Differential Estrogenic Responsiveness of MCF-7 Cells Relationship to the Presence of two Different Estrogen Receptors

Abstract

Estradiol stimulation of thymidine incorporation and progesterone receptor synthesis is at a maximum in exponentially growing cells. These activities are found to disappear in confluent MCF-7 cells. Since no significant differences in the binding of estradiol to its receptor site (Kd = 10⁻¹⁰ M, Bmax = 150 fm/mg protein) are observed in these two conditions, receptor structure was analyzed in both cell populations. Various methods demonstrated that receptor size is related to the state of confluence. The hydrodynamic properties of estradiol receptors complexed with ³H-estradiol from cells in the two different growth phases are similar in low ionic strength but different in high ionic strength media. Moreover, when the cell extracts are analyzed in denaturing