Steroid hormones and temperature induce changes of binding parameters of their receptors in intact cells.

When MCF-7 cells were treated with 17 beta-estradiol, dexamethasone, or promegestone at 37 degrees C, the KD of receptors for their cognate ligands was found to decrease as compared to that measured at 2 degrees C. Cell incubation with hormone at 37 degrees C did not affect the Bmax of glucocorticoid and progesterone receptors, but caused a 40% increase of that of estrogen receptor. This increase required the presence of ligand, was insensitive to cycloheximide, and was completed within 10 min of cell incubation at physiological temperature. We conclude that an early step of estrogen action is the recruitment of pre-existing receptor molecules through activation of their binding capacity.