The Bik BH3-only protein is induced in estrogen-starved and antiestrogen-exposed breast cancer cells and provokes apoptosis.
Evidence has been accumulating that some estrogen-dependent human breast cancers require estrogen for not only proliferation but also survival. To obtain insights into the molecular mechanisms of apoptosis of breast cancer cells subjected to estrogen starvation or exposed to antiestrogens, we characterized changes in the gene expression profile of MCF-7/BUS human breast cancer cells and revealed a strong induction of Bik, a member of the BH3-only proapoptotic proteins. The Bik mRNA transcript and protein were strongly induced by estrogen starvation or exposure to fulvestrant, a pure antiestrogen that competes with the natural estrogens for binding to the estrogen receptors. This Bik induction preceded apoptotic cell death, which was blocked by zVAD-fmk, a pancaspase inhibitor. Amounts of the Bcl-2-related proteins, such as Bcl-2, Bcl-XL, or Bax, showed only marginal changes in the presence or absence of estrogens or antiestrogens. Suppression of Bik expression by using the small interfering RNA effectively blocked the fulvestrant-induced breast cancer cell apoptosis. These results indicate that Bik is induced in MCF-7/BUS cells in the absence of estrogen signaling and plays a critical role in the antiestrogen-provoked breast cancer cell apoptosis.
Department of Tumor Biology, Massachusetts General Hospital Cancer Center, Charlestown, MA 02129, USA.
Jingyung
J
Hur
Jessica
J
Chesnes
Kathryn R
KR
Coser
Roseanna S
RS
Lee
Peter
P
Geck
Kurt J
KJ
Isselbacher
Toshi
T
Shioda
D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D017931:DNA Primers; D004958:Estradiol / Q000494:pharmacology*; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics*; D024101:Mitochondrial Proteins; D034741:RNA, Small Interfering / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D051017:Apoptosis Regulatory Proteins; C096820:BIK protein, human; D017931:DNA Primers; D020847:Estrogen Receptor Modulators; D004967:Estrogens; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D034741:RNA, Small Interfering; D004958:Estradiol