Characterization of human Smg5/7a:: A protein with similarities to Caenorhabditis elegans SMG5 and SMG7 that functions in the dephosphorylation of Upf1
Characterization of human Smg5/7a:: A protein with similarities to Caenorhabditis elegans SMG5 and SMG7 that functions in the dephosphorylation of Upf1
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DOI：
10.1261/rna.2137903
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发表时间：
2003-01-01
期刊：
影响因子：
4.5
通讯作者：
Maquat, LE
中科院分区：
文献类型：
--
作者：
Chiu, SY;Serin, G;Maquat, LE
哺乳动物细胞中无意义介导的mRNA衰退(NMD)依赖于UPF1的磷酸化，UPF1是一种依赖于RNA的ATPase和5‘-to-3’螺旋酶。UPF1的磷酸化是由SMG1介导的，SMG1是一种与磷酸肌醇3-激酶相关的蛋白激酶。在这里，我们描述了一种人类蛋白，我们称之为hSmg5/7a，它与秀丽线虫NMD因子CeSMG5和CeSMG7以及两个也与秀丽线虫NMD因子相似的果蝇黑腹蛋白相似。结果表明，hSmg5/7a在UPF1的去磷酸化中起作用。此外，hSmg5/7a与UPF1、Upf2、Upf3X、SMG1和蛋白磷酸酶2A的催化亚基相互作用。我们还证明了参与NMD的另一个因子Upf2是一种磷酸蛋白。然而，hSmg5/7a在Upf2的去磷酸化过程中没有作用。这些数据表明，hSmg5/7a靶向蛋白磷酸酶2A到UPF1，而不是UPF2。Western blotting结果表明，hSmg5/7a在HEK293T细胞中主要为胞质。
Nonsense-mediated mRNA decay (NMD) in mammalian cells depends on phosphorylation of Upf1, an RNA-dependent ATPase and 5'-to-3' helicase. Upf1 phosphorylation is mediated by Smg1, a phosphoinositol 3-kinase-related protein kinase. Here, we describe a human protein, which we call hSmg5/7a, that manifests similarity to Caenorhabditis elegans NMD factors CeSMG5 and CeSMG7, as well as two Drosophila melanogaster proteins that are also similar to the C elegans NMD factors. Results indicate that hSmg5/7a functions in the dephosphorylation of Upf1. Furthermore, hSmg5/7a copurifies with Upf1, Upf2, Upf3X, Smg1, and the catalytic subunit of protein phosphatase 2A. We also demonstrate that Upf2, another factor involved in NMD, is a phosphoprotein. However, hSmg5/7a plays no role in the dephosphorylation of Upf2. These data indicate that hSmg5/7a targets protein phosphatase 2A to Upf1 but not Upf2. Results of Western blotting reveal that hSmg5/7a is mostly cytoplasmic in HEK293T cells.