Targeting nuclear factor-κB activation pathway by thymoquinone:: Role in suppression of antiapoptotic gene products and enhancement of apoptosis (Publication with Expression of Concern. See vol. 16, pg. 1441, 2018)

Thymoquinone (TO), derived from the medicinal plant Nigella sativa, exhibits anti inflammatory and anticancer activities through mechanism(s) that is not fully understood. Because numerous effects modulated by TO can be linked to interference with the nuclear factor-kappa B (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 TO suppressed tumor necrosis factor-induced NF-kappa B activation in a dose- and time-dependent manner and inhibited NF-kappa B activation induced by various carcinogens and inflammatory stimuli. The suppression of NF-kappa B 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. TO specifically suppressed the direct binding of nuclear p65 and recombinant p65 to the DNA, and this binding was reversed by DTT. However, TO did not inhibit p65 binding to DNA when cells were transfected with the p65 plasmid containing cysteine residue 38 mutated to serine. TO 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 anti inflammatory activities previously assigned to TO 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.