Talk on Saturday 09:30-09:45am submitted by Ansuman Sahoo
Dynamic Phosphorylation Of RNA Helicase eIF4A Mediates Translational Responses To Cell Cycle Transitions And Nutrients Starvation
Ansuman Sahoo (Biological Sciences Department, University at Buffalo), Qian He, Marium Ashraf, Samantha Nelson, Gerald Koudelka (Biological Sciences Department, University at Buffalo), Shichen Shen, Jun Qu (Pharmaceutical Sciences Department, University at Buffalo), Robert A. Zollo, Joseph Barbi (Roswell Park Comprehensive Cancer Center), Sarah E. Walker (Biological Sciences Department, University at Buffalo)
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 cell cycle stages and found that 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 to complete cell division. In addition to these repressive events, we observed reciprocal phosphorylation of S177, a site immediately adjacent to the DEAD-box, with only phosphorylated S177 present during G1/S arrest and dephosphorylated S177 peptides during G2/M arrest. Phosphomimetic S177D eIF4A enhanced normally reduced eIF4A•eIF4G-interaction during G2/M and increased polysomes, while phosphodeficient S177A decreased polysome levels and reduced growth, suggesting phosphorylation of S177 enhances eIF4A-mediated translation during G1/S. S177 also showed reduced phosphorylation upon removal of glucose, coinciding with global translation initiation shut-down. Mutation to S177D mimicking constitutive phosphorylation decreased P body levels upon glucose removal, while phosphodeficient S177A led to decreased growth and translation rates and increased P body levels, suggesting S177 phosphorylation mediates changes in eIF4A activity needed for altering translation and RNA turnover in response to changing cellular states. We also observed enhanced phosphorylation of T146 and other sites, events likely to evict eIF4A from RNA and eIF4G upon glucose removal. Together, these data suggest that parallel phosphorylation and dephosphorylation of alternative sites in the essential translation initiation factor eIF4A stimulates translation during periods of robust growth and holds the capacity to rapidly shut down protein synthesis by impaired eIF4A binding to eIF4G and RNA during unfavorable conditions.
Keywords: Translation, Helicase, Phosphorylation