Sulforaphane-induced cell death in human prostate cancer cells is initiated by reactive oxygen species.
We have shown previously that sulforaphane (SFN), a constituent of many edible cruciferous vegetables including broccoli, suppresses growth of prostate cancer cells in culture as well as in vivo by causing apoptosis, but the sequence of events leading to cell death is poorly defined. Using PC-3 and DU145 human prostate cancer cells as a model, we now demonstrate, for the first time, that the initial signal for SFN-induced apoptosis is derived from reactive oxygen species (ROS). Exposure of PC-3 cells to growth-suppressive concentrations of SFN resulted in ROS generation, which was accompanied by disruption of mitochondrial membrane potential, cytosolic release of cytochrome c, and apoptosis. All these effects were significantly blocked on pretreatment with N-acetylcysteine and overexpression of catalase. The SFN-induced ROS generation was significantly attenuated on pretreatment with mitochondrial respiratory chain complex I inhibitors, including diphenyleneiodonium chloride and rotenone. SFN treatment also caused a rapid and significant depletion of GSH levels. Collectively, these observations indicate that SFN-induced ROS generation is probably mediated by a nonmitochondrial mechanism involving GSH depletion as well as a mitochondrial component. Ectopic expression of Bcl-xL, but not Bcl-2, in PC-3 cells offered significant protection against the cell death caused by SFN. In addition, SFN treatment resulted in an increase in the level of Fas, activation of caspase-8, and cleavage of Bid. Furthermore, SV40-immortalized mouse embryonic fibroblasts (MEFs) derived from Bid knock-out mice displayed significant resistance toward SFN-induced apoptosis compared with wild-type MEFs. In conclusion, the results of the present study indicate that SFN-induced apoptosis in prostate cancer cells is initiated by ROS generation and that both intrinsic and extrinsic caspase cascades contribute to the cell death caused by this highly promising cancer chemopreventive agent.
Singh
Shivendra V
SV
Department of Pharmacology and University of Pittsburgh Cancer Institute, Pennsylvania 15213, USA singhs@msx.upmc.edu
Srivastava
Sanjay K
SK
Choi
Sunga
S
Lew
Karen L
KL
Antosiewicz
Jedrzej
J
Xiao
Dong
D
Zeng
Yan
Y
Watkins
Simon C
SC
Johnson
Candace S
CS
Trump
Donald L
DL
Lee
Yong J
YJ
Xiao
Hui
H
Herman-Antosiewicz
Anna
A
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D017879:Isothiocyanates; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013454:Sulfoxides; D013861:Thiocyanates / Q000494:pharmacology*
D000975:Antioxidants; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; D002352:Carrier Proteins; D017879:Isothiocyanates; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D013454:Sulfoxides; D013861:Thiocyanates; D045304:Cytochromes c; C505530:CASP8 protein, human; C505526:Casp8 protein, mouse; D053181:Caspase 8; D020169:Caspases; C016766:sulforaphane; D000111:Acetylcysteine