The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stressresponse or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole. (Endocrine Reviews 21: 55‐ 89, 2000)

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How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions.

▪ Abstract The transcription factor NF-κB has attracted widespread attention among researchers in many fields based on the following: its unusual and rapid regulation, the wide range of genes that it controls, its central role in immunological processes, the complexity of its subunits, and its apparent involvement in several diseases. A primary level of control for NF-κB is through interactions with an inhibitor protein called IκB. Recent evidence confirms the existence of multiple forms of IκB that appear to regulate NF-κB by distinct mechanisms. NF-κB can be activated by exposure of cells to LPS or inflammatory cytokines such as TNF or IL-1, viral infection or expression of certain viral gene products, UV irradiation, B or T cell activation, and by other physiological and nonphysiological stimuli. Activation of NF-κB to move into the nucleus is controlled by the targeted phosphorylation and subsequent degradation of IκB. Exciting new research has elaborated several important and unexpected findings that...

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THE NF-κB AND IκB PROTEINS: New Discoveries and Insights

▪ Abstract The transcription factor NF-κB, more than a decade after its discovery, remains an exciting and active area of study. The involvement of NF-κB in the expression of numerous cytokines and adhesion molecules has supported its role as an evolutionarily conserved coordinating element in the organism's response to situations of infection, stress, and injury. Recently, significant advances have been made in elucidating the details of the pathways through which signals are transmitted to the NF-κB:IκB complex in the cytosol. The field now awaits the discovery and characterization of the kinase responsible for the inducible phosphorylation of IκB proteins. Another exciting development has been the demonstration that in certain situations NF-κB acts as an anti-apoptotic protein; therefore, elucidation of the mechanism by which NF-κB protects against cell death is an important goal. Finally, the generation of knockouts of members of the NF-κB/IκB family has allowed the study of the roles of these protein...

NF-kappa B and Rel proteins: evolutionarily conserved mediators of immune responses

In chronic inflammatory diseases, such as asthma, rheumatoid arthritis, inflammatory bowel disease, and psoriasis, several cytokines recruit activated immune and inflammatory cells to the site of lesions, thereby amplifying and perpetuating the inflammatory state.1 These activated cells produce many other mediators of inflammation. What causes these diseases is still a mystery, but the disease process results from an interplay of genetic and environmental factors. Genes, such as those for atopy in asthma and for HLA antigens in rheumatoid arthritis and inflammatory bowel disease, may determine a patient's susceptibility to the disease and the disease's severity, but environmental factors, often unknown, . . .

Nuclear factor-kappaB: a pivotal transcription factor in chronic inflammatory diseases.

Sixteen years have passed since the description of the nuclear factor-кB (NF-кB) as a regulator of к light-chain gene expression in murine B lymphocytes (Sen & Baltimore, 1986a) During that time, over 4,000 publications have appeared, characterizing the family of Rel/NF-кB transcription factors involved in the control of a large number of normal and pathological cellular processes The physiological functions of NF-кB proteins include immunological and inflammatory responses, developmental processes, cellular growth and modulating effects on apoptosis In addition, these factors are activated in a number of diseases, including cancer, arthritis, acute and chronic inflammatory states, asthma, as well as neurodegenerative and heart diseases

Activators and target genes of Rel/NF-kappaB transcription factors.

Glucocorticoids are potent immunosuppressive drugs, but their mechanism is poorly understood. Nuclear factor kappa B (NF-κB), a regulator of immune system and inflammation genes, may be a target for glucocorticoid-mediated immunosuppression. The activation of NF-κB involves the targeted degradation of its cytoplasmic inhibitor, IκBα, and the translocation of NF-κB to the nucleus. Here it is shown that the synthetic glucocorticoid dexamethasone induces the transcription of the IκBα gene, which results in an increased rate of IκBα protein synthesis. Stimulation by tumor necrosis factor causes the release of NF-κB from IκBα. However, in the presence of dexamethasone this newly released NF-κB quickly reassociates with newly synthesized IκBα, thus markedly reducing the amount of NF-κB that translocates to the nucleus. This decrease in nuclear NF-κB is predicted to markedly decrease cytokine secretion and thus effectively block the activation of the immune system.

https://science.sciencemag.org/content/sci/270/5234/283.full.pdf

Role of Transcriptional Activation of IκBα in Mediation of Immunosuppression by Glucocorticoids

