expression of phosphatase and tensin homolog (PTEN) through sponging miR-186-5p to inhibit AKT signaling activity. Our study uncovered a novel role and the mechanism of circ_0040414 in controlling CHF, enriched the molecular regulatory network in CHF, and may provide a possible strategy for the treatment of CHF.

CircRNA circFOXK2 facilitates oncogenesis in breast cancer via IGF2BP3/miR-370 axis

Metastasis is the leading cause of breast cancer (BC)-related deaths. Circular RNAs (circRNAs) have emerged as essential regulators for cancer progression and metastasis. Therefore, the objective of this study was to investigate the role of circRNAs in BC metastasis and related mechanism. In this study, we established the BC cell line with high or low potential of metastasis. RNA sequencing, migration and invasion assay, Fluorescence in situ hybridization, luciferase report assay, circRNA pulldown, and transmission electron microscopy were performed to elucidate the molecular mechanism. The results showed that circRNA circFOXK2 was significantly increased in BC cells with high metastatic ability, and the upregulation of circFOXK2 was correlated with poor clinicopathological characteristics. Functional experiments demonstrated that overexpression of circFOXK2 promoted migration and invasion of BC cells. Also. circFOXK2 could act with IGF2BP3, an RNA-binding protein, and miR-370 to synergistically promote BC metastasis. Moreover, miR-370 could be transferred through exosomes to enhance the metastatic ability of recipient cells. In conclusion, circFOXK2 functions as a key regulator in BC metastasis, and the role of circFOXK2 on BC metastasis is tightly associated with the involvement of IGF2BP3 and miR-370. CircFOXK2 might serve as a potential biomarker for the diagnosis and treatment of BC.

Astragalus IV Undermines Multi-Drug Resistance and Glycolysis of MDA-MB-231/ADR Cell Line by Depressing hsa_circ_0001982-miR-206/miR-613 Axis

Background

Allowing for the power of astragalus in improving cancer patients’ response to chemotherapy, we endeavored to clarify if hsa_circ_0001982-centered miRNA axes participated in the impact of astragaloside IV on multi-drug resistance (MDR) of triple-negative breast cancer (TNBC).

Methods

TNBC patients were recruited into an Astragalus detoxification decoction (ADD) treatment group (N=62) and a non-ADD treatment group (N=78), according to whether they consumed ADD after chemotherapy or not. Furthermore, drug resistance of the MDA-MB-231/ADR cell line in response to gemcitabine (GEM), adriamycin (ADM), oxaliplatin (OXA), and cisplatin (DDP) was evaluated, and glycolytic potential of MDA-MB-231/ADR cells was determined after astragaloside IV treatment or si-hsa_circ_0001982/miR-206 inhibitor/miR-613 inhibitor transfection.

Results

TNBC patients receiving ADD adjuvant therapy after chemotherapy, with decreased serum level of hsa_circ_0001982 and increased serum level of miR-206/miR-613 as relative to non-ADD treatment group (P<0.05), were less likely to relapse than TNBC population not undergoing ADD treatment (P<0.05). In addition, GEM/ADM/OXA/DDP-resistance and glycolysis of MDA-MB-231/ADR cell line were debilitated after exposure to astragaloside IV or transfection by si-hsa_circ_0001982 (P<0.05). Nonetheless, miR-206/miR-613 inhibitor transfection reversed inhibitory effects of si-hsa_circ_0001982 and astragaloside IV on glycolysis and MDR of MDA-MB-231/ADR cell line (P<0.05).

Conclusion

Astragaloside IV undermined MDR and glycolysis of MDA-MB-231/ADR cell line by blocking hsa_circ_0001982-miR-206/miR-613 axis.

