title: Brief Report: Functional Interaction of Endoplasmic Reticulum Aminopeptidase 2 and HLA-B27 Activates the Unfolded Protein Response.
abstract: The basic mechanisms underlying the pathogenesis of ankylosing spondylitis (AS) remain unresolved. We previously reported an association of the single-nucleotide polymorphism (SNP) rs2549782 in the endoplasmic reticulum aminopeptidase 2 gene (ERAP2) with AS. It is known that patients homozygous for the G allele (GG) of another ERAP2 SNP, rs2248374, lack expression of ERAP2 (ERAP2 null). The present study utilized this information to study the impact of ERAP2 deficiency on HLA-B27 expression in patients with AS, specifically focusing on the functional interaction of ERAP2 and HLA-B27 in peripheral blood mononuclear cells (PBMCs) from patients with AS and assessing the effects in vitro in specific cell lines.
  
  
  
  Expression of intact peptide HLA-B27 (pB27) or the major histocompatibility complex class I free heavy chains (FHCs) was assessed in PBMCs isolated from HLA-B27-positive patients with AS. ERAP2-suppressed, stable B27-expressing C1R cells (C1R-B27) were tested for the expression levels of pB27 and FHCs, as well as for markers of the unfolded protein response (UPR). Distribution of the ERAP2 SNPs rs2549782 and rs2248374 in patients with AS and in patients with Crohn's disease was assessed.
  
  
  
  PBMCs from AS patients lacking ERAP2 expressed higher levels of FHCs than did PBMCs from patients positive for ERAP2. This finding was replicated in C1R-B27 cells after suppression of ERAP2. In addition, ERAP2 suppression led to increased levels of the UPR markers BiP, CCAAT/enhancer binding protein homologous protein 10, and X-box binding protein 1 [spliced] as compared to that in short hairpin RNA-treated control cells. There was strong linkage disequilibrium in the ERAP2 locus. All patients with the rs2549782 T allele (which reportedly increases the function of the ERAP-2 protein) were homozygous for the G allele of rs2248374, leading to absence of ERAP2.
  
  
  
  ERAP2 deficiency causes increased FHC expression and up-regulation of the UPR pathway.
authors.affiliation: Toronto Western Research Institute, Toronto, Ontario, Canada.
authors.forename: Zhenbo
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Università degli Studi di Palermo, Palermo, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Ciccia
authors.affiliation: Toronto Western Research Institute, Toronto, Ontario, Canada.
authors.forename: Fanxing
authors.initials: F
authors.lastname: Zeng
authors.affiliation: Università degli Studi di Palermo, Palermo, Italy.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Guggino
authors.affiliation: Toronto Western Research Institute, Toronto, Ontario, Canada, and McMaster University, Hamilton, Ontario, Canada.
authors.forename: Kirby
authors.initials: K
authors.lastname: Yee
authors.affiliation: Toronto Western Research Institute and University of Toronto, Toronto, Ontario, Canada.
authors.forename: Hasan
authors.initials: H
authors.lastname: Abdullah
authors.affiliation: University of Toronto and Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Silverberg
authors.affiliation: Università degli Studi di Palermo, Palermo, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Alessandro
authors.affiliation: Università degli Studi di Palermo, Palermo, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Triolo
authors.affiliation: Toronto Western Research Institute, University of Toronto, and University Health Network, Toronto, Ontario, Canada.
authors.forename: Nigil
authors.initials: N
authors.lastname: Haroon
mesh_terms: D000328:Adult; D000483:Alleles; D000626:Aminopeptidases / Q000235:genetics* / Q000276:immunology; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D002460:Cell Line; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D005434:Flow Cytometry; D015796:HLA-B27 Antigen / Q000276:immunology*; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013167:Spondylitis, Ankylosing / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D056811:Unfolded Protein Response / Q000276:immunology*; D015854:Up-Regulation; D000071717:X-Box Binding Protein 1 / Q000378:metabolism
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D015796:HLA-B27 Antigen; D006360:Heat-Shock Proteins; D034741:RNA, Small Interfering; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D000626:Aminopeptidases; C503944:ERAP2 protein, human