Hood Fiona E, Clarke Paul R
Biomedical Research Centre, Level 5, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
J Cell Sci. 2007 Oct 1;120(Pt 19):3436-45. doi: 10.1242/jcs.009092. Epub 2007 Sep 12.
RCC1 is the guanine nucleotide exchange factor for Ran GTPase. Generation of Ran-GTP by RCC1 on chromatin provides a spatial signal that directs nucleocytoplasmic transport, mitotic spindle assembly and nuclear envelope formation. We show that RCC1 is expressed in human cells as at least three isoforms, named RCC1alpha, RCC1beta and RCC1gamma, which are expressed at different levels in specific tissues. The beta and gamma isoforms contain short inserts in their N-terminal regions (NTRs) that are not present in RCC1alpha. This region mediates interaction with chromatin, binds importin alpha3 and/or importin beta, and contains regulatory phosphorylation sites. RCC1gamma is predominantly localised to the nucleus and mitotic chromosomes like RCC1alpha. However, compared to RCC1alpha, RCC1gamma has a greatly reduced interaction with an importin alpha3-beta and a stronger interaction with chromatin that is mediated by the extended NTR. RCC1gamma is also the isoform that is most highly phosphorylated at serine 11 in mitosis. Unlike RCC1alpha, RCC1gamma supports cell proliferation in tsBN2 cells more efficiently when serine 11 is mutated to non-phosphorylatable alanine. Phosphorylation of RCC1gamma therefore specifically controls its function during mitosis. These results show that human RCC1 isoforms have distinct chromatin binding properties, different molecular interactions, and are selectively regulated by phosphorylation, as determined by their different NTRs.
RCC1是Ran GTP酶的鸟嘌呤核苷酸交换因子。RCC1在染色质上生成Ran - GTP提供了一种空间信号，可指导核质运输、有丝分裂纺锤体组装和核膜形成。我们发现RCC1在人类细胞中至少以三种异构体形式表达，分别命名为RCC1α、RCC1β和RCC1γ，它们在特定组织中的表达水平不同。β和γ异构体在其N端区域（NTRs）含有RCC1α中不存在的短插入序列。该区域介导与染色质的相互作用，结合输入蛋白α3和/或输入蛋白β，并含有调节性磷酸化位点。RCC1γ像RCC1α一样主要定位于细胞核和有丝分裂染色体。然而，与RCC1α相比，RCC1γ与输入蛋白α3 - β的相互作用大大减少，而与由延长的NTR介导的染色质的相互作用更强。RCC1γ也是在有丝分裂过程中丝氨酸11处磷酸化程度最高的异构体。与RCC1α不同，当丝氨酸11突变为不可磷酸化的丙氨酸时，RCC1γ在tsBN2细胞中更有效地支持细胞增殖。因此，RCC1γ的磷酸化在有丝分裂期间特异性地控制其功能。这些结果表明，人类RCC1异构体具有不同的染色质结合特性、不同的分子相互作用，并由其不同的NTRs决定，通过磷酸化进行选择性调节。
