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

Adipocytes promote metastasis of breast cancer by attenuating the FOXO1 effects and regulating copper homeostasis

BACKGROUND

Obesity and the forkhead box O1(FOXO1) affect the survival of breast cancer patients, but the underlying mechanism remains unclear. We aimed to investigate the role of FOXO1 in obesity-associated-breast cancer.

METHODS

We screened 383 breast disease patients from the first affiliated hospital with Nanjing Medical University in 2020. We performed wound healing, transwell, matrigel assays to assess the metastatic ability of cancer cells. We adopted mRNAs sequencing to select the differentially expressed transcripts in breast cancer. We applied immunohistochemistry, western blot, tissue microarrays to assess the level of FOXO1 and epithelial-mesenchymal transition (EMT) pathways. We conducted bioinformatic analysis to investigate interactions between FOXO1 and miR-135b. We used fluorescence in situ hybridization, RT-qPCR to confirm the characteristics of circCNIH4. We conducted luciferase reporter assay, rescue experiments to investigate interactions between circCNIH4 and miR-135b.

RESULTS

Obesity was positively correlated with the incidence and progression of breast cancer. Adipocytes enhanced the migration of breast cancer and attenuated the effects of FOXO1. MiR-135b was a binding gene of FOXO1 and was regulated by circCNIH4. CircCNIH4 exhibited antitumor activity in vitro and in vivo.

CONCLUSION

Adipocytes might accelerate the progression of breast cancer by modulating FOXO1/miR-135b/ circCNIH4 /EMT axis and regulating copper homeostasis.

The crosstalk between non-coding RNAs and cell-cycle events: A new frontier in cancer therapy

The cell cycle comprises sequential events during which a cell duplicates its genome and divides it into two daughter cells. This process is tightly regulated to ensure that the daughter cell receives identical copied chromosomal DNA and that any errors in the DNA during replication are correctly repaired. Cyclins and their enzyme partners, cyclin-dependent kinases (CDKs), are critical regulators of G- to M-phase transitions during the cell cycle. Mitogenic signals induce the formation of the cyclin/CDK complexes, resulting in phosphorylation and activation of the CDKs. Once activated, cyclin/CDK complexes phosphorylate specific substrates that drive the cell cycle forward. The sequential activation and inactivation of cyclin-CDK complexes are tightly controlled by activating and inactivating phosphorylation events induced by cell-cycle proteins. The non-coding RNAs (ncRNAs), which do not code for proteins, regulate cell-cycle proteins at the transcriptional and translational levels, thereby controlling their expression at different cell-cycle phases. Deregulation of ncRNAs can cause abnormal expression patterns of cell-cycle-regulating proteins, resulting in abnormalities in cell-cycle regulation and cancer development. This review explores how ncRNA dysregulation can disrupt cell division balance and discusses potential therapeutic approaches targeting these ncRNAs to control cell-cycle events in cancer treatment.

Circular RNAs in Cell Cycle Regulation of Cancers

Cancer has been one of the most problematic health issues globally. Typically, all cancers share a common characteristic or cancer hallmark, such as sustaining cell proliferation, evading growth suppressors, and enabling replicative immortality. Indeed, cell cycle regulation in cancer is often found to be dysregulated, leading to an increase in aggressiveness. These dysregulations are partly due to the aberrant cellular signaling pathway. In recent years, circular RNAs (circRNAs) have been widely studied and classified as one of the regulators in various cancers. Numerous studies have reported that circRNAs antagonize or promote cancer progression through the modulation of cell cycle regulators or their associated signaling pathways, directly or indirectly. Mostly, circRNAs are known to act as microRNA (miRNA) sponges. However, they also hold additional mechanisms for regulating cellular activity, including protein binding, RNA-binding protein (RBP) recruitment, and protein translation. This review will discuss the current knowledge of how circRNAs regulate cell cycle-related proteins through the abovementioned mechanisms in different cancers.

Identification of N7-methylguanosine-related miRNAs as potential biomarkers for prognosis and drug response in breast cancer

Objectives

The impact of N7-methylguanosine (m7G) on tumor progression and the regulatory role of microRNAs (miRNAs) in immune function significantly influence breast cancer (BC) prognosis. Investigating the interplay between m7G modification and miRNAs provides novel insights for assessing prognostics and drug responses in BC.

Materials and methods

RNA sequences (miRNA and mRNA profiles) and clinical data for BC were acquired from the Cancer Genome Atlas (TCGA) database. A miRNA signature associated with 15 m7G in this cohort was identified using Cox regression and LASSO. The risk score model was evaluated using Kaplan-Meier and time-dependent ROC analysis, categorizing patients into high-risk and low-risk groups. Functional enrichment analyses were conducted to explore potential pathways. The immune system, including scores, cell infiltration, function, and drug sensitivity, was examined and compared between high-risk and low-risk groups. A nomogram that combines risk scores and clinical factors was developed and validated. Single-sample gene set enrichment analysis (ssGSEA) was employed to explore m7G-related miRNA signatures and immune cell relationships in the tumor microenvironment. Additionally, drug susceptibility was compared between risk groups.

Results

Fifteen m7G-related miRNAs were independently correlated with overall survival (OS) in BC patients. Time-dependent ROC analysis yielded area under the curve (AUC) values of 0.742, 0.726, and 0.712 for predicting 3-, 5-, and 10-year survival rates, respectively. The Kaplan-Meier analysis revealed a significant disparity in OS between the high-risk and low-risk groups (p = 1.3e-6). Multiple regression identified the risk score as a significant independent prognostic factor. An excellent calibration nomogram with a C-index of 0.785 (95 % CI: 0.728-0.843) was constructed. In immune analysis, low-risk patients exhibited heightened immune function and increased responsiveness to immunotherapy and chemotherapy compared to high-risk patients.

Conclusion

This study systematically analyzed m7G-related miRNAs and revealed their regulatory mechanisms concerning the tumor microenvironment (TME), pathology, and the prognosis of BC patient. Based on these miRNAs, a prognostic model and nomogram were developed for BC patients, facilitating prognostic assessments. These findings can also assist in predicting treatment responses and guiding medication selection.

CircHAS2 activates CCNE2 to promote cell proliferation and sensitizes the response of colorectal cancer to anlotinib

BACKGROUND

Tyrosine kinase inhibitors (TKIs) are crucial in the targeted treatment of advanced colorectal cancer (CRC). Anlotinib, a multi-target TKI, has previously been demonstrated to offer therapeutic benefits in previous studies. Circular RNAs (circRNAs) have been implicated in CRC progression and their unique structural stability serves as promising biomarkers. The detailed molecular mechanisms and specific biomarkers related to circRNAs in the era of targeted therapies, however, remain obscure.

METHODS

The whole transcriptome RNA sequencing and function experiments were conducted to identify candidate anlotinib-regulated circRNAs, whose mechanism was confirmed by molecular biology experiments. CircHAS2 was profiled in a library of patient-derived CRC organoids (n = 22) and patient-derived CRC tumors in mice. Furthermore, a prospective phase II clinical study of 14 advanced CRC patients with anlotinib-based therapy was commenced to verify drug sensitivity (ClinicalTrials.gov identifier: NCT05262335).

RESULTS

Anlotinib inhibits tumor growth in vitro and in vivo by downregulating circHAS2. CircHAS2 modulates CCNE2 activation by acting as a sponge for miR-1244, and binding to USP10 to facilitate p53 nuclear export as well as degradation. In parallel, circHAS2 serves as a potent biomarker predictive of anlotinib sensitivity, both in patient-derived organoids and xenograft models. Moreover, the efficacy of anlotinib inclusion into the treatment regimen yields meaningful clinical responses in patients with high levels of circHAS2. Our findings offer a promising targeted strategy for approximately 52.9% of advanced CRC patients who have high circHAS2 levels.

