Physical and functional association of the high affinity immunoglobulin G receptor (Fc gamma RI) with the kinases Hck and Lyn

The high affinity immunoglobulin G (IgG) receptor Fc gamma RI (CD64) is expressed constitutively on monocytes and macrophages, and is inducible on neutrophils. Fc gamma RI has recently been shown to be associated with the signal transducing gamma subunit of the high-affinity IgE receptor (Fc epsilon RI gamma). Induction of cytoplasmic protein tyrosine phosphorylation by Fc gamma RI cross-linking is known to be important in mediating Fc gamma RI-coupled effector functions. Recently, syk has been implicated in this role. We now report that the src-type kinases hck and lyn are physically and functionally associated with Fc gamma RI. Hck and lyn coimmunoprecipitated with Fc gamma RI from detergent lysates of normal human monocytes and of the monocytic line THP-1. Hck and lyn showed rapidly increased phosphorylation and increased exogenous substrate kinase activity after cross-linking of Fc gamma RI. These results demonstrate both physical and functional association of the Fc gamma RI/Fc epsilon RI gamma receptor complex with hck and lyn, and suggest a potential signal transducing role for these kinases in monocyte/macrophage activation.     

CD40 and IgE: synergism between anti-CD40 monoclonal antibody and interleukin 4 in the induction of IgE synthesis by highly purified human B cells

A novel pathway of IgE-B cell differentiation has been identified. Engagement of the B cell antigen CD40 by F(ab')2 fragments of monoclonal antibody (mAb) 626.1 in the presence of recombinant interleukin 4 (rIL-4) induced intense IgE synthesis, but modest IgG synthesis, by highly purified human B cells. Surface IgE- B cells isolated by cell sorting were induced to produce IgE by mAb 626.1 and IL-4. Thus, IgE synthesis is unlikely to result from expansion of a B cell population precommitted to IgE in vivo. A neutralizing anti-IL-6 antibody strongly, but not completely, inhibited the IgE response. This indicates that autocrine production of IL-6 plays an important amplification role in IgE synthesis triggered by anti-CD40 mAb and IL-4. Although the exact role played by CD40 in IgE responses in vivo remains to be established, this T cell-independent system represents a useful model to characterize the biochemical and molecular events leading to IgE synthesis in human B cells.     

The Src-family kinase, Fyn, regulates the activation of phosphatidylinositol 3-kinase in an interleukin 2-responsive T cell line

The proliferation of antigen-activated T cells is mediated by the T cell-derived growth factor, interleukin 2 (IL-2). The biochemical signaling cascades initiating IL-2-induced growth are dependent upon protein tyrosine kinase (PTK) activity. One IL-2-regulated PTK implicated in this cascade is the Src-family kinase, Fyn. Previous studies have described a physical association between Fyn and a potential downstream substrate, phosphatidylinositol 3-kinase (PI3- kinase) as well as the IL-2-dependent activation of PI3-kinase in T cells; however, the role of Fyn in IL-2-induced PI3-kinase activation remains unclear. In this report, we demonstrate that IL-2 stimulation triggers tyrosine phosphorylation of the p85 subunit of PI3-kinase in the murine T cell line, CTLL-2. Lysates prepared from growth factor- deprived and IL-2-stimulated T cells reconstituted both the binding of CTLL-2 cell-derived Fyn to and the IL-2-inducible tyrosine phosphorylation of exogenously added recombinant p85. Furthermore, overexpression of wild-type Fyn in these cells enhanced both the basal and IL-2-mediated activation of PI3-kinase. Additional studies of the Fyn-PI3-kinase interaction demonstrated that the Src homology 3 (SH3) domain of Fyn constitutes a direct binding site for the p85 subunit of PI3-kinase. These results support the notion that Fyn may be directly involved in the activation of the downstream signaling enzyme, PI3- kinase, in IL-2-stimulated T cells.     

