SURFACE DISTRIBUTION OF THE EGF RECEPTOR DURING DIFFERENTIATION OF THE HUMAN COLON-CARCINOMA CELL-LINE HT29-D4

The clone HT29-D4 can be induced to differentiate into enterocytelike cells, by simply removing glucose from culture medium. In this report, we used the HT29-D4 model to study the membrane segregation of the EGF receptor on epithelial intestinal cells. Differentiated and undifferentiated cells displayed a single class of EGF binding sites with similar dissociation constants. However, differentiation of HT29-D4 led to a 3-fold decrease in the total number of EGF binding sites, while the number of TGF-I binding sites was unchanged. Fifteen percent of EGF receptors present on differentiated HT29-D4 cells were localized in the apical surface, whereas 98% of IGF-T receptors were segregated to the basolateral domain. By covalent cross-linking experiments using I-125-EGF and by immunoprecipitation with an anti-EGF receptor antibody, we have characterized the HT29-D4 EGF receptor as a Mr = 165 000 protein in both differentiated and undifferentiated cells. Apical EGF receptors were functional, as evidenced by their ability to be internalized in response to EGF binding. Thus, intact and functional EGF receptors are present at the apical surface of differentiated HT29-D4 cells, suggesting the presence of EGF receptors on the apical domain of enterocytes.