Src-family kinases: rheostats of immune cell signaling

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Abstract

In immune cells, Src-family kinases have been implicated as critical regulators of a large number of intracellular signaling pathways. Studies of gene knockout mice lacking various family members have both confirmed the requirement for these kinases in some pathways and provided surprising insight into their roles in other pathways. In many cases, loss of a single kinase produces only a modest/moderate defect in the pathway being studied, while combinatorial mutants have more profound defects. In several cases, loss of Src-family kinase activity results in activation of signaling, illuminating the fact that these molecules play important roles in inhibitory signaling. This review will focus on both the positive and negative roles these kinases play in immunoreceptor and integrin signaling pathways. The overall observation that these molecules play such diverse signaling functions leads one to the conclusion that this family of proteins serves as general modulators of immune cell signaling.

Introduction

One of the premier, and original, investigators in the field of Src-family kinases, Dr. Joan Brugge, once made a comment at a meeting she was chairing that there were so many people now working on Src kinases that there was probably one group for each codon of the gene. She made that comment in 1994 at the Oncogene Meeting in Fredrick, Maryland. In a decade since then, the field has grown dramatically. Both in immune cells and non-hematopoietic cells Src-family kinases have been implicated in a multitude intracellular signaling pathways—everything from responses to UV light to regulation of β-adrenergic signaling to sensitivity to ethanol consumption (Cowen et al., 2003, Kabuyama et al., 2002, Ma and Huang, 2002). In blood cells and platelets, the list is no less extensive. Src-family kinases have been implicated in innate immune signaling, responses to cytokines, growth factors, regulators of apoptosis, regulators of antigen signaling, stimulation of cells by immune complexes, phagocytosis, responses to adhesive stimulation—integrin signaling, controllers of K/Cl channels, and key players in G-protein coupled (GPCR) signaling pathways (as examples see Chan et al., 1998, De Franceschi et al., 1997, Fitzer-Attas et al., 2000, Gardai et al., 2002, Lowell and Berton, 1999, Lowell et al., 1996, Nijhuis et al., 2002, Rane and Reddy, 2002). In most of these cases, the loss of Src-family tyrosine kinase activity, either by pharmacologic inhibition, use of dominant-negative inhibitors or more recently using genetically modified cells or mice, results in diminution of the signaling pathway being studied. More convincingly, the use of knockout mouse models to study the overall physiologic outcome of the loss of Src-family kinase-dependent signaling has pointed the field in the direction of the most significant functions for these kinases. In this regard, the requirement for Src-family kinase activity for T- and B-lymphocyte development (Saijo et al., 2003, van Oers et al., 1996) or for osteoclast function, as demonstrated in the original Src mutant made by Soriano et al. (1991), is absolutely clear and correlates with a large number of cell-based experiments. Nevertheless, it is important to realize that the multitude of signaling reactions these kinases have been implicated in using cell based assays or other approaches does not seem to manifest as severe physiologic phenotypes in the various knockout models; an issue that makes interpretation of both types of data complicated. Obviously, there are many explanations for this difference (compensation between kinases or even between different signaling pathways), but the idea that Src-family kinase activity is critical and central to so many different intracellular signaling pathways may be overstating the argument. The concept that these kinases may be contributory to multiple pathways may be a better reference frame—hence the title of this review that Src-family kinases could be viewed as rheostats of intracellular signaling and not as on-off switches.

Even more amazing is the growing realization that these kinases also play critical roles in downmodulating or inhibiting signaling in immune cells; a concept that was only revealed through study of the mutant models. This inhibitory activity of the kinases was first realized in studies attempting to explain the autoimmune phenotype of lyn−/− mice (DeFranco et al., 1998, Harder et al., 2001, Hibbs et al., 1995), which will be discussed below, but has now been observed with other Src-family kinases in other immune cell types (Gresham et al., 2000, Vines et al., 2001). Indeed, the inhibitory function of these kinases may be one of the more active and surprising areas of investigation. The dual specificity of various members of this kinase family contributes to the general idea that they are overall modulators of signaling, like rheostats, and not absolutely critical, at least as single enzymes alone, in any one pathway.

To address this general theme that Src-family kinases are more like rheostats and not switches, this mini-review will focus on several major pathways in immune cells for which there is clear evidence that Src-family kinases play a significant regulatory role. These pathways are:

  • 1.

    The immunoreceptor tyrosine-based activation motif (ITAM)-dependent pathways, used by all immunoreceptors (lymphocyte antigen receptors, Fc receptors, NK activating receptors).

  • 2.

    The immunoreceptor tyrosine-based inhibitory motif (ITIM)-dependent pathways, which negatively regulate both immunoreceptor function as well as a host of other signaling responses, such as cytokines and integrin signaling.

  • 3.