Circular RNAs Interaction with MiRNAs: Emerging Roles in Breast Cancer

Despite significant advances in cancer therapy strategies, breast cancer is one of the most common and lethal malignancies worldwide. Characterization of a new class of RNAs using next-generation sequencing opened new doors toward uncovering etiopathogenesis mechanisms of breast cancer as well as prognostic and diagnostic biomarkers. Circular RNAs (circRNAs) are a novel class of RNA with covalently closed and highly stable structures generated primarily from the back-splicing of precursor mRNAs. Although circRNAs exert their function through various mechanisms, acting as a sponge for miRNAs is their primary mechanism of function. Furthermore, growing evidence has shown that aberrant expression of circRNAs is involved in the various hallmarks of cancers. This paper reviews the biogenesis, characteristics, and mechanism of functions of circRNAs and their deregulation in various cancers. Finally, we focused on the circRNAs roles as a sponge for miRNAs in the development, metastasis, angiogenesis, drug resistance, apoptosis, and immune responses of breast cancer.

The Regulation Network and Clinical Significance of Circular RNAs in Breast Cancer

Breast cancer is one of the most common malignant tumors in women worldwide. Circular RNA (circRNA) is a class of structurally stable non-coding RNA with a covalently closed circular structure. In recent years, with the development of high-throughput RNA sequencing, many circRNAs have been discovered and have proven to be clinically significant in the development and progression of breast cancer. Importantly, several regulators of circRNA biogenesis have been discovered. Here, we systematically summarize recent progress regarding the network of regulation governing the biogenesis, degradation, and distribution of circRNAs, and we comprehensively analyze the functions, mechanisms, and clinical significance of circRNA in breast cancer.

Circular RNA hsa_circ_0005046 and hsa_circ_0001791 May Become Diagnostic Biomarkers for Breast Cancer Early Detection

Breast cancer (BC) is one of the most common lethal diseases in women worldwide. Recent evidence has shown that covalently closed Circular RNA (circRNA) deregulation is observed in different human malignancies and cancers. Lately, circRNAs are being considered as a new diagnostic biomarker; however, the mechanism and the correlation of action between circRNAs and BC are still unclear. In the present study, we try to investigate the expression level of hsa_circ_0005046 and hsa_circ_0001791 in BC. By using quantitative real-time polymerase chain reaction (qRT-PCR), expression profiles of candidate circRNAs were detected in 60 BC tissue and paired adjacent normal tissues. Furthermore, the clinicopathological relation and diagnostic value were estimated. Our results showed the higher expression levels of hsa_circ_0005046 and hsa_circ_0001791 in BC tissues compared to paired adjacent normal tissues with P value (P < 0.0001) for both circRNAs, and the area under the receiver operating characteristic (ROC) curve was 0.857 and 1.0, respectively; in addition, a total 10 miRNAs that can be targeted by each candidate circRNAs was predicted base on bioinformatics databases. Taken together, for the first time, the results of our study presented high expression levels of hsa_circ_0005046 and hsa_circ_00017916 in BC; although there was no direct correlation between the high expression level of both circRNAs with clinic pathological factors, except hsa_circ_0001791 association with estrogen receptors (ER), high ROC curve in expressed samples indicated that both circRNAs could be used as a new diagnostic biomarker for BC. Moreover, miRNAs selection tools predicted that miR-215 and mir-383-5p which have a tumor suppressor role in BC can be targeted by our candidate circRNAs to affect the PI3K/AKT pathway; in conclusion, further studies are required to validate the oncogene role of our candidate circRNAs through the PI3k pathway.

Molecular Mechanism of circRAPGEF5 in Regulating the Molecular Axis of microRNA-4712-5p/Tyrosine 3-Monooxygenase/Tryptophan 5-Monooxygenase Activation Protein Epsilon Affecting Cellular Proliferation and Apoptosis in Mammary Cancer

