PC-SPES is an eight-herbal mixture which has activity against
prostate cancer cells and can reduce the serum level of
prostate specific antigen (PSA) in more than 80% of individuals with
prostate cancer. We conducted this study to begin to clarify the molecular mechanism by which
PC-SPES inhibited the growth of
prostate cancer cells and down-regulated expression of PSA. Western blot analysis,
luciferase reporter assay using a variety of promoters of the PSA gene and the isolated
androgen receptor response elements (ARE), as well as electrophoretic mobility shift assay (EMSA) were employed to study the effect of
PC-SPES on DHT-induced expression of PSA in LNCaP
androgen-dependent human
prostate cancer cells. Also, Western blot analysis and
luciferase reporter assay using 12-0-tetradecanoylphorbol-13-acetate response elements were employed to study the ability of
PC-SPES to activate the c-Jun NH2-terminal
kinase (JNK)/c-Jun/AP-1 signal pathway in these cells. Reporter studies showed that
PC-SPES inhibited DHT-induced PSA promoter/enhancer-
luciferase activity via inhibition of ARE transcriptional activity. Western blot analysis showed that
PC-SPES down-regulated DHT-induced expression of PSA without decreasing DHT-induced nuclear level of AR. EMSA demonstrated that
PC-SPES inhibited the binding of DHT-activated AR to ARE. Moreover, we found that
PC-SPES phosphorylated JNK, increased levels of phosphorylated and unphosphorylated forms of c-Jun, and enhanced
AP-1 transcriptional activity in LNCaP cells. Interestingly, when LNCaP cells were stably tranfected with the dominant negative JNK binding domain (JBD) of JNK-interacting protein-1 (JIP-1), these cells no longer underwent apoptosis and growth inhibition in the presence of
PC-SPES. But,
PC-SPES still decreased levels of PSA in the LNCaP-JIP-1 cells. Taken together,
PC-SPES inhibited binding of DHT-activated AR to AREs of PSA gene resulting in down-regulation of ARE transcriptional activity and expression of PSA, and this occurred independently of the JNK/c-Jun/AP-1 signal pathway. Also,
PC-SPES activated the JNK/c-Jun/AP-1 signal pathway resulting in growth arrest and apoptosis of
prostate cancer cells.