Casein kinase II phosphorylates the fragile X mental retardation protein and modulates its biological properties
Casein kinase II phosphorylates the fragile X mental retardation protein and modulates its biological properties
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DOI：
10.1128/mcb.22.24.8438-8447.2002
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发表时间：
2002-12-01
影响因子：
5.3
通讯作者：
Siomi, H
中科院分区：
文献类型：
--
作者：
Siomi, MC;Higashijima, K;Siomi, H
脆性X综合征是由FMR 1蛋白表达缺失引起的。FMR 1结合RNA并与细胞质中的多聚核糖体结合;因此，已提出在转录后水平上作为基因表达的调节剂发挥作用。先前已经提出FMR 1的翻译后修饰调节其活性，但迄今为止尚未报道该模型的实验支持。在这里，我们报告说，FMR 1在果蝇（dFMR 1）在体内磷酸化和同源体的形成和RNA结合活性的dFMR 1的调节磷酸化在体外。对磷酸化dFMR 1的蛋白质的鉴定表明它是果蝇酪蛋白激酶II（dCKII）。dCKII在体外直接与dFMRI相互作用并使其磷酸化。在dFMR 1的磷酸化位点被确定为Ser 406，这是高度保守的FMR 1家族成员从几个物种。使用质谱法，我们建立了dFMR 1的Ser 406确实在体内被磷酸化。此外，人FMR 1（hFMR 1）在体内也被磷酸化，并且hFMR 1中保守的Ser 500的改变在体外消除了CKII的磷酸化。这些研究支持FMR 1的生物学功能，如基因表达的调节，可能是由其磷酸化调节的模型。
Fragile X syndrome is caused by loss of FMR1 protein expression. FMR1 binds RNA and associates with polysomes in the cytoplasm; thus, it has been proposed to function as a regulator of gene expression at the posttranscriptional level. Posttranslational modification of FMR1 had previously been suggested to regulate its activity, but no experimental support for this model has been reported to date. Here we report that FMR1 in Drosophila melanogaster (dFMR1) is phosphorylated in vivo and that the homomer formation and the RNA-binding activities of dFMR1 are modulated by phosphorylation in vitro. Identification of a protein phosphorylating dFMR1 showed it to be Drosophild casein kinase II (dCKII). dCKII directly interacts with and phosphorylates dFMRI in vitro. The phosphorylation site in dFMR1 was identified as Ser406, which is highly conserved among FMR1 family members from several species. Using mass spectrometry, we established that Ser406 of dFMR1 is indeed phosphorylated in vivo. Furthermore, human FMR1 (hFMR1) is also phosphorylated in vivo, and alteration of the conserved Ser500 in hFMR1 abolishes phosphorylation by CKII in vitro. These studies support the model that the biological functions of FMR1, such as regulation of gene expression, are likely regulated by its phosphorylation.