To understand the molecular mechanism of circRAPGEF5, its effect on the proliferation and apoptosis of mammary cancer cells, and its regulatory effect on the molecular axis of miRNA-4712-5p/YWHAE. qRT-PCR and Western blot were used to test circRAPGEF5, miRNA-4712-5p, and YWHAE expression in mammary cancer and paracancerous tissues. The human mammary cancer cell, MDA-MB-231, was cultured in vitro, and pcDNA-NC, pcDNA-circRAPGEF5, anti-miRNA-NC, anti-miRNA-4712-5p, pcDNA-circRAPGEF5, and miRNA-NC, pcDNA-circRAPGEF5 were transfected into MDA-MB-231 cells with miRNA-4712-5p mimics. qRT-PCR and Western blot were employed to detect circRAPGEF5, miRNA-4712-5p, and YWHAE expression in cells. The CCK-8 methodand plate clone formation experiment were conducted to test cellular proliferation ability. Flow cytometry was performed to detect apoptosis rate. Dual luciferase reporter assays were used to test the targeting association between circRAPGEF5 and miRNA-4712-5p, and the targeting association between miRNA-4712-5p and YWHAE. Western blot was utilized to detect Bcl-2, Bax, and Cleared Caspase-3 protein expression. In comparison with paracancerous tissues, circRAPGEF5 and YWHAE expression levels in mammary cancer tissues were significantly reduced (P < 0.05), and miRNA-4712-5p expression levels were significantly increased (P < 0.05). Transfection of pcDNA-circRAPGEF5 or trans-anti-miRNA-4712-5p could reduce the optical density (OD) value, Bcl-2 protein level and clonal formation number to a significant extent (P < 0.05), and it increases Bax and Cleaved Caspase-3 apoptosis rate and protein levels (P < 0.05). Dual luciferase reporter assays confirmed that there was target binding between circRAPGEF5 and miRNA-4712-5p and between miRNA-4712-5p and YWHAE. Co-transfection of pcDNA-circRAP GEF5 and miRNA-4712-5p could greatly reduce transfection of pcDNA-circRAP GEF5 and its effect on the proliferation and apoptosis of MDA-MB-231 cells. Overexpression of circRAPGEF5 can inhibit the proliferation of mammary cancer cells and induce apoptosis by regulating the molecular axis of miRNA-4712-5p/YWHAE.

Emerging role of circular RNAs in breast cancer

Circular RNAs (cirRNAs) are generally considered as non-coding RNAs which can act as molecular sponges for miRNAs, exert regulatory roles in transcription or splicing, and interplay with RNA binding proteins. These single-stranded transcripts can affect tumor growth, the metastatic ability of cancer cells, stemness properties, and resistance to therapeutic options. Recent investigations have shown the crucial effects of circrNAs in the evolution of breast cancer. Signature of circRNAs in breast cancer samples has been mostly assessed through microarray-based methods revealing up-regulation of some circRNAs such as circ-TFF1, circACAP2, circ-TFCP2L1, hsa_circ_0000519, circDENND4C, circPLK1 and circRNA_069718, while down-regulation of other circRNAs such as hsa_circ_0000375, circYap, hsa_circ_0025202, circTADA2A-E6, circASS1 and circRNA_BARD1 in breast cancer samples. Mechanistically, these transcripts mainly affect breast cancer tumorigenesis via serving as sponges for miRNAs. In the current manuscript, we explore the results of researches that appraised the role of circRNAs in breast cancer.

CircKRT1 drives tumor progression and immune evasion in oral squamous cell carcinoma by sponging miR-495-3p to regulate PDL1 expression

