Endosomal trafficking and DNA damage checkpoint kinases dictate survival to replication stress by regulating amino acid uptake and protein synthesis
Atg6/Beclin 1 mediates autophagy and endosomal trafficking. We investigated how Atg6 influences replication stress. Combining genetic, genomic, metabolomic and proteomic approaches we found that the Vps34-Vps15-Atg6/Beclin 1-Vps38/UVRAG-phosphatydilinositol-3 phosphate (PtdIns(3)P) axis sensitizes cells to replication stress by favoring the degradation of plasma membrane amino acid (AA) transporters via endosomal trafficking and ESCRT proteins, while the PtdIns(3)P phosphatases Ymr1 and Inp53 promote survival to replication stress by reversing this process. An impaired AA uptake triggers activation of Gcn2, which attenuates protein synthesis by phosphorylating eIF2α. Mec1/Atr-Rad53/Chk1/Chk2 activation during replication stress further hinders translation efficiency by counteracting eIF2α dephosphorylation through Glc7/PP1. AA shortage-induced hyperphosphorylation of eIF2α inhibits the synthesis of 65 stress response proteins, thus resulting in cell sensitization to replication stress, while TORC1 promotes cell survival. Our findings reveal an integrated network mediated by endosomal trafficking, translational control pathways and checkpoint kinases linking AA availability to the response to replication stress.