title: Fulvestrant-induced cell death and proteasomal degradation of estrogen receptor α protein in MCF-7 cells require the CSK c-Src tyrosine kinase.
abstract: Fulvestrant is a representative pure antiestrogen and a Selective Estrogen Receptor Down-regulator (SERD). In contrast to the Selective Estrogen Receptor Modulators (SERMs) such as 4-hydroxytamoxifen that bind to estrogen receptor α (ERα) as antagonists or partial agonists, fulvestrant causes proteasomal degradation of ERα protein, shutting down the estrogen signaling to induce proliferation arrest and apoptosis of estrogen-dependent breast cancer cells. We performed genome-wide RNAi knockdown screenings for protein kinases required for fulvestrant-induced apoptosis of the MCF-7 estrogen-dependent human breast caner cells and identified the c-Src tyrosine kinase (CSK), a negative regulator of the oncoprotein c-Src and related protein tyrosine kinases, as one of the necessary molecules. Whereas RNAi knockdown of CSK in MCF-7 cells by shRNA-expressing lentiviruses strongly suppressed fulvestrant-induced cell death, CSK knockdown did not affect cytocidal actions of 4-hydroxytamoxifen or paclitaxel, a chemotherapeutic agent. In the absence of CSK, fulvestrant-induced proteasomal degradation of ERα protein was suppressed in both MCF-7 and T47D estrogen-dependent breast cancer cells whereas the TP53-mutated T47D cells were resistant to the cytocidal action of fulvestrant in the presence or absence of CSK. MCF-7 cell sensitivities to fulvestrant-induced cell death or ERα protein degradation was not affected by small-molecular-weight inhibitors of the tyrosine kinase activity of c-Src, suggesting possible involvement of other signaling molecules in CSK-dependent MCF-7 cell death induced by fulvestrant. Our observations suggest the importance of CSK in the determination of cellular sensitivity to the cytocidal action of fulvestrant.
authors.affiliation: Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, Massachusetts, United States of America.
authors.forename: Wei-Lan
authors.initials: WL
authors.lastname: Yeh
authors.forename: Keiko
authors.initials: K
authors.lastname: Shioda
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Coser
authors.forename: Danielle
authors.initials: D
authors.lastname: Rivizzigno
authors.forename: Kristen R
authors.initials: KR
authors.lastname: McSweeney
authors.forename: Toshi
authors.initials: T
authors.lastname: Shioda
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism; D000081247:CSK Tyrosine-Protein Kinase; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D004967:Estrogens / Q000378:metabolism; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D061986:MCF-7 Cells; D017239:Paclitaxel / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects; D034622:RNA Interference; D013629:Tamoxifen / Q000494:pharmacology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D004967:Estrogens; D047428:Protein Kinase Inhibitors; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D046988:Proteasome Endopeptidase Complex; D017239:Paclitaxel