Alternative splicing produces structural and functional changes in CUGBP2

Identification of molecular targets and small drug candidates for Huntington's disease via bioinformatics and a network-based screening approach

Huntington's disease (HD) is a gradually severe neurodegenerative ailment characterised by an increase of a specific trinucleotide repeat sequence (cytosine-adenine-guanine, CAG). It is passed down as a dominant characteristic that worsens over time, creating a significant risk. Despite being monogenetic, the underlying mechanisms as well as biomarkers remain poorly understood. Furthermore, early detection of HD is challenging, and the available diagnostic procedures have low precision and accuracy. The research was conducted to provide knowledge of the biomarkers, pathways and therapeutic targets involved in the molecular processes of HD using informatic based analysis and applying network-based systems biology approaches. The gene expression profile datasets GSE97100 and GSE74201 relevant to HD were studied. As a consequence, 46 differentially expressed genes (DEGs) were identified. 10 hub genes (TPM1, EIF2S3, CCN2, ACTN1, ACTG2, CCN1, CSRP1, EIF1AX, BEX2 and TCEAL5) were further differentiated in the protein-protein interaction (PPI) network. These hub genes were typically down-regulated. Additionally, DEGs-transcription factors (TFs) connections (e.g. GATA2, YY1 and FOXC1), DEG-microRNA (miRNA) interactions (e.g. hsa-miR-124-3p and has-miR-26b-5p) were also comprehensively forecast. Additionally, related gene ontology concepts (e.g. sequence-specific DNA binding and TF activity) connected to DEGs in HD were identified using gene set enrichment analysis (GSEA). Finally, in silico drug design was employed to find candidate drugs for the treatment HD, and while the possible modest therapeutic compounds (e.g. cortistatin A, 13,16-Epoxy-25-hydroxy-17-cheilanthen-19,25-olide, Hecogenin) against HD were expected. Consequently, the results from this study may give researchers useful resources for the experimental validation of Huntington's diagnosis and therapeutic approaches.

microRNA-mRNA expression profiles in the skeletal muscle of myotonic dystrophy type 1

OBJECTIVES

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults, yet there are currently no disease-modifying treatments. Disrupted miRNA expressions may lead to dysregulation of target mRNAs and dysfunction involved in DM1 pathogenic mechanism.

METHODS

We used microarray platforms to examine the miRNA/mRNA expression profiles in skeletal muscle biopsies derived from DM1 patients and matched controls. Bioinformatics analysis and dual-luciferase reporter assay were conducted to provide insight into miRNA-mRNA regulatory networks altered in DM1.

RESULTS

Twenty-three differentially expressed miRNAs and 135 differentially expressed genes were identified. qPCR confirmed that miR-3201, myogenic factor 5 (MYF5), myogenic differentiation 1 (MYOD1), CUGBP, Elav-like family member 1 (CELF1), and CELF2 were significantly up-regulated, while miR-196a, miR-200c, and miR-146a were significantly down-regulated. Enriched functions and pathways such as multicellular organismal development, RNA splicing, cell differentiation, and spliceosome are relevant to DM1. The miRNA-mRNA interaction network revealed that miR-182, miR-30c-2, and miR-200c were the critical nodes that potentially interacted with hub genes. Luciferase reporter assay confirmed the direct interaction between miR-196a and CELF2.

CONCLUSION

Those results implied that the observed miRNA/mRNA dysregulation could contribute to specific functions and pathways related to DM1 pathogenesis, highlighting the dysfunction of miR-196a and CELF2.

CircLIFR Inhibits Non-small Cell Lung Cancer Progression by Acting as a miR-429 Sponge to Enhance CELF2 Expression

