Zhang Yang, Gaetano Christian M, Williams Kathryn R, Bassell Gary J, Mihailescu Mihaela Rita
a Graduate School of Pharmaceutical Sciences; Mylan School of Pharmacy ; Duquesne University ; Pittsburgh , PA USA.
RNA Biol. 2014;11(11):1364-74. doi: 10.1080/15476286.2014.996464.
Fragile X syndrome (FXS), the most common cause of inherited intellectual disability, is caused by the loss of expression of the fragile X mental retardation protein (FMRP). FMRP, which regulates the transport and translation of specific mRNAs, uses its RGG box domain to bind mRNA targets that form G-quadruplex structures. One of the FMRP in vivo targets, Shank1 mRNA, encodes the master scaffold proteins of the postsynaptic density (PSD) which regulate the size and shape of dendritic spines because of their capacity to interact with many different PSD components. Due to their effect on spine morphology, altered translational regulation of Shank1 transcripts may contribute to the FXS pathology. We hypothesized that the FMRP interactions with Shank1 mRNA are mediated by the recognition of the G quadruplex structure, which has not been previously demonstrated. In this study we used biophysical techniques to analyze the Shank1 mRNA 3'-UTR and its interactions with FMRP and its phosphorylated mimic FMRP S500D. We found that the Shank1 mRNA 3 ' -UTR adopts two very stable intramolecular G-quadruplexes which are bound specifically and with high affinity by FMRP both in vitro and in vivo. These results suggest a role of G-quadruplex RNA motif as a structural element in the common mechanism of FMRP regulation of its dendritic mRNA targets.
脆性X综合征（FXS）是遗传性智力残疾的最常见原因，由脆性X智力低下蛋白（FMRP）表达缺失所致。FMRP可调节特定mRNA的转运和翻译，它利用其RGG框结构域结合形成G-四链体结构的mRNA靶标。FMRP在体内的靶标之一Shank1 mRNA编码突触后致密区（PSD）的主要支架蛋白，该蛋白因能与许多不同的PSD成分相互作用而调节树突棘的大小和形状。由于它们对棘形态的影响，Shank1转录本翻译调控的改变可能导致FXS病理改变。我们推测FMRP与Shank1 mRNA的相互作用是由对G-四链体结构的识别介导的，这一点此前尚未得到证实。在本研究中，我们使用生物物理技术分析了Shank1 mRNA的3'-UTR及其与FMRP及其磷酸化模拟物FMRP S500D的相互作用。我们发现，Shank1 mRNA的3'-UTR形成两个非常稳定的分子内G-四链体，在体外和体内均被FMRP特异性且高亲和力地结合。这些结果表明，G-四链体RNA基序作为一种结构元件，在FMRP对其树突mRNA靶标的调控共同机制中发挥作用。
