title: Two HLA-B27 alleles differently associated with spondylarthritis, B*2709 and B*2705, display similar intracellular trafficking and oligomer formation.
abstract: OBJECTIVE
  To examine whether and to what extent the intracellular trafficking features of HLA-B*2705, which is associated with the development of spondylarthritis (SpA), differ from those of HLA-B*2709 and HLA-B*0702, which are not associated with SpA.
  
  
  METHODS
  HeLa cells were transfected with complementary DNA encoding for HLA-B proteins fused to Renilla luciferase or yellow fluorescent protein. The subcellular distribution of properly folded and unfolded/misfolded HLA-B proteins was examined by flow cytometry and confocal microscopy of cells labeled with ME1 and HC-10 antibodies, respectively. HLA-B/HLA-B interactions were monitored in endoplasmic reticulum (ER)- and plasma membrane-enriched subcellular fractions, by bioluminescence resonance energy transfer (BRET).
  
  
  RESULTS
  All 3 HLA-B alleles displayed a similar distribution pattern (properly folded heavy chain at the cell surface, unfolded/misfolded proteins only in the cytoplasm). By means of BRET, we provided evidence that both HLA-B*2705 and HLA-B*2709 formed more oligomers in the ER and the plasma membrane than did HLA-B*0702. The propensity of HLA-B*2705 to form oligomers in the ER was partly attributable to residue Cys(67) of the molecule. For all 3 alleles, increased expression of HLA-B proteins was associated with intracytoplasmic accumulation of unfolded/misfolded proteins and intracellular vesicles, probably corresponding to expanded ER-Golgi intermediate compartments, in which these proteins accumulated together with the stress sensor BiP.
  
  
  CONCLUSIONS
  Our results suggest that the difference in disease susceptibility conferred by HLA-B*2705 and HLA-B*2709 cannot be explained by their different propensity to form dimers or misfolded proteins, thus presumably implicating other, still unknown factors.
authors.affiliation: Institut Cochin, Université Paris Descartes, CNRS UMR 8104, Paris, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Giquel
authors.forename: Sophie
authors.initials: S
authors.lastname: Carmouse
authors.forename: Céline
authors.initials: C
authors.lastname: Denais
authors.forename: Aïcha
authors.initials: A
authors.lastname: Cherfa
authors.forename: Maria-Sole
authors.initials: MS
authors.lastname: Chimenti
authors.forename: Ingrid
authors.initials: I
authors.lastname: Fert
authors.forename: Cécile
authors.initials: C
authors.lastname: Hacquard-Bouder
authors.forename: Maxime
authors.initials: M
authors.lastname: Breban
authors.forename: Claudine
authors.initials: C
authors.lastname: André
mesh_terms: D018076:DNA, Complementary / Q000235:genetics; D005434:Flow Cytometry; D015796:HLA-B27 Antigen / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D010957:Plasmids; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D025241:Spondylarthritis / Q000235:genetics* / Q000276:immunology; D014162:Transfection
chemical_list: D018076:DNA, Complementary; D015796:HLA-B27 Antigen; D011993:Recombinant Fusion Proteins