New function of NADPH-P450 reductase(NPR) : Regulation of hypoxia-response genes by NPR.

缺氧是许多癌症的共同特征。它促进了局部和全身肿瘤的进展。缺氧也是心肌梗死的一个重要因素。在低氧条件下，低氧诱导因子-1(HIF-1α)通过识别低氧反应元件而稳定并转录调节低氧反应基因如促红细胞生成素和血管内皮生长因子。我们发现NADPH-P450还原酶是稳定HIF-1α所必需的。当基因敲除抑制细胞内npr表达时，HIF-1α蛋白被降解。我们还发现，双酚A(BPA)是一种内分泌干扰物，在低氧条件下能降解HIF-1α。BPA不与NPR相互作用，但与伴侣蛋白HSP90相互作用。HSP90在低氧条件下稳定HEF-1α，并使HSP90从HIF-1α中解离。已知HIF-1α可通过泛素化和蛋白酶体途径降解，即使在泛素化和蛋白酶体降解抑制剂存在的情况下，BPA也能降解HIF-1α。这些结果表明，双酚A通过一种目前未知的途径降解缺氧诱导因子-1α。此外，我们还利用酵母双杂交系统寻找与NPR相互作用的因素。获得了一些候选者，并似乎对细胞的氧化还原调节做出了贡献。有必要对这些因子的生物学功能进行进一步的分析。

Hypoxia is a common feature of many cancers. It contributes local and systemic tumor progression. Hypoxia is also an important factor in myocardial infarction. In hypoxic condition, hypoxia-inducible factor(HIF-1α) is stabilized and transcriptionally regulates hypoxia-response genes such as erythropoietin(EPO) and VEGF, by recognition of hypoxia response element(HRE). We found that NADPH-P450 reductase(NPR) was necessary for stabilization of HIF-1α. When NPR expression in Hep3B cells was suppressed by knockdown, HIF-1α protein was degraded. We also found that bisphenol A(BpA), an endocrine-disrupting chemical, degraded HIF-1α under hypoxia. BpA didn't interact with NPR but did with a chaperon protein, HSP90. HSP90 stabilized HEF-1α under hypoxia and BpA dissociated HSP-90 from HIF-1α. HIF-1α is known to be degraded by ubiquitination and proteasome pathway BpA degraded HIF-1α even in the presence of inhibitors for ubiquitination and proteasome degradation. These results suggested that BpA degraded HIF-1α via a currently unknown pathway. Furthermore, we searched factors which interact with NPR using yeast two-hybrid system. Some candidates were obtained and seem to contribute to the redox regulation of the cells. Further analysis for biological functions of these factors is necessary.