Institute of Biochemistry and Molecular Biology, National Yang Ming University, Taipei 112, Taiwan.
Biochem J. 2012 Jan 1;441(1):119-29. doi: 10.1042/BJ20110739.
Upon environmental insults, SGs (stress granules) aid cell survival by serving as sites of translational silencing. RNA helicase DDX3 was reported to associate with SGs. However, its role in SG physiology remains undefined. We have demonstrated previously that DDX3 acts as an eIF4E (eukaryotic initiation factor 4E)-inhibitory protein to suppress translation. In the present study, we indentified the SG marker PABP1 [poly(A)-binding protein 1] as another direct interaction partner of DDX3. We established various stimuli as novel stressors that direct DDX3 with eIF4E and PABP1 into SGs, but not to processing bodies. Interestingly, down-regulation of DDX3 interfered with SG assembly, led to nuclear accumulation of PABP1 and reduced cell viability following stress. Conversely, supplementation with a shRNA (short hairpin RNA)-resistant DDX3 restored SG formation, the translocation of PABP1 into SGs and cell survival. Notably, the SG-inducing capacity of DDX3 is independent of its ATPase and helicase activities, but mapped to the eIF4E-binding region. Moreover, the eIF4E-binding-defective mutant DDX3 was impaired in its SG-inducing ability and protective effect on cell survival under adverse conditions. All together, the present study has characterized DDX3 as a pivotal SG-nucleating factor and illustrates co-ordinative roles for DDX3, eIF4E and PABP1 in integrating environmental stress with translational regulation.
在受到环境压力时，SG（应激颗粒）通过充当翻译沉默的位点来帮助细胞存活。据报道，RNA 解旋酶 DDX3 与 SG 相关联。然而，其在 SG 生理学中的作用尚未确定。我们之前已经证明，DDX3 作为 eIF4E（真核起始因子 4E）抑制蛋白发挥作用，抑制翻译。在本研究中，我们鉴定了 SG 标记物 PABP1[多聚（A）结合蛋白 1]作为 DDX3 的另一个直接相互作用伙伴。我们确定了各种刺激作为新的应激源，将 DDX3 与 eIF4E 和 PABP1 一起引导到 SG 中，而不是到处理体中。有趣的是，下调 DDX3 会干扰 SG 的组装，导致 PABP1 核积累，并在应激后降低细胞活力。相反，补充具有 shRNA（短发夹 RNA）抗性的 DDX3 恢复了 SG 的形成、PABP1 向 SG 的易位以及细胞的存活。值得注意的是，DDX3 的 SG 诱导能力与其 ATPase 和解旋酶活性无关，但与 eIF4E 结合区有关。此外，DDX3 的 eIF4E 结合缺陷突变体在其 SG 诱导能力和在不利条件下对细胞存活的保护作用受损。总之，本研究将 DDX3 表征为关键的 SG 成核因子，并说明了 DDX3、eIF4E 和 PABP1 在整合环境压力与翻译调节方面的协调作用。
