title: The Mediator subunit MED1/TRAP220 is required for optimal glucocorticoid receptor-mediated transcription activation.
abstract: The MED1/TRAP220 subunit of the Mediator plays a key role in facilitating ligand-dependent interactions of this multisubunit coactivator complex with nuclear receptors through their ligand binding domains. The isolated MED1/TRAP220 protein previously was shown to interact with glucocorticoid receptor (GR) in a ligand-dependent manner. However, the functional role of MED1/TRAP220, within the context of the entire Mediator, is not well studied in GR-mediated transcription. In this study, we show that GR binds directly to the Mediator complex and that both LXXLL motifs of MED1/TRAP220 contribute to its binding to GR. Furthermore, using a Med1/Trap220-/- mouse embryonic fibroblast (MEF) line that lacks entirely MED1/TRAP220, we show that MED1/TRAP220 enhances GR-mediated transcription from an MMTV promoter based-reporter gene and that mutations in the MED1/TRAP220 LXXLL motifs reduce, but do not eliminate, GR-dependent transcription. An analysis of endogenous genes in Med1/Trap220-/- cells has confirmed a variable MED1/TRAP220 requirement for different GR target genes. Taken together, these findings support the idea that Mediator, at least in part through MED1/TRAP220, plays a coregulatory role in ligand-dependent GR-mediated gene expression.
authors.affiliation: Laboratory of Biochemistry and Molecular Biology, The Rockefeller University, New York, NY 10021, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Robert G
authors.initials: RG
authors.lastname: Roeder
mesh_terms: D000818:Animals; D001665:Binding Sites; D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D056913:Mediator Complex Subunit 1; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D017434:Protein Structure, Tertiary; D011965:Receptors, Glucocorticoid / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation