Upregulation of the alternative splicing factor NOVA2 in colorectal cancer vasculature

Targeting the "tumor microenvironment": RNA-binding proteins in the spotlight in colorectal cancer therapy

Colorectal cancer (CRC) is the third most common cancer and has the second highest mortality rate among cancers. The development of CRC involves both genetic and epigenetic abnormalities, and recent research has focused on exploring the ex-transcriptome, particularly post-transcriptional modifications. RNA-binding proteins (RBPs) are emerging epigenetic regulators that play crucial roles in post-transcriptional events. Dysregulation of RBPs can result in aberrant expression of downstream target genes, thereby affecting the progression of colorectal tumors and the prognosis of patients. Recent studies have shown that RBPs can influence CRC pathogenesis and progression by regulating various components of the tumor microenvironment (TME). Although previous research on RBPs has primarily focused on their direct regulation of colorectal tumor development, their involvement in the remodeling of the TME has not been systematically reported. This review aims to highlight the significant role of RBPs in the intricate interactions within the CRC tumor microenvironment, including tumor immune microenvironment, inflammatory microenvironment, extracellular matrix, tumor vasculature, and CRC cancer stem cells. We also highlight several compounds under investigation for RBP-TME-based treatment of CRC, including small molecule inhibitors such as antisense oligonucleotides (ASOs), siRNAs, agonists, gene manipulation, and tumor vaccines. The insights gained from this review may lead to the development of RBP-based targeted novel therapeutic strategies aimed at modulating the TME, potentially inhibiting the progression and metastasis of CRC.

Gentiana macrophylla flavonoids from Tibetan medicine decreases circ_0059665 to alleviate the progression of non-small cell lung cancer under hypoxia

BACKGROUND

Gentiana macrophylla Pall. is a traditional Tibetan medicinal herb possessing antinociceptive and anti-inflammatory activities. Circular RNAs (circRNAs) have been identified to be involved in the tumorigenesis of non-small cell lung cancer (NSCLC). Here, this study focused on investigating the function and mechanism of Gentiana macrophylla flavonoids (GF) and circ_0059665 in NSCLC progression.

METHODS

The contents of mRNA and protein were detected using qRT-PCR and western blotting analysis. Cell proliferative and invasive abilities were evaluated by cell counting kit-8, EdU, colony formation and transwell assays, respectively. M2 macrophage polarization was analyzed by flow cytometry.

RESULTS

GF treatment suppressed NSCLC cell proliferation, invasion and M2 macrophage polarization under hypoxic conditions. Circ_0059665 was highly expressed in NSCLC tissues and cells. Its expression was increased under hypoxic conditions but was reduced following GF treatment. Furthermore, circ_0059665 overexpression reversed the anticancer effects of GF on NSCLC cells under hypoxic conditions. Mechanistically, circ_0059665 acted as a sponge for miR-512-5p to regulate NOVA2 expression. Hypoxia decreased miR-512-5p levels, and increased NOVA2 levels in NSCLC cells, while these tendencies were abolished after GF treatment. Circ_0059665 silencing inhibited NSCLC cell proliferation, invasion and M2 macrophage polarization in hypoxic environments, which were counteracted by NOVA2 overexpression. Moreover, NOVA2 upregulation reversed the suppressive effects of GF on NSCLC cells with hypoxia treatment. In addition, GF impeded NSCLC tumor growth in vivo via suppressing circ_0059665.

CONCLUSION

GF treatment in hypoxic environments suppressed NSCLC cell proliferation, invasion and M2 macrophage polarization via the circ_0059665/miR-512-5p/NOVA2 axis.

METTL14 reverses liver fibrosis by inhibiting NOVA2 through an m6A-YTHDF2-dependent mechanism

BACKGROUND

N6-methyladenosine (m6A), the most prevalent internal RNA modification in eukaryotic cells, is dynamically regulated in response to a wide range of physiological and pathological states. Nonetheless, the involvement of METTL14-induced m6A in liver fibrosis (LF) has yet to be established.

METHODS

In vitro, HSC cell lines with knock-down and overexpression of METTL14 were constructed, and the effects of METTL14 gene on the phenotypic function of activated HSCs were observed. The proliferation rate was measured by CCK8 and EDU, the cell proliferation cycle was measured by flow detector, the migration rate was measured by Transwell, and the contractility of F-actin was observed after phalloidin staining. The downstream target gene NOVA2 of METTL14 was screened by combined sequencing of MeRIP-seq and RNA-seq, combined with signal analysis. Adeno-associated virus (AAV) was injected into the tail vein in vivo to knock down the expression of METTL14, so as to further observe the role of METTL14 in the progress of LF.

