Honokiol inhibits TNF-alpha-stimulated NF-kappaB activation and NF-kappaB-regulated gene expression through suppression of IKK activation.
Honokiol, a small molecular weight lignan originally isolated from Magnolia officinalis, shows anti-angiogenic, anti-invasive and anti-proliferative activities in a variety of cancers. In this study, we investigated whether honokiol affects the transcription factor nuclear factor-kappa B (NF-kappaB) which controls a large number of genes involved in angiogenesis, metastasis and cell survival. We observed that the tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation was blocked by honokiol in four different cancer cell lines as evidenced by EMSA. Honokiol did not directly affect the NF-kappaB-DNA binding. Immunoblot experiments demonstrated that honokiol inhibited the TNF-alpha-stimulated phosphorylation and degradation of the cytosolic NF-kappaB inhibitor IkappaBalpha. Furthermore, honokiol suppressed the intrinsic and TNF-alpha-stimulated upstream IkappaB kinases (IKKs) activities measured by a non-radioactive kinase assay using immunoprecipitated IKKs, suggesting a critical role of honokiol in abrogating the phosphorylation and degradation of IkappaBalpha. In a HeLa cell NF-kappaB-dependent luciferase reporter system, honokiol 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. Honokiol was also found to inhibit the nuclear translocation and phosphorylation of p65 subunit of NF-kappaB. RT-PCR results showed that honokiol suppressed NF-kappaB-regulated inflammatory and carcinogenic gene products including MMP-9, TNF-alpha, IL-8, ICAM-1 and MCP-1. In line with the observation that NF-kappaB activation may up-regulate anti-apoptotic genes, it was shown that honokiol enhanced TNF-alpha-induced apoptotic cell death. In summary, our results demonstrate that honokiol suppresses NF-kappaB activation and NF-kappaB-regulated gene expression through the inhibition of IKKs, which provides a possible mechanism for its anti-tumor actions.
Tse
Anfernee Kai-Wing
AK
Bioactive Products Research Group, Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, China.
Wan
Chi-Keung
CK
Shen
Xiao-Ling
XL
Yang
Mengsu
M
Fong
Wang-Fun
WF
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D024202:Electrophoretic Mobility Shift Assay / Q000379:methods; D015870:Gene Expression / Q000187:drug effects; D017930:Genes, Reporter / Q000502:physiology; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D017705:Lignans / Q000737:chemistry / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008156:Luciferases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000235:genetics; D008233:Lymphotoxin-alpha / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D052002:NF-kappa B p50 Subunit / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000187:drug effects; D051996:Transcription Factor RelA / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D000498:Allyl Compounds; D010636:Phenols
D000970:Antineoplastic Agents; D001713:Biphenyl Compounds; D051550:I-kappa B Kinase; D017705:Lignans; D008070:Lipopolysaccharides; D008156:Luciferases; D008233:Lymphotoxin-alpha; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D013755:Tetradecanoylphorbol Acetate; D018808:Transcription Factor AP-1; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; C005499:honokiol; D000498:Allyl Compounds; D010636:Phenols