The Mina & Everard Goodman Faculty of Life Sciences & Institute of Nanotechnology, Bar-Ilan University, Ramat Gan 5290002, Israel.
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
Nucleic Acids Res. 2019 May 21;47(9):4778-4797. doi: 10.1093/nar/gkz168.
Eukaryotic cells contain sub-cellular compartments that are not membrane bound. Some structures are always present, such as nuclear speckles that contain RNA-binding proteins (RBPs) and poly(A)+ RNAs. Others, like cytoplasmic stress granules (SGs) that harbor mRNAs and RBPs, are induced upon stress. When we examined the formation and composition of nuclear speckles during stress induction with tubercidin, an adenosine analogue previously shown to affect nuclear speckle composition, we unexpectedly found that it also led to the formation of SGs and to the inhibition of several crucial steps of RNA metabolism in cells, thereby serving as a potent inhibitor of the gene expression pathway. Although transcription and splicing persisted under this stress, RBPs and mRNAs were mislocalized in the nucleus and cytoplasm. Specifically, lncRNA and RBP localization to nuclear speckles was disrupted, exon junction complex (EJC) recruitment to mRNA was reduced, mRNA export was obstructed, and cytoplasmic poly(A)+ RNAs localized in SGs. Furthermore, nuclear proteins that participate in mRNA export, such as nucleoporins and mRNA export adaptors, were mislocalized to SGs. This study reveals structural aspects of granule assembly in cells, and describes how the flow of RNA from the nucleus to the cytoplasm is severed under stress.
真核细胞含有非膜结合的亚细胞区室。有些结构总是存在的，如核斑点，它包含 RNA 结合蛋白 (RBPs) 和 poly(A)+RNAs。另一些结构，如细胞质应激颗粒 (SGs)，它含有 mRNAs 和 RBPs，是在应激时诱导产生的。当我们用先前显示影响核斑点组成的腺嘌呤类似物 tubercidin 研究应激诱导时核斑点的形成和组成时，我们意外地发现它也导致 SGs 的形成，并抑制细胞中几个关键的 RNA 代谢步骤，从而成为基因表达途径的有效抑制剂。尽管在这种应激下转录和剪接仍在继续，但 RBPs 和 mRNAs 在核内和细胞质中发生了定位错误。具体来说，lncRNA 和 RBP 定位到核斑点的能力被破坏，mRNA 上的外显子结合复合物 (EJC)募集减少，mRNA 输出受阻，细胞质 poly(A)+RNAs 定位到 SGs 中。此外，参与 mRNA 输出的核蛋白，如核孔蛋白和 mRNA 输出适配器，被错误地定位到 SGs 中。这项研究揭示了细胞中颗粒组装的结构方面，并描述了在应激下 RNA 从细胞核到细胞质的流动是如何被切断的。
