The effect of calcium on mammary epithelial cell proliferation and the plasminogen activating system

The objectives of this study were to examine 1) the effect of extracellular calcium on proliferation of bovine mammary epithelial cells, 2) whether extracellular calcium regulates the mitogenic effect of insulin-like growth factor (IGF-I) and epidermal growth factor (EGF) towards mammary epithelial cells, and 3) whether the effects of calcium on growth are mediated through changes in the plasminogen activating system. The BME-UV1 cells were used as a model system. Results showed that optimal proliferation of BME-UV1 cells grown in the presence of 10% dialyzed FBCS was achieved when the culture medium was supplemented with 1-2 mmol L-1 of extracellular Ca2+. IGF-I (P<0.01) but not EGF, increased proliferation of BME-UV1 cells. Furthermore, calcium does not regulate IGF-I and EGF responsiveness of BME-UV1 cells. Northern blot analysis was performed to examine the effect of extracellular calcium on expression of urokinase-type plasminogen activator (u-PA), PA inhibitor 1 (PAI-1) and u-PA receptor (u-PAR) genes by BME-UV1 cells in culture. Results showed that calcium increased expression of all above-mentioned genes after 24 h of exposure of cells to calcium, at a time that the effect of calcium on growth was not apparent. Calcium had no effect on u-PA and u-PAR expression after 48 and 72 h of exposure of cells to calcium, at a time that the effect of calcium on growth was predominant. Calcium caused a small increase of PAI-1 expression after 48 and 72 h but this small increase is apparently of limited biological value.