Department of Ophthalmology, Harvard Medical School, The Schepens Eye Research Institute and Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.
Department III of Internal Medicine, Cologne University Heart Center, Center for Molecular Medicine, University of Cologne, 50931 Cologne, Germany.
J Mol Cell Biol. 2017 Dec 1;9(6):516-532. doi: 10.1093/jmcb/mjx024.
High temperature requirement A1 (HtrA1) belongs to an ancient protein family that is linked to various human disorders. The precise role of exon 1-encoded N-terminal domains and how these influence the biological functions of human HtrA1 remain elusive. In this study, we traced the evolutionary origins of these N-terminal domains to a single gene fusion event in the most recent common ancestor of vertebrates. We hypothesized that human HtrA1 is implicated in unfolded protein response. In highly secretory cells of the retinal pigmented epithelia, endoplasmic reticulum (ER) stress upregulated HtrA1. HtrA1 co-localized with vimentin intermediate filaments in highly arborized fashion. Upon ER stress, HtrA1 tracked along intermediate filaments, which collapsed and bundled in an aggresome at the microtubule organizing center. Gene silencing of HtrA1 altered the schedule and amplitude of adaptive signaling and concomitantly resulted in apoptosis. Restoration of wild-type HtrA1, but not its protease inactive mutant, was necessary and sufficient to protect from apoptosis. A variant of HtrA1 that harbored exon 1 substitutions displayed reduced efficacy in rescuing cells from proteotoxicity. Our results illuminate the integration of HtrA1 in the toolkit of mammalian cells against protein misfolding and the implications of defects in HtrA1 in proteostasis.
高温需求 A1（HtrA1）属于与各种人类疾病相关的古老蛋白质家族。外显子 1 编码的 N 端结构域的确切作用以及这些结构域如何影响人类 HtrA1 的生物学功能仍然难以捉摸。在这项研究中，我们追溯了这些 N 端结构域的进化起源，发现它们来自脊椎动物最近共同祖先的单个基因融合事件。我们假设人类 HtrA1 与未折叠蛋白反应有关。在视网膜色素上皮的高度分泌细胞中，内质网（ER）应激会上调 HtrA1。HtrA1 与中间丝中的波形蛋白以高度分支的方式共定位。在 ER 应激下，HtrA1 沿着中间丝追踪，中间丝在微管组织中心崩溃并捆绑成聚集体。HtrA1 的基因沉默改变了适应性信号的时间安排和幅度，并同时导致细胞凋亡。野生型 HtrA1 的恢复（而非其蛋白酶失活突变体）是防止凋亡所必需且充分的。携带外显子 1 取代的 HtrA1 变体在挽救细胞免受蛋白毒性方面的效果降低。我们的结果阐明了 HtrA1 在哺乳动物细胞对抗蛋白质错误折叠的工具包中的整合，以及 HtrA1 缺陷在蛋白质稳态中的意义。
