School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, NG7 2UH, UK.
Nat Cell Biol. 2012 Jan 29;14(2):201-8. doi: 10.1038/ncb2424.
There are three prolyl hydroxylases (PHD1, 2 and 3) that regulate the hypoxia-inducible factors (HIFs), the master transcriptional regulators that respond to changes in intracellular O(2) tension. In high O(2) tension (normoxia) the PHDs hydroxylate two conserved proline residues on HIF-1α, which leads to binding of the von Hippel-Lindau (VHL) tumour suppressor, the recognition component of a ubiquitin-ligase complex, initiating HIF-1α ubiquitylation and degradation. However, it is not known whether PHDs and VHL act separately to exert their enzymatic activities on HIF-1α or as a multiprotein complex. Here we show that the tumour suppressor protein LIMD1 (LIM domain-containing protein) acts as a molecular scaffold, simultaneously binding the PHDs and VHL, thereby assembling a PHD-LIMD1-VHL protein complex and creating an enzymatic niche that enables efficient degradation of HIF-1α. Depletion of endogenous LIMD1 increases HIF-1α levels and transcriptional activity in both normoxia and hypoxia. Conversely, LIMD1 expression downregulates HIF-1 transcriptional activity in a manner depending on PHD and 26S proteasome activities. LIMD1 family member proteins Ajuba and WTIP also bind to VHL and PHDs 1 and 3, indicating that these LIM domain-containing proteins represent a previously unrecognized group of hypoxic regulators.
有三种脯氨酰羟化酶（PHD1、2 和 3）可调节缺氧诱导因子（HIFs），HIFs 是对细胞内 O2 张力变化做出反应的主要转录调节因子。在高 O2 张力（常氧）下，PHD 会使 HIF-1α 上的两个保守脯氨酸残基发生羟化，导致 von Hippel-Lindau（VHL）肿瘤抑制因子结合，VHL 是泛素连接酶复合物的识别成分，从而启动 HIF-1α 的泛素化和降解。然而，目前尚不清楚 PHD 和 VHL 是否分别作为一个多蛋白复合物发挥其对 HIF-1α 的酶活性。在这里，我们发现肿瘤抑制蛋白 LIMD1（富含 LIM 结构域的蛋白）作为一种分子支架，同时与 PHD 和 VHL 结合，从而组装 PHD-LIMD1-VHL 蛋白复合物，并创造一个酶活性位，使 HIF-1α 能够有效降解。内源性 LIMD1 的耗竭会增加常氧和低氧条件下 HIF-1α 的水平和转录活性。相反，LIMD1 的表达会下调 HIF-1 的转录活性，其方式取决于 PHD 和 26S 蛋白酶体的活性。LIMD1 家族蛋白 Ajuba 和 WTIP 也与 VHL 和 PHD1 和 3 结合，这表明这些富含 LIM 结构域的蛋白代表了一个以前未被识别的缺氧调节因子群体。