Lung cancer is the most commonly diagnosed cancer and the leading reason for tumor-related mortality, while non-small cell lung cancer (NSCLC) is the most usual type of lung cancer. Circular RNAs (circRNAs) have emerged as vital regulators in the development of human cancers, including NSCLC. We aimed to explore the functions of circRNA leukemia inhibitory factor receptor (circLIFR) in NSCLC progression. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to quantify the expression of circLIFR, microRNA-429 (miR-429), and Elav-like family member 2 (CELF2) in NSCLC tissues and cells. Cell proliferation capability of NSCLC cells was determined by Cell Counting Kit-8 (CCK-8) and colony formation assays. The flow cytometry assay was performed to evaluate cell-cycle distribution and apoptosis of NSCLC cells. The abilities of migration and invasion were measured by transwell assay. In addition, the activities of caspase 3 and caspase 9 were measured by the assay kits. The interaction relationship between miR-429 and circLIFR or CELF2 was analyzed by dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays. The expression levels of related proteins were examined by Western Blot assay. The xenograft experiment was established to explore the role of circLIFR in vivo. CircLIFR, circular, and stable transcript in NSCLC cells, was decreased more than 2 folds in NSCLC tissues and cells than controls (P < 0.0001). Importantly, overexpression of circLIFR impeded cell proliferation, migration, invasion, and inactivated protein kinase B (AKT)/phosphatase and tensin homolog (PTEN)-signaling pathways while enhanced apoptosis and cell-cycle arrest in NSCLC cells, which was overturned by upregulation of miR-429 or silencing of CELF2. Furthermore, the upregulation of circLIFR inhibited NSCLC tumor growth in vivo. Overexpression of circLIFR could suppress NSCLC progress by acting as a sponge of miR-429 to regulate the expression of CELF2 and PTEN/AKT-signaling pathways in NSCLC.

CELF Family Proteins in Cancer: Highlights on the RNA-Binding Protein/Noncoding RNA Regulatory Axis

Post-transcriptional modifications to coding and non-coding RNAs are unquestionably a pivotal way in which human mRNA and protein diversity can influence the different phases of a transcript's life cycle. CELF (CUGBP Elav-like family) proteins are RBPs (RNA-binding proteins) with pleiotropic capabilities in RNA processing. Their responsibilities extend from alternative splicing and transcript editing in the nucleus to mRNA stability, and translation into the cytoplasm. In this way, CELF family members have been connected to global alterations in cancer proliferation and invasion, leading to their identification as potential tumor suppressors or even oncogenes. Notably, genetic variants, alternative splicing, phosphorylation, acetylation, subcellular distribution, competition with other RBPs, and ultimately lncRNAs, miRNAs, and circRNAs all impact CELF regulation. Discoveries have emerged about the control of CELF functions, particularly via noncoding RNAs, and CELF proteins have been identified as competing, antagonizing, and regulating agents of noncoding RNA biogenesis. On the other hand, CELFs are an intriguing example through which to broaden our understanding of the RBP/noncoding RNA regulatory axis. Balancing these complex pathways in cancer is undeniably pivotal and deserves further research. This review outlines some mechanisms of CELF protein regulation and their functional consequences in cancer physiology.

The Emerging Role of Stress Granules in Hepatocellular Carcinoma

Stress granules (SGs) are small membrane-free cytosolic liquid-phase ordered entities in which mRNAs are protected and translationally silenced during cellular adaptation to harmful conditions (e.g., hypoxia, oxidative stress). This function is achieved by structural and functional SG components such as scaffold proteins and RNA-binding proteins controlling the fate of mRNAs. Increasing evidence indicates that the capacity of cells to assemble/disassemble functional SGs may significantly impact the onset and the development of metabolic and inflammatory diseases, as well as cancers. In the liver, the abnormal expression of SG components and formation of SG occur with chronic liver diseases, hepatocellular carcinoma (HCC), and selective hepatic resistance to anti-cancer drugs. Although, the role of SG in these diseases is still debated, the modulation of SG assembly/disassembly or targeting the expression/activity of specific SG components may represent appealing strategies to treat hepatic disorders and potentially cancer. In this review, we discuss our current knowledge about pathophysiological functions of SGs in HCC as well as available molecular tools and drugs capable of modulating SG formation and functions for therapeutic purposes.

