INCREASE IN EPIDERMAL GROWTH-FACTOR RECEPTOR AND ITS MESSENGER-RIBONUCLEIC-ACID LEVELS WITH DIFFERENTIATION OF HUMAN TROPHOBLAST CELLS IN CULTURE

Epidermal growth factor receptor (EGFR) expression was studied during the differentiation of human trophoblast cells in culture. In vitro, intravillous mononuclear cytotrophoblasts aggregate and fuse within 24 h to form a syncytium. This morphological differentiation was associated with a significant twofold increase in SpeCifiC I-125-EGF binding capacity (P < 0.01). Scatchard analyses showed an apparent rise in the number of high-affinity binding sites (0.33 +/- 0.04 and 0.63 +/- 0.07 pmol/mg protein at 24 and 48 h, respectively), with no change in their affinity (1.34 and 1.42 x 10(-10) mol/L). Affinity labeling of I-125-EGF in cultured trophoblast cells followed by SDS-PAGE and autoradiography revealed a band of 175 KDa corresponding to EGFR, the intensity of which increased with the time in culture. EGF-dependent phosphorylation of membrane proteins from cultured trophoblast cells revealed major phosphorylated proteins of 170 KDa (EGFR) and 35 KDa, which were both increased at 48 h, indicating a rise in EGFR-kinase activity during syncytium formation. Northern blot analysis of EGFR-mRNA, followed by hybridization with a P-32-cDNA probe for EGFR, revealed an increase in EGFR gene expression in syncytiotrophoblasts, as compared to cytotrophoblasts. Thus, the increase in bioactive EGFR observed during the differentiation of trophoblast cells was due to an increase in their synthesis. Cultured trophoblast cells are therefore a good model of spontaneous up-regulation of EGFR expression with cell differentiation.