title: Activation of caspase-3 and c-Jun NH2-terminal kinase-1 signaling pathways in tamoxifen-induced apoptosis of human breast cancer cells.
abstract: 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.
authors.affiliation: Department of Pharmaceutics and Pharmacodynamics, Center for Pharmaceutical Biotechnology, University of Illinois at Chicago, Illinois 60612, USA.
authors.forename: S
authors.initials: S
authors.lastname: Mandlekar
authors.forename: R
authors.initials: R
authors.lastname: Yu
authors.forename: T H
authors.initials: TH
authors.lastname: Tan
authors.forename: A N
authors.initials: AN
authors.lastname: Kong
mesh_terms: 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
chemical_list: 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