Promoter of the CDKN1B gene, encoding CDK inhibitor p27Kip1, contains forkhead box elements that are required for induction of CDKN1B gene transcription by FOXO transcription factors FOXO1, FOXO3 (Dijkers et al. 2000, Lees et al. 2008) and FOXO4 (Medema et al. 2000). Direct binding of FOXO transcription factors to the CDKN1B gene promoter has not been demonstrated. Acetylation of FOXO4 by EP300 (p300) or CREBBP (CBP) in response to oxidative stress interferes with FOXO4-mediated induction of CDKN1B gene transcription (Dansen et al. 2009).