LFA-1-Dependent HuR Nuclear Export and Cytokine mRNA Stabilization in T Cell Activation

Yale University, New Haven, Connecticut, United States
The Journal of Immunology (Impact Factor: 4.92). 03/2006; 176(4):2105-13. DOI: 10.4049/jimmunol.176.4.2105
Source: PubMed


Lymphokine gene expression is a precisely regulated process in T cell-mediated immune responses. In this study we demonstrate that engagement of the beta(2) integrin LFA-1 in human peripheral T cells markedly extends the half-life of TNF-alpha, GM-CSF, and IL-3 mRNA, as well as a chimeric beta-globin mRNA reporter construct containing a strongly destabilizing class II AU-rich element from the GM-CSF mRNA 3'-untranslated region. This integrin-enhanced mRNA stability leads to augmented protein production, as determined by TNF-alpha ELISPOT assays. Furthermore, T cell stimulation by LFA-1 promotes rapid nuclear-to-cytoplasmic translocation of the mRNA-stabilizing protein HuR, which in turn is capable of binding an AU-rich element sequence in vitro. Abrogation of HuR function by use of inhibitory peptides, or marked reduction of HuR levels by RNA interference, prevents LFA-1 engagement-mediated stabilization of T cell TNF-alpha or IFN-gamma transcripts, respectively. Thus, HuR-mediated mRNA stabilization, stimulated by integrin engagement and controlled at the level of HuR nuclear export, is critically involved in T cell activation.

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Available from: Mark Collinge
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    • "We found previously that b-catenin interacts with HuR in the cytoplasm of cancer cells and promotes stability of the oncogenic gene target mRNA [14] [15]. As various signaling pathways are involved in b-catenin cytoplasmic export and regulation of RNA stability by HuR [18] [19] [20] [21], we tested whether Wnt signaling is relevant to subcellular localization of HuR. Act D was used as the positive control for HuR export to the cytoplasm [19]. "
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    ABSTRACT: β-Catenin is the key transcriptional activator of canonical Wnt signaling in the nucleus; thus, nuclear accumulation of β-catenin is a critical step for expressing target genes. β-Catenin accumulates in the nucleus of cancer cells where it activates oncogenic target genes. Hu antigen R (HuR) is a RNA binding protein that regulates multiple post-transcriptional processes including RNA stability. Thus, cytoplasmic HuR protein may be involved in tumorigenesis by stabilizing oncogenic transcripts, but the molecular mechanism remains unclear. Here, we observed that Wnt/β-catenin signaling induced export of the HuR protein, whereas HuR overexpression promoted accumulation of the β-catenin protein in the cytoplasm. Thus, Wnt/β-catenin-mediated transcriptional activity in the nucleus was reduced by overexpressing HuR. These results suggest novel and uncharacterized cytoplasmic β-catenin functions related to HuR-mediated RNA metabolism in cancer cells. Copyright © 2014 Elsevier Inc. All rights reserved.
    Full-text · Article · Dec 2014 · Biochemical and Biophysical Research Communications
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    • "While the ubiquitous RBP HuR is functionally characterized mainly as a positive regulator of mRNA stability and translation, TTP limits the inflammatory response by accelerating the mRNA decay of its targets [13]. In particular, cell activation induces HuR nucleocytoplasmic shuttling [20–24], an event reflecting its functional activation, which leads to increased protein output for several inflammatory genes, by making their mRNA more stable and/or by increasing their translation rates [22, 25–31] acting through multiple, often independent mechanisms yet to be fully characterized [32]. "
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    ABSTRACT: Posttranscriptional gene regulation (PTR) is a fundamental biological process that integrates with the master transcriptional control of gene expression, in ways that only in the last decade have been increasingly understood [1, 2]. While epigenetic and transcriptional events shape cell response qualitatively, deciding the pattern of gene expression to 'switch on or off' in response to endogenous or environmental triggers, the key task of PTR is to act as a 'rheostat' and rapidly adapt the cellular response by providing the appropriate amplitude and timing to the protein expression patterns [3, 4]. The pivotal role of this mechanism comes to the forefront in inflammatory and immune response, where the changes in amplitude and duration in the expression of dangerous and protective genes are in delicate balance, and are critical in determining either the successful resolution of the immune response or its chronic overexpression [5]. This brief review introduces members of the main classes of molecules mediating the cytoplasmic arm of gene regulation, namely RNA-binding proteins and micro-RNA (miRNA), and summarizes experimental data that underscore the role of these molecules in the pathophysiology of chronic inflammation, as well as their promising value as mechanisms conveying the anti-inflammatory effect of synthetic glucocorticoids.
    Full-text · Article · May 2012
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    • "The mRNA-stabilizing downstream molecular target of LFA-1 signaling is HuR, an ARE-binding and stabilizing protein that is constitutively expressed in the T cell nucleus. We have recently demonstrated that T cell HuR can undergo rapid nuclear-to-cytoplasmic translocation solely by engagement of LFA-1 with its ligand ICAM-1 [3]. Such altered subcellular localization of HuR has been shown to correlate with its mRNA stabilizing activity [4]. "
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    ABSTRACT: Engagement of the β2 integrin, lymphocyte function-associated antigen-1 (LFA-1), results in stabilization of T cell mRNA transcripts containing AU-rich elements (AREs) by inducing rapid nuclear-to-cytosolic translocation of the RNA-stabilizing protein, HuR. However, little is known regarding integrin-induced signaling cascades that affect mRNA catabolism. This study examines the role of the GTPases, Rac 1 and Rac 2, and their downstream effectors, in the LFA-1-induced effects on mRNA. Engagement of LFA-1 to its ligand, ICAM-1, in human peripheral T cells resulted in rapid activation of Rac1 and Rac2. siRNA-mediated knockdown of either Rac1 or Rac2 prevented LFA-1-stimulated stabilization of the labile transcripts encoding IFN-γ and TNF-α, and integrin mediated IFN-γ mRNA stabilization was absent in T cells obtained from Rac2 gene-deleted mice. LFA-1 engagement-induced translocation of HuR and stabilization of TNF- α mRNA was lost in Jurkat cells deficient in the Rac guanine nucleotide exchange factor Vav-1 (J.Vav1). The transfection of J.Vav1 cells with constitutively active Rac1 or Rac2 stabilized a labile β-globin reporter mRNA, in a HuR-dependent manner. Furthermore, LFA-1-mediated mRNA stabilization and HuR translocation in mouse splenic T cells was dependent on the phosphorylation of the mitogen-activated protein kinase kinase, MKK3, and its target MAP kinase p38MAPK, and lost in T cells obtained from MKK3 gene-deleted mice. Collectively, these results demonstrate that LFA-1-induced stabilization of ARE-containing mRNAs in T cells is dependent on HuR, and occurs through the Vav-1, Rac1/2, MKK3 and p38MAPK signaling cascade. This pathway constitutes a molecular switch that enhances immune and pro-inflammatory gene expression in T cells undergoing adhesion at sites of activation and effector function.
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