title: No evidence that soluble TACI induces signalling via membrane-expressed BAFF and APRIL in myeloid cells.
abstract: Myeloid cells express the TNF family ligands BAFF/BLyS and APRIL, which exert their effects on B cells at different stages of differentiation via the receptors BAFFR, TACI (Transmembrane Activator and CAML-Interactor) and/or BCMA (B Cell Maturation Antigen). BAFF and APRIL are proteins expressed at the cell membrane, with both extracellular and intracellular domains. Therefore, receptor/ligand engagement may also result in signals in ligand-expressing cells via so-called "reverse signalling". In order to understand how TACI-Fc (atacicept) technically may mediate immune stimulation instead of suppression, we investigated its potential to activate reverse signalling through BAFF and APRIL. BAFFR-Fc and TACI-Fc, but not Fn14-Fc, reproducibly stimulated the ERK and other signalling pathways in bone marrow-derived mouse macrophages. However, these effects were independent of BAFF or APRIL since the same activation profile was observed with BAFF- or APRIL-deficient cells. Instead, cell activation correlated with the presence of high molecular mass forms of BAFFR-Fc and TACI-Fc and was strongly impaired in macrophages deficient for Fc receptor gamma chain. Moreover, a TACI-Fc defective for Fc receptor binding elicited no detectable signal. Although these results do not formally rule out the existence of BAFF or APRIL reverse signalling (via pathways not tested in this study), they provide no evidence in support of reverse signalling and point to the importance of using appropriate specificity controls when working with Fc receptor-expressing myeloid cells.
authors.affiliation: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors.forename: Josquin
authors.initials: J
authors.lastname: Nys
authors.forename: Cristian R
authors.initials: CR
authors.lastname: Smulski
authors.forename: Aubry
authors.initials: A
authors.lastname: Tardivel
authors.forename: Laure
authors.initials: L
authors.lastname: Willen
authors.forename: Christine
authors.initials: C
authors.lastname: Kowalczyk
authors.forename: Olivier
authors.initials: O
authors.lastname: Donzé
authors.forename: Bertrand
authors.initials: B
authors.lastname: Huard
authors.forename: Henry
authors.initials: H
authors.lastname: Hess
authors.forename: Pascal
authors.initials: P
authors.lastname: Schneider
mesh_terms: D000818:Animals; D053264:B-Cell Activating Factor / Q000378:metabolism*; D053265:B-Cell Activation Factor Receptor / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002850:Chromatography, Gel; D057809:HEK293 Cells; D006801:Humans; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D022423:Myeloid Cells / Q000166:cytology* / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D012995:Solubility; D000074050:TWEAK Receptor; D053303:Transmembrane Activator and CAML Interactor Protein / Q000378:metabolism*; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13 / Q000378:metabolism*
chemical_list: D053264:B-Cell Activating Factor; D053265:B-Cell Activation Factor Receptor; D011961:Receptors, Fc; D018124:Receptors, Tumor Necrosis Factor; D011993:Recombinant Fusion Proteins; C000613297:TNFRSF12A protein, human; D000074050:TWEAK Receptor; C000613299:Tnfrsf12a protein, mouse; D053303:Transmembrane Activator and CAML Interactor Protein; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13; C524618:TACI receptor-IgG Fc fragment fusion protein