Estrogenic and antiestrogenic effects of raloxifene on collagen metabolism in breast cancer MCF-7 cells.

We compared the effects of different concentrations of raloxifene (1, 4 and 10 microM) on collagen biosynthesis, gelatinolytic and prolidase activities and matrix metalloproteinase (MMP) expression (MMP-2 and MMP-9) in estradiol-stimulated (2 nM) breast cancer MCF-7 cells. Raloxifene inhibited in a dose-dependent manner the proliferation of MCF-7 cells, independently of the presence or absence of estradiol in the growth medium. Raloxifene at concentrations of 1 microM and 4 microM inhibited collagen biosynthesis by about 10-fold and prolidase activity by about 50%, while at a concentration of 10 microM it inhibited these processes by only about 25%. This phenomenon was accompanied by differences in gelatinolytic activity and MMP (MMP-2 and MMP-9) expression as demonstrated by zymography and Western immunoblot analysis, respectively. In estrogen-stimulated MCF-7 cells, cultured in the presence of 1 microM raloxifene, a dramatic increase in the activity of both collagenases was found. In contrast, addition of raloxifene at a concentration of 10 microM to the medium of the cells resulted in restoration of gelatinolytic activity to that found in control cells. Similarly, but at both doses (1 and 10 microM), raloxifene was able to reduce MMP-2 expression in the cells. However, when used alone (without estradiol) a concentration of 1 microM raloxifene strongly stimulated MMP-2 expression, while at a concentration of 10 microM the effect was not observed. In the case of MMP-9, only trace amounts of this gelatinase were detected, although in contrast to MMP-2, an increase in its expression was noticed at a concentration of 10 microM raloxifene. The data raise the possibility that in estrogen-stimulated MCF-7 cells, raloxifene at low concentrations (1 and 4 microM) evokes antiestrogenic effect on collagen biosynthesis and prolidase activity on the one hand, and an estrogenic effect on gelatinolytic activity on the other, while at higher concentrations (about 10 microM) it evokes an estrogenic effect on collagen biosynthesis and prolidase activity, and an antiestrogenic effect on gelatinolytic activity. Our data suggest that the effects of raloxifene on collagen synthesis, prolidase and metalloproteinase activities in breast cancer may explain its role in the prevention of breast cancer development.