Human mast cell activation through Fc receptors and Toll-like receptors

ABSTRACTMast cells express high-affinity IgE receptors (FcεRI) on their surface and can be activated to secrete a variety of biologically active mediators by cross-linking of receptor-bound IgE. Recent studies in animal models indicate that mouse mast cells may play a protective role in host defense against bacteria through the production of tumor necrosis factor-α, mainly as a result of Toll-like receptor (TLR) 4- or CD48-mediated activation. Moreover, several recent observations in animal models have indicated that mast cells may also play a pivotal role in coordinating the early phases of autoimmune diseases, particularly those involving auto-antibodies. We recently identified functional TLR4 and FcγRI on human mast cells, in which their expression had been upregulated by interferon-γ. We compared each of the receptor-mediated gene expression profiles with the FcεRI-mediated gene expression profile using high-density oligonucleotide probe arrays and discovered that human mast cells may modulate the immune system in a receptor-specific manner

Potential therapeutic applications of targeting signal-transducing adaptor protein-2 in autoimmune diseases

Adaptor proteins are involved in various immune responses via the modulation of many signaling pathways. Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains typical domains such as the pleckstrin homology (PH) domain, Src homology domain, and a proline-rich region from the N-terminal region. In T cells, STAP-2 positively regulates T cell receptor (TCR)-mediated signaling by associating with CD3ζ immunoreceptor tyrosine-based activation motifs (ITAMs) and lymphocyte-specific protein tyrosine kinase (LCK). Therefore, a peptide that inhibits the interaction between STAP-2 and CD3ζ ITAMs is likely to suppress TCR-mediated T cell activation, as well as T cell-mediated diseases. As expected, the peptide successfully inhibited the STAP-2/CD3ζ ITAM interaction and suppressed TCR-mediated signaling, cell proliferation, and interleukin (IL)-2 production in human/murine T cells. Furthermore, this inhibitor suppressed the pathogenesis of experimental autoimmune encephalomyelitis (EAE), which is widely recognized as a mouse model of multiple sclerosis, via the downregulation of T cell activation and infiltration of T helper (Th) 1/Th17 cells. These results suggest a new strategy for the treatment of multiple sclerosis and other immune diseases

Phospholipase C-β3 Regulates FcɛRI-Mediated Mast Cell Activation by Recruiting the Protein Phosphatase SHP-1

SummaryMast cells are major effectors in high-affinity IgE receptor (FcɛRI)-dependent allergic reactions. Here we show that phospholipase C (PLC)-β3 is crucial for FcɛRI-mediated mast cell activation. Plcb3−/− mice showed blunted FcɛRI-dependent late-phase, but not acute, anaphylactic responses and airway inflammation. Accordingly, FcɛRI stimulation of Plcb3−/− mast cells exhibited reduced cytokine production but normal degranulation. Reduced cytokine production in Plcb3−/− cells could be accounted for by increased activity of the negative regulatory Src family kinase Lyn and reduced activities of the positive regulatory protein kinases MAPKs. Mechanistically, PLC-β3 constitutively interacts with FcɛRI, Lyn, and SHP-1 (protein phosphatase). SHP-1 probably recognizes its substrates Lyn and MAPKs via the recently described kinase tyrosine-based inhibitory motif, KTIM. Consistent with PLC-β3- and SHP-1-mediated repression of Lyn activity by dephosphorylation at Tyr396, FcɛRI-mediated phenotypes were similar in Plcb3−/− and SHP-1 mutant mast cells. Thus, we have defined a PLC-β3- and SHP-1-mediated signaling pathway for FcɛRI-mediated cytokine production

Signal-transducing adaptor protein-2 modulates T-cell functions

Immune responses are orchestrated by controlling the initiation, magnitude, and duration of various signaling pathways. Adaptor proteins act as positive or negative regulators by targeting critical molecules of signaling cascades. Signal-transducing adaptor protein-2 (STAP-2) contains typical features of adaptor proteins, like a pleckstrin homology (PH) domain in the N-terminal region and a Src homology 2 (SH2) domain in the central region. STAP-2 binds to a variety of signaling or transcriptional molecules to control multiple steps of inflammatory/immune responses. STAP-2 enhances T-cell receptor (TCR)-mediated signaling via the association with TCR-proximal CD3ζ immunoreceptor tyrosine-based activation motifs (ITAMs) and lymphocyte-specific protein tyrosine kinase (Lck). STAP-2 decreases adherence of T-cells to fibronectin (FN) through an association with focal adhesion kinase (Fak) and Casitas B-lineage Lymphoma (c-Cbl), and increases chemotaxis of T-cells toward stromal cell-derived factor-1α (SDF-1α) through interactions with Vav1 and Ras-related C3 botulinum toxin substrate 1 (Rac1). STAP-2 positively regulates activation-induced cell deathrough the association with Fas and caspase-8. This review describes the current knowledge of the roles of STAP-2 in T-cell-dependent immune responses and the possible clinical utility of STAP-2-targeting therapies

