Dynamic Phosphorylation Regulates Eukaryotic Translation Initiation Factor 4A Activity During the Cell Cycle

Abstract

The eukaryotic translation initiation factor 4A (eIF4A) resolves mRNA structures to support protein synthesis, yet little is known about its regulation. Here we analyzed eIF4A phosphorylation during alternate stages of the cell cycle, and found three residues near the DEAD box motif (T73, T146, and S177) underwent substantial phosphorylation changes. Phosphomimetic mutations T73D and T146D led to G2/M phase arrest, and abolished eIF4A interaction with RNA, suggesting eIF4A activity is needed for completion of cell division. In addition to these repressive events, we found that S177, a site immediately adjacent to the DEAD-box, showed diametrically opposed phosphorylation, with only phosphorylated S177 present during G1/S arrest and dephosphorylated S177 peptides during G2/M arrest. Phosphomimetic S177D eIF4A increased polysome levels and enhanced normally reduced eIF4A-eIF4G-interaction during G2/M, while phosphodeficient S177A decreased polysome levels and reduced growth, suggesting phosphorylation of S177 enhances eIF4A-mediated translation during G1/S. Together these results suggest that dynamic phosphorylation of eIF4A S177 serves to stimulate translation during G1/S, while inhibitory phosphorylation of additional sites holds the potential to rapidly transition eIF4A to an inactive state and turn off translation. These results also suggest an important role for eIF4A in coupling translation to cell cycle stages.