title: The MICA-129Met/Val dimorphism affects plasma membrane expression and shedding of the NKG2D ligand MICA.
abstract: The MHC class I chain-related molecule A (MICA) is a ligand for the activating natural killer (NK) cell receptor NKG2D. A polymorphism causing a valine to methionine exchange at position 129 affects binding to NKG2D, cytotoxicity, interferon-γ release by NK cells and activation of CD8(+) T cells. It is known that tumors can escape NKG2D-mediated immune surveillance by proteolytic shedding of MICA. Therefore, we investigated whether this polymorphism affects plasma membrane expression (pmMICA) and shedding of MICA. Expression of pmMICA was higher in a panel of tumor (n = 16, P = 0.0699) and melanoma cell lines (n = 13, P = 0.0429) carrying the MICA-129Val/Val genotype. MICA-129Val homozygous melanoma cell lines released more soluble MICA (sMICA) by shedding (P = 0.0015). MICA-129Met or MICA-129Val isoforms differing only in this amino acid were expressed in the MICA-negative melanoma cell line Malme, and clones with similar pmMICA expression intensity were selected. The MICA-129Met clones released more sMICA (P = 0.0006), and a higher proportion of the MICA-129Met than the MICA-129Val variant was retained in intracellular compartments (P = 0.0199). The MICA-129Met clones also expressed more MICA messenger RNA (P = 0.0047). The latter phenotype was also observed in mouse L cells transfected with the MICA expression constructs (P = 0.0212). In conclusion, the MICA-129Met/Val dimorphism affects the expression density of MICA on the plasma membrane. More of the MICA-129Met variants were retained intracellularly. If expressed at the cell surface, the MICA-129Met isoform was more susceptible to shedding. Both processes appear to limit the cell surface expression of MICA-129Met variants that have a high binding avidity to NKG2D.
authors.affiliation: Institute of Cellular and Molecular Immunology, University Medical Center Göttingen, Humboldtallee 34, 37073, Göttingen, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Isernhagen
authors.affiliation: Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München (TUM), Munich, Germany.|Institute of Innovative Radiotherapy (iRT), Radiation Immune Biology, Department of Radiation Sciences (DRS), Helmholtz Zentrum München, Munich, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Schilling
authors.affiliation: Institute of Cellular and Molecular Immunology, University Medical Center Göttingen, Humboldtallee 34, 37073, Göttingen, Germany.|DZHK (German Center for Cardiovascular Research), Partner site Göttingen, Göttingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Monecke
authors.affiliation: Institute of Cellular and Molecular Immunology, University Medical Center Göttingen, Humboldtallee 34, 37073, Göttingen, Germany.
authors.forename: Pranali
authors.initials: P
authors.lastname: Shah
authors.affiliation: Institute of Cellular and Molecular Immunology, University Medical Center Göttingen, Humboldtallee 34, 37073, Göttingen, Germany.
authors.forename: Leslie
authors.initials: L
authors.lastname: Elsner
authors.affiliation: Primate Genetics Laboratory, German Primate Center, Göttingen, Germany.|DZHK (German Center for Cardiovascular Research), Partner site Göttingen, Göttingen, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Walter
authors.affiliation: Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München (TUM), Munich, Germany.|Institute of Innovative Radiotherapy (iRT), Radiation Immune Biology, Department of Radiation Sciences (DRS), Helmholtz Zentrum München, Munich, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Multhoff
authors.affiliation: Institute of Cellular and Molecular Immunology, University Medical Center Göttingen, Humboldtallee 34, 37073, Göttingen, Germany. rdresse@gwdg.de.|DZHK (German Center for Cardiovascular Research), Partner site Göttingen, Göttingen, Germany. rdresse@gwdg.de.
authors.forename: Ralf
authors.initials: R
authors.lastname: Dressel
mesh_terms: D019943:Amino Acid Substitution; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D015870:Gene Expression; D005838:Genotype; D015395:Histocompatibility Antigens Class I / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D055655:NK Cell Lectin-Like Receptor Subfamily K / Q000378:metabolism*; D020641:Polymorphism, Single Nucleotide; D011485:Protein Binding; D020033:Protein Isoforms
chemical_list: D015395:Histocompatibility Antigens Class I; C099187:MHC class I-related chain A; D055655:NK Cell Lectin-Like Receptor Subfamily K; D020033:Protein Isoforms
keywords: Major histocompatibility complex (MHC) class I chain-related molecules A (MICA); Plasma membrane expression; Proteolytic shedding; Single nucleotide polymorphism; Tumor cells