title: A natural tapasin isoform lacking exon 3 modifies peptide loading complex function.
abstract: To assure efficient MHC class I (MHC-I) peptide loading, the peptide loading complex (PLC) recruits the peptide-receptive form of MHC-I, and in this process, tapasin (tpn) connects MHC-I with the peptide transporter TAP and forms a stable disulfide bond with ERp57. Here, we describe an alternatively spliced tpn transcript lacking exon 3, observed in cells infected with human cytomegalovirus. Recognition of exon 3 was regulated via G-runs, suggesting that members of the hnRNP (heterogeneous nuclear ribonucleoprotein)-family regulate expression of the ΔExon3 variant of tpn. Exon 3 includes Cys-95, which is responsible for the disulfide bond formation with ERp57 and, consequently, interaction of the ΔExon3 variant with ERp57 was strongly impaired. Although the ΔExon3 variant specifically stabilized TAP expression but not MHC-I in tpn-deficient cells, in tpn-proficient cells, the ΔExon3 tpn reduced cell surface expression of the tpn-dependent HLA-B*44:02 allele; the stability of the tpn-independent HLA-B*44:05 was not affected. Most importantly, detailed analysis of the PLC revealed a simultaneous binding of the ΔExon3 variant and tpn to TAP, suggesting modification of PLC functions. Indeed, an altered MHC-I ligandome was observed in HeLa cells overexpressing the ΔExon3 variant, highlighting the potential of the alternatively spliced tpn variant to impact CD8(+) T-cell responses.
authors.affiliation: Institute for Virology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors.forename: Nele
authors.initials: N
authors.lastname: Beutler
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hauka
authors.forename: Alexandra
authors.initials: A
authors.lastname: Niepel
authors.forename: Daniel Johannes
authors.initials: DJ
authors.lastname: Kowalewski
authors.forename: Julia
authors.initials: J
authors.lastname: Uhlmann
authors.forename: Esther
authors.initials: E
authors.lastname: Ghanem
authors.forename: Steffen
authors.initials: S
authors.lastname: Erkelenz
authors.forename: Constanze
authors.initials: C
authors.lastname: Wiek
authors.forename: Helmut
authors.initials: H
authors.lastname: Hanenberg
authors.forename: Heiner
authors.initials: H
authors.lastname: Schaal
authors.forename: Stefan
authors.initials: S
authors.lastname: Stevanović
authors.forename: Sebastian
authors.initials: S
authors.lastname: Springer
authors.forename: Frank
authors.initials: F
authors.lastname: Momburg
authors.forename: Hartmut
authors.initials: H
authors.lastname: Hengel
authors.forename: Anne
authors.initials: A
authors.lastname: Halenius
mesh_terms: D017398:Alternative Splicing; D017951:Antigen Presentation / Q000235:genetics; D005091:Exons / Q000235:genetics; D059948:HLA-B44 Antigen / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D010446:Peptide Fragments / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D019076:Transgenes / Q000235:genetics
chemical_list: D059948:HLA-B44 Antigen; D026901:Membrane Transport Proteins; D010446:Peptide Fragments; D020033:Protein Isoforms; C107762:tapasin; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human