4＇, 6-Dihydroxy-4-methoxyisoaurone inhibits TNF-α-induced NF-KB activation and expressions of NF-KB-regulated target gene products

The nuclear factor-KB （NF-KB） transcription factors control many physiological processes including in- flammation, immunity, apoptosis, and angiogenesis. In our search for NF-KB inhibitors from natural resources, we identified 4＇,6-dihydroxy-4-methoxyisoaurone （ISOA） as an inhibitor of NF-KB activation from the seeds of Tricho- santhes kirilowii. However, the mechanism by which ISOA inhibits NF-KB activation is not fully understood. In the present study, we demonstrated the effect of ISOA on NF-KB activation in TNF-α-stimulated HeLa cells. This com- pound suppressed NF-KB activation through the inhibition of IKB kinase （IKK） activation. ISOA also has an influ- ence on upstream signaling of IKK through the inhibition of expression of adaptor proteins, TNF receptor-associated factor 2 （TRAF2） and receptor interacting protein 1 （RIP1）. Consequently, ISOA blocked the phosphorylation and degradation of the inhibitor of NF-KB alpha （IKBα） , and subsequent phosphorylation and nuclear translocation of p65. The suppression of NF-KB activation by ISOA led to the down-regulation of target genes involved in inflam- mation, proliferation, angiogenesis and invasion, as well as potentiation of TNF-α-induced apoptosis at least in part through activation of caspase-8. Taken together, this study extends our understanding on the mechanisms underly- ing the anti-inflammatory and anti-cancer activities of ISOA. Our findings provide new insight into the molecular mechanisms and a potential application of ISOA for inflammatory diseases as well as certain cancers associated with abnormal NF-KB activation.