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.
A 60-year-old man had been administered diphenylhydantoin (DPH) for prevention of convulsive seizures following clipping of an aneurysm of the middle cerebral artery. About one month after the commencement of DPH administration, he developed cough and low grade fever. He was treated with various antibiotics, but his condition increasingly worsened. Chest X-ray film revealed bilateral interstitial processes throughout the entire lung fields. Transbronchial lung biopsy was performed and the obtained specimen showed histological findings compatible with drug-induced pneumonitis. Administration of DPH was stopped immediately and 50 mg/day of prednisolone was started. The patient's condition rapidly improved, and the abnormal shadows on chest X-ray film gradually diminished. The lymphocyte stimulation test by DPH was positive with a stimulation index of 282%.
In CKD patients, arteriosclerotic lesions, including calcification, can occur in vascular smooth muscle cells in a process called Moenckeberg's medial arteriosclerosis. Iron overload induces several complications, including the acceleration of arteriosclerosis. However, the relationship between Moenckeberg's arteriosclerosis in vascular smooth muscle cells and iron accumulation has remained unknown. We tested the accelerated effect of iron on calcification in cultured human aortic vascular smooth muscle cells (HASMCs). After establishment of this model, we performed a microarray analysis using mRNA from early stage culture HASMCs after iron stimulation with or without TNF-alpha stimulation. The role of interleukin-24 (IL-24) was confirmed from candidate genes that might contribute to calcification. HASMCs demonstrated calcification induced by iron and TNF-alpha. Calcification of HASMCs was synergistically enhanced by stimulation with both iron and TNF-alpha. In the early phase of calcification, microarray analysis revealed up-regulation of IL-24. Stimulation of HASMCs by IL-24 instead of iron induced calcification. The anti-IL-24 antibody reversed the effect of IL-24, supporting the important role of IL-24 in HASMCs calcification. In conclusion, iron-induced calcification in vascular smooth muscle cells occurred via IL-24, IL-24 was increased during the calcification process induced by iron, and IL-24 itself caused calcification in the absence of iron.
