Soluble Tapasin Restores MHC Class I Expression and Function in the Tapasin-Negative Cell Line .220

Lehner, Paul J.; Surman, Michael; Cresswell, Peter

doi:10.1016/s1074-7613(00)80474-4

Cited by 271 publications

(359 citation statements)

References 48 publications

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“…Tapasin bridges the class I complex to the transporters associated with antigen processing (TAP) and plays a critical role in class I assembly, as in its absence cell surface MHC class I levels are decreased [3]. Tapasin also enhances TAP expression and increases peptide translocation [4]. Once loaded with appropriate peptide, the trimeric class I heavy chain/ g 2 m/peptide complex traverses the ER-Golgi apparatus, undergoes further glycosylation and is expressed on the cell surface.…”

Section: Introductionmentioning

confidence: 99%

Lymphoblastoid cells express HLA‐B27 homodimers both intracellularly and at the cell surface following endosomal recycling

et al. 2003

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The MHC class I allele HLA-B27 is very strongly associated with development of autoimmune spondyloarthritis, although the disease mechanism remains unknown. Class I molecules classically associate in the endoplasmic reticulum (ER) with g 2-microglobulin ( g 2 m) and antigenic peptides for cell surface expression and presentation to T cells. We have previously shown that HLA-B27 is capable of forming g 2 m-free disulfide-bonded homodimers in vitro. Here we show that HLA-B27 forms disulfide-bonded homodimers in vivo by two distinct pathways. HLA-B27 homodimers form in the ER but appear unable to egress to the cell surface in human cells. Cell surface HLA-B27 homodimers are abundantly expressed in a variety of lymphoid cell lines. Experiments with inhibitors indicate that HLA-B27 homodimers can arise from cell-surface heterodimers via an endosome-dependent recycling pathway. HLA-B27 homodimer expression on the cell surface of 721.220 is dependent on the unpaired cysteine 67 and is inhibited by restoration of tapasin function or by incubation with peptides that bind strongly to HLA-B27 heterodimers. Cell surface expressed HLA-B27 homodimers are likely to be immunologically reactive ligands for NK family immunoreceptors and, hence, could play a pathogenic role in spondyloarthritis.

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Section: Introductionmentioning

confidence: 99%

Lymphoblastoid cells express HLA‐B27 homodimers both intracellularly and at the cell surface following endosomal recycling

et al. 2003

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“…It functions to bridge peptide receptive class I loading complexes with the TAP (4,6) such that up to four loading complexes associate with each TAP heterodimer (7). Tapasin expression also enhances TAP expression, leading to increased peptide translocation into the ER (8,9). This suggests that tapasin increases overall peptide transport from the cytosol into the lumen of the ER, but it does not appear to affect the rate of peptide translocation (8).…”

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confidence: 99%

“…In addition, tapasin retains class I molecules that fail to bind peptide in the ER of insect cells (10) and may also be involved in the retention of peptide-bound class I molecules during a peptide optimization step in mammalian cells (11,12). Paradoxically, most class I molecules expressed in human cells lacking functional tapasin are retained in the ER and are inefficiently expressed at the cell surface (4,7,9,(13)(14)(15)(16). Introduction of functional tapasin into these cells restores normal class I expression and functional Ag presentation (7,9,(13)(14)(15)(16).…”

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confidence: 99%

Tapasin-Mediated Retention and Optimization of Peptide Ligands During the Assembly of Class I Molecules

Barnden

Purcell

Gorman³

et al. 2000

The Journal of Immunology

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The murine class I H-2Kb molecule achieves high level surface expression in tapasin-deficient 721.220 human cells. Compared with their behavior in wild-type cells, Kb molecules expressed on 721.220 cells are more receptive to exogenous peptide, undergo more rapid surface decay, and fail to form macromolecular peptide loading complexes. As a result, they are rapidly transported to the cell surface, reflecting a failure of endoplasmic reticulum retention mechanisms in the absence of loading complex formation. Despite the failure of Kb molecules to colocalize to the TAP and their rapid egress to the cell surface, Kb is still capable of presenting TAP-dependent peptides in the absence of tapasin. Furthermore, pool sequencing of peptides eluted from these molecules revealed strict conservation of their canonical H-2Kb-binding motif. There was a reduction in the total recovery of peptides associated with Kb molecules purified from the surface of tapasin-deficient cells. Comparison of the peptides bound to Kb in the presence and absence of tapasin revealed considerable overlap in peptide repertoire. These results indicate that in the absence of an interaction with tapasin, Kb molecules fail to assemble with calreticulin and TAP, yet they are still capable of acquiring a diverse array of peptides. However, a significant proportion of these peptides appear to be suboptimal, resulting in reduced cell surface stability of Kb complexes. Taken together, the findings indicate that tapasin plays an essential role in the formation of the class I loading complex, which retains class I heterodimers in the endoplasmic reticulum until optimal ligand selection is completed.

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“…However, this could reflect a lower affinity of interaction that does not survive detergent solubilization. Second, a mutant tapasin molecule lacking the transmembrane domain restored peptide loading of MHC class I molecules when expressed in a tapasin-negative cell line even though it failed to mediate the class I-TAP interaction (19). This soluble tapasin variant retained the ability to bind class I molecules but not TAP.…”

Section: The Mechanism Of Peptide Loadingmentioning

confidence: 97%

Intracellular Surveillance: Controlling the Assembly of MHC Class I‐Peptide Complexes

Cresswell

2000

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MHC class I molecules bind with high affinity to peptides in the endoplasmic reticulum and display them on the cell surface. Here they are screened by CD8-positive Tlymphocytes for the presence of foreign, pathogenderived peptides within the mass of self-peptides expressed. MHC class I assembly is a complicated process involving a number of accessory molecules, including specialized components as well as common chaperones. Our understanding of the mechanisms involved, while quite advanced, is far from complete.Key words: Calnexin, calreticulin, chaperone, ERp57, HLA, MHC, TAP, tapasin Received 13 December 1999, revised and accepted for publication 28 December 1999The expression of major histocompatibility complex (MHC) class I molecules on the surface of a cell is the end-point of a complicated process of assembly and transport which is initiated in the endoplasmic reticulum (ER). Class I molecules are effectively trimeric, consisting of a transmembrane glycoprotein, which is the product of the MHC-linked gene, a small protein called b 2 microglobulin (b 2 m), and a short peptide of 8 -10 amino acids. The peptide binds in a groove formed by two homologous polymorphic domains of the class I molecule. Binding is sequence-dependent and the specificity is mediated by interactions of the side chains of two or more amino acids of the peptide, the so-called anchor residues, with complementary 'pockets' in the binding groove. Additional binding energy is provided by interactions of the groove with the amino and carboxy-termini, and by hydrogen bonding interactions with the peptide backbone. In the absence of associated peptide, class I-b 2 m dimers are unstable in vitro and are not efficiently transported out of the ER in vivo.

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Soluble Tapasin Restores MHC Class I Expression and Function in the Tapasin-Negative Cell Line .220

Cited by 271 publications

References 48 publications

Lymphoblastoid cells express HLA‐B27 homodimers both intracellularly and at the cell surface following endosomal recycling

Lymphoblastoid cells express HLA‐B27 homodimers both intracellularly and at the cell surface following endosomal recycling

Tapasin-Mediated Retention and Optimization of Peptide Ligands During the Assembly of Class I Molecules

Intracellular Surveillance: Controlling the Assembly of MHC Class I‐Peptide Complexes

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