Regulatory functions of circRNAs by targeting the micro RNA (miRNA)/mRNA axis have been increasingly found in oral squamous cell carcinoma (OSCC). CircRNA keratin 1 (CircKRT1) and miR-495-3p were dysregulated in OSCC. Programmed death ligand 1 (PDL1) was an important immunotherapeutic molecule in OSCC. Our objective was to explore whether circKRT1 could regulate cancer progression and immune evasion in OSCC by affecting the miR-495-3p/PDL1 axis. RNA expression was examined by quantitative real-time polymerase chain reaction. All protein levels were detected by western blot. OSCC cell growth was assessed by CCK-8 and colony formation assays. Cell migratory and invasive abilities were evaluated by transwell assay. CD8⁺ T-cell cytotoxicity was determined via lactate dehydrogenase assay. CD8⁺ T-cell percentage and apoptosis were analyzed by flow cytometry. Target screening was performed by Veen Diagram and RNA pull-down assay. Target binding was verified using dual-luciferase reporter and RNA immunoprecipitation assays. A xenograft in mice was conducted for in vivo experiment. CircKRT1 and PDL1 were highly expressed in OSCC tissues and cells. CircKRT1 knockdown repressed OSCC cell growth, migration, invasion, epithelial-mesenchymal transition, and CD8⁺ T-cell apoptosis, but enhanced CD8⁺ T cytotoxicity and percentage. The inhibitory effects of circKRT1 downregulation on OSCC progression and immune evasion were related to PDL1 expression inhibition. CircKRT1 sponged miR-495-3p and miR-495-3p targeted PDL1. OSCC progression and immune evasion were regulated by circKRT1 via the miR-495-3p/PDL1 axis. CircKRT1 also facilitated OSCC progression in vivo by regulating miR-495-3p and PDL1. This study clarified that circKRT1 worked as a miR-495-3p sponge to regulate PDL1, consequently affecting cancer progression and immune evasion in OSCC.

Circular RNA circ_0000337 contributes to osteosarcoma via the miR-4458/BACH1 pathway

BACKGROUND

As the most prevalent primary bone malignancy in children and adolescents, osteosarcoma (OS) has attracted increasing attention. The role of circRNAs in OS has been elucidated in some reports, but many circRNAs remain unexplored. Circ_0000337 has only been revealed as an oncogenic circRNA in esophageal squamous cell carcinoma. Yet whether circ_0000337 exerts any specific function in OS has not been unmasked.

METHODS

RT-qPCR was used for measurement of circ_0000337, miR-4458 and BACH1 mRNA levels. Western blot was conducted to detect BACH1 protein. CCK-8 assay, Casepase-3 activity assay and transwell assay were utilized to assess changes on cellular processes. Cytoplasmic/nuclear fractionation assay was conducted for circ_0000337 localization in OS cells. Luciferase reporter assay and RIP assay were performed to validate the interaction between miR-4458 and circ_0000337 or BACH1.

RESULTS

Circ_0000337 expression was upregulated in OS cell lines and it silence hindered OS cell proliferation and migration. MiR-4458 was downregulated in OS cells and miR-4458 upregulation suppressed OS cell growth and migration. Importantly, circ_0000337 sponged miR-4458 to elevate BACH1 expression, thus facilitating OS development.

CONCLUSIONS

This research for the first time documented that circ_0000337 promoted OS progression via sponging miR-4458 and thus elevating BACH1 expression, offering rational therapeutic target for OS.

Identification of novel dysregulated circular RNAs in early-stage breast cancer

Breast cancer is a major cause of cancer-related death in women worldwide. Non-coding RNAs are a potential resource to be used as an early diagnostic biomarker for breast cancer. Circular RNAs are a recently identified group of non-coding RNA with a significant role in disease development with potential utility in diagnosis/prognosis in cancer. In this study, we identified 26 differentially expressed circular RNAs associated with early-stage breast cancer. RNA sequencing and two circRNA detection tools (find_circ and DCC) were used to understand the circRNA expression signature in breast cancer. We identified hsa_circ_0006743 (circJMJD1C) and hsa_circ_0002496 (circAPPBP1) to be significantly up-regulated in early-stage breast cancer tissues. Co-expression analysis identified four pairs of circRNA-miRNA (hsa_circ_0023990 : hsa-miR-548b-3p, hsa_circ_0016601 : hsa_miR-1246, hsa_circ_0001946 : hsa-miR-1299 and hsa_circ_0000117:hsa-miR-502-5p) having potential interaction. The miRNA target prediction and network analysis revealed mRNA possibly regulated by circRNAs. We have thus identified circRNAs of diagnostic implications in breast cancer and also observed circRNA-miRNA interaction which could be involved in breast cancer development.

