K-RAS GTPase- and B-RAF kinase-mediated T-cell tolerance defects in rheumatoid arthritis

• Authors: Karnail Singh, Emory University; Pratima Deshpande, Stanford University; Guangjin Li, Stanford University; Mingcan Yu, Stanford University; Sergey Pryshchep, Emory University; Mary Cavanagh, Stanford University; Cornelia M. Weyand, Stanford University; Jörg J. Goronzy, Stanford University
• Journal Title: Proceedings of the National Academy of Sciences
• Volume: Volume 109, Number 25
• Publisher: National Academy of Sciences | 2012-06-19, Pages E1629-E1637
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1073/pnas.1117640109
• Subjects: Health Sciences, Immunology; Health Sciences, Medicine and Surgery

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.