Yamaguchi Atsushi, Takanashi Keisuke
Department of Neurobiology, Graduate School of Medicine, Chiba University, Chiba, Japan.
Sci Rep. 2016 Oct 12;6:35195. doi: 10.1038/srep35195.
FUS (Fused-in-Sarcoma) is a multifunctional DNA/RNA binding protein linked to familial amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). Since FUS is localized mainly in the nucleus with nucleo-cytoplasmic shuttling, it is critical to understand physiological functions in the nucleus to clarify pathogenesis. Here we report a yeast two-hybrid screening identified FUS interaction with nuclear matrix-associated protein SAFB1 (scaffold attachment factor B1). FUS and SAFB1, abundant in chromatin-bound fraction, interact in a DNA-dependent manner. N-terminal SAP domain of SAFB1, a DNA-binding motif, was required for its localization to chromatin-bound fraction and splicing regulation. In addition, depletion of SAFB1 reduced FUS's localization to chromatin-bound fraction and splicing activity, suggesting SAFB1 could tether FUS to chromatin compartment thorough N-terminal DNA-binding motif. FUS and SAFB1 also interact with Androgen Receptor (AR) regulating ligand-dependent transcription. Moreover, FUS interacts with another nuclear matrix-associated protein Matrin3, which is muted in a subset of familial ALS cases and reportedly interacts with TDP-43. Interestingly, ectopic ALS-linked FUS mutant sequestered endogenous Matrin3 and SAFB1 in the cytoplasmic aggregates. These findings indicate SAFB1 could be a FUS's functional platform in chromatin compartment to regulate RNA splicing and ligand-dependent transcription and shed light on the etiological significance of nuclear matrix-associated proteins in ALS pathogenesis.
FUS（肉瘤融合蛋白）是一种多功能DNA/RNA结合蛋白，与家族性肌萎缩侧索硬化症/额颞叶痴呆（ALS/FTD）相关。由于FUS主要定位于细胞核并在核质间穿梭，了解其在细胞核中的生理功能对于阐明发病机制至关重要。在此，我们报告通过酵母双杂交筛选发现FUS与核基质相关蛋白SAFB1（支架附着因子B1）相互作用。FUS和SAFB1在染色质结合组分中含量丰富，以DNA依赖的方式相互作用。SAFB1的N端SAP结构域是一种DNA结合基序，是其定位于染色质结合组分和剪接调控所必需的。此外，SAFB1的缺失降低了FUS在染色质结合组分中的定位和剪接活性，表明SAFB1可通过N端DNA结合基序将FUS拴系到染色质区室。FUS和SAFB1还与调节配体依赖性转录的雄激素受体（AR）相互作用。此外，FUS与另一种核基质相关蛋白Matrin3相互作用，Matrin3在一部分家族性ALS病例中发生突变且据报道与TDP-43相互作用。有趣的是，异位表达的与ALS相关的FUS突变体将内源性Matrin3和SAFB1隔离在细胞质聚集体中。这些发现表明SAFB1可能是FUS在染色质区室中调节RNA剪接和配体依赖性转录的功能平台，并揭示了核基质相关蛋白在ALS发病机制中的病因学意义。
