Regulation der B-Zellaktivierung durch Swiprosin-1/EFhd2
Zusammenfassung der Projektergebnisse
Establishment of the peripheral B cell repertoire and control of antigen-specific B cell activation are key to adaptive immunity. Signals elicited by the B cell receptor (BCR) play central roles in these processes. BCR signalling can lead to apoptosis or anergy of developing B cells. Signals from the BCR also control the selection of antigen-specific B cells in germinal centers (GC) during T cell-dependent immune responses. The function of the BCR involves numerous co-receptors and signalling adaptor proteins that remain to be fully characterized. We recently found that Swiprosin-1/EFhd2 (EFhd2), which is a Ca2+ binding adaptor protein, contributes to BCR-induced Ca2+ signalling and apoptosis in B cell lines. The first aim of this project was the generation of conditionally EFhd2 deficient mice. The second aim was to analyze B cell development and induced humoral immunity in EFhd2 deficient mice. It had been suggested moreover that EFhd2 is a cytoskeletal protein. The third aim of this project was therefore to analyze the mechanism of EFhd2-promoted apoptosis in B cells by taking into account cytoskeletal pathways. We were able to generate constitutively EFhd2-deficient mice and mice carrying a conditionally deletable efhd2 allele. Genetic inactivation of EFhd2 resulted in an accumulation of transitional, especially T3 B cells (AA4+CD23+IgMlow), which are suspected to represent self-reactive anergic B cells, in mixed bone marrow chimeras. In addition, EFhd2-/- mice displayed increased antibody responses after immunization with sheep red blood cells (IgG1, IgG2), or primary and secondary helminth infection, in this case with strongly increased serum IgM, IgG1, and IgE. These mutant mice additionally showed accelerated and enhanced GC responses after challenge with sheep red blood cells or helminths. This propensity to increased humoral immunity was also reflected by the fact that EFhd2-/- mice spontaneously developed anti-dsDNA IgG antibodies. In order to decipher how EFhd2 contributed to B cell responses we analyzed BCR induced signaling pathways and cytoskeletal changes. We observed altered BCR induced cell spreading, BCR trafficking and lysosomal structures in EFhd2-deficient B cells. BCR induced Ca2+ signaling was unaltered but EFhd2 appeared to control dephosphorylation of the F-Actin severing factor Codillin. Finally, we identified and confirmed several cytoskeletal interaction partners of EFhd2 in B cells. In summary, we showed that EFhd2 limits humoral immunity and we provide evidence that EFhd2 is involved in cytoskeletal pathways in B cells.
Projektbezogene Publikationen (Auswahl)
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(2010). Antibodies to the endoplasmic reticulum-resident chaperones calnexin, BiP and Grp94 in patients with rheumatoid arthritis. Rheumatology 49 (12):2255-63
Weber, C.K., Haslbeck, M., Englbrecht, M., Sehnert, B., Mielenz, D., Graef, D., Distler, J., Burkhardt, H., Schett, G., Voll, R.E. and Fürnrohr, B.G.
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(2010). Comment on: Antibodies to the endoplasmic reticulum-resident chaperones calnexin, BiP and Grp94 in patients with rheumatoid arthritis and systemic lupus erythematosus: reply. Rheumatology, 2010 Dec 21
Weber, C.K., Mielenz, D., Voll, R.E., Fürnrohr, B.G.
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(2010). Swiprosin-1/EFhd2 controls B cell receptor signaling through the assembly of the B cell receptor, Syk, and phospholipase C gamma2 in membrane rafts. J Immunol 184, 3665-3676
Kroczek, C., Lang, C., Brachs, S., Grohmann, M., Dütting, S., Schweizer, A., Nitschke, L., Feller, S. M., Jäck, H. M., and Mielenz, D.
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(2010). The early marginal zone B cell initiated T-independent type 2 response resists the proteasome inhibitor bortezomib. J. Immunol. 185 (9):5637-47
Lang, V.R., Mielenz, D., Neubert, K., Böhm, C., Schett, G., Jäck, H.M., Voll, R.E., Meister, S.
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(2011). Fraternal twins: Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1, two homologous EF-hand containing calcium binding adaptor proteins with distinct functions. Cell Commun Signal 9, 2
Dütting, S., Brachs, S., and Mielenz, D.
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(2012). The B cell receptor-induced calcium flux involves a calcium mediated positive feedback loop. Cell Calcium 51, 411-417
Hagen, S., Brachs, S., Kroczek, C., Fürnrohr, B. G., Lang, C., and Mielenz, D.
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(2013). Monoclonal antibodies to discriminate the EF hand containing calcium binding adaptor proteins EFhd1 and EFhd2. Monoclon Antib Immunodiagn Immunother 32, 237-245
Brachs, S., Lang, C., Buslei, R., Purohit, P., Fürnrohr, B., Kalbacher, H., Jäck, H. M., and Mielenz, D.
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(2014). Inhibition of bone remodeling in young mice by bisphosphonate displaces the plasma cell niche into the spleen. J Immunol 193, 223-233
Teufel, S., Grotsch, B., Luther, J., Derer, A., Schinke, T., Amling, M., Schett, G., Mielenz, D.*, and David, J. P.
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(2014). Swiprosin-1/EFhd2 limits the germinal center reaction and humoral type 2 immunity. European Journal of Immunology
Brachs, S., Turqeti-Neves, A., Lang, C., Brachvogel, B., Bösl, M., Winkler, T., Voehringer, D., Jäck, H.M., Mielenz, D.
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(2014). The AP-1 transcription factor Fra1 inhibits follicular B cell differentiation into plasma cells. The Journal of Experimental Medicine, pii: jem.20130795
Grötsch, B., Brachs, S., Lang, C., Luther, J., Derer, A., Schlötzer-Schrehardt, U., Bozec, A., Fillatreau, S., Berberich, I., Hobeika, E., Reth, M., Wagner, E.F., Schett, G., Mielenz, D., David, J.P.
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(2014). The Ca2+ sensor protein Swiprosin-1/EFhd2 is present in neurites and involved in kinesin-mediated axonal transport in neurons. PLOSOne
Purohit, P., Perez-Branguli, F., Prots, I., Borger, E., Gunn-Moore, F., Welzel, O., Loy, K., Wenzel, E.M., Grömer, T.W., Brachs, S., Holzer, M., Buslei, R., Fritsch, K., Regensburger, M., Böhm, K.J., Winner, B., Mielenz, D.
