Tamoxifen-induced [Ca2+]i rise and apoptosis in corneal epithelial cells
Chorng-Chih Huang1, He-Hsiung Cheng, Ko-Long Lin
1Department of Nursery, Tzu Hui Institute of Technology, Pingtung 926, Taiwan.
Abstract:
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.
Insights
Tamoxifen increases intracellular calcium ([Ca2+]i) in corneal cells by releasing it from the endoplasmic reticulum and causing influx, leading to cell death via apoptosis.
Area of Science:
- Ophthalmology
- Cell Biology
- Pharmacology
Background:
- The effects of tamoxifen on corneal epithelial cell calcium homeostasis and viability are unknown.
- Corneal epithelial cells are crucial for maintaining ocular surface integrity.
Purpose of the Study:
- To investigate tamoxifen's impact on cytosolic free calcium concentrations ([Ca2+]i) and cell viability in SIRC corneal epithelial cells.
- To elucidate the mechanisms underlying tamoxifen-induced calcium changes and cytotoxicity.
Main Methods:
- Measurement of [Ca2+]i using fura-2 fluorescence in SIRC cells.
- Assessment of cell viability and apoptosis induction.
- Pharmacological manipulation using thapsigargin, U73122, BAPTA/AM, and calcium-free media.
Main Results:
- Tamoxifen (≥1 µM) increased [Ca2+]i in a concentration-dependent manner (EC50 = 6 µM), involving extracellular calcium influx.
- Calcium rises were dependent on endoplasmic reticulum calcium stores and independent of phospholipase C.
- Tamoxifen (5-30 µM) induced concentration-dependent cytotoxicity and apoptosis, partly via a calcium-independent pathway.
Conclusions:
- Tamoxifen elevates [Ca2+]i in corneal epithelial cells through ER calcium release and influx via undefined pathways.
- Tamoxifen exhibits cytotoxic effects and induces apoptosis, partially independent of calcium signaling.
- These findings provide insights into tamoxifen's ocular side effects and cellular mechanisms.
