Disruption of mitochondrial respiration by melatonin in MCF-7 cells.
Clinical and laboratory studies have provided evidence of oncostatic activity by the pineal neurohormone melatonin. However, these studies have not elucidated its mechanism of action. The following series of MCF-7 breast tumor cell studies conducted in the absence of exogenous steroid hormones provide evidence for a novel mechanism of oncostatic activity by this endogenous hormone. We observed a 40--60% loss of MCF-7 cells after 20-h treatment with 100 nM melatonin, which confirmed and extended previous reports of its oncostatic potency. Interestingly, there were no observed changes in tritiated thymidine uptake, suggesting a lack of effect on cell cycle/nascent DNA synthesis. Further evidence of a cytocidal effect came from morphologic observations of acute cell death and autophagocytosis accompanied by degenerative changes in mitochondria. Studies of mitochondrial function via standard polarography revealed a significant increase in oxygen consumption in melatonin-treated MCF-7 cells. Enzyme-substrate studies of electron transport chain (complex IV) activity in detergent permeabilized cells demonstrated a concomitant 53% increase (p < 0.01) in cytochrome c oxidase activity. Additional studies of succinate dehydrogenase activity (complex II) as determined by reduction of (3-4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide demonstrated a significant increase (p < 0.05) in melatonin-treated cells and further confirmed the accelerated ET activity. Finally, there was a 64% decrease (p < 0.05) in cellular ATP levels in melatonin-treated cells. The G-protein-coupled melatonin receptor antagonist luzindole abrogated the cytotoxic and mitochondrial effects. These studies suggest a receptor-modulated pathway of cytotoxicity in melatonin-treated MCF-7 tumor cells with apparent uncoupling of oxidative phosphorylation.
Department of Environmental Health, Colorado State University, Fort Collins, Colorado, USA. Aaron.Scott@uchsc.edu
A E
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Scott
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Cosma
A A
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Frank
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Wells
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Gardner
D000230:Adenocarcinoma / Q000378:metabolism / Q000648:ultrastructure; D000255:Adenosine Triphosphate / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism / Q000648:ultrastructure; D019069:Cell Respiration / Q000187:drug effects*; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D008163:Luminescent Measurements; D008550:Melatonin / Q000494:pharmacology*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D011048:Polarography; D011956:Receptors, Cell Surface / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects; D044094:Receptors, Melatonin; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014363:Tryptamines / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000975:Antioxidants; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D014363:Tryptamines; C057154:luzindole; D000255:Adenosine Triphosphate; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV; D019204:GTP-Binding Proteins; D008550:Melatonin; D013936:Thymidine