CONCLUSIONS

CircHAS2 promotes cell proliferation via the miR-1244/CCNE2 and USP10/p53/CCNE2 bidirectional axes. Patient-derived organoids and xenograft models are employed to validate the sensitivity to anlotinib. Furthermore, our preliminary Phase II clinical study, involving advanced CRC patients treated with anlotinib, confirmed circHAS2 as a potential sensitivity marker.

Recent advances in the investigation of fusion RNAs and their role in molecular pathology of cancer

Gene fusions have had a significant role in the development of various types of cancer, oftentimes involved in oncogenic activities through dysregulation of gene expression or signalling pathways. Some cancer-associated chromosomal translocations can undergo backsplicing, resulting in fusion-circular RNAs, a more stable isoform immune to RNase degradation. This stability makes fusion circular RNAs a promising diagnostic biomarker for cancer. While the detection of linear fusion RNAs and their function in certain cancers have been described in literature, fusion circular RNAs lag behind due to their low abundance in cancer cells. This review highlights current literature on the role of linear and circular fusion transcripts in cancer, tools currently available for detecting of these chimeric RNAs and their function and how they play a role in tumorigenesis.

CircGUCY2C regulates cofilin 1 by sponging miR-425-3p to promote the proliferation of porcine skeletal muscle satellite cells

Circular ribonucleic acids (or circRNAs) are an emerging class of endogenous noncoding RNAs that are involved in physiological and pathological processes. Increasing evidence suggests that circRNAs play an important regulatory role in skeletal muscle development and meat quality regulation. In this study, it was found that circGUCY2C exhibits a high expression level in the longissimus dorsi muscle. It shows resistance to RNase R and additionally promotes the mRNA expression of cyclin-dependent kinase 2 (CDK2) and proliferating cell nuclear antigen (PCNA). Specifically, it was observed that the overexpression of circGUCY2C could promote the transition of porcine skeletal muscle satellite cells into the S and G2 phases of the cell cycle and that it regulates the proliferation of porcine skeletal muscle satellite cells. In contrast, miR-425-3p plays the opposite role and has an inhibitory effect on the proliferation of porcine skeletal muscle satellite cells. MiR-425-3p has been described as a target of circGUCY2C; consequently, the depletion of miR-425-3p promoted the proliferation of porcine skeletal muscle satellite cells. CFL1 (cofilin 1) is a target of miR-425-3p, and circGUCY2C upregulated CFL1 expression by inhibiting miR-425-3p. Collectively, our research outcomes demonstrate that circGUCY2C significantly influences the proliferation of porcine skeletal muscle satellite cells by selectively targeting the miR-425-3p-CFL1 axis, and our work partially clarified the role of circGUCY2C in porcine skeletal muscle satellite cells. Thus, the study provides new insight into the function of circGUCY2C and adds to the knowledge of the post-transcriptional regulation of pork quality.

Estrogen-regulated miRs in bone enhance osteoblast differentiation and matrix mineralization

Estrogen signaling is critical for the development and maintenance of healthy bone, and age-related decline in estrogen levels contributes to the development of post-menopausal osteoporosis. Most bones consist of a dense cortical shell and an internal mesh-like network of trabecular bone that respond differently to internal and external cues such as hormonal signaling. To date, no study has assessed the transcriptomic differences that occur specifically in cortical and trabecular bone compartments in response to hormonal changes. To investigate this, we employed a mouse model of post-menopausal osteoporosis (ovariectomy, OVX) and estrogen replacement therapy (ERT). mRNA and miR sequencing revealed distinct transcriptomic profiles between cortical and trabecular bone in the setting of OVX and ERT. Seven miRs were identified as likely contributors to the observed estrogen-mediated mRNA expression changes. Of these, four miRs were prioritized for further study and decreased predicted target gene expression in bone cells, enhanced the expression of osteoblast differentiation markers, and altered the mineralization capacity of primary osteoblasts. As such, candidate miRs and miR mimics may have therapeutic relevance for bone loss resulting from estrogen depletion without the unwanted side effects of hormone replacement therapy and therefore represent novel therapeutic approaches to combat diseases of bone loss.

Estrogen-Induced LncRNA, LINC02568, Promotes Estrogen Receptor-Positive Breast Cancer Development and Drug Resistance Through Both In Trans and In Cis Mechanisms

Endocrine therapy is the frontline treatment for estrogen receptor (ER) positive breast cancer patients. However, the primary and acquired resistance to endocrine therapy drugs remain as a major challenge in the clinic. Here, this work identifies an estrogen-induced lncRNA, LINC02568, which is highly expressed in ER-positive breast cancer and functional important in cell growth in vitro and tumorigenesis in vivo as well as endocrine therapy drug resistance. Mechanically, this work demonstrates that LINC02568 regulates estrogen/ERα-induced gene transcriptional activation in trans by stabilizing ESR1 mRNA through sponging miR-1233-5p in the cytoplasm. Meanwhile, LINC02568 contributes to tumor-specific pH homeostasis by regulating carbonic anhydrase CA12 in cis in the nucleus. The dual functions of LINC02568 together contribute to breast cancer cell growth and tumorigenesis as well as endocrine therapy drug resistance. Antisense oligonucleotides (ASO) targeting LINC02568 significantly inhibits ER-positive breast cancer cell growth in vitro and tumorigenesis in vivo. Furthermore, combination treatment with ASO targeting LINC02568 and endocrine therapy drugs or CA12 inhibitor U-104 exhibits synergistic effects on tumor growth. Taken together, the findings reveal the dual mechanisms of LINC02568 in regulating ERα signaling and pH homeostasis in ER-positive breast cancer, and indicated that targeting LINC02568 might represent a potential therapeutic avenue in the clinic.

Comprehensive analysis of circRNAs for N7-methylguanosine methylation modification in human oral squamous cell carcinoma

N7-methylguanosine (m7G) modification is closely related to the occurrence of tumors. However, the m7G modification of circRNAs in oral squamous cell carcinoma (OSCC) remains to be investigated. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) was used to measure the methylation levels of m7G and identify m7G sites in circRNAs in human OSCC and normal tissues. The host genes of differentially methylated and differentially expressed circRNAs were analyzed by Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, and circRNA-miRNA-mRNA networks were predicted using the miRanda and miRDB databases. The analysis identified 2348 m7G peaks in 624 circRNAs in OSCC tissues. In addition, the source of m7G-methylated circRNAs in OSCC was mainly the sense overlap region compared with normal tissues. The most conserved m7G motif in OSCC tissues was CCUGU, whereas the most conserved motif in normal tissues was RCCUG (R = G/A). Importantly, GO enrichment and KEGG pathway analysis showed that the host genes of differentially methylated and differentially expressed circRNAs were involved in many cellular biological functions. Furthermore, the significantly differentially expressed circRNAs were analyzed to predict the circRNA-miRNA-mRNA networks. This study revealed the whole profile of circRNAs of differential m7G methylation in OSCC and suggests that m7G-modified circRNAs may impact the development of OSCC.

