FoxO (forkhead box, class O) belongs to the large family of forkhead transcription factors that are characterized by a conserved “forkhead box” DNA-binding domain (1-3). Four mammalian FoxO transcription factors, FoxO1, FoxO3a, FoxO4, and FoxO6 (4-8), have been identified as orthologs of DAF16, an insulin-responsive transcription factor involved in regulating longevity of worms (9) and flies (10).
