Papers by Gabriella Sarmay
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.
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.
Biochimica et Biophysica Acta (BBA) - General Subjects, 2003
Activated B cells may cleave their surface receptors due to the proteolytic activity on the cell ... more Activated B cells may cleave their surface receptors due to the proteolytic activity on the cell membrane or in its vicinity. We attempted to isolate and characterize the protease(s) responsible for this cleavage. Zymograms prepared from the supernatant and the plasma membrane fraction of activated human B cells and BL41/95 cell line exhibited a 85 -90 kDa doublet band with protease activity, while that of resting B cells did not. Soybean trypsin inhibitor (STI), Na-p-tosyl-L-lysine chloromethyl ketone (TLCK) and EDTA treatment abolished the activity of this protease. The excess of Zn 2 + ions in EDTA did not restore the enzymatic activity, while it was completely recovered in the presence of Ca 2 + . We affinity-purified a 85 -90 kDa protease from the supernatant of BL41/95 cells using STI coupled to Sepharose 4B beads, and measured its kinetic parameters. For the arginyl substrate K M was 358 F 59 AM and for the lysyl substrate 582 F 103 AM. TLCK and benzamidine inhibited the protease at micromolar, while STI at nanomolar concentrations. Both the inhibition profile and the substrate specificity suggest that it is a trypsin-like serine protease. We assume that the 85 -90 kDa serine protease expressed on and secreted by activated B cells and BL41/95 cell line is responsible for the cleavage of various membrane proteins, including Fcg receptors; thus it may play a crucial role in regulating B cell's function. D
Immunology Letters, 2008
The survival of the mature resting B cells depends on signaling from B cell receptor (BCR), and a... more The survival of the mature resting B cells depends on signaling from B cell receptor (BCR), and a plethora of positive and negative regulators, that maintain cellular homeostasis and ultimately determine cell's fate, i.e., survival or programmed death (apoptosis). Among these regulators we have investigated the B cell activating factor belonging to tumor necrosis factor family (BAFF) and the prototypic death receptor Fas/CD95 mediated signals. We have shown that BAFF inhibits Fas-mediated cell death, however, the BCR-driven survival signals were not strengthened by BAFF. Therefore, we propose that BAFF may function independently of the antigen specificity of BCR, thus may enhance the risk of autoimmune diseases by promoting the survival of bystander B cells in the germinal center.
Immunology Today, 1992
occupied by its separate ligand does not affect proliferation. Therefore, this signal might drive... more occupied by its separate ligand does not affect proliferation. Therefore, this signal might drive B cells to an alternative differentiation pathway: the formation of memory B cells 12-14.
Proceedings of the 16th …, 1985
Fc receptors (FcR) are immunoglobulin- binding molecules that enable antibodies to perform severa... more Fc receptors (FcR) are immunoglobulin- binding molecules that enable antibodies to perform several biological functions by forming a link between specific antigen recognition and effector cells. FcRs are involved in regulating antibody production as well. Most FcRs belong to the immunoglobulin superfamily, and show structural homology with each other and with their ligands. Recent data on the structure of IgG
Advances in Cancer Research, 1994
Immunology, 1979
The association between Fc receptors and other surface molecules was examined by EArosette (EAR) ... more The association between Fc receptors and other surface molecules was examined by EArosette (EAR) inhibition experiments. Twenty to 30% EAR were detected in suspensions of peripheral blood lymphocytes from normal individuals. Anti-fl2 microglobulin (flMi) sera fully suppressed EAR whereas anti-Ig, anti-Ia sera and heat aggregated IgG inhibited only 50-60% EAR. Thus almost half of the detected EAR were apparently not surface Ig positive B cells. Rabbit and monkey anti-flMi sera suppressed EAR effectively whereas rat and chicken antisera, despite strong flMi binding capacity, inhibited EAR poorly. The latter result was ascribed on the basis of immunofluorescent analysis to inadequate capping of .JMi. Incubation of PBL with whole antisera suppressed EAR to a similar degree at either 00 or 370, whereas F(ab')2 fragments were inhibitory only at 37°. Taken together the results suggest that Fc receptors can be inhibited by antibodies with specificity against any cell surface antigen. The blocking mechanism may be due to steric hindrance by the Fc part of antibody molecules and/or F(ab')2 fragment mediated co-capping.
