Two HLA-B27 alleles differently associated with spondylarthritis, B*2709 and B*2705, display similar intracellular trafficking and oligomer formation.
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.
Giquel
Benoit
B
Institut Cochin, Université Paris Descartes, CNRS UMR 8104, Paris, France.
Carmouse
Sophie
S
Denais
Céline
C
Cherfa
Aïcha
A
Chimenti
Maria-Sole
MS
Fert
Ingrid
I
Hacquard-Bouder
Cécile
C
Breban
Maxime
M
André
Claudine
C
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
D018076:DNA, Complementary; D015796:HLA-B27 Antigen; D011993:Recombinant Fusion Proteins