title: Requirement of the extracellular cysteine at position six for CD40/CD40 dimer formation and CD40-induced IL-8 expression.
abstract: We recently showed that oligomerization of CD40 molecules on cell surface leads to disulfide-linked CD40/CD40 dimer formation, an event that is necessary for CD40-induced B7-2 expression in human B cells. Here, we demonstrate that CD40/CD40 dimers formation also occurs in different cell types such as T24 bladder cancer cells and CD40-transfected HEK 293 cells. Disulfide bonds mediate the formation of CD40/CD40 homodimers in CD40-activated cells. To determine the potential residue(s) involved in disulfide bonds formation and subsequent CD40-induced IL-8 expression, we generated a CD40 mutant in which the extracellular cysteine 6 was replaced by a glutamine (CD40-C6Q). CD40-induced IL-8 mRNA expression and protein synthesis were studied in stably transfected HEK 293 cells that were sorted out along with similar levels of expression of wild type (CD40-WT) and CD40-C6Q molecules. In contrast to cells expressing CD40-WT protein, disulfide-linked CD40/CD40 dimer formation was completely abolished in HEK 293 cells expressing CD40-C6Q proteins. Abolishment of disulfide-linked CD40/CD40 dimers in these transfected cells was sufficient to inhibit CD40-induced mRNA expression and secretion of IL-8. This study identifies the extracellular cysteine 6 of CD40 molecules as a potential molecular target to disrupt the expression of CD40-induced pro-inflammatory cytokines by epithelial cells.
authors.affiliation: Centre de Recherche en Rhumatologie et Immunologie (CRRI), Centre Hospitalier de l'Université Laval, 2705 boulevard Laurier, T1-49, Quebec City, Que., Canada G1V 4G2.
authors.forename: Julie
authors.initials: J
authors.lastname: Girouard
authors.forename: Carlos
authors.initials: C
authors.lastname: Reyes-Moreno
authors.forename: André
authors.initials: A
authors.lastname: Darveau
authors.forename: Ali
authors.initials: A
authors.lastname: Akoum
authors.forename: Walid
authors.initials: W
authors.lastname: Mourad
mesh_terms: D001402:B-Lymphocytes / Q000378:metabolism; D019013:CD40 Antigens / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D005786:Gene Expression Regulation; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D016297:Mutagenesis, Site-Directed; D012333:RNA, Messenger / Q000096:biosynthesis; D014162:Transfection
chemical_list: D019013:CD40 Antigens; D016209:Interleukin-8; D012333:RNA, Messenger; D003545:Cysteine