Endosomal trafficking protein TBC‐2 modulates stress resistance and lifespan through DAF‐16‐dependent and independent mechanisms

The FOXO transcription factor, DAF‐16, plays an integral role in insulin/IGF‐1 signaling (IIS) and stress response. In conditions of stress or decreased IIS, DAF‐16 moves to the nucleus where it activates genes that promote survival. To gain insight into the role of endosomal trafficking in resistance to stress, we disrupted tbc‐2, which encodes a GTPase activating protein that inhibits RAB‐5 and RAB‐7. We found that tbc‐2 mutants have decreased nuclear localization of DAF‐16 in response to heat stress, anoxia, and bacterial pathogen stress, but increased nuclear localization of DAF‐16 in response to chronic oxidative stress and osmotic stress. tbc‐2 mutants also exhibit decreased upregulation of DAF‐16 target genes in response to stress. To determine whether the rate of nuclear localization of DAF‐16 affected stress resistance in these animals, we examined survival after exposure to multiple exogenous stressors. Disruption of tbc‐2 decreased resistance to heat stress, anoxia, and bacterial pathogen stress in both wild‐type worms and stress‐resistant daf‐2 insulin/IGF‐1 receptor mutants. Similarly, deletion of tbc‐2 decreases lifespan in both wild‐type worms and daf‐2 mutants. When DAF‐16 is absent, the loss of tbc‐2 is still able to decrease lifespan but has little or no impact on resistance to most stresses. Combined, this suggests that disruption of tbc‐2 affects lifespan through both DAF‐16‐dependent and DAF‐16‐independent pathways, while the effect of tbc‐2 deletion on resistance to stress is primarily DAF‐16‐dependent. Overall, this work demonstrates the importance of endosomal trafficking for the proper nuclear localization of DAF‐16 during stress and that perturbation of normal endosomal trafficking is sufficient to decrease both stress resistance and lifespan.