HUMAN CACO-2 CELLS TRANSFECTED WITH C-HA-RAS AS A MODEL FOR ENDOCRINEDIFFERENTIATION IN THE LARGE-INTESTINE

Endocrine cells occur in approximately 30% of all colorectal adenocarc inomas, and this feature appears to correlate with a relatively poor p rognosis. To study the factors regulating endocrine differentiation in colorectal cancer, which may bear resemblance to the regulation of en docrine differentiation in normal intestinal mucosa, models in which d ifferentiation can be manipulated are essential. However, endocrine fe atures in colorectal cancer cell lines are scarce and are almost exclu sively observed in xenografts, presumably as a result of differentiati on induction by stromal components. We attempted to demonstrate endocr ine differentiation in the colonic adenocarcinoma cell line Caco-2, wh ich is frequently used as a model for enterocytic differentiation. In vitro endocrine tumor cells were not encountered. In vivo studies were cumbersome, because of the low take rate of Caco-2 cells. We did mana ge to establish nude mouse xenografts of Caco-2 cells by inoculating c ells in collagen gel and by suppressing natural killer cell activity. In an attempt to induce a better take rate and to investigate the effe ct of Ras oncoprotein overexpression on endocrine differentiation, Cac o-2 cells were transfected with a point-mutated c-Ha-Ras gene. The cel l line Caco-2 EJ6, generated from these experiments, could be xenograf ted in nude mice with a high take rate, yielding a moderately well dif ferentiated adenocarcinoma, morphologically identical to the tumors de rived from untransfected Caco-2 cells. The xenografts displayed goblet cell, enterocytic, Paneth cell and endocrine differentiation. In vitr o endocrine differentiation was observed neither under standard condit ions nor with extracellular matrix components as differentiation induc ers. We conclude that the Caco-2 cell line and its c-Ha-Ras transfecte d subline Caco-2 EJ6 in vivo display endocrine differentiation. Ras ov erexpression does not enhance endocrine differentiation. Due to its fa vorable growth properties in vivo, Caco-2 EJ6 is a suitable model for studies on endocrine differentiation in colorectal cancer.