Suppression of NF-κB and NF-κB-regulated gene expression by sulforaphane and PEITC through IκBα, IKK pathway in human prostate cancer PC-3 cells

Recent studies indicate that natural isothiocyanates, such as sulforaphane (SFN) and phenethyl isothiocyanate ( PEITC) possess strong antitumor activities in vitro and in vivo. The nuclear factor kappa B (NF-kappa B) is believed to play an important role in cancer chemoprevention due to its involvement in tumor cell growth, proliferation, angiogenesis, invasion, apoptosis, and survival. In this study, we investigated the effects and the molecular mechanisms of SFN and PEITC on NF-kappa B transcriptional activation and NF-kappa B-regulated gene expression in human prostate cancer PC-3 C4 cells. Treatment with SFN ( 20 and 30 mu M) and PEITC ( 5 and 7.5 mu M) significantly inhibited NF-kappa B transcriptional activity, nuclear transloction of p65, and gene expression of NF-kappa B-regulated VEGF, cylcin D1, and Bcl-X-L in PC- 3 C4 cells. To further elucidate the mechanism, we utilized the dominant-negative mutant of inhibitor of NF-kappa B alpha (I kappa B alpha) (SR-I kappa B alpha). Analogous to treatments with SFN and PEITC, SR-I kappa B alpha also strongly inhibited NF-kappa B transcriptional activity as well as VEGF, cylcin D1, and Bcl-X-L expression. Furthermore, SFN and PEITC also inhibited the basal and UVC-induced phosphorylation of I kappa B alpha and blocked UVC-induced I kappa B alpha degradation in PC-3 C4 cells. In examining the upstream signaling, we found that the dominant-negative mutant of IKK beta (dnIKK beta) possessed inhibitory effects similar to SFN and PEITC on NF-kappa B, VEGF, cylcin D1, Bcl-X-L as well as I kappa B alpha phosphorylation. In addition, treatment with SFN and PEITC potently inhibited phosphorylation of both IKKb and IKK alpha and significantly inhibited the in vitro phosphorylation of I kappa B alpha mediated by IKKb. Taken together, these results suggest that the inhibition of SFN and PEITC on NF-kappa B transcriptional activation as well as NF-kappa B-regulated VEGF, cyclin D1, and Bcl-X-L gene expression is mainly mediated through the inhibition of IKK phosphorylation, particularly IKK beta, and the inhibition of I kappa B alpha phosphorylation and degradation, as well as the decrease of nuclear translocation of p65 in PC-3 cells.