Magnesium depletion causes growth inhibition, reduced expression of cyclin D1, and increased expression of P27Kip1 in normal but not in transformed mammary epithelial cells.

In this study, we have evaluated the effects of extracellular magnesium restriction on the growth and cell cycle parameters of normal (HC11) and transformed (MCF-7) breast epithelial cell lines. Cells were incubated in medium with different concentrations of Mg2+ (from 0.5 to 0 mM) and the growth rates were determined by [3H]-thymidine incorporation and cell counting. The growth of the HC11 cells was drastically inhibited by Mg2+ depletion whereas the MCF-7 cells were only slightly inhibited (about 50% and 15%, respectively, after incubation in 0.05 mM Mg for 48 h). Cell cycle analyses showed a decrease in the percentage of cells in the S phase when both cell lines were incubated at low Mg2+ concentration. However, while the percentage of cells in both the G0/G1 and G2/M phases was increased in the HC11 cells, only the percentage of cells in the G2/M phase was increased in the MCF-7 cell line. Extracellular magnesium depletion was associated with increased expression of the cyclin-dependent kinase inhibitor p27Kip1 and decreased expression of cyclin D1 in the HC11 but not in the MCF-7 cells. We also demonstrated that Mg2+ depletion does not inhibit kinase activities in the normal HC11 cells and that Mg2+-restricted HC11 cells are still responsive to the epidermal growth factor (EGF)- and insulin-mediated stimulation of cell growth. These data suggest that normal but not transformed mammary epithelial cells are inhibited by extracellular Mg2+ restriction and that this effect might be mediated by changes in the levels of expression of both cyclin D1 and p27Kip1.