Protein kinase C-δ (PKC-δ) and PKC-ε are reported to be effective in
cancer prevention via S-thiolation-mediated mechanisms. This may be through stimulation of the pro-apoptotic,
tumor-suppressive
isozyme PKC-δ and/or inactivation of the growth stimulatory, oncogenic
isozyme PKC-ε. We investigated oxidative regulatory responses of PKC-δ and PKC-ε to
cystine dimethyl ester (CDME), a metabolic precursor of
cystine, which, by inducing release of cellular
cystine stimulates apoptosis in different
prostate cancer cells, PC3 and LNCaP, compared to normal RWPE1 cells. Treatment of CDME in doses of 0.5mM and 5mM significantly induces apoptosis due to regulation of concentration-dependent PKC-δ stimulation and PKC-ε reduction in these
prostate cancer cells. This apoptotic regulation was confirmed by immunoblot analyses and specific PKC
enzyme assays in immunoprecipitated samples. Additionally, inhibition of PKC-δ by
small interfering RNA (
siRNA) proved that CDME-induced cell death was dependent on PKC-δ activity in
prostate cancer cells. These data demonstrated that CDME induces apoptosis by cysteinylation of both PKC-δ and PKC-ε in tumorigenic prostate epithelial cells compared to control nontumorigenic cells. Cellular
cystine may play a critical role in treatment and/or prevention of
prostate cancer by regulating PKC activity.