Project description:Activation of CD4 T cells is a reaction to challenges such as microbial pathogens, cancer and toxins that defines adaptive immune responses. The roles of T cell receptor crosslinking, intracellular signaling, and transcription factor activation are well described, but the importance of post-transcriptional regulation by RNA-binding proteins (RBPs) has not been considered in depth. We describe a new model expanding and activating primary human CD4 T cells and applied this to characterizing activation-induced assembly of splicing factors centered on U2AF2. We immunoprecipitated U2AF2 to identify what mRNA transcripts were bound as a function of activation by TCR crosslinking and costimulation. In parallel, mass spectrometry revealed the proteins incorporated into the U2AF2-centered RNA/protein interactome. Molecules that retained interaction with the U2AF2 complex after RNAse treatment were designated as “central” interactome members (CIMs). Mass spectrometry also identified a second class of activation-induced proteins, “peripheral” interactome members (PIMs), that bound to the same transcripts but were not in physical association with U2AF2 or its partners. siRNA knockdown of two CIMs and two PIMs caused changes in activation marker expression, cytokine secretion, and gene expression that were unique to each protein and mapped to pathways associated with key aspects of T cell activation. While knocking down the PIM, SYNCRIP, impacts a limited but immunologically important set of U2AF2-bound transcripts, knockdown of U2AF1 significantly impairs assembly of the majority of protein and mRNA components in the activation-induced interactome. These results demonstrated that CIMs and PIMs, either directly or indirectly through RNA, assembled into activation-induced U2AF2 complexes and play roles in post-transcriptional regulation of genes related to cytokine secretion. These data suggest an additional layer of regulation mediated by the activation-induced assembly of RNA splicing interactomes that is important for understanding T cell activation.

Project description:T cell activation leads to dramatic changes in cellular phenotype. We used CD3/CD28-activated human CD4 T cells to study how RNA binding proteins define the post-transcriptional landscape. Using RIPseq, we identified the RNA interactome of U2AF2 and show at the global level that U2AF2 binds the majority of transcripts that are differentially expressed and/or alternatively spliced during CD4 T cell activation. A unique protein interactome centered on U2AF2 is assembled in response to activation. Knocking down specific U2AF2 interacting partners (U2AF1, SYNCRIP, SRRM2, ILF2) selectively affects cytokine secretion and expression of activation markers. Furthermore, the expression and/or alternative splicing of transcripts important for immune cell function are also affected by knocking down these U2AF2 interacting proteins. U2AF1 and SYNCRIP knockdowns affect the proteins and transcripts bound to U2AF2, altering the transcriptome. Our work highlights the importance of RNA binding protein complexes in regulating the differential expression and alternative splicing that defines T cell activation. HTA 2.0 microarray results of total from a primary CD4 T cell culture after treatment with siRNAs (Control, U2AF1, SRRM2, SYNCRIP, and ILF2) and 24 hours after anti-CD3/CD28 bead activation Please note that the Series supplementary 'TotalRNA_HTA2_all_siRNA_100414.xslx' file has multiple worksheets containing: 1) Differentially expressed genes in ctrl siRNA vs. U2AF1 siRNA; 2) Differntially spliced genes in ctrl siRNA vs. U2AF1 siRNA; 3) Differentially spliced exons in ctrl siRNA vs. U2AF1 siRNA; 4) Differentially expressed genes in ctrl siRNA vs. SRRM2 siRNA; 5) Differntially spliced genes in ctrl siRNA vs. SRRM2 siRNA; 6) Differentially spliced exons in ctrl siRNA vs. SRRM2 siRNA; 7) Differentially expressed genes in ctrl siRNA vs. SYNCRIP siRNA; 8) Differntially spliced genes in ctrl siRNA vs. SYNCRIP siRNA; 9) Differentially spliced exons in ctrl siRNA vs. SYNCRIP siRNA; 10) Differentially expressed genes in ctrl siRNA vs. ILF2 siRNA; 11) Differntially spliced genes in ctrl siRNA vs. ILF2 siRNA; 12) Differentially spliced exons in ctrl siRNA vs. ILF2 siRNA

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The Activation-Induced Assembly of an RNA/Protein Interactome Centered on the Splicing Factor U2AF2 Regulates Gene Expression in Human CD4 T Cells [RIP-Seq]

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