Formation of HLA-B27 Homodimers and Their Relationship to Assembly Kinetics

Antoniou, Antony N.; Ford, Stuart; Taurog, Joel D.; Butcher, Geoffrey W.; Powis, Simon J.

doi:10.1074/jbc.m311757200

Cited by 99 publications

(159 citation statements)

References 67 publications

(72 reference statements)

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“…Use of HC-10 Abs, which recognize misfolded and/or partially folded HLA class I molecules, revealed that the pool of HC-10-reactive molecules staying in the ER during the course of the chase period for both WT and mutant HLA-B27 molecules was similar, even though the loss of HC-10-reactive material observed in HLA-B7-transfected cell did not take place. The relatively slow assembly kinetics of HLA-B27 molecules is in accordance with previous reports (25)(26)(27), and the differences in the signal levels for class I H chains brought down by ME1 and HC-10 Abs are the result of the much lower immunoprecipitation capacity of the ME1 Ab. Finally, cell surface thermostability studies demonstrated that both WT and mutant HLA-B27 molecules reach the cell surface and are stably folded (Fig.…”

Section: Lack Of Tyr 320 Does Not Influence Steady State Levels Of Hlsupporting

confidence: 92%

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Santos

Antoniou

Sampaio³

et al. 2006

The Journal of Immunology

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Several lines of evidence suggest that endocytosis of MHC class I molecules requires conserved motifs within the cytoplasmic domain. In this study, we show, in the C58 rat thymoma cell line transfected with HLA-B27 molecules, that replacement of the highly conserved tyrosine (Tyr320) in the cytoplasmic domain of HLA-B27 does not hamper cell surface expression of β2-microglobulin H chain heterodimers or formation of misfolded molecules. However, Tyr320 replacement markedly impairs spontaneous endocytosis of HLA-B27. Although wild-type molecules are mostly internalized via endosomal compartments, Tyr320-mutated molecules remain at the plasma membrane in which partial colocalization with endogenous transferrin receptors can be observed, also impairing their endocytosis. Finally, we show that Tyr320 substitution enhances release of cleaved forms of HLA-B27 from the cell surface. These studies show for the first time that Tyr320 is most likely part of a cytoplasmic sorting motif involved in spontaneous endocytosis and shedding of MHC class I molecules.

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Section: Lack Of Tyr 320 Does Not Influence Steady State Levels Of Hlsupporting

confidence: 92%

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Santos

Antoniou

Sampaio³

et al. 2006

The Journal of Immunology

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“…The S67 mutant behaved similarly to the Cys 67 - containing natural subtypes in these experiments, indicating that the Cys 67 residue, which has been implicated in the formation of B27 heavy chain homodimers in vitro (40), in the ER (12,41), and at the surface of tapasindeficient 721.220 cells (3), did not significantly affect the percentage of irreversible forms of ␤ 2 m-free heavy chains on the surface of C1R cells. Lack of correlation between surface stability of B27 subtypes on TAP-deficient cells and an association with AS.…”

Section: Resultsmentioning

confidence: 70%

Similar cell surface expression of β₂‐microglobulin–free heavy chains by HLA–B27 subtypes differentially associated with ankylosing spondylitis

Vázquez

Castro

2005

Arthritis & Rheumatism

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Objective. To determine whether the cell surface features of HLA-B27 subtypes reported to be differentially associated with ankylosing spondylitis (AS) differ in a way that correlates with disease susceptibility.Methods. Human cell transfectants expressing or lacking the transporter associated with antigen processing were used to determine the cell surface expression of B27 subtypes by flow cytometry with antibodies recognizing the B27 heterodimer or ␤ 2 -microglobulin (␤ 2 m)-free heavy chains.Results. In lymphoid cells with an intact peptideloading complex, all B27 subtypes, irrespective of their association with disease, showed similar ratios of free heavy chain to heterodimer, suggesting similar surface stability. A substantial decrease in dissociated heavy chains, which never reached 100%, was observed upon addition of a B27 ligand, with no significant differences among subtypes. This is compatible with similar surface expression of irreversible ␤ 2 m-free heavy chain forms among subtypes differentially associated with disease. In cells lacking the transporter associated with antigen processing, both disease-associated and non-diseaseassociated subtypes expressed a population of heterodimers at 26°C that was less stable than the population expressed at 37°C. In the presence of exogenous peptide, the expression of heterodimers increased, without a concomitant decrease in ␤ 2 m-free heavy chains. This suggests that in these cells, and for all subtypes tested, most of the dissociated heavy chains at the cell surface are in irreversible forms. At 37°C, the expression of ␤ 2 m-free B27 heavy chains was very low on T2 transfectant cells. Conclusion. HLA-B27 subtypes showing differential associations with AS are similar in their extent of ␤ 2 m dissociation and surface expression of free heavy chains.Class I major histocompatibility complex (MHC) proteins are heterodimers consisting of a polymorphic heavy chain that is noncovalently bound to ␤ 2 -microglobulin (␤ 2 m), a nonpolymorphic polypeptide. Assembly of MHC molecules takes place in the endoplasmic reticulum (ER), where they constitutively bind peptides. These arise mainly from proteasomal degradation in the cytosol, are transported into the lumen of the ER by means of the transporter associated with antigen processing (TAP), and bind, sometimes after trimming, to the class I molecule in a process involving several proteins collectively known as the peptide-loading complex (1). Peptides bound with sufficient affinity stabilize the native conformation of the nascent class I molecule. When this happens, the peptide-MHC complex is released from the ER and traffics to the cell surface. In cells lacking TAP, the peptide supply into the ER and the expression of class I MHC are drastically reduced. However, at 26°C, MHC molecules that are presumably devoid of peptide can be sufficiently stable to leave the ER and reach the cell surface (2).The ␤ 2 m-free class I MHC polypeptides are found at the cell surface. This can be revealed, for example, by cell surface stain...

