Selenium distribution in mammary epithelial cells reveals its possible mechanism of inhibition of cell growth.

The subcellular and macromolecular distribution of 75Se-selenite was determined in murine mammary epithelial cell lines which demonstrated marked differences in their growth response to 5 microM selenite. MOD cells responded sooner to the inhibitory effects of selenite than COMMA-D cells. The MOD cells also incorporated a slightly higher percentage of 75Se-selenite into proteins and attained a higher ratio of selenoprotein to selenonucleic acids than did COMMA-D cells. Most selenium and selenoproteins were located in the cytoplasm as revealed by autoradiography and subcellular fractionations. These data suggest that a cytoplasmic selenoprotein may be an intermediate for selenite's nontoxic growth inhibitory effects.