[27] Steroid hormone-receptor interactions with nuclear constituents

Publisher Summary Over the past decade, considerable evidence has accumulated to support the concept that steroid hormones act to alter the expression of genes for specific proteins in target cells. This regulation appears to occur in the nucleus, where radioactive steroids administered in vivo rapidly accumulate tightly associated with the chromatin. The steroids are found first bound to cytoplasmic receptor proteins, and subsequently, these complexes appear in the nuclei. To study these nuclear processes more fully, it has been necessary to develop or adopt procedures for observing nuclear uptake and steroid-receptor binding in vitro. The chick oviduct has been studied extensively as a model system for steroid hormone action. In this tissue, estrogens induce growth and differentiation of the immature oviduct and induce the synthesis de novo of the egg white proteins ovalbumin and lysozyme. Progesterone administration to the oviduct results in the induction of a new protein—avidin. As stable receptor proteins can be isolated for this steroid, the intranuclear accumulation mechanism for progesterone could be readily studied in this system.