title: Regulation of protein translation initiation in response to ionizing radiation.
abstract: BACKGROUND
  Proliferating tumor cells require continuous protein synthesis. De novo synthesis of most proteins is regulated through cap-dependent translation. Cellular stress such as ionizing radiation (IR) blocks cap-dependent translation resulting in shut-down of global protein translation which saves resources and energy needed for the stress response. At the same time, levels of proteins required for stress response are maintained or even increased. The study aimed to analyze the regulation of signaling pathways controlling protein translation in response to IR and the impact on Mcl-1, an anti-apoptotic and radioprotective protein, which levels rapidly decline upon IR.
  
  
  METHODS
  Protein levels and processing were analyzed by Western blot. The assembly of the translational pre-initiation complex was examined by Immunoprecipitation and pull-down experiments with 7-methyl GTP agarose. To analyze IR-induced cell death, dissipation of the mitochondrial membrane potential and DNA fragmentation were determined by flow cytometry. Protein levels of the different initiation factors were down-regulated using RNA interference approach.
  
  
  RESULTS
  IR induced caspase-dependent cleavage of the translational initiation factors eIF4G1, eIF3A, and eIF4B resulting in disassembly of the cap-dependent initiation complex. In addition, DAP5-dependent initiation complex that regulates IRES-dependent translation was disassembled in response to IR. Moreover, IR resulted in dephosphorylation of 4EBP1, an inhibitor of cap-dependent translation upstream of caspase activation. However, knock-down of eIF4G1, eIF4B, DAP5, or 4EBP1 did not affect IR-induced decline of the anti-apoptotic protein Mcl-1.
  
  
  CONCLUSIONS
  Our data shows that cap-dependent translation is regulated at several levels in response to IR. However, the experiments indicate that IR-induced Mcl-1 decline is not a consequence of translational inhibition in Jurkat cells.
authors: Department of Radiation Oncology, University Hospital of Tuebingen, Hoppe-Seyler-Str, 3, 72076, Tübingen, Germany.
authors: Donatella
authors: D
authors: Trivigno
authors: Laura
authors: L
authors: Bornes
authors: Stephan M
authors: SM
authors: Huber
authors: Justine
authors: J
authors: Rudner
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D020169:Caspases / Q000502:physiology; D018797:Cell Cycle Proteins; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism; D039601:Eukaryotic Initiation Factor-4A / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism / Q000502:physiology; D006801:Humans; D019169:Jurkat Cells; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010442:Peptide Chain Initiation, Translational / Q000528:radiation effects*; D010750:Phosphoproteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011839:Radiation, Ionizing
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C113920:EIF4G1 protein, human; C491300:EIF4G2 protein, human; D039621:Eukaryotic Initiation Factor-3; D039603:Eukaryotic Initiation Factor-4G; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010750:Phosphoproteins; D019253:Proto-Oncogene Proteins c-bcl-2; D039601:Eukaryotic Initiation Factor-4A; D020169:Caspases
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