DAF-21/Hsp90 is required for C. elegans longevity by ensuring DAF-16/FOXO isoform A function

The FOXO transcription factor family is a conserved regulator of longevity and the downstream target of insulin/insulin-like signaling. In Caenorhabditis elegans, the FOXO ortholog DAF-16A and D/F isoforms extend lifespan in daf-2 insulin-like receptor mutants. Here we identify the DAF-21/Hsp90 chaperone as a longevity regulator. We find that reducing DAF-21 capacity by daf-21(RNAi) initiated either at the beginning or at the end of larval development shortens wild-type lifespan. daf-21 knockdown employed from the beginning of larval development also decreases longevity of daf-2 mutant and daf-2 silenced nematodes. daf-16 loss-of-function mitigates the lifespan shortening effect of daf-21 silencing. We demonstrate that DAF-21 specifically promotes daf-2 and heat-shock induced nuclear translocation of DAF-16A as well as the induction of DAF-16A-specific mRNAs, without affecting DAF-16D/F localization and transcriptional function. DAF-21 is dispensable for the stability and nuclear import of DAF-16A, excluding a chaperone-client interaction and suggesting that DAF-21 regulates DAF-16A activation upstream of its cellular traffic. Finally, we show a selective requirement for DAF-21 to extend lifespan of DAF-16A, but not DAF-16D/F, transgenic daf-2 mutant strains. Our findings indicate a spatiotemporal determination of multiple DAF-21 roles in fertility, development and longevity and reveal an isoform-specific regulation of DAF-16 activity. © 2018, The Author(s)

mTORC1 Phosphorylation Sites Encode Their Sensitivity to Starvation and Rapamycin

The mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) protein kinase promotes growth and is the target of rapamycin, a clinically useful drug that also prolongs life span in model organisms. A persistent mystery is why the phosphorylation of many bona fide mTORC1 substrates is resistant to rapamycin. We find that the in vitro kinase activity of mTORC1 toward peptides encompassing established phosphorylation sites varies widely and correlates strongly with the resistance of the sites to rapamycin, as well as to nutrient and growth factor starvation within cells. Slight modifications of the sites were sufficient to alter mTORC1 activity toward them in vitro and to cause concomitant changes within cells in their sensitivity to rapamycin and starvation. Thus, the intrinsic capacity of a phosphorylation site to serve as an mTORC1 substrate, a property we call substrate quality, is a major determinant of its sensitivity to modulators of the pathway. Our results reveal a mechanism through which mTORC1 effectors can respond differentially to the same signals.National Institutes of Health (U.S.) (Grant CA103866)National Institutes of Health (U.S.) (Grant AI047389)National Institutes of Health (U.S.) (Grant ES015339)National Institutes of Health (U.S.) (Grant GM59281)National Institutes of Health (U.S.) (Grant CA112967)United States. Dept. of Defense (Grant W81XWH-07-0448)W. M. Keck FoundationLAM Foundatio

DAF-16/FOXO and HLH-30/TFEB function as combinatorial transcription factors to promote stress resistance and longevity

The ability to perceive and respond to harmful conditions is crucial for the survival of any organism. The transcription factor DAF-16/FOXO is central to these responses, relaying distress signals into the expression of stress resistance and longevity promoting genes. However, its sufficiency in fulfilling this complex task has remained unclear. Using C. elegans, we show that DAF-16 does not function alone but as part of a transcriptional regulatory module, together with the transcription factor HLH-30/TFEB. Under harmful conditions, both transcription factors translocate into the nucleus, where they often form a complex, co-occupy target promoters, and co-regulate many target genes. Interestingly though, their synergy is stimulus-dependent: They rely on each other, functioning in the same pathway, to promote longevity or resistance to oxidative stress, but they elicit heat stress responses independently, and they even oppose each other during dauer formation. We propose that this module of DAF-16 and HLH-30 acts by combinatorial gene regulation to relay distress signals into the expression of specific target gene sets, ensuring optimal survival under each given threat