Differential expression of cell death regulators in response to thapsigargin and adriamycin in Bcl-2 transfected DU145 prostatic cancer cells

Functional overexpression of Bcl-2 has been reported to confer an anti-apoptotic potential in a variety of cell types. The role of Bcl-2 in epithelial cell-cycle control and in interactions with other cell-cycle regulators is not clearly understood. Its expression has been correlated with the hormono- and chemo-resistant phenotype in advanced prostate cancer. The aim of this study was to investigate the mechanisms through which Bcl-2 mediates increased cytotoxic chemoresistance by assessing alterations in the expression of cell death regulatory molecules. The DU145 human prostatic adenocarcinoma cell line was stably transfected with a Bcl-2 encoding expression plasmid. Two Bcl 2 transfectants, DKC9 and DKC11, were expanded for further study. The effects of Bcl-2 expression on cellular proliferation, cell death (± adriamycin or thapsigargin), and expression of cell-cycle/death regulators (p53, PCNA, Bax, Bak, Bcl-X_L) were evaluated. Compared with controls, Bcl-2 transfectants showed no difference in the rate of proliferation, a decrease in p53 (∼ two-fold), an increase in Bax (∼ two-fold) and PCNA (∼ three-fold), and no change in the levels of Bcl-X_L and Bak proteins. DKC9 and DKC11 also exhibited a significantly increased chemoresistance to adriamycin (0.0025 5 μM) and thapsigargin (0.0025 5 μM) compared with controls. In the presence of thapsigargin or adriamycin, levels of Bcl-2 and its heterodimeric partner Bax were elevated ∼ two-fold with no change in Bak in Bcl-2 transfectants in contrast to controls, where Bak was increased (two-fold). This is the first study to demonstrate that Bcl-2 transfection modulates the expression of mutant p53, Bax, and PCNA in prostate cancer cells. Moreover, Bcl-2 overexpression conferred a significant cytotoxic chemoresistance and altered the balance of expression of death promoters (from Bak, a dominant death promoter in controls, to Bax) in response to thapsigargin and adriamycin.