Tamoxifen-induced increases in cytoplasmic free Ca2+ levels in human breast cancer cells.
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.
Chang
Hong-Tai
HT
Department of Surgery, Kaohsiung Veterans General Hospital, Taiwan.
Huang
Jong-Khing
JK
Wang
Jue-Long
JL
Cheng
Jin-Shiung
JS
Lee
Kam-Chung
KC
Lo
Yuk-Keung
YK
Liu
Chun-Pin
CP
Chou
Kang-Ju
KJ
Chen
Wei-Chung
WC
Su
Warren
W
Law
Yee-Ping
YP
Jan
Chung-Ren
CR
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
D013629:Tamoxifen; D019284:Thapsigargin; D010738:Type C Phospholipases; D002118:Calcium