Long-term starvation and ageing induce AGE-1/PI 3-kinase-dependent translocation of DAF-16/FOXO to the cytoplasm.
BACKGROUND
The provision of stress resistance diverts resources from development and reproduction and must therefore be tightly regulated. In Caenorhabditis elegans, the switch to increased stress resistance to promote survival through periods of starvation is regulated by the DAF-16/FOXO transcription factor. Reduction-of-function mutations in AGE-1, the C. elegans Class IA phosphoinositide 3-kinase (PI3K), increase lifespan and stress resistance in a daf-16 dependent manner. Class IA PI3Ks downregulate FOXOs by inducing their translocation to the cytoplasm. However, the circumstances under which AGE-1 is normally activated are unclear. To address this question we used C. elegans first stage larvae (L1s), which when starved enter a developmentally-arrested diapause stage until food is encountered.


RESULTS
We find that in L1s both starvation and daf-16 are necessary to confer resistance to oxidative stress in the form of hydrogen peroxide. Accordingly, DAF-16 is localised to cell nuclei after short-term starvation. However, after long-term starvation, DAF-16 unexpectedly translocates to the cytoplasm. This translocation requires functional age-1. H2O2 treatment can replicate the translocation and induce generation of the AGE-1 product PIP3. Because feeding reduces to zero in ageing adult C. elegans, these animals may also undergo long-term starvation. Consistent with our observation in L1s, DAF-16 also translocates to the cytoplasm in old adult worms in an age-1-dependent manner.


CONCLUSIONS
DAF-16 is activated in the starved L1 diapause. The translocation of DAF-16 to the cytoplasm after long-term starvation may be a feedback mechanism that prevents excessive expenditure on stress resistance. H2O2 is a candidate second messenger in this feedback mechanism. The lack of this response in age-1(hx546) mutants suggests a novel mechanism by which this mutation increases longevity.
Weinkove
David
D
Department of Biology, University College London, London WC1E 6BT, UK. d.weinkove@ucl.ac.uk
Halstead
Jonathan R
JR
Gems
David
D
Divecha
Nullin
N
D000375:Aging; D000483:Alleles; D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D025461:Feedback, Physiological; D005508:Food Deprivation; D051858:Forkhead Transcription Factors; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology; D007295:Inositol Phosphates / Q000737:chemistry; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D018384:Oxidative Stress; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D021381:Protein Transport; D013696:Temperature; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D019076:Transgenes
D029742:Caenorhabditis elegans Proteins; D051858:Forkhead Transcription Factors; D049452:Green Fluorescent Proteins; D006861:Hydrogen Peroxide; D007295:Inositol Phosphates; D019869:Phosphatidylinositol 3-Kinases; D014157:Transcription Factors; C108831:daf-16 protein, C elegans; C118500:inositol 3,4,5-trisphosphate; C100662:AGE-1 protein, C elegans