Magnolol suppresses NF-kappaB activation and NF-kappaB regulated gene expression through inhibition of IkappaB kinase activation

Mol Immunol. 2007 Apr;44(10):2647-58. doi: 10.1016/j.molimm.2006.12.004. Epub 2007 Jan 22.

Abstract

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.

MeSH terms

  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Apoptosis / drug effects
  • Biphenyl Compounds / pharmacology*
  • Cell Line, Tumor
  • Cytokines / genetics
  • Dimerization
  • Down-Regulation
  • Gene Expression Regulation / drug effects*
  • Humans
  • I-kappa B Kinase / antagonists & inhibitors*
  • I-kappa B Kinase / metabolism
  • Lignans / pharmacology*
  • Lipopolysaccharides / pharmacology
  • Matrix Metalloproteinase 9 / genetics
  • NF-kappa B / drug effects*
  • NF-kappa B / metabolism
  • NF-kappa B p50 Subunit / antagonists & inhibitors
  • NF-kappa B p50 Subunit / metabolism
  • Phosphorylation / drug effects
  • Transcription Factor RelA / antagonists & inhibitors
  • Transcription Factor RelA / metabolism
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / pharmacology

Substances

  • Anti-Inflammatory Agents, Non-Steroidal
  • Biphenyl Compounds
  • Cytokines
  • Lignans
  • Lipopolysaccharides
  • NF-kappa B
  • NF-kappa B p50 Subunit
  • Transcription Factor RelA
  • Tumor Necrosis Factor-alpha
  • magnolol
  • I-kappa B Kinase
  • Matrix Metalloproteinase 9