Hypoxia Up-regulates CD36 Expression and Function via Hypoxia-inducible Factor-1-and Phosphatidylinositol 3-Kinase-dependent Mechanisms
Hypoxia Up-regulates CD36 Expression and Function via Hypoxia-inducible Factor-1-and Phosphatidylinositol 3-Kinase-dependent Mechanisms
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DOI：
10.1074/jbc.m109.033480
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发表时间：
2009-09-25
影响因子：
4.8
通讯作者：
Hardy, Pierre
中科院分区：
文献类型：
--
作者：
Mwaikambo, Bupe R.;Yang, Chun;Hardy, Pierre
眼睛的新生血管病和退行性疾病是世界上视力受损和失明的主要原因。缺氧或氧张力降低被认为是这些疾病发病机制的核心。尽管CD36清扫剂受体在眼内稳态和病理中发挥着重要作用，但对其在缺氧中的调节作用知之甚少。在此，我们研究了CD36在缺氧和主要缺氧效应物缺氧诱导因子(HIF)-1中的作用和调控。在体内，缺氧显著诱导角膜和视网膜组织中CD36 mRNA表达。随后对人视网膜色素上皮细胞的实验表明，缺氧时间依赖性地增加了CD36 mRNA、蛋白和表面表达；这些反应依赖于活性氧的产生。作为一项重要的新发现，我们证明了低氧刺激CD36是由HIF-1介导的；HIF-1 α下调可消除缺氧和氯化钴诱导的CD36。人类CD36启动子区域的序列分析揭示了一个功能性的HIF-1结合位点。含有该启动子片段的荧光素酶报告结构体在缺氧时被激活，而HIF-1一致位点的突变降低了启动子的激活。在缺氧细胞中，HIF-1特异性结合到这个假定的位点是通过染色质免疫沉淀试验检测到的。有趣的是，抑制磷脂酰肌醇3-激酶途径阻断了低氧依赖性诱导CD36表达和启动子活性。CD36依赖的清除和抗血管生成活性的增加证明了CD36缺氧积累的功能分支。总之，我们的发现表明了缺氧通过激活HIF-1和磷脂酰肌醇3-激酶途径诱导CD36表达的新机制。
Neovascular and degenerative diseases of the eye are leading causes of impaired vision and blindness in the world. Hypoxia or reduced oxygen tension is considered central to the pathogenesis of these disorders. Although the CD36 scavenger receptor features prominently in ocular homeostasis and pathology, little is known regarding its modulation by hypoxia. Herein we investigated the role and regulation of CD36 by hypoxia and by the major hypoxia effector, hypoxia-inducible factor (HIF)-1. In vivo, hypoxia markedly induced CD36 mRNA in corneal and retinal tissue. Subsequent experiments on human retinal pigment epithelial cells revealed that hypoxia time-dependently increased CD36 mRNA, protein, and surface expression; these responses were reliant upon reactive oxygen species production. As an important novel finding, we demonstrate that hypoxic stimulation of CD36 is mediated by HIF-1; HIF-1 alpha down-regulation abolished CD36 induction by both hypoxia and cobalt chloride. Sequence analysis of the human CD36 promoter region revealed a functional HIF-1 binding site. A luciferase reporter construct containing this promoter fragment was activated by hypoxia, whereas mutation at the HIF-1 consensus site decreased promoter activation. Specific binding of HIF-1 to this putative site in hypoxic cells was detected by a chromatin immunoprecipitation assay. Interestingly, inhibition of the phosphatidylinositol 3-kinase pathway blocked the hypoxia-dependent induction of CD36 expression and promoter activity. Functional ramifications of CD36 hypoxic accumulation were evinced by CD36-dependent increases in scavenging and anti-angiogenic activities. Together, our findings indicate a novel mechanism by which hypoxia induces CD36 expression via activation of HIF-1 and the phosphatidylinositol 3-kinase pathway.