Regulation of eukaryotic translation initiation factor 6 dynamics through multisite phosphorylation by GSK3.

Eukaryotic translation initiation factor 6 (eIF6) is essential for the synthesis of 60S ribosomal subunits and for regulating the association of 60S and 40S subunits. A mechanistic understanding of how eIF6 modulates translation in response to stress, specifically starvation-induced stress, is lacking. We here show a novel mode of eIF6 regulation by glycogen synthase kinase 3 (GSK3) that is predominantly active in response to serum starvation. Both GSK3α and GSK3β phosphorylate human eIF6. Multiple residues in the C terminus of eIF6 are phosphorylated by GSK3 in a sequential manner. In response to serum starvation, eIF6 accumulates in the cytoplasm, and this altered localization depends on phosphorylation by GSK3. Disruption of eIF6 phosphorylation exacerbates the translation inhibitory response to serum starvation and stalls cell growth. These results suggest that eIF6 regulation by GSK3 contributes to the attenuation of global protein synthesis that is critical for adaptation to starvation-induced stress.