Influence of tumor derived fibroblasts and 1,25-dihydroxyvitamin D3 on growth of breast cancer cell lines.

Fibroblasts are known to be present in variable amounts in human breast adenocarcinoma tissue. In order to investigate if they influence in some way the proliferation rate of the carcinoma cells, we developed a coculture model in which cells of well characterized breast epithelial cell lines were seeded and grown in microchamber slides along with fibroblasts derived from breast tumor biopsies. As representatives of hormone dependent and independent tumor cells, we used MCF-7 and BT-20 cell lines. A third line, NPM-21T, derived from non proliferating mastopathy cells immortalized by SV-40 T DNA transfection, was representative of non tumor epithelial cells. The proliferation rate of the adenocarcinoma and epithelial cells was assessed by measurement of the BrdU labeling index, the cells being identified by specific beta-actin immunostaining. It was found that the proliferation of the adenocarcinoma cells was significantly increased in the presence of fibroblasts, while that of immortalized cells was not. Moreover, 1,25(OH)2D3, which was known to be a negative regulator of carcinoma cell growth, was found to be able also to blunt the overgrowth in the presence of fibroblasts. The absence of response of NPM-21T cells to the presence of fibroblasts suggests that the tumor cells could be the origin of their own overgrowth, through an indirect mechanism mediated by the fibroblasts. The factors which are involved and the 1,25(OH)2D3 mechanism of action are not yet identified.