FoxO1 and FoxA1/2 form a complex on DNA and cooperate to open chromatin at insulin-regulated genes.

We have previously shown that cooperative, interdependent binding by the pioneer factors FoxO1 and FoxA1/2 is required for recruitment of RNA polymerase II and H3K27 acetylation to the promoters of insulin-regulated genes. However, the underlying mechanisms are unknown. In this study, we demonstrate that, in HepG2 cells, FoxO1 and FoxA2 form a complex on DNA that is disrupted by insulin treatment.

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.

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.

Stable chromatin binding prevents FoxA acetylation, preserving FoxA chromatin remodeling.

FoxA1-3 (formerly HNF3alpha, -beta, and -gamma), members of the FoxA subfamily of forkhead transcription factors, function as initial chromatin-binding and chromatin-remodeling factors in a variety of tissues, including liver and pancreas. Despite essential roles in development and metabolism, regulation of FoxA factors is not well understood. This study examines a potential role for acetylation in the regulation of FoxA chromatin binding and remodeling.

Chromatin opening and stable perturbation of core histone:DNA contacts by FoxO1.

FoxO1, a member of the forkhead rabdomyosarcoma (FoxO) subfamily of transcription factors, binds DNA via a highly conserved winged-helix "forkhead box" motif used by other regulatory proteins to mediate their effects through chromatin binding and remodeling. To examine how FoxO1 regulates target genes in chromatin, we studied the binding of purified recombinant FoxO1 protein to nucleosome particles and chromatin arrays containing the insulin-like growth factor-binding protein 1 promoter. We found that FoxO1 is able to bind to its cognate sites within the insulin-like growth factor-binding protein 1 promoter on a nucleosome.

Integrase-specific enhancement and suppression of retroviral DNA integration by compacted chromatin structure in vitro.

Integration of viral DNA into the host chromosome is an obligatory step in retroviral replication and is dependent on the activity of the viral enzyme integrase. To examine the influence of chromatin structure on retroviral DNA integration in vitro, we used a model target comprising a 13-nucleosome extended array that includes binding sites for specific transcription factors and can be compacted into a higher-ordered structure. We found that the efficiency of in vitro integration catalyzed by human immunodeficiency virus type 1 (HIV-1) integrase was decreased after compaction of this target with histone H1.

The CBP bromodomain and nucleosome targeting are required for Zta-directed nucleosome acetylation and transcription activation.

The Epstein-Barr virus (EBV)-encoded lytic activator Zta is a bZIP protein that can stimulate nucleosomal histone acetyltransferase (HAT) activity of the CREB binding protein (CBP) in vitro. We now show that deletion of the CBP bromo- and C/H3 domains eliminates stimulation of nucleosomal HAT activity in vitro and transcriptional coactivation by Zta in transfected cells. In contrast, acetylation of free histones was not affected by the addition of Zta or by deletions in the bromo or C/H3 domain of CBP.

Opening of compacted chromatin by early developmental transcription factors HNF3 (FoxA) and GATA-4.

The transcription factors HNF3 (FoxA) and GATA-4 are the earliest known to bind the albumin gene enhancer in liver precursor cells in embryos. To understand how they access sites in silent chromatin, we assembled nucleosome arrays containing albumin enhancer sequences and compacted them with linker histone. HNF3 and GATA-4, but not NF-1, C/EBP, and GAL4-AH, bound their sites in compacted chromatin and opened the local nucleosomal domain in the absence of ATP-dependent enzymes.