I. Introduction
II. Nuclear Factor-κB (NF-κB)
A. Introduction
B. NF-κB is a dimeric transcription factor
C. The regulatory subunit IκB is an inhibitor of NF-κB
D. Activation and function of NF-κB
E. ...The transcription factor NF-κB interacts with multiple transcription
factors and transcriptional co-factors
F. Transgenic animals suggest a complex role for NF-κB family members in
immunity and development
III. Steroid Hormones/Receptors: Glucocorticoids and the Glucocorticoid
Receptor (GR)
A. General background
B. Glucocorticoid mechanism of action: the GR
C. Glucocorticoid physiology
D. GR/NF-κB interactions
E. GR interacts with other transcription factors and transcriptional
cofactors
IV. NF-κB and GR Antagonism: Physiological Significance?
V. Interactions Between NF-κB and Other Steroid Hormone Receptors
A. Androgen receptor (AR)
B. Estrogen receptor (ER)
C. Progesterone receptor (PR)
VI. Summary/Conclusions
Nuclear factor κB (NF-κB) is an inducible
transcription factor that positively regulates the expression of
proimmune and proinflammatory genes, while glucocorticoids are potent
suppressors of immune ...and inflammatory responses. NF-κB and the
glucocorticoid receptor (GR) physically interact, resulting in
repression of NF-κB transactivation. In transient cotransfection
experiments, we demonstrate a dose-dependent, mutual antagonism between
NF-κB and GR. Functional dissection of the NF-κB p50 and p65
subunits and deletion mutants of GR indicate that the GR antagonism is
specific to the p65 subunit of NF-κB heterodimer, whereas multiple
domains of GR are essential to repress p65-mediated transactivation.
Despite its repression of GR transactivation, p65 failed to block the
transrepressive GR homologous down-regulation function. We also
demonstrate that negative interactions between p65 and GR are not
selective for GR, but also occur between NF-κB and androgen,
progesterone B, and estrogen receptors. However, although each of these
members of the steroid hormone receptor family is repressed by NF-κB,
only GR effectively inhibits p65 transactivation. Further, in
cotransfections using a chimeric estrogen-GR, the presence of the GR
DNA-binding domain is insufficient to confer mutual antagonism to the
p65-estrogen receptor interaction. Selectivity of p65 repression for
each steroid receptor is demonstrated by IκB rescue from
NF-κB-mediated inhibition. Together these data suggest that NF-κB
p65 physically interacts with multiple steroid hormone receptors, and
this interaction is sufficient to transrepress each steroid receptor.
Further, the NF-κB status of a cell has the potential to
significantly alter multiple steroid signaling pathways within that
cell.
Nuclear factor–κB (NF-κB) and the
glucocorticoid receptor (GR) are transcription factors with opposing
actions in the modulation of immune/inflammatory responses. NF-κB
induces the expression of ...proinflammatory genes, while GR suppresses
immune function in part by suppressing expression of the same genes.
Previously, we demonstrated that physiological antagonism between
NF-κB and GR is due to a mutual transcriptional antagonism that
requires the p65 subunit of NF-κB and multiple domains of GR
(1). To elucidate the mechanism(s) of NF-κB p65 and GR
transcriptional antagonism, we analyzed the interactions of wild-type
p65 and p65 RHD (rel homology domain, a dominant negative mutant of p65
which lacks a transactivation domain) with GR. We show that p65RHD
blocks p65-mediated transactivation, yet does not block the repression
of GR transactivation by p65, indicating that transcriptional activity
by p65 is not required to repress GR function. Both p65 and p65 RHD
physically interact with GR, but only intact p65 represses GR-mediated
signaling, implicating the p65 transactivation domain in the
transcriptional repression of GR. To further characterize p65-GR
interactions, we examined the role of the transcriptional co-integrator
CREB binding protein (CBP) in their mutual antagonism. GR-mediated
repression of p65 transactivation and p65-mediated repression of GR
transactivation, as well as the physical interaction between NF-κB
and GR, are enhanced by CBP. GR bound to the antagonist RU 486,
although transcriptionally inactive, retains the ability to repress p65
transactivation. However, CBP does not physically interact with
antagonist-bound GR and does not enhance its repressive effect on p65.
