Inoue Akira, Tsugawa Katsuji, Tokunaga Kazuaki, Takahashi Kenichi P, Uni Shigehiko, Kimura Masatsugu, Nishio Koji, Yamamoto Naoki, Honda Ken-ichi, Watanabe Takanori, Yamane Hideo, Tani Tokio
Molecular Mechanisms of Biological Regulation, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan.
Biol Cell. 2008 Sep;100(9):523-35. doi: 10.1042/BC20070142.
The RNA-binding protein S1-1, also called RBM10 (RNA-binding motif 10), is a paralogue of putative tumour suppressor RBM5 and has been correlated with cancer proliferation and apoptosis. In the present study, we have investigated the cell biology of S1-1.
In the extranucleolar nucleoplasm, S1-1 occurred in hundreds of punctate and irregular domains. Some 10-40 of these domains were larger than 0.5 mum and prominent for S1-1 immunostaining. These domains (S1-1 nuclear bodies) were commonly present in tissue cells and in cultured cells. When cellular transcription was globally reduced by heat shock, serum starvation, culture at high cell densities or inhibition with RNA polymerase II inhibitors, small S1-1 domains (S1-1 granules), with weak immunostaining signals, reduced in number, whereas S1-1 nuclear bodies became prominent and increased in size. These altered S1-1 domains were returned to initial states when the cells were placed under normal conditions. Similar to paraspeckles, S1-1 nuclear bodies occurred closely adjacent to nuclear speckles or IGCs (interchromatin granule clusters), as determined by immunoelectron microscopy. However, the S1-1 nuclear bodies did not correspond to paraspeckles or IGAZs (interchromatin-granule-associated zones), but coincided with TIDRs (transcription-inactivation-dependent RNA domains), which we had characterized previously at the RNA level. The enlarged S1-1 nuclear bodies/TIDRs accumulated the S1-1 protein and microinjected primary and spliced mRNAs, presumably for later elevation of gene expression. In addition, electron microscopy revealed that S1-1 was also present on perichromatin fibrils, suggesting the structure of S1-1 granules seen at higher resolution.
S1-1 constitutes hundreds of nuclear domains, which dynamically change their structures in a reversible manner. Upon globally reducing RNA polymerase II transcription, S1-1 nuclear bodies enlarge and decrease in number. They are novel domains different from paraspeckles or IGAZs, despite their similar occurrence adjacent to nuclear speckles. We discuss S1-1 granules in terms of their association with gene expression. In addition, this is the first report of a TIDR-localized protein.
RNA结合蛋白S1-1，也称为RBM10（RNA结合基序10），是假定的肿瘤抑制因子RBM5的旁系同源物，与癌症增殖和凋亡相关。在本研究中，我们研究了S1-1的细胞生物学特性。
在核仁外核质中，S1-1出现在数百个点状和不规则结构域中。其中约10-40个结构域大于0.5μm，S1-1免疫染色明显。这些结构域（S1-1核体）普遍存在于组织细胞和培养细胞中。当通过热休克、血清饥饿、高细胞密度培养或用RNA聚合酶II抑制剂抑制使细胞全局转录降低时，具有弱免疫染色信号的小S1-1结构域（S1-1颗粒）数量减少，而S1-1核体变得突出且尺寸增大。当细胞置于正常条件下时，这些改变的S1-1结构域恢复到初始状态。通过免疫电子显微镜确定，与副斑点类似，S1-1核体紧邻核斑点或染色质间颗粒簇（IGC）出现。然而，S1-1核体并不对应于副斑点或染色质间颗粒相关区（IGAZ），而是与我们之前在RNA水平上鉴定的转录失活依赖性RNA结构域（TIDR）重合。扩大的S1-1核体/TIDR积累了S1-1蛋白以及显微注射的初级和剪接mRNA，推测这是为了随后提高基因表达。此外，电子显微镜显示S1-1也存在于染色质周围纤维上，这表明在更高分辨率下看到的S1-1颗粒的结构。
S1-1构成数百个核结构域，其结构以可逆方式动态变化。在全局降低RNA聚合酶II转录时，S1-1核体增大且数量减少。尽管它们在核斑点附近的出现情况相似，但它们是不同于副斑点或IGAZ的新型结构域。我们根据S1-1颗粒与基因表达的关联进行了讨论。此外，这是关于TIDR定位蛋白的首次报道。
