title: Hypoxia downregulates the expression of cell surface MICA without increasing             soluble MICA in osteosarcoma cells in a HIF-1α-dependent manner.
abstract: Tumor cells express NKG2D ligands on their cell surface, which are the ligands             of the activating receptor, NKG2D, that is expressed on the surface of NK cells.             The binding of NK cells to tumor cells through the interaction of NKG2D and its             ligands induces the cytolysis of the tumor cells. In the present study, we investigated             the effects of hypoxia on the expression of NKG2D ligands on the surface of human             osteosarcoma cells using three cell lines. To produce hypoxic and normoxic conditions,             the osteosarcoma cell lines were cultured under 1 and 20% O2 conditions, respectively.             The osteosarcoma cells expressed NKG2D ligands such as MHC class I-related chain             molecules A and B (MICA and MICB) and the UL16-binding proteins 1, 2 and 3 (ULBP             1, 2 and 3). MICA was the most frequently expressed NKG2D ligand in the osteosarcoma             cells. Hypoxia decreased the expression of cell surface MICA only without increasing             the secretion of soluble MICA, which is produced by proteolytic cleavage of cell             surface MICA. Hypoxia consistently decreased the susceptibility of the osteosarcoma             cells to the cytotoxicity of the NK cells. Hypoxia induced the expression of hypoxia-inducible             factor-1α (HIF-1α), and knockdown of the expression of HIF-1α using small interfering             RNA increased the expression of cell surface MICA and concomitantly increased             the level of soluble MICA. Hypoxia decreased the production of nitric oxide (NO)             metabolites (nitrite and nitrate), thus, indicating a decreasing effect on NO             production. However, a NO donor, NOC18, decreased the expression of cell surface             MICA without any apparent effects on the expression of HIF-1α under both hypoxic             and normoxic conditions. The present results indicate that hypoxia downregulates             the expression of cell surface MICA without increasing the level of soluble MICA             in a HIF-1α-dependent manner and suggest that the effects of hypoxia are not linked             to the hypoxia-induced reduction of NO production.
authors.affiliation: Department of Pathology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan. ynaoko@hyo-med.ac.jp
authors.forename: Naoko
authors.initials: N
authors.lastname: Yamada
authors.forename: Koji
authors.initials: K
authors.lastname: Yamanegi
authors.forename: Hideki
authors.initials: H
authors.lastname: Ohyama
authors.forename: Masaki
authors.initials: M
authors.lastname: Hata
authors.forename: Keiji
authors.initials: K
authors.lastname: Nakasho
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Futani
authors.forename: Haruki
authors.initials: H
authors.lastname: Okamura
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Terada
mesh_terms: D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003602:Cytotoxicity, Immunologic / Q000276:immunology; D015536:Down-Regulation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D015395:Histocompatibility Antigens Class I / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007694:Killer Cells, Natural / Q000276:immunology; D008024:Ligands; D055655:NK Cell Lectin-Like Receptor Subfamily K / Q000378:metabolism; D009569:Nitric Oxide; D012516:Osteosarcoma / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*
chemical_list: D015395:Histocompatibility Antigens Class I; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C527085:KLRK1 protein, human; D008024:Ligands; C099187:MHC class I-related chain A; D055655:NK Cell Lectin-Like Receptor Subfamily K; D009569:Nitric Oxide