DNA damage induces p53-independent apoptosis through ribosome2 stalling

Human cells respond to excessive DNA damage by undergoing cell death, known as37apoptosis. This involves the transcription factor p53, which activates pro-apoptotic38target genes. Cells lacking p53 can still activate apoptosis upon DNA damage although the39responsible pathways are unknown. Here we characterized DNA damage-induced apoptosis40that was independent of p53 and observed that it occurred in cells that displayed a shutdown41of protein synthesis. Ribosome footprinting demonstrated that DNA damage globally curtailed42translation initiation accompanied by a transcriptome-wide ribosome stalling phenotype at rare43leucine-encoding UUA codons. Using a genetic screen we identified the tRNA endonuclease44SLFN11, the strongest known predictor for chemotherapy responsiveness in human cancer, as45well as the translational regulator GCN2 as factors required for the translation46shutdown. SLFN11 was essential for the UUA stalling phenotype which was accompanied by47a reduction of the corresponding tRNA. Stalled ribosomes, but not the GCN2-dependent global48translation shutdown, activated a ribotoxic stress signal conveyed by the ribosome-sensor49ZAK to the mitochondrial apoptosis machinery. These results provide an explanation for the50frequent inactivation of SLFN11 in chemotherapy-unresponsive tumors and highlight51ribosome stalling as a signaling event to affect cell fate in response to DNA damage.