Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
Center for Advanced Genome Engineering, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
Nat Commun. 2024 Nov 11;15(1):9531. doi: 10.1038/s41467-024-53904-z.
NPM1 is an abundant nucleolar chaperone that, in addition to facilitating ribosome biogenesis, contributes to nucleolar stress responses and tumor suppression through its regulation of the p14 Alternative Reading Frame tumor suppressor protein (p14). Oncogenic stress induces p14 to inhibit MDM2, stabilize p53 and arrest the cell cycle. Under non-stress conditions, NPM1 stabilizes p14 in nucleoli, preventing its degradation and blocking p53 activation. However, the mechanisms underlying the regulation of p14 by NPM1 are unclear because the structural features of the p14-NPM1 complex were elusive. Here we show that p14 assembles into a gel-like meso-scale network upon phase separation with NPM1. This assembly is mediated by intermolecular contacts formed by hydrophobic residues in an α-helix and β-strands within a partially folded N-terminal portion of p14. These hydrophobic interactions promote phase separation with NPM1, enhance p14 nucleolar partitioning, restrict NPM1 diffusion within condensates and nucleoli, and reduce cellular proliferation. Our structural analysis provides insights into the multifaceted chaperone function of NPM1 in nucleoli by mechanistically linking the nucleolar localization of p14 to its partial folding and meso-scale assembly upon phase separation with NPM1.
NPM1 是一种丰富的核仁伴侣蛋白，除了促进核糖体生物发生外，还通过调节 p14 替代阅读框肿瘤抑制蛋白 (p14) 来参与核仁应激反应和肿瘤抑制。致癌应激诱导 p14 抑制 MDM2，稳定 p53 并使细胞周期停滞。在非应激条件下，NPM1 将 p14 稳定在核仁中，防止其降解并阻止 p53 激活。然而，NPM1 调节 p14 的机制尚不清楚，因为 p14-NPM1 复合物的结构特征难以捉摸。在这里，我们表明 p14 与 NPM1 相分离后会组装成凝胶状的介观网络。这种组装是由 p14 中一个α螺旋和β链内部分折叠的 N 端部分的疏水残基形成的分子间接触介导的。这些疏水相互作用促进与 NPM1 的相分离，增强 p14 的核仁分区，限制凝聚物和核仁内 NPM1 的扩散，并减少细胞增殖。我们的结构分析通过将 p14 的核仁定位与其与 NPM1 相分离时的部分折叠和介观组装在机制上联系起来，为 NPM1 在核仁中的多方面伴侣功能提供了深入的了解。