Regulatory miRNAs, circRNAs and lncRNAs in cell cycle progression of breast cancer

Breast cancer is a complex and heterogeneous disease that poses a significant public health concern worldwide, and it remains a major challenge despite advances in treatment options. One of the main properties of cancer cells is the increased proliferative activity that has lost regulation. Dysregulation of various positive and negative modulators in the cell cycle has been identified as one of the driving factors of breast cancer. In recent years, non-coding RNAs have garnered much attention in the regulation of cell cycle progression, with microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs) being of particular interest. MiRNAs are a class of highly conserved and regulatory small non-coding RNAs that play a crucial role in the modulation of various cellular and biological processes, including cell cycle regulation. CircRNAs are a novel form of non-coding RNAs that are highly stable and capable of modulating gene expression at posttranscriptional and transcriptional levels. LncRNAs have also attracted considerable attention because of their prominent roles in tumor development, including cell cycle progression. Emerging evidence suggests that miRNAs, circRNAs and lncRNAs play important roles in the regulation of cell cycle progression in breast cancer. Herein, we summarized the latest related literatures in breast cancer that emphasize the regulatory roles of miRNAs, circRNAs and lncRNAs in cell cycle progress of breast cancer. Further understanding of the precise roles and mechanisms of non-coding RNAs in breast cancer cell cycle regulation could lead to the development of new diagnostic and therapeutic strategies for breast cancer.

Effect of circ_0000009 on lung adenocarcinoma progression by regulating PDZD2 in a ceRNA- and RBP- dependent manner

Accumulating evidence now demonstrated that circular RNAs (circRNAs) are closely related to the pathogenesis of lung adenocarcinoma (LUAD). Through GEO2R online analysis, we screened hsa_circ_0000009 (circ_0000009) from the GEO database (GSE158695), and its expression in LUAD cancer tissues and cell lines was detected by RT-qPCR. The looping structure of circ_0000009 was tested by RNase R and actinomycin D experiments. The changes of proliferation were tested by CCK-8 or EdU assay. And the changes of apoptosis in A549 and H1299 cells were measured via flow cytometry. The A549 BALB/c tumor model was established to evaluate the influence of circ_0000009 on LUAD cell growth in vivo. In addition, experiments connected with ceRNA direction (mainly including bioinformatics prediction and luciferase reporter assay) and RNA Binding Protein (RBP) direction (mainly including RNA pull-down assay, RIP assay and mRNA stability assay) were further developed to reveal the regulatory mechanism of circ_0000009. The gene and protein levels in this project were assessed by RT-qPCR and western blotting analysis, respectively. The data manifested that circ_0000009 was in low expression in LUAD. The in vitro and in vivo experiments threw light on that overexpression of circ_0000009 dramatically suppressing LUAD tumorigenesis. Mechanistically, circ_0000009 promoted the expression of PDZD2 by sponging miR-154-3p. Furthermore, circ_0000009 stabilized PDZD2 by recruiting IGF2BP2. This study illustrated the mechanism that overexpressing of circ_0000009 suppressed LUAD progression by upregulating PDZD2 expression, providing an original treatment direction for LUAD.

CircPVT1 promotes ER-positive breast tumorigenesis and drug resistance by targeting ESR1 and MAVS

The molecular mechanisms underlying estrogen receptor (ER)-positive breast carcinogenesis and endocrine therapy resistance remain incompletely understood. Here, we report that circPVT1, a circular RNA generated from the lncRNA PVT1, is highly expressed in ERα-positive breast cancer cell lines and tumor samples and is functionally important in promoting ERα-positive breast tumorigenesis and endocrine therapy resistance. CircPVT1 acts as a competing endogenous RNA (ceRNA) to sponge miR-181a-2-3p, promoting the expression of ESR1 and downstream ERα-target genes and breast cancer cell growth. Furthermore, circPVT1 directly interacts with MAVS protein to disrupt the RIGI-MAVS complex formation, inhibiting type I interferon (IFN) signaling pathway and anti-tumor immunity. Anti-sense oligonucleotide (ASO)-targeting circPVT1 inhibits ERα-positive breast cancer cell and tumor growth, re-sensitizing tamoxifen-resistant ERα-positive breast cancer cells to tamoxifen treatment. Taken together, our data demonstrated that circPVT1 can work through both ceRNA and protein scaffolding mechanisms to promote cancer. Thus, circPVT1 may serve as a diagnostic biomarker and therapeutic target for ERα-positive breast cancer in the clinic.

Inhibition of circular RNA ASPH reduces the proliferation and promotes the apoptosis of hepatic stellate cells in hepatic fibrosis

Circular RNAs (circRNAs) are a newly identified form of non-coding RNA that play a crucial role in various pathological processes. However, the expression profile and function of circRNAs in hepatic fibrosis (HF) remain largely unknown. In this study, we showed that a novel circRNA ASPH (circASPH) mediates HF by targeting the miR-139-5p/Notch1 axis. We investigated the expression profile of circRNAs in hepatocyte exosomes of mice with HF using circRNA-sequencing and found significant upregulation of circASPH. Loss- and gain-of-function analysis of circASPH was performed to assess its role in HF. Furthermore, we performed luciferase reporter assay, RNA pull-down, and fluorescence in situ hybridization analyses and confirmed that circASPH directly binds to miR-139-5p. We also found that circASPH was upregulated in liver fibrogenesis. Downregulation of circASPH expression inhibited hepatic stellate cell (HSC) activation and proliferation, induced apoptosis, and attenuated mouse liver fibrogenic injury. Mechanistically, circASPH directly targeted miR-139-5p to regulate the expression of Notch1 in HF. Thus, downregulation of circASPH may suppress the activation of HSCs and HF through the circASPH/miR-139-5p/Notch1 axis. Our findings indicated that circASPH may be a potential biomarker for HF diagnosis and therapy.

RNA helicase DDX5-induced circPHF14 promotes gastric cancer cell progression

As a well-established member of a strongly conserved protein family, DDX5 binds to RNA helicase in a specific manner, which can regulate mRNA transcription, protein translation and synthesis and precursor messenger RNA processing or alternative splicing. The effects of DDX5 on carcinogenesis and cancer progression are increasingly evident. Circular RNAs (circRNAs), a novel group of functionally non-coding RNAs (ncRNAs) with disordered expression, are associated with various pathological processes (e.g., tumors). circRNA pattern and its function regulated by DDX5 have not yet been determined. According to our findings, DDX5 was dramatically upregulated for stomach cancer tissues, and its overexpression contributed to the cell growth and invasion of GC cells. Based on the analysis of genome-wide circRNAs conducted with circRNA sequencing, DDX5 induces a large number of circRNAs. Further to screen several circRNAs from PHF14 for function, it was found that circPHF14 was essential for the growth and tumorigenesis of DDX5-positive gastric cancer cells. These findings suggest that in addition to the messenger RNA and microRNA patterns, DDX5 also effects a circRNA pattern, as demonstrated by circPHF14. DDX5-induced circRNAs have been found to be of crucial importance for the growth of DDX5-positive gastric cancer cells, providing a new therapeutic target.

Hsa_circ_0000129 drives tumor growth via sequestering miR-485-3p and upregulating SPIN1 in breast cancer

BACKGROUND

Breast cancer (BC) is second cancer frequently occurring worldwide. Circular RNA hsa_circ_0000129 (circ_0000129) exerts a tumor-promoting effect in BC. Nevertheless, the molecular mechanisms mediated by the upregulation of circ_0000129 during BC progression are not well understood.

METHODS

Forty-five BC patients were recruited for the research. Changes in circ_0000129 levels were detected with quantitative reverse transcription-polymerase chain reaction. Cell proliferation, apoptosis, migration, invasion, and angiopoiesis were determined by cell counting, 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, transwell, and tube formation assays. Protein levels were detected by western blot analysis. The regulatory mechanism of circ_0000129 was predicted by bioinformatics analysis and validated by dual-luciferase reporter and RNA immunoprecipitation assays. In vivo experiments were carried out to verify the function of circ_0000129.

