Subcellular localization of estradiol receptor in MCF7 cells studied with nanogold-labelled antibody fragments

Ultrastructural localization studies of estradiol receptor in hormone-depri ved and hormone-stimulated MCF7 cells were done using F(ab') fragments of t hree different antibodies (#402, 13H2, HT277) covalently linked to nanogold . These ultrasmall, non-charged immunoreagents, combined with a size-enlarg ement by silver enhancement, localized estradiol receptor in both nuclear a nd cytoplasmic areas of non-stimulated target cells; stimulation with the s teroid induced a predominantly nuclear labelling. In the cytoplasm of resti ng cells, tagging was often observed at or in the proximity of stress fiber s. In the nucleus a large proportion of receptor was found inside the nucle olus, specially with the reagent derived from antibody 13H2. We postulate t hat different accessibilities of receptor epitopes account for the differen t labelling densities observed at cytoskeletal elements and the nucleoli.