title: Loss of Interdependent Binding by the FoxO1 and FoxA1/A2 Forkhead Transcription Factors Culminates in Perturbation of Active Chromatin Marks and Binding of Transcriptional Regulators at Insulin-sensitive Genes.
abstract: FoxO1 binds to insulin response elements located in the promoters of insulin-like growth factor-binding protein 1 (IGFBP1) and glucose-6-phosphatase (G6Pase), activating their expression. Insulin-mediated phosphorylation of FoxO1 promotes cytoplasmic translocation, inhibiting FoxO1-mediated transactivation. We have previously demonstrated that FoxO1 opens and remodels chromatin assembled from the IGFBP1 promoter via a highly conserved winged helix motif. This finding, which established FoxO1 as a "pioneer" factor, suggested a model whereby FoxO1 chromatin remodeling at regulatory targets facilitates binding and recruitment of additional regulatory factors. However, the impact of FoxO1 phosphorylation on its ability to bind chromatin and the effect of FoxO1 loss on recruitment of neighboring transcription factors at its regulatory targets in liver chromatin is unknown. In this study, we demonstrate that an amino acid substitution that mimics insulin-mediated phosphorylation of a serine in the winged helix DNA binding motif curtails FoxO1 nucleosome binding. We also demonstrate that shRNA-mediated loss of FoxO1 binding to the IGFBP1 and G6Pase promoters in HepG2 cells significantly reduces binding of RNA polymerase II and the pioneer factors FoxA1/A2. Knockdown of FoxA1 similarly reduced binding of RNA polymerase II and FoxO1. Reduction in acetylation of histone H3 Lys-27 accompanies loss of FoxO1 and FoxA1/A2 binding. Interdependent binding of FoxO1 and FoxA1/A2 possibly entails cooperative binding because FoxO1 and FoxA1/A2 facilitate one another's binding to IGFPB1 promoter DNA. These results illustrate how transcription factors can nucleate transcriptional events in chromatin in response to signaling events and suggest a model for regulation of hepatic glucose metabolism through interdependent FoxO/FoxA binding.
authors.affiliation: From the Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors.forename: Akua
authors.initials: A
authors.lastname: Yalley
authors.affiliation: From the Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors.forename: Daniel
authors.initials: D
authors.lastname: Schill
authors.affiliation: From the Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors.forename: Mitsutoki
authors.initials: M
authors.lastname: Hatta
authors.affiliation: From the Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
authors.forename: Nicole
authors.initials: N
authors.lastname: Johnson
authors.affiliation: From the Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 lcirillo@mcw.edu.
authors.forename: Lisa Ann
authors.initials: LA
authors.lastname: Cirillo
mesh_terms: D000818:Animals; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D056945:Hep G2 Cells; D051541:Hepatocyte Nuclear Factor 3-alpha / Q000235:genetics / Q000378:metabolism*; D051542:Hepatocyte Nuclear Factor 3-beta / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D010766:Phosphorylation / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000502:physiology*; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology*
chemical_list: C496499:FOXA1 protein, human; C496502:FOXA2 protein, human; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C496500:Foxa1 protein, mouse; C496503:Foxa2 protein, mouse; C467200:Foxo1 protein, mouse; D051541:Hepatocyte Nuclear Factor 3-alpha; C032231:IGFBP1 protein, human; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D051542:Hepatocyte Nuclear Factor 3-beta; D012319:RNA Polymerase II
keywords: FoxA1; FoxA2; FoxO1; chromatin; gene regulation; histone modification; insulin; nucleosome