AU-rich element-binding proteins in colorectal cancer

Trans-acting factors controlling mRNA fate are critical for the post-transcriptional regulation of inflammation-related genes, as well as for oncogene and tumor suppressor expression in human cancers. Among them, a group of RNA-binding proteins called “Adenylate-Uridylate-rich elements binding proteins” (AUBPs) control mRNA stability or translation through their binding to AU-rich elements enriched in the 3’UTRs of inflammation- and cancer-associated mRNA transcripts. AUBPs play a central role in the recruitment of target mRNAs into small cytoplasmic foci called Processing-bodies and stress granules (also known as P-body/SG). Alterations in the expression and activities of AUBPs and P-body/SG assembly have been observed to occur with colorectal cancer (CRC) progression, indicating the significant role AUBP-dependent post-transcriptional regulation plays in controlling gene expression during CRC tumorigenesis. Accordingly, these alterations contribute to the pathological expression of many early-response genes involved in prostaglandin biosynthesis and inflammation, along with key oncogenic pathways. In this review, we summarize the current role of these proteins in CRC development. CRC remains a major cause of cancer mortality worldwide and, therefore, targeting these AUBPs to restore efficient post-transcriptional regulation of gene expression may represent an appealing therapeutic strategy.

MicroRNA-20a Regulates Glioma Cell Proliferation, Invasion, and Apoptosis by Targeting CUGBP Elav-Like Family Member 2

OBJECTIVE

MicroRNAs (miRNAs) are a class of small noncoding RNAs that play important roles in tumor development and progression. miR-20a acts as an oncogene in many cancers; however, the underlying role of miR-20a in human glioma remains unknown.

METHODS

Glioma tissue samples were obtained from 32 patients with primary glioma who had undergone surgery at the First Affiliated Hospital of Sun Yat-sen University (Guangzhou, China). Twenty-two normal brain tissue samples used as controls were obtained by internal decompression in patients who had undergone surgery for cerebral injury and cerebral hemorrhage at the same hospital.

RESULTS

Quantitative reverse transcription polymerase chain reaction showed upregulation of miR-20a in glioma tissues and cell lines compared with normal brain tissue and normal human astrocytes. Functional assays showed that miR-20a promotes proliferation and invasion and inhibits apoptosis in glioma cells. The bioinformatic analysis showed that CELF2 (CUGBP Elav-like family member 2) is a direct target gene of miR-20a, which was confirmed using a luciferase reporter assay. Downregulation of CELF2 reversed the effects of inhibiting miR-20a expression.

CONCLUSIONS

Collectively, these results suggest a critical role for miR-20a in glioma cell apoptosis, proliferation, and invasion via the direct targeting of CELF2 and indicate its potential application in cancer therapy.

Activation-Dependent TRAF3 Exon 8 Alternative Splicing Is Controlled by CELF2 and hnRNP C Binding to an Upstream Intronic Element

Cell-type-specific and inducible alternative splicing has a fundamental impact on regulating gene expression and cellular function in a variety of settings, including activation and differentiation. We have recently shown that activation-induced skipping of TRAF3 exon 8 activates noncanonical NF-κB signaling upon T cell stimulation, but the regulatory basis for this splicing event remains unknown. Here we identify cis- and trans-regulatory elements rendering this splicing switch activation dependent and cell type specific. The cis-acting element is located 340 to 440 nucleotides upstream of the regulated exon and acts in a distance-dependent manner, since altering the location reduces its activity. A small interfering RNA screen, followed by cross-link immunoprecipitation and mutational analyses, identified CELF2 and hnRNP C as trans-acting factors that directly bind the regulatory sequence and together mediate increased exon skipping in activated T cells. CELF2 expression levels correlate with TRAF3 exon skipping in several model systems, suggesting that CELF2 is the decisive factor, with hnRNP C being necessary but not sufficient. These data suggest an interplay between CELF2 and hnRNP C as the mechanistic basis for activation-dependent alternative splicing of TRAF3 exon 8 and additional exons and uncover an intronic splicing silencer whose full activity depends on the precise location more than 300 nucleotides upstream of the regulated exon.

ORF13 in the Type III secretion system gene cluster of Edwardsiella tarda binds to the mammalian factor Cugbp2

The Type III secretion system (TTSS) is essential for the intracellular replication of Edwardsiella tarda in phagocytes of fish and mammals, and a hypothetical gene (orf13) located in the TTSS gene cluster is required for intracellular replication and virulence of E. tarda. Here, we show that under TTSS-inducing conditions, the protein ORF13 was secreted into culture supernatant. Then, using a yeast 2-hybrid screen, we show that the mammalian factor Cugbp2, which regulates apoptosis in breast cancer cells, directly interacts with ORF13. A pull-down assay revealed that ORF13 binds to the C-terminal region of Cugbp2. Our results suggest that ORF13 may facilitate E. tarda replication in phagocytes by binding to Cugbp2.

