Characterization of Quantitative Mucin Variants from a Human Colon Cancer Cell Line1

Colonie mucins are high molecular weight glycoproteins produced by goblet cells of colonie epithelium. Some studies have indicated that patients with colonie cancers that produce high amounts of mucin have a poorer prognosis than patients whose tumors produce low amounts of mucin. At present, however, the role of mucin in affecting the behavior of colon cancer cells is not well understood. To further elucidate the relationship between cellular mucin content and the growth characteris tics and morphology of tumor cells, we utilized a replica plating technique and immunoscreening method to identify and purify variant clones of the human colon cancer cell line 1 SI741 that produce high and low levels of mucin. This procedure enabled us to isolate two high mucin-containing variants (HM3 and HM7) and one low mucin-containing variant (I.M 12). These variants exhibited different morphology. Both high mucin variants tended to form cell aggregates and suspended cells with adjoining mucoid threads. The low mucin variant formed spread monolayers on the sub stratum with the formation of cell processes. Metabolic labeling using [3H]glucosamine demonstrated that high mucin variants synthesized 2fold more mucin in the cell layer and secreted 3-fold more mucin into the culture medium than the low mucin variant. The colony-forming efficiency in semisolid agar for these variants positively correlated with their mucin content. High mucin variant cells when injected into athymic nude mice formed tumors 2-fold larger than those of the parental cells while the low mucin variant formed tumors only one-half as large as those of the parental cell line. These mucin variants should provide a useful model for understanding the biological behavior of mucinous colon cancer cells in vivo and in vitro.