Mimosine is a toxic nonprotein amino acid that is a major constituent of the tropical legumes Leucaena and Mimosa. Mimosine has been shown to cause acute and chronic toxicosis in livestock fed from forage containing these plants. Recently, mimosine has been demonstrated to reversibly block cell cycle progression in mammalian cells in culture. In this study, we compared the effects of mimosine to desferrioxamine (DFO), a well-characterized iron chelator, and found that both chemicals similarly altered cell cycle progression in MDA-MB-453 human breast cancer cells. Mimosine (400 μM) and DFO (150 μM) both reduced DNA synthesis by greater than 90% of control within 4 hr of treatment, and suppressed total proline-directed protein kinase activity to less than 10% of control after 16 hr treatment. These effects were antagonized by the addition of iron as ferrous sulfate (250 μM), which is bound to transferrin and imported into the cell via transferrin receptor endocytosis, or as hemin (100 μM), which passes through the cell membrane and releases iron into the cytosol. After 24 hr treatment with the chelators, a large portion of the available transferrin receptors moved to the cell surface, indicating that the cells were iron-starved. Our data demonstrate that mimosine, through iron chelation, blocks cell cycle progression in MDA-MB-453 human breast cancer cells.
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