Tài liệu Báo cáo khoa học: LAT – an important raft-associated transmembrane adaptor protein pptx

THÔNG TIN TÀI LIỆU

Thông tin cơ bản

Định dạng
Số trang	15
Dung lượng	198,01 KB

Nội dung

THE SIR HANS KREBS LECTURE LAT – an important raft-associated transmembrane adaptor protein Delivered on 6 July 2009 at the 34th FEBS Congress in Prague, Czech Republic Va ´ clav Hor ˇ ejs ˇ ı ´ , Pavel Ota ´ hal and Toma ´ s ˇ Brdic ˇ ka Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague, Czech Republic Introduction A number of immunologically important receptors, e.g. T cell and B cell antigen receptors (TCR, BCR), Fc-receptors, natural killer (NK) ⁄ myeloid cell activating receptors, collagen receptor on platelets, some cytokine receptors, employ common functional princi- ples for signal transduction. These multichain receptor complexes consist of a ligand-recognition module and noncovalently associated signalling subunits. The signalling subunits are transmembrane proteins containing in their intracellular domains tyrosine residues that can be phosphorylated by kinases associated constitutively or, more often just very transiently, with the receptor. Extracellular domains of these signalling subunits are in some cases large, sometimes contributing to ligand binding (many cytokine receptors). In other cases the extracellular domains are relatively small and participate rather in interactions with the ligand-binding chains of the receptor complexes, such as the CD3c, d, e subunits of the TCR complex [1] or CD79a, b components of the BCR complex [2]. Some of the receptor-associated signalling chains have only very short extracellular segments (f chain of the TCR complex [3], c chain of several Fc receptors [4], DAP12 and DAP10 chains of several NK ⁄ myeloid cell activating receptors [5]). Keywords immunoreceptor signalling; LAT; raft; transmembrane adaptor protein; tyrosine phosphorylation Correspondence V. Hor ˇ ejs ˇ ı ´ , Institute of Molecular Genetics, AS CR, Vı ´ den ˇ ska ´ 1083, 142 20 Prague 4, Czech Republic Fax: 420 244472282 Tel: 420 241729908 E-mail: horejsi@biomed.cas.cz (Received 8 July 2010, revised 12 August 2010, accepted 24 August 2010) doi:10.1111/j.1742-4658.2010.07831.x Membrane rafts are microdomains involved in a number of biologically important processes, including immunoreceptor signalling. Among the functionally important protein components of these microdomains are transmembrane adaptor proteins, containing in their intracellular domains tyrosine residues that can be phosphorylated and bind other cytoplasmic signalling proteins. The most important leukocyte transmembrane adaptor protein is LAT (linker for activation of T cells), which is critically involved in T cell receptor signalling, but also plays important roles in signal initiation by several other immunologically important receptors. Here we review recent progress in the elucidation of several aspects of this protein, e.g. the controversy concerning the importance of LAT being present in membrane rafts, the involvement in signalling through a number of receptors other than the T cell receptor and the puzzling phenotype of some LAT mutants. Abbreviations BCR, B cell receptor; cSMAC, central supramolecular activation cluster; DRM, detergent-resistant membrane complex; GPVI, glycoprotein VI; LAT, linker for activation of T cells; NK, natural killer; PI3K, phosphatidylinositol 3-kinase; TCR, T cell receptor; TRAP, transmembrane adaptor protein. FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4383 Several other proteins structurally similar to the last group (f chain-like) exist that are not directly associated with any receptor, but also play more or less important roles in the regulation of receptor signalling. Some of these transmembrane adaptor proteins (TRAPs) are palmitoylated and targeted to membrane rafts (LAT, NTAL, LIME, PAG), others are found in nonraft membrane (SIT, TRIM, LAX, GAPT) [6,7]. In our opinion, the term TRAP can also be used for the abovementioned proteins closely associated with receptors, i.e. f, c chains, DAP12, DAP10. Common features of TRAPs thus include: short extracellular domain, single transmembrane domain, intracellular domain containing signalling-relevant motifs, such as potentially phosphorylated tyrosine motifs, polyproline sequences, PDZ-binding motifs, etc. This review deals mainly with the functionally most important TRAP, linker for activation of T cells (LAT). We will concentrate mainly on the latest developments in the field, but will also review the literature on rather neglected roles of LAT in non-T cells. Several relatively recent reviews exist, dealing with TRAPs in general or specifically with some of them [4,5,8–16]. Membrane rafts Membrane rafts are membrane microdomains enriched in cholesterol, sphingolipids and glycerolipids containing mainly saturated fatty acid residues. These lipids have a tendency to form a specific ‘ordered liquid phase’ distinguished from the less ordered rest of the membrane composed mainly of lipids possessing mostly polyunsaturated fatty acids. The term ‘lipid raft’ has been used more frequently in the literature, but because not only lipids, but also proteins, are essential for the formation of this type of membrane microdomain, the term ‘membrane rafts’ has been recommended [17] and therefore will be used through- out this review. Most transmembrane proteins are excluded from the rafts, exceptions being mostly palmitoylated molecules, such as several members of the tumour necrosis factor (TNF) receptor family, TRAPs LAT, NTAL, PAG, LIME or the coreceptors CD4 and CD8. Typical components of membrane rafts are extracellularly oriented proteins anchored in the membrane through a glycolipid moiety (glycosylphosphatidylinositol) [18,19] such as CD14, CD16b, CD24, CD48, CD52, CD55, CD58, CD59, CD73, CD87, CD90 (Thy-1), CD108, CD109, CD157, CD160, CD177, CD228, CD230 (prion protein), Ly-6 family. Importantly, several lipid-modified cytoplasmic molecules are present in the rafts, e.g. Src family kinases [20] heterotrimeric and small G-proteins [21]. Because of the presence of important signalling molecules, membrane rafts have been implicated in signalling through a wide range of receptors, including immunoreceptors, and also in many other biologically important processes, such as antigen presentation, cell interactions with pathogens and bacterial toxins, bud- ding of viruses from a host cell membrane, pathogene- sis of prion and other neurodegenerative diseases, specific forms of endocytosis, vesicle trafficking and establishing cell polarity [22–28]. Although native rafts are, due to their small size and dynamic nature, difficult