Synthetic stigmastanes with dual antiherpetic and immunomodulating activities inhibit ERK and Akt signaling pathways without binding to glucocorticoid receptors.

BACKGROUND: We have previously shown that some synthetic hydroxylated stigmastanes derived from plant sterols inhibit in vitro HSV-1 replication in ocular cell lines and decrease cytokine production in stimulated macrophages, suggesting that these steroids might combine antiviral and immunomodulating properties. In this paper we report the synthesis of some analogs fluorinated at C-6 in order to study the effect of this modification on bioactivity. METHODS: The following methods were used: organic synthesis of fluorinated analogs, cytotoxicity determination with MTT assays, cytokine production quantification with ELISAs, glucocorticoid activity determination by displacement assays, immunofluorescence and transcriptional activity assays, studies of the activation of signaling pathways by Western blot, antiviral activity evaluation through virus yield reduction assays. RESULTS: We report the chemical synthesis of new fluorinated stigmastanes and show that this family of steroidal compounds exerts its immunomodulating activity by inhibiting ERK and Akt signaling pathways, but do not act as glucocorticoids. We also demonstrate that fluorination enhances the antiviral activity. CONCLUSIONS: Fluorination on C-6 did not enhance the anti-inflammatory effect, however, an increase in the in vitro antiviral activity was observed. Thus, our results suggest that it is possible to introduce chemical modifications on the parent steroids in order to selectively modulate one of the effects. GENERAL SIGNIFICANCE: This family of steroids could allow the development of an alternative treatment for ocular immunopathologies triggered by HSV-1, without the undesirable side effects of the currently used drugs.

NF-κB transcriptional activity is modulated by FK506-binding proteins FKBP51 and FKBP52: a role for peptidyl-prolyl isomerase activity.

Hsp90 binding immunophilins FKBP51 and FKBP52 modulate steroid receptor trafficking and hormone-dependent biological responses. With the purpose to expand this model to other nuclear factors that are also subject to nuclear-cytoplasmic shuttling, we analyzed whether these immunophilins modulate NF-κB signaling. It is demonstrated that FKBP51 impairs both the nuclear translocation rate of NF-κB and its transcriptional activity. The inhibitory action of FKBP51 requires neither the peptidylprolyl-isomerase activity of the immunophilin nor its association with Hsp90. The TPR domain of FKBP51 is essential. On the other hand, FKBP52 favors the nuclear retention time of RelA, its association to a DNA consensus binding sequence, and NF-κB transcriptional activity, the latter effect being strongly dependent on the peptidylprolyl-isomerase activity and also on the TPR domain of FKBP52, but its interaction with Hsp90 is not required. In unstimulated cells, FKBP51 forms endogenous complexes with cytoplasmic RelA. Upon cell stimulation with phorbol ester, the NF-κB soluble complex exchanges FKBP51 for FKBP52, and the NF-κB biological effect is triggered. Importantly, FKBP52 is functionally recruited to the promoter region of NF-κB target genes, whereas FKBP51 is released. Competition assays demonstrated that both immunophilins antagonize one another, and binding assays with purified proteins suggest that the association of RelA and immunophilins could be direct. These observations suggest that the biological action of NF-κB in different cell types could be positively regulated by a high FKBP52/FKBP51 expression ratio by favoring NF-κB nuclear retention, recruitment to the promoter regions of target genes, and transcriptional activity.

Molecular basis of mineralocorticoid receptor action in the nervous system.

The most relevant biological action of aldosterone in epithelial tissues is the regulation of sodium reabsorption through binding to the mineralocorticoid receptor (MR). Glucocorticoids also bind with high affinity to MR, which is usually protected by the enzyme 11ß-hydroxysteroid dehydrogenase. This activity prevents MR activation by cortisol despite the large prevalence of this steroid in plasma. Nonetheless, there are some aspects of the mechanism of action of MR that are not entirely explained by this competitive metabolic mechanism of protection. The picture is even more complicated in those tissues such as the nervous system where the enzyme is expressed at very low levels or is directly absent in various areas of the brain. Therefore, other cellular and molecular mechanisms must also intervene to allow specific aldosterone biological effects in the presence of overwhelming concentrations of glucocorticoids. In this article, we discuss some possible mechanisms that permit the specificity of action for each type of steroid, including those related to the recently discovered novel molecular mechanism of activation of corticosteroid receptors and the structural requirements of a given ligand to favor the mineralocorticoid action via MR. The relative contribution of these mechanisms may vary in different target cells allowing the fine tuning of cellular functions depending on the degree of cooperation between steroids, receptors, chaperones associated to receptors, and other factors. All these regulatory interactions can be altered in some pathophysiological situations, most of them related to stressing situations.