Yu Yue, Maggi Leonard B, Brady Suzanne N, Apicelli Anthony J, Dai Mu-Shui, Lu Hua, Weber Jason D
Department of Internal Medicine, Division of Molecular Oncology, Siteman Cancer Center, Washington University School of Medicine, Campus Box 8069, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA.
Mol Cell Biol. 2006 May;26(10):3798-809. doi: 10.1128/MCB.26.10.3798-3809.2006.
Nucleophosmin (NPM/B23) is a key regulator in the regulation of a number of processes including centrosome duplication, maintenance of genomic integrity, and ribosome biogenesis. While the mechanisms underlying NPM function are largely uncharacterized, NPM loss results in severe dysregulation of developmental and growth-related events. We show that NPM utilizes a conserved CRM1-dependent nuclear export sequence in its amino terminus to enable its shuttling between the nucleolus/nucleus and cytoplasm. In search of NPM trafficking targets, we biochemically purified NPM-bound protein complexes from HeLa cell lysates. Consistent with NPM's proposed role in ribosome biogenesis, we isolated ribosomal protein L5 (rpL5), a known chaperone for the 5S rRNA. Direct interaction of NPM with rpL5 mediated the colocalization of NPM with maturing nuclear 60S ribosomal subunits, as well as newly exported and assembled 80S ribosomes and polysomes. Inhibition of NPM shuttling or loss of NPM blocked the nuclear export of rpL5 and 5S rRNA, resulting in cell cycle arrest and demonstrating that NPM and its nuclear export provide a unique and necessary chaperoning activity to rpL5/5S.
核磷蛋白（NPM/B23）是多种细胞过程的关键调节因子，这些过程包括中心体复制、基因组完整性维持以及核糖体生物合成。虽然NPM功能的潜在机制在很大程度上尚不明确，但NPM缺失会导致发育和生长相关事件的严重失调。我们发现，NPM在其氨基末端利用一个保守的依赖CRM1的核输出序列，使其能够在核仁/细胞核与细胞质之间穿梭。为了寻找NPM的运输靶点，我们从HeLa细胞裂解物中通过生化方法纯化了与NPM结合的蛋白复合物。与NPM在核糖体生物合成中所起的作用一致，我们分离出了核糖体蛋白L5（rpL5），它是一种已知的5S rRNA伴侣蛋白。NPM与rpL5的直接相互作用介导了NPM与成熟的核60S核糖体亚基以及新输出和组装的80S核糖体及多核糖体的共定位。抑制NPM穿梭或缺失NPM会阻断rpL5和5S rRNA的核输出，导致细胞周期停滞，并表明NPM及其核输出为rpL5/5S提供了一种独特且必要的伴侣活性。