to observe directly, they can be visualized using, for example, specific lipid probes [29] or electron microscopy [30,31]. A special type of raft microdomain, caveolae, can be readily observed by electron microscopy [32]. ‘Elementary rafts’ are probably quite small (diameter < 20 nm) and dynamic and contain very few (perhaps even single and some none at all) protein molecules surrounded by a ‘shell’ of several hundreds of the specific lipid molecules. These ‘elementary rafts’ may easily coalesce into larger patches, especially after membrane exposure to certain types of detergent or after cross-linking of their protein or glycolipid components by antibodies or natural multivalent ligands [25,27,33,34]. Because of their specific lipid composition, membrane rafts are, especially at low temperatures, relatively resistant to solubilization by some detergents commonly used for membrane solubilization, such as polyoxyethylene type (Brij-series, Triton X-100), but are readily solubilized in other detergents, such as octyl- glucoside or SDS. The detergent-resistant membrane complexes (DRMs) derived from the rafts can be easily purified by density gradient ultracentrifugation or size- exclusion chromatography [35]. There are probably several types of membrane raft in the plasma membrane of a cell type, differing in their lipid and protein composition. Recently we described a novel type of raft (‘heavy rafts’) producing upon detergent solubilization complexes that do not flotate in a density gradient [36]. It is not clear to what extent the DRM preparations obtained from detergent-solubilized cells correspond to the native rafts. The detergent usually used as a stan- dard in the raft studies, Triton X-100, is probably a bad choice, as it may dissolve the raft membrane essentially completely at increased temperature or after prolonged exposure. Brij-98 appears to be a much better alternative, as it produces much more stable and reproducible DRMs, presumably corresponding much LAT, a key membrane raft-associated protein V. Hor ˇ ejs ˇ ı ´ et al. 4384 FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS better to raft microdomains present in the membrane before detergent exposure [26,37,38]. In the following text, ‘rafts’ usually refers to ‘DRMs’ derived from the native rafts. We are fully aware of the fact that the DRMs are not identical to native rafts, but we believe that this simplification is useful. LAT – basic properties, roles in TCR signalling One of the functionally most important leukocyte raft molecules is the TRAP LAT. LAT was originally called pp36-38 and was of great interest as it was the most rapidly tyrosine-phosphorylated protein upon TCR engagement, associated with several signalling molecules (see [39] and references therein). Cloning of the LAT cDNA [40,41] revealed it as a type III (leaderless) transmembrane protein of 262 amino acids (human) or 242 amino acids (mouse). A shorter human isoform exists (233 amino acids), which arises by alternative splicing and lacks residues 114– 142 of the long form. So far nothing is known about the possible functional importance of this difference between the two LAT forms. This prototypic TRAP (Fig. 1) is expressed in thymocytes and T cells, NK cells and mast cells; later it was also found in pre-B cells (but not in mature B cells) [42,43], myeloid cells [44], megakaryocytes and platelets [45,46]. The LAT polypeptide chain contains in its membrane-proximal part two cysteine residues (C26, C29 in humans, C27, C30 in mouse), which can be palmitoylated by a so far unidentified palmitoyl transferase(s). This post-translational modification is essential for LAT membrane and raft association (see below); recent data demonstrate that monopalmitoylation of LAT on C26 is sufficient for its association with the plasma membrane and function (however, it was not reported whether the monopalmitoylated mutant is present in membrane rafts to the same extent as the double-palmitoylated wild-type protein) [47]. Upon immunoreceptor engagement of several receptors [most notably TCR, FccR, FceRI, collagen receptor glycoprotein VI (GPVI), but see below for more examples] at least five of its nine tyrosine motifs can be phosphorylated by ZAP-70 or Syk kinases [40], but also by Itk [48] and possibly Lck [49]. Phosphorylated LAT associates with several SH2-containing molecules [Grb2, Gads, Grap, PLCc1, p85, phosphatidylinositol 3-kinase (PI3K), Vav], thereby organizing signalosomes needed for the initiation of several intracellular signalling pathways [40,50–52]. A key cytoplasmic adaptor, SLP-76, is recruited to phospho-LAT via its constitutive association with Gads [53]. It is not known how many different phospho-LAT containing complexes exist, differing in their composition. The formation of phosphotyrosine-dependent multiprotein signalling complexes organized around phospho-LAT was also examined more rigorously in an in vitro system based on recombinant LAT incorporated in liposomes and recruitment of signalling protein complexes from Jurkat cell cytosol [54]. Little is known about the structural details of differential recognition of tyrosine-phosphorylated sites in LAT by SH2-containing ligands, an exception being the adaptor Gads; high-resolution structures of Gads–SH2 complexed with phosphopeptides corresponding to sites 171, 191 and 226 revealed the structural basis for prefer- ential recognition of specific phospho-LAT sites by Gads, as well as for the related adaptor Grb2 [55]. LAT – negative regulation in TCR signalling LAT was reported to interact with the active (open) form of Lck in rafts and possibly induce its transition into the inactive (closed) conformation [56]. The interaction of LAT with a negative regulator of the Ras–MAPK pathway of receptor tyrosine kinases, Sprouty1, negatively regulates LAT phosphorylation. A C-terminal deletion mutant of Sprouty1 is unable to translocate to the immune synapse and interact with LAT [57]. Cytoskeletal protein 4.1R negatively regulates T cell activation by directly binding to LAT, and thereby inhibiting its phosphorylation by ZAP-70 [58]. Tyrosine phosphatase SHP-2 is recruited to the LAT– Gads–SLP-76 complex and regulates the phosphorylation of signalling proteins Vav1 and ADAP. This enzyme is transiently inactivated by reactive oxygen species produced after TCR stimulation [59]. The inhibitory Fc receptor FccRIIB (present also on activated T cells) associates with phosphatases SHP-1, SHP-2 and SHIP-1 inhibit TCR-mediated Ca 2+ mobi- lization, in part through the inhibition of LAT phosphorylation followed by the inhibition of PI3K activation [60]. Cellular localization and functionality