Increased tumorigenicity after differentiation of colon cancer cell line: Absence of association with mucin synthesis

Background/Aims: Postconfluence differentiation followed by a decrease in mucin synthesis has been described for the colonic adenocarcinoma cell line Caco-2. Because the onset of differentiation usually heralds the end of proliferation, we expected Caco-2 would be more tumorigenic in the exponential phase. Thus, we compared tumorigenicity, clonigenicity, and mucin synthesis in the exponential and stationary growth phases. Methods: We estimated mucin synthesis in Caco-2 cells by measuring the amount of high-molecular-weight [³H]glucosamine-labeled glycoprotein released into the culture medium and in the cytosolic fraction. Colony forming efficiency in soft agar and tumorigenicity in nude mice were assessed. Results: Cells in the exponential phase synthesized significantly more mucin compared with stationary phase cells. Pretreatment with benzyl-GalNAc reduced production in both phases but did not change clonigenicity. Colonics did not grow from cells seeded in the exponential phase. The average weight of xenografts raised from postconfluence cells was twice that of xenografts raised from cells in the exponential phase. Conclusions: Neither exponential cell growth nor increased mucin production predicts clonigenicity and tumorigenicity. It is speculated that a stable process takes place in Caco-2 cells after confluence which makes them more clonigenic in vitro and enhances tumor growth in vivo.