Requirement for tyrosine residues 315 and 319 within zeta chain-associated protein 70 for T cell development

Engagement of the T cell antigen receptor (TCR) induces the transphosphorylation of the zeta chain-associated protein of 70,000 Mr (ZAP-70) protein tyrosine kinase (PTK) by the CD4/8 coreceptor associated Lck PTK. Phosphorylation of Tyr 493 within ZAP-70's activation loop results in the enzymatic activation of ZAP-70. Additional tyrosines (Tyrs) within ZAP-70 are phosphorylated that play both positive and negative regulatory roles in TCR function. Phosphorylation of Tyr residues (Tyrs 315 and 319) within the Interdomain B region of the ZAP-70 PTK plays important roles in the generation of second messengers after TCR engagement. Here, we demonstrate that phosphorylation of these two Tyr residues also play important roles in mediating the positive and negative selection of T cells in the thymus.     

Stimulation of Fc gamma RIIIA results in phospholipase C-gamma 1 tyrosine phosphorylation and p56lck activation

Binding of ligand to the alpha subunit of Fc gamma RIIIA(CD16), expressed at the natural killer (NK) cell membrane in association with homo or heterodimers of proteins of the zeta family, results in phosphorylation of several proteins on tyrosine residues. We have analyzed the role of protein tyrosine phosphorylation in the regulation of molecular events induced upon stimulation of Fc gamma RIIIA in NK cells and in T cells expressing the Fc gamma RIII alpha chain in association with endogenous zeta 2 homodimers and devoid of other (CD3, CD2) transducing molecules. Our data indicate that treatment of these cells with protein tyrosine kinase inhibitors prevents not only Fc gamma RIIIA-induced protein tyrosine phosphorylation but also phosphatidylinositol 4,5 diphosphate hydrolysis and increased intracellular Ca2+ concentration, indicating a primary role of tyrosine kinase(s) in the induction of these early activation events. Occupancy of Fc gamma RIIIA by ligand results in phospholipase C (PLC)-gamma 1 tyrosine phosphorylation in NK cells and in Fc gamma RIIIA-transfected CD3-/CD2- T cells, and induces functional activation of p56lck in Fc gamma RIIIA alpha/zeta 2-transfected T cells, suggesting the possibility that the receptor-induced PLC-gamma 1 activation occurs upon phosphorylation of its tyrosine residues mediated by this kinase and is, at least in part, responsible for the signal transduction mediated via CD16 upon ligand binding.     

Association of the tyrosine kinase LCK with phospholipase C-gamma 1 after stimulation of the T cell antigen receptor

Stimulation of the T cell antigen receptor (TCR) activates a protein tyrosine kinase and leads to the tyrosine phosphorylation of phosphoinositide-specific phospholipase C-gamma 1 (PLC gamma 1). The molecular interactions involved in this phosphorylation are not known. After stimulation of the TCR on Jurkat T cells, tyrosine-phosphorylated proteins of 36, 38, 58, and 63 kD coprecipitate with PLC gamma 1. An identical pattern of proteins precipitate with TrpE fusion proteins that contain the Src homology (SH) 2 domains of PLC gamma 1, indicating that these regions of PLC gamma 1 are responsible for binding. TCR stimulation leads to an association between the SH2 domains of PLC gamma 1 and a protein tyrosine kinase, which, by peptide mapping, is identical to p56lck. These studies establish that p56lck associates with PLC gamma 1 as a result of TCR stimulation of Jurkat cells, suggesting that p56lck plays a central role in coupling the TCR to the activation of PLC gamma 1.     