of LAT was reported to be sensitive to intracellular redox status. Oxidative stress results in conformational changes (the formation of intramolecular dislufidic bridges) causing membrane displacement of LAT and consequent hyporesponsiveness of T lymphocytes [61]. LAT, as a key component of the TCR activation pathways, may be expected to be a target of pathogens trying to eliminate T cell-based immune responses. Indeed, Yersinia suppresses T lymphocyte activation through the virulence factor YopH, a tyrosine V. Hor ˇ ejs ˇ ı ´ et al. LAT, a key membrane raft-associated protein FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4385 phosphatase that dephosphorylates LAT and SLP-76 in activated T cells [62]. LAT – signalling clusters, membrane rafts and interactions with TCR complexes One of the current models postulates that TCR molecules or their clusters in the plasma membrane of resting T cells are physically separated from raft microdomains containing several important signalling molecules, e.g. Lck, Fyn, LAT, PAG, PIP2 (it is not clear whether individual rafts contain several of the proteins or rather there are separate LAT-containing, Lck- containing, etc. rafts) [23]. A variant of the model assumes that TCR clusters and a subset of rafts are preassembled even in resting T cells and TCR ligation just reorients them such that the raft signalling proteins start to interact functionally with the TCR [37]. After TCR ligation, the TCR clusters are either mixed or concatenated with the rafts, which may be simulta- neously fused to form larger patches. Such processes also apparently accompany the formation of physio- logical immunological synapses or ‘patches’ or ‘caps’ induced by artificial cross-linking of TCR [63]. The understanding of the involvement of rafts in this process is complicated by unresolved problems, such as the heterogeneity of raft microdomains and techni- cal problems in studies on the nature of apparently highly dynamic raft assemblies. An illustration of the raft heterogeneity is provided by the observations that cholesterol extraction destabilizes the membrane microdomains containing Lck, whereas those containing LAT remain almost intact. As shown by electron microscopy, following T cell activation, both LAT and Lck colocalize in 50–100 nm microdomains, which cor- relates with the initiation of T cell signal transduction [64]. The involvement of LAT-containing rafts in TCR-initiated activation was demonstrated using transfectants expressing LAT-GFP [65]. After stimulation with anti- CD3-coated beads, LAT-GFP translocated to the area of T cell contact with the beads. The LAT-GFP present in the contact area was markedly immobilized compared with the membrane outside the contact. The mobility increased after raft disruption by cholesterol depletion, and was also dependent on the integrity of critical binding sites (PLCc) in the cytoplasmic domain of LAT. At present it is not entirely clear why the presence of LAT in membrane rafts is functionally important and how these LAT-containing rafts are related to ‘signalling clusters’ described in several papers. Transmembrane glycoprotein CD2 involved in T cell costimulation, LAT, and tyrosine kinase Lck were reported to be coclustered in discrete T cell plasma membrane microdomains. The integrity of these microdomains was dependent on protein–protein interactions based on phosphorylated LAT, but apparently independent of interactions with rafts or actin [66]. In quiescent T cells, LAT and TCR were observed in separate ‘protein islands’, which became concatenated upon T cell activation [67]. The signalling complexes organized around phospho-LAT and apparently vital for intracellular signalling appear to be oligomerized by multipoint co-operative binding of several cytoplasmic SH2 and SH3 domain-containing signalling proteins to LAT [68–70]. The involvement of LAT in T cell activation is also regulated by another type of membrane microdomain heterogeneity. LAT molecules are preferentially located in the uropod of migrating T cells. In activated T cells forming stable immunological synapses with antigen- loaded B cells, LAT accumulates at the contact between the two cells (immunological synapse) [71]. LAT was reported to exist in two distinct cellular pools, one at the plasma membrane and the other in endocytic vesicles also containing a transferrin receptor and the TCR f chain [72]. The plasma membrane-associated LAT is rapidly recruited to the immune synapse, whereas the intracellular pool is first polarized and Y37 Y46 Y67 Y113 Y132 Y175 (Gads, Grb2) Y195 (Gads, Grb2) Y235 (Grb2) Y136 (PLCγ) Plasma membrane Membrane raft Fig. 1. A model of the LAT molecule. A schematic representation of mouse LAT with a palmitoylation site (orange) and the positions of all tyrosines (yellow). The binding partners for the key phosphotyrosine residues are indicated. LAT, a key membrane raft-associated protein V. Hor ˇ ejs ˇ ı ´ et al. 4386 FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS recruited to the immunological synapse with a delay. Critical tyrosine residues of LAT are necessary for recruitment to the immunological synapse and a juxta- membrane region of LAT is involved in the intracellular pool localization of LAT and T cell signalling. This aspect was recently examined in more detail by Purbhoo et al. [73]. The study found that the kinase ZAP-70 and the adaptor proteins LAT and SLP-76 accumulate in separate clusters at the immunological synapse. Importantly, a sizeable fraction of LAT was found in vesicles that migrated to surface microclusters containing SLP-76 and the adaptor protein GADS, where they became temporarily immobilized. The results suggest a surprising additional mechanism of LAT participation in the TCR signalling process. The involvement of LAT-containing membrane rafts in the formation and signalling of TCR microclusters and central supramolecular activation clusters (cSMACs) at the immunological synapse remains con- troversial. A recent study [74] did not find accumulation of raft probes at TCR microclusters or cSMACs. Raft association of LAT mutants was dispensable for TCR microcluster formation. Observable accumulation of raft probes in the cell interface actually occurred after cSMAC formation and could rather be due to membrane ruffling or endocytosis. The results of this study suggest that membrane rafts may actually not serve as a platform for T cell activation. Is the presence of LAT in rafts necessary for its function in TCR signalling? Proper functioning of LAT appeared to be dependent on its targeting to membrane rafts [75–77]. This targeting was thought to be due to palmitoylation of its