RESULTS

our research showed that the methylase METTL14 content was decreased in hepatic tissue from patients with LF, leading to a lowered degree of m6A modification. Functionally, we discovered that knocking down m6A methyltransferase METTL14 led to increased HSC activation and a substantial worsening of LF. Mechanically, as shown in a multiomics study of HSCs, depleting METTL14 levels decreased m6A deposition onNOVA2 mRNA transcripts, which prompted the activation of YTHDF2 to detect and degrade the decrease of NOVA2 mRNA.

CONCLUSIONS

METTL14 functioned as a profibrotic gene by suppressing NOVA2 activity in a mechanism dependent on m6A-YTHDF2. Moreover, knocking down METTL14 exacerbated LF, while NOVA2 prevented its development and partly reversed the damage.

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

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

Alternative Splicing Changes Promoted by NOVA2 Upregulation in Endothelial Cells and Relevance for Gastric Cancer

Angiogenesis is crucial for cancer progression. While several anti-angiogenic drugs are in use for cancer treatment, their clinical benefits are unsatisfactory. Thus, a deeper understanding of the mechanisms sustaining cancer vessel growth is fundamental to identify novel biomarkers and therapeutic targets. Alternative splicing (AS) is an essential modifier of human proteome diversity. Nevertheless, AS contribution to tumor vasculature development is poorly known. The Neuro-Oncological Ventral Antigen 2 (NOVA2) is a critical AS regulator of angiogenesis and vascular development. NOVA2 is upregulated in tumor endothelial cells (ECs) of different cancers, thus representing a potential driver of tumor blood vessel aberrancies. Here, we identified novel AS transcripts generated upon NOVA2 upregulation in ECs, suggesting a pervasive role of NOVA2 in vascular biology. In addition, we report that NOVA2 is also upregulated in ECs of gastric cancer (GC), and its expression correlates with poor overall survival of GC patients. Finally, we found that the AS of the Rap Guanine Nucleotide Exchange Factor 6 (RapGEF6), a newly identified NOVA2 target, is altered in GC patients and associated with NOVA2 expression, tumor angiogenesis, and poor patient outcome. Our findings provide a better understanding of GC biology and suggest that AS might be exploited to identify novel biomarkers and therapeutics for anti-angiogenic GC treatments.

Neuro-oncological Ventral Antigen 2 Regulates Splicing of Vascular Endothelial Growth Factor Receptor 1 and Is Required for Endothelial Function

Pre-eclampsia (PE) affects 2-8% of pregnancies and is responsible for significant morbidity and mortality. The maternal clinical syndrome (defined by hypertension, proteinuria, and organ dysfunction) is the result of endothelial dysfunction. The endothelial response to increased levels of soluble FMS-like Tyrosine Kinase 1 (sFLT1) is thought to play a central role. sFLT1 is released from multiple tissues and binds VEGF with high affinity and antagonizes VEGF. Expression of soluble variants of sFLT1 is a result of alternative splicing; however, the mechanism is incompletely understood. We hypothesize that neuro-oncological ventral antigen 2 (NOVA2) contributes to this. NOVA2 was inhibited in human umbilical vein endothelial cells (HUVECs) and multiple cellular functions were assessed. NOVA2 and FLT1 expression in the placenta of PE, pregnancy-induced hypertension, and normotensive controls was measured by RT-qPCR. Loss of NOVA2 in HUVECs resulted in significantly increased levels of sFLT1, but did not affect expression of membrane-bound FLT1. NOVA2 protein was shown to directly interact with FLT1 mRNA. Loss of NOVA2 was also accompanied by impaired endothelial functions such as sprouting. We were able to restore sprouting capacity by exogenous VEGF. We did not observe statistically significant regulation of NOVA2 or sFLT1 in the placenta. However, we observed a negative correlation between sFLT1 and NOVA2 expression levels. In conclusion, NOVA2 was found to regulate FLT1 splicing in the endothelium. Loss of NOVA2 resulted in impaired endothelial function, at least partially dependent on VEGF. In PE patients, we observed a negative correlation between NOVA2 and sFLT1.

