Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, Salt Lake City, UT 84132, USA.
Hum Mol Genet. 2012 Feb 1;21(3):692-710. doi: 10.1093/hmg/ddr503. Epub 2011 Nov 2.
Whirlin mutations cause retinal degeneration and hearing loss in Usher syndrome type II (USH2) and non-syndromic deafness, DFNB31. Its protein recruits other USH2 causative proteins to form a complex at the periciliary membrane complex in photoreceptors and the ankle link of the stereocilia in hair cells. However, the biological function of this USH2 protein complex is largely unknown. Using a yeast two-hybrid screen, we identified espin, an actin-binding/bundling protein involved in human deafness when defective, as a whirlin-interacting protein. The interaction between these two proteins was confirmed by their coimmunoprecipitation and colocalization in cultured cells. This interaction involves multiple domains of both proteins and only occurs when espin does not bind to actin. Espin was partially colocalized with whirlin in the retina and the inner ear. In whirlin knockout mice, espin expression changed significantly in these two tissues. Further studies found that whirlin increased the mobility of espin and actin at the actin bundles cross-linked by espin and, eventually, affected the dimension of these actin bundles. In whirlin knockout mice, the stereocilia were thickened in inner hair cells. We conclude that the interaction between whirlin and espin and the balance between their expressions are required to maintain the actin bundle network in photoreceptors and hair cells. Disruption of this actin bundle network contributes to the pathogenic mechanism of hearing loss and retinal degeneration caused by whirlin and espin mutations. Espin is a component of the USH2 protein complex and could be a candidate gene for Usher syndrome.
Whirlin 突变导致 Usher 综合征 II 型（USH2）和非综合征性耳聋、DFNB31 的视网膜变性和听力损失。其蛋白将其他 USH2 致病蛋白募集到光感受器的纤毛膜复合体和毛细胞的静纤毛踝部，形成复合物。然而，这个 USH2 蛋白复合物的生物学功能在很大程度上是未知的。通过酵母双杂交筛选，我们鉴定出 espin，一种在缺陷时与人耳聋有关的肌动蛋白结合/束蛋白，作为 whirlin 的相互作用蛋白。这两种蛋白质的相互作用通过它们在培养细胞中的共免疫沉淀和共定位得到证实。这种相互作用涉及这两种蛋白质的多个结构域，并且仅在 espin 不与肌动蛋白结合时发生。Espin 在视网膜和内耳中与 whirlin 部分共定位。在 whirlin 敲除小鼠中，这两种组织中的 espin 表达发生了显著变化。进一步的研究发现，whirlin 增加了 espin 和肌动蛋白在 espin 交联的肌动蛋白束中的流动性，并最终影响了这些肌动蛋白束的尺寸。在 whirlin 敲除小鼠中，内毛细胞的静纤毛变厚。我们得出结论，whirlin 和 espin 之间的相互作用以及它们表达之间的平衡对于维持光感受器和毛细胞中的肌动蛋白束网络是必需的。这种肌动蛋白束网络的破坏导致 whirlin 和 espin 突变引起的听力损失和视网膜变性的发病机制。Espin 是 USH2 蛋白复合物的一个组成部分，可能是 Usher 综合征的候选基因。
