Curcumin Blocks Cytokine-Mediated NF-κB Activation and Proinflammatory Gene Expression by Inhibiting Inhibitory Factor I-κB Kinase Activity

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NF-κB plays a critical role in the transcriptional regulation of proinflammatory gene expression in various cells. Cytokine-mediated activation of NF-κB requires activation of various kinases, which ultimately leads to the phosphorylation and degradation of IκB, the NF-κB cytoplasmic inhibitor. The food derivative curcumin has been shown to inhibit NF-κB activity in some cell types. In this report we investigate the mechanism of action of curcumin on cytokine-induced proinflammatory gene expression using intestinal epithelial cells (IEC). Curcumin inhibited IL-1β-mediated ICAM-1 and IL-8 gene expression in IEC-6, HT-29, and Caco-2 cells. Cytokine-induced NF-κB DNA binding activity, RelA nuclear translocation, IκBα degradation, IκB serine 32 phosphorylation, and IκB kinase (IKK) activity were blocked by curcumin treatment. Wound-induced p38 phosphorylation was not inhibited by curcumin treatment. In addition, mitogen-activated protein kinase/ERK kinase kinase-1-induced IL-8 gene expression and 12-O-tetraphorbol 12-myristate 13-acetate-responsive element-driven luciferase expression were inhibited by curcumin. However, IκBα degradation induced by ectopically expressed NF-κB-inducing kinase or IKK was not inhibited by curcumin treatment. Therefore, curcumin blocks a signal upstream of NF-κB-inducing kinase and IKK. We conclude that curcumin potently inhibits cytokine-mediated NF-κB activation by blocking a signal leading to IKK activity.