Integrin signaling in neutrophils and macrophages uses adaptors containing immunoreceptor tyrosine-based activation motifs

Abstract

At sites of inflammation, ligation of leukocyte integrins is critical for the activation of cellular effector functions required for host defense. However, the signaling pathways linking integrin ligation to cellular responses are poorly understood. Here we show that integrin signaling in neutrophils and macrophages requires adaptors containing immunoreceptor tyrosine-based activation motifs (ITAMs). Neutrophils and macrophages lacking two ITAM-containing adaptor proteins, DAP12 and FcRγ, were defective in integrin-mediated responses. Activation of the tyrosine kinase Syk by integrins required that DAP12 and FcRγ were first phosphorylated by Src family kinases. Retroviral transduction of neutrophils and macrophages with wild-type and mutant Syk or DAP12 demonstrated that the Src homology 2 domains of Syk and the ITAM of DAP12 were required for integrin signaling. Our data show that integrin signaling for the activation of cellular responses in neutrophils and macrophages proceeds by an immunoreceptor-like mechanism.Integrins are transmembrane adhesion receptors that coordinate cellular responses with the extracellular environment. Integrin function is especially important in neutrophils and macrophages, key effector cells that kill or suppress invading microorganisms during the innate immune response. In neutrophils and macrophages, integrin signaling is critical for cellular functions such as firm adhesion, cell spreading, chemotaxis, the production of COMPETING INTERESTS STATEMENTThe authors declare that they have no competing financial interests. Although several molecules required for relaying signals 'downstream' of leukocyte integrins (often called 'outside-in' signaling) have been identified, the initial steps of β 2 integrin signaling remain poorly understood. Src family kinases are involved in an early step of integrin signaling in neutrophils 6 and macrophages 7,8 . Also, the Syk tyrosine kinase is essential for integrin signaling in neutrophils 9 , macrophages 10 and platelets 11 . As Syk is probably involved in a receptor-proximal event during integrin signal transduction, the mechanism of activation of Syk by integrins and its relationship to Src family kinases may be the key to understanding the initiation of integrin signaling. Unfortunately, despite attempts to clarify that issue, the mechanism of activation of Syk by integrins remains poorly understood. HHS Public AccessSyk and the related kinase Zap70 are also essential for signaling downstream of immunoreceptors, such as B cell and T cell receptors and Fc receptors. In contrast to integrin signal transduction, the mechanism of Syk activation initiated by ligation of these immunoreceptors is well characterized. Engagement of immunoreceptors leads to Src family kinase-mediated phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) on receptor-associated transmembrane adaptor proteins 12 . Those adaptors provide docking sites for the tandem Src homology 2 (SH2) domains of the Syk or Zap70 tyrosine kinases, which leads...

SLP-76-ADAP adaptor module regulates LFA-1 mediated costimulation and T cell motility

“…Last, our findings are consistent with a possible requirement for ITAMs in integrin signaling (28). In neutrophils or macrophages, phosphorylation of ITAMs in FcR␥ and adaptor DAP12 can recruit SYK kinase for outside-in signaling (28).…”

“…In neutrophils or macrophages, phosphorylation of ITAMs in FcR␥ and adaptor DAP12 can recruit SYK kinase for outside-in signaling (28). Although an analogous ITAM dependent system in T cells has yet to be defined, SLP-76 is phosphorylated by ZAP-70 (6), a kinase recruited by upstream ITAMs.…”

“…␣4␤1 integrin VLA-4 binding to its ligands fibronectin or VCAM-1 (vascular cell adhesion molecule-1) enhances T cell proliferation via FAK (focal adhesion kinase) (26) and the stabilization of microclusters (27). In neutrophils or macrophages, phosphorylation of ITAMs (immunoreceptor tyrosine-based activation motifs) in adaptor DAP12 or FcR␥ is needed to recruit SYK for outside-in signaling (28). An analogous ITAM-dependent scenario in T cells has yet to be defined.…”

Signaling pathways activated by a protease allergen in basophils

“…Interestingly, activation of cytokine production requires expression of the FcRγ-chain, including intact expression of its ITAM domain. Papain would not be expected to signal through an Fc receptor, but the FcRγ-chain has been shown to play signaling roles in several non-Fc receptors (35,36). Surprisingly, FcRγ is not phosphorylated upon stimulation with papain, nor are its downstream mediators Syk and PLCγ.…”

Redundant role for Zap70 in B cell development and activation

“…Syk has also been shown to signal from GPVI, the collagen receptor on platelets, by recruitment to the associated ITAMbearing FcRc subunit [7], from the NKG2D receptor of NK cells, from the C-type lectin Dectin-1 on dendritic cells [8], and from integrins on neutrophils, macrophages and osteoclasts via FcRc and the related DAP12 proteins [9][10][11].…”