European journal of immunology, 1999
Co-clustering of the type II receptors binding the Fc part of IgG (FcgammaRIIb) and B cell recept... more Co-clustering of the type II receptors binding the Fc part of IgG (FcgammaRIIb) and B cell receptors results in the translocation of cytosolic, negative regulatory molecules to the phosphorylated immunoreceptor tyrosine-based inhibitory motif (P-ITIM) of the FcgammaRIIb. SH2 domain-containing protein tyrosine phosphatases (SHP-1 and SHP-2), and the polyphosphoinositol 5'-phosphatase (SHIP) have been reported earlier to bind to murine FcgammaRIIb P-ITIM. However, neither the functional substrates of these enzymes, nor the mechanism of the inhibition are fully resolved. We show here that the human FcgammaRIIb binds SHP-2 when co-clustered with the B cell receptors, whereas its synthetic P-ITIM peptide bindes SHP-2 and SHIP in lysates of the Burkitt's lymphoma cell line BL41. The P-ITIM peptide binding enhances SHP-2 activity, resulting in dephosphorylation and release of P-ITIM-bound SHIP and Shc. Moreover, P-ITIM-bound SHP-2 dephosphorylates synthetic peptides corresponding t...
Immunology letters, 1997
Co-clustering of Fc gamma RIIb and B-cell receptor (BCR) inhibits cell activation by interrupting... more Co-clustering of Fc gamma RIIb and B-cell receptor (BCR) inhibits cell activation by interrupting BCR stimulated signal transduction. The immunoreceptor tyrosine-based inhibitory motif (ITIM) of Fc gamma RIIb becomes tyrosyl phosphorylated (P-ITIM) upon co-clustering with BCR then P-ITIM interacts with several signalling molecules, some of which negatively regulate the cell activation process. The molecules recruited by the P-ITIM of human Fc gamma RIIb have not been characterised yet. In order to affinity isolate the potential functional partner molecules of human Fc gamma RIIb, synthetic peptides were designed to cover almost the entire intracellular Fc gamma RIIb domain, including Fc gamma RIIb2 specific sequences and stretches containing the phosphorylated and non-phosphorylated ITIM. We report here that several tyrosyl phosphorylated proteins bind to the P-ITIM peptide from both resting and activated B-cell lysates, the 53-56 kDa being the most prominent one. A fraction of the ...
Cellular immunology, 1983
The effect of anti-beta 2-microglobulin (anti-B2Mi) on the expression of Fc receptors (FcR) of hu... more The effect of anti-beta 2-microglobulin (anti-B2Mi) on the expression of Fc receptors (FcR) of human lymphocytes was compared on resting and activated cells. Previously we reported that anti-B2Mi induces a "co-shedding" of FcR with the beta 2-microglobulin (B2Mi)-anti-B2Mi complexes when used under the conditions where the redistribution of membrane molecules is allowed (Sármay et al., Cell. Immunol. 56, 452, 1980; Sármay et al. Immunology 36, 339, 1979). Furthermore our group also described two types of FcR-bearing cells, one which shed their FcR during a temperature shift from 4 to 37 degrees C (FcRI+ cells) and the other which has an immobile type FcR under the same circumstances (FcRI+ cells) (Sándor et al., Immunology 38, 553, 1979; Sármay et al., Immunology 34, 315, 1978). In this work we have characterized the FcR released from the membrane as a consequence of anti-B2Mi treatment. We have found that they are the mobile, FcRI type. It was proved that the shedding of ...
European Journal of Cancer Supplements, 2003
Proceedings of the National Academy of Sciences, 1994
Stimulation of B cells by clustering their surface immunoglobulins (sIg) leads to enhanced phosph... more Stimulation of B cells by clustering their surface immunoglobulins (sIg) leads to enhanced phosphorylation of several cellular proteins on Ser and Tyr residues. The type II Fc gamma receptor (Fc gamma RII) is one of those proteins that undergo Ser phosphorylation. Upon affinity isolation of the Fc gamma RII, several molecular entities are coisolated from Triton X-100 lysates of BL41 Burkitt lymphoma line which undergo "in vitro" (cell free) phosphorylation in the immune complex-associated kinase assay. Furthermore, several molecules phosphorylated on Tyr upon sIgM cross-linking in the intact cells are coisolated with Fc gamma RII. The 59-kDa coprecipitated component is identified as the protein-tyrosine kinase (PTK) fyn. Clustering the sIgM molecules enhanced the in vitro phosphorylation of all molecules coprecipitated with Fc gamma RII as well as that of the exogenously added PTK substrate, enolase. Kinase renaturation assays suggest that at least two major renaturable protein kinases (59 kDa and 85-90 kDa) associate with Fc gamma RII. Whereas the 59-kDa component comigrates with the PTK fyn, the 85- to 90-kDa one is an unidentified Ser/Thr kinase. These data suggest that Fc gamma RII exists in the B-cell membrane as part of a multimolecular complex including protein kinases, activities of which are regulated by clustering of the antigen receptors.
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Papers by Gabriella Sarmay