Reprogramación de la respuesta a glucocorticoides por interleuquina-1 b

Abstract

Glucocorticoids (GC) are one of the main anti-inflammatory drugs used. GC-resistance is a frequent problem found in patients with lung disorders under severe inflammatory conditions. Treatment of GC-resistant patients with GC course with the adverse effects of steroid therapy with any beneficial. Although some inflammatory mediators can affect GC response of lung cells, little is known about the interplay between inflammatory conditions of alveolar space and GC-responsiveness. Here we show that chronic exposure of epithelial alveolar type 2 cells (AE2-A549 cells) to Interleukin-1 beta (IL-1ß) reprograms glucocorticoid receptor (GR), modifying the transcriptional activity of GC responsive endogenous genes. After chronic exposure of A549 cells to IL-1ß, GR nuclear translocation and nuclear GR phosphorylated at Serine 211 (S211) were measured with two independent methods: slide-based citometry and western blot hybridization (WB) of separated cellular compartments. GR phosphorylated at S203 and total GR were measured with WB, and transcriptional activity of GC-responsive genes were measured with RT-qPCR. Chronic exposure to IL-1ß diminish nuclear translocation of total GR and nuclear GR phosphorylated at S211, the transcriptional active form of GR for many GC-responsive genes. The mechanisms underlying this effects are augmentation of GR degradation induced by IL-1ß, and diminished GR phosphorylation at S203 after chronic exposure to IL-1ß. This account for an altered expression of GC-responsive genes like fkbp5, ttp, irf8 and igfbp1, but not dusp1 or gilz. Interestingly, chronic exposure to IL-1ß abolishes GC-induced mRNA and protein expression of tristetraprolin (TTP), a known ARE-binding protein that mediates GC anti-inflammatory effects acting as post-transcriptional regulator of ARE-containing inflammatory mRNAs like tumor necrosis factor alpha (TNF¿). Loss of function of TTP is associated with severe inflammatory response caused by altered stability and expression of inflammatory cytokine mRNA. Chronic exposure with IL-1ß deprive AE2 cells of TTP, a mechanism of anti-inflammatory action of GC therapy, and may represent a new mechanism of chronic inflammation with important biomedical implications.