IκBα reverses the potentiation of curcumin-induced apoptosis after RelA overexpression. ( A ) Cells were co-transfected with pCMV4, p65 and ΔNIκBα expression vectors and an NFκB-responsive luciferase reporter plasmid 3EnhConALuc, as indicated. Cells were treated with curcumin (35 µM) for 18 h, and luciferase activity of cell lysates was measured and normalized to β-galactosidase activity obtained by co-transfection with a pCMVβGal internal control plasmid. Results represent the mean ± SD of three separate experiments. * , P < 0.001, significantly different compared with pCMV4-transfected cells; ** , P < 0.01, significantly different compared with p65-transfected cells, without ΔNIκB. ( B ) Cells were transfected as in (A) and treated with curcumin (35 µM) for 24 h. Cell death was assessed by MTT assay. Results, showing percentage cell viability compared with vehicle-treated cells, represent the mean ± SD of three separate experiments. * , P < 0.001, significantly different from pCMV4-transfected cells. ( C ) Cells were transfected as in (A) and treated with curcumin (35 µM) for 24 h. Apoptosis was assessed by western blotting for PARP cleavage using whole-cell lysates.