Phosphatidylinositol-3 kinase activation induced upon Fc gamma RIIIA- ligand interaction

Induced activation of protein tyrosine kinase(s) is a central event in signal transduction mediated via the low affinity receptor for IgG (Fc gamma RIIIA, CD16) in natural killer (NK) cells. Tyrosine phosphorylation may affect the function of several protein directly, or indirectly by inducing their association with other tyrosine phosphorylated proteins. Here, we report that Fc gamma RIII stimulation induces activation of phosphatidylinositol (PI)-3 kinase in NK cells. Phosphotyrosine immunoprecipitates from Fc gamma RIII-stimulated NK cells contain PI-kinase activity and PI-3 kinase can be directly precipitated from them. Conversely, a series of tyrosine-phosphorylated proteins is coprecipitated with PI-3 kinase from the stimulated, but not from control cells. Analogous results obtained using Jurkat T cells expressing transfected Fc gamma RIIIA alpha ligand binding chain in association with gamma 2 or zeta 2 homodimers indicate that both complexes transduce this effect, although the Fc gamma RIIIA-zeta 2 complexes do so with greater efficiency. Accumulation of phosphoinositide D3 phosphorylated products in stimulated cells confirms PI-3 kinase activation, indicating the participation of this enzyme in Fc gamma RIIIA-mediated signal transduction.     

Fc gamma receptor activation induces the tyrosine phosphorylation of both phospholipase C (PLC)-gamma 1 and PLC-gamma 2 in natural killer cells

Crosslinking of the low affinity immunoglobulin G (IgG) Fc receptor (Fc gamma R type III) on natural killer (NK) cells initiates antibody-dependent cellular cytotoxicity. During this process, Fc gamma R stimulation results in the rapid activation of phospholipase C (PLC), which hydrolyzes membrane phosphoinositides, generating inositol-1,4,5-trisphosphate and sn-1,2-diacylglycerol as second messengers. We have recently reported that PLC activation after Fc gamma R stimulation can be inhibited by a protein tyrosine kinase (PTK) inhibitor. Based on the paradigm provided by the receptor tyrosine kinases, we investigated whether PLC-gamma 1 and/or PLC-gamma 2 are expressed in NK cells, and whether the PLC-gamma isoforms are tyrosine phosphorylated in response to Fc gamma R stimulation. Immunoblotting analyses with PLC-gamma 1- and PLC-gamma 2-specific antisera demonstrate that both isoforms are expressed in human NK cells. Furthermore, Fc gamma R crosslinking triggers the tyrosine phosphorylation of both PLC-gamma 1 and PLC-gamma 2 in these cells. Phosphorylation of both isoforms is detectable within 1 min, and returns to basal level within 30 min. Pretreatment with herbimycin A, a PTK inhibitor, blocked the Fc gamma R-induced tyrosine phosphorylation of PLC-gamma 1 and PLC-gamma 2, and the subsequent release of inositol phosphates. These results suggest that Fc gamma R-initiated phosphoinositide turnover in human NK cells is regulated by the tyrosine phosphorylation of PLC-gamma. More broadly, these observations demonstrate that nonreceptor PTK(s) activated by crosslinkage of a multisubunit receptor can phosphorylate both PLC-gamma isoforms.     

Ligation of VLA-4 on T cells stimulates tyrosine phosphorylation of a 105-kD protein

The VLA/integrins are a family of heterodimeric adhesion receptors shown to be involved in cell-to-cell and cell-to-extracellular matrix (ECM) interactions. Given recent evidence that VLA molecules can synergize with the CD3/T cell receptor (TCR) pathway to activate T cells, it is important to identify biochemical event(s) generated by these molecules. Here, we report that the engagement of VLA-4 on T cells with specific antibodies or its ligand activates protein-tyrosine kinase (PTK) activity as detected by antiphosphotyrosine immunoblotting. The crosslinking of VLA-beta 1 (CD29) with a specific monoclonal antibody (mAb) (anti-4B4) plus anti-mouse immunoglobulin resulted in the rapid tyrosine phosphorylation of a 105-kD protein (pp105) in the human T cell line H9, as well as in peripheral resting T cells. The increase in tyrosine phosphorylation of pp105 was specifically mediated by VLA-4, since mAbs against alpha 4, but not against other VLA alpha chains, could induce this phosphorylation. In addition, the binding of T cells with the CS1 alternatively spliced segment of fibronectin (the binding site recognized by VLA-4) induced pp105 tyrosine phosphorylation. Crosslinking the CD3 complex or VLA-4 molecules with mAbs demonstrated that each of these molecules stimulated the tyrosine phosphorylation of unique sets of proteins with different kinetics, suggesting that these two receptor systems are coupled to distinct PTKs. Since tyrosine phosphorylation of cellular proteins has been shown to be a crucial biochemical event in cell growth, our findings suggest that the induction of pp105 tyrosine phosphorylation via VLA-4 may play a role in the transduction of activation signals through this molecule.     

