Talk abstracts
Talk on Friday 03:30-03:45pm submitted by Ansuman Sahoo
Dynamic Phosphorylation Regulates Eukaryotic Translation Initiation Factor 4A Activity During The Cell Cycle
Ansuman Sahoo (Department of Biological Sciences, University at Buffalo), Marium Ashraf (Department of Biological Sciences, University at Buffalo), Sarah E. Walker (Department of Biological Sciences, University at Buffalo)
Abstract:
The eukaryotic translation initiation factor 4A (eIF4A) supports mRNA recruitment to the ribosomal preinitiation complex, thus controlling cell-wide protein synthesis. A conserved Threonine residue of eIF4A (T146 in yeast) near the catalytically-important DEAD motif is present in a consensus CDK1/CDKA/Cdc28 motif and found to be phosphorylated in large-scale studies (Soulard et al., 2010). In plants, eIF4A is phosphorylated at this site by CDKA (a key regulator of the cell cycle) and this event decreased eIF4A activity (Bush et al., 2016). To further dissect the molecular function of eIF4A phosphorylation, we analyzed specific in vitro and in vivo changes that take place because of phosphorylation of eIF4A at different stages of the cell cycle. We mutated several phosphosites in eIF4A to phosphodeficient (Ala) and phosphomimetic (Asp/Glu) forms and analyzed the effects of these mutations on yeast growth and translation. Our data show that besides T146, multiple residues in eIF4A were phosphorylated at the G2 to M transition, and versions of eIF4A that could not be phosphorylated or mimicked constitutive phosphorylation were lethal, suggesting dynamic phosphorylation of eIF4A is essential. A phosphomimetic version of eIF4A (T146D) abolished RNA binding, suggesting that translation of mRNAs that occurs during mitosis (when eIF4A is phosphorylated) is independent of the eIF4F cap-binding complex. The activity of the essential Glc7/PP1 complex promoted dephosphorylation of eIF4A and cell division. Together these data suggest that eIF4A acts as a switch to couple production of specific proteins to phases of the cell cycle. Phosphorylation arrests canonical translation during mitosis, while dephosphorylation of eIF4A is needed to derepress cap dependent translation to complete cell division.
References:
1. Soulard, Alexandre, et al. "The rapamycin-sensitive phosphoproteome reveals that TOR controls protein kinase A toward some but not all substrates." Molecular biology of the cell 21.19 (2010): 3475-3486.
2. Bush, Maxwell S., et al. "eIF4A RNA helicase associates with cyclin-dependent protein kinase A in proliferating cells and is modulated by phosphorylation." Plant physiology 172.1 (2016): 128-140.
Keywords: eIF4A, Phosphorylation, Cell cycle