Selenite-mediated production of superoxide radical anions in A549 cancer cells is accompanied by a selective increase in SOD1 concentration, enhanced apoptosis and Se–Cu bonding
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Selenite may exert its cytotoxic effects against cancer cells via the generation of reactive oxygen species (ROS). We investigated sources of, and the cellular response to, superoxide radical anion (O2 ·−) generated in human A549 lung cancer cells after treatment with selenite. A temporal delay was observed between selenite treatment and increases in O2 ·− production and biomarkers of apoptosis/necrosis, indicating that the reduction of selenite by the glutathione reductase/NADPH system (yielding O2 ·−) is a minor contributor to ROS production under these conditions. By contrast, mitochondrial and NADPH oxidase O2 ·− generation were the major contributors. Treatment with a ROS scavenger [poly(ethylene glycol)-conjugated superoxide dismutase (SOD) or sodium 4,5-dihydroxybenzene-1,3-disulfonate] 20 h after the initial selenite treatment inhibited both ROS generation and apoptosis determined at 24 h. In addition, SOD1 was selectively upregulated and its perinuclear cytoplasmic distribution was colocalised with the cellular distribution of selenium. Interestingly, messenger RNA for manganese superoxide dismutase, catalase, inducible haem oxygenase 1 and glutathione peroxidase either remained unchanged or showed a delayed response to selenite treatment. Colocalisation of Cu and Se in these cells (Weekley et al. in J. Am. Chem. Soc. 133:18272–18279, 2011) potentially results from the formation of a Cu–Se species, as indicated by Cu K-edge extended X-ray absorption fine structure spectra. Overall, SOD1 is upregulated in response to selenite-mediated ROS generation, and this likely leads to an accumulation of toxic hydrogen peroxide that is temporally related to decreased cancer cell viability. Increased expression of SOD1 gene/protein coupled with formation of a Cu–Se species may explain the colocalisation of Cu and Se observed in these cells.
KeywordsSelenium Cell viability Reactive oxygen species Synchrotron radiation Superoxide radical anion
Electron paramagnetic resonance
Extended X-ray absorption fine structure
Selenocysteine variant of the human copper chaperone
Haem oxygenase 1
Poly(ethylene glycol)-conjugated superoxide dismutase
Reactive oxygen species
X-ray absorption near-edge structure
A549 cells and tiron were gifts from Aviva Levina and Shane Thomas, respectively. We thank Jade Aitken, Stefan Vogt and Lydia Finney for assistance with synchrotron data collection and Ian Musgrave for assistance with cell culture. We are grateful to Ninian Blackburn for providing spectra of hCCS245Sec, and to Graham George and Enzo Lombi for providing small-molecule Cu spectra. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, and Office of Basic Energy Sciences, under contract DE-AC02-06CH11357. We acknowledge travel funding provided by the International Synchrotron Access Program managed by the Australian Synchrotron and funded by the Australian Government and research funding from the Australian Research Council (DP0985807) and the Australian Synchrotron Postgraduate Award (C.M.W.). We acknowledge that part of this work was undertaken at the XAS beamline at the Australian Synchrotron (Clayton, Australia).
- 33.Vogt S (2003) J Phys IV 104:635–638Google Scholar