Raloxifene, a Mixed Estrogen Agonist/Antagonist, Induces Apoptosis through Cleavage of BAD in TSU-PR1 Human Cancer Cells*

Selective estrogen receptor modulator is a proven agent for chemoprevention and chemotherapy of cancer. Raloxifene, a mixed estrogen agonist/antagonist, was developed to prevent osteoporosis and potentially reduce the risk of breast cancer. In this study, we examined the effect of raloxifene on the TSU-PR1 cell line. This cell line was originally reported to be a prostate cancer cell line, but recently it has been shown to be a human bladder transitional cell carcinoma cell line. The TSU-PR1 cell line contains high levels of estrogen receptor beta. Following treatment with raloxifene, evidence of apoptosis, including change in nuclear morphology, DNA fragmentation, and cytochrome c release, was observed in a dose-dependent manner in the TSU-PR1 cells (10(-9) to 10(-6) m range). We observed no detectable change in the steady-state levels of Bax, Bcl-2, and Bcl-X(L) following raloxifene treatment. However, raloxifene induced caspase-dependent cleavage of BAD to generate a 15-kDa truncated protein. Overexpression of a double mutant BAD resistant to caspase 3 cleavage blocked raloxifene-induced apoptosis. These results demonstrate that raloxifene induces apoptosis through the cleavage of BAD in TSU-PR1 cells. This molecular mechanism of apoptosis suggests that raloxifene may be a therapeutic agent for human bladder cancer.