HeberleRazquinNavas2019 - The PI3K and MAPK/p38 pathways control stress granuleassembly in a hierarchical manner model 3

All cells and organisms exhibit stress-coping mechanisms toensure survival. Cytoplasmic protein-RNA assemblies termedstress granules are increasingly recognized to promote cellularsurvival under stress. Thus, they might represent tumor vul-nerabilities that are currently poorly explored. The translation-inhibitory eIF2αkinases are established as main drivers ofstress granule assembly. Using a systems approach, we identifythe translation enhancers PI3K and MAPK/p38 as pro-stress-granule-kinases. They act through the metabolic master regu-lator mammalian target of rapamycin complex 1 (mTORC1) topromote stress granule assembly. When highly active, PI3K is themain driver of stress granules; however, the impact of p38becomes apparent as PI3K activity declines. PI3K and p38 thusact in a hierarchical manner to drive mTORC1 activity and stressgranule assembly. Of note, this signaling hierarchy is also presentin human breast cancer tissue. Importantly, only the recognition ofthe PI3K-p38 hierarchy under stress enabled the discovery of p38’srole in stress granule formation. In summary, we assign a new pro-survival function to the key oncogenic kinases PI3K and p38, as theyhierarchically promote stress granule formation