CONVERGENT EFFECTS OF GROWTH-FACTORS, HORMONES, AND FIBRONECTIN ARE NECESSARY FOR THE ENTEROCYTE DIFFERENTIATION OF A COLON ADENOCARCINOMA CELL-LINE (HT29-D4)

The aim of this work was to show in serum-free medium a convergent eff ect of physiological factors and extracellular matrix proteins on the differentiation process of enterocytes by taking as a model the HT29-D 4 clone that has the feature of differentiating when subcultured in fe tal bovine serum glucose-free medium. We show that triiodothyronine (T 3) as well as insulin promotes limited cell growth and differentiation , whereas fibronectin or bovine serum albumin (BSA) induces cell growt h and a low level of differentiation. However, insulin, T3, fibronecti n, and BSA together with epidermal growth factor and transferrin promo ted satisfactory growth and enterocyte morphology with epithelial elec trophysiological properties in HT29-D4 cells. With these factors adequ ate protein targeting was achieved since cells apically expressed the carcinoembryonic antigen, and basolaterally transferrin and insulin re ceptors, beta 1 and alpha v beta 6 integrins, talin, vinculin, and foc al adhesion kinase (FAK). Talin, vinculin, FAK, and alpha v beta 6 int egrin, the fibronectin receptor, were clustered in focal contacts, whi ch agrees with a possible role of fibronectin in final cell growth, th e latter process mediating the final phase of differentiation. This le vel of differentiation can be maintained for a long time. Thus HT29-D4 cells appear to be a suitable model to study the implication of integ rins in the differentiation process of human enterocytes.