Ca2+ and Mg2+ requirements for growth are not concomitantly reduced during cell transformation

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Abstract
The effects of Mg2+ and Ca2+ deprivation on survival and growth of normal and transformed cultured cells were studied. Normal fibroblast from several origins (mouse, hamster and human) did not grow in 2 µM Mg2+ medium, whereas transformed fibroblasts (mouse and rat) and tumor cells of other types (mouse adrenocortical and rat glial cells) grew optimal. All transformed or tumorogenic cells that showed low growth requirement for Mg2+ were able to develop colonies in agarose suspension cultures, i.e., were anchorage-independent for growth. Mg2+ deprivation of normal cells did not lead to cell cycle arresting at Go/ Gl and cell death accounts for the limited growth of these cells in medium containing low Mg2+ concentration. Contrary to Mg2+, starvation for serum or for Ca2+ caused normal cells to undergo cell cycle arrest at the Go/Gl phase. During the progressive spontaneous transformation of Swiss mouse 3T3 fibroblasts, the decrease in growth requirements for Mg2+ and Ca2+ do not occur at the same time. The requirement for external Ca2+ lowers before the onset of anchorage-independent growth while the Mg2+ requirement only decreases after cells become anchorage-independent. Therefore the reductions in growth requirement for Mg2+ and Ca2+ that take place in cell transformation are not linked events.