Zhang Suisheng, Köhler Carsten, Hemmerich Peter, Grosse Frank
Department of Biochemistry, Institute of Molecular Biotechnology, Beutenbergstrasse 11, D-07708 Jena, Germany.
Exp Cell Res. 2004 Feb 15;293(2):248-58. doi: 10.1016/j.yexcr.2003.10.018.
Nuclear DNA helicase II (NDH II), alternatively named RNA helicase A (RHA), is an F-actin binding protein that is particularly enriched in the nucleolus of mouse cells. Here, we show that the nucleolar localization of NDH II of murine 3T3 cells depended on an ongoing rRNA synthesis. NDH II migrated out of the nucleolus after administration of 0.05 microg/ml actinomycin D, while nucleolin and the upstream binding factor (UBF) remained there. In S phase-arrested mouse cells, NDH II was frequently found at the nucleolar periphery, where it was accompanied by newly synthesized nucleolar RNA. Human NDH II was mainly distributed through the whole nucleoplasm and not enriched in the nucleoli. However, in the human breast carcinoma cell line MCF-7, NDH II was also found at the nucleolar periphery, together with the tumor suppressor protein p53. Both NDH II and p53 were apparently attached to the F-actin-based filamentous network that surrounded the nucleoli. Accordingly, this subnuclear structure was sensitive to F-actin depolymerizing agents. Depolymerization with gelsolin led to a striking accumulation of NDH II in the nucleoli of MCF-7 cells. This effect was abolished by RNase, which extensively released nucleolus-bound NDH II when added together with gelsolin. Taken together, these results support the idea that an actin-based filamentous network may anchor NDH II at the nucleolar periphery for pre-ribosomal RNA processing, ribosome assembly, and/or transport.
核DNA解旋酶II（NDH II），也被称为RNA解旋酶A（RHA），是一种F-肌动蛋白结合蛋白，在小鼠细胞的核仁中尤其丰富。在此，我们表明小鼠3T3细胞中NDH II的核仁定位依赖于正在进行的rRNA合成。在用0.05微克/毫升放线菌素D处理后，NDH II从核仁中移出，而核仁素和上游结合因子（UBF）仍留在那里。在处于S期阻滞的小鼠细胞中，经常在核仁周边发现NDH II，在那里它伴随着新合成的核仁RNA。人NDH II主要分布在整个核质中，在核仁中不富集。然而，在人乳腺癌细胞系MCF-7中，也在核仁周边发现了NDH II，同时还有肿瘤抑制蛋白p53。NDH II和p53显然都附着在围绕核仁的基于F-肌动蛋白的丝状网络上。因此，这种亚核结构对F-肌动蛋白解聚剂敏感。用凝溶胶蛋白解聚导致MCF-7细胞核仁中NDH II显著积累。当与凝溶胶蛋白一起添加时，RNase可消除这种效应，RNase能大量释放与核仁结合的NDH II。综上所述，这些结果支持这样一种观点，即基于肌动蛋白的丝状网络可能将NDH II锚定在核仁周边，用于核糖体前体RNA加工、核糖体组装和/或运输。