Design and Characterization of Mutated Variants of the Oncotoxic Parvoviral Protein NS1

Oncotoxic proteins such as the non-structural protein 1 (NS1), a constituent of the rodent parvovirus H1 (H1-PV), offer a novel approach for treatment of tumors that are refractory to other treatments. In the present study, mutated NS1 variants were designed and tested with respect to their oncotoxic potential in human hepatocellular carcinoma cell lines. We introduced single point mutations of previously described important residues of the wild-type NS1 protein and a deletion of 114 base pairs localized within the N-terminal domain of NS1. Cell-viability screening with HepG2 and Hep3B hepatocarcinoma cells transfected with the constructed NS1-mutants led to identification of the single-amino acid NS1-mutant NS1-T585E, which led to a 30% decrease in cell viability as compared to NS1 wildtype. Using proteomics analysis, we could identify new interaction partners and signaling pathways of NS1. We could thus identify new oncotoxic NS1 variants and gain insight into the modes of action of NS1, which is exclusively toxic to human cancer cells. Our in-vitro studies provide mechanistic explanations for the observed oncolytic effects. Expression of NS1 variants had no effect on cell viability in NS1 unresponsive control HepG2 cells or primary mouse hepatocytes. The availability of new NS1 variants in combination with a better understanding of their modes of action offers new possibilities for the design of innovative cancer treatment strategies.

Identification of drug targets and prognosis projection for uterine carcinosarcoma based on alternative splicing events

BACKGROUND

Uterine carcinosarcoma (UCS) is an invasive variant of endometrial cancer. The complicated heterogeneity and low frequency of UCS suggest the relevant research is lack. There is an urgent need to further explore the pathogenic mechanism and identify new biomarkers of UCS from different angels to improve its diagnosis and prognosis.

OBJECTIVE

This study is to explore the importance of alternative splicing (AS) events in UCS, construct AS-based prognosis model and excavate key splicing factors (SFs).

METHOD

UCS related gene transcriptome data and AS events data were collected from The Cancer Genome Atlas (TCGA) and TCGA SpliceSeq database. The AS events related to survival were determined by Cox regression analysis, Least absolute shrinkage and selection operator (Lasso) regression analysis and optimal subset analysis. The corresponding risk score was calculated and its efficiency on prognosis was evaluated by Kaplan-Meier (K-M) survival estimate and validated by the receiver operating characteristic (ROC) curve. The prognosis model was constructed with risk score and clinic characters as independent variables to predict patients' survival. On the other hand, Kendall test was applied to inspect the correlation between the SFs and the prognosis-related AS events and a AS-SF network was constructed. Finally, the key SFs were screened through network nodes analysis and survival analysis.

RESULT

Seven AS events the most related to survival were detected and the risk score was obtained. K-M survival estimate and ROC curve validation suggested the risk score was effective. Then Cox model was constructed based on the risk score and a nomogram model was obtained which provided the highest prediction accuracy of 95%. Through the AS-SF network analysis, 16 SFs were screened, among which four survival-related SFs were eventually obtained.

CONCLUSION

The prognosis model could predict the survival rate of UCS patients by their clinical characters and AS-based risk score. And four newly discovered SFs could reveal the molecular mechanism of UCS and act as the potential drug targets and prognosis biomarkers.

Circ-EIF3I facilitates proliferation, migration, and invasion of lung cancer via regulating the activity of Wnt/β-catenin pathway through the miR-1253/NOVA2 axis

Many studies have shown that circular RNA (circRNA) is an important regulator mediating the malignant progression of cancer. However, the role and mechanism of circ-EIF3I in lung cancer (LC) development are still unclear. A total 36 paired LC tumor tissues and adjacent normal tissues were enrolled. The expression of circ-EIF3I, microRNA (miR)-1253, and neuro-oncological ventral antigen 2 (NOVA2) was measured by quantitative real-time PCR. The proliferation, apoptosis, migration, and invasion of LC cells were determined by MTT assay, colony formation assay, flow cytometry, and transwell assay. Dual-luciferase reporter assay was performed to verify the interaction between miR-1253 and circ-EIF3I or NOVA2. The protein levels of NOVA2 and Wnt/β-catenin pathway-related markers were detected by western blot analysis. Xenograft tumor was constructed to explore the function of circ-EIF3I on LC tumor growth. Circ-EIF3I was upregulated in LC tumor tissues and cells. Silenced circ-EIF3I could suppress the proliferation, migration, invasion, and enhance the apoptosis of LC cells in vitro, as well as reduce LC tumor growth in vivo. Circ-EIF3I could sponge miR-1253, and miR-1253 inhibitor overturned the regulation of circ-EIF3I knockdown on LC cell progression. NOVA2 was confirmed to be a target of miR-1253, which could reverse the inhibitory effects of miR-1253 on LC cell progression. Further experiments showed that circ-EIF3I regulated NOVA2 expression by sponging miR-1253. In addition, circ-EIF3I silencing could inhibit the activity of Wnt/β-catenin pathway via regulating the miR-1253/NOVA2 axis. Circ-EIF3I might function as an oncogene in LC, which promoted LC progression by the miR-1253/NOVA2/Wnt/β-catenin network.

