ALS-associated missense and nonsense TBK1 mutations can both cause loss of kinase function

Martina De Majo,Orla Hardiman,Frank Baas,Kevin Talbot,Cinzia Tiloca,Jesús Esteban-Pérez,Stefano Duga,Antonia Ratti,Caroline Vance,Bradley N Smith,Janine Kirby,Jacqueline De Belleroche,Federico Verde,Kevin P Kenna,Cinzia Gellera,Anneloor L.M.A Ten Asbroek,Robert H Brown,Nicola Ticozzi,Athina Soragia Gkazi,John E Landers,Pamela J Shaw,Agnes L Nishimura,Chun Hao Wong,Christopher E Shaw,Vincenzo Silani,Jonathan D Glass,Ammar Al‐Chalabi ,Alberto García Redondo ,Simon Topp ,Han Jou Chen ,Karen Morrison ,Martin R Turner ,Jack W Miller

doi:10.1016/j.neurobiolaging.2018.06.015

Abstract

Mutations in TANK binding kinase 1 (TBK1) have been linked to amyotrophic lateral sclerosis. Some TBK1 variants are nonsense and are predicted to cause disease through haploinsufficiency; however, many other mutations are missense with unknown functional effects. We exome sequenced 699 familial amyotrophic lateral sclerosis patients and identified 16 TBK1 novel or extremely rare protein-changing variants. We characterized a subset of these: p.G217R, p.R357X, and p.C471Y. Here, we show that the p.R357X and p.G217R both abolish the ability of TBK1 to phosphorylate 2 of its kinase targets, IRF3 and optineurin, and to undergo phosphorylation. They both inhibit binding to optineurin and the p.G217R, within the TBK1 kinase domain, reduces homodimerization, essential for TBK1 activation and function. Finally, we show that the proportion of TBK1 that is active (phosphorylated) is reduced in 5 lymphoblastoid cell lines derived from patients harboring heterozygous missense or in-frame deletion TBK1 mutations. We conclude that missense mutations in functional domains of TBK1 impair the binding and phosphorylation of its normal targets, implicating a common loss of function mechanism, analogous to truncation mutations.

Highlights

Amyotrophic lateral sclerosis (ALS) is an adult onset and progressive neurodegenerative disorder that targets the upper and lower motor neurons in the brain and spinal cord
Exome Sequencing in familial ALS detects 16 protein-changing TANK binding kinase 1 (TBK1) variants
The variant p.R357X is present in a single FALS case in the ALS data browser (ALSdb); this is unlikely to be closely related to the p.R357X carrier identified in this study as they lack any other shared rare variants

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is an adult onset and progressive neurodegenerative disorder that targets the upper and lower motor neurons in the brain and spinal cord. Death usually occurs within 3 to 5 years from the symptom onset, and treatment is largely palliative (Morgan and Orrell, 2016). ALS is often associated with cognitive changes linked to mild frontotemporal dementia (FTD) (Gijselinck et al, 2015), and up to 50% of the FTD cases develop signs of motor neuron disease (van der Zee et al, 2017). 10% of ALS cases have a familial history of ALS or FTD (fALS, fALS/FTD) (Tiwari et al, 2005). More than 40 genes have been identified to be associated with ALS through linkage studies, genome-wide association studies, whole exome sequencing, and whole genome sequencing. Four genes account for over 50% of fALS cases: SOD1, C9ORF72, TARDBP, and FUS/TLS in population of European ancestry, and most other genes are rare, each accounting for w1% of the cases (Taylor et al, 2016)

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