Hsa_circ_0053063 inhibits breast cancer cell proliferation via hsa_circ_0053063/hsa-miR-330-3p/PDCD4 axis

Breast cancer (BC) is one of the most common malignancies and its mortality is the highest among females. Circular RNAs (circRNAs), a novel group of non-coding RNAs, play an important regulatory role in angiogenesis and cancer progression. Hsa_circ_0053063 is a circRNA generated from several exons of HADHA. The potential role of hsa_circ_0053063 in BC remains unknown and needs to be explored. Hsa_circ_0053063 was mainly located in the cytoplasm and activated in BC tissues and cell lines. The binding position between hsa_circ_0053063 and miR-330-3p was confirmed by luciferase reporter assay. Moreover, hsa_circ_0053063 inhibited cell viability, proliferation, and progression of BC through the negative regulation of miR-330-3p. Programmed cell death 4 (PDCD4) is a direct target of miR-330-3p. Besides, the over-expression of miR-330-3p promoted cell progression by directly targeting and regulating PDCD4. Mechanistically, hsa_circ_0053063 activated PDCD4 by targeting miR-330-3p to inhibit BC progression. In conclusion, hsa_circ_0053063 inhibits breast cancer cell proliferation via hsa_circ_0053063/hsa-miR-330-3p/PDCD4 axis, which may provide a new therapeutic target for BC patients.

Circular RNAs: Their Role in the Pathogenesis and Orchestration of Breast Cancer

As one of the most frequently occurring malignancies in women, breast cancer (BC) is still an enormous threat to women all over the world. The high mortality rates in BC patients are associated with BC recurrence, metastatic progression to distant organs, and therapeutic resistance. Circular RNAs (circRNAs), belonging to the non-coding RNAs (ncRNAs), are connected end to end to form covalently closed single-chain circular molecules. CircRNAs are widely found in different species and a variety of human cells, with the features of diversity, evolutionary conservation, stability, and specificity. CircRNAs are emerging important participators in multiple diseases, including cardiovascular disease, inflammation, and cancer. Recent studies have shown that circRNAs are involved in BC progress by regulating gene expression at the transcriptional or post-transcriptional level via binding to miRNAs then inhibiting their function, suggesting that circRNAs may be potential targets for early diagnosis, treatment, and prognosis of BC. Herein, in this article, we have reviewed and summarized the current studies about the biogenesis, features, and functions of circRNAs. More importantly, we emphatically elucidate the pivotal functions and mechanisms of circRNAs in BC growth, metastasis, diagnosis, and drug resistance. Deciphering the complex networks, especially the circRNA-miRNA target gene axis, will endow huge potentials in developing therapeutic strategies for combating BC.

Circular RNA RHOT1 promotes progression and inhibits ferroptosis via mir-106a-5p/STAT3 axis in breast cancer

To explore the effect of circRHOT1 on breast cancer progression and the underlying mechanism. Significantly, our data revealed that the depletion of circRHOT1 was able to repress the proliferation and induce the apoptosis of breast cancer cells. CircRHOT1 knockdown could remarkably inhibit the invasion and migration in the breast cancer cells. Meanwhile, the depletion of circRHOT1 enhanced the erastin-induced inhibition effect on cell growth of breast cancer cells. The circRHOT1 knockdown notably increased the levels of reactive oxygen species (ROS), iron, and Fe²⁺ in breast cancer cells. Mechanically, circRHOT1 was able to sponge microRNA-106a-5p (miR-106a-5p) and inhibited ferroptosis by down-regulating miR-106a-5p in breast cancer cells. Besides, miR-106a-5p induced ferroptosis by targeting signal transducer and activator of transcription 3 (STAT3) in the system. Moreover, the overexpression of STAT3 and miR-106a-5p inhibitor could reverse circRHOT1 knockdown-mediated breast cancer progression. Functionally, circRHOT1 promoted the tumor growth of breast cancer in vivo. In conclusion, we discovered that circRHOT1 contributed to malignant progression and attenuated ferroptosis in breast cancer by the miR-106a-5p/STAT3 axis. Our finding provides new insights into the mechanism by which circRHOT1 promotes the development of breast cancer. CircRHOT1 and miR-106a-5p may serve as potential targets for breast cancer therapy.