The Functional Properties and Physiological Roles of Signal-Transducing Adaptor Protein-2 in the Pathogenesis of Inflammatory and Immune Disorders

Adaptor molecules play a crucial role in signal transduction in immune cells. Several adaptor molecules, such as the linker for the activation of T cells (LAT) and SH2 domain-containing leukocyte protein of 76 kDa (SLP-76), are essential for T cell development and activation following T cell receptor (TCR) aggregation, suggesting that adaptor molecules are good therapeutic targets for T cell-mediated immune disorders, such as autoimmune diseases and allergies. Signal-transducing adaptor protein (STAP)-2 is a member of the STAP family of adaptor proteins. STAP-2 functions as a scaffold for various intracellular proteins, including BRK, signal transducer, and activator of transcription (STAT)3, STAT5, and myeloid differentiation primary response protein (MyD88). In T cells, STAP-2 is involved in stromal cell-derived factor (SDF)-1α-induced migration, integrin-dependent cell adhesion, and Fas-mediated apoptosis. We previously reported the critical function of STAP-2 in TCR-mediated T cell activation and T cell-mediated autoimmune diseases. Here, we review how STAP-2 affects the pathogenesis of T cell-mediated inflammation and immune diseases in order to develop novel STAP-2-targeting therapeutic strategies

Positive interactions between STAP-1 and BCR-ABL influence chronic myeloid leukemia cell proliferation and survival

Chronic myeloid leukemia (CML) is a clonal disease characterized by the presence of the Philadelphia chromosome and its oncogenic product, BCR-ABL, which activates multiple pathways involved in cell survival, growth promotion, and disease progression. We recently reported that signal-transducing adaptor protein 1 (STAP-1) is upregulated in CML stem cells (LSCs) and functions to reduce the apoptosis of CML LSCs by upregulating the STAT5-downstream anti-apoptotic genes. In this study, we demonstrate the detailed molecular interactions among BCR-ABL, STAP-1, and signal transducer and activator of transcription 5 (STAT5). Studies with deletion mutants have revealed that STAP-1 interacts with BCR-ABL and STAT5a through its SH2 and PH domains, respectively, suggesting the possible role of STAP-1 as a scaffold protein. Furthermore, the binding of STAP-1 to BCR-ABL stabilizes the BCR-ABL protein in CML cells. Since STAP-1 is highly expressed in CML cells, we also analyzed the STAP-1 promoter activity using a luciferase reporter construct and found that NFATc1 is involved in activating the STAP-1 promoter and inducing STAP-1 mRNA expression. Our results demonstrate that STAP-1 contributes to the BCR-ABL/STAT5 and BCR-ABL/Ca2+/NFAT signals to induce proliferation and STAP-1 mRNA expression in CML cells, respectively

Signal-transducing adaptor protein-2 modulates T-cell functions

Immune responses are orchestrated by controlling the initiation, magnitude, and duration of various signaling pathways. Adaptor proteins act as positive or negative regulators by targeting critical molecules of signaling cascades. Signal-transducing adaptor protein-2 (STAP-2) contains typical features of adaptor proteins, like a pleckstrin homology (PH) domain in the N-terminal region and a Src homology 2 (SH2) domain in the central region. STAP-2 binds to a variety of signaling or transcriptional molecules to control multiple steps of inflammatory/immune responses. STAP-2 enhances T-cell receptor (TCR)-mediated signaling via the association with TCR-proximal CD3ζ immunoreceptor tyrosine-based activation motifs (ITAMs) and lymphocyte-specific protein tyrosine kinase (Lck). STAP-2 decreases adherence of T-cells to fibronectin (FN) through an association with focal adhesion kinase (Fak) and Casitas B-lineage Lymphoma (c-Cbl), and increases chemotaxis of T-cells toward stromal cell-derived factor-1α (SDF-1α) through interactions with Vav1 and Ras-related C3 botulinum toxin substrate 1 (Rac1). STAP-2 positively regulates activation-induced cell deathrough the association with Fas and caspase-8. This review describes the current knowledge of the roles of STAP-2 in T-cell-dependent immune responses and the possible clinical utility of STAP-2-targeting therapies