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 EG F receptor on epithelial intestinal cells. Differentiated and undiffer entiated cells displayed a single class of EGF binding sites with simi lar 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 r eceptors 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 recepto rs were functional, as evidenced by their ability to be internalized i n response to EGF binding. Thus, intact and functional EGF receptors a re present at the apical surface of differentiated HT29-D4 cells, sugg esting the presence of EGF receptors on the apical domain of enterocyt es.