Naturally occurring phenethyl isothiocyanate (PEITC) selectively inhibits growth of cancer cells by causing apoptosis, but the mechanism of cell death induction is not fully understood. We now show, for the first time, that growth factor adapter protein p66(Shc) is indispensable for PEITC-induced apoptosis. Mouse embryonic fibroblasts derived from p66(Shc) knockout mice were significantly more 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 Ser(36) phosphorylation of p66(Shc) in PC-3 and LNCaP human prostate cancer cells. Knockdown of p66(Shc) protein conferred significant protection against PEITC-mediated cytoplasmic histone-associated DNA fragmentation as well as production of reactive oxygen species in both PC-3 and LNCaP cells. The PEITC-treated PC-3 and LNCaP cells exhibited increased binding of p66(Shc) with prolyl isomerase Pin1, a protein implicated in translocation of p66(Shc) to mitochondria. Consistent with these results, treatment of PC-3 cells with PEITC resulted in translocation of p66(Shc) to the mitochondria as judged by immunoblotting using cytosolic and mitochondrial fractions and immunofluorescence microscopy. Growth suppression and apoptosis induction in tumor xenografts in vivo by oral administration of PEITC to the PC-3 tumor-bearing male athymic mice were accompanied by statistically significant increase in the level of Ser(36)-phosphorylated p66(Shc). Collectively, these results provide novel insight into the critical role of p66(Shc) in regulation of PEITC-induced apoptotic cell death in human prostate cancer cells.
(c)2010 AACR.