Mitochondrial inclusions in selenium-treated mouse mammary epithelial cell lines.

The effects of selenium on three mammary epithelial cell lines (YN-4, WAZ-2t, and CL-S1) grown in vitro were examined by immunocytochemical and transmission electron microscopy technique. The primary effect of selenium at the ultrastructural level was the appearance of electron-dense inclusions within the mitochondrial matrix. The mitochondrial inclusions were seen in all three cell lines, although most readily induced in YN-4 cells, the cell line which is most sensitive to selenium-mediated growth inhibition. Selenium at 5 x 10(-8) and 5 x 10(-6) M did not alter cytoplasmic microtubules or intermediate filament networks, as determined by immunocytochemical staining. Immunocytochemical staining for cytoplasmic filaments and microtubules, and transmission electron microscopy observations, supported the contention that cells from all three cell lines were epithelial in origin, since they contained abundant desmosomes and were uniformly positive for keratin intermediate filaments. Whereas line YN-4 was negative for vimentin intermediate filaments, a minority (5 to 24%) of the cells in lines CL-S1 and WAZ-2t stained positively. In addition, the tumorigenicity of these three cell lines was assessed by in vitro growth assays and in vivo transplantation assays. Cell lines YN-4 and WAZ-2t, but not line CL-S1, were tumorigenic in syngeneic mice. All tumors were mammary adenocarcinomas. Cytochalasin B-induced multinucleation assay and growth as multicellular spheroides correlated positively with in vivo tumorigenicity, whereas saturation density and growth in low Ca2+ medium were not correlated with tumorigenicity. It is speculated that one of the early effects of selenium-mediated growth inhibition may be a modulation of mitochondrial function.