The proteoglycan (heparan sulfate proteoglycan) binding domain of APRIL serves as a platform for ligand multimerization and cross-linking.
A proliferation-inducing ligand (APRIL) (also known as TALL-2 and TRDL-1) is a member of the tumor necrosis factor (TNF) superfamily that has tumorigenic properties but is also important for the induction of humoral immune responses. APRIL binds two TNF receptors: transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and B-cell maturation antigen (BCMA) as well as heparan sulfate proteoglycans (HSPGs). The aim of this study was to clarify the role of the HSPG interaction in canonical APRIL signaling, because it has been proposed to act as a docking site and also to play a role in direct signaling. In this study, we generated point mutants of soluble APRIL that lack either the capacity to bind HSPGs or TACI and BCMA and then tested the function of these mutants in mouse B-cell assays. In contrast to previous reports, we found that APRIL alone is sufficient to costimulate B-cell proliferation and drive IgA production and does not require artificial antibody cross-linking. We found no evidence that APRIL requires signaling through HSPGs but, notably, were able to show that binding of APRIL to HSPGs is crucial for mediating natural APRIL cross-linking to allow for optimal activation of murine B cells.
Kimberley
Fiona C
FC
Laboratory of Experimental Oncology and Radiobiology, Center for Experimental Molecular Medicine, University of Amsterdam, Amsterdam, The Netherlands.
van Bostelen
Liesbeth
L
Cameron
Katherine
K
Hardenberg
Gijs
G
Marquart
J Arnoud
JA
Hahne
Michael
M
Medema
Jan Paul
JP
D000818:Animals; D053301:B-Cell Maturation Antigen / Q000378:metabolism; D001402:B-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000378:metabolism; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism*; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis; D051917:Leukosialin / Q000276:immunology; D008024:Ligands; D051379:Mice; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D053303:Transmembrane Activator and CAML Interactor Protein / Q000502:physiology; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13 / Q000235:genetics* / Q000378:metabolism
D053301:B-Cell Maturation Antigen; D003432:Cross-Linking Reagents; D019812:Heparan Sulfate Proteoglycans; D007070:Immunoglobulin A; D051917:Leukosialin; D008024:Ligands; C108467:TNFRSF13B protein, human; C114631:TNFSF13 protein, human; D053303:Transmembrane Activator and CAML Interactor Protein; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13