Laxifolone A Suppresses LPS/IFN-γ-Induced NO Synthesis by Attenuating NF-κB Translocation: Role of NF-κB p105 Level

Abstract

Laxifolone A is a triterpene isolated from Euonymus laxiflorus Champ. Exposure of RAW264.7 macrophages to laxifolone A concentration-dependently suppressed lipopolysaccharide/interferon-γ (LPS/IFN-γ)-induced nitrite production (IC₅₀ = 0.37 ± 0.05 μM), inducible NO synthase (iNOS) protein, and iNOS mRNA expression. Translocation of nuclear factor-κB (NF-κB) into the nucleus with subsequent activation of iNOS gene transcription is essential in NO signaling. Western blot analysis indicated that the cytosolic NF-κB/p65 was obviously decreased after LPS/IFN-γ stimulation for 30 min and this phenomenon could be reversed by laxifolone A. Similarly, a time-related NF-κB/p65 nuclear translocation induced by LPS/IFN-γ was diminished in the presence of laxifolone A. However, laxifolone A failed to interfere in LPS/IFN-γ-evoked IκB degradation. Our results also showed that LPS/IFN-γ-stimulation resulted in the degradation of NF-κB p105, the NF-κB precursor, and laxifolone A treatment significantly counteracted this effect. Furthermore, laxifolone A itself was able to enhance NF-κB p105 protein expression. In summary, these results suggest that inhibition of NF-κB p105 degradation in cytoplasm may participate in the abrogation of LPS/IFN-γ-induced NF-κB translocation and subsequent NO synthesis by laxifolone A.

Key words

Laxifolone A - NO - INOS - NF-κB - IκB - NF-κB p105

References

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