RESUMO
The lifespan of Caenorhabditis elegans is regulated by the insulin/insulin-like growth factor (IGF)-1 receptor homolog DAF-2, which signals through a conserved phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Mutants in this pathway remain youthful and active much longer than normal animals and can live more than twice as long. This lifespan extension requires DAF-16, a forkhead/winged-helix transcription factor. DAF-16 is thought to be the main target of the DAF-2 pathway. Insulin/IGF-1 signaling is thought to lead to phosphorylation of DAF-16 by AKT activity, which in turn shortens lifespan. Here, we show that the DAF-2 pathway prevents DAF-16 accumulation in nuclei. Disrupting Akt-consensus phosphorylation sites in DAF-16 causes nuclear accumulation in wild-type animals, but, surprisingly, has little effect on lifespan. Thus the DAF-2 pathway must have additional outputs. Lifespan in C. elegans can be extended by perturbing sensory neurons or germ cells. In both cases, lifespan extension requires DAF-16. We find that both sensory neurons and germline activity regulate DAF-16 accumulation in nuclei, but the nuclear localization patterns are different. Together these findings reveal unexpected complexity in the DAF-16-dependent pathways that regulate aging.
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans/fisiologia , Proteínas de Helminto/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Transdução de Sinais , Fatores de Transcrição/metabolismo , Animais , Núcleo Celular/metabolismo , Fatores de Transcrição Forkhead , Regulação da Expressão Gênica , Células Germinativas/metabolismo , Proteínas de Helminto/genética , Insulina/metabolismo , Longevidade/genética , Mutação , Neurônios Aferentes/patologia , Neurônios Aferentes/fisiologia , Fosforilação , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Proteínas Proto-Oncogênicas c-akt , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Estresse Fisiológico , Fatores de Transcrição/genética , Transcrição GênicaRESUMO
Iron is essential for many cellular functions; consequently, disturbances of iron homeostasis, leading to either iron deficiency or iron overload, can have significant clinical consequences. Despite the clinical prevalence of these disorders, the mechanism by which dietary iron is absorbed into the body is poorly understood. We have identified a key component in intestinal iron transport by study of the sex-linked anaemia (sla) mouse, which has a block in intestinal iron transport. Mice carrying the sla mutation develop moderate to severe microcytic hypochromic anaemia. Although these mice take up iron from the intestinal lumen into mature epithelial cells normally, the subsequent exit of iron into the circulation is diminished. As a result, iron accumulates in enterocytes and is lost during turnover of the intestinal epithelium. Biochemical studies have failed to identify the underlying difference between sla and normal mice, therefore, we used a genetic approach to identify the gene mutant in sla mice. We describe here a novel gene, Heph, encoding a transmembrane-bound ceruloplasmin homologue that is mutant in the sla mouse and highly expressed in intestine. We suggest that the hephaestin protein is a multicopper ferroxidase necessary for iron egress from intestinal enterocytes into the circulation and that it is an important link between copper and iron metabolism in mammals.
