Makino Y, Cao R, Svensson K, Bertilsson G, Asman M, Tanaka H, Cao Y, Berkenstam A, Poellinger L
Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, S-171 77 Stockholm, Sweden.
Nature. 2001 Nov 29;414(6863):550-4. doi: 10.1038/35107085.
Alteration of gene expression is a crucial component of adaptive responses to hypoxia. These responses are mediated by hypoxia-inducible transcription factors (HIFs). Here we describe an inhibitory PAS (Per/Arnt/Sim) domain protein, IPAS, which is a basic helix-loop-helix (bHLH)/PAS protein structurally related to HIFs. IPAS contains no endogenous transactivation function but demonstrates dominant negative regulation of HIF-mediated control of gene expression. Ectopic expression of IPAS in hepatoma cells selectively impairs induction of genes involved in adaptation to a hypoxic environment, notably the vascular endothelial growth factor (VEGF) gene, and results in retarded tumour growth and tumour vascular density in vivo. In mice, IPAS was predominantly expressed in Purkinje cells of the cerebellum and in corneal epithelium of the eye. Expression of IPAS in the cornea correlates with low levels of expression of the VEGF gene under hypoxic conditions. Application of an IPAS antisense oligonucleotide to the mouse cornea induced angiogenesis under normal oxygen conditions, and demonstrated hypoxia-dependent induction of VEGF gene expression in hypoxic corneal cells. These results indicate a previously unknown mechanism for negative regulation of angiogenesis and maintenance of an avascular phenotype.
基因表达的改变是对缺氧适应性反应的关键组成部分。这些反应由缺氧诱导转录因子（HIFs）介导。在此，我们描述了一种抑制性PAS（Per/Arnt/Sim）结构域蛋白，即IPAS，它是一种与HIFs在结构上相关的碱性螺旋-环-螺旋（bHLH）/PAS蛋白。IPAS不具有内源性反式激活功能，但对HIF介导的基因表达调控具有显性负调控作用。IPAS在肝癌细胞中的异位表达选择性地损害了参与缺氧环境适应的基因的诱导，特别是血管内皮生长因子（VEGF）基因，并导致体内肿瘤生长迟缓和肿瘤血管密度降低。在小鼠中，IPAS主要在小脑的浦肯野细胞和眼睛的角膜上皮中表达。IPAS在角膜中的表达与缺氧条件下VEGF基因的低表达水平相关。将IPAS反义寡核苷酸应用于小鼠角膜可在正常氧条件下诱导血管生成，并证明缺氧角膜细胞中VEGF基因表达的缺氧依赖性诱导。这些结果表明了一种以前未知的血管生成负调控和无血管表型维持机制。
