Nitric oxide mediates NMDA-induced persistent inhibition of protein synthesis through dephosphorylation of eukaryotic initiation factor 4E-binding protein 1 and eukaryotic initiation factor 4G proteolysis

Valerie Petegnief (1) , Miriam Font-Nieves , M. Elena Martin , Matilde Salinas , Anna M. Planas

1 Brain ischemia and neurodegeneration

Cerebral ischemia causes long-lasting protein synthesis inhibition that is believed to contribute to brain damage. Energy depletion promotes translation inhibition during ischemia and the phosphorylation of eukaryotic initiation factor 2α (eIF2α) is involved in the translation inhibition induced by early ischemic reperfusion. However, the molecular mechanisms underlying prolonged translation downregulation remain elusive. NMDA excitotoxicity is also involved in ischemic damage, as exposure to NMDA impairs translation and promotes the synthesis of nitric oxide (NO), which can also inhibit translation. Here we investigated whether NO was involved in NMDA-induced protein synthesis inhibition in neurons and studied the underlying molecular mechanisms. NMDA and the NO-donor DEA/NO both inhibited protein synthesis and this effect persisted after a 30-min-exposure. Treatments with NMDA or NO promoted calpain-dependent eIF4G cleavage and 4E-BP1 dephosphorylation and also abolished the formation of eIF4E/eIF4G complexes, however they did not induce eIF2α phosphorylation. Although NO synthase (NOS) inhibitors did not prevent protein synthesis inhibition during 30-min NMDA exposure, they did abrogate the persistent inhibition of translation observed after NMDA removal. NOS inhibitors also prevented NMDA-induced eIF4G degradation, 4E-BP1 dephosphorylation, eIF4E-eIF4G binding reduction and cell death. Although the calpain inhibitor calpeptin blocked NMDAinduced eIF4G degradation, it did not prevent 4E-BP1 dephosphorylation, which precludes eIF4E availability, and thus translation inhibition was maintained. This study suggests that eIF4G integrity and hyperphosphorylated 4E-BP1 are needed to ensure appropriate translation in neurons. In conclusion, our data show that NO mediates NMDA-induced persistent translation inhibition and suggest that deficient eIF4F activity contributes to this process.

Mots clés: Life Sciences

Valerie Petegnief, Miriam Font-Nieves, M. Elena Martin, Matilde Salinas, Anna M. Planas. Nitric oxide mediates NMDA-induced persistent inhibition of protein synthesis through dephosphorylation of eukaryotic initiation factor 4E-binding protein 1 and eukaryotic initiation factor 4G proteolysis. Biochemical Journal, 2008, 411 (3), pp.667-677. ⟨10.1042/BJ20071060⟩. ⟨hal-00478865⟩