D. Medgyesi - Academia.edu (original) (raw)

Papers by D. Medgyesi

Tyrosine phosphorylation of signaling molecules that mediate B cell activation in response to var... more Tyrosine phosphorylation of signaling molecules that mediate B cell activation in response to various stimuli is tightly regulated by protein tyrosine phosphatases (PTPs). PTP1B is a ubiquitously expressed tyrosine phosphatase with well-characterized functions in metabolic signaling pathways. We show here that PTP1B negatively regulates CD40, B cell activating factor receptor (BAFF-R), and TLR4 signaling in B cells. Specifically, PTP1B counteracts p38 mitogen-activated protein kinase (MAPK) activation by directly dephosphorylating Tyr(182) of this kinase. Mice with a B cell-specific PTP1B deficiency show increased T cell-dependent immune responses and elevated total serum IgG. Furthermore, aged animals develop systemic autoimmunity with elevated serum anti-dsDNA, spontaneous germinal centers in the spleen, and deposition of IgG immune complexes and C3 in the kidney. In a clinical setting, we observed that B cells of rheumatoid arthritis patients have significantly reduced PTP1B expression. Our data suggest that PTP1B plays an important role in the control of B cell activation and the maintenance of immunological tolerance.

Journal of Molecular Medicine, 2015

It is becoming more and more accepted that, in addition to producing autoantibodies, B lymphocyte... more It is becoming more and more accepted that, in addition to producing autoantibodies, B lymphocytes have other important functions that influence the development of autoimmunity. For example, autoreactive B cells are able to produce inflammatory cytokines and activate pathogenic T cells. B lymphocytes can react to extracellular signals with a range of responses from anergy to autoreactivity. The final outcome is determined by the relative contribution of signaling events mediated by activating and inhibitory pathways. Besides the B cell antigen receptor (BCR), several costimulatory receptors expressed on B cells can also induce B cell proliferation and survival, or regulate antibody production. These include CD19, CD40, the B cell activating factor receptor, and Toll-like receptors. Hyperactivity of these receptors clearly contributes to breaking B-cell tolerance in several autoimmune diseases. Inhibitors of these activating signals (including protein tyrosine phosphatases, deubiquitinating enzymes and several adaptor proteins) are crucial to control Bcell activation and maintain B-cell tolerance. In this review, we summarize the inhibitory signaling mechanisms that counteract B-cell activation triggered by the BCR and the coreceptors.

The Journal of Immunology, 2014

Journal of Leukocyte Biology, 2013

B cells acquire membrane-bound cognate antigens from the surface of the APCs by forming an IS, si... more B cells acquire membrane-bound cognate antigens from the surface of the APCs by forming an IS, similar to that seen in T cells. Recognition of membrane-bound antigens on the APCs initiates adhesion of B lymphocytes to the antigen-tethered surface, which is followed by the formation of radial lamellipodia-like structures, a process known as B cell spreading. The spreading response requires the rearrangement of the submembrane actin cytoskeleton and is regulated mainly via signals transmitted by the BCR. Here, we show that cytoplasmic calcium is a regulator of actin cytoskeleton dynamics in B lymphocytes. We find that BCR-induced calcium mobilization is indispensible for adhesion and spreading of B cells and that PLC␥ and CRAC-mediated calcium mobilization are critical regulators of these processes. Measuring calcium and actin dynamics in live cells, we found that a generation of actin-based membrane protrusion is strongly linked to the dynamics of a cytoplasmic-free calcium level. Finally, we demonstrate that PLC␥ and CRAC channels regulate the activity of actin-severing protein cofilin, linking BCR-induced calcium signaling to the actin dynamics. J. Leukoc. Biol. 93: 537-547; 2013.

Cell Communication and Signaling, 2009

Each B cell contains up to 100,000 B cell antigen receptor (BCR) complexes on its surface, which ... more Each B cell contains up to 100,000 B cell antigen receptor (BCR) complexes on its surface, which only become fully active on exposure of the B cell to its cognate antigen. Most studies on BCR function aims at a better understanding how the BCR becomes active and transmits its signal to the many signaling pathways inside the cell. Another, albeit related question, is how the B cells ensure that the many BCR complexes stay (in most cases) in a silent inert conformation. This problem of activation control the BCR shares with many of its signaling elements, be it kinases, phosphatases or adaptors, which all have to be regulated tightly in their localization and activity. For the later element autoinhibition plays an essential role in this regulation. In a biochemical study we previously have found that on resting B cells the BCR resides in oligomeric and monomeric forms. We now have conducted experiments that suggest that the BCR also can resume an autoinhibitory conformation and that BCR oligomerization plays an important role in this process. Specifically oligomerization of the BCR in conjunction with the kinase-phosphatase equilibrium at the BCR contributes to the tight control of BCR activation. Our studies resulted in a new model of the resting BCR and its activation.

International Immunology, 2010

Fcg receptors (FcgRs) play an essential role in the regulation of immune response due to their ab... more Fcg receptors (FcgRs) play an essential role in the regulation of immune response due to their ability to bind immune complexes. Activating FcgRs may facilitate antigen presentation and dendritic-cell maturation, while in the late phase of the immune response, the inhibitory FcgRIIb may down-regulate B-cell activation upon cross-linking with activating receptors. In this study, we investigated the in vivo role of FcgRs on the modulation of humoral immune response. In order to get well-defined immune complexes that can bind to both the activating and the inhibitory FcgRs, we designed a mono-biotinylated single-chain fragment variable construct from the rat anti-mouse CD16/32 clone 2.4G2, linked to avidin-FITC, and tested its effect on the FITC-hapten-specific T-independent type 2 (TI-2) and T-dependent (TD) immune response. When injected intravenously in mice, the complex bound to a small portion of B2201, CD11b high and CD11c high cells and was localized in the spleen on marginal zone macrophages 15 min after treatment. When applied as a booster following primary immunization with TI-2 (FITC-dextran) or TD (FITC-keyhole limpet haemocyanin) antigens, the complex elevated the number of hapten-specific IgM/IgG-producing B cells. This effect was diminished in CD16KO mice, suggesting that the activating-type FcgRIII might be a key mediator of this mechanism.

