Magnolol suppresses NF-kappaB activation and NF-kappaB regulated gene expression through inhibition of IkappaB kinase activation.
The mis-regulation of nuclear factor-kappa B (NF-kappaB) signal pathway is involved in a variety of inflammatory diseases that leds to the production of inflammatory mediators. Our studies using human U937 promonocytes cells suggested that magnolol, a low molecular weight lignan isolated from the medicinal plant Magnolia officinalis, differentially down-regulated the pharmacologically induced expression of NF-kappaB-regulated inflammatory gene products MMP-9, IL-8, MCP-1, MIP-1alpha, TNF-alpha. Pre-treatment of magnolol blocked TNF-alpha-induced NF-kappaB activation in different cell types as evidenced by EMSA. Magnolol did not directly affect the binding of p65/p50 heterodimer to DNA. Immunoblot analysis demonstrated that magnolol inhibited the TNF-alpha-stimulated phosphorylation and degradation of the cytosolic NF-kappaB inhibitor IkappaBalpha and the effects were dose-dependent. Mechanistically, a non-radioactive IkappaB kinases (IKK) assay using immunoprecipitated IKKs protein demonstrated that magnolol inhibited both intrinsic and TNF-alpha-stimulated IKK activity, thus suggesting a critical role of magnolol in abrogating the phosphorylation and degradation of IkappaBalpha. The involvement of IKK was further verified in a HeLa cell NF-kappaB-dependent luciferase reporter system. In this system magnolol suppressed luciferase expression stimulated by TNF-alpha and by the transient transfection and expression of NIK (NF-kappaB-inducing kinase), wild type IKKbeta, constitutively active IKKalpha and IKKbeta, or the p65 subunit. Magnolol was also found to inhibit the nuclear translocation and phosphorylation of p65 subunit of NF-kappaB. In line with the observation that NF-kappaB activation may up-regulate anti-apoptotic genes, it was shown in U937 cells that magnolol enhanced TNF-alpha-induced apoptotic cell death. Our results suggest that magnolol or its derivatives may have potential anti-inflammatory actions through IKK inactivation.
Tse
Anfernee Kai-Wing
AK
Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, China.
Wan
Chi-Keung
CK
Zhu
Guo-Yuan
GY
Shen
Xiao-Ling
XL
Cheung
Hon-Yeung
HY
Yang
Mengsu
M
Fong
Wang-Fun
WF
D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000494:pharmacology*; D045744:Cell Line, Tumor; D016207:Cytokines / Q000235:genetics; D019281:Dimerization; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017705:Lignans / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D020780:Matrix Metalloproteinase 9 / Q000235:genetics; D016328:NF-kappa B / Q000187:drug effects* / Q000378:metabolism; D052002:NF-kappa B p50 Subunit / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051996:Transcription Factor RelA / Q000037:antagonists & inhibitors / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000494:pharmacology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D001713:Biphenyl Compounds; D016207:Cytokines; D017705:Lignans; D008070:Lipopolysaccharides; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; C005498:magnolol; D051550:I-kappa B Kinase; D020780:Matrix Metalloproteinase 9