Autoantibodies to BRAF, a new family of autoantibodies associated with rheumatoid arthritis.
BACKGROUND
BRAF (v raf murine sarcoma viral oncogene homologue B1) is a serine-threonine kinase involved in the mitogen-activated protein kinase (MAPK) signalling pathway, known to be implicated in the production of pro-inflammatory cytokines.We have observed that sera from rheumatoid arthritis (RA) patients recognize the BRAF's catalytic domain, which encompasses amino acids 416 to 766. Here, we identify peptide targets of anti-BRAF autoantibodies and test whether anti-BRAF autoantibodies may interfere with BRAF kinase activity.


METHODS
Anti-BRAF autoantibodies were detected by ELISA (enzyme-linked immunosorbent assay) in the serum of RA patients and controls, using 40 overlapping 20mer peptides encompassing the catalytic domain of BRAF as immunosorbents. To test whether autoantibodies to BRAF influence BRAF kinase activity, we developed an in vitro phosphorylation assay of MEK1 (mitogen extracellular regulated kinase), a major BRAF substrate. MEK1 phosphorylation by BRAF was tested in the presence of purified anti-BRAF autoantibodies from RA patients or control antibody.


RESULTS
We found that one BRAF peptide, P25 (656 to 675), is specifically recognized by autoantibodies from RA patients. Of interest, anti-P25 autoantibodies are detected in 21% of anti-CCP (cyclic citrullinated peptides) negative RA patients. Anti-BRAF autoantibodies activate the in vitro phosphorylation of MEK1 mediated by BRAF.


CONCLUSIONS
Anti-BRAF autoantibodies from RA patients preferentially recognize one BRAF peptide: P25. Autoantibody responses to P25 are detected in 21% of anti-CCP negative RA patients. Most anti-BRAF autoantibodies activate BRAF kinase activity.
Charpin
Caroline
C
INSERM UMR 639, Parc scientifique et technologique de Luminy, 163 avenue de Luminy, 13288 Marseille cedex 09, France. caroline.charpin@gmail.com
Martin
Marielle
M
Balandraud
Nathalie
N
Roudier
Jean
J
Auger
Isabelle
I
D000918:Antibody Specificity / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D001324:Autoantigens / Q000097:blood / Q000276:immunology*; D000090266:Chromobox Protein Homolog 5; D004789:Enzyme Activation / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D018985:Epitopes, B-Lymphocyte / Q000276:immunology; D006801:Humans; D010455:Peptides / Q000276:immunology; D048493:Proto-Oncogene Proteins B-raf / Q000097:blood / Q000276:immunology*
D001323:Autoantibodies; D001324:Autoantigens; C000715594:CBX5 protein, human; D018985:Epitopes, B-Lymphocyte; D010455:Peptides; D000090266:Chromobox Protein Homolog 5; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf