The transcription factor NFκB plays a role in cell survival. Apoptosis, programmed cell death, via numerous triggers including death receptor ligand binding is antagonized by NFκB activation and potentiated by its inhibition. In the present study, we found that caffeic acid phenethyl ester (CAPE), known to inhibit NFκB, induced apoptosis via Fas signal activation in human breast cancer MCF-7 cells. CAPE activated Fas by a Fas ligand (Fas-L)-independent mechanism, induced p53-regulated Bax protein, and activated caspases. CAPE also activated MAPK family proteins p38 and JNK. SB203580, a specific inhibitor of p38 MAPK, partially suppressed CAPE-induced p53 activation, Bax expres. sion, and apoptosis, consistent with a mechanism by which CAPE leads to Bax activation, known to be regulated by p38 and p53. The expression of dominant negative c-Jun, which inhibits the JNK signal, also suppresses CAPE-induced apoptosis, suggesting MAPKs are involved in CAPE-induced apoptosis. The expression of Fas antisense oligomers significantly suppressed the CAPE-induced activations of JNK and p38 and apoptosis as compared with Fas sense oligomers. To ascertain whether these phenomena are attributable to the inhibition of NFκB by CAPE, we examined the effect of a truncated form of IκBα (IκBΔN) lacking the phosphorylation sites essential for NFκB activation. IκBΔN expression not only inhibited NFκB activity but also induced Fas activation, Bax expression, and apoptosis. Our findings demonstrate that NFκB inhibition is sufficient to induce apoptosis and that Fas activation plays a role in NFκB inhibition-induced apoptosis in MCF-7 cells.
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