Phospholipase C-gamma 1 association with CD3 structure in T cells

Recently, we and others have reported tyrosine phosphorylation of phospholipase C-gamma 1 (PLC gamma 1) enzyme after CD3 activation of T cells, and have proposed that PLC gamma 1 mediates signal transduction through the T cell receptor (TCR/CD3). Here, using immunoblotting and immune complex PLC assays, we show that CD3 stimulation of Jurkat cells induces the association of PLC gamma 1 enzyme with CD3 complex. PLC activity is also found to co-precipitate with the CD3 zeta chain from activated cells. In addition, in vitro PLC assays show that CD3 activation leads to about 10-fold stimulation of PLC gamma 1 activity. These results, along with the observation that Jurkat cells preferentially express PLC gamma 1, indicate that PLC gamma 1 participates in CD3 signaling.     

The intracellular signal transduction mechanism of interleukin 5 in eosinophils: the involvement of lyn tyrosine kinase and the Ras-Raf-1- MEK-microtubule-associated protein kinase pathway

Interleukin 5 (IL-5) regulates the growth and function of eosinophils. The objective of this study was to investigate the intracellular signal transduction mechanism of IL-5 in eosinophils. Purified eosinophils were stimulated with IL-5, and the involvement of various kinases was investigated by immunoblotting, immune complex kinase assay, and in situ denatured/renatured kinase assay. We found that IL-5 induced tyrosine phosphorylation and activation of a number of kinases. Two species of lyn kinases (53 and 56 kD) were present in eosinophils. Both forms were Tyr-phosphorylated and activated rapidly within 1 min. Further, lyn kinase was physically associated with the IL-5 beta receptor in eosinophils. Ras was studied by immunoprecipitation followed by thin-layer chromatography. Ras bound higher quantities of [alpha-32P]guanosine 5'triphosphate upon stimulation with IL-5. Raf-1 kinase showed increased Tyr phosphorylation on immunoblotting and increased activity in the immune complex kinase assay. Two species of MEK (MAP or Erk kinase) (41 and 45 kD) were identified in eosinophils, which underwent autophosphorylation upon stimulation. Microtubule- associated protein (MAP) kinase (p44) was Tyr-phosphorylated on immunoblotting and had increased activity in the immune-complex kinase assay. MAP kinases were also studied after metabolic radiolabeling of the cells with [32P]orthophosphates. IL-5 stimulated phosphorylation of MAP kinases in situ. Thus, we have delineated major components of an important signaling pathway in eosinophils. We believe that one of the signals generated by IL-5 receptor activation is propagated through the lyn-Ras-Raf-1-MEK-MAP kinase pathway.     

The 86-kD subunit of Ku autoantigen mediates homotypic and heterotypic adhesion of multiple myeloma cells.

Previous studies have shown that triggering multiple myeloma (MM) cells via CD40 induces IL-6-mediated autocrine growth as well as increased expression of cell surface adhesion molecules including CD11a, CD11b, CD11c, and CD18. In this study, we generated the 5E2 mAb which targets an antigen that is induced upon CD40 ligand (CD40L) activation of MM cells. Immunofluorescence, immunoprecipitation, and protein sequencing studies identified the target antigen of 5E2 mAb as the 86-kD subunit of the Ku autoantigen. We demonstrate that increased cell surface expression of Ku on CD40L-treated cells is due to migration of Ku from the cytoplasm to the cell surface membrane. Moreover, cell surface Ku on CD40L-treated MM cells mediates homotypic adhesion of tumor cells, as well as heterotypic adhesion of tumor cells to bone marrow stromal cells and to human fibronectin; and 5E2 mAb abrogates IL-6 secretion triggered by tumor cell adherence to bone marrow stromal cells. These data suggest that CD40L treatment induces a shift of Ku from the cytoplasm to the cell surface, and are the first to show that Ku functions as an adhesion molecule. They further suggest that cell surface Ku may play a role in both autocrine and paracrine IL-6-mediated MM cell growth and survival.     

