Notch-1 down-regulation by curcumin is associated with the inhibition of cell growth and the induction of apoptosis in pancreatic cancer cells

Background: Notch signaling plays a critical role in maintaining the balance between cell proliferation, differentiation, and apoptosis, and thereby may contribute to the development of pancreatic cancer. Therefore, the down-regulation of Notch signaling may be a novel approach for pancreatic cancer therapy. It has been reported that curcumin down-regulates many genes that are known to promote survival and also up-regulates genes that are known promoters of apoptosis in pancreatic cancer cells in vitro. It also has been reported that there is cross-talk between Notch-1 and another major cell growth and apoptotic regulatory pathway, the nuclear factor kappaB (NF-kappaB) pathway, which is down-regulated by both curcumin and reduction of Notch-1 levels. However, to the authors' knowledge to date, no studies have determined whether the down-regulation of Notch-1 signaling, resulting in the inactivation of NF-kappaB activity, contributes to curcumin-induced cell growth inhibition and apoptosis in pancreatic cancer cells.

Methods: The authors used multiple molecular approaches, such as the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, an apoptosis assay, gene transfection, real-time reverse transcriptase-polymerase chain reaction analysis, Western blot analysis, and an electrophoretic mobility shift assay to measure the DNA binding activity of NF-kappaB.

Results: Curcumin inhibited cell growth and induced apoptosis in pancreatic cancer cells. Notch-1, Hes-1, and Bcl-XL expression levels concomitantly were down-regulated by curcumin treatment. These results correlated with the inactivation of NF-kappaB activity and increased apoptosis induced by curcumin. The down-regulation of Notch-1 by small-interfering RNA prior to curcumin treatment resulted in enhanced cell growth inhibition and apoptosis.

Conclusions: The current results provide the first demonstration to the authors' knowledge that the Notch-1 signaling pathway is associated mechanistically with NF-kappaB activity during curcumin-induced cell growth inhibition and apoptosis of pancreatic cells. These results suggest that the down-regulation of Notch signaling by curcumin may be a novel strategy for the treatment of patients with pancreatic cancer.