A risk progression breast epithelial 3D culture model reveals Cx43/hsa_circ_0077755/miR-182 as a biomarker axis for heightened risk of breast cancer initiation

mRNA-circRNA-miRNAs axes have been characterized in breast cancer, but not as risk-assessment axes for tumor initiation in early-onset breast cancer that is increasing drastically worldwide. To address this gap, we performed circular RNA (circRNA) microarrays and microRNA (miRNA) sequencing on acini of HMT-3522 S1 (S1) breast epithelial risk-progression culture model in 3D and chose an early-stage population miRNome for a validation cohort. Nontumorigenic S1 cells form fully polarized epithelium while pretumorigenic counterparts silenced for gap junction Cx43 (Cx43-KO-S1) lose epithelial polarity, multilayer and mimic premalignant in vivo mammary epithelial morphology. Here, 121 circRNAs and 65 miRNAs were significantly dysregulated in response to Cx43 silencing in cultured epithelia and 15 miRNAs from the patient cohort were involved in epithelial polarity disruption. Focusing on the possible sponging activity of the validated circRNAs to their target miRNAs, we found all miRNAs to be highly enriched in cancer-related pathways and cross-compared their dysregulation to actual miRNA datasets from the cultured epithelia and the patient validation cohort. We present the involvement of gap junction in post-transcriptional axes and reveal Cx43/hsa_circ_0077755/miR-182 as a potential biomarker signature axis for heightened-risk of breast cancer initiation, and that its dysregulation patterns might predict prognosis along breast cancer initiation and progression.

Upregulated hsa_circ_0000129 expression promotes proliferation and migration of breast cancer cells

Circular RNAs (circRNAs) are considered potential biomarkers in the pathogenesis and detection of several types of cancer. The present study aimed to investigate the role of hsa_circ_0000129 in the pathogenesis and molecular mechanism underlying breast cancer. A total of 68 pairs of breast cancer and corresponding paracancerous tissue samples, three different breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and a normal human breast cell line (MCF-10A) were used to investigate the expression of hsa_circ_0000129. The effect of hsa_circ_0000129 on cell proliferation, migration and colony formation was assessed in MCF-7 and MDA-MB-468 cells, along with the expression of enhancer of zeste homolog 2 (EZH2). The results demonstrated that hsa_circ_0000129 expression was significantly higher in breast cancer tissues compared with normal tissues. In addition, high hsa_circ_0000129 expression was significantly associated with lymph node metastasis and a higher tumor-node-metastasis stage. Comparisons between the breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and MCF-10A cells indicated similar results. MCF-7 cells overexpressed with hsa_circ_0000129 significantly increased cell proliferation, migration and colony formation compared with the negative control group, the effects of which were reversed following hsa_circ_0000129 knockdown in MDA-MB-468 cells. Furthermore, EZH2 expression was positively associated with hsa_circ_0000129 expression. Taken together, the results of the present study suggest that hsa_circ_0000129 may represent a promising prognostic biomarker for breast cancer. In addition, the role of hsa_circ_0000129 in breast cancer cell lines indicates a mechanism for tumorigenesis, as well as a potent target for the treatment of malignant progression.

Recent Discoveries of Macromolecule- and Cell-Based Biomarkers and Therapeutic Implications in Breast Cancer

Breast cancer is the most commonly diagnosed cancer type and the leading cause of cancer-related mortality in women worldwide. Breast cancer is fairly heterogeneous and reveals six molecular subtypes: luminal A, luminal B, HER2+, basal-like subtype (ER−, PR−, and HER2−), normal breast-like, and claudin-low. Breast cancer screening and early diagnosis play critical roles in improving therapeutic outcomes and prognosis. Mammography is currently the main commercially available detection method for breast cancer; however, it has numerous limitations. Therefore, reliable noninvasive diagnostic and prognostic biomarkers are required. Biomarkers used in cancer range from macromolecules, such as DNA, RNA, and proteins, to whole cells. Biomarkers for cancer risk, diagnosis, proliferation, metastasis, drug resistance, and prognosis have been identified in breast cancer. In addition, there is currently a greater demand for personalized or precise treatments; moreover, the identification of novel biomarkers to further the development of new drugs is urgently needed. In this review, we summarize and focus on the recent discoveries of promising macromolecules and cell-based biomarkers for the diagnosis and prognosis of breast cancer and provide implications for therapeutic strategies.

