Differential regulation of normal and tumoral breast epithelial cell growth by fibroblasts and 1,25-dihydroxyvitamin D^sub 3

Mesenchymal-epithelial interactions are of paramount importance during normal and tumoral breast developments. We have investigated the paracrine growth regulation of normal and tumoral breast epithelial cells by fibroblasts derived from normal or pathological breast tissues. In some cases, breast cancer MCF-7 cells or normal epithelial cells in primary culture were cocultured with fibroblasts in a Transwell system allowing diffusible factor exchanges. Alternatively, conditioned medium produced by fibroblast cultures was added to epithelial cell cultures. Fibroblasts were shown to stimulate the proliferation of normal and carcinoma cells through paracrine mechanisms. However, the paracrine exchanges appeared to be different in normal versus tumoral breast epithelial cell growth regulation. Moreover, vitamin D-related compounds that have been proposed as anti-tumoral drugs were studied for their ability to affect normal and tumoral mammary epithelial cell proliferation and to interfere with the growth-regulatory activity of fibroblasts. Whereas vitamin D compounds inhibited MCF-7 cell growth, they led to a marked stimulation of the proliferation of normal mammary epithelial cells. Moreover, it was shown that the vitamin D analog EB 1089 can block the mitogenic effect of fibroblast-conditioned medium on tumoral but not normal breast epithelial cells. The differential effects of vitamin D compounds on cell proliferation provide further data in favor of the different behaviours of normal and tumoral mammary epithelial cells. The potential therapeutic use of vitamin D derivatives in the treatment of breast cancer is supported by these results but their growth-stimulatory properties on normal epithelial cells cannot be overlooked.