Phenethyl isothiocyanate (PEITC), a cancer chemopreventive constituent of edible cruciferous vegetables such as watercress, suppresses growth of human prostate cancer cells by causing apoptosis but the mechanism of cell death induction is not fully understood. Here, we provide experimental evidence to implicate adapter protein p66shc in regulation of PEITC-induced apoptotic cell death. Mouse embryonic fibroblasts lacking p66shc isoform were resistant to PEITC-mediated growth inhibition, cytoplasmic histone-associated apoptotic DNA fragmentation, and caspase-3 activation compared with wild-type fibroblasts. The PEITC treatment resulted in induction as well as increased Ser36 phosphorylation of p66shc in PC-3 (an androgen-independent cell line lacking functional p53) and LNCaP (an androgen-responsive cell line with intact p53) human prostate cancer cells. Moreover, siRNA knockdown of p66shc protein in PC-3 and LNCaP cells conferred significant protection against PEITC-induced cytoplasmic histone-associated DNA fragmentation, caspase-3 activation, and production of reactive oxygen species. Immunoprecipitation-immunoblotting experiments revealed increased binding of p66shc with prolyl isomerase 1 (Pin1), which is implicated in translocation of p66shc to mitochondria, upon treatment of PC-3 and LNCaP cells with PEITC compared with vehicle-treated control cells. Consistent with these results, treatment of PC-3 cells with PEITC resulted in translocation of p66shc to the mitochondria as judged by immunoblotting using cytosolic and mitochondrial fractions and immunofluorescence microscopy. Growth of PC-3 cells subcutaneously implanted in male athymic mice was significantly retarded by gavage with 9 μmol PEITC five times per week. The PEITC-mediated inhibition of PC-3 xenograft growth correlated with reduced cell proliferation, increased apoptosis, hyperphosphorylation of p66shc, and down-regulation of Pin1 protein level. Collectively, these results provide novel insight into the mechanism of PEITC-induced apoptosis to indicate critical role of p66shc in regulation of cell death. This investigation was supported by the National Cancer Institute grant 2 RO1 CA101753-06.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3788.