juxta- membrane cysteine motif (CxxC) because the cysteine mutants were not able to reconstitute TCR signalling in LAT-negative T cell lines [76,77]. Furthermore, targeting of SLP-76 constitutively to plasma membrane rafts in LAT-deficient Jurkat T cells largely restores the signalling defects, indicating that recruitment of SLP-76 to the membrane raft environment via phospho-LAT is the crucial LAT-dependent signalling event [78]. Also, the displacement of LAT from membrane rafts was demonstrated as a molecular mechanism responsible for the inhibition of T cell signalling by polyunsaturated fatty acids [79]. Furthermore, palmitoylation of LAT was shown to be defective in anergic T cells [80]. Although f chain or ZAP-70 phosphorylation were normal in these cells, LAT tyrosine phosphorylation and PLCc1 activation were markedly decreased. Inhibi- tion of T cell activation by a cytoplasmic LAT mutant lacking the transmembrane domain is accompanied by reduced recruitment of signalling molecules to glycolipid-enriched microdomains [81]. However, the importance of LAT localization in membrane rafts became recently doubtful as a result of several studies. First, the nonpalmitoylated LAT cysteine mutants were shown to be not only absent from membrane rafts, but not even properly transported to the plasma membrane and remained retained in the endoplasmic reticulum [47,82,83]. It was suggested that in addition to proper acylation, homotypic or hetero- typic protein–protein interactions may also contribute to LAT targeting to rafts [83]. Second, it was demonstrated that a LAT construct composed of the cytoplasmic region of LAT fused with the extracellular and transmembrane regions of the nonraft transmembrane adaptor, LAX, restored TCR signalling in LAT-deficient cell line and normal development of T cells from LAT ) ⁄ ) haematopoietic precursors [84]. A similar con- clusion was reached using another LAT construct (the cytoplasmic part of LAT equipped with a membrane- anchoring motif of Src) not targeted to membrane rafts but yet fully functional [47]. These results, which might demolish the generally accepted concept of the membrane raft’s importance in immunoreceptor signalling, were recently explained by results from our laboratory [36]. We demonstrated the existence of a novel type of membrane raft-like microdomain (‘heavy rafts’) containing a number of membrane molecules, including, for example, the LAX and the LAX-LAT chimaeric construct. The LAT constructs targeted to the newly identified ‘heavy rafts’ are also able to support TCR signalling, albeit less effi- ciently than the wild-type LAT present in ‘classical rafts’; the least efficient are constructs targeted to nonraft membrane. This difference may be minimized by increased levels of LAT-construct expression in the heavy rafts or nonraft membrane. Therefore, different types of membrane microdomain appear to provide environment regulating functional efficiency of signalling molecules present therein. Role of LAT in anergy induction LAT was reported to be hypophosphorylated and mis-localized in anergic T cells, apparently as a conse- quence of a selective palmitoylation defect; it was largely absent from DRM fractions corresponding to rafts and was not normally recruited to the immunological synapse. The defects were selective for LAT, because DRM localization and palmitoylation of Fyn were intact. These defects were not due to enhanced LAT degradation [80]. It should be noted that induction V. Hor ˇ ejs ˇ ı ´ et al. LAT, a key membrane raft-associated protein FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4387 of T cell anergy is accompanied by defective palmitoylation and displacement from rafts of yet another TRAP, PAG [85]. Regulation of palmitoylation of LAT (and of other palmitoylated membrane proteins) and its functional consequences remain a rather unknown and potentially very important area. The use of LAT by T lymphocyte receptors other than TCR LAT is an important component of signalling pathways initiated not only by TCR, but also by other T cell surface receptors. LAT was reported to associate with CD4 and CD8 coreceptors via the cysteine motifs in these coreceptors that mediate Lck binding [86]. However, this potentially important result has not been confirmed by other studies and it is perhaps only because of the concomi- tant presence of these molecules in membrane rafts. TCR-independent ligation of the T cell surface glycoprotein ⁄ coreceptor CD2 induces LAT tyrosine phosphorylation and association with other tyrosine phosphorylated proteins, including PLCc-1, Grb-2 and SLP-76 [87,88]. LAT is associated (evidently via lipid- based raft microdomains) with a glycosylphosphatidylinositol-anchored glycoprotein, CD48; functional association of the CD48 ⁄ LAT raft complex with TCR was dependent on CD2 [89]. Stimulation of Eph- rinB1receptor (a receptor tyrosine kinase interacting with the transmembrane ligand EphrinB1) led to increased LAT phosphorylation and p44 ⁄ 42 and p38 MAPK activation [90]. This signalling pathway may be essential in T cell–T cell costimulation and in the regulation of a T cell response threshold in response to antigen stimulation. LAT is involved in apoptosis induced in double positive thymocytes by ligation of CD8 in the absence of TCR engagement (a mechanism that may remove thymocytes that have failed positive selection) [91]. LAT (as well as several other signalling proteins) becomes tyrosine phosphorylated during CXCR3-mediated T cell chemotaxis [92]. On the other hand, the treatment of T cells with the chemokine SDF-1 (ligand of the CXCR4 receptor) caused a reduction in tyrosine phosphorylation of the TCR downstream effectors, ZAP-70, SLP-76 and LAT (and also of ZAP-70 and SLP-76), indicating that this chemokine may negatively regulate the threshold of T cell activation [93]. Regulation of LAT expression LAT expression is markedly increased upon TCR-mediated activation; this is inhibited by rapamycin at the translational level. In contrast, cyclosporin A and FK506 strongly enhance TCR-induced LAT expression in T cells [94]. LAT protein levels are regulated by ubiquitination, recycling through trans-Golgi ⁄ endo- some compartments and clathrin-dependent internalization and proteasome-dependent degradation [95]. Interestingly, the amount of LAT (and its phosphorylation) in membrane rafts is increased in cells lacking the structurally related adaptor NTAL (LAB) [96]. This is probably due to the competition between NTAL and LAT for the limited raft space available. Signalling clusters containing LAT are internalized and dissociate rapidly upon TCR activation. This process is linked to the