Insights on glucocorticoid receptor activity modulation through the binding of rigid steroids

PRESMAN, DIEGO M.; ALVAREZ, LAUTARO D.; LEVI, VALERIA; EDUARDO, SILVINA L.; DIGMAN, MICHELLE A.; MARTÍ, MARCELO A.; VELEIRO, ADRIANA S.; BURTON, GERARDO; PECCI, ADALÍ

PLOS ONE

PUBLIC LIBRARY SCIENCE

Año: 2010 p. 13279 - 13279

1932-6203

Background: The glucocorticoid receptor (GR) is a transcription factor that regulates gene expression in a ligand-dependentfashion. This modular protein is one of the major pharmacological targets due to its involvement in both cause andtreatment of many human diseases. Intense efforts have been made to get information about the molecular basis of GRactivity.Methodology/Principal Findings: Here, the behavior of four GR-ligand complexes with different glucocorticoid andantiglucocorticoid properties were evaluated. The ability of GR-ligand complexes to oligomerize in vivo was analyzed byperforming the novel Number and Brightness assay. Results showed that most of GR molecules form homodimers inside thenucleus upon ligand binding. Additionally, in vitro GR-DNA binding analyses suggest that ligand structure modulates GRDNAinteraction dynamics rather than the receptor’s ability to bind DNA. On the other hand, by coimmunoprecipitationstudies we evaluated the in vivo interaction between the transcriptional intermediary factor 2 (TIF2) coactivator anddifferent GR-ligand complexes. No correlation was found between GR intranuclear distribution, cofactor recruitment and thehomodimerization process. Finally, Molecular determinants that support the observed experimental GR LBD-ligand/TIF2interaction were found by Molecular Dynamics simulation.Conclusions/Significance: The data presented here sustain the idea that in vivo GR homodimerization inside the nucleuscan be achieved in a DNA-independent fashion, without ruling out a dependent pathway as well. Moreover, since at leastone GR-ligand complex is able to induce homodimer formation while preventing TIF2 coactivator interaction, resultssuggest that these two events might be independent from each other. Finally, 21-hydroxy-6,19-epoxyprogesterone arises asa selective glucocorticoid with potential pharmacological interest. Taking into account that GR homodimerization andcofactor recruitment are considered essential steps in the receptor activation pathway, results presented here contribute tounderstand how specific ligands influence GR behavior.