Ikeda E, Achen M G, Breier G, Risau W
Max-Planck-Institut für physiologische und klinische Forschung, W.G. Kerckhoff-Institut, Abteilung Molekulare Zellbiologie, Bad Nauheim, Germany.
J Biol Chem. 1995 Aug 25;270(34):19761-6. doi: 10.1074/jbc.270.34.19761.
Vascular endothelial growth factor (VEGF) is an endothelial specific angiogenic mitogen secreted from various cell types including tumor cells. Increasing evidence suggests that VEGF is a major regulator of physiological and pathological angiogenesis, and the VEGF/VEGF receptor system has been shown to be necessary for glioma angiogenesis. Hypoxia seems to play a critical role in the induction of VEGF expression during glioma progression. C6 glioma cells provide an in vivo glioma model for the study of tumor angiogenesis, and the expression of VEGF in C6 cells has been shown to be up-regulated by hypoxia in vitro. However, little is known about the molecular mechanism of hypoxic induction of VEGF. Here, we demonstrate that hypoxic induction of VEGF in C6 cells is due to both transcriptional activation and increased stability of mRNA. Nuclear run-on assays revealed a fast and lasting transcriptional activation, whereas the determination of mRNA half-life showed a slower increase of mRNA stability during hypoxia. Reporter gene studies revealed that hypoxia responsive transcription-activating elements were present in the 5'-flanking region of the VEGF gene. These results suggested that several distinct molecular mechanisms were involved in hypoxia-induced gene expression and were activated in a biphasic manner.
血管内皮生长因子（VEGF）是一种由包括肿瘤细胞在内的多种细胞类型分泌的内皮特异性促血管生成有丝分裂原。越来越多的证据表明，VEGF是生理性和病理性血管生成的主要调节因子，并且VEGF/VEGF受体系统已被证明是胶质瘤血管生成所必需的。缺氧似乎在胶质瘤进展过程中VEGF表达的诱导中起关键作用。C6胶质瘤细胞为肿瘤血管生成的研究提供了一种体内胶质瘤模型，并且已表明C6细胞中VEGF的表达在体外可被缺氧上调。然而，关于缺氧诱导VEGF的分子机制知之甚少。在此，我们证明C6细胞中VEGF的缺氧诱导是由于转录激活和mRNA稳定性增加所致。核转录分析显示快速且持久的转录激活，而mRNA半衰期的测定表明在缺氧期间mRNA稳定性的增加较为缓慢。报告基因研究表明，缺氧反应性转录激活元件存在于VEGF基因的5'侧翼区域。这些结果表明，几种不同的分子机制参与了缺氧诱导的基因表达，并以双相方式被激活。
