Estrogen receptor status and estradiol sensitivity of MCF-7 cells in exponential growth phase

Proliferative patterns of MCF-7 human breast cancer cells have been reported to influence their estrogen receptor (ER) contents. However, the experimental conditions under which these variations in ER contents were described differed from those commonly used for maintaining exponential growth. We, therefore, investigated whether or not MCF-7 receptor status also fluctuated under normal growth conditions. MCF-7 cells were cultured up to 4 days in 96-multiwell dishes. On each day, cell number was spectrophotometrically assessed after fixation and coloration of the cells with hematoxylin; corresponding ER content was measured by the Abbott enzyme immunoassay in KCl extracts. At the three plating densities tested (5, 10 and 20 x 10(3) cells/ml), an obvious parallel was found between the cell number and the ER content suggesting an unchanged receptor status throughout the culture period. Regression analysis confirmed this impression. Additional fractionation by SDS-PAGE of total MCF-7 proteins extracted at various times of the culture (up to 7 days in 35 mm Petri dishes) gave identical patterns suggesting that ER synthesis is regulated as the majority of proteins. Growth experiments indicated that this situation conferred a constant estrogenic sensitivity to the cells: 24 h exposure to 10(-8) M estradiol on either the 1st, 2nd, 3rd or 4th day after plating resulted in the same increase in cell number. All these data indicated that ER contents of MCF-7 cells were maintained at a constant level under exponential growth which resulted in a constant estrogenic sensitivity.