Clinical and functional characterization of a novel STUB1 frameshift mutation in autosomal dominant spinocerebellar ataxia type 48 (SCA48)

Han-Yi Lin,Chin-Hsien Lin,Yung-Feng Lin,Huan-Yun Chen,Jin-Wu Tsai,Shu-Chun Teng,Ye-Ru Li,Shih-Feng Tsai,Yu-Jung Ho,Chia-Lang Hsu

doi:10.1186/s12929-021-00763-1

Abstract

BackgroundHeterozygous 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.MethodsWe 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.ResultsWe 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.ConclusionsOur 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.

Highlights

Heterozygous pathogenic variants in STUB1 are implicated in autosomal dominant spinocerebellar ataxia type 48 (SCA48), which is a rare familial ataxia disorder
Ectopic expression of the C-terminus of heat shock protein 70 (HSC70)-interacting protein (CHIP) mutants increased the cleavage product of caspase-3 compared with its level in cells transfected with CHIP WT (Fig. 5B). These results suggest that the mutant CHIP proteins may cause cellular apoptosis, which would further promote the progression of cerebellar ataxia
Knockdown of CHIP delayed granule neuron progenitors (GNPs) migration in the inner EGL (Fig. 5D, E). These cells were negative for Ki67, indicating that they had exited the cell cycle (Fig. 5F). These results suggest that variation in CHIP expression levels plays a critical role in GNP proliferation and migration during cerebellar development, reinforcing the role of STUB1 mutations in SCA48

Summary

Introduction

Heterozygous pathogenic variants in STUB1 are implicated in autosomal dominant spinocerebellar ataxia type 48 (SCA48), which is a rare familial ataxia disorder. C-terminus of HSC70-interacting protein (CHIP), encoded by the gene STUB1, functions as both a molecular co-chaperone and a ubiquitin E3 ligase, which plays a pivotal role in regulating cellular protein homeostasis [1]. CHIP is ubiquitously expressed, its expression is elevated in tissues with high metabolic rates, especially brain tissues [2]. The degradation of those proteins or organelles via the ubiquitin– proteasome system (UPS) plays a crucial role in protein quality control and sustains proper cellular homeostasis, important in neurons [6, 7]

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