In Vitro Conversion of Estradiol-Receptor Protein to Its Nuclear Form: Dependence on Hormone and DNA

Early events in the action of 17-beta-estradiol can be studied in soluble extracts of rat uterus by exposure of the estradiol-receptor protein to a DNA-cellulose matrix. After complexing with [(3)H]estradiol, the 4S receptor protein binds to the DNA, and it can be eluted with buffer of high ionic strength as a more tightly binding, 5S form. This parallels the in vivo situation, where migration of the receptor to the nucleus follows addition of hormone and is concomitant with a similar increase in sedimentation rate to 5 S. In both cases, the formation of a 5S receptor requires the presence of 17-beta-estradiol. The rate at which 5S receptor forms is sensitive to extract concentration in a way that suggests that this receptor is a complex created by addition of a second subunit to the hormone-binding 4S component; physical studies on both in vivo and in vitro 5S receptors also support this view. These results are interpreted in terms of a model for action of estrogen in which the hormone potentiates binding of receptor to DNA, and in turn, the DNA-binding process triggers the cell response.