Katahira Jun, Miki Takashi, Takano Keizo, Maruhashi Mitsuji, Uchikawa Masanori, Tachibana Taro, Yoneda Yoshihiro
Biomolecular Networks Laboratories, Biomolecular Dynamics Laboratory, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Japan.
Nucleic Acids Res. 2008 Feb;36(2):616-28. doi: 10.1093/nar/gkm556. Epub 2007 Dec 5.
The nuclear RNA export factor (NXF) family proteins have been implicated in various aspects of post-transcriptional gene expression. This study shows that mouse NXF7 exhibits heterologous localization, i.e. NXF7 associates with translating ribosomes, stress granules (SGs) and processing bodies (P-bodies), the latter two of which are believed to be cytoplasmic sites of storage, degradation and/or sorting of mRNAs. By yeast two-hybrid screening, a series of heterogeneous nuclear ribonucleoproteins (hnRNPs) were identified as possible binding partners for NXF7. Among them, hnRNP A3, which is believed to be involved in translational control and/or cytoplasmic localization of certain mRNAs, formed a stable complex with NXF7 in vitro. Although hnRNP A3 was not associated with translating ribosomes, it was co-localized with NXF7 in P-bodies. After exposing to oxidative stress, NXF7 trans-localized to SGs, whereas hnRNP A3 did not. In differentiated neuroblastoma Neuro2a cells, NXF7 was co-localized with hnRNP A3 in cell body and neurites. The amino terminal half of NXF7, which was required for stable complex formation with hnRNP A3, coincided with the region required for localization in both P-bodies and neuronal RNA granules. These findings suggest that NXF7 plays a role in sorting, transport and/or storage of mRNAs through interactions with hnRNP A3.
核RNA输出因子（NXF）家族蛋白与转录后基因表达的各个方面有关。本研究表明，小鼠NXF7表现出异源定位，即NXF7与正在翻译的核糖体、应激颗粒（SGs）和加工小体（P小体）相关联，后两者被认为是mRNA储存、降解和/或分选的细胞质位点。通过酵母双杂交筛选，一系列异质性核核糖核蛋白（hnRNPs）被鉴定为NXF7可能的结合伴侣。其中，据信参与某些mRNA翻译控制和/或细胞质定位的hnRNP A3在体外与NXF7形成了稳定的复合物。虽然hnRNP A3不与正在翻译的核糖体相关联，但它与NXF7在P小体中共定位。在暴露于氧化应激后，NXF7转位至SGs，而hnRNP A3则没有。在分化的神经母细胞瘤Neuro2a细胞中，NXF7与hnRNP A3在细胞体和神经突中共定位。NXF7与hnRNP A3形成稳定复合物所需的氨基末端一半，与在P小体和神经元RNA颗粒中定位所需的区域一致。这些发现表明，NXF7通过与hnRNP A3相互作用，在mRNA的分选、运输和/或储存中发挥作用。
