Maselli Andrew, Furukawa Ruth, Thomson Susanne A M, Davis Richard C, Fechheimer Marcus
Department of Cellular Biology, University of Georgia, Athens, Georgia 30602, USA.
Eukaryot Cell. 2003 Aug;2(4):778-87. doi: 10.1128/EC.2.4.778-787.2003.
Hirano bodies are paracrystalline actin filament-containing structures reported to be associated with a variety of neurodegenerative diseases. However, the biological function of Hirano bodies remains poorly understood, since nearly all prior studies of these structures were done with postmortem samples of tissue. In the present study, we generated a full-length form of a Dictyostelium 34-kDa actin cross-linking protein with point mutations in the first putative EF hand, termed 34-kDa DeltaEF1. The 34-kDa DeltaEF1 protein binds calcium normally but has activated actin binding that is unregulated by calcium. The expression of the 34-kDa DeltaEF1 protein in Dictyostelium induces the formation of Hirano bodies, as assessed by both fluorescence microscopy and transmission electron microscopy. Dictyostelium cells bearing Hirano bodies grow normally, indicating that Hirano bodies are not associated with cell death and are not deleterious to cell growth. Moreover, the expression of the 34-kDa DeltaEF1 protein rescues the phenotypes of cells lacking the 34-kDa protein and cells lacking both the 34-kDa protein and alpha-actinin. Finally, the expression of the 34-kDa DeltaEF1 protein also initiates the formation of Hirano bodies in cultured mouse fibroblasts. These results show that the failure to regulate the activity and/or affinity of an actin cross-linking protein can provide a signal for the formation of Hirano bodies. More generally, the formation of Hirano bodies is a cellular response to or a consequence of aberrant function of the actin cytoskeleton.
平野小体是一种含有平行排列肌动蛋白丝的结构，据报道与多种神经退行性疾病有关。然而，平野小体的生物学功能仍知之甚少，因为几乎所有关于这些结构的先前研究都是使用组织的尸检样本进行的。在本研究中，我们生成了一种盘基网柄菌34 kDa肌动蛋白交联蛋白的全长形式，其第一个假定的EF手结构域存在点突变，称为34 kDa DeltaEF1。34 kDa DeltaEF1蛋白能正常结合钙，但具有不受钙调节的激活肌动蛋白结合能力。通过荧光显微镜和透射电子显微镜评估，盘基网柄菌中34 kDa DeltaEF1蛋白的表达诱导了平野小体的形成。带有平野小体的盘基网柄菌细胞正常生长，这表明平野小体与细胞死亡无关，对细胞生长也无害。此外，34 kDa DeltaEF1蛋白的表达挽救了缺乏34 kDa蛋白的细胞以及同时缺乏34 kDa蛋白和α-辅肌动蛋白的细胞的表型。最后，34 kDa DeltaEF1蛋白的表达也在培养的小鼠成纤维细胞中引发了平野小体的形成。这些结果表明，未能调节肌动蛋白交联蛋白的活性和/或亲和力可提供平野小体形成的信号。更普遍地说，平野小体的形成是细胞对肌动蛋白细胞骨架异常功能的一种反应或结果。
