T Cell LFA-1 Engagement Induces HuR-Dependent Cytokine mRNA Stabilization through a Vav-1, Rac1/2, p38MAPK and MKK3 Signaling Cascade

Abstract

BackgroundEngagement 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.Methodology/Principal FindingsEngagement 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.Conclusions/SignificanceCollectively, 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.

β1-Adrenoceptor Autoantibodies from DCM Patients Enhance the Proliferation of T Lymphocytes through the β1-AR/cAMP/PKA and p38 MAPK Pathways

“…In immune cells, p38 MAPK plays a role in regulating the production of mature T cells [21]–[22]. To investigate the role of activation of p38 MAPK in β 1 -AA-stimulated T cell proliferation, the selective p38 MAPK antagonist SB203580 (1 µmol/l) was used to block the pathway before stimulation with β 1 -AA (25 µg/ml), and then the activity of p38 MAPK was determined.…”

TCR-CXCR4 signaling stabilizes cytokine mRNA transcripts via a PREX1-Rac1 pathway: implications for CTCL

“…Activation of TCR leads to CXCR4-mediated stabilization of cytokine mRNA via activation of a PREX1-Rac1-signaling pathway Rac1 has previously been described to mediate mRNA stability in various cell types [23][24][25][26][27] and is activated in response to both TCR-and CXCR4-induced signaling. 8,28,29 Therefore, we hypothesized that TCR-CXCR4 signaling activates Rac1 in order to stabilize cytokine mRNA.…”

“…[20][21][22] The GTPase, Rac1, has previously been linked to mRNA stabilization in various cell types. [23][24][25][26][27] In T cells, Rac1 has been mainly studied for its role in migration and cellular signaling. 28,29 CXCR4 has been shown to activate Rac1 via the Rac-GEF, PREX1, in various cell types, 17,19,30,31 however, a role for PREX1 in T-cell signaling had not been previously described.…”

RNA-binding proteins as a point of convergence of the PI3K and p38 MAPK pathways

“…In neuronal cell line p38 activation following treatment with anisomycin promotes the cytoplasmic accumulation of HuR where it interacts with and stabilizes the survival motor neuron (SMN) transcript (Farooq et al, 2009). In mouse splenic T cells, LFA-1 engagement activates p38 which promotes HuR translocation and stabilization of IFN-γ and TNF mRNA (Ramgolam et al, 2010). In none of these studies was it established whether HuR was directly phosphorylated by p38 or MK2.…”