Chromatin Remodeling Complexes Interact Dynamically with a Glucocorticoid Receptor–regulated Promoter

Abstract

Brahma (BRM) and Brahma-related gene 1 (BRG1) are the ATP-dependent catalytic subunits of the SWI/SNF family of chromatin-remodeling complexes. These complexes are involved in essential processes such as cell cycle, growth, differentiation, and cancer. Using imaging approaches in a cell line that harbors tandem repeats of stably integrated copies of the steroid responsive MMTV-LTR (mouse mammary tumor virus-long terminal repeat), we show that BRG1 and BRM are recruited to the MMTV promoter in a hormone-dependent manner. The recruitment of BRG1 and BRM resulted in chromatin remodeling and decondensation of the MMTV repeat as demonstrated by an increase in the restriction enzyme accessibility and in the size of DNA fluorescence in situ hybridization (FISH) signals. This chromatin remodeling event was concomitant with an increased occupancy of RNA polymerase II and transcriptional activation at the MMTV promoter. The expression of ATPase-deficient forms of BRG1 (BRG1-K-R) or BRM (BRM-K-R) inhibited the remodeling of local and higher order MMTV chromatin structure and resulted in the attenuation of transcription. In vivo photobleaching experiments provided direct evidence that BRG1, BRG1-K-R, and BRM chromatin-remodeling complexes have distinct kinetic properties on the MMTV array, and they dynamically associate with and dissociate from MMTV chromatin in a manner dependent on hormone and a functional ATPase domain. Our data provide a kinetic and mechanistic basis for the BRG1 and BRM chromatin-remodeling complexes in regulating gene expression at a steroid hormone inducible promoter. INTRODUCTIONThe eukaryotic genome is organized into higher order chromatin structures in the nucleus. The regulation of eukaryotic gene expression in the context of chromatin is a complex event and is essential for numerous cellular processes (Lemon and Tjian, 2000;Orphanides and Reinberg, 2002;Labrador and Corces, 2002;Maniatis and Reed, 2002;Felsenfeld and Groudine, 2003;Roberts and Orkin, 2004). Maintenance, establishment, and modification of global chromatin organization and local chromatin structure are modulated by a large number of chromatin-binding proteins that generate transcriptionally permissive or repressed chromatin domains in response to environmental stimuli (Workman and Kingston, 1998;Peterson and Workman, 2000;Jones and Kadonaga, 2000;Wu and Grunstein, 2000;Wolffe and Hansen, 2001;Becker et al., 2002). The association of linker histones and nonhistone and heterochromatin-specific proteins such as high mobility group proteins and HP1 play key roles in the generation of higher order chromatin structures (Arents et al., 1991; Luger et al., 1997;Bustin, 1999;Eissenberg and Elgin, 2000;Hill, 2001;Thomas and Travers, 2001;Woodcock and Dimitrov, 2001;Grewal and Elgin, 2002;Bianchi and Agresti, 2005;Bustin et al., 2005;Verschure et al., 2005). The stearically restricted environment presented by chromatin is in part overcome by multisubunit protein complexes that enzymatically regulate chromatin structure. These complexes can e...

Sensitization of retinoids and corticoids to epigenetic drugs in MYC-activated lung cancers by antitumor reprogramming

“…Components of the SWI/SNF complex bind to various nuclear receptors, such as those of estrogen, progesterone, androgen, glucocorticoids (GCs) and retinoic acid (RA), thereby adapting the gene expression programs to the demands of the cell environmental requirements. [14][15][16][17][18] RA and GC are well-known modulators of cell differentiation, embryonic development and morphogenesis 19 and are used therapeutically to treat some types of cancers. GC are part of the curative treatment of acute lymphoblastic leukemia while RA is the therapeutic agent for some neuroblastomas and acute promyelocytic leukemia, which both carry the promyelocytic leukemia-RA receptor alpha gene fusion.…”

Recruitment of the SWI/SNF Chromatin Remodeling Complex to Steroid Hormone-regulated Promoters by Nuclear Receptor Coactivator Flightless-I

“…The role of SWI/SNF complexes in nuclear receptor (NR)-mediated transcriptional activation was first studied for the glucocorticoid receptor in a heterologous yeast model system and later in mammalian cells (3,6,7). SWI/SNF complexes play critical roles in establishing hypersensitive chromatin architecture associated with steroid hormone receptor binding sites on DNA and are recruited to these sites in a hormone-dependent manner (4,8,9).…”

Novel Mechanism of Negative Regulation of 1,25-Dihydroxyvitamin D3-induced 25-Hydroxyvitamin D3 24-Hydroxylase (Cyp24a1) Transcription

“…It has been suggested that estrogen receptor ␣ recruits the BRG1 complex through the BRG1 complex subunit BAF57 (36). Transcriptional dependence for BRG1 activity has also been observed for GR-responsive promoters including mouse mammary tumor virus, p21, and 11␤-hydroxysteroid dehydrogenase type 2 (11,37). Studies examining hormone-mediated transcriptional activation of mouse mammary tumor virus have shown that the progesterone receptor can compete with GR for available BRG1, resulting in inhibition of GR-mediated transactivation (38).…”