Endo Akinori, Matsumoto Masaki, Inada Toshifumi, Yamamoto Akitsugu, Nakayama Keiichi I, Kitamura Naomi, Komada Masayuki
Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
J Cell Sci. 2009 Mar 1;122(Pt 5):678-86. doi: 10.1242/jcs.044461. Epub 2009 Feb 10.
The nucleolus is a subnuclear compartment and the site of ribosome biogenesis. Previous studies have implicated protein ubiquitylation in nucleolar activity. Here we show that USP36, a deubiquitylating enzyme of unknown function, regulates nucleolar activity in mammalian cells. USP36 localized to nucleoli via the C-terminal region, which contains basic amino acid stretches. Dominant-negative inhibition of USP36 caused the accumulation of ubiquitin-protein conjugates in nucleoli, suggesting that nucleoli are the site of USP36 action. USP36 deubiquitylated the nucleolar proteins nucleophosmin/B23 and fibrillarin, and stabilized them by counteracting ubiquitylation-mediated proteasomal degradation. RNAi-mediated depletion of cellular USP36 resulted in reduced levels of rRNA transcription and processing, a less-developed nucleolar morphology and a slight reduction in the cytoplasmic ribosome level, which eventually led to a reduced rate of cell proliferation. We conclude that by deubiquitylating various nucleolar substrate proteins including nucleophosmin/B23 and fibrillarin, USP36 plays a crucial role in regulating the structure and function of nucleoli.
核仁是一种亚核区室，也是核糖体生物发生的场所。先前的研究表明蛋白质泛素化与核仁活性有关。在此我们表明，USP36，一种功能未知的去泛素化酶，在哺乳动物细胞中调节核仁活性。USP36通过包含碱性氨基酸序列的C末端区域定位于核仁。对USP36的显性负抑制导致泛素 - 蛋白质缀合物在核仁中积累，这表明核仁是USP36的作用位点。USP36使核仁蛋白核磷蛋白/B23和纤维蛋白原去泛素化，并通过抵消泛素化介导的蛋白酶体降解来使其稳定。RNAi介导的细胞USP36缺失导致rRNA转录和加工水平降低、核仁形态发育不良以及细胞质核糖体水平略有降低，最终导致细胞增殖速率降低。我们得出结论，通过使包括核磷蛋白/B23和纤维蛋白原在内的各种核仁底物蛋白去泛素化，USP36在调节核仁的结构和功能中起关键作用。