A regulatory role for Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) in phagocytosis mediated by Fc gamma receptors and complement receptor 3 (alpha(M)beta(2); CD11b/CD18)

The Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) is recruited to immunoreceptor tyrosine-based inhibition motif (ITIM)-containing proteins, thereby suppressing phosphatidylinositol 3-kinase (PI 3-kinase)-dependent pathways. The role of SHIP in phagocytosis, a PI 3-kinase-dependent pathway, is unknown. Overexpression of SHIP in macrophages led to an inhibition of phagocytosis mediated by receptors for the Fc portion of IgG (Fc gamma Rs). In contrast, macrophages expressing catalytically inactive SHIP or lacking SHIP expression demonstrated enhanced phagocytosis. To determine whether SHIP regulates phagocytosis mediated by receptors that are not known to recruit ITIMs, we determined the effect of SHIP expression on complement receptor 3 (CR3; CD11b/CD18; alpha(M)beta(2))-dependent phagocytosis. Macrophages overexpressing SHIP demonstrated impaired CR3-mediated phagocytosis, whereas macrophages expressing catalytically inactive SHIP demonstrated enhanced phagocytosis. CR3-mediated phagocytosis in macrophages derived from SHIP(-/-) mice was up to 2.5 times as efficient as that observed in macrophages derived from littermate controls. SHIP was localized to Fc gamma R- and CR3-containing phagocytic cups and was recruited to the cytoskeleton upon clustering of CR3. In a transfected COS cell model of activation-independent CR3-mediated phagocytosis, catalytically active but not inactive SHIP also inhibited phagocytosis. We conclude that PI 3-kinase(s) and SHIP regulate multiple forms of phagocytosis and that endogenous SHIP plays a role in modulating beta(2) integrin outside-in signaling.     

流式细胞术检测狼疮患者白细胞分化抗原40配体

目的　了解在系统性红斑狼疮（ Ｓ Ｌ Ｅ） 患者血液中辅助性 Ｔ细胞（ Ｔｈ） 与 Ｂ 细胞间的白细胞分化抗原（ Ｃ Ｄ）４０ Ｃ Ｄ４０ 配体（ Ｌ） 的共刺激作用。方法　用抗 Ｃ Ｄ３ 单克隆抗体（ 单抗） 刺激 Ｓ Ｌ Ｅ 活动期和缓解期各１０ 例患者外周血单个核细胞（ Ｐ Ｂ Ｍ Ｃ） ,采用流式细胞术检测不同时段 Ｃ Ｄ４０ Ｌ 的表达水平,并与正常对照组比较。结果　活动期 Ｓ Ｌ Ｅ 组 Ｃ Ｄ４０ Ｌ 的表达在抗 Ｃ Ｄ３ 单抗刺激前后均显著高于正常对照组,差异均有非常显著意义;而缓解期 Ｓ Ｌ Ｅ 组 Ｔ 细胞在抗 Ｃ Ｄ３ 单抗刺激前的 Ｃ Ｄ４０ Ｌ 表达在正常范围内,在刺激后显著高于正常对照组,差异有非常显著意义。结论　 Ｃ Ｄ４０ Ｌ Ｃ Ｄ４０ 共刺激作用在 Ｓ Ｌ Ｅ发病机制和病程中起着重要作用。     

