Choo Hyo-Jung, Cutler Alicia, Rother Franziska, Bader Michael, Pavlath Grace K
Department of Pharmacology.
Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University, Atlanta, Georgia, USA.
Stem Cells. 2016 Nov;34(11):2784-2797. doi: 10.1002/stem.2467. Epub 2016 Aug 1.
Satellite cells are stem cells with an essential role in skeletal muscle repair. Precise regulation of gene expression is critical for proper satellite cell quiescence, proliferation, differentiation and self-renewal. Nuclear proteins required for gene expression are dependent on the nucleocytoplasmic transport machinery to access to nucleus, however little is known about regulation of nuclear transport in satellite cells. The best characterized nuclear import pathway is classical nuclear import which depends on a classical nuclear localization signal (cNLS) in a cargo protein and the heterodimeric import receptors, karyopherin alpha (KPNA) and beta (KPNB). Multiple KPNA1 paralogs exist and can differ in importing specific cNLS proteins required for cell differentiation and function. We show that transcripts for six Kpna paralogs underwent distinct changes in mouse satellite cells during muscle regeneration accompanied by changes in cNLS proteins in nuclei. Depletion of KPNA1, the most dramatically altered KPNA, caused satellite cells in uninjured muscle to prematurely activate, proliferate and undergo apoptosis leading to satellite cell exhaustion with age. Increased proliferation of satellite cells led to enhanced muscle regeneration at early stages of regeneration. In addition, we observed impaired nuclear localization of two key KPNA1 cargo proteins: p27, a cyclin-dependent kinase inhibitor associated with cell cycle control and lymphoid enhancer factor 1, a critical cotranscription factor for β-catenin. These results indicate that regulated nuclear import of proteins by KPNA1 is critical for satellite cell proliferation and survival and establish classical nuclear import as a novel regulatory mechanism for controlling satellite cell fate. Stem Cells 2016;34:2784-2797.
卫星细胞是在骨骼肌修复中起关键作用的干细胞。基因表达的精确调控对于卫星细胞的静止、增殖、分化和自我更新至关重要。基因表达所需的核蛋白依赖于核质运输机制进入细胞核，然而，关于卫星细胞中核运输的调控知之甚少。最具特征的核输入途径是经典核输入，它依赖于货物蛋白中的经典核定位信号（cNLS）以及异二聚体输入受体核转运蛋白α（KPNA）和β（KPNB）。存在多个KPNA1旁系同源物，它们在导入细胞分化和功能所需的特定cNLS蛋白方面可能有所不同。我们发现，在肌肉再生过程中，小鼠卫星细胞中六个Kpna旁系同源物的转录本发生了明显变化，同时细胞核中的cNLS蛋白也发生了变化。KPNA1是变化最显著的KPNA，其缺失导致未受伤肌肉中的卫星细胞过早激活、增殖并发生凋亡，随着年龄增长导致卫星细胞耗竭。卫星细胞增殖增加导致再生早期肌肉再生增强。此外，我们观察到两种关键的KPNA1货物蛋白的核定位受损：p27，一种与细胞周期控制相关的细胞周期蛋白依赖性激酶抑制剂；以及淋巴样增强因子1，一种β-连环蛋白的关键共转录因子。这些结果表明，KPNA1对蛋白质的调控核输入对于卫星细胞的增殖和存活至关重要，并确立经典核输入作为控制卫星细胞命运的一种新型调控机制。《干细胞》2016年；34卷：2784 - 2797页
