Airways Inflammation Research Group, Snyder Institute for Chronic Diseases, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
PLoS One. 2013;8(1):e53936. doi: 10.1371/journal.pone.0053936. Epub 2013 Jan 14.
Binding of glucocorticoid to the glucocorticoid receptor (GR/NR3C1) may repress inflammatory gene transcription via direct, protein synthesis-independent processes (transrepression), or by activating transcription (transactivation) of multiple anti-inflammatory/repressive factors. Using human pulmonary A549 cells, we showed that 34 out of 39 IL-1β-inducible mRNAs were repressed to varying degrees by the synthetic glucocorticoid, dexamethasone. Whilst these repressive effects were GR-dependent, they did not correlate with either the magnitude of IL-1β-inducibility or the NF-κB-dependence of the inflammatory genes. This suggests that induction by IL-1β and repression by dexamethasone are independent events. Roles for transactivation were investigated using the protein synthesis inhibitor, cycloheximide. However, cycloheximide reduced the IL-1β-dependent expression of 13 mRNAs, which, along with the 5 not showing repression by dexamethasone, were not analysed further. Of the remaining 21 inflammatory mRNAs, cycloheximide significantly attenuated the dexamethasone-dependent repression of 11 mRNAs that also showed a marked time-dependence to their repression. Such effects are consistent with repression occurring via the de novo synthesis of a new product, or products, which subsequently cause repression (i.e., repression via a transactivation mechanism). Conversely, 10 mRNAs showed completely cycloheximide-independent, and time-independent, repression by dexamethasone. This is consistent with direct GR transrepression. Importantly, the inflammatory mRNAs showing attenuated repression by dexamethasone in the presence of cycloheximide also showed a significantly greater extent of repression and a higher potency to dexamethasone compared to those mRNAs showing cycloheximide-independent repression. This suggests that the repression of inflammatory mRNAs by GR transactivation-dependent mechanisms accounts for the greatest levels of repression and the most potent repression by dexamethasone. In conclusion, our data indicate roles for both transrepression and transactivation in the glucocorticoid-dependent repression of inflammatory gene expression. However, transactivation appears to account for the more potent and efficacious mechanism of repression by glucocorticoids on these IL-1β-induced genes.
糖皮质激素与糖皮质激素受体（GR/NR3C1）的结合可能通过直接的、不依赖于蛋白质合成的过程（反式转录抑制）或通过激活多种抗炎/抑制因子的转录（反式激活）来抑制炎症基因的转录。我们使用人肺 A549 细胞表明，39 种 IL-1β诱导的 mRNA 中有 34 种被合成的糖皮质激素地塞米松不同程度地抑制。虽然这些抑制作用依赖于 GR，但它们与 IL-1β 诱导的幅度或炎症基因的 NF-κB 依赖性无关。这表明 IL-1β 诱导和地塞米松抑制是独立的事件。使用蛋白质合成抑制剂环己酰亚胺研究了反式激活的作用。然而，环己酰亚胺降低了 13 种 mRNAs 的 IL-1β 依赖性表达，这些 mRNAs与 5 种不受地塞米松抑制的 mRNAs一起，没有进一步分析。在其余的 21 种炎症 mRNAs 中，环己酰亚胺显著减弱了地塞米松对 11 种 mRNAs 的抑制作用，这些 mRNAs的抑制作用也表现出明显的时间依赖性。这些影响与通过新产物的从头合成或随后导致抑制的产物（即通过反式激活机制的抑制）来抑制一致。相反，10 种 mRNAs 对地塞米松的抑制具有完全的环己酰亚胺独立性和时间独立性。这与直接的 GR 反式转录抑制一致。重要的是，在环己酰亚胺存在下，地塞米松抑制作用减弱的炎症 mRNAs 也表现出更高程度的抑制和更高的地塞米松效价，与那些表现出环己酰亚胺非依赖性抑制的 mRNAs 相比。这表明，通过 GR 反式激活依赖性机制抑制炎症 mRNAs 解释了糖皮质激素对这些 IL-1β 诱导基因的最大抑制水平和最强抑制作用。总之，我们的数据表明，反式转录抑制和反式激活在糖皮质激素依赖性炎症基因表达抑制中都有作用。然而，反式激活似乎解释了糖皮质激素对这些 IL-1β 诱导基因更有效和更有效的抑制机制。