Circ-PRMT5 promotes breast cancer by the miR-509-3p/TCF7L2 axis activating the PI3K/AKT pathway

BACKGROUND

Breast cancer is the most prevalent malignancy occurring in females. In recent years, emerging evidence has suggested that circular RNAs are involved in the development of multiple cancers. Circ-PRMT5 has recently attracted attention as a tumor-promoting circular RNA. In the present study, we focused on exploring the biological effects of circ-PRMT5 in breast cancer.

METHODS

A quantitative real-time polymerase chain reaction was used to determine the expression of circ-PRMT5 in breast cancer. In vitro experiments, including cell-counting kit-8, 5-ethynyl-2'-deoxyuridine, flow cytometry and tube formation assays, were performed to test the effects of circ-PRMT5 on the cellular progression of breast cancer. Bioinformatic analysis, luciferase reporter, radioimmunoprecipitation and RNA-pull down assays were performed to predict the potential microRNAs interacting with circ-PRMT5 and mRNAs that can be targeted by miR-509-3p.

RESULTS

Circ-PRMT5 is up-regulated in breast cancer tissues and cells. Importantly, an elevation of circ-PRMT5 indicates a poor prognosis in patients with breast cancer. Functionally, knockdown of circ-PRMT5 suppresses cell proliferation and angiogenesis and increases cell apoptosis in breast cancer. Mechanistically, we identified that circ-PRMT5 up-regulates TCF7L2 expression by acting as a miR-509-3p sponge. The negative expression correlation between miR-509-3p and circ-PRMT5 or TCF7L2 in clinical tissues was further demonstrated. Rescue assays showed that TCF7L2 overexpression reverses the antitumoral effects of circ-PRMT5 knockdown on breast cancer cell processes. Additionally, we demonstrated that circ-PRMT5 activates the phosphoinositide 3-kinase (PI3K)/AKT pathway by up-regulation of TCF7L2.

CONCLUSIONS

Overall, our data indicate that the circ-PRMT5/miR-509-3p/TCF7L2 axis can aggravate the malignant character of breast cancer cells by the regulation of the PI3K/AKT pathway.

Circular RNA hsa_circ_0008003 facilitates tumorigenesis and development of non-small cell lung carcinoma via modulating miR-488/ZNF281 axis

As one of the most aggressive malignancies, non‐small cell lung carcinoma (NSCLC) has high risks of death. It has been demonstrated that circRNAs accelerate NSCLC progression, but the underlying molecular mechanisms of circRNAs in NSCLC were still obscure. In the first place, the circRNA microarray of NSCLC was investigated in this study, and hsa_circ_0008003 (circ‐0008003) was chosen as the research object. Then, it was unveiled that the expression of circ‐0008003 examined via qRT‐PCR was elevated in tumour tissues relative to the non‐tumour tissues, which was associated with TNM stage and lymphatic metastasis in NSCLC. Additionally, the prognosis of NSCLC patients with high circ‐0008003 level was poor. Besides, circ‐0008003 silencing dampened the invasion and proliferation of NSCLC cells. Next, according to the mechanistic studies, circ‐0008003 functioned as a ceRNA of ZNF281 in NSCLC by acting as the endogenous sponge for miR‐488, which was proved to be a tumour suppressor in NSCLC. Additionally, ZNF281 overexpression and miR‐488 suppression recovered the influences of repressed circ‐0008003 on NSCLC cellular processes. It was validated in this research that circ‐0008003 triggered tumour formation in NSCLC, which was adjusted via miR‐488/ZNF281 axis, casting a novel light on the resultful target for treating NSCLC and predicting the prognosis.