Background Recent studies have shown that genetic variation within ERAP1, encoding endoplasmic reticulum aminopeptidase 1, is strongly associated with ankylosing spondylitis (AS)1. Within the endoplasmic reticulum, ERAP1 is involved in the trimming of peptides to the optimal length for their presentation by major histocompatibility complex (MHC) class 1 proteins 2, such as HLA-B27 that is also associated with AS 3.
Objectives Compare the enzyme activity of wildtype and mutant ERAP1 in vitro, and study the effect of ERAP1 silencing on peptide processing and epitopes presentation by HLA-B27.
Methods 1)The N-terminal-extended HLA-B27 Chlamydia epitope (13-mer, QITANRELIQQEL) was incubated with WT and mutant ERAP1s in time course experiments at 37° (Up to 6h). The digestion products were analysed using Q-TOF mass analyzer. 2)ERAP1-shRNA lentivirus were produced to stably silence the expression of ERAP1 on LCL.721.221.B27 cells. Then these cells were infected with recombinant HIV-gag vaccinia and co-cultured with HIV-gag B27 epitope specific cytotoxic T lymphocyte (CTLs). IFN-gamma ELISpot were used to measure the number of CTLs activated.
Results 1)A protective ERAP1 mutant, K528R-ERAP1, was found to trim elongated B27 epitopes slower than WT-ERAP1 and stopped at 11mer. 2)ERAP1-silenced 221.B27 cells are less effective at generating and presenting HIV-gag B27 epitope to CTLs.
Conclusions The functional interaction of ERAP1 and HLA-B27 is likely very important in AS pathogenesis. My data suggest that ERAP1 may contribute to AS predisposition through aberrant peptide processing for presentation by HLA-B27.
Evans DM et al. Interaction between ERAP1 and HLA-B27 in ankylosing spondylitis implicates peptide handling in the mechanism for HLA-B27 in disease susceptibility. Nat Genet. 2011 Jul 10;43(8):761-7.
York IA, Chang SC, Saric T, Keys JA, Favreau JM, Goldberg AL, Rock KL. The ER aminopeptidase ERAP1 enhances or limits antigen presentation by trimming epitopes to 8-9 residues. Nat Immunol, 2002. 3(12): p. 1177-84.
Brewerton DA, Hart FD, Nicholls A, Caffrey M, James DC, Sturrock RD. Ankylosing spondylitis and HL-A 27. Lancet, 1973. 1: p. 904-907.
Disclosure of Interest None Declared