ABSTRACT
Lipopolysaccharide activates plasma-membrane signaling and endosomal signaling by Toll-like receptor 4 (TLR4) through the TIRAP-MyD88 and TRAM-TRIF adaptor complexes, respectively, but it is unclear how the signaling switch between these cell compartments is coordinated. In dendritic cells, we found that the p110δ isoform of phosphatidylinositol-3-OH kinase (PI(3)K) induced internalization of TLR4 and dissociation of TIRAP from the plasma membrane, followed by calpain-mediated degradation of TIRAP. Accordingly, inactivation of p110δ prolonged TIRAP-mediated signaling from the plasma membrane, which augmented proinflammatory cytokine production while decreasing TRAM-dependent endosomal signaling that generated anti-inflammatory cytokines (interleukin 10 and interferon-ß). In line with that altered signaling output, p110δ-deficient mice showed enhanced endotoxin-induced death. Thus, by controlling the 'topology' of TLR4 signaling complexes, p110δ balances overall homeostasis in the TLR4 pathway.
Subject(s)
Class Ia Phosphatidylinositol 3-Kinase/immunology , Dendritic Cells/immunology , Signal Transduction/immunology , Toll-Like Receptor 4/immunology , Animals , Calpain/pharmacology , Cell Compartmentation/immunology , Cell Membrane/drug effects , Cell Membrane/genetics , Cell Membrane/immunology , Cells, Cultured , Class Ia Phosphatidylinositol 3-Kinase/genetics , Dendritic Cells/cytology , Dendritic Cells/drug effects , Endosomes/drug effects , Endosomes/genetics , Endosomes/immunology , Gene Expression/drug effects , Gene Expression/immunology , Interferon-beta/biosynthesis , Interferon-beta/immunology , Interleukin-10/biosynthesis , Interleukin-10/immunology , Isoenzymes/genetics , Isoenzymes/immunology , Lipopolysaccharides/pharmacology , Membrane Glycoproteins/genetics , Membrane Glycoproteins/immunology , Mice , Mice, Knockout , Receptors, Interleukin/genetics , Receptors, Interleukin/immunology , Receptors, Interleukin-1/genetics , Receptors, Interleukin-1/immunology , Shock, Septic/genetics , Shock, Septic/immunology , Signal Transduction/drug effects , Signal Transduction/genetics , Toll-Like Receptor 4/geneticsABSTRACT
The leukocyte-enriched p110gamma and p110delta isoforms of PI3K have been shown to control in vitro degranulation of mast cells induced by cross-linking of the high affinity receptor of IgE (FcepsilonRI). However, the relative contribution of these PI3K isoforms in IgE-dependent allergic responses in vivo is controversial. A side-by-side comparative analysis of the role of p110gamma and p110delta in mast cell function, using genetic approaches and newly developed isoform-selective pharmacologic inhibitors, confirms that both PI3K isoforms play an important role in FcepsilonRI-activated mast cell degranulation in vitro. In vivo, however, only p110delta was found to be required for optimal IgE/Ag-dependent hypersensitivity responses in mice. These observations identify p110delta as a key therapeutic target among PI3K isoforms for allergy- and mast cell-related diseases.
Subject(s)
Hypersensitivity/enzymology , Hypersensitivity/immunology , Phosphatidylinositol 3-Kinases/physiology , Animals , Catalytic Domain/drug effects , Catalytic Domain/genetics , Cell Degranulation/drug effects , Cell Degranulation/immunology , Cells, Cultured , Class I Phosphatidylinositol 3-Kinases , Epitopes/physiology , Hypersensitivity/genetics , Hypersensitivity/pathology , Immunoglobulin E/physiology , Inflammation Mediators/administration & dosage , Inflammation Mediators/pharmacology , Isoenzymes/antagonists & inhibitors , Isoenzymes/genetics , Isoenzymes/physiology , MAP Kinase Signaling System/drug effects , MAP Kinase Signaling System/genetics , Male , Mast Cells/drug effects , Mast Cells/enzymology , Mast Cells/immunology , Mice , Mice, Inbred C57BL , Mice, Knockout , Phosphatidylinositol 3-Kinases/genetics , Phosphoinositide-3 Kinase Inhibitors , Protein Kinase Inhibitors/administration & dosage , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-akt/deficiency , Proto-Oncogene Proteins c-akt/genetics , Proto-Oncogene Proteins c-akt/metabolism , Receptors, IgG/physiologyABSTRACT
CD4+CD25+Foxp3+ regulatory T cells (Tregs) contribute to the maintenance of peripheral tolerance by inhibiting the expansion and function of conventional T cells. Treg development and homeostasis are regulated by the Ag receptor, costimulatory receptors such as CD28 and CTLA-4, and cytokines such as IL-2, IL-10, and TGF-beta. Here we show that the proportions of Tregs in the spleen and lymph nodes of mice with inactive p110delta PI3K (p110deltaD910A/D910A) are reduced despite enhanced Treg selection in the thymus. p110deltaD910A/D910A CD4+CD25+Foxp3+ Tregs showed attenuated suppressor function in vitro and failed to secrete IL-10. In adoptive transfer experiments, p110deltaD910A/D910A T cells failed to protect against experimental colitis. The identification of p110delta as an intracellular signaling protein that regulates the activity of CD4+CD25+Foxp3+ Tregs may facilitate the further elucidation of the molecular mechanisms responsible for Treg-mediated suppression.
