Effect of the anti-breast cancer drug tamoxifen on Ca(2+) movement in human osteosarcoma cells.
The anti-breast cancer drug tamoxifen has recently been shown to cause an increase in [Ca(2+)]i in renal tubular cells, breast cells and bladder cells. Because tamoxifen is known to interact with oestrogens leading to modulation of bone metabolism, the present study was aimed at exploring whether tamoxifen could alter Ca(2+) signaling in human osteoblast-like MG63 cells. Cytosolic free Ca(2+) levels were recorded by using the Ca(2+)-sensitive dye fura-2. Tamoxifen induced a sustained [Ca(2+)]i increase at concentrations above 1 microM with an EC(50) of 8 microM. Removal of extracellular Ca(2+) reduced the response by 40%, suggesting that tamoxifen induced both Ca(2+) influx and store Ca(2+) release. Tamoxifen-induced Ca(2+) influx was confirmed as tamoxifen caused Mn(2+) influx-induced quench of fura-2 fluorescence. In Ca(2+)-free medium, pretreatment with 10 microM tamoxifen abolished the [Ca(2+)]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor), and by 2 microM carbonylcyanide m-chlorophenylhydrazone (a mitochondrial uncoupler). Conversely, pretreatment with thapsigargin and carbonylcyanide m-chlorophenylhydrazone only reduced 64% of tamoxifen-induced [Ca(2+)]i increases. Addition of 2 microM U73122 to inhibit phospholipase C activity abolished the [Ca(2+)]i increase induced by 1 microM histamine, a phospholipase C-dependent Ca(2+) mobilizer, without affecting 10 microM tamoxifen-induced Ca(2+) release. The [Ca(2+)]i increase induced by 10 microM tamoxifen was not altered by 10 microM of nifedipine, verapamil and diltiazem. Together, the data show that tamoxifen induced a lasting increase in [Ca(2+)]i in human osteoblast-like cells by causing Ca(2+) influx and releasing Ca(2+) from multiple stores in a phospholipase C-independent manner.
Department of Orthopaedic Surgery, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan 813.
Yih-Chau
YC
Lu
Bang-Ping
BP
Jiann
Hong-Tai
HT
Chang
Jong-Khing
JK
Huang
Wei-Chung
WC
Chen
Warren
W
Su
Chung-Ren
CR
Jan
D000970:Antineoplastic Agents / Q000009:adverse effects*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000493:pharmacokinetics; D020013:Calcium Signaling / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004347:Drug Interactions; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D012516:Osteosarcoma; D013629:Tamoxifen / Q000009:adverse effects*; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D013629:Tamoxifen; D019284:Thapsigargin; D010738:Type C Phospholipases; D002118:Calcium