Coupled Activation and Degradation of eEF2K Regulates Protein Synthesis in Response to Genotoxic Stress

The kinase eEF2K [eukaryotic elongation factor 2 (eEF2) kinase] controls the rate of peptide chain elon- gation by phosphorylating eEF2, the protein that mediates the movement of the ribosome along the mRNA by promoting translocation of the transfer RNA from the A to the P site in the ribosome. eEF2K-mediated phosphorylation of eEF2 on threonine 56 (Thr56) decreases its affinity for the ribosome, thereby inhibiting elongation. Here, we show that in response to genotoxic stress, eEF2K was activated by AMPK (adenosine monophosphate–activated protein kinase)–mediated phosphorylation on serine 398. Activated eEF2K phosphorylated eEF2 and induced a temporary ribosomal slowdown at the stage of elongation. Subsequently, during DNA damage checkpoint silencing, a process required to allow cell cycle reentry, eEF2K was degraded by the ubiquitin-proteasome system through the ubiquitin ligase SCFbTrCP (Skp1–Cul1–F-box protein, b-transducin repeat–containing protein) to enable rapid resumption of translation elongation. This event required autophosphorylation of eEF2K on a canonical bTrCP- binding domain. The inability to degrade eEF2K during checkpoint silencing caused sustained phos- phorylation of eEF2 on Thr56 and delayed the resumption of translation elongation. Our study therefore establishes a link between DNA damage signaling and translation elongation.