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“…HLA-B27 is an MHC-encoded class I protein that is linked to the development of spondyloarthritis (SpA) including ankylosing spondylitis [22,23], and when expressed in rats along with human b 2 m (HLA-B27-Tg) results in the development of an inflammatory disease that recapitulates many features of human SpA [24]. A proportion of HLA-B27 misfolds in the ER, resulting in increased degradation by ERAD [25], and formation of disulfide-linked and BiP-bound complexes [26][27][28]. Up-regulation of HLA-B27 exacerbates misfolding and activates the UPR in macrophages from Tg rats [29,30].…”

mentioning

confidence: 99%

Endoplasmic reticulum stress and the unfolded protein response are linked to synergistic IFN‐β induction via X‐box binding protein 1

et al. 2008

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Type I IFN are strongly induced upon engagement of certain pattern recognition receptors by microbial products, and play key roles in regulating innate and adaptive immunity. It has become apparent that the endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR), in addition to restoring ER homeostasis, also influences the expression of certain inflammatory cytokines. However, the extent to which UPR signaling regulates type I IFN remains unclear. Here we show that cells undergoing a UPR respond to TLR4 and TLR3 ligands, and intracellular dsRNA, with log-fold greater IFN-b induction. This synergy is not dependent on autocrine type I IFN signaling, but unexpectedly requires the UPR transcription factor X-box binding protein 1 (XBP-1). Synergistic IFN-b induction also occurs in HLA-B27/human b 2 m-transgenic rat macrophages exhibiting a UPR as a consequence of HLA-B27 up-regulation, where it correlates with activation of XBP-1 splicing. Together these findings indicate that the cellular response to endogenous 'danger' that disrupts ER homeostasis is coupled to IFN-b induction by XBP-1, which has implications for the immune response and the pathogenesis of diseases involving the UPR.Key words: HLA-B27 Á Interferons Á Protein misfolding Á Unfolded protein response IntroductionInitially identified as antiviral cytokines, type I IFN (IFN-a/b) are now recognized to have diverse immunoregulatory effects activating macrophages and NK cells, promoting T cell survival and dendritic cell (DC) maturation, and increasing the production of Th1-polarizing cytokines to mediate innate and adaptive immune responses [1]. Type I IFN also exert biological effects at low and even constitutive levels of expression [2]. For example, weak IFN-b-mediated signaling augments IFN-a/b induction in response to LPS through positive feedback involving autocrine/ paracrine up-regulation of IFN regulatory factor (IRF)7. In addition, low levels of IFN-a/b prime cells to respond to IFN-c and IL-6 by providing a phosphorylated type I IFN receptor 'niche' for commonly used signaling molecules in proximity to other cytokine receptor complexes [3,4]. Mice deficient in IFN-b are more susceptible to viral infection, have lower numbers of macrophages and mature B cells, and exhibit reduced bone mass [5], as IFN-b is a positive regulator of bone formation through inhibition of osteoclast differentiation [6]. Thus, even constitutive levels of this cytokine are important in osteo-immune homeostasis.IFN-b is produced by most cell types upon viral infection, and in large amounts by macrophages and DC, following engagement of pattern recognition receptors (PRR) by conserved molecular structures referred to as pathogen-associated molecular patterns [7, 8]. PRR that mediate IFN-b induction include cell surface TLR4 and endosomal TLR3 for LPS and dsRNA, respectively [9]. In both instances increased IFN-b gene transcription occurs via TLR/IL-1R domain-containing adapter inducing IFN-b (TRIF)-dependent IRF3 and NF-jB activation. PRR in the retinoic ...

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Formation of HLA-B27 Homodimers and Their Relationship to Assembly Kinetics

Cited by 99 publications

References 67 publications

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Similar cell surface expression of β₂‐microglobulin–free heavy chains by HLA–B27 subtypes differentially associated with ankylosing spondylitis

Endoplasmic reticulum stress and the unfolded protein response are linked to synergistic IFN‐β induction via X‐box binding protein 1

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Formation of HLA-B27 Homodimers and Their Relationship to Assembly Kinetics

Cited by 99 publications

References 67 publications

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Lack of Tyrosine 320 Impairs Spontaneous Endocytosis and Enhances Release of HLA-B27 Molecules

Similar cell surface expression of β2‐microglobulin–free heavy chains by HLA–B27 subtypes differentially associated with ankylosing spondylitis

Endoplasmic reticulum stress and the unfolded protein response are linked to synergistic IFN‐β induction via X‐box binding protein 1

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Similar cell surface expression of β₂‐microglobulin–free heavy chains by HLA–B27 subtypes differentially associated with ankylosing spondylitis