title: The activated glucocorticoid receptor inhibits the transcription factor T-bet by direct protein-protein interaction.
abstract: Glucocorticoids (GCs) immunosuppression acts via regulation of several transcription factors (TF), including activating protein (AP)-1, NF-kappaB, and NFAT. GCs inhibit Th1 cytokines and promote a shift toward Th2 differentiation. Th1 phenotype depends on TF T-bet. In this study, we examined GC regulation of T-bet. We found that GCs inhibit T-bet transcriptional activity. We show that glucocorticoid receptor (GR) physically interacts with T-bet both in transfected cell lines and in primary splenocyte cultures with endogenous GR and T-bet. This interaction also blocks GR-dependent transcription. We show both in vitro and in vivo at endogenous binding sites that the mechanism underlying T-bet inhibition further involves reduction of T-bet binding to DNA. Using specific mutations of GR, we demonstrate that the first zinc finger region of GR is required for T-bet inhibition. GCs additionally inhibit T-bet both at mRNA and protein expression levels, revealing another layer of GR action on T-bet. Finally, we examined the functional consequences of GR/T-bet interaction on IFN-gamma, showing that GCs inhibit transcriptional activity of T-bet on its promoter. In view of the crucial role of T-bet in T cell differentiation and inflammation, we propose that GR inhibitory interaction with T-bet may be an important mechanism underlying the immunosuppressive properties of GCs.
authors.affiliation: Laboratorio de Fisiología y Biología Molecular, Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBYNE-CONICET, Buenos Aires, Argentina.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Liberman
authors.forename: Damian
authors.initials: D
authors.lastname: Refojo
authors.forename: Jimena
authors.initials: J
authors.lastname: Druker
authors.forename: Marta
authors.initials: M
authors.lastname: Toscano
authors.forename: Theo
authors.initials: T
authors.lastname: Rein
authors.forename: Florian
authors.initials: F
authors.lastname: Holsboer
authors.forename: Eduardo
authors.initials: E
authors.lastname: Arzt
mesh_terms: D000818:Animals; D002460:Cell Line; D005938:Glucocorticoids / Q000378:metabolism; D007249:Inflammation; D007371:Interferon-gamma / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D013154:Spleen / Q000166:cytology / Q000276:immunology; D020825:T-Box Domain Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D000098815:T-bet Transcription Factor
chemical_list: D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; D020825:T-Box Domain Proteins; D000098815:T-bet Transcription Factor; D007371:Interferon-gamma