ubiquitin ligase c-Cbl [97]. Sustained tyrosine phosphorylation of LAT and SLP-76 is observed in thymocytes deficient in c-Cbl [98]. Functional defects of LAT tyrosine mutants in vivo – possible negative regulatory roles of LAT The essential importance of LAT for T cell development (and therefore functioning of pre-TCR) is evi- denced by the fact that LAT ) ⁄ ) mice have thymocyte development completely blocked at the double-negative stage [99]. LAT-negative Jurkat T cell line mutants have severely impaired TCR signalling [100,101]. Interestingly, the development of other cells naturally expressing LAT is not impaired in LAT ) ⁄ ) mice [99]. Thorough studies on genetically engineered mice using the mutant gene-knock-in approach revealed the relative importance of LAT individual tyrosine residues. Mutants lacking all four distal tyrosine residues (Y136, Y175, Y195 and Y235 in mice, i.e. those binding after phosphorylation PLCg, PI3K, Gads, Grb2) had identical severe defects in thymocyte development as the LAT knock-outs [102]; these tyrosine residues were also essential for LAT-dependent signalling in FceRI-mediated mast cell activation [103]. On the other hand, mice with only mutated LAT Y136, which binds (after phosphorylation) PLCc1, or only the other three critical tyrosines (Y175, Y195, and Y235) exhib- ited an incomplete block of thymocyte differentiation accompanied by the development of striking autoim- mune phenotypes [104–107], which may be partially related to a defect in Treg development [108–110]; for a detailed review see [15,111,112]. These results suggest that LAT may also play a negative regulatory role(s) in TCR signalling, in addition to its well-established crucial positive regulatory role. Actually, LAT associates with an inhibitory complex containing cytoplasmic adaptors Dok-2 and Grb2 and SHIP-1 phosphatase [113]. LAT, a key membrane raft-associated protein V. Hor ˇ ejs ˇ ı ´ et al. 4388 FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS Moreover, recruitment of inhibitory SHP-1 phosphatase to rafts and its association with LAT were markedly increased after TCR engagement [114]. Another inhibitory mechanism may be based on threonine 155 phosphorylation of LAT by Erk and JNK following TCR engagement, which leads to defective recruitment of PLC-c1 and SLP-76 [115]. Furthermore, Gab2 (constitutively associating with Gads ⁄ Grb2) is recruited to membrane rafts by LAT upon TCR ligation. Gab2 may inhibit signalling by competing with SLP-76 for Gads ⁄ Grb2 binding and by binding SHP-2 phosphatase, which inhibits TCR signalling by dephosphoryla- tion of the f chain and other important signalling molecules [116,117]. Participation of LAT in signalling by platelet receptors As stated above, LAT is also of essential importance in signalling pathways initiated by the ligation of GPVI (platelet collagen receptor). This receptor resem- bles TCR and some activating Fc-receptors in some respects – it uses the associated FcRc chain as a signalling subunit (similar to the f chain in TCR complex), the signalling is initiated by Src family kinases and involves Syk and further downstream molecules participating in the TCR signalling, including LAT. After stimulation of the receptor by collagen or convulxin, LAT is phosphorylated and associates with multiple cytoplasmic signalling proteins [45,118–121]. However, the GPVI signalling pathway is less dependent on LAT as compared with TCR; platelet activation downstream of GPVI shows a much greater dependency on SLP-76 than on LAT [122], yet the absence of LAT leads to decreased platelet activation, degranulation and aggregation [123]. Studies on mice carrying LAT with mutated tyrosine residues demonstrated a crucial role of tyrosine residues 175, 195 and 235 in the phosphorylation of LAT induced via GPVI. These tyrosine residues appear to be important in the recruitment of the tyrosine kinase Fyn, which may be, in addition to Syk, involved in LAT phosphorylation. The binding of PLCc2 via GPVI is dependent on an interaction with phospho-tyrosine 136 of LAT [124]. Similar to other immunoreceptors, GPVI is down- regulated following activation. This occurs either by ectodomain proteolytic shedding or internalization. In mice lacking LAT, GPVI shedding (but not internalization) is inhibited, indicating that a LAT-dependent signalling pathway is involved in the activation of the process [125]. LAT also participates in platelet activation via cross-linking of FccRIIa, which relocates in membrane rafts where the kinase Lyn and LAT are among the major phosphotyrosyl proteins [126,127]. LAT is also involved in platelet activation through the C-type lectin receptor CLEC-2 after binding the snake venom rhodocytin [123,128] and in platelet activation by the peptide LSARLAF mediated by an unidentified receptor(s) [129]. LAT is also tyrosine phosphorylated in response to stimulation (followed by aggregation) of platelets by ADP and thrombin, impli- cating this adaptor in signalling pathways of the relevant G-protein coupled receptors [130]. Platelet aggregation induced by the C-terminal peptide of thrombospondin-1 (RFYVVMWK) also requires LAT [131]. The tyrosine phosphatase 1B [132] and the 18 kDa low molecular mass phosphotyrosine phosphatase [133] were identified as the enzymes dephosphoryl- ating LAT (and activated FccRIIA) in platelets activated via FccR. Participation of LAT in signalling by Fc receptors on mast cells, monocytes and macrophages LAT was identified as an important component involved in macrophage activation via FccRIII and FccRIV (linked to anaphylatoxin receptor activation and generation of inflammation) [134]. Cross-linking of high-affinity FccRI CD64 on THP-1 monocytic cells induces tyrosine phosphorylation of multiple proteins, including Lck, Syk and LAT, which is inhibited by coligation of an ITIM-bearing immuno- globulin-like receptor LILRB4 [135]. LAT associates with both FccRI and FccRII and enhances signal transduction elicited by these receptors in myeloid cells [44]. LAT is an important component in the activation of mast cells, where it plays similar roles as in activated T cells. Following the ligation of FceRI of mast cells, it becomes tyrosine phosphorylated by Syk kinase and associates with several cytoplasmic signalling proteins [103,136–138]; the lipid environment of membrane rafts appears to be important in these processes [139]. The extent of LAT involvement in FceRI signalling seems to be linked to the strength of the stimulus [140]. Tyro- sine 136 and the three distal tyrosines differentially contribute to exocytosis and the secretion of cytokines; in addition to the positive signalling roles they are