title: Tamoxifen-induced increases in cytoplasmic free Ca2+ levels in human breast cancer cells.
abstract: Tamoxifen has been shown to increase cytoplasmic free Ca2+ levels [Ca2+]i in renal tubular cells and bladder cancer cells, and to after Ca2+ signaling in MCF-7 breast cancer cells. The present study examined the effect of tamoxifen on [Ca2+], in ZR-75-1 human breast cancer cells using fura-2 as an indicator. Tamoxifen increased [Ca2+]i at a concentration above 2 microM with an EC50 of 5 microM. Removing extracellular Ca2+ reduced the response by 48+/-2%. In Ca2+-free medium, after tamoxifen-induced [Ca2+]i increased had returned to baseline, adding 3 mM Ca2+ increased [Ca2+]i in a concentration-dependent manner. Further, pretreatment with 10 microM tamoxifen abolished the [Ca2+]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor); and conversely, pretreatment with thapsigargin prevented tamoxifen from releasing more Ca2+. Tamoxifen (10 microM)-induced Ca2+ release was not changed by inhibiting phospholipase C activity with 2 microM U73122. Trypan blue exclusion assay revealed that tamoxifen (1-10 microM) did not alter viability after 1 min of incubation, but killed 10% of cells after 3-10 min of incubation. Together, this study shows that tamoxifen (>2 microM) induced a significant, immediate increase in [Ca2+]i in ZR-75-1 breast cancer cells. Tamoxifen acted by releasing Ca2+ from the endoplasmic reticulum Ca2+ stores in a manner independent of phospholipase C activity, and by inducing Ca2+ entry from extracellular medium. Tamoxifen may be of mild cytotoxicity after acute exposure.
authors.affiliation: Department of Surgery, Kaohsiung Veterans General Hospital, Taiwan.
authors.forename: Hong-Tai
authors.initials: HT
authors.lastname: Chang
authors.forename: Jong-Khing
authors.initials: JK
authors.lastname: Huang
authors.forename: Jue-Long
authors.initials: JL
authors.lastname: Wang
authors.forename: Jin-Shiung
authors.initials: JS
authors.lastname: Cheng
authors.forename: Kam-Chung
authors.initials: KC
authors.lastname: Lee
authors.forename: Yuk-Keung
authors.initials: YK
authors.lastname: Lo
authors.forename: Chun-Pin
authors.initials: CP
authors.lastname: Liu
authors.forename: Kang-Ju
authors.initials: KJ
authors.lastname: Chou
authors.forename: Wei-Chung
authors.initials: WC
authors.lastname: Chen
authors.forename: Warren
authors.initials: W
authors.lastname: Su
authors.forename: Yee-Ping
authors.initials: YP
authors.lastname: Law
authors.forename: Chung-Ren
authors.initials: CR
authors.lastname: Jan
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D013629:Tamoxifen / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D013629:Tamoxifen; D019284:Thapsigargin; D010738:Type C Phospholipases; D002118:Calcium