Effects of estradiol on components of the plasmbmogenplasmin system en mda-mb-231 breast cancer cells stably transfected with the estrogen receptor

We examined the effect of estradiol (E2) on urokmase-type plasmmogen activator (uPA), tissue-type plasmmogen activator (tPA), plasminogen activator type l (PA1-1) and uPA receptor (uPAR) expression, secretion and activity in MDA-MB-231 breast cancer cells stably expressing either wild type (S30 cells) or mutant estrogen receptor (ER) (BC-2 cells). These ER-tnnsfectants are growth inhibited by E2, yet the mechanism remains unknown (Levenson & Jordan, (1994) J Steroid Biochem Mol Biol, 51:229-239). In the present report we describe down-regulation of uPA, tPA and PAI-1 by E2 on mRNA and protein levels in both S30 and BC-2 cells. Zymographic analyses confirmed the inhibitory effect of E2 on PAs activity in these cells. The pure intiestrogen ICI 182,780 was able to block E2 action, indicating that the regulation of uPA, tPA and PAI-1 is ERmediated. In contrast, the mRNA and protein levels of uPAR was not modulated by E2. The fact that E2 inhibits endogenous uPA synthesis and activity with corresponding growth inhibition while hiving no effect on uPAR, prompted us to examine whether exogenous addition of recombmant uPA could: 1) exert any effect on proliferative behaviour of S30 and BC-2 cells; 2) reverse the inhibitory effect of E2 on growth. We found that exogenousry added uPA did not have any growth stimulatory effects on S30 and BC-2 cells alone and when added with E2, uPA was not able to block the inhibitory effect of E2 on the growth. The possible functional interplay between exogenousry added uPA, endogcnousty-produced uPA, PAI-1 and uPAR will be discussed. In summary, we have shown that uPA, tPA. PAI-1 but not uPAR are regulated by E2 via ER-mediated pathway in breast cancer cells transfected with ER. It is still unclear whether downregulation of uPA by E2 is an upstream event of E2-mediated growth inhibition in these cells.