PI3 kinase function is vital for the function but not formation of LAT-mediated signaling complexes

Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
Molecular Immunology (Impact Factor: 2.97). 06/2009; 46(11-12):2274-83. DOI: 10.1016/j.molimm.2009.04.006
Source: PubMed


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.

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    • "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 [17], [29]), 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 [30]. "
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    • "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). "
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