title: TWEAK inhibits TRAF2-mediated CD40 signaling by destabilization of CD40 signaling complexes.
abstract: We found recently that TNF-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor-inducible-14 (Fn14) by virtue of their strong capability to reduce the freely available cytoplasmic pool of TNFR-associated factor (TRAF)2 and cellular inhibitors of apoptosis (cIAPs) antagonize the functions of these molecules in TNFR1 signaling, resulting in sensitization for apoptosis and inhibition of classical NF-κB signaling. In this study, we demonstrate that priming of cells with TWEAK also interferes with activation of the classical NF-κB pathway by CD40. Likewise, there was strong inhibition of CD40 ligand (CD40L)-induced activation of MAPKs in TWEAK-primed cells. FACS analysis and CD40L binding studies revealed unchanged CD40 expression and normal CD40L-CD40 interaction in TWEAK-primed cells. CD40L immunoprecipitates, however, showed severely reduced amounts of CD40 and CD40-associated proteins, indicating impaired formation or reduced stability of CD40L-CD40 signaling complexes. The previously described inhibitory effect of TWEAK on TNFR1 signaling has been traced back to reduced activity of the TNFR1-associated TRAF2-cIAP1/2 ubiquitinase complex and did not affect the stability of the immunoprecipitable TNFR1 receptor complex. Thus, the inhibitory effect of TWEAK on CD40 signaling must be based at least partly on other mechanisms. In line with this, signaling by the CD40-related TRAF2-interacting receptor TNFR2 was also attenuated but still immunoprecipitable in TWEAK-primed cells. Collectively, we show that Fn14 activation by soluble TWEAK impairs CD40L-CD40 signaling complex formation and inhibits CD40 signaling and thus identify the Fn14-TWEAK system as a potential novel regulator of CD40-related cellular functions.
authors.affiliation: Division of Molecular Internal Medicine, Department of Internal Medicine II, University Hospital Würzburg, 97070 Würzburg, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Salzmann
authors.forename: Isabell
authors.initials: I
authors.lastname: Lang
authors.forename: Alevtina
authors.initials: A
authors.lastname: Rosenthal
authors.forename: Viktoria
authors.initials: V
authors.lastname: Schäfer
authors.forename: Daniela
authors.initials: D
authors.lastname: Weisenberger
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Carmona Arana
authors.forename: Johannes
authors.initials: J
authors.lastname: Trebing
authors.forename: Daniela
authors.initials: D
authors.lastname: Siegmund
authors.forename: Manfred
authors.initials: M
authors.lastname: Neumann
authors.forename: Harald
authors.initials: H
authors.lastname: Wajant
mesh_terms: D015153:Blotting, Western; D019013:CD40 Antigens / Q000276:immunology / Q000378:metabolism*; D023201:CD40 Ligand / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D000074049:Cytokine TWEAK; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D018613:Microscopy, Confocal; D018124:Receptors, Tumor Necrosis Factor / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D047992:TNF Receptor-Associated Factor 2 / Q000276:immunology / Q000378:metabolism*; D000074050:TWEAK Receptor; D048069:Tumor Necrosis Factors / Q000276:immunology / Q000378:metabolism*
chemical_list: D019013:CD40 Antigens; D000074049:Cytokine TWEAK; D018124:Receptors, Tumor Necrosis Factor; D047992:TNF Receptor-Associated Factor 2; C000613297:TNFRSF12A protein, human; C109743:TNFSF12 protein, human; D000074050:TWEAK Receptor; D048069:Tumor Necrosis Factors; D023201:CD40 Ligand