European Journal of Immunology, 2004

Receptors specific for the Fc part of IgG (Fc + R) are expressed by several cell types and play d... more Receptors specific for the Fc part of IgG (Fc + R) are expressed by several cell types and play diverse roles in immune responses. Impaired function of the activating and inhibitory Fc + R may result in autoimmunity. Thus, the modulation of IgG-Fc + R interaction can be a target for the development of treatments for some autoimmune and inflammatory diseases. This study addresses the localization and functional characterization of linear sequences in human IgG1 which bind to Fc + RII. Peptides with overlapping sequences derived from the CH2 domain of human IgG1 between P 234 and S 298 were synthesized and used in binding and functional experiments. Binding of the peptides to Fc + R was assayed in vitro and ex vivo, and peptides found to interact were functionally tested. The shortest effective peptide was T 256 -P 271 , which bound to soluble recombinant Fc + RIIb with K d =6×10 6 M -1 . The biotinylated peptides R 255 -P 271 and T 256 -P 271 complexed by avidin exhibited functional activity; they induced Fc + RIIb-mediated inhibition of the BCR-triggered Ca 2+ response of human Burkitt lymphoma cells, and inflammatory cytokine production (TNF- § and IL-6) by the human monocyte cell line MonoMac. In conclusion, our results suggest that the selected peptides functionally represent the Fc + RII-binding part of IgG1.

Cellular Signalling, 2009

B-cell fate during maturation and the germinal center reaction is regulated through the strength ... more B-cell fate during maturation and the germinal center reaction is regulated through the strength and the duration of the B-cell receptor signal. Signaling pathways discriminating between apoptosis and survival in B cells are keys in understanding adaptive immunity. Gab2 is a member of the Gab/Dos adaptor protein family. It has been shown in several model systems that Gab/Dos family members may regulate both the anti-apoptotic PI3-K/Akt and the mitogenic Ras/MAPK pathways, still their role in B-cells have not been investigated in detail. Here we studied the role of Gab2 in B-cell receptor mediated signaling. We have shown that BCR crosslinking induces the marked phosphorylation of Gab2 through both Lyn and Syk kinases. Subsequently Gab2 recruits p85 regulatory subunit of PI3-K, and SHP-2. Our results revealed that Ig-alpha/Igbeta, signal transducing unit of the B-cell receptor, may function as scaffold recruiting Gab2 to the signalosome. Overexpression of Gab2 in A20 cells demonstrated that Gab2 is a regulator of the PI3-K/Akt but not that of the Ras/MAPK pathway in B cells. Accordingly to the elevated Akt phosphorylation, overexpression of wild-type Gab2 in A20 cells suppressed Fas-mediated apoptosis, and enhanced BCR-mediated rescue from Fas-induced cell death. Although PH-domain has only a stabilizing effect on membrane recruitment of Gab2, it is indispensable in mediating its anti-apoptotic effect.

European Journal of Biochemistry, 2001

q FEBS 2001 Fcg receptor IIb induced dephosphorylation of Gab1 (Eur. J. Biochem. 268) 3899 q FEBS... more q FEBS 2001 Fcg receptor IIb induced dephosphorylation of Gab1 (Eur. J. Biochem. 268) 3899 q FEBS 2001 Fcg receptor IIb induced dephosphorylation of Gab1 (Eur. J. Biochem. 268) 3903 q FEBS 2001 Fcg receptor IIb induced dephosphorylation of Gab1 (Eur. J. Biochem. 268) 3905

Annals of the New York Academy of Sciences, 2006

RNA silencing experiments showed that knocking down Gab1 adaptor protein in BL41 human Burkitt ly... more RNA silencing experiments showed that knocking down Gab1 adaptor protein in BL41 human Burkitt lymphoma cells significantly reduced B cell receptor (BCR)-induced Erk phosphorylation, indicating that Gab1 plays a pivotal role in regulating Erk activity in B cells.

Immunology Letters, 2000

A recombinant soluble form of the human Fcg receptor was produced by engineering a cDNA construct... more A recombinant soluble form of the human Fcg receptor was produced by engineering a cDNA construct containing the extracellular part of the mature protein. After expression in bacteria as inclusion body, the polypeptide was highly purified and was refolded in vitro with a method that was developed for the renaturation of immunoglobulin fragments. With this method oxidation of the disulfide bridges within the domains of the protein is done in the presence of an artificial 'chaperone' which protects the polypeptide molecules from unwanted protein -protein interactions thereby inhibiting the incorrect oxidation of the SH-groups, and misfolding of the protein. The refolded recombinant soluble FcgRIIb showed several characteristics of the native receptor: (i) it was recognized by a series of monoclonal antibodies specific for, and in most cases produced against the native cell-surface receptor; (ii) it is bound to its ligand (the Fc-region of different immunoglobulins) under very diverse conditions; and (iii) it is competed strongly and specifically with the native cell surface receptor for both ligand and antibody binding in experiments with distinct read-outs; (iv) monoclonal antibodies produced against the recombinant protein specifically recognized FcgRIIb on different cells. From these data it was concluded that the recombinant soluble Fc-receptor was in a native, functionally active form, and its function was not affected by the lack of glycosylation.