Suppression of Th2-driven, allergen-induced airway inflammation by sauchinone

Sauchinone, a lignan compound isolated from the root of Saururus chinensis, has been recently demonstrated to exhibit anti-inflammatory activity via the suppression of NF-kB p65 activity in vitro. In an effort to evaluate the in vivo anti-inflammatory function of sauchinone, we have evaluated the effects of sauchinone on allergen-induced airway inflammation using a murine model of allergic asthma. We observed that marked eosinophilic and lymphocyte infiltration in the BAL fluid were suppressed to a significant degree by sauchinone, and that mucus-secreting goblet cell hyperplasia and collagen deposition in the airways were also ameliorated by administration of sauchinone treatment. Moreover, gene expression of the inflammatory cytokines, IL-13, and IL-5 and eotaxin in the lung, and IL-5 in the draining lymph node were significantly decreased in sauchinone-treated mice. We demonstrated that sauchinone repressed Th2 cell development in vitro and IL-4 production by Th2 cells, and also inhibited GATA-3-mediated IL-5 promoter activity in a dose-dependent manner. Collectively, sauchinone ameliorated allergen-induced airway inflammation, in part, by repressing GATA-3 activity for Th2 cell development, indicating the possible therapeutic potential of sauchinone in airway inflammatory diseases including allergic asthma and rhinitis.     

Regulation of Th2 cytokine genes by p38 MAPK-mediated phosphorylation of GATA-3

GATA-3 plays a critical role in allergic diseases by regulating the release of cytokines from Th2 lymphocytes. However, the molecular mechanisms involved in the regulation of GATA-3 in human T lymphocytes are not yet understood. Using small interfering RNA to knock down GATA-3, we have demonstrated its critical role in regulating IL-4, IL-5, and IL-13 release from a human T cell line. Specific stimulation of T lymphocytes by costimulation of CD3 and CD28 to mimic activation by APCs induces translocation of GATA-3 from the cytoplasm to the nucleus, with binding to the promoter region of Th2 cytokine genes, as determined by chromatin immunoprecipitation. GATA-3 nuclear translocation is dependent on its phosphorylation on serine residues by p38 MAPK, which facilitates interaction with the nuclear transporter protein importin-alpha. This provides a means whereby allergen exposure leads to the expression of Th2 cytokines, and this novel mechanism may provide new approaches to treating allergic diseases.     

Suppression of GATA-3 Nuclear Import and Phosphorylation: A Novel Mechanism of Corticosteroid Action in Allergic Disease

Background

GATA-3 plays a critical role in regulating the expression of the cytokines interleukin (IL)-4, IL-5, and IL-13 from T helper-2 (Th2) cells and therefore is a key mediator of allergic diseases. Corticosteroids are highly effective in suppressing allergic inflammation, but their effects on GATA-3 are unknown. We investigated the effect of the corticosteroid fluticasone propionate on GATA-3 regulation in human T-lymphocytes in vitro and in vivo.

Methods and Findings

In a T lymphocyte cell line (HuT-78) and peripheral blood mononuclear cells stimulated by anti-CD3 and anti-CD28 in vitro we demonstrated that fluticasone inhibits nuclear translocation of GATA-3 and expression of Th2 cytokines via a mechanism independent of nuclear factor-κB and is due, in part, to competition between GATA-3 and the ligand-activated glucocorticoid receptor for nuclear transport through the nuclear importer importin-α. In addition, fluticasone induces the expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), the endogenous inhibitor of p38 MAPK, which is necessary for GATA-3 nuclear translocation. These inhibitory effects of fluticasone are rapid, potent, and prolonged. We also demonstrated that inhaled fluticasone inhibits GATA-3 nuclear translocation in peripheral blood lymphocytes of patients with asthma in vivo.

Conclusions

Corticosteroids have a potent inhibitory effect on GATA-3 via two interacting mechanisms that potently suppress Th2 cytokine expression. This novel mechanism of action of corticosteroids may account for the striking clinical efficacy of corticosteroids in the treatment of allergic diseases. Please see later in the article for Editors'' Summary