Activation of caspase-3 and c-Jun NH2-terminal kinase-1 signaling pathways in tamoxifen-induced apoptosis of human breast cancer cells.
Tamoxifen (TAM) is widely used in the treatment of breast cancer. The cytostatic effects of TAM have been attributed to the antagonism of estrogen receptor (ER) and inhibition of estrogen-dependent proliferative events. However, the mechanism by which TAM is also effective against certain ER-negative breast tumors remains to be elucidated. Here we report that TAM induced the activity of caspase-3-like proteases in ER-negative breast cancer cell lines MDA-MB-231 and BT-20, as evidenced by the cleavage of fluorogenic tetrapeptide substrate and of poly(ADP-ribose) polymerase. The activation of caspase-3-like proteases preceded TAM-induced chromatin condensation and nuclear fragmentation, the typical apoptotic morphologies. Pretreatment of cells with a specific inhibitor of caspase-3, acetyl-Asp-Glu-Val-Asp-aldehyde, or with a general inhibitor of caspases, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, prevented TAM-induced apoptosis. TAM also stimulated c-Jun NH2-terminal kinase (JNK) 1 activity, and interfering with the JNK pathway by over-expressing a DN JNK1 mutant attenuated TAM-induced apoptosis. In addition, treatment of cells with a lipid-soluble antioxidant vitamin E blocked TAM-induced caspase-3 and JNK1 activation as well as apoptosis, whereas water-soluble antioxidants N-acetyl L-cysteine and glutathione had little effect. Thus, this study demonstrates that TAM induces apoptosis in ER-negative breast cancer cells through caspase-3 and JNK1 pathways, which are probably initiated at the cell membrane by an oxidative mechanism.
Mandlekar
S
S
Department of Pharmaceutics and Pharmacodynamics, Center for Pharmaceutical Biotechnology, University of Illinois at Chicago, Illinois 60612, USA.
Yu
R
R
Tan
T H
TH
Kong
A N
AN
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D018931:Antineoplastic Agents, Hormonal / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology; D013629:Tamoxifen / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000633:toxicity; D014407:Tumor Cells, Cultured
D000590:Amino Acid Chloromethyl Ketones; D018931:Antineoplastic Agents, Hormonal; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D013629:Tamoxifen; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases