RESUMEN

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease distinguished by synovial hyperplasia and a progressive destruction of joints. T cells are critical players in the pathogenesis of RA. We have previously identified a novel immune checkpoint molecule, TAPBPL, that inhibits T cell functions in vitro. As a model for human RA, we investigated the ability of the TAPBPL protein to ameliorate collagen type II (CII)-induced arthritis (CIA) in mice that were injected with recombinant TAPBPL or a control protein. The mice were analyzed for CIA development, immune cells, and their responses. We found that TAPBPL protein significantly decreased CIA incidence and reduced clinical and pathological arthritis scores, which were related to a lower number of activated CD4 T cells but a greater number of regulatory T cells (Tregs) in the spleen, and a reduction of Th1/Th17 inflammatory cytokines in the joints and serum. Importantly, TAPBPL protein inhibited CII-specific T cell growth and Th1 and Th17 cytokine expression and reduced the production of CII autoantibodies in the serum. Our results suggest that TAPBPL protein can ameliorate CIA in mice and has the potential to be used in the treatment of patients with RA.

Asunto(s)

Artritis Experimental , Artritis Reumatoide , Humanos , Animales , Ratones , Artritis Experimental/tratamiento farmacológico , Artritis Reumatoide/tratamiento farmacológico , Autoanticuerpos , Citocinas , Hiperplasia , Inmunoglobulinas , Proteínas de la Membrana

RESUMEN

Glycosylation plays a crucial role in the folding, structure, quality control and trafficking of glycoproteins. Here, we explored whether the glycosylation status of MHC class I (MHC-I) molecules impacts their affinity for the peptide editor, TAPBPR. We demonstrate that the interaction between TAPBPR and MHC-I is stronger when MHC-I lacks a glycan. Subsequently, TAPBPR can dissociate peptides, even those of high affinity, more easily from non-glycosylated MHC-I compared to their glycosylated counterparts. In addition, TAPBPR is more resistant to peptide-mediated allosteric release from non-glycosylated MHC-I compared to species with a glycan attached. Consequently, we find the glycosylation status of HLA-A*68:02, -A*02:01 and -B*27:05 influences their ability to undergo TAPBPR-mediated peptide exchange. The discovery that the glycan attached to MHC-I significantly influences the affinity of their interactions with TAPBPR has important implications, on both an experimental level and in a biological context.

Asunto(s)

Antígenos de Histocompatibilidad Clase I/metabolismo , Inmunoglobulinas/metabolismo , Proteínas de la Membrana/metabolismo , Presentación de Antígeno/fisiología , Glicosilación , Células HeLa , Humanos

RESUMEN

T cell stimulatory and inhibitory molecules are critical for the regulation of immune responses. In this study, we identify a novel T cell co-inhibitory molecule TAPBPL, whose amino acid sequence shares homology with known B7 family members. TAPBPL protein is expressed on resting and activated T cells, B cells, monocytes, and dendritic cells (DCs), as well as on some tumor tissues. The putative TAPBPL receptor is expressed on activated CD4 and CD8 T cells. A soluble recombinant human TAPBPL-IgG Fc (hTAPBPL-Ig) fusion protein inhibits the proliferation, activation, and cytokine production of both mouse and human T cells in vitro. In vivo administration of hTAPBPL-Ig protein attenuates experimental autoimmune encephalomyelitis (EAE) in mice. Furthermore, an anti-TAPBPL monoclonal antibody neutralizes the inhibitory activity of hTAPBPL-Ig on T cells, enhances antitumor immunity, and inhibits tumor growth in animal models. Our results suggest that therapeutic intervention of the TAPBPL inhibitory pathway may represent a new strategy to modulate T cell-mediated immunity for the treatment of cancer, infections, autoimmune diseases, and transplant rejection.

Asunto(s)

Linfocitos T CD8-positivos , Encefalomielitis Autoinmune Experimental , Secuencia de Aminoácidos , Animales , Linfocitos B , Activación de Linfocitos , Ratones , Monocitos

RESUMEN

Understanding how peptide selection is controlled on different major histocompatibility complex class I (MHC I) molecules is pivotal for determining how variations in these proteins influence our predisposition to infectious diseases, cancer, and autoinflammatory conditions. Although the intracellular chaperone TAPBPR edits MHC I peptides, it is unclear which allotypes are subjected to TAPBPR-mediated peptide editing. Here, we examine the ability of 97 different human leukocyte antigen (HLA) class I allotypes to interact with TAPBPR. We reveal a striking preference of TAPBPR for HLA-A, particularly for supertypes A2 and A24, over HLA-B and -C molecules. We demonstrate that the increased propensity of these HLA-A molecules to undergo TAPBPR-mediated peptide editing is determined by molecular features of the HLA-A F pocket, specifically residues H114 and Y116. This work reveals that specific polymorphisms in MHC I strongly influence their susceptibility to chaperone-mediated peptide editing, which may play a significant role in disease predisposition.

Asunto(s)

Antígenos HLA-A/química , Antígenos HLA-A/metabolismo , Antígenos de Histocompatibilidad Clase I/química , Antígenos de Histocompatibilidad Clase I/metabolismo , Inmunoglobulinas/metabolismo , Proteínas de la Membrana/metabolismo , Presentación de Antígeno , Células HEK293 , Antígeno HLA-A2/química , Antígeno HLA-A2/metabolismo , Antígeno HLA-A24/química , Antígeno HLA-A24/metabolismo , Antígenos HLA-B/genética , Antígenos HLA-B/metabolismo , Antígenos HLA-C/metabolismo , Células HeLa , Antígenos de Histocompatibilidad Clase I/genética , Humanos , Alotipos de Inmunoglobulinas , Inmunoglobulinas/genética , Proteínas de la Membrana/genética , Proteínas de Transporte de Membrana/genética , Proteínas de Transporte de Membrana/metabolismo , Chaperonas Moleculares/química , Chaperonas Moleculares/metabolismo , Péptidos/química , Péptidos/metabolismo , Polimorfismo Genético , Unión Proteica , Dominios Proteicos/genética

RESUMEN

We recently discovered that TAPBPR promotes reglucosylation of the N-linked glycan on MHC class I molecules, a modification that restores their recognition by calreticulin and reincorporation into the peptide-loading complex. We wondered whether TAPBPR displayed some degree of glycan specificity, as is known to be the case for tapasin via its interaction with calreticulin & ERp57, or whether its interaction with MHC class I was glycan independent. Here, we explored this by comparing the ability of TAPBPR to bind to MHC class I containing either an intact or disrupted NxS/T glycosylation consensus sequence. In contrast to tapasin, TAPBPR bound strongly to MHC class I molecules that lacked N-linked glycosylation, suggesting that the TAPBPR:MHC class I interaction is glycan independent. Furthermore, we found that glycosylated HLA-A2 preferentially interacts with tapasin rather than TAPBPR, possibly explaining, in part, why MHC class I molecules bind efficiently to tapasin in the face of an alternative chaperone. The distinction in glycan specificity between the two peptide editors suggests that TAPBPR may bind to MHC class I molecules that are associated with a broader diversity of oligosaccharides attached compared with tapasin. This may explain, to some extent, the ability of TAPBPR to interact with MHC class I molecules outside of the ER.

Asunto(s)

Genes MHC Clase I/fisiología , Antígenos de Histocompatibilidad Clase I/metabolismo , Inmunoglobulinas/metabolismo , Proteínas de la Membrana/metabolismo , Calreticulina/metabolismo , Línea Celular Tumoral , Retículo Endoplásmico/metabolismo , Glicosilación , Células HeLa , Humanos , Proteínas de Transporte de Membrana/metabolismo , Péptidos/metabolismo , Proteína Disulfuro Isomerasas/metabolismo

RESUMEN

Tapasin and TAPBPR are known to perform peptide editing on major histocompatibility complex class I (MHC I) molecules; however, the precise molecular mechanism(s) involved in this process remain largely enigmatic. Here, using immunopeptidomics in combination with novel cell-based assays that assess TAPBPR-mediated peptide exchange, we reveal a critical role for the K22-D35 loop of TAPBPR in mediating peptide exchange on MHC I. We identify a specific leucine within this loop that enables TAPBPR to facilitate peptide dissociation from MHC I. Moreover, we delineate the molecular features of the MHC I F pocket required for TAPBPR to promote peptide dissociation in a loop-dependent manner. These data reveal that chaperone-mediated peptide editing on MHC I can occur by different mechanisms dependent on the C-terminal residue that the MHC I accommodates in its F pocket and provide novel insights that may inform the therapeutic potential of TAPBPR manipulation to increase tumour immunogenicity.

Asunto(s)

Antígenos de Histocompatibilidad Clase I/inmunología , Inmunoglobulinas/inmunología , Proteínas de la Membrana/inmunología , Simulación del Acoplamiento Molecular , Péptidos/inmunología , Secuencia de Aminoácidos , Presentación de Antígeno/inmunología , Sitios de Unión/genética , Antígenos HLA-A/química , Antígenos HLA-A/inmunología , Antígenos HLA-A/metabolismo , Células HeLa , Antígenos de Histocompatibilidad Clase I/química , Antígenos de Histocompatibilidad Clase I/metabolismo , Humanos , Inmunoglobulinas/química , Inmunoglobulinas/metabolismo , Leucina/química , Leucina/inmunología , Leucina/metabolismo , Proteínas de la Membrana/química , Proteínas de la Membrana/metabolismo , Mutación , Péptidos/metabolismo , Unión Proteica , Dominios Proteicos

RESUMEN

The repertoire of peptides displayed at the cell surface by MHC I molecules is shaped by two intracellular peptide editors, tapasin and TAPBPR. While cell-free assays have proven extremely useful in identifying the function of both of these proteins, here we explored whether a more physiological system could be developed to assess TAPBPR-mediated peptide editing on MHC I. We reveal that membrane-associated TAPBPR targeted to the plasma membrane retains its ability to function as a peptide editor and efficiently catalyzes peptide exchange on surface-expressed MHC I molecules. Additionally, we show that soluble TAPBPR, consisting of the luminal domain alone, added to intact cells, also functions as an effective peptide editor on surface MHC I molecules. Thus, we have established two systems in which TAPBPR-mediated peptide exchange on MHC class I can be interrogated. Furthermore, we could use both plasma membrane-targeted and exogenous soluble TAPBPR to display immunogenic peptides on surface MHC I molecules and consequently induce T cell receptor engagement, IFN-γ secretion, and T cell-mediated killing of target cells. Thus, we have developed an efficient way to by-pass the natural antigen presentation pathway of cells and load immunogenic peptides of choice onto cells. Our findings highlight a potential therapeutic use for TAPBPR in increasing the immunogenicity of tumors in the future.

Asunto(s)

Presentación de Antígeno , Antígenos de Histocompatibilidad Clase I/inmunología , Inmunoglobulinas/inmunología , Proteínas de la Membrana/inmunología , Péptidos/inmunología , Animales , Células HeLa , Antígenos de Histocompatibilidad Clase I/genética , Humanos , Inmunidad Celular , Inmunoglobulinas/genética , Interferón gamma/genética , Interferón gamma/inmunología , Células MCF-7 , Proteínas de la Membrana/genética , Ratones , Ratones Noqueados , Péptidos/genética , Receptores de Antígenos de Linfocitos T/genética , Receptores de Antígenos de Linfocitos T/inmunología , Linfocitos T/inmunología

