Cross-Talk between Nuclear Factor-κB and the Steroid Hormone Receptors: Mechanisms of Mutual Antagonism

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.

Section: Glucocorticoid Receptor Ligand-binding Domain Is Required Fomentioning

confidence: 56%

mentioning

confidence: 99%

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

Wang

Gelehrter

2003

“…Until now, attenuation of GR function in inflammation has been mechanistically linked to the action of proinflammatory cytokines, which can induce the accumulation of the dominant negative ␤-isoform of GR and thereby reduce GC sensitivity (33), or to a negative effect of NF-B on GR transactivation (33,34).…”

Section: Discussionmentioning

confidence: 99%

Interaction and Functional Interference of Glucocorticoid Receptor and SOCS1

Haffner

Jurgeit

Berlato

et al. 2008

Cytokine and glucocorticoid (GC) hormone signaling act in an integrated fashion to control inflammation and immune response. Here we establish a new mode of interaction of these two pathways and propose Suppressor of Cytokine Signaling (SOCS)-1 as an essential player in mediating cross-talk. We observed that glucocorticoid receptor (GR) and SOCS1 form an intracellular complex through an interaction, which required the SH2 domain of SOCS1 and the ligand binding domain of GR. Furthermore, GC stimulation was found to increase the nuclear level of SOCS1. SOCS1 binding to the GR did not require ligand binding of the receptor; however, it was abolished after long term GC stimulation, suggesting a functional role of the interaction for the early phase of GC action. The interaction between GR and SOCS1 appeared to negatively influence the transcription of the two GR-regulated genes, FKBP5 and MKP1, because the GC-dependent expression of these genes was inhibited by the SOCS1 inducer IFN␥ and enhanced in SOCS1-deficient murine embryonic fibroblasts as compared with IFN␥ treated wild-type cells. Our results suggest a prominent role of SOCS1 in the early phase of cross-talk between GR and cytokine signaling.Key principles determining the cellular response to cytokine signaling are duration of stimulus, prevalence of inhibitory feedback mechanisms, and operation of cross-talk with other cellular pathways. All of these factors interact to influence the strength and the quality of the physiological response. For cytokines operating via the Janus kinase (JAK) 2 /signal transducers and activators of transcription (STAT) pathway, both suppressor of cytokine signaling (SOCS) proteins and the glucocorticoid receptor (GR) have been identified as important intracellular regulators in this respect.SOCS proteins have been shown to serve both as feedback inhibitors as well as mediators of cross-talk with other signaling pathways. They comprise a family of 8 members, initially described as negative feedback regulators of the JAK/STAT pathway. All SOCS proteins share two functional domains: an SH2 domain, which primarily enables binding of phosphorylated tyrosine residues, and a C-terminal SOCS box, which serves as a recruiting site for ubiquitin ligases, thereby combining specific inhibition of JAK catalytic activity with generic mechanisms such as competition over binding sites and targeting of associated proteins to proteasomal degradation (1, 2).Recent evidence suggests that the negative regulatory function of SOCS is not restricted to the JAK/STAT pathway. Through interaction with other signaling intermediates SOCS proteins can interfere with crucial signaling pathways such as the NF-B and insulin receptor signaling pathways (3). Furthermore glucocorticoids (GC) can also influence cytokine signaling. They act together with cytokines in an integrated fashion to control inflammation, immune response, and other more diverse physiological functions in mammals (4). The effect of GCs is mediated by the GR, a member of the nuclear receptor...

“…A plausible and interesting example of this mechanism has recently come to light, namely the mutual antagonism between GR and nuclear factor-B (NF-B). Direct interaction between GR and NF-B has recently been demonstrated (54 -56), resulting in inhibition of the transactivation functions of each of these factors (56,57). More importantly, heat shock has recently been shown to increase the expression of IB, the negative regulator of NF-B, by a mechanism that probably involves direct transcriptional enhancement of the IB gene by HSF1 (58 -60).…”

Section: Discussionmentioning

confidence: 99%

Heat and Chemical Shock Potentiation of Glucocorticoid Receptor Transactivation Requires Heat Shock Factor (HSF) Activity

Periyasamy

Jones

et al. 2000

Heat shock and other forms of stress increase glucocorticoid receptor (GR) activity in cells, suggesting cross-talk between the heat shock and GR signal pathways. An unresolved question concerning this cross-talk is whether heat shock factor (HSF1) activity is required for this response. We addressed this issue by modulating HSF1 activity with compounds acting by distinct mechanisms: sodium vanadate (SV), an inhibitor of protein phosphatases; and wortmannin, an inhibitor of DNA-dependent protein kinase. Using HSF1-and GR-responsive CAT reporters, we demonstrate that SV inhibits both HSF1 activity and the stress potentiation of GR, while having no effect on the hormone-free GR or HSF1. Paradoxically, SV increased hormone-induced GR activity in the absence of stress. In contrast, wortmannin increased HSF1 activity in stressed cells and had no effect on HSF1 in the absence of stress. Using the pMMTV-CAT reporter containing the negative regulatory element 1 site for DNA-dependent protein kinase, wortmannin was found to increase the GR response. However, in cells expressing a minimal promoter lacking negative regulatory element 1 sites, wortmannin had no effect on the GR in the absence of stress but increased the stress potentiation of GR. Our results show that the mechanism by which GR activity is increased in stressed cells requires intrinsic HSF1 activity. The glucocorticoid receptor (GR)1 is a member of the nuclear receptor family of proteins that act as hormone-activated transcription factors (1, 2). Since the GR is known to be involved in the organismal response to stress (3), and since the hormonefree GR is known to reside in the cytoplasm as a complex containing heat shock proteins (HSPs) (4), we and others have investigated the role of the heat shock response in controlling GR function. Early evidence to suggest a relationship between these responses includes the ability of heat shock or chemical stress (arsenite) to cause nuclear translocation of hormone-free GR in mouse L929 and Chinese hamster ovary cells (5, 6) and a partial increase in GR-mediated gene expression in Chinese hamster ovary cells subjected to heat or chemical shock in the absence of hormone (6). Heat shock-induced nuclear translocation of hormone-free GR has also been documented in the liver of rats subjected to whole-body hyperthermia (7, 8) as well as in COS cells expressing human GR (9). Evidence to suggest that heat shock-induced nuclear translocation of hormone-free GR can result in altered expression of endogenous genes has also been accumulating. For example, heat shock treatment of COS and Hela cells in the absence of hormone results in GR-mediated transrepression of the collagenase promoter (9), while heat shock treatment of murine macrophages results in a pattern of Fc receptor expression or repression that is identical to that observed in response to hormone (10). More recently, heat shock-induced translocation of hormone-free GR has been implicated in the process of stress-induced apoptosis in leukemic cells (11).In the presenc...