Induction of apoptosis in androgen-independent mouse mammary cell line by 1, 25-dihydroxyvitamin D₃

Androgen-dependent tumors eventually progress to independent-tumors after androgen withdrawal. Effective treatment for hormone-independent tumors is therefore needed. Androgen-independent CS-2 cells could grow in serum-free culture whether androgen is present in the medium or not. In the present study, the mechanism of cell death in CS-2 cells was examined after 1, 25-dihydroxyvitamin D₃ [1, 25(OH)₂D₃] treatment. 1, 25(OH)₂D₃ has been examined as an anti-tumor agent, but its role in promoting cell death is poorly understood. Based upon the temporal sequence of DNA fragmentation, morphologic changes and loss of cell viability, the cells underwent apoptosis with 1, 25(OH)₂D₃treatment. Northern-blot analysis was used to identify a series of genes whose expression per cell is enhanced during the apoptotic pathway. In the apoptotic process induced by 1, 25(OH)₂D₃, mRNA expression of testosterone-repressed prostatic message 2, transforming growth factor β1, glucose-regulated 78-kDa protein and calmodulin increased. Flow-cytometric analysis showed that 1, 25(OH)₂D₃ treatment resulted in a block in G₀/G₁ of the cell cycle. These results demonstrate that androgen-independent CS-2 cells retain the ability to undergo apoptosis by 1, 25(OH)₂D₃. This system appears to be a good model for investigating apoptosis of hormone-independent cancer. © 1996 Wiley-Liss, Inc.