Tamoxifen regulates cell fate through mitochondrial estrogen receptor beta in breast cancer.
Tamoxifen (TAM) has both cytostatic and cytotoxic properties for breast cancer. TAM engaged mitochondrial estrogen receptor beta (ERβ) as an antagonist in MCF7-BK cells, increasing reactive oxygen species (ROS) concentrations from the mitochondria that were required for cytotoxicity. In part, this derived from TAM downregulating manganese superoxide dismutase (MnSOD) activity by causing the nitrosylation of tyrosine 34, thereby increasing ROS. ROS-activated protein kinase C delta and c-jun N-terminal kinases, resulting in the mitochondrial translocation of Bax and cytochrome C release. Interestingly, TAM failed to cause high ROS levels or induce cell death in MCF7-BK-TR cells due to stimulation of MnSOD activity through agonistic effects at mitochondrial ERβ. In several mouse xenograft models, lentiviral shRNA-induced knockdown of MnSOD caused tumors that grew in the presence of TAM to undergo substantial apoptosis. Tumor MnSOD and mitochondrial ERβ are therefore targets for therapeutic intervention to reverse TAM resistance and enhance a cell death response.
Division of Endocrinology, Medical Service 111-I, Veterans Affairs Medical Center, Long Beach, CA, USA.
M
M
Razandi
A
A
Pedram
V C
VC
Jordan
S
S
Fuqua
E R
ER
Levin
D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D047629:Estrogen Receptor beta / Q000378:metabolism*; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
D047629:Estrogen Receptor beta; D017382:Reactive Oxygen Species; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; D013482:Superoxide Dismutase