The function of Wtap in N6-adenosine methylation of mRNAs controls T cell receptor signaling and survival of T cells [m6A-CLIP]
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ABSTRACT: T cell antigen receptor (TCR) signaling controls the development, activation and survival of T cells by involving several layers and numerous mechanisms of gene regulation. N6-methyladenosine (m6A) is the most prevalent mRNA modification affecting splicing, translation and stability of transcripts. Here, we describe the Wtap protein as essential for m6A methyltransferase complex function and reveal its crucial role in TCR signaling. Wtap and m6A methyltransferase functions were required for the differentiation of thymocytes, control of activation-induced death of peripheral T cells and prevention of colitis by enabling gut RORγt+ regulatory T cell function. Transcriptome and epitranscriptomic analyses reveal that m6A modification destabilizes Orai1 and Ripk1 mRNAs. Lack of post-transcriptional repression of the encoded proteins correlated with increased store-operated calcium entry (SOCE) activity and diminished survival of T cells. These findings uncover how m6A modification impacts on TCR signal transduction and determines activation and survival of T cells.
Project description:T cell antigen receptor (TCR) signaling controls the development, activation and survival of T cells by involving several layers and numerous mechanisms of gene regulation. N6-methyladenosine (m6A) is the most prevalent mRNA modification affecting splicing, translation and stability of transcripts. Here, we describe the Wtap protein as essential for m6A methyltransferase complex function and reveal its crucial role in TCR signaling. Wtap and m6A methyltransferase functions were required for the differentiation of thymocytes, control of activation-induced death of peripheral T cells and prevention of colitis by enabling gut RORγt+ regulatory T cell function. Transcriptome and epitranscriptomic analyses reveal that m6A modification destabilizes Orai1 and Ripk1 mRNAs. Lack of post-transcriptional repression of the encoded proteins correlated with increased store-operated calcium entry (SOCE) activity and diminished survival of T cells. These findings uncover how m6A modification impacts on TCR signal transduction and determines activation and survival of T cells.
Project description:T cell antigen receptor (TCR) signaling controls the development, activation and survival of T cells by involving several layers and numerous mechanisms of gene regulation. N6-methyladenosine (m6A) is the most prevalent mRNA modification affecting splicing, translation and stability of transcripts. Here, we describe the Wtap protein as essential for m6A methyltransferase complex function and reveal its crucial role in TCR signaling. Wtap and m6A methyltransferase functions were required for the differentiation of thymocytes, control of activation-induced death of peripheral T cells and prevention of colitis by enabling gut RORγt+ regulatory T cell function. Transcriptome and epitranscriptomic analyses reveal that m6A modification destabilizes Orai1 and Ripk1 mRNAs. Lack of post-transcriptional repression of the encoded proteins correlated with increased store-operated calcium entry (SOCE) activity and diminished survival of T cells. These findings uncover how m6A modification impacts on TCR signal transduction and determines activation and survival of T cells.
Project description:SETD2 is the specific methyltransferase of H3K36me3, while METTL3, METTL14 and WTAP are the components of m6A methyltransferase complex. To understand the global effect of H3K36me3 on m6A modification, we compared the m6A profiling in SETD2 and METTL3, METTL14 or WTAP knockdown HepG2 cells, and found depletion of H3K36me3 by SETD2 silencing globally reduced m6A in human transcriptome. What’s more, most of the SETD2-dependent hypomethylation sites also responded to knockdown of METTL3, METTL14, or WTAP.
