Magnesium depletion causes growth inhibition, reduced expression of cyclinD1, and increased expression of p27(Kip1) in normal but not in transformedmammary epithelial cells

In this study, we have evaluated the effects of extracellular magnesium res triction on the growth and cell cycle parameters of normal (HC11) and trans formed (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 ra tes were determined by [H-3] thymidine incorporation and cell counting. The growth of the HC11 cells was drastically inhibited by Mg2+ depletion where as the MCF-7 cells were only slightly inhibited (about 50% and 15%, respect ively, after incubation in 0.05 mM Mg for 48 h). Cell cycle analyses showed a decrease in the percentage of cells in the 8 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, on ly the percentage of cells in the G2/M phase was increased in the MCF-7 cel l line. Extracellular magnesium depletion was associated with increased exp ression of the cyclin-dependent kinase inhibitor p27(Kip1) and decreased ex pression of cyclin D1 in the HC11 but not in the MCF-7 cells. We also demon strated that Mg2+ depletion does not inhibit kinase activities in the norma l HC11 cells and that Mg2+-restricted HC11 cells are still responsive to th e epidermal growth factor (EGF)- and insulin-mediated stimulation of cell g rowth. These data suggest that normal but not transformed mammary epithelia l cells are inhibited by extracellular Mg2+ restriction and that this effec t might be mediated by changes in the levels of expression of both cyclin D 1 and p27(Kip1). (C) 1999 Wiley-Liss, Inc.