The B cell antigen receptor controls integrin activity through Btk and PLCgamma2

Integrin-mediated adhesion and B cell antigen receptor (BCR) signaling play a critical role in B cell development and function, including antigen-specific B cell differentiation. Here we show that the BCR controls integrin alpha4beta1 (VLA-4)-mediated adhesion of B cells to vascular cell adhesion molecule-1 and fibronectin. Molecular dissection of the underlying signaling mechanism by a combined biochemical, pharmacological, and genetic approach demonstrates that this BCR-controlled integrin-mediated adhesion requires the (consecutive) activation of Lyn, Syk, phosphatidylinositol 3-kinase, Bruton's tyrosine kinase (Btk), phospholipase C (PLC)gamma2, IP3R-mediated Ca2+ release, and PKC. In contrast, activation of mitogen-activated protein kinase kinase (MEK) or extracellular signal-regulated kinase (ERK) is not required, and simultaneous activation of MEK, ERK, and PKB is not sufficient either. Furthermore, Btk is also involved in the control of integrin-mediated adhesion of preB cells. The control of integrin alpha4beta1-mediated B cell adhesion by the BCR involves cytoskeletal reorganization and integrin clustering. These results reveal a novel function for the BCR and Btk, i.e., regulation of integrin alpha4beta1 activity, thereby providing new insights into the control of B cell development and differentiation, as well as into the pathogenesis of the immunodeficiency disease X-linked agammaglobulineamia (XLA).     

Platelet GPIb-IX-V-dependent signaling

Although the signaling pathways related to GPIb-IX-V have not been fully elucidated, an accumulating body of evidence suggests that phospholipase C (PLC)gamma2 activation, subsequent Ca++ release and oscillations constitute an essential signal transduction pathway related to GPIb-IX-V. Src family kinases are required for PLCgamma2 activation, while FcR gamma-chain/Fc gammaRIIA may be dispensable for PLCgamma2 activation. Although PI-3K serves to potentiate various signaling events culminating in alpha(IIb)beta3 activation, PI-3K activity may be dispensable for Src-PLCgamma2 activation in GPIb-IX-V-mediated signaling. Glycosphingolipid-enriched microdomains (GEMs) appear to provide platforms for the signal transduction pathway related to GIb-IX-V, as the interaction between GPIb-IX-V and Src or PLCgamma2 tyrosine phosphorylation occurs exclusively in GEMs.     

Involvement of RSK phosphorylation in PTTH-stimulated ecdysone secretion in prothoracic glands of the silkworm,Bombyx mori

It is well known that phosphorylation of extracellular signal-regulated kinase (ERK) is involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in insect prothoracic glands (PGs). In the present study, we further investigated the downstream signalling pathways. Our results showed that PTTH stimulated p90 ribosomal S6 kinase (RSK) phosphorylation at Thr573 in Bombyx mori PGs both in vitro and in vivo. The in vitro PTTH stimulation was stage- and dose-dependent. The absence of Ca²⁺ reduced PTTH-stimulated RSK phosphorylation. Stimulation of RSK phosphorylation was also observed after treatment with either A23187 or thapsigargin. A phospholipase C (PLC) inhibitor, U73122, blocked PTTH-stimulated RSK phosphorylation. These results indicate the involvement of Ca²⁺ and PLC. Treatment with diphenylene iodonium (DPI), a mitochondrial oxidative phosphorylation inhibitor, blocked PTTH-regulated RSK phosphorylation, indicating its redox regulation. A mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor, U0126, but not a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, decreased PTTH-stimulated RSK phosphorylation, indicating that ERK is an upstream signalling. A protein kinase C (PKC) inhibitor, chelerythrine C, inhibited PTTH-stimulated RSK phosphorylation, and a PKC activator, phorbol 12-myristate acetate (PMA) stimulated RSK phosphorylation, indicating the involvement of PKC. BI-D1870, a specific RSK inhibitor, partly prevented PTTH-stimulated RSK phosphorylation and significantly inhibited PTTH-stimulated ecdysteroid secretion, indicating that PTTH-stimulated RSK phosphorylation is involved in ecdysteroidogenesis. Taken together, these data indicate that PTTH activates RSK phosphorylation which plays important roles in PTTH-stimulated ecdysteroidogenesis.