NOM1 targets protein phosphatase I to the nucleolus
NOM1 targets protein phosphatase I to the nucleolus
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DOI：
10.1074/jbc.m706708200
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发表时间：
2008-01-04
影响因子：
4.8
通讯作者：
Conklin, Kathleen F.
中科院分区：
文献类型：
--
作者：
Gunawardena, Shanaka R.;Ruis, Brian L.;Conklin, Kathleen F.
蛋白磷酸酶I（PP 1）是一种重要的真核生物丝氨酸/苏氨酸磷酸酶，参与细胞分裂、信号转导和代谢等多种细胞过程。在哺乳动物细胞中，有三种主要的PP 1催化亚基亚型（PP 1 α、PP 1 β和PP 1 γ），它们具有超过90%的相同性。尽管这种高度的同一性，PP 1催化亚基在间期细胞中显示出不同的定位模式; PP 1 α主要是核，并在很大程度上排除了核仁，而PP 1 γ和较小程度上PP 1 β集中在核仁中。PP 1催化亚基的亚细胞定位和底物特异性由它们与靶向亚基的相互作用决定，其中大多数通过所谓的“RVXF”序列结合PP 1。虽然PP 1靶向亚基已被确定，指导PP 1的亚细胞位置和/或底物的数量，没有靶向亚基已被确定定位PP 1的核仁。核仁PP 1靶向亚基的鉴定很重要，因为所有三种PP 1亚型都包含在核仁蛋白质组中，具有酶活性的PP 1存在于核仁中，而PP 1 γ高度集中在间期细胞的核仁中。在这项研究中，我们确定NOM 1（核仁蛋白与MIF 4G结构域1）作为PP 1相互作用的蛋白质，并进一步确定NOM 1 RVXF基序所需的结合PP 1。我们还定义了NOM 1的核仁定位序列。最后，我们证明了NOM 1可以将PP 1靶向到核仁，并表明这种靶向活性需要特定的NOM 1 RVXF基序和NOM 1核仁定位序列。因此，我们得出结论，NOM 1是PP 1核仁靶向亚基，在真核细胞中首次发现。
Protein phosphatase I (PP1) is an essential eukaryotic serine/threonine phosphatase required for many cellular processes, including cell division, signaling, and metabolism. In mammalian cells there are three major isoforms of the PP1 catalytic subunit (PP1 alpha, PP1 beta, and PP1 gamma) that are over 90% identical. Despite this high degree of identity, the PP1 catalytic subunits show distinct localization patterns in interphase cells; PP1 alpha is primarily nuclear and largely excluded from nucleoli, whereas PP1 gamma and to a lesser extent PP1 beta concentrate in the nucleoli. The subcellular localization and the substrate specificity of PP1 catalytic subunits are determined by their interaction with targeting subunits, most of which bind PP1 through a so-called "RVXF" sequence. Although PP1 targeting subunits have been identified that direct PP1 to a number of subcellular locations and/or substrates, no targeting subunit has been identified that localizes PP1 to the nucleolus. Identification of nucleolar PP1 targeting subunit(s) is important because all three PP1 isoforms are included in the nucleolar proteome, enzymatically active PP1 is present in nucleoli, and PP1 gamma is highly concentrated in nucleoli of interphase cells. In this study, we identify NOM1 ( nucleolar protein with MIF4G domain 1) as a PP1-interacting protein and further identify the NOM1 RVXF motif required for its binding to PP1. We also define the NOM1 nucleolar localization sequence. Finally, we demonstrate that NOM1 can target PP1 to the nucleolus and show that a specific NOM1 RVXF motif and the NOM1 nucleolar localization sequence are required for this targeting activity. We therefore conclude that NOM1 is a PP1 nucleolar targeting subunit, the first identified in eukaryotic cells.