also apparently involved in complex negative regulations, which is probably based on the assembly of signalling complexes composed of a set of intracellular molecules with antagonistic properties [137]. Electron micro- scopic studies found that following Fc eRI activation, FceRI and LAT are present in distinct membrane V. Hor ˇ ejs ˇ ı ´ et al. LAT, a key membrane raft-associated protein FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4389 domains containing associated cytoplasmic signalling molecules [141]. In addition to LAT, mast cells also express a similar adaptor, NTAL (also called LAB or LAT2). LAT and NTAL are phosphorylated after ligation of FceRI and co-operate positively and negatively in regulation of the response [10,12,142,143]. In the absence of LAT, NTAL can partially take over the positive signalling role of LAT, whereas if both adaptors are present, NTAL rather serves as a negative regulator of the activation process. Participation of LAT in signalling by NK cell receptors CD2 cross-linking in NK cells induced tyrosine phosphorylation of LAT, resulting in SH2-based association with PI3K and PLC-c1 [144,145]. This functional relationship was dependent on intact membrane rafts, as cholesterol depletion inhibited LAT tyrosine phosphorylation and NK cell cytotoxicity and degranulation [144]. LAT is tyrosine phosphorylated upon stimulation of NK cells through FccRIII receptors and following direct contact with NK-sensitive target cells. This NK stimulation induces the association of LAT with several phosphotyrosine-containing proteins, including PLCc. Over-expression of LAT in NK cells enhances their cytotoxic responses [146]. 2B4 (CD244), a receptor belonging to the Ig super- family expressed on NK cells and a subset of T cells, was reported to be constitutively associated with LAT in membrane rafts. 2B4-mediated cytotoxicity is defective in the absence of LAT, indicating that LAT is an important component in the 2B4 signal transduction pathway. Engagement of 2B4 results in tyrosine phosphorylation of both 2B4 and the associated LAT, recruitment of PLCc and Grb2 [147–149]. The 2B4- LAT association was independent of the cytoplasmic tail of 2B4, but required a CxC cysteine motif (presumably palmitoylated) found in the transmembrane region [148]. Therefore, the association is probably indirect, based on the association of both molecules with membrane rafts. Similar to myeloid cells, in addition to LAT, NK cells also express the abovementioned similar adaptor, NTAL (also called LAB or LAT2) [12]. LAT and NTAL are phosphorylated after ligation of an NK cell, activating receptors CD16 (FccRIIIa, associated with the FcRc signalling chain containing ITAM motifs) and NK1.1 (associated with the DAP12 signalling chain containing ITAM motifs). Mice lacking either LAT or NTAL have abnormalities in the reper- toire of the inhibitory receptors of the Ly49 family and respond poorly to stimulation through NK1.1. The absence of both LAT and NTAL markedly reduces NK1.1 signalling in both resting and activated NK cells [150]. LAT in B cell lineage In contrast to T cells, BCR does not seem to use a LAT-like molecule as a critical component of its signalling machinery; LAT is actually absent in immature and mature B cells. A cytoplasmic adapter SLP- 65 (BLNK) of B cells, functionally analogous to SLP-76 in T cells, appears to associate directly with the activated BCR complex [151]. However, LAT is expressed in mouse pro-B and pre-B cells; in pre-B cells it becomes tyrosine phosphorylated upon cross- linking of the pre-BCR. LAT may thus play a role in the regulation of early phases of B cell development at the transition from pre-B to immature B cell stage [42,152]. LAT and SLP-76 are recruited to the pre- BCR after its experimental cross-linking; LAT is spontaneously associated with SLP-76 in untreated pre-B cells [43]. Four distal tyrosines (Y136, Y175, Y195, Y235) are required for LAT activity in murine and human pre-B cells [153]. LAT is also found in B-ALL cells, probably reflecting their developmental origin [154]. Concluding remarks Although LAT is one of the most thoroughly studied leukocyte signalling molecules, some of its aspects remain poorly understood. As discussed above, its possible role in negative TCR regulatory pathways remains to be clarified, as well as the details of the importance of its association with raft-like microdomains. Another exciting field of research is the regulation of LAT palmitoylation and its role in membrane microdomain distribution and the outcome of TCR signalling. Furthermore, details of mutual functional interactions between LAT and the structurally related NTAL (LAB) in myeloid cells remain to be eluci- dated. Acknowledgements This work was supported in part by project no. AV0Z50520514 awarded by the Academy of Sciences of the Czech Republic, GACR (project MEM ⁄ 09 ⁄ E011) and by the Center of Molecular and Cellular Immunology (project 1M0506, Ministry of Education, Youth and Sports of the Czech Republic). LAT, a key membrane raft-associated protein V. Hor ˇ ejs ˇ ı ´ et al. 4390 FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS References 1 Martinez-Martin N, Risueno RM, Morreale A, Zaldi- var I, Fernandez-Arenas E, Herranz F, Ortiz AR & Alarcon B (2009) Cooperativity between T cell receptor complexes revealed by conformational mutants of CD3e. Sci Signal 2, ra43. 2 Dylke J, Lopes J, Dang-Lawson M, Machtaler S & Matsuuchi L (2007) Role of the extracellular and transmembrane domain of Ig-a ⁄ b in assembly of the B cell antigen receptor (BCR). Immunol Lett 112 , 47–57. 3 Humphrey MB, Lanier LL & Nakamura MC (2005) Role of ITAM-containing adapter proteins and their receptors in the immune system and bone. Immunol Rev 208, 50–65. 4 Hamerman JA, Ni M, Killebrew JR, Chu CL & Lowell CA (2009) The expanding roles of ITAM adapters FcRc and DAP12 in myeloid cells. Immunol Rev 232, 42–58. 5 Lanier LL (2009) DAP10- and DAP12-associated receptors in innate immunity. Immunol Rev 227, 150– 160. 6 Horejsi V (2004) Transmembrane adaptor proteins in membrane microdomains: important regulators of immunoreceptor signaling. Immunol Lett 92, 43–49. 7 Liu Y & Zhang W (2008) Identification of a new transmembrane adaptor protein that constitutively binds Grb2 in B cells. J Leukoc Biol 84, 842–851. 8 Horejsi V, Zhang W & Schraven B (2004) Transmem- brane adaptor proteins: organizers of immunoreceptor signalling. Nat Rev Immunol 4, 603–616. 9 Baniyash M (2004) TCR f-chain downregulation: curtailing an excessive inflammatory immune response. Nat Rev Immunol 4, 675–687. 10 Rivera J (2005) NTAL ⁄ LAB and LAT: a balancing act in mast-cell activation and function. Trends Immunol 26, 119–122. 