Project description:N6-methyladenosine (m6A) is the most abundant internal modification in the messenger RNA (mRNA) of all higher eukaryotes. This modification has been shown to be reversible in mammals; it is installed by a methyltransferase heterodimer complex of METTL3 and METTL14 bound with WTAP, and reversed by iron(II)- and α-ketoglutarate-dependent demethylases FTO and ALKBH5. This modification exhibits significant functional roles in various biological processes. The m6A modification as a RNA mark is recognized by reader proteins, such as YTH domain family proteins and HNRNPA2B1; m6A can also act as a structure switch to affect RNA-protein interactions for biological regulation. In Arabidopsis thaliana, the methyltransferase subunit MTA (the plant orthologue of human METTL3, encoded by At4g10760) was well characterized and FIP37 (the plant orthologue of human WTAP) was first identified as the interacting partner of MTA. Here we report the discovery and characterization of reversible m6A methylation mediated by AtALKBH10B (encoded by At4g02940) in A. thaliana, and noticeable roles of this RNA demethylase in affecting plant development and floral transition. Our findings reveal potential broad functions of reversible mRNA methylation in plants. m6A peaks were identified from wild type Columbia-0 and atalkbh10b-1 mutant in two biological replicates
Project description:N6-methyladenosine (m6A) is the most prevalent internal modification found in mammalian messenger and non-coding RNAs. The discoveries of functionally significant demethylases that reverse this methylation as well as the recently revealed m6A distributions in mammalian transcriptomes strongly indicate regulatory functions of this modification. Here we report the identification and characterization of the mammalian nuclear RNA N6-adenosine methyltransferase core (RNMTC) complex. Besides METTL3, a methyltransferase which was the only known component of RNMTC in the past, we discovered that a previously uncharacterized methyltransferase, METTL14, exhibits a N6-adenosine methyltransferase activity higher than METTL3. Together with WTAP, the third component that dramatically affects the cellular m6A level, these three proteins form the core complex that orchestrates m6A deposition on mammalian nuclear RNA. Biochemistry assays, imaging experiments, as well as transcriptome-wide analyses of the binding sites and their effects on m6A methylation support methylation function and reveal new insights of RNMTC. PAR-CLIP and m6A-seq in HeLa cells
Project description:N(6)-methyladenosine (m6A) plays an important role in the tumorigenesis and progression of cancers. However, the clinical significance of m6A and their regulatory mechanisms in nasopharyngeal carcinogenesis (NPC) remain largely unknown. In this study, we used the microarray analysis to study WTAP-mediated m6A modification profiles in human nasopharyngeal carcinoma cell line, HONE-1, by comparing 3 pairs of samples with or without WTAP knockdown.
Project description:WTAP is an essential component of the RNA N-6-methyladenosine (m6A) modification complexes that guides METLL3-METLL14 heteroduplexes to target RNAs in the nucleus of mammalian cells. Through mining the genotype-tissue expression (GTEx) datasets, we initially found that TTC22 expression was highly correlated with WTAP and FTO in many normal human tissues. Our experimental results indicate that TTC22 could directly capture RNA binding protein RPL4, induce the binding between RPL4 and WTAP mRNA in the cytoplasm, which increased the m6A level, induced alterative splicing, enhanced the stability and translation efficiency of WTAP mRNA, and consequently upregulated the level of total m6A RNA. These results indicate that WTAP mRNA is a m6A target and there is a positive feedback loop between total m6A and WTAP expression. YTHDF1 was found to be an essential m6A WTAP mRNA binding protein. Downregulation of RPL4, WTAP, or YTHDF1 expression could reverse TTC22-enhanced total m6A RNA level. m6A-specific antibody immunoprecipitated RNA-sequencing (meRIP-seq) demonstrated that TTC22 caused dramatic expression changes of genes related to metabolic pathways, ribosome biogenesis, and RNA spliceosome. Furthermore, we also found that TTC22 upregulated the expression of epithelial-mesenchymal transition (EMT)-related gene SNAI1 via m6A, and promoted metastasis of colon cancer in vitro and in mice. In conclusion, our study illustrates that WTAP mRNA is a m6A target using YTHDF1 as the binding protein. TTC22 could upregulate the levels of WTAP expression and total m6A RNA through the PRL4 binding. The m6A-mediated upregulation of SNAI1 expression may contribute to TTC22-enhanced colon cancer metastasis.
