FUNCTIONAL NUCLEAR EPIDERMAL GROWTH-FACTOR RECEPTORS IN HUMAN CHORIOCARCINOMA JEG-3 CELLS AND NORMAL HUMAN PLACENTA

Immunocytochemistry with a monoclonal antiepidermal growth factor (ant i-EGF) receptor antibody directed against the extracellular domain whi ch can inhibit ligand binding to the receptors showed that nuclei of c horiocarcinoma JEG-3 cells and normal placental trophoblasts were dist inctly immunostained for EGF receptors. This finding led us to investi gate the structure and function of nuclear EGF receptors. Western immu noblotting revealed that cell membranes, isolated intact pure nuclei, and nuclear membranes contain a 170-kilodalton EGF receptor protein. C ovalent receptor cross-linking demonstrated that the 170-kilodalton re ceptor protein in nuclei and nuclear membranes can bind [I-125]EGF jus t as in cell membranes, and that this binding is inhibited by excess u nlabeled EGF. As in cell membranes, the addition of EGF resulted in an increased receptor autophosphorylation in the nuclei and nuclear memb ranes. In addition, the activated receptor kinase stimulated, and in s ome cases inhibited, tyrosine phosphorylation of a number of lower mol ecular size proteins, especially in nuclei and nuclear membranes. Alth ough the identity of these proteins is not known, none of them could b ind [I-125]EGF. The addition of EGF to isolated nuclei resulted in a t ime-dependent specific transcriptional inhibition of hCG/LH receptor g ene. In summary, our data demonstrating the presence of functional nuc lear EGF receptors are novel, potentially important, and go against th e traditional concepts of growth factors action. The nuclear receptors have the capacity to transduce signals from EGF and may mediate intra crine and paracrine actions of EGF in the regulation of trophoblast fu nctions.