daf-2;wwp-1

Dietary restriction extends longevity in diverse species, suggesting that there is a conserved mechanism for nutrient regulation and prosurvival responses. Here we show a role for the HECT (homologous to E6AP carboxy terminus) E3 ubiquitin ligase WWP-1 as a positive regulator of lifespan in Caenorhabditis elegans in response to dietary restriction. We find that overexpression of wwp-1 in worms extends lifespan by up to 20% under conditions of ad libitum feeding. This extension is dependent on the FOXA transcription factor pha-4, and independent of the FOXO transcription factor daf-16. Reduction of wwp-1 completely suppresses the extended longevity of diet-restricted animals. However, the loss of wwp-1 does not affect the long lifespan of animals with compromised mitochondrial function or reduced insulin/IGF-1 signalling. Overexpression of a mutant form of WWP-1 lacking catalytic activity suppresses the increased lifespan of diet-restricted animals, indicating that WWP-1 ubiquitin ligase activity is essential for longevity. Furthermore, we find that the E2 ubiquitin conjugating enzyme, UBC-18, is essential and specific for diet-restriction-induced longevity. UBC-18 interacts with WWP-1 and is required for the ubiquitin ligase activity of WWP-1 and the extended longevity of worms overexpressing wwp-1. Taken together, our results indicate that WWP-1 and UBC-18 function to ubiquitinate substrates that regulate diet-restriction-induced longevity.

Genetic and RNA interference (RNAi) screens for life span regulatory genes have revealed that the daf-2 insulin-like signaling pathway plays a major role in Caenorhabditis elegans longevity. This pathway converges on the DAF-16 transcription factor and may regulate life span by controlling the expression of a large number of genes, including free-radical detoxifying genes, stress resistance genes, and pathogen resistance genes. We conducted a genome-wide RNAi screen to identify genes necessary for the extended life span of daf-2 mutants and identified approximately 200 gene inactivations that shorten daf-2 life span. Some of these gene inactivations dramatically shorten daf-2 mutant life span but less dramatically shorten daf-2; daf-16 mutant or wild-type life span. Molecular and behavioral markers for normal aging and for extended life span in low insulin/IGF1 (insulin-like growth factor 1) signaling were assayed to distinguish accelerated aging from general sickness and to examine age-related phenotypes. Detailed demographic analysis, molecular markers of aging, and insulin signaling mutant test strains were used to filter progeric gene inactivations for specific acceleration of aging. Highly represented in the genes that mediate life span extension in the daf-2 mutant are components of endocytotic trafficking of membrane proteins to lysosomes. These gene inactivations disrupt the increased expression of the DAF-16 downstream gene superoxide dismutase sod-3 in a daf-2 mutant, suggesting trafficking between the insulin-like receptor and DAF-16. The activities of these genes may normally decline during aging.