The role of eIF2Bα in the integrity of eIF2B bodies

The eukaryotic initiation factor 2B (eIF2B) is a multisubunit protein composed of two sets of five subunits (α-ε) forming a heterodecamer. eIF2B is a guanine exchange factor (GEF) recycling inactive eukaryotic initiation factor 2 (eIF2) to its active state, being an essential checkpoint for translational control. Following induction of stress, kinases phosphorylate eIF2α, activating the integrated stress response (ISR), subsequently inhibiting eIF2B activity. Mutations within the eIF2Bα-ε subunits can lead to vanishing white matter disease (VWMD) and eIF2Bα variants may cause permanent neonatal diabetes mellitus (PNDM). VWMD and PNDM mutations, primarily affect glial cells and pancreatic β-cells, respectively, suggesting cell type-specific functions of eIF2B. eIF2B bodies are cytoplasmic bodies containing the eIF2B protein. In this study, we highlight bioinformatic tools to optimise the immunocytochemistry detection of eIF2Bα-ε foci. We investigated cell type-specific localisation of eIF2B subunits within neuronal and glial cell types, showing that oligodendrocytes and neuronal cells possess additional eIF2Bα foci, independent of other eIF2B subunits. Additionally, eIF2Bα has been found to be essential for eIF2B foci formation. We have further revealed that eIF2Bɑ spatially interacts with G3BP-containing stress granules (SGs), induced by endoplasmic reticulum (ER) and oxidative stress in a p-eIF2α-dependent manner. EIF2B1L100P/WT mutant cell line shows decreasedformation of SGs following p-eIF2α induction, while SG assembly independent of p-eIF2α was not impacted. Our study showed that in cells depleted of eIF2Bα, large eIF2Bβ-ε foci were not able to form. ISRIB, a molecule known to stabilise the decamer, was able to rescue large foci assembly, establishing a similar functional role to eIF2Bα regarding eIF2B foci formation. Additionally, the assembly of SGs and the localisation of eIF2Bα to these aggregates appeared to play an important role in eIF2B subcomplex formation during ISR activation and the sensing of stress through the p-eIF2α pathway.