Oulu Center for Cell-Matrix Research, Biocenter Oulu and Department of Medical Biochemistry and Molecular Biology, University of Oulu, Finland.
Cell Mol Life Sci. 2011 Dec;68(23):3885-901. doi: 10.1007/s00018-011-0679-5. Epub 2011 Apr 10.
The hypoxia-inducible transcription factor (HIF) controls (in an oxygen-dependent manner) the expression of a large number of genes whose products are involved in the response of cells to hypoxia. HIF is an αβ dimer that binds to hypoxia response elements (HREs) in its target genes. Human HIF-α has three isoforms, HIF-1α, HIF-2α and HIF-3α, of which the roles of HIF-3α are largely unknown, although it is usually regarded as a negative regulator of HIF-1α and HIF-2α. The human HIF-3α locus is subject to extensive alternative splicing, leading to at least seven variants. We analyzed here the effects of the long variants and the short variant HIF-3α4 on the hypoxia response. All these variants were found to interact with HIF-β, HIF-1α and HIF-2α. The long HIF-3α variants were localized in the nucleus in hypoxia, while HIF-3α4 was cytoplasmic. Interaction of the HIF-3α variants with HIF-1α inhibited the nuclear translocation of both. None of the long HIF-3α variants was capable of efficient induction of an HRE reporter in overexpression experiments, but instead inhibited the transcriptional activation of the reporter by HIF-1 and HIF-2. Unexpectedly, siRNA knock-down of the endogenous HIF-3α variants led to downregulation of certain HIF target genes, while overexpression of individual long HIF-3α variants upregulated certain HIF target genes in a variant and target gene-specific manner under conditions in which HIF-β was not a limiting factor. These data indicate that the HIF-3α variants may have more versatile and specific roles in the regulation of the hypoxia response than previously anticipated.
缺氧诱导因子 (HIF) 以氧依赖的方式控制大量基因的表达，这些基因产物参与细胞对缺氧的反应。HIF 是一种 αβ 二聚体，它与靶基因中的缺氧反应元件 (HRE) 结合。人 HIF-α 有三种亚型，HIF-1α、HIF-2α 和 HIF-3α，其中 HIF-3α 的作用在很大程度上尚不清楚，尽管它通常被认为是 HIF-1α 和 HIF-2α 的负调节剂。人 HIF-3α 基因座受到广泛的选择性剪接，导致至少七种变体。我们在这里分析了长变体和短变体 HIF-3α4 对缺氧反应的影响。所有这些变体都被发现与 HIF-β、HIF-1α 和 HIF-2α 相互作用。长 HIF-3α 变体在缺氧时定位于细胞核内，而 HIF-3α4 位于细胞质中。HIF-3α 变体与 HIF-1α 的相互作用抑制了两者的核转位。在过表达实验中，长 HIF-3α 变体均不能有效地诱导 HRE 报告基因的表达，反而抑制了 HIF-1 和 HIF-2 对报告基因的转录激活。出乎意料的是，内源性 HIF-3α 变体的 siRNA 敲低导致某些 HIF 靶基因下调，而在 HIF-β 不是限制因素的情况下，单个长 HIF-3α 变体的过表达以变体和靶基因特异性的方式上调某些 HIF 靶基因。这些数据表明，与之前的预期相比，HIF-3α 变体在调节缺氧反应方面可能具有更通用和更具体的作用。