TR3 Enhances AR Variant Production and Transactivation, Promoting Androgen Independence of Prostate Cancer Cells

Simple Summary

Advanced prostate cancer development is associated with androgen-independent AR signaling. TR3 overexpression alters AR expression, splicing process, and transactivation towards increasing the androgen independence of AR signaling in prostate cancer cells. These results suggest that TR3 is a pivotal factor in the progression of prostate cancer to advanced form.

Abstract

The pro-oncogenic function of TR3, an orphan nuclear receptor, has been reported in prostate cancer. However, the roles of TR3 in androgen receptor (AR) expression and signaling in prostate cancer cells are poorly understood. Database analysis revealed that TR3 expression level is elevated in prostate tumors, and is positively, although weakly, correlated with that of AR. TR3 overexpression increased the production of AR splice variants in addition to general upregulation of AR expression. TR3 interacted with some spliceosomal complex components and AR precursor mRNA, altering the splice junction rates between exons. TR3 also enhanced androgen-independent AR function. Furthermore, TR3 overexpression increased cell proliferation and mobility of AR-positive prostate cancer cells and stimulated tumorigenesis of androgen-independent prostate cancer cells in mouse xenograft models. This is the first study to report that TR3 is a multifunctional regulator of AR signaling in prostate cancer cells. TR3 alters AR expression, splicing process, and activity in prostate cancer cells, increasing the androgen independence of AR signaling. Therefore, TR3 may play a crucial role in the progression of prostate cancer to an advanced castration-resistant form.

Genetic variants of the hypoxia-inducible factor 3 alpha subunit (Hif3a) gene in the Fat and Lean mouse selection lines

BACKGROUND

Adipose tissue hypoxia and members of the hypoxia-inducible factor alpha (HIFA) are involved in development of obesity. However, the mechanism and functions of HIF3A, one of three HIFA paralogs, in fat deposition have not been sufficiently studied.

METHODS AND RESULTS

In the present study, we investigated whether Hif3a sequence variants are associated with divergent fat deposition in mouse selection lines for fatness and leanness. Sequencing and RFLP were used to analyse sequence variants within Hif3a. To identify candidate regulatory variants, we performed literature screening and used databases and bioinformatics tools like Ensembl, MethPrimer, TargetScanMouse, miRDB, PolyAsite, RISE, LncRRIsearch, RNAfold, PredictProtein, CAIcal, and switches.ELM Resource. There are 90 sequence variants in Hif3a between the two mouse lines. While most Fat line variants locate within intronic regions, Lean line variants are mainly in 3' UTR. We constructed a map of Hif3a potential regulatory regions and identified 39 regulatory variants by integrating data on constrained and regulatory elements, CpGs, and miRNAs and lncRNAs binding sites. Moreover, 3' UTR and two exonic variants may influence mRNA stability, translation rate and protein functionality. We propose as priority candidates for further functional studies a missense (rs37398126) and synonymous (rs37739792) variants, and intronic (rs47471302) variant that overlap conserved element in promoter region and predicted lncRNAs binding site.

CONCLUSION

The results indicate a potential involvement of Hif3a in fat deposition. Additionally, approach used in the present study may serve as a general guideline for constructing an integrative gene map for prioritizing candidate gene variants with phenotypic effects.

PART1 destabilized by NOVA2 regulates blood-brain barrier permeability in endothelial cells via STAU1-mediated mRNA degradation

Blood-brain barrier dysfunction is recognized as a precursor of Alzheimer's disease development. Endothelial cells as structural basis of blood-brain barrier were observed tight junction failure in amyloid-β(1-42)-stimulated environment. In this study, we found NOVA2, PPP2R3A were down-regulated while PART1, p-NFκB-p65 were up-regulated in amyloid-β(1-42)-incubated endothelial cells. Knockdown of either NOVA2 or PPP2R3A and overexpression of PART1 all increased blood-brain barrier permeability. Lower blood-brain barrier permeability was observed in overexpression of NOVA2 and PPP2R3A and knockdown of PART1 and NFκB-p65. Same tendencies were found in the tight junction-related proteins expressions. Furthermore, overexpression and knockdown of NOVA2 and PART1 had no effect on cell viability. Mechanistically, NOVA2 overexpression was confirmed to reduce half-life of PART1. PART1 could destabilize PPP2R3A messenger RNA (mRNA) by interacting with STAU1. In addition, p-NFκB-p65 functioning as transcription factor reduced the expression of tight junction-related proteins, which was prompted by low protein level of PPP2R3A. Our study highlights the crucial role of NOVA2/PART1/PPP2R3A/p-NFκB-p65 pathway in amyloid-β(1-42)-incubated endothelial cells to modulating blood-brain barrier permeability through STAU1-mediated messenger RNA degradation, implying a potential mechanism of lncRNA and protein interaction in pathogenesis of Alzheimer's disease.

