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 A challenge in the field of transcriptional regulation is to discover how signaling pathways exert their influence on chromatin structure through DNA binding proteins. Targeted modification of transcription factors, which provides rapid alterations in their activities in response to external and internal stimuli, is an important mechanism in the regulation of their target genes. The perturbations in chromatin structure required to poise genes for activation and modulate their expression are mediated, at least in part, by initial "pioneer" chromatin binding factors capable of binding to and remodeling chromatin in response to environmental and/or developmental cues (1-12) (reviewed in Refs. 13 and 14). Previous studies have revealed that targeted post-translational modification of these pioneer factors can substantially alter their ability to interact with cellular chromatin (15-18) and in vitro assembled chromatin templates (19,20). However, the impact of these alterations in pioneer factor chromatin binding on epigenetic modification and regulatory factor recruitment necessary for the transcriptional response to extracellular signaling cascades is largely unstudied.To address this, we have investigated the impact of insulinmediated phosphorylation on chromatin binding and regulatory factor recruitment by the pioneer forkhead transcription factor FoxO1. FoxO1 (formerly FKHR) belongs to the FoxO 3 subfamily of forkhead transcription factors that also includes FoxO3, FoxO4, and FoxO6 (21,22). The FoxO factors regulate the expression of multiple genes encoding glucose metabolic enzymes, pro-apoptotic factors, and cell cycle regulators in multiple tissues . In particular, FoxO1 regulates the expression of the insulin-like growth factor-binding protein 1 (IGFBP1) and glucose-6-phosphatase (G6PC) genes in response to insulin signaling in liver (26 -29), and ablation or inactivation of FoxO1 in mice leads to insulin-mediated repression of gluconeogenesis (30,31).The function of FoxO factors is dynamically regulated by post-translational modification. In response to insulin, protein kinase B (PKB)/Akt-mediated phosphorylation of FoxO1 at three conserved sites, located in the N-terminal, DNA binding, and C-terminal domains of the protein, respectively, leads to the cytoplasmic retention of FoxO1 and the consequent inhibition of its transcriptio...

Mitochondrial-epigenetic crosstalk in environmental toxicology

“…Activation of these gene targets requires local chromatin remodeling to enable recruitment of transcriptional machinery. Binding of “pioneer” transcription factors triggers opening of chromatin to enable binding and recruitment of additional factors necessary for transcription ([9], reviewed in [10]). For example, the TFs FoxO1 and FoxA1/2 function as pioneer factors at the insulin target genes insulin-like growth factor-binding protein 1 ( IGFBP1 ) and glucose-6-phosphatase ( G6PC ) [10].…”

“…Binding of “pioneer” transcription factors triggers opening of chromatin to enable binding and recruitment of additional factors necessary for transcription ([9], reviewed in [10]). For example, the TFs FoxO1 and FoxA1/2 function as pioneer factors at the insulin target genes insulin-like growth factor-binding protein 1 ( IGFBP1 ) and glucose-6-phosphatase ( G6PC ) [10]. FOXO TFs’ pioneer capabilities are due to a highly conserved winged helix DNA binding motif; this variant of a helix-turn-helix motif in which the recognition helix is flanked by two polypeptide “wings” is structurally similar to the winged helix DNA binding globular domain of the linker histone protein [11, 12].…”

“…This structural similarity enables FoxO1 and FoxA1/A2 to stably bind recognition sequences within nucleosome particles and open linker histone-compacted nucleosome arrays in vitro [13, 14]. Cooperative binding of FoxO1 and FoxA1/A2 to adjacent IREs at both IGFBP1 and G6PC in HepG2 cells triggers changes to histone PTMs and recruitment of RNA polymerase II (RNAPII) to stimulate target gene transcription [10]. Specifically, TF binding led to statistically significant increases in acetylation of lysine 27 on histone H3 (H3K27ac), a mark of transcriptionally active chromatin, at the IGFBP1 promoter, as well as an apparent but not statistically significant increases in active marks acetylated H3K9 (H3K9ac) and trimethylated H3K4 (H3K4me3), as well as H3K4 dimethylation (H3K4me2), a mark of transcriptionally poised chromatin [11].…”

Crystal structures reveal a new and novel FoxO1 binding site within the human glucose-6-phosphatase catalytic subunit 1 gene promoter

“…Furthermore, interdependent binding of Fox family members, i.e. FoxO1 and FoxA1/A2, to insulin-sensitive genes including G6PC1 is known to nucleate transcriptional events in chromatin in response to signaling events leading to regulation of hepatic glucose metabolism (Yalley et al, 2016). Therefore, whether or not other members of the FoxO family bind to all IRE sites and how these multiple IRE sites on the G6PC1 promoter are synergistically utilized for coactivator recruitment and chromatin remodeling warrant further investigation.…”

Bombyx mori transcription factors FoxA and SAGE divergently regulate the expression of wing cuticle protein gene 4 during metamorphosis

“…In Caenorhabditis elegans, DAF-16/FOXO and PHA-4/FOXA co-regulated a set of downstream transcription factor genes (41). In HepG2 cells, the interdependent binding of FoxO1 and FoxA1/A2 influenced the IGFBP1 promoter activity to regulate the glucose metabolism of hepatic patients (42). Both FoxC and FoxJ were involved in the regulation of individual development (43,44).…”