Mutations Causing Childhood Ataxia with Central Nervous System Hypomyelination Reduce Eukaryotic Initiation Factor 2B Complex Formation and Activity

Abstract

Childhood ataxia with central nervous system hypomyelination (CACH), or vanishing white matter leukoencephalopathy (VWM), is a fatal brain disorder caused by mutations in eukaryotic initiation factor 2B (eIF2B). eIF2B is essential for protein synthesis and regulates translation in response to cellular stresses. We performed mutagenesis to introduce changes equivalent to 12 human CACH/VWM mutations in three subunits of the equivalent factor from yeast (Saccharomyces cerevisiae) and analyzed effects on cell growth, translation, and gene expression in response to stresses. None of the mutations is lethal or temperature sensitive, but almost all confer some defect in eIF2B function significant enough to alter growth or gene expression under normal or stress conditions. Biochemical analyses indicate that mutations analyzed in eIF2Bα and -ε reduce the steady-state level of the affected subunit, while the most severe mutant tested, eIF2Bβ^V341D (human eIF2B^βV316D), forms complexes with reduced stability and lower eIF2B activity. eIF2Bδ is excluded from eIF2Bβ^V341D complexes. eIF2B^βv341D function can be rescued by overexpression of eIF2Bδ alone. Our findings imply CACH/VWM mutations do not specifically impair responses to eIF2 phosphorylation, but instead cause protein structure defects that impair eIF2B activity. Altered protein folding is characteristic of other diseases, including cystic fibrosis and neurodegenerative disorders such as Huntington, Alzheimer's, and prion diseases.

We thank Michael Tonge for construction of plasmid pAV1778 and genetic analysis of the eIF2Bα mutant, Mark Ashe and Chris Grant for helpful discussions, and Alan Hinnebusch for comments on the manuscript.

This work was supported by a project grant from the BBSRC to G.D.P.