title: CD40 ligand binds to alpha5beta1 integrin and triggers cell signaling.
abstract: It was originally thought that the critical role of the CD40 ligand (CD40L) in normal and inflammatory immune responses was mainly mediated through its interaction with the classic receptor, CD40. However, data from CD40L(-/-) and CD40(-/-) mice suggest that the CD40L-induced inflammatory immune response involves at least one other receptor. This hypothesis is supported by the fact that CD40L stabilizes arterial thrombi through an alphaIIbbeta3-dependent mechanism. Here we provide evidence that soluble CD40L (sCD40L) binds to cells of the undifferentiated human monocytic U937 cell line in a CD40- and alphaIIbbeta3-independent manner. Binding of sCD40L to U937 cells was inhibited by anti-CD40L monoclonal antibody 5C8, anti-alpha5beta1 monoclonal antibody P1D6, and soluble alpha5beta1. The direct binding of sCD40L to purified alpha5beta1 was confirmed in a solid phase binding assay. Binding of sCD40L to alpha5beta1 was modulated by the form of alpha5beta1 expressed on the cell surface as the activation of alpha5beta1 by Mn(2+) or dithiothreitol resulted in the loss of sCD40L binding. Moreover, sCD40L induced the translocation of alpha5beta1 to the Triton X-100-insoluble fraction of U937 cells, the rapid activation of the MAPK pathways ERK1/2, and interleukin-8 gene expression. The binding of sCD40L to CD40 on BJAB cells, an alpha5beta1-negative B cell line, and the resulting activation of ERK1/2 was not inhibited by soluble alpha5beta1, suggesting that sCD40L can bind concomitantly to both receptors. These results document the existence of novel CD40L-dependent pathways of physiological relevance for cells expressing multiple receptors (CD40, alpha5beta1, and alphaIIbbeta3) for CD40L.
authors.affiliation: Centre de Recherche en Rhumatologie et Immunologie, Centre Hospitalier de l'Université Laval, Québec City, Quebec G1V 4G2, Canada.
authors.forename: Claire
authors.initials: C
authors.lastname: Léveillé
authors.forename: Marlène
authors.initials: M
authors.lastname: Bouillon
authors.forename: Wen
authors.initials: W
authors.lastname: Guo
authors.forename: Julie
authors.initials: J
authors.lastname: Bolduc
authors.forename: Ehssan
authors.initials: E
authors.lastname: Sharif-Askari
authors.forename: Youssef
authors.initials: Y
authors.lastname: El-Fakhry
authors.forename: Carlos
authors.initials: C
authors.lastname: Reyes-Moreno
authors.forename: Rejean
authors.initials: R
authors.lastname: Lapointe
authors.forename: Yahye
authors.initials: Y
authors.lastname: Merhi
authors.forename: John A
authors.initials: JA
authors.lastname: Wilkins
authors.forename: Walid
authors.initials: W
authors.lastname: Mourad
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D019013:CD40 Antigens / Q000172:deficiency / Q000276:immunology; D023201:CD40 Ligand / Q000276:immunology*; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D007249:Inflammation / Q000276:immunology; D039081:Integrin alpha5beta1 / Q000276:immunology*; D016209:Interleukin-8 / Q000276:immunology; D020935:MAP Kinase Signaling System / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000276:immunology; D048052:Mitogen-Activated Protein Kinase 3 / Q000276:immunology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology; D011485:Protein Binding / Q000276:immunology; D021381:Protein Transport / Q000276:immunology; D020298:U937 Cells
chemical_list: D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; C508606:CXCL8 protein, human; D039081:Integrin alpha5beta1; D016209:Interleukin-8; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D023201:CD40 Ligand; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3