title: K-RAS GTPase- and B-RAF kinase-mediated T-cell tolerance defects in rheumatoid arthritis.
abstract: Autoantibodies to common autoantigens and neoantigens, such as IgG Fc and citrullinated peptides, are immunological hallmarks of rheumatoid arthritis (RA). We examined whether a failure in maintaining tolerance is mediated by defects in T-cell receptor activation threshold settings. RA T cells responded to stimulation with significantly higher ERK phosphorylation (P < 0.001). Gene expression arrays of ERK pathway members suggested a higher expression of KRAS and BRAF, which was confirmed by quantitative PCR (P = 0.003), Western blot, and flow cytometry (P < 0.01). Partial silencing of KRAS and BRAF lowered activation-induced phosphorylated ERK levels (P < 0.01). In individual cells, levels of these signaling molecules correlated with ERK phosphorylation, attesting that their concentrations are functionally important. In confocal studies, B-RAF/K-RAS clustering was increased in RA T cells 2 min after T-cell receptor stimulation (P < 0.001). Overexpression of B-RAF and K-RAS in normal CD4 T cells amplified polyclonal T-cell proliferation and facilitated responses to citrullinated peptides. We propose that increased expression of B-RAF and K-RAS lowers T-cell activation thresholds in RA T cells, enabling responses to autoantigens.
authors.affiliation: Lowance Center for Human Immunology and Rheumatology, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Karnail
authors.initials: K
authors.lastname: Singh
authors.forename: Pratima
authors.initials: P
authors.lastname: Deshpande
authors.forename: Guangjin
authors.initials: G
authors.lastname: Li
authors.forename: Mingcan
authors.initials: M
authors.lastname: Yu
authors.forename: Sergey
authors.initials: S
authors.lastname: Pryshchep
authors.forename: Mary
authors.initials: M
authors.lastname: Cavanagh
authors.forename: Cornelia M
authors.initials: CM
authors.lastname: Weyand
authors.forename: Jörg J
authors.initials: JJ
authors.lastname: Goronzy
mesh_terms: D001172:Arthritis, Rheumatoid / Q000276:immunology*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D011905:Genes, ras; D006801:Humans; D007108:Immune Tolerance; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism*; D016176:T-Lymphocyte Subsets; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D048493:Proto-Oncogene Proteins B-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D020558:GTP Phosphohydrolases