Dexamethasone prevents interleukin-1β-induced nuclear factor-κB activation by upregulating IκB-α synthesis, in lymphoblastic cells

Abstract

AIMS: Glucocorticoids (GCs) exert some of their anti-inflammatory actions by preventing the activation of the transcription factor nuclear factor (NF)-κB. The GC-dependent inhibition of NF-κB may occur at different levels, but the mechanisms involved are still incompletely understood. In this work, we investigated whether the synthetic GC, dexamethasone (Dex), modulates the activity of NF-κB in the lymphoblastic CCRF-CEM cell line. We also evaluated the ability of Dex to prevent the activation of NF-κB in response to the potent proinflammatory cytokine, interleukin (IL)-Iβ. Results: Exposure of the cells to Dex (1 μM) induced the rapid degradation of IκB-α, leading to the transient translocation of the NF-κB family members p65 and p50 from the cytoplasm to the nucleus, as evaluated by western blot. Electrophoretic mobility shift assays revealed that, in the nucleus, these NF-κB proteins formed protein-DNA complexes, indicating a transient activation of NF-κB. Additionally, Dex also induced de novo synthesis of IκB-α, following its degradation. Finally, when the cells were exposed to Dex (1 μM) prior to stimulation with IL-Iβ (20 ng/ml), Dex was efficient in preventing IL-1β-induced NF-κB activation. The GC antagonist, RU 486 (10 μM), did not prevent any of the effects of Dex reported here. Conclusion: Our results indicate that, in CCRF-CEM cells, Dex prevents NF-κB activation, induced by IL-lβ, by a mechanism that involves the upregulation of IκB-α synthesis, and that depends on the early and transient activation of NF-κB.