RESULTS

Circ_0000129 was overexpressed in BC samples and cell lines. Functionally, circ_0000129 silencing reduced cell proliferation, migration, invasion, and promoted cell apoptosis, as well as induced HUVEC angiopoiesis in vitro. Furthermore, circ_0000129 knockdown decreased BC cell growth in mouse xenograft models. Mechanically, circ_0000129 interacted with miR-485-3p to mediate the inhibiting effect of miR-485-3p on SPIN1. Silenced miR-485-3p expression weakened the inhibiting effect of circ_0000129 knockdown on BC cell malignant behaviors. Also, forced SPIN1 expression weakened miR-485-3p upregulation mediated effects on BC cell malignant behaviors.

CONCLUSION

Circ_0000129 acted as a miR-485-3p sponge molecular to mediate expression, thus promoting BC progression.

Hsa_circ_0001944 regulates apoptosis by regulating the binding of PARP1 and HuR in leukemia and malignant transformed cells induced by hydroquinone

Hydroquinone (HQ) is one of the major metabolites of benzene and can cause abnormal gene expression. It is a known carcinogen that alters cell cycle disruption and cell proliferation. However, its chemical mechanism remain a mystery. Circular RNAs (circRNAs) are a subtype of noncoding RNAs (ncRNAs) that play a variety of roles in biological processes. Hsa_circ_001944 expression was upregulated in 30 leukemia patients and HQ-induced malignant transformed TK6 cells. Hsa_circ_001944 silencing inhibited the growth of HQ-TK6 cells and halted the cell cycle. The silencing of hsa_circ_0001944 led to increased cell accumulation in G1 versus S phase, increased apoptosis in the sh1944 versus the shNC group, and increased levels of DNA damage (γ-H2AX), leading to cell cycle arrest. In summary, inhibition of hsa_circ_001944 restricted cell growth by inhibiting cell cycle arrest and induced growth of HQ-TK6 cells by modulating PARP1 expression. Hsa_circ_0001944 targeted HuR, which is a kind of RNA-binding protein, to control PARP1 expression via RNAinter, RBPmap, and RBPdb. Fluorescence in situ hybridization combined with immunofluorescent labeling and western blotting experiments showed that hsa_circ_001944 was able to dissociate HuR and PARP1 binding in HQ-TK6 cells, control PARP1 production, and ultimately alter the PARP1/H-Ras pathway.

Evaluation of Circ_0000977-Mediated Regulatory Network in Breast Cancer: A Potential Discriminative Biomarker for Triple-Negative Tumors

Previous investigations have revealed that circular RNAs (circRNAs) play pivotal roles in cancer development and progression by participating in several biological procedures, such as competing endogenous RNA (ceRNA) networks. Recently, circRNAs have been proposed as non-invasive, stable, and affordable cell-free biomarkers for cancer screening and test monitoring. Although, their clinical usefulness vastly remains to be evaluated in breast cancer (BC). Triple-negative breast cancer (TNBC), as the most challenging BC subtype, is an urgent requirement of identifying specific biomarkers and discovering the molecular mechanisms that lead to aggressive behaviors of tumor cells. The therapeutic strategies for TN patients have remained limited due to the impracticality of endocrine therapies and a remarkable portion of patients with TNBC experience recurrence, chemoresistance, and metastasis. TNBC Microarray expression profile analysis found that circ_0000977 is one of the most dysregulated circRNA in TNBC in comparison with non-TNBC. It could be a clue referring to the potential clinical utility of circ_0000977 in TNBC. The current study aims to assess the clinical implications and potential ceRNA regulatory network of circ_0000977 in TNBC. We confirmed circ_0000977 down-regulation in TNBC cell lines and tumors versus non-TNBC samples by real-time PCR. Subsequently, an assessment of the diagnostic value of circ_0000977 in plasma samples from triple-negative patients revealed a potential diagnostic cell-free biomarker in triple-negative BC. Finally, our integrative approach uncovered potential circ-0000977/miR-135b-5p/mRNAs regulatory network in TNBC. The inhibitory effect of miR-135b-5p on its downstream mRNAs was assessed by knocking down it in MDA-MB-231 cells. Functional and correlation analyses revealed APC and GATA3 could be regulated by circ_0000977/miR-135b-5p ceRNA axis, which presents valuable insight into circ-0000977-mediated gene silencing involved in the ceRNA network of TNBC. This study uncovered the potential clinical implication of circ_0000977 for the diagnosis and treatment of TNBC patients.

Circular RNAs: biology and clinical significance of breast cancer

Circular RNAs (circRNAs) are novel noncoding RNAs with covalently closed-loop structures that can regulate eukaryotic gene expression. Due to their stable structure, circRNAs are widely distributed in the cytoplasm and have important biological functions, including as microRNA sponges, RNA-binding protein conjugates, transcription regulators, and translation templates. Breast cancer is among the most common malignant cancers diagnosed in women worldwide. Despite the development of comprehensive treatments, breast cancer still has high mortality rates. Recent studies have unmasked critical roles for circRNAs in breast cancer as regulators of tumour initiation, progression, and metastasis. Further, research has revealed that some circRNAs have the potential for use as diagnostic and prognostic biomarkers in clinical practice. Herein, we review the biogenesis and biological functions of circRNAs, as well as their roles in different breast cancer subtypes. Moreover, we provide a comprehensive summary of the clinical significance of circRNAs in breast cancer. CircRNAs are believed to be a hot focus in basic and clinical research of breast cancer, and innovative future research directions of circRNAs could be used as biomarkers, therapeutic targets, or novel drugs.Abbreviations: CeRNA: Competitive endogenous RNA; ciRNA: Circular intronic RNA; circRNA: Circular RNA; EIciRNA: Exon-intron circRNA; EMT: Epithelial-mesenchymal transition; IRES: Internal ribosome entry site; lncRNA: Long non-coding RNA; miRNA: MicroRNA; MRE: MiRNA response element; ncRNA: Non-coding RNA; RBP: RNA-binding protein; RNA-seq: RNA sequencing; RT-PCR: Reverse transcription-polymerase chain reaction.

Tamoxifen resistance-related ceRNA network for breast cancer

Background: Tamoxifen (TMX) is one of the most widely used drugs to treat breast cancer (BC). However, acquired drug resistance is still a major obstacle to its application, rendering it crucial to explore the mechanisms of TMX resistance in BC. This aims of this study were to identify the mechanisms of TMX resistance and construct ceRNA regulatory networks in breast cancer. Methods: GEO2R was used to screen for differentially expressed mRNAs (DEmRNAs) leading to drug resistance in BC cells. MiRTarbase and miRNet were used to predict miRNAs and lncRNAs upstream, and the competing endogenous RNA (ceRNA) regulatory network of BC cell resistance was constructed by starBase. We used the Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis (GEPIA) to analyze the expression and prognostic differences of genes in the ceRNA network with core axis, and qRT-PCR was used to further verify the above conclusions. Results: We found that 21 DEmRNAs were upregulated and 43 DEmRNA downregulated in drug-resistant BC cells. DEmRNAs were noticeably enriched in pathways relevant to cancer. We then constructed a protein-protein interaction (PPI) network based on the STRING database and defined 10 top-ranked hub genes among the upregulated and downregulated DEmRNAs. The 20 DEmRNAs were predicted to obtain 113 upstream miRNAs and 501 lncRNAs. Among them, 7 mRNAs, 22 lncRNAs, and 11 miRNAs were used to structure the ceRNA regulatory network of drug resistance in BC cells. 4 mRNAs, 4 lncRNAs, and 3 miRNAs were detected by GEPIA and the Kaplan-Meier plotter to be significantly associated with BC expression and prognosis. The differential expression of the genes in BC cells was confirmed by qRT-PCR. Conclusion: The ceRNA regulatory network of TMX-resistant BC was successfully constructed and confirmed. This will provide an important resource for finding therapeutic targets for TMX resistance, where the discovery of candidate conventional mechanisms can aid clinical decision-making. In addition, this resource will help discover the mechanisms behind this type of resistance.

