J Biol Chem. 2014 Jul 25;289(30):21163-80. doi: 10.1074/jbc.M114.556365.
RNA granules are large messenger ribonucleoprotein complexes that regulate translation and mRNA translocation to control the timing and location of protein synthesis. The regulation of RNA granule assembly and disassembly is a structural basis of translational control, and its disorder is implicated in degenerative disease. Here, we used proteomic analysis to identify proteins associated with RNA granule protein 105 (RNG105)/caprin1, an RNA-binding protein in RNA granules. Among the identified proteins, we focused on nuclear factor (NF) 45 and its binding partner, nuclear factor associated with dsRNA 2 (NFAR2), and we demonstrated that NF45 promotes disassembly of RNA granules, whereas NFAR2 enhances the assembly of RNA granules in cultured cells. The GQSY domain of NFAR2 was required to associate with messenger ribonucleoprotein complexes containing RNG105/caprin1, and it was structurally and functionally related to the low complexity sequence domain of the fused in sarcoma protein, which drives the assembly of RNA granules. Another domain of NFAR2, the DZF domain, was dispensable for association with the RNG105 complex, but it was involved in positive and negative regulation of RNA granule assembly by being phosphorylated at double-stranded RNA-activated kinase sites and by association with NF45, respectively. These results suggest a novel molecular mechanism for the modulation of RNA granule assembly and disassembly by NFAR2, NF45, and phosphorylation at double-stranded RNA-activated kinase PKR sites.
RNA 颗粒是大型信使核糖核蛋白复合物，可调节翻译和 mRNA 易位，以控制蛋白质合成的时间和位置。RNA 颗粒组装和拆卸的调节是翻译控制的结构基础，其无序与退行性疾病有关。在这里，我们使用蛋白质组学分析来鉴定与 RNA 颗粒蛋白 105（RNG105）/帽蛋白 1 相关的蛋白质，该蛋白是 RNA 颗粒中的 RNA 结合蛋白。在鉴定的蛋白质中，我们专注于核因子（NF）45 及其结合伴侣双链 RNA 相关核因子 2（NFAR2），并证明 NF45 促进 RNA 颗粒的解体，而 NFAR2 增强培养细胞中 RNA 颗粒的组装。NFAR2 的 GQSY 结构域需要与含有 RNG105/帽蛋白 1 的信使核糖核蛋白复合物结合，并且与肉瘤融合蛋白的低复杂度序列结构域在结构和功能上相关，该序列结构域驱动 RNA 颗粒的组装。NFAR2 的另一个结构域 DZF 结构域对于与 RNG105 复合物的结合是可有可无的，但它通过在双链 RNA 激活激酶位点磷酸化以及与 NF45 结合，分别参与 RNA 颗粒组装的正向和负向调节。这些结果表明 NFAR2、NF45 和双链 RNA 激活激酶 PKR 位点磷酸化通过一种新的分子机制来调节 RNA 颗粒的组装和解体。