These data suggest that CBP functions as an integrator of p65/GR
physical interaction, rather than as a limiting cofactor for which p65
and GR compete.
Muscle wasting and excessive fat deposition are side effects attendant to chronic corticosteroid treatment. Corticosteroid immunosuppression is necessary in circumstances such as transplantation. ...Pharmacokinetic/pharmacodynamic (PK/PD) modeling was used to help elucidate the relationships between the events in the molecular cascade that result in muscle wasting and fat deposition by corticosteroids. Specifically, the relationships for receptor/gene-mediated effects that result in increased glutamine synthetase (GS) activity in skeletal muscle were quantitatively analyzed after an i.v. bolus dose of 50 mg/kg methylprednisolone in male adrenalectomized Wistar rats. Profiles of methylprednisolone pharmacokinetics, glucocorticoid receptor density, and its mRNA, GS mRNA, and GS activity in gastrocnemius muscles were determined. The results were used to develop PK/PD models using differential equations in the ADAPT II program. Two indirect response models were tested for the dynamics of glucocorticoid receptor mRNA regulation by activated steroid/receptor complex. Both reduction in message synthesis and message destabilization may be involved but with some tissue specificity. The recovery of active receptor after down-regulation is biphasic. The initial recovery may involve receptor recycling from the nucleus, whereas the later phase may involve de novo synthesis of new receptor protein. The nuclear events and GS mRNA/GS induction in rat skeletal muscle show sequential relationships for each component for corticosteroid actions. The PK/PD models provide mechanism-based methods of quantifying complex processes in receptor/gene-mediated enzyme induction featuring the characteristics of time delay and possible nonlinearity in intact tissues.
A series of 2,2-dimethyl-3,3-diphenyl-propanamides as novel glucocorticoid receptor modulators is reported. SAR exploration led to the identification of 4-hydroxyphenyl propanamide derivatives ...displaying good agonist activity in GR-mediated transrepression assays and reduced agonist activity in GR-mediated transactivation assays. Compounds 17 and 30 showed anti-inflammatory activity comparable to prednisolone in the rat carrageenan-induced paw edema model, with markedly decreased side effects with regard to increases in blood glucose and expression of hepatic tyrosine aminotransferase. A hypothetical binding mode accounting for the induction of the functional activity by a 4-hydroxyl group is proposed.
Modification of a phenolic lead structure based on lessons learned from increasing the potency of steroidal glucocorticoid agonists lead to the discovery of exceptionally potent, nonsteroidal, ...indazole GR agonists. SAR was developed to achieve good selectivity against other nuclear hormone receptors with the ultimate goal of achieving a dissociated GR agonist as measured by human in vitro assays. The specific interactions by which this class of compounds inhibits GR was elucidated by solving an X-ray co-crystal structure.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
SAR was used to further develop an indazole class of non-steroidal glucocorticoid receptor agonists aided by a GR LBD (ligand-binding domain)-agonist co-crystal structure described in the ...accompanying paper. Progress towards discovering a dissociated GR agonist guided by human in vitro assays biased the optimization of this compound series towards partial agonists that possessed excellent selectivity against other nuclear hormone receptors.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A series of dihydro-9,10-ethano-anthracene-11-carboxamides as novel glucocorticoid receptor modulators is reported. SAR exploration identified compounds from this series displaying a promising ...dissociation profile in discriminating between transrepression and transactivation activities.
17a is a partial agonist of GR-mediated transactivation which elicits potent and efficacious transrepression in reporter gene assays. A hypothetical binding mode is provided which accounts for the induction of functional activity by a bridgehead methyl group.
A series of dihydro-9,10-ethano-anthracene-11-carboxamides as novel glucocorticoid receptor modulators is reported. SAR exploration identified compounds from this series displaying a promising dissociation profile in discriminating between transrepression and transactivation activities.
17a is a partial agonist of GR-mediated transactivation which elicits potent and efficacious transrepression in reporter gene assays. A hypothetical binding mode is provided which accounts for the induction of functional activity by a bridgehead methyl group.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
