Thymoquinone (TQ), derived from the medicinal plant Nigella sativa, exhibits antiinflammatory and anticancer activities through mechanism(s) that is not fully understood. Because numerous effects modulated by TQ can be linked to interference with the
nuclear factor-kappaB (
NF-kappa B) signaling, we investigated in detail the effect of this
quinone on
NF-kappa B pathway. As examined by
DNA binding, we found that TQ suppressed
tumor necrosis factor-induced
NF-kappa B activation in a dose- and time-dependent manner and inhibited
NF-kappaB activation induced by various
carcinogens and inflammatory stimuli. The suppression of
NF-kappaB activation correlated with sequential inhibition of the activation of
I kappa B alpha
kinase, I kappa B alpha phosphorylation,
I kappa B alpha degradation, p65 phosphorylation, p65 nuclear translocation, and the
NF-kappa B-dependent reporter gene expression. TQ specifically suppressed the direct binding of nuclear p65 and recombinant p65 to the
DNA, and this binding was reversed by DTT. However, TQ did not inhibit p65 binding to
DNA when cells were transfected with the p65 plasmid containing
cysteine residue 38 mutated to
serine. TQ also down-regulated the expression of
NF-kappa B-regulated antiapoptotic (IAP1, IAP2, XIAP Bcl-2, Bcl-xL, and
survivin), proliferative (
cyclin D1,
cyclooxygenase-2, and c-Myc), and angiogenic (
matrix metalloproteinase-9 and
vascular endothelial growth factor) gene products. This led to potentiation of apoptosis induced by
tumor necrosis factor and chemotherapeutic agents. Overall, our results indicate that the anticancer and antiinflammatory activities previously assigned to TQ may be mediated in part through the suppression of the
NF-kappa B activation pathway, as shown here, and thus may have potential in treatment of
myeloid leukemia and other
cancers.