Lymphatic metastasis-associated circRNA‒miRNA‒mRNA network for exploring the pathogenesis and therapeutic target of triple negative breast cancer based on whole-transcriptome sequencing analysis: an experimental verification study

BACKGROUND

The metastatic mechanisms of axillary lymph nodes (ALNs) in triple-negative breast cancer (TNBC) remain unclear. We aimed to identify the potential circRNA regulatory network in ALN metastasis.

METHODS

We performed whole transcriptome sequencing (WTS) to determine the expression profiles of RNAs and screen out differentially expressed messenger RNAs (DEMs), microRNAs (DEMis), and circRNAs (DECs) between ALN-positive and ALN-negative TNBC patients. Functional enrichment analysis and Kaplan-Meier survival analysis were utilized to unearth the potential regulatory mechanisms of the DEMs. A competing endogenous RNA (ceRNA) network was constructed using computational biology. The expression levels of DECs in cell lines were confirmed by real-time polymerase chain reaction (RT‒PCR).

RESULTS

Following WTS and differential expression analysis, 739 DEMs, 110 DEMis, and 206 DECs were identified between ALN-positive and ALN-negative TNBC patients. Functional analysis indicated that the DEMs mainly functioned in carcinogenesis and tumor progression-related pathways. ceRNA networks containing eight circRNAs, six miRNAs, and eighteen mRNAs were developed. In the ceRNA network, two mRNAs (RAB3D and EDARADD) that were significantly associated with better overall survival and one mRNA (GSR) that predicted favorable recurrence-free survival in TNBC patients were chosen for further analysis. Then, a survival-related ceRNA network containing two DECs (hsa_circ_0061260 and hsa_circ_0060876), two DEMis (hsa-miR-5000-3p and hsa-miR-4792), and three mRNAs (GSR, RAB3D, and EDARADD) was identified. Then, two candidate DECs were validated by real-time PCR.

CONCLUSION

Our research constructed a ceRNA network that provides novel insights into the molecular mechanism of ALN metastasis and potential therapeutic targets in TNBC.

Circular RNA Controls Tumor Occurrence and Development via Cell Cycle Regulation

Circular RNAs (circRNAs) participate in the occurrence and development of various diseases through different mechanisms, such as by acting as a microRNA (miRNA) sponge, interacting with RNA-binding proteins, and regulating gene transcription and protein translation. For example, the abnormal expression of specific circRNAs in tumor cells can alter key regulatory factors and the cell cycle network, resulting in cell cycle disorders and the development and metastasis of tumors. Here, we summarize the mechanisms involved in the circRNA-mediated processes that lead to uncontrolled cell cycle and tumor cell proliferation. Extensive studies investigating the abnormal expression of circRNAs in different cancer types have been conducted. The unique characteristics of circRNAs and their ability to regulate the cell cycle through diverse mechanisms is extremely valuable in tumor diagnosis, treatment, and prognosis. Our review may assist in further understanding the circRNA-mediated regulation of the cell cycle in tumors and provide insights for research on circRNA-based therapeutic strategies and biological diagnosis for cancer.

Therapeutic prospects of ceRNAs in COVID-19

Since the end of 2019, COVID-19 caused by SARS-CoV-2 has spread worldwide, and the understanding of the new coronavirus is in a preliminary stage. Currently, immunotherapy, cell therapy, antiviral therapy, and Chinese herbal medicine have been applied in the clinical treatment of the new coronavirus; however, more efficient and safe drugs to control the progress of the new coronavirus are needed. Long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) may provide new therapeutic targets for novel coronavirus treatments. The first aim of this paper is to review research progress on COVID-19 in the respiratory, immune, digestive, circulatory, urinary, reproductive, and nervous systems. The second aim is to review the body systems and potential therapeutic targets of lncRNAs, miRNAs, and circRNAs in patients with COVID-19. The current research on competing endogenous RNA (ceRNA) (lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA) in SARS-CoV-2 is summarized. Finally, we predict the possible therapeutic targets of four lncRNAs, MALAT1, NEAT1, TUG1, and GAS5, in COVID-19. Importantly, the role of PTEN gene in the ceRNA network predicted by lncRNA MALAT1 and lncRNA TUG1 may help in the discovery and clinical treatment of effective drugs for COVID-19.

Circ-TRIO promotes TNBC progression by regulating the miR-432-5p/CCDC58 axis

Numerous studies have shown that circRNAs are aberrantly expressed in various cancers and play a significant role in tumor progression. However, the molecular mechanisms of circRNAs in triple-negative breast cancer (TNBC) remain ambiguous. By intersecting throughput data and qRT-PCR results from tissues and cell lines, circ-TRIO was identified as a potential oncogenic regulator of TNBC. Moreover, circ-TRIO expression was detected in TNBC tissues and was correlated with the recurrence and prognosis of TNBC patients. The circular characteristics of circ-TRIO were verified by RNase R and CHX assays. Functionally, the knockdown of circ-TRIO inhibited the proliferation, migration and invasion of TNBC cells, while the overexpression of circ-TRIO resulted in the opposite impacts. Mechanistically, a dual luciferase reporter assay and RNA immunoprecipitation were performed and indicated that circ-TRIO could combine with miR-432-5p to regulate the expression of coiled-coil domain containing 58 (CCDC58). In summary, our study illustrates that circ-TRIO plays an important role in the progression of TNBC by regulating the miR-432-5p/CCDC58 axis, which could broaden our insight into the underlying mechanisms and provide a novel prognostic marker of TNBC in the clinic.

Differential expression profile of mRNAs, lncRNAs and circRNAs reveals potential molecular mechanism in breast cancer

In recent years, breast cancer attracts more and more attention because of its high incidence. To explore the molecular functions and mechanisms, we performed RNA sequencing on the tumor tissues and their paired normal tissues from three breast cancer patients. By differential expression analysis, we found 3764 differentially expressed (DE) mRNAs, 5416 DE lncRNAs, and 148 DE circRNAs. Enrichment analysis suggested that the DE lncRNAs and DE circRNAs were enriched in mitochondria and nucleus, which indicated that they may participate in the vital metabolism directly or indirectly, such as fatty acid metabolism. Subsequently, the protein–protein interaction (PPI) network was constructed and we got 8 key proteins, of which the matrix metalloproteinase-9 (MMP9; degree 5) draws our attention. Based on the 38 up-regulated circRNAs and 14 down-regulated circRNAs, we constructed competing endogenous RNA (ceRNA) networks, from which the has-miR-6794-5p has been identified to enriched in the up-regulated network and correlated with the circNFIX directly. At this point, we presented that the circNFIX and MMP9 may play a significant role by regulating fatty acid metabolism in breast cancer.

Sus_circPAPPA2 Regulates Fat Deposition in Castrated Pigs through the miR-2366/GK Pathway

CircRNAs play an important role in fat deposition, and testosterone-deficient boars exhibit significantly increased fat deposition; however, the mechanism by which testosterone regulates fat deposition through circRNAs remains unclear. In this study, circRNA-seq of backfat and abdominal fat from castrated and intact full-sib Yorkshire pigs was performed. The GO and KEGG enrichment analyses revealed that the host genes of the dorsal DE circRNAs were mainly involved in fatty acid transport, while in abdominal tissues, these genes were mainly involved in adipogenesis and inflammation. The interaction among sus_circPAPPA2, ssc-miR-2366 and GK was verified by dual fluorescence experiments and in porcine preadipocytes. The overexpression of sus_circPAPPA2 significantly inhibited the differentiation of preadipocytes. The expression of sus_circPAPPA2 was increased after adding 100 nM of testosterone, and preadipocyte differentiation was significantly inhibited. Testosterone can affect preadipocyte differentiation by upregulating the expression of sus_circPAPPA2, sponging miR-2366 and regulating the expression of genes, such as GK. These results indicate that testosterone can regulate the expression of adipocyte differentiation- and lipid metabolism-related genes by regulating the expression of circRNA, and ceRNA networks are different in the testosterone regulation of adipose deposition in different parts. This study provides basic data enhancing the understanding of the interaction between the hormone environment and mir-2366/GK to regulate trait performance in pigs.