11 Simeoni L, Smida M, Posevitz V, Schraven B & Lind- quist JA (2005) Right time, right place: the organiza- tion of membrane proximal signaling. Semin Immunol 17, 35–49. 12 Iwaki S, Jensen BM & Gilfillan AM (2007) Ntal ⁄ Lab ⁄ Lat2. Int J Biochem Cell Biol 39, 868–873. 13 Abram CL & Lowell CA (2007) The expanding role for ITAM-based signaling pathways in immune cells. Sci STKE 2007, re2. 14 Turnbull IR & Colonna M (2007) Activating and inhibitory functions of DAP12. Nat Rev Immunol 7, 155–161. 15 Fuller DM & Zhang W (2009) Regulation of lymphocyte development and activation by the LAT family of adapter proteins. Immunol Rev 232, 72–83. 16 Park I & Yun Y (2009) Transmembrane adaptor proteins positively regulating the activation of lymphocytes. Immune Netw 9, 53–57. 17 Pike LJ (2006) Rafts defined: a report on the Keystone Symposium on Lipid Rafts and Cell Function. J Lipid Res 47, 1597–1598. 18 Horejsi V, Cebecauer M, Cerny J, Brdicka T, Angelisova P & Drbal K (1998) Signal transduction in leucocytes via GPI-anchored proteins: an experimental artefact or an aspect of immunoreceptor function? Immunol Lett 63 , 63–73. 19 Paulick MG & Bertozzi CR (2008) The glycosylphosphatidylinositol anchor: a complex membrane-anchoring structure for proteins. Biochemistry 47, 6991–7000. 20 Zaman SN, Resek ME & Robbins SM (2008) Dual acylation and lipid raft association of Src-family protein tyrosine kinases are required for SDF-1 ⁄ CXCL12-mediated chemotaxis in the Jurkat human T cell lymphoma cell line. J Leukoc Biol 84, 1082–1091. 21 Barnett-Norris J, Lynch D & Reggio PH (2005) Lipids, lipid rafts and caveolae: their importance for GPCR signaling and their centrality to the endocanna- binoid system. Life Sci 77, 1625–1639. 22 van der Goot FG & Harder T (2001) Raft membrane domains: from a liquid-ordered membrane phase to a site of pathogen attack. Semin Immunol 13, 89–97. 23 Horejsi V (2005) Lipid rafts and their roles in T-cell activation. Microbes Infect 7, 310–316. 24 Pizzo P & Viola A (2004) Lipid rafts in lymphocyte activation. Microbes Infect 6, 686–692. 25 Lingwood D & Simons K (2010) Lipid rafts as a membrane-organizing principle. Science 327, 46–50. 26 Lindner R & Naim HY (2009) Domains in biological membranes. Exp Cell Res 315, 2871–2878. 27 Lajoie P, Goetz JG, Dennis JW & Nabi IR (2009) Lattices, rafts, and scaffolds: domain regulation of receptor signaling at the plasma membrane. J Cell Biol 185, 381–385. 28 Jacobson K, Mouritsen OG & Anderson RG (2007) Lipid rafts: at a crossroad between cell biology and physics. Nat Cell Biol 9, 7–14. 29 Duggan J, Jamal G, Tilley M, Davis B, McKenzie G, Vere K, Somekh MG, O’Shea P & Harris H (2008) Functional imaging of microdomains in cell membranes. Eur Biophys J 37, 1279–1289. 30 Wilson BS, Steinberg SL, Liederman K, Pfeiffer JR, Surviladze Z, Zhang J, Samelson LE, Yang LH, Kotula PG & Oliver JM (2004) Markers for detergent-resistant lipid rafts occupy distinct and dynamic domains in native membranes. Mol Biol Cell 15, 2580–2592. 31 Lillemeier BF, Pfeiffer JR, Surviladze Z, Wilson BS & Davis MM (2006) Plasma membrane-associated proteins are clustered into islands attached to the cytoskeleton. Proc Natl Acad Sci USA 103, 18992– 18997. 32 Hansen CG & Nichols BJ (2010) Exploring the caves: cavins, caveolins and caveolae. Trends Cell Biol 20, 177–186. V. Hor ˇ ejs ˇ ı ´ et al. LAT, a key membrane raft-associated protein FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4391 33 Lingwood D, Kaiser HJ, Levental I & Simons K (2009) Lipid rafts as functional heterogeneity in cell membranes. Biochem Soc Trans 37, 955–960. 34 Harder T & Sangani D (2009) Plasma membrane rafts engaged in T cell signalling: new developments in an old concept. Cell Commun Signal 7, 21. 35 Horejsi V (2003) The roles of membrane microdomains (rafts) in T cell activation. Immunol Rev 191, 148–164. 36 Otahal P, Angelisova P, Hrdinka M, Brdicka T, Novak P, Drbal K & Horejsi V (2010) A new type of membrane raft-like microdomains and their possible involvement in TCR signaling. J Immunol 184, 3689–3696. 37 Drevot P, Langlet C, Guo XJ, Bernard AM, Colard O, Chauvin JP, Lasserre R & He HT (2002) TCR signal initiation machinery is pre-assembled and activated in a subset of membrane rafts. EMBO J 21, 1899–1908. 38 Knorr R, Karacsonyi C & Lindner R (2009) Endocy- tosis of MHC molecules by distinct membrane rafts. J Cell Sci 122, 1584–1594. 39 Fukazawa T, Reedquist KA, Panchamoorthy G, Solt- off S, Trub T, Druker B, Cantley L, Shoelson SE & Band H (1995) T cell activation-dependent association between the p85 subunit of the phosphatidylinositol 3-kinase and Grb2 ⁄ phospholipase C-c 1-binding phosphotyrosyl protein pp36 ⁄ 38. J Biol Chem 270, 20177– 20182. 40 Zhang W, Sloan-Lancaster J, Kitchen J, Trible RP & Samelson LE (1998) LAT: the ZAP-70 tyrosine kinase substrate that links T cell receptor to cellular activation. Cell 92, 83–92. 41 Weber JR, Orstavik S, Torgersen KM, Danbolt NC, Berg SF, Ryan JC, Tasken K, Imboden JB & Vaage JT (1998) Molecular cloning of the cDNA encoding pp36, a tyrosine-phosphorylated adaptor protein selec- tively expressed by T cells and natural killer cells. J Exp Med 187, 1157–1161. 42 Oya K, Wang J, Watanabe Y, Koga R & Watanabe T (2003) Appearance of the LAT protein at an early stage of B-cell development and its possible role. Immunology 109, 351–359. 43 Su YW & Jumaa H (2003) LAT links the pre-BCR to calcium signaling. Immunity 19, 295–305. 44 Tridandapani S, Lyden TW, Smith JL, Carter JE, Coggeshall KM & Anderson CL (2000) The adapter protein LAT enhances fcgamma receptor-mediated signal transduction in myeloid cells. J Biol Chem 275, 20480–20487. 45 Gibbins JM, Briddon S, Shutes A, van Vugt MJ, van de Winkel JG, Saito T & Watson SP (1998) The p85 subunit of phosphatidylinositol 3-kinase associates with the Fc receptor c-chain and linker for activitor of T cells (LAT) in platelets stimulated by collagen and convulxin. J Biol Chem 273, 34437–34443. 46 Facchetti F, Chan JK, Zhang W, Tironi A, Chilosi M, Parolini S, Notarangelo LD & Samelson LE (1999) Linker for activation of T cells (LAT), a novel immunohistochemical marker for T cells, NK cells, mast cells, and megakaryocytes: evaluation in normal and pathological conditions. Am J Pathol 154, 1037–1046. 47 Hundt M, Harada Y, De Giorgio L, Tanimura N, Zhang W & Altman A (2009) Palmitoylation-dependent plasma membrane transport but lipid raft-independent signaling by linker for activation of T cells. J Immunol 183, 1685–1694. 48 Pullar CE, Morris PJ & Wood KJ (2003) Altered proximal T-cell receptor signalling events in mouse CD4+ T cells in the presence of anti-CD4 monoclonal antibodies: evidence for reduced phosphorylation of Zap-70 and LAT. Scand J Immunol 57, 333–341. 