Since the identification of B‐cell translocation gene 1 (BTG1) and BTG2 as antiproliferation genes more than two decades ago, their protein products have been implicated in a variety of cellular processes including cell division, DNA repair, transcriptional regulation and messenger RNA stability. In addition to affecting differentiation during development and in the adult, BTG proteins play an important role in maintaining homeostasis under conditions of cellular stress. Genomic profiling of B‐cell leukemia and lymphoma has put BTG1 and BTG2 in the spotlight, since both genes are frequently deleted or mutated in these malignancies, pointing towards a role as tumor suppressors. Moreover, in solid tumors, reduced expression of BTG1 or BTG2 is often correlated with malignant cell behavior and poor treatment outcome. Recent studies have uncovered novel roles for BTG1 and BTG2 in genotoxic and integrated stress responses, as well as during hematopoiesis. This review summarizes what is currently known about the roles of BTG1 and BTG2 in these and other cellular processes. In addition, we will highlight the molecular mechanisms and biological consequences of BTG1 and BTG2 deregulation during cancer progression and elaborate on the potential clinical implications of these findings.
eEF2K is a kinase that controls the rate of peptide chain elongation by phosphorylating eukaryotic Elongation Factor 2 (eEF2), the protein that mediates the movement of the ribosome along the mRNA by promoting translocation from the A to the P site. eEF2K-mediated phosphorylation of eEF2 on Thr56 decreases its affinity for the ribosome, thereby inhibiting elongation. Here we show that in response to genotoxic stress, eEF2K is activated by AMPK-mediated phosphorylation on Ser398. Activated eEF2K phosphorylates eEF2 and induces a temporary ribosomal slowdown at the stage of elongation. Subsequently, during checkpoint silencing, eEF2K is degraded by the ubiquitin-proteasome system via the SCFβTrCP ubiquitin ligase to allow rapid resumption of translation elongation. This event requires eEF2K autophosphorylation on a canonical βTrCP-binding domain. The inability to degrade eEF2K during checkpoint silencing caused sustained phosphorylation of eEF2 on Thr56 and delayed resumption of translation elongation. Our study establishes an important link between DNA damage signaling and translation elongation.
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