Carcinogenesis Advance Access originally published online on February 23, 2006
Carcinogenesis 2006 27(6):1285-1291; doi:10.1093/carcin/bgi368
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Overexpression of p65/RelA potentiates curcumin-induced apoptosis in HCT116 human colon cancer cells
Department of Surgery, Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast BT12 6BJ, UK
* To whom correspondence should be addressed. Tel: +44 2890 322276; Fax: +44 2890 321811; Email: f.c.campbell{at}qub.ac.uk
Curcumin, the yellow pigment in the spice turmeric, has potent chemopreventive activities that involve diverse molecular pathways. It is widely believed that curcumin pro-apoptotic properties are mediated by downregulation of NF kappa B (NF
B). The p65/RelA subunit of NF
B may influence cell death, in part by activation of NF
B anti-apoptotic target genes including X-linked inhibitor of apoptosis (XIAP), A20, bcl-xL and inhibition of sustained activation of c-Jun N-terminal kinase (JNK). We have shown previously that curcumin inhibits NF
B, activates JNK and promotes apoptosis in HCT116 colorectal cancer cells. Here, we show that forced overexpression of p65 does not affect curcumin-induced JNK activation. Indeed, overexpression of p65 enhanced curcumin-mediated apoptosis as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay and poly(ADP-ribose) polymerase (PARP) cleavage. This potentiating effect of p65 upon curcumin-mediated apoptosis was reversed by transfection of cells with an I
B super-repressor (
NI
B). Curcumin treatment inhibited expression of NF
B anti-apoptotic target genes in mock-transfected and in p65-overexpressing HCT116 cells, although expression levels remained higher in the latter. Taken together, these results show that curcumin-mediated activation of JNK or induction of apoptosis does not require inhibition of p65. Furthermore, curcumin/p65 synergy in promotion of apoptosis cannot be attributed to active repression of NF
B anti-apoptotic genes.