Bad Dephosphorylation And Decreased Expression Of Mcl-1 Induce Rapid Apoptosis In Prostate Cancer Cells

PTEN loss and constitutive activation of the PI3K signaling pathway have been associated with advanced androgenin-dependent prostate cancer. PTEN-deficient prostate cancer C42Luc cells survive in serum-free media and show relative resistance to apoptosis even in the presence of the PI3K inhibitor ZSTK474. Yet, when ZSTK474 is combined with the translation inhibitor cycloheximide, C42Luc cells undergo apoptosis within 6 hours. We identified dephosphorylation of BAD (Bcl2-associated death promoter) as a main apoptosis-regulatory molecule downstream from PI3K, and loss of MCL-1 (Myel (o) over bar id c (e) over bar ll leukemi (a) over bar -1) as a major target of cycloheximide. The combination of MCL-1 knockdown and expression of p (h) over bar osphor (y) over bar lation-deficient mutant BAD2SA is sufficient to trigger rapid apoptosis in prostate cancer cells. These results establish the mechanism for the synergistic induction of apoptosis by the combination of a PI3K inhibitor and of a protein synthesis inhibitor in PTEN-deficient prostate cancer cells.