Circ_0016760 Serves as a Cancer Promoter in Non-small Cell Lung Cancer Through miR-876-3p/NOVA2 Axis

Non-small cell lung cancer (NSCLC) is a serious threaten to human health globally. Circular RNAs (circRNAs) were testified to alter the progression of NSCLC. This work intended to investigate the functional role of circ_0016760 in NSCLC development and the potential mechanism. Expression of circ_0016760, microRNA (miR)-876-3p and NOVA alternative splicing regulator 2 (NOVA2) was determined via quantitative reverse transcription-PCT (qRT-PCR) or western blotting. Cell viability, clonogenicity and apoptosis were assessed by Cell Counting Kit-8 (CCK-8) assay, colony formation assay and flow cytometry, respectively. Transwell assay was performed to examine cell migration and invasion. Western blotting was also conducted to detect the levels of epithelial-to-mesenchymal transition (EMT)-related proteins. Role of circ_0016760 in vivo was evaluated via xenograft model assay. Moreover, the interaction between miR-876-3p and circ_0016760 or NOVA2 was verified by dual-luciferase reporter assay or RNA Immunoprecipitation (RIP) assay. Circ_0016760 and NOVA2 were upregulated, while miR-876-3p expression was decreased in NSCLC tissues and cells. Circ_0016760 depletion suppressed NSCLC cell proliferation and metastasis in vitro, as well as hampered tumor growth in vivo. Circ_0016760 acted as a sponge of miR-876-3p, and miR-876-3p could target NOVA2. Circ_0016760 might play vital roles in NSCLC by regulating miR-876-3p/NOVA2 axis. Circ_0016760 could promote the malignant development of NSCLC through miR-876-3p/NOVA2 axis, at least in part.

A ligand-insensitive UNC5B splicing isoform regulates angiogenesis by promoting apoptosis

The Netrin-1 receptor UNC5B is an axon guidance regulator that is also expressed in endothelial cells (ECs), where it finely controls developmental and tumor angiogenesis. In the absence of Netrin-1, UNC5B induces apoptosis that is blocked upon Netrin-1 binding. Here, we identify an UNC5B splicing isoform (called UNC5B-Δ8) expressed exclusively by ECs and generated through exon skipping by NOVA2, an alternative splicing factor regulating vascular development. We show that UNC5B-Δ8 is a constitutively pro-apoptotic splicing isoform insensitive to Netrin-1 and required for specific blood vessel development in an apoptosis-dependent manner. Like NOVA2, UNC5B-Δ8 is aberrantly expressed in colon cancer vasculature where its expression correlates with tumor angiogenesis and poor patient outcome. Collectively, our data identify a mechanism controlling UNC5B’s necessary apoptotic function in ECs and suggest that the NOVA2/UNC5B circuit represents a post-transcriptional pathway regulating angiogenesis.

UNC5B is a Netrin-1 receptor expressed in endothelial cells that in the absence of ligand induces apoptosis. Here the authors identify an UNC5B splicing isoform that is insensitive to the pro-survival ligand Netrin-1 and is required for apoptosis-dependent blood vessel development.

Integrated Analysis of the Roles of RNA Binding Proteins and Their Prognostic Value in Clear Cell Renal Cell Carcinoma

Methods

We downloaded the RNA sequencing data of ccRCC from the Cancer Genome Atlas (TCGA) database and identified differently expressed RBPs in different tissues. In this study, we used bioinformatics to analyze the expression and prognostic value of RBPs; then, we performed functional analysis and constructed a protein interaction network for them. We also screened out some RBPs related to the prognosis of ccRCC. Finally, based on the identified RBPs, we constructed a prognostic model that can predict patients' risk of illness and survival time. Also, the data in the HPA database were used for verification.

Results

In our experiment, we obtained 539 ccRCC samples and 72 normal controls. In the subsequent analysis, 87 upregulated RBPs and 38 downregulated RBPs were obtained. In addition, 9 genes related to the prognosis of patients were selected, namely, RPL36A, THOC6, RNASE2, NOVA2, TLR3, PPARGC1A, DARS, LARS2, and U2AF1L4. We further constructed a prognostic model based on these genes and plotted the ROC curve. This ROC curve performed well in judgement and evaluation. A nomogram that can judge the patient's life span is also made.

Conclusion

In conclusion, we have identified differentially expressed RBPs in ccRCC and carried out a series of in-depth research studies, the results of which may provide ideas for the diagnosis of ccRCC and the research of new targeted drugs.

