MRC Cancer Cell Unit, Hutchison/MRC Research Centre, Hills Road, Cambridge CB2 0XZ, UK.
Curr Biol. 2010 Jan 12;20(1):25-31. doi: 10.1016/j.cub.2009.10.078. Epub 2009 Dec 10.
Bulk nuclear export of messenger ribonucleoproteins (mRNPs) through nuclear pore complexes (NPCs) is mediated by NXF1. It binds mRNPs through adaptor proteins such as ALY and SR splicing factors and mediates translocation through the central NPC transport channel via transient interactions with FG nucleoporins. Here, we show that mammalian cells require GANP (germinal center-associated nuclear protein) for efficient mRNP nuclear export and for efficient recruitment of NXF1 to NPCs. Separate regions of GANP show local homology to FG nucleoporins, the yeast mRNA export factor Sac3p, and the mammalian MCM3 acetyltransferase. GANP interacts with both NXF1 and NPCs and partitions between NPCs and the nuclear interior. GANP depletion inhibits mRNA export, with retention of mRNPs and NXF1 in punctate foci within the nucleus. The GANP N-terminal region that contains FG motifs interacts with the NXF1 FG-binding domain. Overexpression of this GANP fragment leads to nuclear accumulation of both poly(A)(+)RNA and NXF1. Treatment with transcription inhibitors redistributes GANP from NPCs into foci throughout the nucleus. These results establish GANP as an integral component of the mammalian mRNA export machinery and suggest a model whereby GANP facilitates the transfer of NXF1-containing mRNPs to NPCs.
通过核孔复合物（NPC）的信使核糖核蛋白（mRNP）的批量核输出是由 NXF1 介导的。它通过衔接蛋白（如ALY 和 SR 剪接因子）与 mRNP 结合，并通过与 FG 核孔蛋白的瞬时相互作用，介导穿过中央 NPC 转运通道的易位。在这里，我们表明哺乳动物细胞需要 GANP（生殖中心相关核蛋白）来有效地进行 mRNP 核输出，并有效地将 NXF1 募集到 NPC 上。GANP 的不同区域与 FG 核孔蛋白、酵母 mRNA 出口因子 Sac3p 和哺乳动物 MCM3 乙酰转移酶具有局部同源性。GANP 与 NXF1 和 NPC 相互作用，并在 NPC 和核内部之间分配。GANP 耗竭会抑制 mRNA 输出，导致 mRNP 和 NXF1 在核内点状焦点中滞留。含有 FG 基序的 GANP N 端区域与 NXF1 的 FG 结合域相互作用。该 GANP 片段的过表达导致多聚（A）（+）RNA 和 NXF1 在核内的积累。转录抑制剂的处理将 GANP 从 NPC 重新分配到整个核内的焦点中。这些结果确立了 GANP 作为哺乳动物 mRNA 出口机制的一个组成部分，并提出了一种模型，即 GANP 促进含有 NXF1 的 mRNP 向 NPC 的转移。
