Yim Sujin, Choi Su Mi, Choi Youngyeon, Lee Naery, Chung Jieun, Park Hyunsung
Department of Life Science, University of Seoul, Seoul 130-743, Korea.
J Biol Chem. 2003 Oct 3;278(40):38260-8. doi: 10.1074/jbc.M306016200. Epub 2003 Jul 21.
Both hypoxia and insulin induce common target genes, including vascular endothelial growth factors and several glycolytic enzymes. However, these two signals eventually trigger quite different metabolic pathways. Hypoxia induces glycolysis, resulting in anaerobic ATP production, while insulin increases glycolysis for energy storage. Hypoxia-induced gene expression is mediated by the hypoxia-inducible factor-1 (HIF-1) that consists of HIF-1alpha and the aromatic hydrocarbon nuclear translocator (Arnt). Hypoxia-induced gene expression is initiated by the stabilization of the HIF-1alpha subunit. Here we investigated whether insulin-induced gene expression also requires stabilization of HIF-1alpha. Our results indicate that hypoxia but not insulin stabilizes HIF-1alpha protein levels, whereas both insulin- and hypoxia-induced gene expression require the presence of the Arnt protein. Insulin treatment fails to inactivate proline hydroxylation of HIF-1alpha, which triggers recruitment of the von Hippel-Lindau protein and oxygen-dependent degradation of HIF-1alpha. Insulin-induced gene expression is inhibited by the presence of the phosphoinositide (PI) 3-kinase inhibitor LY294002 and the dominant negative mutant of the p85 subunit of PI 3-kinase, whereas hypoxia-induced gene expression is not. Pyrrolidine dithiocarbamate, a scavenger of H2O2, reduces insulin-induced gene expression but not hypoxia-induced gene expression. Although both hypoxia and insulin induce the expression of common target genes through a hypoxia-responsive element- and Arnt-dependent mechanism, insulin cannot stabilize the HIF-1alpha protein. We believe that insulin activates other putative partner proteins for Arnt in PI 3-kinase- and H2O2-dependent pathways.
缺氧和胰岛素均可诱导共同的靶基因，包括血管内皮生长因子和几种糖酵解酶。然而，这两种信号最终会触发截然不同的代谢途径。缺氧诱导糖酵解，导致无氧ATP生成，而胰岛素则增加糖酵解以进行能量储存。缺氧诱导的基因表达由缺氧诱导因子-1（HIF-1）介导，HIF-1由HIF-1α和芳烃核转运体（Arnt）组成。缺氧诱导的基因表达由HIF-1α亚基的稳定化启动。在此，我们研究了胰岛素诱导的基因表达是否也需要HIF-1α的稳定化。我们的结果表明，缺氧而非胰岛素可稳定HIF-1α蛋白水平，而胰岛素和缺氧诱导的基因表达均需要Arnt蛋白的存在。胰岛素处理未能使HIF-1α的脯氨酸羟基化失活，脯氨酸羟基化会触发冯·希佩尔-林道蛋白的募集以及HIF-1α的氧依赖性降解。胰岛素诱导的基因表达受到磷酸肌醇（PI）3激酶抑制剂LY294002和PI 3激酶p85亚基的显性负突变体的抑制，而缺氧诱导的基因表达则不受影响。吡咯烷二硫代氨基甲酸盐（一种H2O2清除剂）可降低胰岛素诱导的基因表达，但不影响缺氧诱导的基因表达。尽管缺氧和胰岛素均通过缺氧反应元件和Arnt依赖性机制诱导共同靶基因的表达，但胰岛素无法稳定HIF-1α蛋白。我们认为，胰岛素在PI 3激酶和H2O2依赖性途径中激活了Arnt的其他假定伴侣蛋白。