Emerging functions of circular RNA in the regulation of adipocyte metabolism and obesity

As noncoding RNAs, circular RNAs (circRNAs) are covalently enclosed endogenous biomolecules in eukaryotes that have tissue specificity and cell specificity. circRNAs were once considered a rare splicing byproduct. With the development of high-throughput sequencing, it has been confirmed that they are expressed in thousands of mammalian genes. To date, only a few circRNA functions and regulatory mechanisms have been verified. Adipose is the main tissue for body energy storage and energy supply. Adipocyte metabolism is a physiological process involving a series of genes and affects biological activities in the body, such as energy metabolism, immunity, and signal transmission. When adipocyte formation is dysregulated, it will cause a series of diseases, such as atherosclerosis, obesity, fatty liver, and diabetes. In recent years, many noncoding RNAs involved in adipocyte metabolism have been revealed. This review provides a comprehensive overview of the basic structure and biosynthetic mechanism of circRNAs, and further discusses the circRNAs related to adipocyte formation in adipose tissue and liver. Our review will provide a reference for further elucidating the genetic regulation mechanism of circRNAs involved in adipocyte metabolism.

The functional roles of the circRNA/Wnt axis in cancer

CircRNAs, covalently closed noncoding RNAs, are widely expressed in a wide range of species ranging from viruses to plants to mammals. CircRNAs were enriched in the Wnt pathway. Aberrant Wnt pathway activation is involved in the development of various types of cancers. Accumulating evidence indicates that the circRNA/Wnt axis modulates the expression of cancer-associated genes and then regulates cancer progression. Wnt pathway-related circRNA expression is obviously associated with many clinical characteristics. CircRNAs could regulate cell biological functions by interacting with the Wnt pathway. Moreover, Wnt pathway-related circRNAs are promising potential biomarkers for cancer diagnosis, prognosis evaluation, and treatment. In our review, we summarized the recent research progress on the role and clinical application of Wnt pathway-related circRNAs in tumorigenesis and progression.

Regulation of Pyroptosis by ncRNA: A Novel Research Direction

Pyroptosis is a novel form of programmed cell death (PCD), which is characterized by DNA fragmentation, chromatin condensation, cell swelling and leakage of cell contents. The process of pyroptosis is performed by certain inflammasome and executor gasdermin family member. Previous researches have manifested that pyroptosis is closely related to human diseases (such as inflammatory diseases) and malignant tumors, while the regulation mechanism of pyroptosis is not yet clear. Non-coding RNA (ncRNA) such as microRNA (miRNA), long non-coding RNA (lncRNA) and circular RNA (circRNA) have been widely identified in the genome of eukaryotes and played a paramount role in the development of cell function and fate after transcription. Accumulating evidences support the importance of ncRNA biology in the hallmarks of pyroptosis. However, the associations between ncRNA and pyroptosis are rarely reviewed. In this review, we are trying to summarize the regulation and function of ncRNA in cell pyroptosis, which provides a new research direction and ideas for the study of pyroptosis in different diseases.

An update on the roles of circular RNAs in spinal cord injury

Spinal cord injury (SCI) is a disabling condition for which therapeutic options are limited. Increasing number of microarray and next-generation sequencing studies have demonstrated that SCI coincides with altered expression of circular RNAs (circRNAs) in the damaged tissue. Emerging functional evidence further pinpointed specific differentially expressed circRNAs (e.g., circ-HIPK3, cicRNA.7079, circRNA_01477, circRNA-2960, and circ_0001723) for their effects on cellular processes relevant to SCI repair and regeneration, including neuronal apoptosis, astrocyte activation, and neuroinflammation, via sponging SCI-related microRNAs. Although circRNAs and their target microRNAs appear to be good candidates for therapeutic exploitation in SCI, further investigation into the efficient delivery of these regulatory molecules in a cell-type specific manner is a pre-requisite for translating these basic discoveries into clinical benefits.

The crosstalk between reactive oxygen species and noncoding RNAs: from cancer code to drug role

Oxidative stress (OS), characterized by the excessive accumulation of reactive oxygen species (ROS), is an emerging hallmark of cancer. Tumorigenesis and development driven by ROS require an aberrant redox homeostasis, that activates onco-signaling and avoids ROS-induced programmed death by orchestrating antioxidant systems. These processes are revealed to closely associate with noncoding RNAs (ncRNAs). On the basis of the available evidence, ncRNAs have been widely identified as multifarious modulators with the involvement of several key redox sensing pathways, such as NF-κB and Nrf2 signaling, therefore potentially becoming effective targets for cancer therapy. Furthermore, the vast majority of ncRNAs with property of easy detected in fluid samples (e.g., blood and urine) facilitate clinicians to monitor redox homeostasis, indicating a novel method for cancer diagnosis. Herein, focusing on carcinoma initiation, metastasis and chemoradiotherapy resistance, we aimed to discuss the ncRNAs-ROS network involved in cancer progression, and the potential clinical application as biomarkers and therapeutic targets.

CircMET promotes tumor proliferation by enhancing CDKN2A mRNA decay and upregulating SMAD3

BACKGROUND

Functions of CircMET (hsa_circ_0082002) which is a circular RNA and derived from MET gene remain understood incompletely. In the present study, Xp11.2 translocation/NONO-TFE3 fusion renal cell carcinoma (NONO-TFE3 tRCC) with up-regulated CircMET was employed to investigate its mechanism in cancer progression and post-transcriptional regulation.

METHODS

FISH and real-time PCR were performed to explore the expression and localization circMET in NONO-TFE3 tRCC tissues and cells. The functions of circMET in tRCC were investigated by proliferation analysis, EdU staining, colony and sphere formation assay. The regulatory mechanisms among circMET, CDKN2A and SMAD3 were investigated by luciferase assay, RNA immunoprecipitation, RNA pulldown and targeted RNA demethylation system.

RESULTS

The expression of circMET was upregulated by NONO-TFE3 fusion in NONO-TFE3 tRCC tissues and cells, and overexpression of circMET significantly promoted the growth of NONO-TFE3 tRCC. Mechanistic studies revealed that circMET was delivered to cytosol by YTHDC1 in N⁶-methyladenosine (m⁶A)-depend manner. CircMET enhances mRNA decay of CDKN2A by direct interaction and recruitment of YTHDF2. Meanwhile, circMET competitively absorbed miR-1197 and prevented those from SMAD3 mRNA.

CONCLUSIONS

CircMET promotes the development of NONO-TFE3 tRCC, and the regulation to both CDKN2A and SMAD3 of circMET was revealed. CircMET has the potential to serve as a novel target for the molecular therapy of NONO-TFE3 tRCC as well as the other cancer with high-expressing circMET.

