A fully dissociated compound of plant origin for inflammatory gene repression

Withaferin a strongly elicits IkappaB kinase beta hyperphosphorylation concomitant with potent inhibition of its kinase activity

The transcription factor NFkappaB plays a critical role in normal and pathophysiological immune responses. Therefore, NFkappaB and the signaling pathways that regulate its activation have become a major focus of drug development programs. Withania somnifera (WS) is a medicinal plant that is widely used in Palestine for the treatment of various inflammatory disorders. In this study we show that the leave extract of WS, as well as its major constituent withaferin A (WA), potently inhibits NFkappaB activation by preventing the tumor necrosis factor-induced activation of IkappaB kinase beta via a thioalkylation-sensitive redox mechanism, whereas other WS-derived steroidal lactones, such as withanolide A and 12-deoxywithastramonolide, are far less effective. To our knowledge, this is the first communication of IkappaB kinase beta inhibition by a plant-derived inhibitor, coinciding with MEK1/ERK-dependent Ser-181 hyperphosphorylation. This prevents IkappaB phosphorylation and degradation, which subsequently blocks NFkappaB translocation, NFkappaB/DNA binding, and gene transcription. Taken together, our results indicate that pure WA or WA-enriched WS extracts can be considered as a novel class of NFkappaB inhibitors, which hold promise as novel anti-inflammatory agents for treatment of various inflammatory disorders and/or cancer.

Cross-talk between nuclear receptors and nuclear factor kappaB

A variety of studies have shown that some activated nuclear receptors (NRs), especially the glucorticoid receptor, the estrogen receptor and peroxisome proliferator-activated receptor, can inhibit the activity of the transcription factor nuclear factor kappaB (NF-kappaB), which plays a key role in the control of genes involved in inflammation, cell proliferation and apoptosis. This review describes the molecular mechanisms of cross-talk between NRs and NF-kappaB and the biological relevance of this cross-talk. The importance and mechanistic aspects of selective NR modulation are discussed. Also included are future research prospects, which will lead to a new era in the field of NR research with the aim of specifically inhibiting NF-kappaB-driven gene expression for anti-inflammatory, anti-tumor and immune-modulatory purposes.

Modelling the glucocorticoid receptor and producing therapeutic agents with anti-inflammatory effects but reduced side-effects

Glucocorticoid hormones exert a wide spectrum of metabolic and immunological effects. They are synthesized from a cholesterol precursor and are structurally related to the other steroid hormones, progesterone, aldosterone and oestrogen. They act through the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily. The GR is an intracellular receptor; the hydrophobic ligand accesses its receptor by diffusion across the plasma membrane. The ligand-activated GR translocates to the nucleus to regulate expression of its target genes. The GR, in common with the rest of the receptor family, can be functionally divided into an N-terminal transcription activation domain, a central DNA binding domain and a C-terminal ligand binding domain, which also includes a second transactivation domain. Although synthetic glucocorticoids are the most potent anti-inflammatory agents known, their use is limited owing to the range and severity of their side-effects. The structure of the ligand binding domain of the glucocorticoid receptor has now been solved, and a series of studies has shown that even subtle changes to the ligand structure alter the final conformation of the ligand-receptor complex, with consequences for further protein recruitment and for the function of the receptor. This, coupled with the successful development of selective oestrogen receptor agonists, has led to concerted efforts to find selective GR ligands, with preserved beneficial anti-inflammatory activity, but reduced side-effect profile. Current efforts have identified several useful tool compounds, and further molecules are in development in several pharmaceutical companies.

Insight into the molecular mechanisms of glucocorticoid receptor action promotes identification of novel ligands with an improved therapeutic index

Glucocorticoids are highly effective in the therapy of inflammatory and autoimmune disorders. Their beneficial action is restricted because of their adverse effects upon prolonged usage. Topical glucocorticoids that act locally have been developed to significantly reduce systemic side effects. Nonetheless, undesirable cutaneous effects such as skin atrophy persist from the use of topical glucocorticoids. There is therefore a high medical need for drugs as effective as glucocorticoids but with a reduced side-effect profile. Glucocorticoids function by binding to and activating the glucocorticoid receptor that positively or negatively regulates the expression of specific genes. Several experiments suggest that the negative regulation of gene expression by the glucocorticoid receptor accounts for its anti-inflammatory action. This occurs through direct or indirect binding of the receptor to transcription factors such as activator protein-1, nuclear factor-kappaB or interferon regulatory factor-3 that are already bound to their regulatory sites. The positive action of the receptor occurs through homodimer binding of the receptor to discrete nucleotide sequences and this possibly contributes to some of the adverse effects of the hormone. Glucocorticoid receptor ligands that promote the negative regulatory action of the receptor with reduced positive regulatory function should therefore show improved therapeutic potential. A complete separation of the positive from the negative regulatory activities of the receptor has so far not been possible because of the interdependent nature of the two regulatory processes. Nevertheless, considerable improvement in the therapeutic action of glucocorticoid receptor ligands is being achieved through the use of key molecular targets for screening novel glucocorticoid receptor ligands.

Understanding stress through the genome

Stress-induced glucocorticoid hormones support coping with and adaptation to different stressors. They act to modulate gene expression in a tissue and stressor-specific manner through activation of corticosteroid receptors, which act as transcription factors. Here, a number of recent insights in gene regulation under the influence of glucocorticoids are discussed. Emphasis is put on distinct classes of target genes that may be defined, based on categorization of (combinations of) transcription factor binding sites in responsive genes. These categories depend on insights into different mechanisms of transcriptional regulation, such as transactivation vs transrepression, and high affinity vs low affinity hormone receptor response elements. It is argued that such classes, based on mechanistic understanding of transcription regulation, in combination with the availability of complete genomic sequences and expression data from different organs, may enhance our understanding of the way in which organisms deal with different forms of stress.

Role of glucocorticoids in dopamine-related neuropsychiatric disorders

'Psychoneuroendocrinology' is now quickly emerging as a hot interdisciplinary research field that addresses the interplay between neuronal and endocrine signaling in psychiatric diseases. Both glucocorticoid hormones and dopamine have an important role in maintaining normal brain functions. In this review, molecular and mechanistic aspects of glucocorticoid effects on brain function and behavior will be discussed with specific reference to dopamine signaling.