den Engelsman John, Gerrits Danny, de Jong Wilfried W, Robbins Jeffrey, Kato Kanefusa, Boelens Wilbert C
Department of Biochemistry 161, Nijmegen Center for Molecular Life Sciences, Radboud University of Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
J Biol Chem. 2005 Nov 4;280(44):37139-48. doi: 10.1074/jbc.M504106200. Epub 2005 Aug 28.
Phosphorylation modulates the functioning of alphaB-crystallin as a molecular chaperone. We here explore the role of phosphorylation in the nuclear import and cellular localization of alphaB-crystallin in HeLa cells. Inhibition of nuclear export demonstrated that phosphorylation of alphaB-crystallin is required for import into the nucleus. As revealed by mutant analysis, phosphorylation at Ser-59 is crucial for nuclear import, and phosphorylation at Ser-45 is required for speckle localization. Co-immunoprecipitation experiments suggested that the import of alphaB-crystallin is possibly regulated by its phosphorylation-dependent interaction with the survival motor neuron (SMN) protein, an important factor in small nuclear ribonucleoprotein nuclear import and assembly. This interaction was supported by co-localization of endogenous phosphorylated alphaB-crystallin with SMN in nuclear structures. The cardiomyopathy-causing alphaB-crystallin mutant R120G was found to be excessively phosphorylated, which disturbed SMN interaction and nuclear import, and resulted in the formation of cytoplasmic inclusions. Like for other protein aggregation disorders, hyperphosphorylation appears as an important aspect of the pathogenicity of alphaB-crystallin R120G.
磷酸化可调节αB-晶状体蛋白作为分子伴侣的功能。我们在此探讨磷酸化在HeLa细胞中αB-晶状体蛋白的核输入和细胞定位中的作用。核输出抑制表明，αB-晶状体蛋白的磷酸化是其进入细胞核所必需的。突变分析显示，Ser-59位点的磷酸化对核输入至关重要，而Ser-45位点的磷酸化是斑点定位所必需的。免疫共沉淀实验表明，αB-晶状体蛋白的输入可能受其与生存运动神经元（SMN）蛋白的磷酸化依赖性相互作用调控，SMN蛋白是小核核糖核蛋白核输入和组装中的一个重要因子。内源性磷酸化αB-晶状体蛋白与SMN在核结构中的共定位支持了这种相互作用。发现导致心肌病的αB-晶状体蛋白突变体R120G过度磷酸化，这扰乱了SMN相互作用和核输入，并导致细胞质内含物的形成。与其他蛋白质聚集疾病一样，过度磷酸化似乎是αB-晶状体蛋白R120G致病性的一个重要方面。