Gender specific eRNA TBX5-AS1 as the immunological biomarker for male patients with lung squamous cell carcinoma in pan-cancer screening

As an innate feature of human beings, gender differences have an influence on various biological phenotypes, yet it does not attract enough attention in genomics studies. The prognosis of multiple carcinomas usually exhibits a favorable ending for female patients, but the neglect of gender differences can cause serious bias in survival analysis. Enhancer RNAs (eRNAs) are mostly downstream of androgens or estrogen. The present study was aimed to screen eRNAs in patients with non-small-cell lung cancer. The findings revealed that eRNA TBX5-AS1 was expressed differently between female and male patients. Meanwhile, its prognostic significance appeared only in male patients with squamous cell carcinoma (SCC) type. The Gene Set Enrichment Analysis proved that the expression level of TBX5-AS1 increased following the activation of the androgen signaling pathway. In pan-cancer analysis, the prognostic prediction based on gender grouping obtained more meaningful results, and the synergy between TBX5-AS1 and its homologous target was more consistent. Furthermore, immunity variations between sexes prompted us to explore the role that TBX5-AS1 played in tumor microenvironment and immunotherapy. The robust evidence proved that male patients with high expression of TBX5-AS1 possessed a malignant immune microenvironment and urgently needed immune checkpoint inhibitor treatment. In conclusion, TBX5-AS1 may be one of the strongest candidates to predict prognosis for male patients with SCC and provide a reference for immunotherapy.

A Novel Meiosis-Related lncRNA, Rbakdn, Contributes to Spermatogenesis by Stabilizing Ptbp2

Spermatocyte meiosis is the cornerstone of mammalian production. Thousands of long noncoding RNAs (lncRNAs) have been reported to be functional in various cellular processes, but the function of lncRNAs in meiosis remains largely unknown. Here, we profiled lncRNAs in spermatocytes at stage I of meiosis and identified a testis-specific lncRNA, Rbakdn, as a vital regulator of meiosis. Rbakdn is dynamically expressed during meiosis I, and Rbakdn knockdown inhibits meiosis in vitro. Furthermore, Rbakdn knockdown in testes in mice by intratesticular injection disturbs meiosis, reduces testicular volume, and increases apoptosis of spermatocytes, resulting in vacuolation of the seminiferous tubules. Rbakdn can bind to Ptbp2, an RNA-binding protein that is important in the regulation of the alternative splicing of many genes in spermatogenesis. Rbakdn knockdown leads to a decrease in Ptbp2 through the ubiquitination degradation pathway, indicating that Rbakdn maintains the stability of Ptbp2. In conclusion, our study identified an lncRNA, Rbakdn, with a crucial role in meiosis.

MicroRNA-2355-5p Promotes the Proliferation of Head and Neck Squamous Cell Carcinoma via Suppressing NISCH Expression

Background. MicroRNAs (miRNAs) have emerged as crucial regulators in various cancers. However, the potential role of miR-2355-5p in head and neck squamous cell carcinoma (HNSC) remains unclear. Methods. Bioinformatics methods were implemented to find the candidate target gene of miR-2355-5p. Quantitative real-time PCR was performed to detect RNA expression levels of miR-2355-5p and NISCH, while western blot was carried out for the detection of protein levels of NISCH and cell cycle-related biomarkers. CCK-8, EdU staining, and flow cytometry were employed to measure cell proliferation and cell cycle progression. Dual-luciferase assay and RNA pulldown were conducted to verify the binding relationship between miR-2355-5p and NISCH. Results. The expression levels of miR-2355-5p and NISCH were, respectively, higher and lower in HNSC tissues than those in normal adjacent tissues. The transfection of the miR-2355-5p inhibitor suppressed cell proliferation by arresting the cells at the G1/S transition. The results of luciferase activity and RNA pulldown assays indicated that miR-2355-5p directly targeted the NISCH 3′-untranslated region. Furthermore, the effects of miR-2355-5p inhibition on cell proliferation were reversed after treatment with siRNA against NISCH. Conclusion. In summary, our findings indicate that miR-2355-5p promotes cell cycle progression in HNSC by targeting NISCH. Hence, targeting miR-2355-5p could be a promising therapeutic strategy for the treatment of HNSC

Circular RNAs in cell cycle regulation: Mechanisms to clinical significance

Circular RNAs (circRNAs), a type of non‐coding RNA, are single‐stranded circularized molecules characterized by high abundance, evolutionary conservation and cell development‐ and tissue‐specific expression. A large body of studies has found that circRNAs exert a wide variety of functions in diverse biological processes, including cell cycle. The cell cycle is controlled by the coordinated activation and deactivation of cell cycle regulators. CircRNAs exert mutifunctional roles by regulating gene expression via various mechanisms. However, the functional relevance of circRNAs and cell cycle regulation largely remains to be elucidated. Herein, we briefly describe the biogenesis and mechanistic models of circRNAs and summarize their functions and mechanisms in the regulation of critical cell cycle modulators, including cyclins, cyclin‐dependent kinases and cyclin‐dependent kinase inhibitors. Moreover, we highlight the participation of circRNAs in cell cycle‐related signalling pathways and the clinical value of circRNAs as promising biomarkers or therapeutic targets in diseases related to cell cycle disorder.

Cadmium promotes apoptosis and inflammation via the circ08409/miR-133a/TGFB2 axis in bovine mammary epithelial cells and mouse mammary gland

Cadmium is a common environmental heavy metal pollutant that can accumulate over long periods of time and cause disease. Thus, analysis of the molecular mechanisms affected by cadmium in the body could be of great significance for the prevention and treatment of cadmium-related diseases. In this study, flow cytometry, immunofluorescence, transmission electron microscopy, H&E (Hematoxylin Eosin) staining and TUNEL (TdT-mediated dUTP Nick-End Labeling) assays were used to verify that cadmium induced apoptosis and immune responses in bovine mammary epithelial cells (BMECs) and in mouse mammary gland. Isolated BMECs cultured with or without cadmium were collected to screen miRNA (microRNA) using high-throughput sequencing. There were 42 differentially-expressed miRNAs among which 27 were upregulated and 15 downregulated including bta-miR-133a, bta-miR-23b-5p, bta-miR-29e, bta-miR-365-5p, bta-miR-615, bta-miR-7, bta-miR-11975, bta-miR-127, and bta-miR-411a. Among those, miR-133a (which can specifically target TGFB2 (Recombinant Transforming Growth Factor Beta 2) was the most significantly downregulated with a fold-change of 5.27 in BMECs cultured with cadmium. Application of the double luciferase reporter system, western blotting, and qRT-PCR (Quantitative Real-time PCR) revealed that circ08409 can directly bind to miR-133a. Experiments demonstrated that circRNA-08409 could adsorb bta-miR-133a. Both circ08409 and TGFB2 significantly increased apoptosis and altered expression level of a series of inflammatory factors in BMECs. In contrast, miR-133a decreased significantly apoptosis and inflammation in the cells. Compared with cultures receiving only cadmium, the miR-133a+cadmium cultures exhibited significant reductions in the occurrence of late apoptosis. Overall, results indicated that circ08409 could relieve the inhibitory effect of miR-133a on TGFB2 expression by combining with miR-133a and subsequently modulating cell proliferation, apoptosis and inflammation. Overall, the data suggested that the circ08409/miR-133a/TGFB2 axis might play a role in mediating the effect of cadmium on BMECs. As such, data provide novel insights into controlling hazards that cadmium could induce in the mammary gland.

MiR-92b-3p Inhibits Proliferation of HER2-Positive Breast Cancer Cell by Targeting circCDYL

Objectives

Circular RNA (circRNA) is a novel class of RNA, which exhibits powerful biological function in regulating cellular fate of various tumors. Previously, we had demonstrated that over-expression of circRNA circCDYL promoted progression of HER2-negative (HER2^–) breast cancer via miR-1275-ULK1/ATG7-autophagic axis. However, the role of circCDYL in HER2-positive (HER2⁺) breast cancer, in particular its role in modulating cell proliferation, one of the most important characteristics of cellular fate, is unclear.