    The integrin pathways, which regulate leukocyte activation by adhesion.

Section snippets

Structure and expression of immune cell Src-family kinases

The members of the Src-family kinases consist of Src, Fyn, Yes, Lck, Hck, Fgr, Lyn, Blk, and Yrk (for an excellent prior review of Src-family kinases in leukocytes see Korade-Mirnics and Corey, 2000). Each of these proteins are about 60 kD in molecular weight and have a common structure consisting of an N-terminal unique domain, followed by SH3, SH2 and tyrosine kinases domains (see Fig. 1). Several of the Src-family proteins are expressed as two proteins due to alternative splicing patterns or

ITAM-dependent signaling pathways

Immunoreceptors such as the T- and B-lymphocyte antigen receptors, Fcγ and Fcε receptors, NK activating receptors and the platelet receptor GPVI, all depend on Src-family kinases for appropriate signaling. The vast majority of immunoreceptors are physically associated with ITAM-containing subunit proteins, each of which have paired YXXL motifs (Fig. 2). Examples of these ITAM subunits are the TCRζ, CD3γ/δ/ε chains in T-cells, the Igα/β chains in the B-cell receptor, the FcRγ chain in Fc

ITIM-mediated inhibitory signaling

The realization that Src-family kinases play an important physiologic role in downmodulating or inhibiting signaling responses first came to light in studies examining lyn−/− mutant mice. The initial phenotype described for lyn−/− animals was quite surprising: the mice had hyperresponsive B-cells, increased Ig levels and autoimmunity (immune complex nephritis) (reviewed in DeFranco et al., 1998). The mechanism for this surprising result was demonstrated by examination of cell surface receptors

Src-family kinases in leukocyte integrin signaling pathways

There is a large body of evidence implicating Src-family tyrosine kinases in integrin signaling pathways, both in blood cells and non-hematopoietic cells. Integrins are major cellular receptors that mediate cell–cell and cell–substratum interactions. These receptors signal in two fashions, which are commonly referred to as “inside-out” versus “outside-in” (integrin signaling pathways in T-lymphocytes have recently been reviewed in Hogg et al., 2003, Shimizu, 2003). The “inside-out” pathway

Conclusions

This review has focused on only a limited number of the signaling pathways in which Src-family kinases have been implicated. In immune cells, this list could be extended to include responses to chemokines/chemoattractants (Barlic et al., 2000, Mocsai et al., 2000), cytokines (Rane and Reddy, 2002), innate immune stimuli, such as LPS (Yazawa et al., 2003) as well as the myriad of non-immune cell specific stimuli, such as responses to UV irradiation, heat, osmotic shock and others. In many of

References (105)

  • S Latour et al.

    Proximal protein tyrosine kinases in immunoreceptor signaling

    Curr. Opin. Immunol.

    (2001)
  • X Liang et al.

    Heterogeneous fatty acylation of Src family kinases with polyunsaturated fatty acids regulates raft localization and signal transduction

    J. Biol. Chem.

    (2001)
  • X Liang et al.

    Phosphatidylinositol 3-kinase and Src family kinases are required for phosphorylation and membrane recruitment of Dok-1 in c-Kit signaling

    J. Biol. Chem.

    (2002)
  • D.C Link et al.

    The proto-oncogene c-fgr is expressed in normal mantle zone B lymphocytes and is developmentally regulated during myelomonocytic differentiation in vivo

    Blood

    (1995)
  • M.R Marwali et al.

    Membrane cholesterol regulates LFA-1 function and lipid raft heterogeneity

    Blood

    (2003)
  • C.K Miranti et al.

    Identification of a novel integrin signaling pathway involving the kinase Syk and the guanine nucleotide exchange factor Vav1

    Curr. Biol.

    (1998)
  • A Mocsai et al.

    Syk is required for integrin signaling in neutrophils

    Immunity

    (2002)
  • S.A Newbrough et al.

    SLP-76 regulates Fcγ receptor and integrin signaling in neutrophils

    Immunity

    (2003)
  • A Obergfell et al.

    The molecular adapter SLP-76 relays signals from platelet integrin aIIbb3 to the actin cytoskeleton

    J. Biol. Chem.

    (2001)
  • M Ojaniemi et al.

    The proto-oncogene product p120cbl links c-Src and phosphatidylinositol 3’-kinase to the integrin signaling pathway

    J. Biol. Chem.

    (1997)
  • M.D Resh

    Fatty acylation of proteins: new insights into membrane targeting of myristoylated and palmitoylated proteins

    Biochim. Biophys. Acta

    (1999)
  • J Rivera et al.

    Macromolecular protein signaling complexes and mast cell responses: a view of the organization of IgE-dependent mast cell signaling

    Mol. Immunol.

    (2002)
  • R Sampath et al.

