Kinase Assay: |
Biochem Pharmacol. 2011 Mar 15;81(6):752-60. | 1,3,5-trihydroxy-4-prenylxanthone represses lipopolysaccharide-induced iNOS expression via impeding posttranslational modification of IRAK-1.[Pubmed: 21232528] | 1,3,5-Trihydroxy-4-prenylxanthone (TH-4-PX) isolated from Cudrania cochinchinensis repressed lipopolysaccharide (LPS)-induced NO production in RAW264.7 macrophages. METHODS AND RESULTS: Here we further examined the underlying mechanisms using RT-PCR and Western blot analyses. Consistent with NO inhibition, suppression of LPS-induced iNOS expression by 1,3,5-Trihydroxy-4-prenylxanthone through abolishing IκB kinase (IKK) phosphorylation, IκB degradation and nuclear factor-κB (NF-κB) nuclear translocation was observed. After LPS stimulation, the increased nuclear level of c-Fos and c-Jun (major components of activator protein-1, AP-1) and the phosphorylated level of upstream signal molecules, such as c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase, (ERK) were all significantly suppressed by 1,3,5-Trihydroxy-4-prenylxanthone, while p38 remained unaffected. A further experiment revealed that 1,3,5-Trihydroxy-4-prenylxanthone inhibited the phosphorylation of transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1), an upstream signaling molecule required for IKK and mitogen-activated protein kinases (MAPKs) activation. Interestingly, the modified pattern of IRAK-1 in the presence LPS was significantly attenuated by 1,3,5-Trihydroxy-4-prenylxanthone treatment. CONCLUSIONS: In conclusion, 1,3,5-Trihydroxy-4-prenylxanthone inhibited LPS-induced NF-κB and AP-1 activations by interfering with the posttranslational modification (phosphorylation and/or ubiquitinylation) of IRAK-1 in the cell membrane to impede TAK1-mediated activation of IKK and MAPKs signal transduction. |
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