Diverse regulation of 3' splice site usage

The regulation of splice site (SS) usage is important for alternative pre-mRNA splicing and thus proper expression of protein isoforms in cells; its disruption causes diseases. In recent years, an increasing number of novel regulatory elements have been found within or nearby the 3'SS in mammalian genes. The diverse elements recruit a repertoire of trans-acting factors or form secondary structures to regulate 3'SS usage, mostly at the early steps of spliceosome assembly. Their mechanisms of action mainly include: (1) competition between the factors for RNA elements, (2) steric hindrance between the factors, (3) direct interaction between the factors, (4) competition between two splice sites, or (5) local RNA secondary structures or longer range loops, according to the mode of protein/RNA interactions. Beyond the 3'SS, chromatin remodeling/transcription, posttranslational modifications of trans-acting factors and upstream signaling provide further layers of regulation. Evolutionarily, some of the 3'SS elements seem to have emerged in mammalian ancestors. Moreover, other possibilities of regulation such as that by non-coding RNA remain to be explored. It is thus likely that there are more diverse elements/factors and mechanisms that influence the choice of an intron end. The diverse regulation likely contributes to a more complex but refined transcriptome and proteome in mammals.

Computational extraction of a neural molecular network through alternative splicing

BACKGROUND

Generally, the results of high throughput analyses contain information about gene expressions, and about exon expressions. Approximately 90% of primary protein-coding transcripts undergo alternative splicing in mammals. However, changes induced by alternative exons have not been properly analyzed for their impact on important molecular networks or their biological events. Even when alternative exons are identified, they are usually subjected to bioinformatics analysis in the same way as the gene ignoring the possibility of functionality change because of the alteration of domain caused by alternative exon. Here, we reveal an effective computational approach to explore an important molecular network based on potential changes of functionality induced by alternative exons obtained from our comprehensive analysis of neuronal cell differentiation.

RESULTS

From our previously identified 262 differentially alternatively spliced exons during neuronal cell differentiations, we extracted 241 sets that changed the amino acid sequences between the alternatively spliced sequences. Conserved domain searches indicated that annotated domain(s) were changed in 128 sets. We obtained 49 genes whose terms overlapped between domain description and gene annotation. Thus, these 49 genes have alternatively differentially spliced in exons that affect their main functions. We performed pathway analysis using these 49 genes and identified the EGFR (epidermal growth factor receptor) and mTOR (mammalian target of rapamycin) signaling pathway as being involved frequently. Recent studies reported that the mTOR pathway is associated with neuronal cell differentiation, vindicating that our approach extracted an important molecular network successfully.

CONCLUSIONS

Effective informatics approaches for exons should be more complex than those for genes, because changes in alternative exons affect protein functions via alterations of amino acid sequences and functional domains. Our method extracted alterations of functional domains and identified key alternative splicing events. We identified the EGFR and mTOR signaling pathway as the most affected pathway. The mTOR pathway is important for neuronal differentiation, suggesting that this in silico extraction of alternative splicing networks is useful. This preliminary analysis indicated that automated analysis of the effects of alternative splicing would provide a rich source of biologically relevant information.

Identification of differentially expressed genes and small molecule drugs for the treatment of tendinopathy using microarray analysis