Materials and methods

qRT-PCR and in situ hybridization analyses were performed to examine the expression of circCDYL and miR-92b-3p in breast cancer tissues or cell lines. The biological function of circCDYL and miR-92b-3p were assessed by plate colony formation and cell viability assays and orthotopic animal models. In mechanistic study, circRNAs pull-down, RNA immunoprecipitation, dual luciferase report, western blot, immunohistochemical and immunofluorescence staining assays were performed.

Results

CircCDYL was high-expressed in HER2⁺ breast cancer tissue, similar with that in HER2^– breast cancer tissue. Silencing HER2 gene had no effect on expression of circCDYL in HER2⁺ breast cancer cells. Over-expression of circCDYL promoted proliferation of HER2⁺ breast cancer cells but not through miR-1275-ULK1/ATG7-autophagic axis. CircRNA pull down and miRNA deep-sequencing demonstrated the binding of miR-92b-3p and circCDYL. Interestingly, circCDYL did not act as miR-92b-3p sponge, but was degraded in miR-92b-3p-dependent silencing manner. Clinically, expression of circCDYL and miR-92b-3p was associated with clinical outcome of HER2⁺ breast cancer patients.

Conclusion

MiR-92b-3p-dependent cleavage of circCDYL was an essential mechanism in regulating cell proliferation of HER2⁺ breast cancer cells. CircCDYL was proved to be a potential therapeutic target for HER2⁺ breast cancer, and both circCDYL and miR-92b-3p might be potential biomarkers in predicting clinical outcome of HER2⁺ breast cancer patients.

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_0110389 promotes gastric cancer progression through upregulating SORT1 via sponging miR-127-5p and miR-136-5p

Increasing studies have found that circular RNAs (circRNAs) are aberrantly expressed and play important roles in the occurrence and development of human cancers. However, the function of circRNAs on environmental carcinogen-induced gastric cancer (GC) progression remains poorly elucidated. In the present study, hsa_circ_0110389 was identified as a novel upregulated circRNA in malignant-transformed GC cells through RNA-seq, and subsequent quantitative real-time PCR verified that hsa_circ_0110389 was significantly increased in GC tissues and cells. High hsa_circ_0110389 expression associates with advanced stages of GC and predicts poor prognosis. Knockdown and overexpression assays demonstrated that hsa_circ_0110389 regulates proliferation, migration, and invasion of GC cells in vitro. In addition, hsa_circ_0110389 was identified to sponge both miR-127-5p and miR-136-5p and SORT1 was validated as a direct target of miR-127-5p and miR-136-5p through multiple mechanism assays; moreover, hsa_circ_0110389 sponged miR-127-5p/miR-136-5p to upregulate SORT1 expression and hsa_circ_0110389 promoted GC progression through the miR-127-5p/miR-136-5p-SORT1 pathway. Finally, hsa_circ_0110389 knockdown suppressed GC growth in vivo. Taken together, our findings firstly identify the role of hsa_circ_0110389 in GC progression, which is through miR-127-5p/miR-136-5p-SORT1 pathway, and our study provides novel insight for the identification of diagnostic/prognostic biomarkers and therapeutic targets for GC.

Circular RNA hsa_circ_0044234 as distinct molecular signature of triple negative breast cancer: a potential regulator of GATA3

BACKGROUND

Circular RNAs (circRNAs) have been implicated in the initiation and development of breast cancer as functional non-coding RNAs (ncRNA). The roles of circRNAs as the competing endogenous RNAs (ceRNAs) to sponge microRNAs (miRNAs) have also been indicated. However, the functions of circRNAs in breast cancer have not been totally elucidated. This study aimed to explore the clinical implications and possible roles of circ_0044234 in carcinogenesis of the most problematic BC subtype, triple negative breast cancer (TNBC), which are in desperate need of biomarkers and targeted therapies.

METHODS

The importance of circ_0044234 as one of the most dysregulated circRNAs in TNBC was discovered through microarray expression profile analysis. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to confirm the downregulation of circ_0044234 in triple negative tumors and cell lines versus non-triple negative ones. The bioinformatics prediction revealed that circ_0044234 could act as an upstream sponge in the miR-135b/GATA3 axis, two of the most dysregulated transcripts in TNBC.

RESULTS

Our experimental investigation of circ_0044234 expressions in various BC subtypes as well as cell lines reveals that TNBC expresses circ_0044234 at a substantially lower level than non-TNBC. The ROC curve analysis indicates that it could be applied as a discriminative biomarker to identify TNBC from other BC subtypes. Moreover, circ_0044234 expression could be an independent prognostic biomarker in BC. Interestingly, a substantial inverse expression correlation was detected between circ_0044234 and miR-135b-5p as well as between miR-135b-5p and GATA3 in breast tumors.

CONCLUSIONS

The possible clinical usefulness of circ_0044234 as a promising distinct biomarker and upcoming therapeutic target for TNBC have been indicated in this research. Our comprehensive approach revealed the potential circ_0044234/miR135b-5p/GATA3 ceRNA axis in TNBC.

Knockdown of circ_0075503 suppresses cell migration and invasion by regulating miR-15a-5p and KLF12 in endometriosis

Endometriosis is an estrogen-dependent disease. Several researches have reported the dysregulated circular RNAs (circRNAs) in endometriosis, whereas the functions of circRNAs are largely unknown. This study aims to explore the role and mechanism of circ_0075503 in migration and invasion of eutopic endometrial stromal cells. 30 paired ectopic and eutopic endometrium tissues were collected from patients with endometriosis. And primary endometrial stromal cells (ESCs) were stimulated with estradiol (E2) to establish the in vitro cellular model of endometriosis. The levels of circ_0075503, miR-15a-5p and Krüppel-like factor 12 (KLF12) were measured by quantitative reverse transcription polymerase chain reaction or western blot assays. Cell viability, migration and invasion were examined via 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide, transwell assay or western blot assays. The target relationship between miR-15a-5p and circ_0075503 or KLF12 was analyzed by dual-luciferase reporter assay and RNA Immunoprecipitation (RIP) assay. Circ_0075503 expression was elevated in ectopic endometrium and ectopic ESCs. Down-regulation of circ_0075503 suppressed E2-induced promotion of cell viability, migration and invasion in eutopic ESCs. Circ_0075503 could act as a sponge for miR-15a-5p, and KLF12 was targeted by miR-15a-5p. Inhibition of miR-15a-5p reversed the effects of circ_0075503 knockdown on E2-treated ESCs migration and invasion. Besides, miR-15a-5p repressed E2-induced promotion effects on cell migration and invasion via targeting KLF12. Circ_0075503 could regulate KLF12 expression by sponging miR-15a-5p. Knockdown of circ_0075503 inhibited E2-induced enhancement of cell migration and invasion in eutopic ESCs by regulating miR-15a-5p/KLF12 axis, indicating a novel target for the treatment of endometriosis.

Non-coding RNAs in Wilms' tumor: biological function, mechanism, and clinical implications

Non-coding RNAs are involved with maintenance and regulation of physiological mechanisms and are involved in pathological processes, such as cancer. Among the small ncRNAs, miRNAs are the most explored in tumorigenesis, metastasis development, and resistance to chemotherapy. These small molecules of ~ 22 nucleotides are modulated during early renal development, involved in the regulation of gene expression and Wilms' tumor progression. Wilms' tumors are embryonic tumors with few mutations and complex epigenetic dysregulation. In recent years, the small ncRNAs have been explored as potentially related both in physiological development and in the tumorigenesis of several types of cancer. Besides, genes regulated by miRNAs are related to biological pathways as PI3K, Wnt, TGF-β, and Hippo signaling pathways, among others, which may be involved with the underlying mechanisms of resistance to chemotherapy, and in this way, it has emerged as potential targets for cancer therapies, including for Wilms' tumors.