IMPAIRED CARCINOEMBRYONIC ANTIGEN RELEASE DURING THE PROCESS OF SURAMIN-INDUCED DIFFERENTIATION OF THE HUMAN COLIC ADENOCARCINOMA CELL CLONE HT29-D4

The establishment of a differentiated state of the human colic adenocarcinoma cell clone HT29‐D4 can be obtained by two ways: 1) the removal of glucose and its replacement by galactose in the culture medium (Fantini et al.:Biology of the Cell65:163–169, 1989); 2) the addition of suramin, a polyanionic compound, in the glucose‐containing medium (Fantini et al.:Journal of Biological Chemistry264:10282–10286, 1989). We investigated the release of CEA in the culture medium of glucose‐deprived HT29‐D4 cells (HT29‐D4‐Gal) and studied its alteration in suramin‐treated HT29‐D4 cells (HT29‐D4‐S). The amount of CEA released in the medium in function of time in culture of undifferentiated HT29‐D4‐Glu cells was very low (5 to 8 ng/106 cells/24 hours) and almost constant throughout the experiment whereas it increased sharply during differentiation of HT29‐D4‐Gal cells (380 ng/106 cells/24 hours after 9 days in culture). Surprisingly the amount of CEA released by differentiated HT29‐D4‐S cells remained very low and comparable with the one of HT29‐D4‐Glu cells. Moreover suramin, when added to CEA‐producing HT29‐D4‐Gal cells, strongly inhibited its release. Radioiodination of cell surface proteins followed by immunoprecipitation using an anti‐CEA monoclonal antibody showed the presence of a 180 kDa poly‐peptide, i.e., CEA, predominantly labeled in HT29‐D4‐Gal and ‐S cells. The total CEA cellular content was higher in HT29‐D4‐Glu and HT29‐D4‐S cells than in HT29‐D4‐Gal cells. When HT29‐D4‐Gal or ‐S cells were treated with the bacterial phosphatidylinositol phospholipase C (PI‐PLC) a similar level of CEA was released suggesting a similar type of CEA anchorage. The present data demonstrate that a decrease in CEA release (i.e., in HT29‐D4‐Glu and ‐S cells) corresponds to an increase in its overall cellular expression. These results are in favour of a regulatory mechanism, impaired by suramin, which determines the balance between the soluble and the membrane bound forms of CEA. Copyright © 1990 Wiley‐Liss, Inc.