The induction of the T cell receptor (TCR) is necessary for the activation and function of human T cells. TCR activation results in the tyrosine phosphorylation of LAT, leading to the direct interaction with several proteins, including PLC-gamma 1, Grb2 and Gads. These direct ligands then mediate the indirect interaction of LAT with proteins, such as SLP-76, Vav1 and Itk. PLC-gamma 1, Vav1 and Itk contain pleckstrin homology (PH) domains that interact with the enzymatic product of phosphoinositide-3-kinase (PI3K), suggesting the function of PI3K may modulate LAT-mediated complexes. Therefore, we characterized the poorly understood role of PI3K activity in the formation and function of multiprotein signaling complexes that form at LAT. Inhibition of PI3K catalytic function had little effect on the phosphorylation of LAT, SLP-76, Vav1 or PLC-gamma 1 or on the ability of PLC-gamma 1 to interact with LAT or SLP-76. However, PI3K activity appeared to be required for the induction of downstream signaling events. These data indicate that the formation of LAT-mediated complexes do not appear to depend on PI3K activity, whereas the optimal downstream function of these complexes requires the catalytic function of PI3K.
"To investigate if the enzymatic function of PI3K controls the late phase of TCR-mediated adhesion, we pre-treated hAPBTs with two PI3K inhibitors, wortmannin and LY294002, and stimulated them on plates coated with anti-TCR for 30 minutes. While the TCR-inducible phosphorylation of Akt and Erk1/Erk2 was inhibited by these treatments (data not shown and , ), the cellular binding was not significantly impacted by wortmannin or LY294002 pre-treatment, suggesting that PI3K activity was not required for the second wave of TCR-mediated adhesion (Figure 8A). Interestingly, the highest dose of wortmannin did modestly suppress binding, potentially because wortmannin inhibits myosin light chain kinase activity at this dose . "
[Show abstract][Hide abstract] ABSTRACT: T cell activation drives the protective immune response against pathogens, but is also critical for the development of pathological diseases in humans. Cytoskeletal changes are required for downstream functions in T cells, including proliferation, cytokine production, migration, spreading, and adhesion. Therefore, investigating the molecular mechanism of cytoskeletal changes is crucial for understanding the induction of T cell-driven immune responses and for developing therapies to treat immune disorders related to aberrant T cell activation. In this study, we used a plate-bound adhesion assay that incorporated near-infrared imaging technology to address how TCR signaling drives human T cell adhesion. Interestingly, we observed that T cells have weak adhesion early after TCR activation and that binding to the plate was significantly enhanced 30-60 minutes after receptor activation. This late stage of adhesion was mediated by actin polymerization but was surprisingly not dependent upon Src family kinase activity. By contrast, the non-catalytic functions of the kinases Fyn and Pyk2 were required for late stage human T cell adhesion. These data reveal a novel TCR-induced signaling pathway that controls cellular adhesion independent of the canonical TCR signaling cascade driven by tyrosine kinase activity.
PLoS ONE 12/2012; 7(12):e53011. DOI:10.1371/journal.pone.0053011 · 3.23 Impact Factor
"The next step in the signaling cascade is the recruitment and phosphorylation of linker for activation of T cells (LAT) that is essential for TCR signaling (Finco et al., 1998), T cell activation (Zhang et al., 1999a) and development (Zhang et al., 1999b). LAT serves as a platform for several adapter and effector molecules (Figure 1A) including phospholipase C gamma (PLCγ) (Zhang et al., 2000), phosphatidylinositol 3-kinase (PI3K) (Cruz-Orcutt and Houtman, 2009) Src-homology-2-domain-containing leukocyte protein of 76 kDa (SLP76) (Wu and Koretzky, 2004), growth factor receptor-bound protein 2 (Grb2) (Zhang et al., 2000) and the Grb2-homologous adapter (GADS) (Zhang et al., 2000; Liu et al., 2001). The mechanism of LAT recruitment is controversial, as discussed below, and it has been suggested that there are LAT-dependent and -independent signaling pathways (Malissen and Marguet, 2011). "
[Show abstract][Hide abstract] ABSTRACT: Engagement of the T cell antigen receptor (TCR) triggers signaling pathways that lead to T cell selection, differentiation and clonal expansion. Superimposed onto the biochemical network is a spatial organization that describes individual receptor molecules, dimers, oligomers and higher order structures. Here we discuss recent findings and new concepts that may regulate TCR organization in naïve and memory T cells. A key question that has emerged is how antigen-TCR interactions encode spatial information to direct T cell activation and differentiation. Single molecule super-resolution microscopy may become an important tool in decoding receptor organization at the molecular level.
Frontiers in Immunology 11/2012; 3:352. DOI:10.3389/fimmu.2012.00352
[Show abstract][Hide abstract] ABSTRACT: The Tec family tyrosine kinases regulate lymphocyte development, activation, and differentiation. In T cells, the predominant Tec kinase is Itk, which functions downstream of the T-cell receptor to regulate phospholipase C-gamma. This review highlights recent advances in our understanding of Itk kinase structure and enzymatic regulation, focusing on Itk protein domain interactions and mechanisms of substrate recognition. We also discuss the role of Itk in the development of conventional versus innate T-cell lineages, including both alphabeta and gammadelta T-cell subsets. Finally, we describe the complex role of Itk signaling in effector T-cell differentiation and the regulation of cytokine gene expression. Together, these data implicate Itk as an important modulator of T-cell signaling and function.
Cold Spring Harbor perspectives in biology 07/2010; 2(7):a002287. DOI:10.1101/cshperspect.a002287 · 8.68 Impact Factor
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