Glucocorticoids are potent immunosuppressants which work in part by inhibiting cytokine gene transcription. We show here that NF-kappa B, an important regulator of numerous cytokine genes, is functionally inhibited by the synthetic glucocorticoid dexamethasone (DEX). In transfection experiments, DEX treatment in the presence of cotransfected glucocorticoid receptor (GR) inhibits NF-kappa B p65-mediated gene expression and p65 inhibits GR activation of a glucocorticoid response element. Evidence is presented for a direct interaction between GR and the NF-kappa B subunits p65 and p50. In addition, we demonstrate that the ability of p65, p50, and c-rel subunits to bind DNA is inhibited by DEX and GR. In HeLa cells, DEX activation of endogenous GR is sufficient to block tumor necrosis factor alpha or interleukin 1 activation of NF-kappa B at the levels of both DNA binding and transcriptional activation. DEX treatment of HeLa cells also results in a significant loss of nuclear p65 and a slight increase in cytoplasmic p65. These data reveal a second mechanism by which NF-kappa B activity may be regulated by DEX. We also report that RU486 treatment of wild-type GR and DEX treatment of a transactivation mutant of GR each can significantly inhibit p65 activity. In addition, we found that the zinc finger domain of GR is necessary for the inhibition of p65. This domain is also required for GR repression of AP-1. Surprisingly, while both AP-1 and NF-kappa B can be inhibited by activated GR, synergistic NF-kappa B/AP-1 activity is largely unaffected. These data suggest that NF-kappa B, AP-1, and GR interact in a complex regulatory network to modulate gene expression and that cross-coupling of NF-kappa B and GR plays an important role in glucocorticoid-mediated repression of cytokine transcription.

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Characterization of mechanisms involved in transrepression of NF-kappa B by activated glucocorticoid receptors.

Characterization of mechanisms involved in transrepression of NF-κB by activated glucocorticoid receptors

NF-kappa B is an inducible transcription factor comprised of a 50-kD (p50) and a 65-kD (p65) subunit. Induction of NF-kappa B activity, which is a critical event in many signal transduction pathways, involves release from a cytoplasmic inhibitory protein, I kappa B, followed by translocation of the active transcription factor complex into the nucleus. Earlier studies suggested that I kappa B targets the p65 subunit of NF-kappa B. However, we demonstrate by in vitro and in vivo methods that the recently cloned I kappa B/MAD-3 interacts with both the p50 and p65 subunits of NF-kappa B, as well as c-Rel. Furthermore, an alternatively spliced, dimerization-deficient transforming variant of p65 (p65 delta) interacts extremely weakly with I kappa B/MAD-3, suggesting that dimerization is important for interaction. We demonstrate that the conserved nuclear localization sequences (NLSs) of NF-kappa B and c-Rel are the targets for I kappa B/MAD-3 interaction. Indirect immunofluorescence experiments demonstrate that I kappa B/MAD-3 expression retains both p65 and p50 in the cytoplasm. Furthermore, and most important, a p65 that contains an SV40 large T antigen NLS in addition to its own NLS is no longer retained in the cytoplasm in the presence of I kappa B/MAD-3. We propose that I kappa B/MAD-3 masks the NLSs of NF-kappa B and c-Rel and that this constitutes the mechanism for cytoplasmic retention of these proteins.

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I kappa B interacts with the nuclear localization sequences of the subunits of NF-kappa B: a mechanism for cytoplasmic retention.

Deposition of complement factors (opsonization) on nanoparticles may promote clearance from the blood by macrophages and trigger proinflammatory responses, but the mechanisms regulating the efficiency of complement activation are poorly understood. We previously demonstrated that opsonization of superparamagnetic iron oxide (SPIO) nanoworms with the third complement protein (C3) was dependent on the biomolecule corona of the nanoparticles. Here we show that natural antibodies play a critical role in C3 opsonization of SPIO nanoworms and a range of clinically approved nanopharmaceuticals. The dependency of C3 opsonization on immunoglobulin binding is almost universal and is observed regardless of the complement activation pathway. Only a few surface-bound immunoglobulin molecules are needed to trigger complement activation and opsonization. Although the total amount of plasma proteins adsorbed on nanoparticles does not determine C3 deposition efficiency, the biomolecule corona per se enhances immunoglobulin binding to all nanoparticle types. We therefore show that natural antibodies represent a link between biomolecule corona and C3 opsonization, and may determine individual complement responses to nanomedicines. Immunoglobulins mediate deposition of the third complement protein (C3) on the biomolecule corona of nanoparticles, promoting complement activation.

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Robert I. Scheinman

Papers

Role of Transcriptional Activation of IκBα in Mediation of Immunosuppression by Glucocorticoids

Characterization of mechanisms involved in transrepression of NF-kappa B by activated glucocorticoid receptors.

Characterization of mechanisms involved in transrepression of NF-κB by activated glucocorticoid receptors

I kappa B interacts with the nuclear localization sequences of the subunits of NF-kappa B: a mechanism for cytoplasmic retention.

Immunoglobulin deposition on biomolecule corona determines complement opsonization efficiency of preclinical and clinical nanoparticles.