Binding of hormone accelerates the kinetics of glucocorticoid and progesterone receptor binding to DNA

Abstract

Steroid hormone receptors induce genes by virtue of their interaction with DNA regulatory sequences. The hormonal response of a particular gene in vivo correlates with binding of the hormone to the receptor and supposedly reflects the degree of occupancy of the corresponding DNA regulatory sequences. However, in vitro the steroid-free glucocorticoid and progesterone receptors bind specifically to the regulatory sequences of mouse mammary tumor virus, thus raising questions on the role of the hormone in DNA binding in vivo. By using monoclonal antibodies, gel retardation assays, and filter binding techniques we show here that binding of a functional steroid to either the glucocorticoid or the progesterone receptors influences the kinetics of the protein-DNA interaction in vitro. In the presence of hormone the on rate of receptor binding to DNA fragments with or without regulatory sequences is accelerated 2- to 5-fold, and the off rate is accelerated 10- to 20-fold. The receptors complexed to an antihormone bind to DNA with kinetics intermediate between those of the steroid-free and the hormone-bound protein. Thus, ligand binding accelerates the kinetics of receptor binding to DNA and this could partly account for the behavior of the hormone receptor observed in vivo.