Eukaryotic Translation Initiation Factor 2A (eIF2A) Protects Pancreatic Beta Cells During ER Stress-Induced ApoptosisImage 6

Abstract

Unfolded protein response (UPR) induced in response to endoplasmic reticulum (ER) stress is a well-known mechanism mediating beta cell dysfunction and death in diabetes. Inhibition of general protein translation via PERK-dependent phosphorylation of eIF2α is key event during UPR, which if unresolved induces apoptosis. eIF2A has been implicated in the translation of specific mRNAs during viral infection, when translation is similarly suppressed. We hypothesized that eIF2A plays a key role in translation of specific mRNAs during UPR in beta cells. We found that UPR inducers thapsigargin (1 µmol/L) and palmitate (0.5 mmol/L in BSA) induced mRNA (3.5±0.4-fold and 2.0±0.3) and protein (2.2±0.2-fold and 2.1±0.2) expression of eIF2A in mouse and human islets. We found 84.7±6.9% and 63.7±7.8% reductions in thapsigargin- and palmitate-induced apoptosis in mouse islet cells overexpressing eIF2A (3-fold), respectively. To elucidate molecular mechanism, we used a stable MIN6 cell line overexpressing eIF2A. Reduced cell death was associated with 88.3±8.4% decrease in translation of CHOP mRNA. MIN6 cells showed decreased protein synthesis rate by 80.2±10% after 2 hours of thapsigargin treatment. However, the protein synthesis rate was unchanged in cells overexpressing eIF2A. Immunoprecipitation of eIF2A showed increase in the interaction of eIF2A with eIF2α during UPR in MIN6 cells with the maximum of 5.9±1.1-fold increase 24 hours after thapsigargin treatment. We conclude that eIF2A suppresses UPR-induced apoptosis in beta cells via inhibition of translational repression. We identified a novel protective role for eIF2A in the context of ER-stressed beta cells via the selective inhibition of CHOP mRNA translation.