Chromatin remodeling complexes involved in gene activation by the glucocorticoid receptor

Abstract

The glucocorticoid receptor (GR) belongs to a large family of ligand-inducible nuclear receptors and consists of a ligand binding domain, a DNA binding domain and transactivation domains. The main transcriptional activation domain, c1, is located in the N-terminus of the receptor. The r1c represents the minimal core activation domain of r1. We have studied the molecular mechanisms by which the GR can activate transcription through its N-terminal transactivation domain [tau]1 domain or [tau]1c.

We have shown that the vIc, can interact with purified proteins domain domain and CBP. In addition, the r1 can interact with purified histone acetyltransferase (HAT) complexes SAGA and domain and the domain chromatin remodeling complex. Interestingly, mutations in rl that affect the transactivation activity in vivo, also directly affect rl-interaction with all of the target factors we have tested (i.e. domain TBP, CBP, SAGA, SWl/SNF), indicating that these factors share binding determinants on [tau]1.

The activity of the c1 mutants in vivo also correlates with their activity in an in vitro transcription assay with target factors present. Both SAGA and domain can stimulate GAL4-[tau]1-driven transcription from chromatin templates in vitro and the transcriptional efficiency is affected by mutations in the r1 domain. The SWI/SNF complex can also potentiate r1-driven transcription from chromatin templates in vitro. These results indicate that [tau]1 may mediate transactivation in vivo through the recruitment of multiple chromatin remodeling complexes to the promoters of target genes.

By measuring the activity of several r1 domain with different activities in yeast cells deficient for Ada proteins, we have shown that other gene activation mechanisms, in addition to the Ada pathway, are involved in the activity of the [tau]1c domain. Using the same approach, we could determine that a SWI/SNF-independent pathway also exists in yeast, suggesting that Ada-containing HAT complexes and the SWI/SNF complex represent independent pathways when mediating r1c activity.