Heterogeneous apoptotic responses of prostate cancer cell lines identify an association between sensitivity to staurosporine-induced apoptosis, expression of Bcl-2 family members, and caspase activation

BACKGROUND. The goal of this work was to identify mechanisms for the inabil ity of metastatic prostate cancer cells to engage the apoptotic pathway fol lowing hormonal or cytotoxic therapy. METHODS. Genotypically diverse cell lines isolated from patients with metas tatic disease were used. RESULTS. The LNCaP and TsuPr(1) lines exhibited quintessential apoptotic fe atures in response to the pleiotropic apoptotic inducer staurosporine (STS) : rapid cytochrome c translocation to the cytosol, proteolytic processing a nd catalytic activation of caspase-3 and -7, proteolytic inactivation of th e death substrates DNA fragmentation factor (DFF) and poly-ADP-ribose polym erase (PARP), and TUNEL-positive polyfragmented nuclei. In contrast, DU-145 and PC-3 cells exhibited few, if any, of these features, while appearing n ecrotic by confocal microscopy. The presence of caspase-3 and -7 without pr oteolytic processing suggested that the apoptotic blockade was upstream of executioner caspases in these resistant cell Lines. To identify the locus o f this block, Western blot analysis of cytochrome c subcellular localizatio n and of pro- and antiapoptotic Bcl-2 family members was performed, and sug gested that heterogeneous expression of these proteins might be the underly ing mechanism for apoptotic resistance to STS in these cell lines. Thus, th e absence of the proapoptotic Bar in DU-145 cells indicated a mechanism for apoptotic resistance of these cells. Similarly, decreased Bar expression d uring STS treatment, coupled with overexpression of the antiapoptotic Bd-x( L) and inability to translocate cytochrome c to the cytosol, provided a mec hanism for the insensitivity of PC-3 cells. CONCLUSIONS. These observations suggest that activation of the apoptotic ma chinery in metastatic prostate cancer cell lines may be determined by expre ssion levels of Bcl-2 family members, by the ability of cytochrome c to tra nslocate to the cytosol, and by the ability of the caspase pathway to react in response to activation of the mitochondrial phase. Prostate 42: 260-273 , 2000. (C) 2000 Wiley-Liss, Inc.