Inhibition of nuclear factor κB induces apoptosis following treatment with tumor necrosis factor α and an antioxidant in human prostate cancer cells

Transforming growth factor beta-1 (TGFβ-1) and tumor necrosis factor alpha (TNF-α), an activator of nuclear factor kappa B (NF-κB), modulate apoptosis and/or cell growth. This study was designed to investigate the activity of NF-κB and its regulation of inhibitor of apoptosis gene (c-IAP2) in two human prostate cancer cell lines, DU-145 (which is androgen unresponsive) and ALVA-101 (which is moderately androgen responsive). These cells were treated with and without various concentrations of a strong antioxidant, pyrrolidinedithiocarbamate (PDTC), and TNF-α at various time intervals. Following treatments, cell growth and apoptosis were determined by ELISA techniques. NF-κB activity was determined by electrophoretic mobility shift assay (EMSA), and c-IAP2 mRNA production was determined with Northern blot analysis. PDTC treatment significantly reduced cell growth up to 80% in both DU-145 and ALVA-101 cells. TNF-α and lower but not higher doses of PDTC combined demonstrated an additive inhibition of cell growth in both cell lines. Active NF-κB and c-IAP2 was blocked significantly following PDTC treatments, whereas treatments with TNF-α alone showed increased NF-κB activity and c-IAP2. However, when both PDTC and TNF-α were combined, nuclear presence of NF-κB and c-IAP2 were reduced significantly (P<0.05) to levels observed with PDTC alone. In conclusion, the antioxidant, PDTC, appears to initiate apoptosis by blocking cytoplasmic NF-κB translocation to the nucleus where it normally activates the production of apoptosis-inhibitory proteins like c-IAP2. Both TNF-α and PDTC alone cause apoptosis and reduce cell growth, but their combined effects are additive in reducing cell growth of DU-145 and ALVA-101 human prostate cancer cells.