Project description:Store operated calcium entry (SOCE) downstream of T cell receptor (TCR) activation in T lymphocytes has been shown to be mediated mainly through the Calcium Release Activated Calcium (CRAC) channel. Here, we compared the effects of a novel, potent and selective CRAC inhibitor, 2,6-Difluoro-N-{5-[4-methyl-1-(5-methyl-thiazol-2-yl)-1,2,5,6-tetrahydro-pyridin-3-yl]-pyrazin-2-yl}-benzamide (RO2959), on T cell effector functions with that of a previously reported CRAC channel inhibitor, YM-58483, and a calcineurin inhibitor Cyclosporin A (CsA). Using both electrophysiological and calcium-based fluorescence measurements, we showed that RO2959 is a potent SOCE inhibitor that blocked an IP3-dependent current in CRAC-expressing RBL-2H3 cells and CHO cells stably expressing human Orai1 and Stim1, as well as SOCE in human primary CD4+ T cells triggered by either TCR stimulation or thapsigargin treatment. Furthermore, we demonstrated that RO2959 completely inhibited cytokine production as well as T cell proliferation mediated by TCR stimulation or MLR (Mixed Lymphocyte Reaction). Lastly, we showed by gene expression array analysis that RO2959 potently blocked TCR triggered gene expression and T cell functional pathways similar to CsA and FK506. Thus, both from a functional and transcriptional level, our data provide evidence that RO2959 is a novel and selective CRAC inhibitor that potently inhibits human T cell functions. PBMC from healthy donors (n=4) were stimulated with anti-CD3/CD28 in the presence or absence of CRAC inhibitor, CsA or FK506 for 24 hrs
Project description:Calcium signals are initiated in immune cells by the process of store-operated calcium entry (SOCE), where receptor activation triggers transient calcium release from the endoplasmic reticulum, followed by opening of plasma membrane calcium-release activated calcium (CRAC) channels. ORAI1, ORAI2 and ORAI3 are known to comprise the CRAC channel, however the contributions of individual isoforms to neutrophil function is not well understood. Here we show that loss of ORAI1 partially decreases calcium influx while loss of both ORAI1 and ORAI2 completely abolishes store-operated calcium entry. In other immune cell types, loss of ORAI2 enhances SOCE. In contrast, we find that ORAI2-deficient neutrophils display decreased calcium influx, which is correlated with measurable differences in regulation of neutrophil membrane potential via KCa3.1. Decreased SOCE in ORAI1-, ORAI2- and ORAI1/2-deficient neutrophils impairs multiple neutrophil functions including phagocytosis, degranulation, leukotriene and ROS production, rendering ORAI1/2-deficient mice highly susceptible to staphylococcal infection. This study demonstrates that ORAI1 and ORAI2 are the primary components of the neutrophil CRAC channel and identifies novel subpopulations of neutrophils where cell membrane potential functions as a rheostat to modulate the SOCE response. These findings have implications for new mechanisms that modulate neutrophil function during infection, acute and chronic inflammatory conditions, and cancer.
Project description:Alternative splicing is a potent modifier of protein function. Stromal interaction molecule 1 (Stim1) is the essential activator of store-operated Ca2+ entry (SOCE) triggering activation of transcription factors. Here, we characterize Stim1A, a splice variant with an additional 31 amino acid domain inserted in frame within its cytosolic domain. Prominent expression of exon A is found in astrocytes, heart, kidney and testes. Full length Stim1A functions as a dominant-negative regulator of SOCE and ICRAC, facilitating sequence specific fast calcium dependent inactivation and destabilizing gating or Orai1. Downregulation or absence of native Stim1A results in increased SOCE. Despite reducing SOCE, Stim1A leads to increased NFAT translocation. Differential proteomics revealed interference of Stim1A with the cAMP-SOCE crosstalk by altered modulation of phosphodiesterase (PDE8B), resulting in reduced cAMP degradation and increased PIP5K activity, facilitating an increased NFAT activation. Our study uncovers a hitherto unknown mechanism regulating NFAT activation and indicates that cell type specific splicing of Stim1 is a potent means to regulate the NFAT signalosome and cAMP-SOCE crosstalk.