Endoplasmic reticulum aminopeptidase 1 (ERAP1) plays a critical role in determining the length and sequence of peptides bound and presented by HLA-B27
Chen L., Fischer R., Peng Y., Reeves E., McHugh K., Ternette N., Hanke T., Dong T., Elliott T., Shastri N., Kollnberger S., James E., Kessler B., Bowness P.
Objective. HLA-B27 and ERAP1 are the two strongest predisposing genetic factors to Ankylosing Spondylitis (AS). A key aminopeptidase in MHC class I presentation, ERAP1 potentially contributes to AS pathogenesis through altering HLA-B27 peptide presentation. We studied the effects of ERAP1 on the HLA-B27 peptide repertoire and peptide presentation to Cytotoxic T lymphocytes (CTLs).Methods. ERAP1-silenced and -competent HeLa.B27/C1R.B27 cells were isotope labeled, mixed, lysed and then immuno-precipitated using W6/32 or ME1. Peptides bound to HLA-B27 were eluted and analyzed by tandem Mass Spectrometry. Selected peptides were synthesized and tested for HLA-B27 binding ability. The effect of ERAP1 silencing/mutation on presentation of an immunodominant viral HLA-B27 epitope, KK10, to CTL was also studied.Results. In both HeLa.B27 and C1R.B27 cells, the proportion of 9mer HLA-B27-bound peptides was decreased by ERAP1 silencing, whereas the percentage of longer peptides (11-13mers) increased. Surprisingly, following ERAP1 silencing, C-terminally extended peptides were readily identified. These were better able to bind to HLA-B27 than N-terminally extended peptides lacking a P2 Arginine. In both HeLa.B27 and mouse fibroblasts expressing HLA-B27, the absence of ERAP1 reduced recognition by HLA-B27-restricted KK10-specific CTLs following recombinant vaccinia viral infection or transfection with minigenes expressing KK10 precursors. Lastly, an AS protective variant, K528R-ERAP1, reduced KK10 CTL recognition following extended-KK10 minigene transfection compared to WT-ERAP1.Conclusion. Our study shows that ERAP1 directly alters peptide binding and presentation by HLA-B27, supporting a pathogenic mechanism in AS. ERAP1 inhibition could potentially be used for treatment of AS and other ERAP1-associated diseases. © 2013 American College of Rheumatology.