Identification of Glucocorticoid Receptor Domains Involved in Transrepression of Transforming Growth Factor-β Action

Abstract

The transforming growth factor-␤ (TGF-␤) and glucocorticoid signaling pathways interact both positively and negatively in regulating a variety of physiological and pathologic processes. We previously reported that liganded glucocorticoid receptor (GR) repressed TGF-␤ induction of human plasminogen activator inhibitor-1 gene transcription by directly targeting the transcriptional activation function of Smad3. To identify the domain(s) in the glucocorticoid receptor involved in this repression, we have examined the ability of various GR truncation, deletion, and substitution mutants to repress TGF-␤ transactivation in Hep3B human hepatoma cells that lack functional endogenous GR. Partial deletions in the ligand-binding domain (LBD), including the 2 and c regions, greatly reduced or eliminated GR repression, whereas deletion of the N-terminal AF1 ( 1) domain and substitution mutations in the DNA-binding domain had little or no effect. Liganded androgen receptor repressed TGF-␤ transactivation, whereas mineralocorticoid receptor did not, and studies with rat GRmineralocorticoid receptor chimeras confirmed that the GR C-terminal domains were required for repression. RU486, a strong antagonist of transactivation by GR, partially reversed repression by wild type GR. Co-immunoprecipitation experiments in Hep3B cells indicated that physical interaction between GR and Smad3 is necessary but not sufficient for repression. Physical interaction required activation of Smad3 by TGF-␤ but not dexamethasone binding to GR. Glutathione S-transferase pull-down assays demonstrated that several regions of the LBD could mediate GR-Smad3 physical interaction. We conclude that the LBD of GR, but not the DNAbinding domain or the N-terminal activation domain, is required for GR-mediated transrepression of TGF-␤ transactivation.

Mechanisms of FSH synthesis: what we know, what we don't, and why you should care

“…Consistent with some of the observations in rat pituitary cultures, suppression of endogenous activin signaling in LbT2 cells attenuates, but does not completely block, dexamethasone-or R5020 (synthetic progestin)-stimulated Fshb promoter activity (189,206). SMAD3 physically interacts with PR (both forms A and B) and GR, and the PR/SMAD3 or GR/SMAD3 combinations synergistically regulate murine promoter activity in the presence of ligand (i.e., exogenous steroid) (189,206,257). Mutagenesis analyses indicate that the proteins must bind to their respective cis-elements to synergistically stimulate promoter activity.…”

Activation of a TGF-β-Specific Multistep Gene Expression Program in Mature Macrophages Requires Glucocorticoid-Mediated Surface Expression of TGF-β Receptor II

“…Taken together with the microarray data (Fig. 1B), our results indicate that dexamethasone has a global effect on the TGF-␤-dependent gene expression program in M2 macrophages rather than solely modulating the expression of single genes, such as IL17RB or others (14,30). We hypothesized that M2 IL-4 and M2 IL-4/dex might show fundamental molecular differences in TGF-␤ signaling.…”

The tumor suppressor effect of the glucocorticoid receptor in skin is mediated via its effect on follicular epithelial stem cells

“…The cross-talk between the GR and either IGF or TGF-b signaling is known (Li et al, 2003;Li et al, 2005), while the effect of glucocorticoids on Wnt pathway has not been well studied. However, recent publications strongly suggest that Wnt pathway is clinically and developmentally an important target for the effect of GR/glucocorticoids (Takayama et al, 2006).…”