The RNA-Binding Protein, Polypyrimidine Tract-Binding Protein 1 (PTBP1) Is a Key Regulator of CD4 T Cell Activation

Abstract

We have previously shown that the RNA binding protein, polypyrimidine tract-binding protein (PTBP1) plays a critical role in regulating the expression of CD40L in activated CD4 T cells. This is achieved mechanistically through message stabilization at late times of activation as well as by altered distribution of CD40L mRNA within distinct cellular compartments. PTBP1 has been implicated in many different processes, however whether PTBP1 plays a broader role in CD4 T cell activation is not known. To examine this question, experiments were designed to introduce shRNA into primary human CD4 T cells to achieve decreased, but not complete ablation of PTBP1 expression. Analyses of shPTB-expressing CD4 T cells revealed multiple processes including cell proliferation, activation-induced cell death and expression of activation markers and cytokines that were regulated in part by PTBP1 expression. Although there was an overall decrease in the steady-state level of several activation genes, only IL-2 and CD40L appeared to be regulated by PTBP1 at the level of RNA decay suggesting that PTBP1 is critical at different regulatory steps of expression that is gene-specific. Importantly, even though the IL-2 protein levels were reduced in cells with lowered PTBP1, the steady-state level of IL-2 mRNA was significantly higher in these cells suggesting a block at the translational level. Evaluation of T cell activation in shPTB-expressing T cells revealed that PTBP1 was linked primarily to the activation of the PLCγ1/ERK1/2 and the NF-κB pathways. Overall, our results reveal the importance of this critical RNA binding protein in multiple steps of T cell activation.

Uncovering the Role of RNA-Binding Proteins in Gene Expression in the Immune System

“…hnRNPK also limits Vav-1-mediated proteolysis and enables IL-2 production ( 191 , 192 ). Other RBPs such as ELAVL1, PTBP1, and ZFP36 have also been involved in IL2 mRNA translational regulation and protein synthesis upon TCR engagement ( 174 , 193 , 194 ).…”

Polypyrimidine Tract Binding Proteins are essential for B cell development

“…PTBP1 suppression of entry into S-phase was unanticipated since in other systems, including germinal centre (GC) B cells, PTBP1 promoted proliferation (Suckale et al, 2011;Shibayama et al, 2009;La Porta et al, 2016) and progression through late S-phase (Monzon-Casanova et al, 2018). GC B cells did not tolerate deletion of both PTBP1 and PTBP2 (Monzon-Casanova et al, 2018) and previous studies addressing proliferation in PTBP1-deficient cells were done in the presence of PTBP2 (Suckale et al, 2011;Shibayama et al, 2009;La Porta et al, 2016). Therefore, the role of PTBP1 in suppressing S-phase entry could be unique to pro-B cells or could be found in other cell types if they resist the absence of PTBP1 and PTBP2 long enough to assess cellcycle progression.…”

“…The enhanced entry into S-phase of pro-B cells lacking PTBP1 and PTBP2 was unanticipated since in other systems, including GC B cells, PTBP1 promoted proliferation (Suckale et al, 2011;Shibayama et al, 2009;La Porta et al, 2016) and progression through late S-phase (Monzon-Casanova et al, 2018). These previous studies were done in the presence of PTBP2 (Suckale et al, 2011;Shibayama et al, 2009;La Porta et al, 2016) and GC B cells did not tolerate deletion of both PTBP1 and PTBP2 (Monzon-Casanova et al, 2018). Thus, our findings may not be unique to pro-B cells and may be found in other cell types if they survive the absence of PTBP1 and PTBP2 long enough to assess cell-cycle progression.…”

A Single Nucleotide ADA Genetic Variant Is Associated to Central Inflammation and Clinical Presentation in MS: Implications for Cladribine Treatment

“…Then, by RBPmap Version 1.1 [ 15 ], we searched consensus sequences for RNA binding proteins (RBPs), which included the identified SNPs with minor allele frequency of 8% or more. Finally, by the functional annotation with DAVID 6.8 [ 16 ] and PubMed [ 17 ] we selected rs244072 as good candidate for further studies in MS, being the SNP located into putative binding sites for RBPs crucial in lymphocyte activation [ 18 , 19 , 20 ].…”