RESUMEN

Recently, we revealed that TAPBPR is a peptide exchange catalyst that is important for optimal peptide selection by MHC class I molecules. Here, we asked whether any other co-factors associate with TAPBPR, which would explain its effect on peptide selection. We identify an interaction between TAPBPR and UDP-glucose:glycoprotein glucosyltransferase 1 (UGT1), a folding sensor in the calnexin/calreticulin quality control cycle that is known to regenerate the Glc1Man9GlcNAc2 moiety on glycoproteins. Our results suggest the formation of a multimeric complex, dependent on a conserved cysteine at position 94 in TAPBPR, in which TAPBPR promotes the association of UGT1 with peptide-receptive MHC class I molecules. We reveal that the interaction between TAPBPR and UGT1 facilities the reglucosylation of the glycan on MHC class I molecules, promoting their recognition by calreticulin. Our results suggest that in addition to being a peptide editor, TAPBPR improves peptide optimisation by promoting peptide-receptive MHC class I molecules to associate with the peptide-loading complex.

Asunto(s)

Presentación de Antígeno , Glucosiltransferasas/metabolismo , Antígenos de Histocompatibilidad Clase I/metabolismo , Inmunoglobulinas/metabolismo , Proteínas de la Membrana/metabolismo , Línea Celular , Humanos , Mapeo de Interacción de Proteínas , Multimerización de Proteína

RESUMEN

In order to provide specificity for T cell responses against pathogens and tumours, major histocompatibility complex (MHC) class I molecules present high-affinity peptides at the cell surface to T cells. A key player for peptide loading is the MHC class I-dedicated chaperone tapasin. Recently we discovered a second MHC class I-dedicated chaperone, the tapasin-related protein TAPBPR. Here, we review the major steps in the MHC class I pathway and the TAPBPR data. We discuss the potential function of TAPBPR in the MHC class I pathway and the involvement of this previously uncharacterised protein in human health and disease.

Asunto(s)

Células Presentadoras de Antígenos/inmunología , Antígenos de Histocompatibilidad Clase I/inmunología , Inmunoglobulinas/inmunología , Proteínas de la Membrana/inmunología , Proteínas de Transporte de Membrana/inmunología , Secuencia de Aminoácidos , Presentación de Antígeno , Células Presentadoras de Antígenos/citología , Membrana Celular/química , Membrana Celular/inmunología , Retículo Endoplásmico/inmunología , Retículo Endoplásmico/metabolismo , Expresión Génica , Antígenos de Histocompatibilidad Clase I/genética , Humanos , Inmunoglobulinas/genética , Proteínas de la Membrana/genética , Proteínas de Transporte de Membrana/genética , Modelos Moleculares , Datos de Secuencia Molecular , Péptidos/química , Péptidos/genética , Péptidos/inmunología , Transporte de Proteínas , Transducción de Señal

RESUMEN

The tapasin-related protein TAPBPR is a novel component of the antigen processing and presentation pathway, which binds to MHC class I coupled with ß2-microglobulin. We describe six alternatively spliced TAPBPR transcripts from the TAPBPL gene and investigate three of these at a protein level. TAPBPR transcripts lacking exon 5 result in loss of the membrane proximal IgC domain and loss of ability to bind to MHC class I. Alternative acceptor and donor splice sites in exon 4 of TAPBPR altered the reading frame in the IgV domain and produced a truncated TAPBPR product. An additional exon in the TAPBPL gene was identified that encodes extra residues in the cytoplasmic tail of TAPBPR. This longer TAPBPR protein interacted with MHC class I but was attenuated in its ability to down-regulate surface expression of MHC class I. The abundance of these alternative transcripts in peripheral blood mononuclear cells and dendritic cells suggests an important role of TAPBPR isoforms in vivo.

Asunto(s)

Antígenos de Histocompatibilidad Clase I/inmunología , Inmunoglobulinas/inmunología , Proteínas de la Membrana/inmunología , Células Dendríticas/citología , Células Dendríticas/inmunología , Células HeLa , Humanos , Inmunoglobulinas/genética , Proteínas de la Membrana/genética , Isoformas de Proteínas/genética , Isoformas de Proteínas/inmunología