HLA-B27 up-regulation causes accumulation of misfolded heavy chains and correlates with the magnitude of the unfolded protein response in transgenic rats: Implications for the pathogenesis of spondylarthritis-like disease.
OBJECTIVE
HLA-B27 is implicated in the pathogenesis of spondylarthritis (SpA), yet the molecular mechanisms are incompletely defined. HLA-B27 misfolding has been associated with endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in macrophages from HLA-B27/human beta(2)-microglobulin-transgenic (B27-transgenic) rats. This study was performed to assess the mechanisms that drive activation of the HLA-B27-induced UPR and to determine whether splenocytes respond in a similar manner.


METHODS
Splenocytes were isolated and bone marrow macrophages were derived from B27-transgenic and wild-type rats. Cells were treated for up to 24 hours with cytokines that induce class I major histocompatibility complex expression. HLA-B27 expression and misfolding were assessed by real-time reverse transcription-polymerase chain reaction, flow cytometry, and immunoblotting. Activation of the UPR was measured by quantifying UPR target gene expression and X-box binding protein 1 messenger RNA (mRNA) splicing.


RESULTS
HLA-B27 mRNA up-regulation was accompanied by a dramatic increase in the accumulation of misfolded heavy chains and preceded robust activation of the UPR in macrophages. When macrophages were treated with various cytokines, the magnitude of the UPR correlated strongly with the degree of HLA-B27 up-regulation. In contrast, B27-transgenic splenocytes exhibited only low-level differences in the expression of UPR target genes after exposure to interferon-gamma or concanavalin A, which resulted in minimal HLA-B27 up-regulation.


CONCLUSIONS
These results suggest that HLA-B27-associated activation of the UPR in macrophages is attributable to the accumulation of misfolded heavy chains, and that certain cell types may be more susceptible to the effects of HLA-B27 misfolding. Strategies that eliminate HLA-B27 up-regulation and/or the accumulation of misfolded heavy chains may be useful in evaluating the role of these events in the pathogenesis of SpA.
Turner
Matthew J
MJ
Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA.
Delay
Monica L
ML
Bai
Shuzhen
S
Klenk
Erin
E
Colbert
Robert A
RA
D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002460:Cell Line; D003208:Concanavalin A / Q000494:pharmacology; D004268:DNA-Binding Proteins; D015796:HLA-B27 Antigen / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D018832:Molecular Chaperones / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D030781:Organisms, Genetically Modified; D017510:Protein Folding; D012326:RNA Splicing; D051381:Rats; D000071701:Regulatory Factor X Transcription Factors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013167:Spondylitis, Ankylosing / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D015854:Up-Regulation
D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D015796:HLA-B27 Antigen; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D003208:Concanavalin A; D007371:Interferon-gamma