Hsa_circ_0046263 Drives the Carcinogenesis and Metastasis of Non-Small Cell Lung Cancer Through the Promotion of NOVA2 by Absorbing Mir-940 as a Molecular Sponge

Background

Circular RNAs (circRNAs) have increasingly been investigated in different cancers due to their regulatory roles. In this study, hsa_circ_0046263 will be detailedly researched in non-small cell lung cancer (NSCLC).

Methods

The analyses of hsa_circ_0046263, microRNA-940 (miR-940), and neuro-oncological ventral antigen 2 (NOVA2) levels were administrated by quantitative real-time polymerase chain reaction (qRT-PCR). The proliferation detection was conducted using Cell Counting Kit-8 (CCK-8) and colony formation assays. Cell cycle and apoptosis were evaluated by flow cytometry. Transwell assay for migration and invasion was used to determine cell metastatic capacity. Overall protein levels were examined adopting Western blot. Target binding analysis was completed via dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The effect of hsa_circ_0046263 on NSCLC in vivo was studied by xenograft model in mice.

Results

Hsa_circ_0046263 was overtly upregulated in NSCLC with important prognostic value. In vitro experiments indicated that hsa_circ_0046263 knockdown caused inhibitory effects on NSCLC cell proliferation, cell cycle, and metastasis but stimulative effect on apoptosis. Molecular mechanism analysis demonstrated that hsa_circ_0046263 served as a miR-940 sponge to act in the development of NSCLC. Moreover, miR-940 targeted NOVA2 and NOVA2 was regulated by hsa_circ_0046263/miR-940 axis. NOVA2 overexpression also neutralized the miR-940-mediated progression inhibition of NSCLC cells. In vivo assays suggested that hsa_circ_0046263 enhanced NSCLC tumorigenesis by targeting miR-940/NOVA2 axis.

Conclusion

Hsa_circ_0046263 was identified as a cancer-promoting factor in NSCLC via sponging miR-940 and upregulating NOVA2, which presented a clear mechanism of NSCLC occurrence and progression.

Alternative splicing in endothelial cells: novel therapeutic opportunities in cancer angiogenesis

Alternative splicing (AS) is a pervasive molecular process generating multiple protein isoforms, from a single gene. It plays fundamental roles during development, differentiation and maintenance of tissue homeostasis, while aberrant AS is considered a hallmark of multiple diseases, including cancer. Cancer-restricted AS isoforms represent either predictive biomarkers for diagnosis/prognosis or targets for anti-cancer therapies. Here, we discuss the contribution of AS regulation in cancer angiogenesis, a complex process supporting disease development and progression. We consider AS programs acting in a specific and non-redundant manner to influence morphological and functional changes involved in cancer angiogenesis. In particular, we describe relevant AS variants or splicing regulators controlling either secreted or membrane-bound angiogenic factors, which may represent attractive targets for therapeutic interventions in human cancer.

Prognostic alternative splicing signature in cervical squamous cell carcinoma

Basing on alternative splicing events (ASEs) databases, the authors herein aim to explore potential prognostic biomarkers for cervical squamous cell carcinoma (CESC). mRNA expression profiles and relevant clinical data of 223 patients with CESC were obtained from The Cancer Genome Atlas (TCGA). Correlated genes, ASEs and percent-splice-in (PSI) were downloaded from SpliceSeq, respectively. The PSI values of survival-associated alternative splicing events (SASEs) were used to construct the basis of a prognostic index (PI). A protein-protein interaction (PPI) network of genes related to SASEs was generated by STRING and analysed with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Consequently, 41,776 ASEs were discovered in 19,724 genes, 2596 of which linked with 3669 SASEs. The PPI network of SASEs related genes revealed that TP53 and UBA52 were core genes. The low-risk group had a longer survival period than high-risk counterparts, both groups being defined according to PI constructed upon the top 20 splicing events or PI on the overall splicing events. The AUC value of ROC reached up to 0.88, demonstrating the prognostic potential of PI in CESC. These findings suggested that ASEs involve in the pathogenesis of CESC and may serve as promising prognostic biomarkers for this female malignancy.

Circ_0000376, a Novel circRNA, Promotes the Progression of Non-Small Cell Lung Cancer Through Regulating the miR-1182/NOVA2 Network

Background

Hypoxia has been shown to induce the malignant progression of cancer, including non-small cell lung cancer (NSCLC). Circular RNA (circRNA) is considered to be an important regulator of cancer progression. However, the role of a newly discovered circRNA, circ_0000376, in the progression of NSCLC is unclear.

