Tamoxifen-induced [Ca2+]i rise and apoptosis in corneal epithelial cells.
The effect of tamoxifen on cytosolic free Ca2+ concentrations ([Ca2+]i) and viability has not been explored in corneal epithelial cells. This study examined whether tamoxifen altered [Ca2+]i and viability in SIRC corneal epithelial cells. Tamoxifen at concentrations > or = 1 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 6 microM. The Ca2+ signal was reduced substantially by removing extracellular Ca2+. Tamoxifen induced Mn2+ quench of fura-2 fluorescence implicating Ca2+ influx. The Ca2+ influx was insensitive to Ca2+ entry inhibitors and protein kinase C modulators. After pretreatment with thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), tamoxifen-induced [Ca2+]i rises were abolished; conversely, tamoxifen pretreatment abolished thapsigargin-induced [Ca2+]i rises. Inhibition of phospholipase C with U73122 did not change the [Ca2+]i rises. At concentrations of 5-30 microM, tamoxifen killed cells in a concentration-dependent manner. The cytotoxic effect of 15 microM tamoxifen was not reversed by prechelating cytosolic Ca2+ with BAPTA/AM. Apoptosis was induced by 5-30 microM tamoxifen. Tamoxifen (30 microM did not induce production of reactive oxygen species (ROS). Collectively, in SIRC cells, tamoxifen induced [Ca2+]i rises by causing Ca2+ release from the endoplasmic reticulum in a phospholipase C-independent manner, and Ca2+ influx via unknown pathways. Tamoxifen-caused cytotoxicity was partly mediated by a Ca2+-independent apoptotic pathway.
Huang
Chorng-Chih
CC
Department of Nursery, Tzu Hui Institute of Technology, Pingtung 926, Taiwan.
Cheng
He-Hsiung
HH
Lin
Ko-Long
KL
Cheng
Jin-Shiung
JS
Tsai
Jeng-Yu
JY
Liao
Wei-Chuan
WC
Fang
Yi-Chien
YC
Jan
Chung-Ren
CR
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D002470:Cell Survival / Q000187:drug effects; D004171:Diploidy; D004847:Epithelial Cells / Q000187:drug effects*; D019573:Epithelium, Corneal / Q000166:cytology* / Q000187:drug effects; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology / Q000633:toxicity*; D005434:Flow Cytometry; D000077267:Fulvestrant; D066298:In Vitro Techniques; D008345:Manganese / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism; D013629:Tamoxifen / Q000633:toxicity*; D010738:Type C Phospholipases / Q000378:metabolism
D002121:Calcium Channel Blockers; D004965:Estrogen Antagonists; D017382:Reactive Oxygen Species; D013629:Tamoxifen; D000077267:Fulvestrant; D008345:Manganese; D004958:Estradiol; D011493:Protein Kinase C; D010738:Type C Phospholipases