ABSTRACT
FoxO transcription factors promote longevity across taxa. How they do so is poorly understood. In the nematode Caenorhabditis elegans, the A- and F-isoforms of the FoxO transcription factor DAF-16 extend life span in the context of reduced DAF-2 insulin-like growth factor receptor (IGFR) signaling. To elucidate the mechanistic basis for DAF-16/FoxO-dependent life span extension, we performed an integrative analysis of isoform-specific daf-16/FoxO mutants. In contrast to previous studies suggesting that DAF-16F plays a more prominent role in life span control than DAF-16A, isoform-specific daf-16/FoxO mutant phenotypes and whole transcriptome profiling revealed a predominant role for DAF-16A over DAF-16F in life span control, stress resistance, and target gene regulation. Integration of these datasets enabled the prioritization of a subset of 92 DAF-16/FoxO target genes for functional interrogation. Among 29 genes tested, two DAF-16A-specific target genes significantly influenced longevity. A loss-of-function mutation in the conserved gene gst-20, which is induced by DAF-16A, reduced life span extension in the context of daf-2/IGFR RNAi without influencing longevity in animals subjected to control RNAi. Therefore, gst-20 promotes DAF-16/FoxO-dependent longevity. Conversely, a loss-of-function mutation in srr-4, a gene encoding a seven-transmembrane-domain receptor family member that is repressed by DAF-16A, extended life span in control animals, indicating that DAF-16/FoxO may extend life span at least in part by reducing srr-4 expression. Our discovery of new longevity genes underscores the efficacy of our integrative strategy while providing a general framework for identifying specific downstream gene regulatory events that contribute substantially to transcription factor functions. As FoxO transcription factors have conserved functions in promoting longevity and may be dysregulated in aging-related diseases, these findings promise to illuminate fundamental principles underlying aging in animals.
Subject(s)
Aging/genetics , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans/growth & development , Forkhead Transcription Factors/genetics , Longevity/genetics , Transcription, Genetic , Animals , Caenorhabditis elegans/genetics , Caenorhabditis elegans Proteins/biosynthesis , Forkhead Transcription Factors/biosynthesis , Gene Expression Regulation, Developmental , Insulin/genetics , Mutation , Protein Isoforms , Receptors, Somatomedin/genetics , Signal Transduction/geneticsABSTRACT
FoxO transcription factors (TFs) extend lifespan in invertebrates and may participate in the control of human longevity. The role of FoxO TFs in lifespan regulation has been studied most extensively inC. elegans, where a conserved insulin/insulin-like growth factor signaling (IIS) pathway and the germline both control lifespan by regulating the subcellular localization of the FoxO transcription factor DAF-16. Although the control of FoxO activity through modulation of its subcellular localization is well established, nuclear translocation of FoxO is not sufficient for full FoxO activation, suggesting that undiscovered inputs regulate FoxO activity after its translocation to the nucleus. We have recently discovered a new conserved pathway, the EAK (enhancer-of-akt-1) pathway, which acts in parallel to the Akt/PKB family of serine-threonine kinases to regulate DAF-16/FoxO activity. Whereas mutation of Akt/PKB promotes the nuclear accumulation of DAF-16/FoxO, mutation of eak genes increases nuclear DAF-16/FoxO activity without influencing DAF-16/FoxO subcellular localization. Thus, EAK proteins regulate the activity of nuclear DAF-16/FoxO. Two EAK proteins, EAK-2/HSD-1 and EAK-7, influence C. elegans lifespan and are conserved in mammals. The discovery of the EAK pathway defines a new conserved FoxO regulatory input and may have implications relevant to aging and the pathogenesis of aging-associated diseases.
Subject(s)
Caenorhabditis elegans Proteins/physiology , Caenorhabditis elegans/physiology , Longevity/physiology , 3-Hydroxysteroid Dehydrogenases/genetics , 3-Hydroxysteroid Dehydrogenases/metabolism , Active Transport, Cell Nucleus/physiology , Aging/physiology , Animals , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Cytochrome P-450 Enzyme System/metabolism , Diabetes Mellitus, Type 2/etiology , Diabetes Mellitus, Type 2/metabolism , Disease/etiology , Forkhead Transcription Factors/metabolism , Humans , Mice , Models, Biological , Osteoporosis/etiology , Osteoporosis/metabolism , Oxygenases/metabolism , Proto-Oncogene Proteins c-akt/genetics , Proto-Oncogene Proteins c-akt/metabolism , Signal Transduction/physiology , Transcription Factors/metabolismABSTRACT
FoxO transcription factors control development and longevity in diverse species. Although FoxO regulation via changes in its subcellular localization is well established, little is known about how FoxO activity is regulated in the nucleus. Here, we show that the conserved C. elegans protein EAK-7 acts in parallel to the serine/threonine kinase AKT-1 to inhibit the FoxO transcription factor DAF-16. Loss of EAK-7 activity promotes diapause and longevity in a DAF-16/FoxO-dependent manner. Whereas akt-1 mutation activates DAF-16/FoxO by promoting its translocation from the cytoplasm to the nucleus, eak-7 mutation increases nuclear DAF-16/FoxO activity without influencing DAF-16/FoxO subcellular localization. Thus, EAK-7 and AKT-1 inhibit DAF-16/FoxO activity via distinct mechanisms. Our results implicate EAK-7 as a FoxO regulator and highlight the biological impact of a regulatory pathway that governs the activity of nuclear FoxO without altering its subcellular location.