Methods

The relative expression levels of circ_0000376, miR-1182 and neuro-oncological ventral antigen 2 (NOVA2) were detected via quantitative real-time polymerase chain reaction (qRT-PCR). Glucose consumption and lactate production were determined using Glucose Assay Kit and Lactate Assay Kit, respectively. Moreover, the protein levels of glycolysis markers and NOVA2 were measured using Western blot (WB) analysis. Furthermore, 3-(4, 5-dimethyl-2 thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay was performed to assess cell viability, and transwell assay was employed to evaluate cell migration and invasion. The interaction between miR-1182 and circ_0000376 or NOVA2 was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. In addition, animal experiments were conducted to assess the influence of circ_0000376 silencing on NSCLC tumor growth in vivo.

Results

Circ_0000376 was upregulated in NSCLC, and its high expression was related to the poor overall survival of NSCLC patients. Hypoxia could enhance circ_0000376 expression and promote the glycolysis, viability, migration, and invasion of NSCLC cells. However, silencing of circ_0000376 could inhibit the glycolysis, viability, migration, and invasion of hypoxia-induced NSCLC cells. Additionally, circ_0000376 could sponge miR-1182, and miR-1182 could target NOVA2. MiR-1182 silencing could reverse the inhibitory effect of circ_0000376 knockdown on NSCLC progression, and NOVA2 overexpression also could reverse the suppressive effect of miR-1182 overexpression on NSCLC progression. Meanwhile, miR-1182 inhibitor could invert the negative regulation effect of circ_0000376 silencing on NOVA2 expression. In addition, circ_0000376 knockdown inhibited the NSCLC tumor growth via regulating the miR-1182 and NOVA2 expression in vivo.

Conclusion

Circ_0000376 promoted NSCLC progression by regulating the miR-1182/NOVA2 axis, suggesting that circ_0000376 might be a potential biomarker for NSCLC treatment.

Hypoxia-induced alternative splicing: the 11th Hallmark of Cancer

Hypoxia-induced alternative splicing is a potent driving force in tumour pathogenesis and progression. In this review, we update currents concepts of hypoxia-induced alternative splicing and how it influences tumour biology. Following brief descriptions of tumour-associated hypoxia and the pre-mRNA splicing process, we review the many ways hypoxia regulates alternative splicing and how hypoxia-induced alternative splicing impacts each individual hallmark of cancer. Hypoxia-induced alternative splicing integrates chemical and cellular tumour microenvironments, underpins continuous adaptation of the tumour cellular microenvironment responsible for metastatic progression and plays clear roles in oncogene activation and autonomous tumour growth, tumor suppressor inactivation, tumour cell immortalization, angiogenesis, tumour cell evasion of programmed cell death and the anti-tumour immune response, a tumour-promoting inflammatory response, adaptive metabolic re-programming, epithelial to mesenchymal transition, invasion and genetic instability, all of which combine to promote metastatic disease. The impressive number of hypoxia-induced alternative spliced protein isoforms that characterize tumour progression, classifies hypoxia-induced alternative splicing as the 11th hallmark of cancer, and offers a fertile source of potential diagnostic/prognostic markers and therapeutic targets.

Identification of prognostic alternative splicing signatures in hepatitis B or/and C viruses related hepatocellular carcinoma

BACKGROUND

Alternative splicing (AS) takes a crucial part in tumor process. We aim to analyze AS in Hepatitis B virus (HBV) or/and hepatitis C virus (HCV) related hepatocellular carcinoma (HCC).

METHODS

Cox regression analysis was conducted to screen survival-associated AS events. The receiver operating characteristic curve used to evaluate the predictive accuracy. Splicing network was built to investigate the relationship between splicing factors and AS events.

RESULTS

Ninety-six survival-associated AS events were obtained by univariate Cox regression. Final prognostic model could significantly distinguish the prognosis. We identified RBFOX2 as the hub gene in splicing network based on differentially expressed splicing factors, and obtained MAP3K13_AT as the key AS event in survival-related splicing network.

CONCLUSION

Our results highlight the AS signatures in HCC patients with HBV or/and HCV infection. Meanwhile, AS events and splicing factors in different virus-infected HCC subgroups can provide novel perspectives as biomarkers and individualized therapeutic targets.