    Cytoskeletal interactions with the leukocyte integrin β2 cytoplasmic tail. Activation-dependent regulation of associations with talin and α-actinin

    J. Biol. Chem.

    (1998)
  • F Sicheri et al.

    Structures of Src-family tyrosine kinases

    Curr. Opin. Struct. Biol.

    (1997)
  • Z Songyang et al.

    Recognition and specificity in protein tyrosine kinase-mediated signalling

    Trends Biochem. Sci.

    (1995)
  • P Soriano et al.

    Targeted disruption of the c-src proto-oncogene leads to osteopetrosis in mice

    Cell

    (1991)
  • M.L Thomas et al.

    Positive and negative regulation of Src-family membrane kinases by CD45

    Immunol. Today

    (1999)
  • J.M Turner et al.

    Interaction of the unique N-terminal region of tyrosine kinase p56lck with cytoplasmic domains of CD4 and CD8 is mediated by cysteine motifs

    Cell

    (1990)
  • A Urzainqui et al.

    ITAM-based interaction of ERM proteins with Syk mediates signaling by the leukocyte adhesion receptor PSGL-1

    Immunity

    (2002)
  • N.S van Oers et al.

    Aab T cell development is abolished in mice lacking both Lck and Fyn protein tyrosine kinases

    Immunity

    (1996)
  • C.M Vines et al.

    Inhibition of β2 integrin receptor and Syk kinase signaling in monocytes by the Src family kinase Fgr

    Immunity

    (2001)
  • D.G Woodside et al.

    Activation of Syk protein tyrosine kinase through interaction with integrin β cytoplasmic domains

    Curr. Biol.

    (2001)
  • R Xavier et al.

    Membrane compartmentation is required for efficient T cell activation

    Immunity

    (1998)
  • L Ardouin et al.

    Vav1 transduces TCR signals required for LFA-1 function and cell polarization at the immunological synapse

    Eur. J. Immunol.

    (2003)
  • E.G Arias-Salgado et al.

    Src kinase activation by direct interaction with the integrin β cytoplasmic domain

    Proc. Natl. Acad. Sci. U.S.A.

    (2003)
  • J Barlic et al.

    Regulation of tyrosine kinase activation and granule release through β-arrestin by CXCRI

    Nat. Immunol.

    (2000)
  • E Caveggion et al.

    Expression and tyrosine phosphorylation of Cbl regulates macrophage chemokinetic and chemotactic movement

    J. Cell. Physiol.

    (2003)
  • V.W Chan et al.

    The molecular mechanism of B cell activation by toll-like receptor protein RP-105

    J. Exp. Med.

    (1998)
  • D.H Chu et al.

    Pre-T cell receptor signals are responsible for the down-regulation of Syk protein tyrosine kinase expression

    J. Immunol.

    (1999)
  • M.S Cowen et al.

    Role of Fyn tyrosine kinase in ethanol consumption by mice

    Alcohol Clin. Exp. Res.

    (2003)
  • D Davidson et al.

    Phosphorylation-dependent regulation of T-cell activation by PAG/Cbp, a lipid raft-associated transmembrane adaptor

    Mol. Cell. Biol.

    (2003)
  • L De Franceschi et al.

    Deficiency of Src family kinases Fgr and Hck results in activation of erythrocyte K/Cl cotransport

    J. Clin. Invest.

    (1997)
  • M Dykstra et al.

    Location is everything: lipid rafts and immune cell signaling

    Annu. Rev. Immunol.

    (2003)
  • M Ernst et al.

    Constitutive activation of the SRC family kinase Hck results in spontaneous pulmonary inflammation and an enhanced innate immune response

    J. Exp. Med.

    (2002)
  • C.J Fitzer-Attas et al.

    Fcgamma receptor-mediated phagocytosis in macrophages lacking the Src family tyrosine kinases Hck, Fgr, and Lyn

    J. Exp. Med.

    (2000)
  • R.C Fuhlbrigge et al.

    Regulation of interleukin 1 gene expression by adherence and lipopolysaccharide

    J. Immunol.

    (1987)
  • H.D Gresham et al.

    Negative regulation of phagocytosis in murine macrophages by the Src kinase family member

    Fgr. J. Exp. Med.

    (2000)
  • A Grishin et al.

    Involvement of Shc and Cbl-PI 3-kinase in Lyn-dependent proliferative signaling pathways for G-CSF

    Oncogene

    (2000)
  • N Gupta et al.

    Visualizing lipid raft dynamics and early signaling events during antigen receptor-mediated B-lymphocyte activation

    Mol. Biol. Cell

    (2003)
  • M.L Hermiston et al.

    Reciprocal regulation of lymphocyte activation by tyrosine kinases and phosphatases

    J. Clin. Invest.

    (2002)
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