Effects of serum-free defined medium on MCF-7 cell nuclear estrogen-receptor levels

We have examined the effects of serum-free defined medium on filled and unfilled nuclear estrogen-receptor levels in the MCF-7 breast tumor cell line. Transfer of the cells to defined medium resulted in an initial increase in nuclear receptor levels, primarily of unfilled receptors, followed by a decrease of both receptor types to starting levels. Cells maintained in 10% fetal calf serum-containing medium, and sampled identically to those transferred to defined medium, exhibited a gradual but continuous increase in filled nuclear receptor levels accompanied by a decrease in unfilled receptors occurring toward the end of the 1-week experimental period. These results suggest that experiments requiring maximal depletion of endogenous MCF-7 nuclear estrogen will be optimized by repeated washing with estrogen-depleted medium, while limited washing with the same medium may be counter-productive.