Structure and Dynamic Properties of a Glucocorticoid Receptor-Induced Chromatin Transition

Abstract

Activation of the mouse mammary tumor virus (MMTV) promoter by the glucocorticoid receptor (GR) is associated with a chromatin structural transition in the B nucleosome region of the viral long terminal repeat (LTR). Recent evidence indicates that this transition extends upstream of the B nucleosome, encompassing a region larger than a single nucleosome (G. Fragoso, W. D. Pennie, S. John, and G. L. Hager, Mol. Cell. Biol. 18:3633-3644). We have reconstituted MMTV LTR DNA into a polynucleosome array using Drosophila embryo extracts. We show binding of purified GR to specific GR elements within a large, multinucleosome array and describe a GR-induced nucleoprotein transition that is dependent on ATP and a HeLa nuclear extract. Previously uncharacterized GR binding sites in the upstream C nucleosome region are involved in the extended region of chromatin remodeling. We also show that GR-dependent chromatin remodeling is a multistep process; in the absence of ATP, GR binds to multiple sites on the chromatin array and prevents restriction enzyme access to recognition sites. Upon addition of ATP, GR induces remodeling and a large increase in access to enzymes sites within the transition region. These findings suggest a dynamic model in which GR first binds to chromatin after ligand activation, recruits a remodeling activity, and is then lost from the template. This model is consistent with the recent description of a "hit-and-run" mechanism for GR action in living cells

Glutaraldehyde Modified Mica: A New Surface for Atomic Force Microscopy of Chromatin

“…For that purpose, an ϳ2-kb DNA fragment from the MMTV promoter region was reconstituted in vitro with HeLa histones. This chromatin region was chosen because it undergoes nucleosome remodeling in response to hormone induction in vivo (Hager, 2001;Hager et al, 1995) and in vitro (Fletcher et al, 2000) and has become an extremely important model system for studying the nucleosome changes associated with gene activation in eukaryotes. The images of these arrays on GD-mica are as clear as those from the 172-12 arrays.…”

Control of nuclear receptor function by local chromatin structure

“…Furthermore, we suggest that the vast majority of localized reorganization events are not stable but in fact represent a highly dynamic process. We have proposed that the rapid exchange observed for TFs and response elements in chromatin [38,39,89,90] has a direct correlation to chromatin remodeling [37,39,91,92]. The nucleosomes at promoter regions are also characterized by a high turnover rate independent of whether they are in active or repressed state [71,93].…”

Intrinsic DNA bends: an organizer of local chromatin structure for transcription

“…Chromatin transition then follows. (76) In addition to these two examples, there is general indication of the significance of translational and rotational positionings of nucleosome in the access of specific DNA-binding proteins to regulatory DNA elements. (77±80) What drives the nucleosome positioning that allows the activators binding?…”