title: A conserved WW domain-like motif regulates invariant chain-dependent cell-surface transport of the NKG2D ligand ULBP2.
abstract: Malignant cells expressing NKG2D ligands on their cell surface can be directly sensed and killed by NKG2D-bearing lymphocytes. To ensure this immune recognition, accumulating evidence suggests that NKG2D ligands are trafficed via alternative pathways to the cell surface. We have previously shown that the NKG2D ligand ULBP2 traffics over an invariant chain (Ii)-dependent pathway to the cell surface. This study set out to elucidate how Ii regulates ULBP2 cell-surface transport: We discovered conserved tryptophan (Trp) residues in the primary protein sequence of ULBP1-6 but not in the related MICA/B. Substitution of Trp to alanine resulted in cell-surface inhibition of ULBP2 in different cancer cell lines. Moreover, the mutated ULBP2 constructs were retained and not degraded inside the cell, indicating a crucial role of this conserved Trp-motif in trafficking. Finally, overexpression of Ii increased surface expression of wt ULBP2 while Trp-mutants could not be expressed, proposing that this Trp-motif is required for an Ii-dependent cell-surface transport of ULBP2. Aberrant soluble ULBP2 is immunosuppressive. Thus, targeting a distinct protein module on the ULBP2 sequence could counteract this abnormal expression of ULBP2.
authors.affiliation: Laboratory of Immunology, Section for Experimental Animal Models, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, DK-1870 Frederiksberg, Denmark. Electronic address: fku@sund.ku.dk.
authors.forename: Franziska
authors.initials: F
authors.lastname: Uhlenbrock
authors.affiliation: Laboratory of Immunology, Section for Experimental Animal Models, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, DK-1870 Frederiksberg, Denmark.
authors.forename: Esther
authors.initials: E
authors.lastname: van Andel
authors.affiliation: Laboratory of Immunology, Section for Experimental Animal Models, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, DK-1870 Frederiksberg, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Andresen
authors.affiliation: Laboratory of Immunology, Section for Experimental Animal Models, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, DK-1870 Frederiksberg, Denmark. Electronic address: sosk@sund.ku.dk.
authors.forename: Søren
authors.initials: S
authors.lastname: Skov
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D001665:Binding Sites; D045744:Cell Line, Tumor; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D015972:Gene Expression Regulation, Neoplastic; D057809:HEK293 Cells; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D019169:Jurkat Cells; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055655:NK Cell Lectin-Like Receptor Subfamily K / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D021381:Protein Transport; D016415:Sequence Alignment; D015398:Signal Transduction; D014364:Tryptophan / Q000737:chemistry / Q000235:genetics* / Q000276:immunology
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D058851:GPI-Linked Proteins; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D036341:Intercellular Signaling Peptides and Proteins; C527085:KLRK1 protein, human; C099187:MHC class I-related chain A; C098080:MICB antigen; D055655:NK Cell Lectin-Like Receptor Subfamily K; D020033:Protein Isoforms; C423230:ULBP2 protein, human; C045084:invariant chain; D014364:Tryptophan; D000409:Alanine
keywords: Cell-surface transport; Invariant chain; NKG2D ligands; ULBP2; WW domain