Department of Pathology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan.
Int J Oncol. 2012 Dec;41(6):2005-12. doi: 10.3892/ijo.2012.1630. Epub 2012 Sep 18.
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.
肿瘤细胞在其细胞表面表达 NKG2D 配体，这些配体是 NK 细胞表面表达的激活受体 NKG2D 的配体。NK 细胞通过 NKG2D 与其配体的相互作用与肿瘤细胞结合，诱导肿瘤细胞的细胞溶解。在本研究中，我们使用三种细胞系研究了缺氧对人骨肉瘤细胞表面 NKG2D 配体表达的影响。为了产生缺氧和常氧条件，将骨肉瘤细胞系分别在 1%和 20%O2 条件下培养。骨肉瘤细胞表达 NKG2D 配体，如 MHC Ⅰ类相关链分子 A 和 B（MICA 和 MICB）和 UL16 结合蛋白 1、2 和 3（ULBP 1、2 和 3）。MICA 是骨肉瘤细胞中表达最频繁的 NKG2D 配体。缺氧仅降低细胞表面 MICA 的表达，而不增加通过细胞表面 MICA 的蛋白水解裂解产生的可溶性 MICA 的分泌。缺氧一致降低了骨肉瘤细胞对 NK 细胞细胞毒性的敏感性。缺氧诱导缺氧诱导因子-1α（HIF-1α）的表达，并用小干扰 RNA 敲低 HIF-1α 的表达增加了细胞表面 MICA 的表达，并同时增加了可溶性 MICA 的水平。缺氧减少了一氧化氮（NO）代谢物（亚硝酸盐和硝酸盐）的产生，因此表明对 NO 产生的抑制作用。然而，NO 供体 NOC18 在缺氧和常氧条件下均降低了细胞表面 MICA 的表达，而对 HIF-1α 的表达没有任何明显影响。本研究结果表明，缺氧以 HIF-1α 依赖的方式下调细胞表面 MICA 的表达，而不增加可溶性 MICA 的水平，并表明缺氧的作用与缺氧诱导的 NO 产生减少无关。