Tendinopathy is a critical clinical problem as it is often asymptomatic at onset and during development, and is only recognized upon rupture of the tendon. It is common among recreational and competitive athletes. The present study sought to examine the molecular mechanism of the progression of tendinopathy by screening out differentially expressed genes (DEGs) and investigating their functions. In addition, the present study aimed to identify the small molecules, which exhibit potential effects, which could be utilized for the treatment of tendinopathy. The gene expression profile of tendinopathy, GSE26051 was downloaded from the Gene Expression Omnibus database, which included 23 control samples and 18 samples of tendinopathy. The DEGs were identified using the Limma package in the R programming language, and gene ontology and pathway enrichment analysis were performed. In addition, the potential regulatory microRNAs and the target sites of the transcription factors were screened out based on the molecular signature database. In addition, the DEGs were mapped to the connectivity map database to identify the potential small molecule drugs. A total of 318 genes were filtered as DEGs between diseased samples and normal control tendons. Additionally, genes, including laminin, α4, platelet‑derived growth factor α, laminin γ1 and Src homology 2 transforming protein 1 may induce tendinopathy through the focal adhesion pathway. Furthermore, the transcription factor, lymphoid enhancer‑binding factor 1 and its target genes, pantothenate kinase 2 and G protein‑coupled receptor kinase 5 were identified. The most significant microRNA, miR‑499, was screened and was found to regulate specific genes, including CUGBP2 and MYB. Additionally, the small molecules, Prestwick‑1082 and viomycin were identified to have the potential to repair disordered metabolic pathways and furthermore to remedy tendinopathy. The results of the present study assessed the mechanism of tendinopathy and screened small molecule drugs as potential treatments for this condition. In addition, the present findings have the potential for use in a clinical setting for the treatment of tendinopathy in the future.

Alternative splicing regulation of APP exon 7 by RBFox proteins

RBFox proteins are well-known alternative splicing regulators. We have shown previously that during neuronal differentiation of P19 cells induced by all-trans retinoic acid and cell aggregation, RBFox1 shows markedly increased temporal expression. To find its key splicing regulation, we examined the effect of RBFox1 on 33 previously reported and validated neuronal splicing events of P19 cells. We observed that alternative splicing of three genes, specifically, amyloid precursor protein (APP), disks large homolog 3 (DLG3), and G protein, alpha activating activity polypeptide O (GNAO1), was altered by transient RBFox1 expression in HEK293 and HeLa cells. Moreover, an RBFox1 mutant (RBFox1FA) that was unable to bind the target RNA sequence ((U)GCAUG) did not induce these splicing events. APP generates amyloid beta peptides that are involved in the pathology of Alzheimer's disease, and therefore we examined APP alternative splicing regulation by RBFox1 and other splicing regulators. Our results indicated that RBFox proteins promote the skipping of APP exon 7, but not the inclusion of exon 8. We made APP6789 minigenes and observed that two (U)GCAUG sequences, located upstream of exon 7 and in exon 7, functioned to induce skipping of exon 7 by RBFox proteins. Overall, RBFox proteins may shift APP from exon 7 containing isoforms, APP770 and APP751, toward the exon 7 lacking isoform, APP695, which is predominant in neural tissues.

Genome-wide association study of liver enzymes in korean children

Liver enzyme elevations, as an indicator of liver function, are widely associated with metabolic diseases. Genome-wide population-based association studies have identified a genetic susceptibility to liver enzyme elevations and their related traits; however, the genetic architecture in childhood remains largely unknown. We performed a genome-wide association study to identify new genetic loci for liver enzyme levels in a Korean childhood cohort (n = 484). We observed three novel loci (rs4949718, rs80311637, and rs596406) that were multiply associated with elevated levels of alanine transaminase and aspartate transaminase. Although there are some limitations, including genetic power, additional replication and functional characterization will support the clarity on the genetic contribution that the ST6GALNAC3, ADAMTS9, and CELF2 genes have in childhood liver function.

CELFish ways to modulate mRNA decay

The CELF family of RNA-binding proteins regulates many steps of mRNA metabolism. Although their best characterized function is in pre-mRNA splice site choice, CELF family members are also powerful modulators of mRNA decay. In this review we focus on the different modes of regulation that CELF proteins employ to mediate mRNA decay by binding to GU-rich elements. After starting with an overview of the importance of CELF proteins during development and disease pathogenesis, we then review the mRNA networks and cellular pathways these proteins regulate and the mechanisms by which they influence mRNA decay. Finally, we discuss how CELF protein activity is modulated during development and in response to cellular signals. We conclude by highlighting the priorities for new experiments in this field. This article is part of a Special Issue entitled: RNA Decay mechanisms.