Alternative Splicing by NOVA Factors: From Gene Expression to Cell Physiology and Pathology

NOVA1 and NOVA2, the two members of the NOVA family of alternative splicing factors, bind YCAY clusters of pre-mRNAs and assemble spliceosomes to induce the maintenance/removal of introns and exons, thus governing the development of mRNAs. Members of other splicing families operate analogously. Activity of NOVAs accounts for up to 700 alternative splicing events per cell, taking place both in the nucleus (co-transcription of mRNAs) and in the cytoplasm. Brain neurons express high levels of NOVAs, with NOVA1 predominant in cerebellum and spinal cord, NOVA2 in the cortex. Among brain physiological processes NOVAs play critical roles in axon pathfinding and spreading, structure and function of synapses, as well as the regulation of surface receptors and voltage-gated channels. In pathology, NOVAs contribute to neurodegenerative diseases and epilepsy. In vessel endothelial cells, NOVA2 is essential for angiogenesis, while in adipocytes, NOVA1 contributes to regulation of thermogenesis and obesity. In many cancers NOVA1 and also NOVA2, by interacting with specific miRNAs and by additional mechanisms, activate oncogenic roles promoting cell proliferation, colony formation, migration, and invasion. In conclusion, NOVAs regulate cell functions of physiological and pathological nature. Single cell identification and distinction, and new therapies addressed to NOVA targets might be developed in the near future.

Gene Expression Profiles Controlled by the Alternative Splicing Factor Nova2 in Endothelial Cells

Alternative splicing (AS) plays an important role in expanding the complexity of the human genome through the production of specialized proteins regulating organ development and physiological functions, as well as contributing to several pathological conditions. How AS programs impact on the signaling pathways controlling endothelial cell (EC) functions and vascular development is largely unknown. Here we identified, through RNA-seq, changes in mRNA steady-state levels in ECs caused by the neuro-oncological ventral antigen 2 (Nova2), a key AS regulator of the vascular morphogenesis. Bioinformatics analyses identified significant enrichment for genes regulated by peroxisome proliferator-activated receptor-gamma (Ppar-γ) and E2F1 transcription factors. We also showed that Nova2 in ECs controlled the AS profiles of Ppar-γ and E2F dimerization partner 2 (Tfdp2), thus generating different protein isoforms with distinct function (Ppar-γ) or subcellular localization (Tfdp2). Collectively, our results supported a mechanism whereby Nova2 integrated splicing decisions in order to regulate Ppar-γ and E2F1 activities. Our data added a layer to the sequential series of events controlled by Nova2 in ECs to orchestrate vascular biology.

A novel L1CAM isoform with angiogenic activity generated by NOVA2-mediated alternative splicing

The biological players involved in angiogenesis are only partially defined. Here, we report that endothelial cells (ECs) express a novel isoform of the cell-surface adhesion molecule L1CAM, termed L1-ΔTM. The splicing factor NOVA2, which binds directly to L1CAM pre-mRNA, is necessary and sufficient for the skipping of L1CAM transmembrane domain in ECs, leading to the release of soluble L1-ΔTM. The latter exerts high angiogenic function through both autocrine and paracrine activities. Mechanistically, L1-ΔTM-induced angiogenesis requires fibroblast growth factor receptor-1 signaling, implying a crosstalk between the two molecules. NOVA2 and L1-ΔTM are overexpressed in the vasculature of ovarian cancer, where L1-ΔTM levels correlate with tumor vascularization, supporting the involvement of NOVA2-mediated L1-ΔTM production in tumor angiogenesis. Finally, high NOVA2 expression is associated with poor outcome in ovarian cancer patients. Our results point to L1-ΔTM as a novel, EC-derived angiogenic factor which may represent a target for innovative antiangiogenic therapies.

Growing tumors stimulate the formation of new blood vessels to supply the oxygen and nutrients the cancerous cells need to stay alive. Stopping tumors from forming the blood vessels could therefore help us to treat cancer. To do so, we need to understand how different proteins control when and how blood vessels develop.

Cells make proteins by first ‘transcribing’ genes to form RNA molecules. In many cases, the RNA then goes through a process called alternative splicing. Proteins known as splicing factors cut out different segments of the RNA molecule and stick together the remaining segments to form templates for protein production. This enables a single gene to produce many different variants of a protein.

Angiolini, Belloni, Giordano et al. have now studied mouse and human versions of the cells that line the blood vessels grown by tumors. This revealed that a splicing factor called NOVA2 targets a protein called L1CAM, which is normally responsible for gluing adjacent cells together. Angiolini et al. found that NOVA2 splices L1CAM into a form not seen before. Instead of remaining anchored to cell surfaces, the newly identified form of L1CAM is released into the blood circulation, where it stimulates new blood vessels to grow.

Samples taken from the blood vessels of human ovarian tumors showed high levels of both NOVA2 and the modified form of L1CAM, while blood vessels in healthy tissue contain no, or very low levels of both proteins. Therefore, if the new form of L1CAM can be detected in the blood, it could be used to help cancer diagnosis, and to indicate which patients would benefit from treatments that restrict the growth of blood vessels in tumors. Further work is now needed to explore these possibilities.