VRK1 functional insufficiency due to alterations in protein stability or kinase activity of human VRK1 pathogenic variants implicated in neuromotor syndromes

Elena Martín-Doncel,Lara Cantarero,Pedro A Lazo,Ana M Rojas

doi:10.1038/s41598-019-49821-7

Abstract

Very rare polymorphisms in the human VRK1 (vaccinia-related kinase 1) gene have been identified in complex neuromotor phenotypes associated to spinal muscular atrophy (SMA), pontocerebellar hypoplasia (PCH), microcephaly, amyotrophic lateral sclerosis (ALS) and distal motor neuron dysfunctions. The mechanisms by which these VRK1 variant proteins contribute to the pathogenesis of these neurological syndromes are unknown. The syndromes are manifested when both of these rare VRK1 polymorphic alleles are implicated, either in homozygosis or compound heterozygosis. In this report, to identify the common underlying pathogenic mechanism of VRK1 polymorphisms, we have studied all human VRK1 variants identified in these neurological phenotypes from a biochemical point of view by molecular modeling, protein stability and kinase activity assays. Molecular modelling predicted that VRK1 variant proteins are either unstable or have an altered kinase activity. The stability and kinase activity of VRK1 pathogenic variants detected two groups. One composed by variants with a reduced protein stability: R133C, R358X, L195V, G135R and R321C. The other group includes VRK1variants with a reduced kinase activity tested on several substrates: histones H3 and H2AX, p53, c-Jun, coilin and 53BP1, a DNA repair protein. VRK1 variants with reduced kinase activity are H119R, R133C, G135R, V236M, R321C and R358X. The common underlying effect of VRK1 pathogenic variants with reduced protein stability or kinase activity is a functional insufficiency of VRK1 in patients with neuromotor developmental syndromes. The G135 variant cause a defective formation of 53BP1 foci in response to DNA damage, and loss Cajal bodies assembled on coilin.

Highlights

Understanding the pathogenesis of neurodegenerative diseases is a major medical challenge, which is needed to improve their early diagnosis or development of protocols to control or better the life conditions of affected individuals
The homozygous R358X pathogenic variant was associated to a spinal muscular atrophy (SMA) and pontocerebellar hypoplasia type 1 (PCH1)[22]
We have biochemically characterized the human VRK1 pathogenic variants associated to neuromotor and neurodevelopmental phenotypes in order to detect their mechanistic contribution to the pathogenesis of these syndromes

Summary

Introduction

Understanding the pathogenesis of neurodegenerative diseases is a major medical challenge, which is needed to improve their early diagnosis or development of protocols to control or better the life conditions of affected individuals. The homozygous R358X pathogenic variant was associated to a spinal muscular atrophy (SMA) and pontocerebellar hypoplasia type 1 (PCH1)[22] This VRK1-R358X variant codes for a truncated protein that is unstable and mislocalizes to the cytosol[23]. Additional cases with a deletion proximal to the VRK1 gene have been reported in several members of a family, but it is not known whether the VRK1 gene expression was altered[27] The heterogeneity of these pathogenic variants and the neurodevelopmental defects, all are distal neuromotor problems, suggested that VRK1 is underlying some basic functions in the affected neurons by unidentified mechanisms. We have biochemically characterized the human VRK1 pathogenic variants associated to neuromotor and neurodevelopmental phenotypes in order to detect their mechanistic contribution to the pathogenesis of these syndromes

Methods

Results

Conclusion