title: 1,3,5-trihydroxy-4-prenylxanthone represses lipopolysaccharide-induced iNOS expression via impeding posttranslational modification of IRAK-1.
abstract: Both high level of nitric oxide (NO) and its generating enzyme, inducible NO synthase (iNOS), play important roles in pathophysiological conditions such as inflammatory processes. We previously found that 1,3,5-trihydroxy-4-prenylxanthone (TH-4-PX) isolated from Cudrania cochinchinensis repressed lipopolysaccharide (LPS)-induced NO production in RAW264.7 macrophages. 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 TH-4-PX 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 TH-4-PX, while p38 remained unaffected. A further experiment revealed that TH-4-PX 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. Stimulation with LPS also triggered the modification (phosphorylation and ubiquitination) and eventually the proteasomal degradation of membrane-associated interleukin (IL)-1 receptor-associated serine/threonine kinase 1 (IRAK-1), an essential signaling component to toll-like receptor (TLR)-mediated TAK-1 activation. Interestingly, the modified pattern of IRAK-1 in the presence LPS was significantly attenuated by TH-4-PX treatment. In conclusion, TH-4-PX 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.
authors.affiliation: National Research Institute of Chinese Medicine, Taipei, Taiwan. wfchiou@nricm.edu.tw
authors.forename: Wen-Fei
authors.initials: WF
authors.lastname: Chiou
authors.forename: Chien-Chih
authors.initials: CC
authors.lastname: Chen
authors.forename: I-Hsin
authors.initials: IH
authors.lastname: Lin
authors.forename: Jen-Hwey
authors.initials: JH
authors.lastname: Chiu
authors.forename: Yi-Ju
authors.initials: YJ
authors.lastname: Chen
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D053592:Interleukin-1 Receptor-Associated Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000633:toxicity*; D051379:Mice; D029586:Moraceae; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D018517:Plant Roots; D011499:Protein Processing, Post-Translational / Q000187:drug effects* / Q000502:physiology; D044004:Xanthones / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D008070:Lipopolysaccharides; D010936:Plant Extracts; D044004:Xanthones; D052247:Nitric Oxide Synthase Type II; D053592:Interleukin-1 Receptor-Associated Kinases