Oestradiol regulation of the components of the plasminogen-plasmin system in MDA-MB-231 human breast cancer cells stably expressing the oestrogen receptor

To understand the hormonal regulation of the components of the plasminogen-plasmin system in human breast cancer, we examined the oestradiol (E-2) regulation of plasminogen activators (PAs), namely urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1) and uPA receptor (uPAR), in our model system. We used stable transfectants of the MDA-MB-231 human breast cancer cells that express either the wild-type (S30 cells) or the mutant 351(asp-->tyr) oestrogen receptor (ER) (BC-2 cells). Northern blot analysis showed that there was a concentration-dependent down-regulation of uPA, tPA and PAI-I mRNAs by E-2. In contrast, uPAR mRNA was not modulated by E-2. The pure anti-oestrogen ICI 182,780 was able to block E-2 action, indicating that the regulation of these genes is ER mediated. The E-2 also inhibited the expression and secretion of uPA, tPA and PAI-1 proteins as determined by enzyme-linked immunosorbent assay (ELISA) in cell extracts (CEs) and conditioned media (CM). Zymography of the CM confirmed the inhibitory effect of E-2 on uPA activity. Thus, we now report the regulation of uPA, PAI-1 and tPA by E-2 in both mRNA and protein levels in ER transfectants. The association between down-regulation of the uPA by E-2 and known E-2-mediated growth inhibition of these cells was also explored. Our findings indicate that down-regulation of uPA by E-2 is an upstream event of inhibitory effects of E-2 on growth of these cells as the addition of exogenous uPA did not block the growth inhibition by E-2.