Cellular Compartments and Translocation of Receptor-Steroid Complexes

Abstract

As discussed in the preceeding chapters, steroid-hormone receptors are generally considered to exist as soluble macromolecules in the cytoplasm of target cells (Fig. 1). When these receptors (R_c) bind to steroid hormones (S) they form receptor-steroid complexes (R_cS), which undergo translocation to the nucleus (R_nS). These conclusions were reached from experiments by Jensen et al. (1968) and Gorski et al. (1968). Figure 24, taken from an experiment by Gorski et al. (1968), demonstrates the rapid shift of ³H-estradiol from the cytoplasmic to the nuclear compartment of the rat uterus in vitro. Cytoplasmic receptor declines after either in vivo or in vitro exposure to estradiol and, as if in a concerted or ordered process, there occurs a concomitant increase in the quantity of a salt-extractable 55 complex in the nucleus (Jensen et al., 1968; Gorski et al., 1968). Similar results have been obtained by O’Malley et al. (1970) for the chick oviduct and are shown in Fig. 25.