Down-regulation of Notch-1 contributes to cell growth inhibition and apoptosis in pancreatic cancer cells

Pancreatic cancer remains the fourth most common cause of cancer-related death in the United States. Notch signaling plays a critical role in maintaining the balance among cell proliferation, differentiation, and apoptosis, and thereby may contribute to the development of pancreatic cancer. To characterize Notch pathway function in pancreatic cancer cells, we explored the consequences of down-regulation of Notch-1 in BxPC-3, HPAC, and PANC-1 pancreatic cancer cells. Using multiple cellular and molecular approaches such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, apoptosis assay, flow cytometry, gene transfection, real-time reverse transcription-PCR (RT-PCR), Western blotting, and electrophoretic mobility shift assay for measuring DNA binding activity of nuclear factor κB (NF-κB), we found that down-regulation of Notch-1 inhibited cell growth and induced apoptosis in pancreatic cancer cells. Notch-1 down-regulation also increased cell population in the G₀-G₁ phase. Compared with control, small interfering RNA-transfected cells decreased expression of cyclin A, cyclin D1, and cyclin-dependent kinase 2. We found up-regulation of p21 and p27, which was correlated with the cell cycle changes. In addition, Notch-1 down-regulation also induced apoptosis, which could be due to decreased Bcl-2 and Bcl-X_L protein expression in pancreatic cancer cells. Because Notch-1 is known to cross-talk with another major cell growth and apoptotic regulatory pathway (i.e., NF-κB), we found that NF-κB is a downstream target of Notch because down-regulation of Notch reduced NF-κB activity. We also found that genistein, a prominent isoflavone, could be an active agent for the down-regulation of the Notch pathway. These findings suggest that Notch-1 down-regulation, especially by genistein, could be a novel therapeutic approach for the treatment of pancreatic cancer.