Regulation of C. elegans DAF-16 and its human ortholog FKHRL1 by the daf-2 insulin-like signaling pathway.
C. elegans insulin-like signaling regulates metabolism, development, and life span. This signaling pathway negatively regulates the activity of the forkhead transcription factor DAF-16. daf-16 encodes multiple isoforms that are expressed in distinct tissue types and are probable orthologs of human FKHRL1, FKHR, and AFX. We show that human FKHRL1 can partially replace DAF-16, proving the orthology. In mammalian cells, insulin and insulin-like growth factor signaling activate AKT/PKB kinase to negatively regulate the nuclear localization of DAF-16 homologs (reviewed in ). We show that the absence of AKT consensus sites on DAF-16 is sufficient to cause dauer arrest in daf-2(+) animals, proving that daf-16 is the major output of insulin signaling in C. elegans. FKHR, FKRHL1, and AFX may similarly be the major outputs of mammalian insulin signaling. daf-2 insulin signaling, via AKT kinases, negatively regulates DAF-16 by controlling its nuclear localization. Surprisingly, we find that daf-7 TGF-beta signaling also regulates DAF-16 nuclear localization specifically at the time when the animal makes the commitment between diapause and reproductive development. daf-16 function is supported by the combined action of two distinct promoter/enhancer elements, whereas the coding sequences of two major DAF-16 isoforms are interchangeable. Together, these observations suggest that the combined effects of transcriptional and posttranslational regulation of daf-16 transduce insulin-like signals in C. elegans and perhaps more generally.
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Present addresses: WormBase, Division of Biology, California Institute of Technology 156-29, Pasadena, CA 91125, USA. ruvkun@frodo.mgh.harvard.edu
Hench
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Ruvkun
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D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins / Q000502:physiology*; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D011972:Receptor, Insulin / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology*
D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D007328:Insulin; D014157:Transcription Factors; C108831:daf-16 protein, C elegans; C107483:DAF-2 protein, C elegans; D011972:Receptor, Insulin