Drutel G, Kathmann M, Héron A, Gros C, Macé S, Schwartz J C, Arrang J M
Unité de Neurobiologie et Pharmacologie Moléculaire (U.109) INSERM, Centre Paul Broca, 2ter rue d'Alésia, 75014 Paris, France.
Eur J Neurosci. 2000 Oct;12(10):3701-8. doi: 10.1046/j.1460-9568.2000.00266.x.
The hypoxia-inducible factor (HIF-1alpha), a basic helix-loop-helix transcription factor, is known to heterodimerize with ARNT1, a nuclear translocator, to trigger the overexpression in many cells of genes involved in resistance to hypoxia. Although HIF-1alpha and ARNT1 are both expressed in brain, their cellular localization and function therein are unknown. Here, using in situ hybridization and immunocytochemistry, we show that HIF-1alpha is expressed in normoxic cerebral neurons together with not only ARNT1 but also ARNT2, a cerebral translocator homologous to ARNT1 but displaying, unlike ARNT1, a selective neuronal expression. In contrast, other potential partners of the translocators, i.e. the aryl hydrocarbon receptor (AHR) and the single-minded protein 2 (SIM2), are not expressed in the adult brain. We also identify two splice variants of HIF-1alpha in brain, one of which dimerizes with ARNT2 even more avidly than with ARNT1. The resulting heterodimer, in contrast with the HIF-1alpha/ARNT1 complex, does not recognize the HIF-1-binding site of the hypoxia-induced erythropoietin (Epo) gene, suggesting that it controls transcription of a distinct set of genes. We therefore propose that HIF-1alpha and ARNT2 function as preferential dimerization partners in neurons to control specific responses, some of which may not be triggered by hypoxia. In support of this proposal, in nonhypoxic PC12 cells constitutively coexpressing HIF-1alpha, ARNT1 and ARNT2, downregulation of either HIF-1alpha or ARNT2, obtained with selective antisense nucleotides, resulted in inhibition of [3H]thymidine incorporation.
缺氧诱导因子（HIF-1α）是一种碱性螺旋-环-螺旋转录因子，已知它能与核转运蛋白ARNT1形成异二聚体，从而在许多细胞中触发参与缺氧抵抗的基因的过表达。尽管HIF-1α和ARNT1在大脑中均有表达，但它们在细胞中的定位及其在大脑中的功能尚不清楚。在此，我们利用原位杂交和免疫细胞化学技术表明，HIF-1α不仅与ARNT1一起在常氧脑神经元中表达，还与ARNT2一起表达，ARNT2是一种与ARNT1同源的脑转运蛋白，但与ARNT1不同，它表现出选择性神经元表达。相比之下，转运蛋白的其他潜在伙伴，即芳烃受体（AHR）和单 minded蛋白2（SIM2），在成人大脑中不表达。我们还在大脑中鉴定出HIF-1α的两种剪接变体，其中一种与ARNT2形成二聚体的亲和力甚至比与ARNT1形成二聚体的亲和力更高。与HIF-1α/ARNT1复合物相反，由此产生的异二聚体不识别缺氧诱导的促红细胞生成素（Epo）基因的HIF-1结合位点，这表明它控制着一组不同基因的转录。因此，我们提出HIF-1α和ARNT2作为神经元中的优先二聚体伙伴发挥作用，以控制特定反应，其中一些反应可能不是由缺氧触发的。为支持这一观点，在组成性共表达HIF-1α、ARNT1和ARNT2的非缺氧PC12细胞中，用选择性反义核苷酸下调HIF-1α或ARNT2会导致[3H]胸苷掺入受到抑制。