49 Jiang Y & Cheng H (2007) Evidence of LAT as a dual substrate for Lck and Syk in T lymphocytes. Leuk Res 31, 541–545. 50 Zhang W, Trible RP, Zhu M, Liu SK, McGlade CJ & Samelson LE (2000) Association of Grb2, Gads, and phospholipase C-c 1 with phosphorylated LAT tyrosine residues. Effect of LAT tyrosine mutations on T cell antigen receptor-mediated signaling. J Biol Chem 275, 23355–23361. 51 Lin J & Weiss A (2001) Identification of the minimal tyrosine residues required for linker for activation of T cell function. J Biol Chem 276, 29588–29595. 52 Paz PE, Wang S, Clarke H, Lu X, Stokoe D & Abo A (2001) Mapping the Zap-70 phosphorylation sites on LAT (linker for activation of T cells) required for recruitment and activation of signalling proteins in T cells. Biochem J 356, 461–471. 53 Liu SK, Fang N, Koretzky GA & McGlade CJ (1999) The hematopoietic-specific adaptor protein Gads functions in T-cell signaling via interactions with the SLP- 76 and LAT adaptors. Curr Biol 9, 67–75. 54 Sangani D, Venien-Bryan C & Harder T (2009) Phosp- hotyrosine-dependent in vitro reconstitution of recombinant LAT-nucleated multiprotein signalling complexes on liposomes. Mol Membr Biol 26, 159–170. 55 Cho S, Velikovsky CA, Swaminathan CP, Houtman JC, Samelson LE & Mariuzza RA (2004) Structural basis for differential recognition of tyrosine-phosphorylated sites in the linker for activation of T cells (LAT) by the adaptor Gads. EMBO J 23, 1441–1451. 56 Kabouridis PS (2003) Selective interaction of LAT (linker of activated T cells) with the open-active form of Lck in lipid rafts reveals a new mechanism for the regulation of Lck in T cells. Biochem J 371, 907–915. 57 Lee JS, Lee JE, Oh YM, Park JB, Choi H, Choi CY, Kim IH, Lee SH & Choi K (2009) Recruitment of Sprouty1 to immune synapse regulates T cell receptor signaling. J Immunol 183, 7178–7186. 58 Kang Q, Yu Y, Pei X, Hughes R, Heck S, Zhang X, Guo X, Halverson G, Mohandas N & An X (2009) LAT, a key membrane raft-associated protein V. Hor ˇ ejs ˇ ı ´ et al. 4392 FEBS Journal 277 (2010) 4383–4397 ª 2010 The Authors Journal compilation ª 2010 FEBS [...]... (2006) Negative regulation of T cell activation and autoimmunity by the transmembrane adaptor protein LAB Immunity 25, 75 7–7 68 97 Balagopalan L, Barr VA, Sommers CL, Barda-Saad M, Goyal A, Isakowitz MS & Samelson LE (2007) c-Cbl-mediated regulation of LAT- nucleated signaling complexes Mol Cell Biol 27, 862 2–8 636 98 Thien CB, Bowtell DD & Langdon WY (1999) Perturbed regulation of ZAP-70 and sustained tyrosine... (2004) Binding specificity of multiprotein signaling complexes is determined by both cooperative interactions and affinity preferences Biochemistry 43, 417 0–4 178 Houtman JC, Barda-Saad M & Samelson LE (2005) Examining multiprotein signaling complexes from all angles FEBS J 272, 542 6–5 435 LAT, a key membrane raft-associated protein 70 Houtman JC, Yamaguchi H, Barda-Saad M, Braiman A, Bowden B, Appella E, Schuck... Cell Biol 30, 342 1–3 429 75 Brdicka T, Cerny J & Horejsi V (1998) T cell receptor signalling results in rapid tyrosine phosphorylation of the linker protein LAT present in detergent-resistant membrane microdomains Biochem Biophys Res Commun 248, 35 6–3 60 76 Zhang W, Trible RP & Samelson LE (1998) LAT palmitoylation: its essential role in membrane microdomain targeting and tyrosine phosphorylation during... created by protein protein networks that exclude or trap signaling molecules in T cells Cell 121, 93 7– 950 Lillemeier BF, Mortelmaier MA, Forstner MB, Huppa JB, Groves JT & Davis MM (2010) TCR and Lat are expressed on separate protein islands on T cell membranes and concatenate during activation Nat Immunol 11, 9 0–9 6 Houtman JC, Higashimoto Y, Dimasi N, Cho S, Yamaguchi H, Bowden B, Regan C, Malchiodi... both LAT and SOS1 Nat Struct Mol Biol 13, 79 8–8 05 71 Azar GA, Lemaitre F, Robey EA & Bousso P (2010) Subcellular dynamics of T cell immunological synapses and kinases in lymph nodes Proc Natl Acad Sci USA 107, 367 5–3 680 72 Bonello G, Blanchard N, Montoya MC, Aguado E, Langlet C, He HT, Nunez-Cruz S, Malissen M, Sanchez-Madrid F, Olive D et al (2004) Dynamic recruitment of the adaptor protein LAT: LAT. .. Takeuchi A, Ohnishi H, Hirano T & Saito T (2001) Docking protein Gab2 is phosphorylated by ZAP-70 and negatively regulates T cell receptor signaling by recruitment of inhibitory molecules J Biol Chem 276, 4517 5–4 5183 LAT, a key membrane raft-associated protein 117 Yamasaki S, Nishida K, Sakuma M, Berry D, McGlade CJ, Hirano T & Saito T (2003) Gads ⁄ Grb2mediated association with LAT is critical for the... Streptococcus sanguis-induced platelet activation involves two waves of tyrosine phosphorylation mediated by FccRIIA and aIIb3 Thromb Haemost 93, 93 2–9 39 FEBS Journal 277 (2010) 438 3–4 397 ª 2010 The Authors Journal compilation ª 2010 FEBS 4395 ˇ ˇı V Horejs´ et al LAT, a key membrane raft-associated protein 128 Suzuki-Inoue K, Fuller GL, Garcia A, Eble JA, Pohlmann S, Inoue O, Gartner TK, Hughan SC, Pearce AC,... activation: tyrosine phosphorylation and association of LAT with phosphatidylinositol 3-kinase and phospholipase C-c following CD2 stimulation Eur J Immunol 32, 218 8–2 198 145 Umehara H, Inoue H, Huang J, Kono T, Minami Y, Tanaka Y, Okazaki T, Mimori T, Bloom ET & Domae N (2002) Role for adapter proteins in costimulatory signals of CD2 and IL-2 on NK cell activation Mol Immunol 38, 58 7–5 96 146 Jevremovic D,... Syk-dependent mechanism of platelet activation by the C-type lectin receptor CLEC-2 Blood 107, 54 2–5 49 129 Pearce AC, Wonerow P, Marshall SJ, Frampton J, Gartner TK & Watson SP (2004) The heptapeptide LSARLAF mediates platelet activation through phospholipase Cc2 independently of glycoprotein IIb-IIIa Biochem J 378, 19 3–1 99 130 Sarkar S (1998) Tyrosine phosphorylation and translocation of LAT in platelets FEBS... stimulation of the collagen receptor glycoprotein VI in human platelets Eur J Biochem 263, 61 2–6 23 120 Asazuma N, Wilde JI, Berlanga O, Leduc M, Leo A, Schweighoffer E, Tybulewicz V, Bon C, Liu SK, McGlade CJ et al (2000) Interaction of linker for activation of T cells with multiple adapter proteins in platelets activated by the glycoprotein VI-selective ligand, convulxin J Biol Chem 275, 3342 7–3 3434 . THE SIR HANS KREBS LECTURE LAT – an important raft-associated transmembrane adaptor protein Delivered on 6 July 2009 at the. that can be phosphorylated and bind other cytoplasmic signalling proteins. The most important leukocyte transmembrane adaptor protein is LAT (linker for activation

Ngày đăng: 18/02/2014, 04:20

Xem thêm