A hormone pulse induces transient changes in the subcellular distribution and leads to a lysosomal accumulation of the estradiol receptor alpha in target tissues

An intrauterine pulse-stimulation with estradiol induced changes in the sub cellular localization of estrogen receptor a in porcine endometrium, as det ected with F(ab') fragments of various anti-receptor antibodies covalently linked to nanogold, The low-sterically hindered immunoreagents - recognizin g different epitopes within the hormone binding domain allowed for an effic ient immunolabeling of estradiol receptor a, defecting it both in the cytop lasm and the nucleus of nonstimulated epithelium cells, In the cytoplasm, t he receptor often seemed to be associated with actin filaments and the endo plasmatic reticulum, After the stimulation with estradiol, a predominantly nuclear localization and a labeling of nucleoli was observed. Our immunoele ctron microscopy study demonstrates a localization of the receptor in cytop lasmic organelles that increased after the hormone pulse. These organelles exhibited the morphological properties of lysosomes and relocated to the pe rinuclear area. In analogous cytoplasmic organelles, the presence of cathep sin D was detected via indirect immunogold labeling, justifying their class ification as lysosomes, Quantitative examinations revealed that not only th e number of lysosomes in the proximity of the nucleus but also their immuno staining for estradiol receptor a increased significantly after the hormone pulse. Thus, estradiol induces both the rapid shift of receptor into the n ucleus, a slower perinuclear accumulation of lysosomes and an increase of l ysosomal ER alpha-immunoreactivity. These results suggest a role for lysoso mes in the degradation of receptor shuttling out of the nucleus. This could serve as termination of the estradiol receptor a-dependent activation of t arget cells. This hypothesis is strengthened by the fact that the receptor content in uterine tissue declined drastically few hours after the hormone pulse.