Department of Microbiology, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei, 10051, Taiwan.
Department of Medical Research, National Taiwan University Hospital, Taipei, Taiwan.
J Biomed Sci. 2021 Sep 26;28(1):65. doi: 10.1186/s12929-021-00763-1.
Heterozygous pathogenic variants in STUB1 are implicated in autosomal dominant spinocerebellar ataxia type 48 (SCA48), which is a rare familial ataxia disorder. We investigated the clinical, genetic and functional characteristics of STUB1 mutations identified from a Taiwanese ataxia cohort.
We performed whole genome sequencing in a genetically undiagnosed family with an autosomal dominant ataxia syndrome. Further Sanger sequencing of all exons and intron-exon boundary junctions of STUB1 in 249 unrelated patients with cerebellar ataxia was performed. The pathogenicity of the identified novel STUB1 variant was investigated.
We identified a novel heterozygous frameshift variant, c.832del (p.Glu278fs), in STUB1 in two patients from the same family. This rare mutation is located in the U-box of the carboxyl terminus of the Hsc70-interacting protein (CHIP) protein, which is encoded by STUB1. Further in vitro experiments demonstrated that this novel heterozygous STUB1 frameshift variant impairs the CHIP protein's activity and its interaction with the E2 ubiquitin ligase, UbE2D1, leading to neuronal accumulation of tau and α-synuclein, caspase-3 activation, and promoting cellular apoptosis through a dominant-negative pathogenic effect. The in vivo study revealed the influence of the CHIP expression level on the differentiation and migration of cerebellar granule neuron progenitors during cerebellar development.
Our findings provide clinical, genetic, and a mechanistic insight linking the novel heterozygous STUB1 frameshift mutation at the highly conserved U-box domain of CHIP as the cause of autosomal dominant SCA48. Our results further stress the importance of CHIP activity in neuronal protein homeostasis and cerebellar functions.
STUB1 中的杂合致病性变异与常染色体显性小脑共济失调 48 型（SCA48）有关，这是一种罕见的家族性共济失调疾病。我们研究了从台湾共济失调队列中鉴定出的 STUB1 突变的临床、遗传和功能特征。
我们对一个具有常染色体显性共济失调综合征的遗传未确诊的家族进行了全基因组测序。对 249 名无相关小脑共济失调患者的 STUB1 所有外显子和内含子-外显子边界进行了 Sanger 测序。研究了鉴定出的新型 STUB1 变异的致病性。
我们在来自同一家庭的两名患者中发现了 STUB1 中的新型杂合移码变异，c.832del（p.Glu278fs）。这种罕见的突变位于 STUB1 编码的 Hsc70 相互作用蛋白（CHIP）羧基末端的 U 盒中。进一步的体外实验表明，这种新型杂合 STUB1 移码变异会损害 CHIP 蛋白的活性及其与 E2 泛素连接酶 UbE2D1 的相互作用，导致 tau 和 α-突触核蛋白在神经元中的积累、半胱天冬酶-3 的激活，并通过显性致病作用促进细胞凋亡。体内研究揭示了 CHIP 表达水平对小脑发育过程中小脑颗粒神经元祖细胞分化和迁移的影响。
我们的研究结果提供了临床、遗传和机制方面的见解，将 CHIP 高度保守的 U 盒结构域中的新型杂合 STUB1 移码突变与常染色体显性 SCA48 联系起来。我们的结果进一步强调了 CHIP 活性在神经元蛋白平衡和小脑功能中的重要性。
