Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
J Biochem. 2013 Dec;154(6):561-7. doi: 10.1093/jb/mvt088. Epub 2013 Oct 3.
Inhibitory Per/Arnt/Sim (PAS) domain protein (IPAS) is a splice variant of hypoxia-inducible factor (HIF)-3α, and possesses two entirely different functions. One is as a transcriptional repressor against HIF-dependent hypoxic gene activation. The other is as a pro-apoptotic factor by direct binding to the pro-survival protein Bcl-xL and its related proteins on mitochondria. Presently, the regulatory mechanism that determines the intracellular distribution of IPAS to fulfill each of the two functions is unknown. As a first step towards elucidation of the mechanism, nucleocytoplasmic transport signals of IPAS were explored. A bipartite-like nuclear localization signal (NLS) was found in the N-terminal region by the deletion and mutation analysis of EGFP-IPAS. In addition, the helix-loop-helix domain showed weak nuclear import/retention activity. A leptomycin B-sensitive nuclear export signal (NES) was localized in the C-terminal region of the protein. A proline-rich region supported the NES activity. These NLS and NES are not carried by the other variants of HIF-3α due to differential exon usage. These results strongly suggest that IPAS is a nucleocytoplasmic shuttling protein.
抑制性 Per/Arnt/Sim（PAS）结构域蛋白（IPAS）是缺氧诱导因子（HIF）-3α的剪接变体，具有两种完全不同的功能。一种是作为转录抑制剂，针对 HIF 依赖性缺氧基因激活。另一种是作为促凋亡因子，通过直接与线粒体上的生存蛋白 Bcl-xL 及其相关蛋白结合。目前，决定 IPAS 细胞内分布以实现两种功能的调节机制尚不清楚。作为阐明该机制的第一步，研究了 IPAS 的核质转运信号。通过 EGFP-IPAS 的缺失和突变分析，在 N 端区域发现了一个二聚体样核定位信号（NLS）。此外，螺旋-环-螺旋结构域表现出较弱的核输入/保留活性。一个莱普霉素 B 敏感的核输出信号（NES）定位于蛋白质的 C 端区域。一个富含脯氨酸的区域支持 NES 活性。这些 NLS 和 NES 由于外显子使用的差异，不存在于 HIF-3α 的其他变体中。这些结果强烈表明 IPAS 是一种核质穿梭蛋白。
