Ornithine decarboxylase and diamine oxidase in human colon carcinoma cell line CaCo-2 in culture

Abstract

The human colon carcinoma cell line CaCo-2, grown in vitro under standard culture conditions and in the absence of differentiation inducers, spontaneously exhibits structural and functional characteristics of mature small bowel enterocytes. Differentiation is complete at late confluency. High activities of ornithine decarboxylase and diamine oxidase are present in enterocytes. Although these enzymes are involved in polyamine metabolism and therefore in cell replication, their function in small bowel epithelium remains to be defined. In this study ornithine decarboxylase and diamine oxidase activities were assessed in CaCo-2 cells at different stages of proliferation and differentiation. Diamine oxidase was also assayed in spent culture media to assess its spontaneous release by CaCo-2 cells. The trigger effect of medium replacement on ornithine decarboxylase activity was also investigated. Cell growth and cell cycle kinetics were determined by hemocytometric cell count and [3H]thymidine labeling index. Sucrase activity was assayed to evaluate brush-border functional maturation. Elevated ornithine decarboxylase activity was recorded during the replication phase (highest value 0.3 ± 0.02 U/mg) characterized by high thymidine labeling index (43%), and was greatly enhanced by medium replacement (2.1 ± 0.3 U/mg). Diamine oxidase activity was low in both cells and medium during the active phase of cell growth, and during the differentiation period it progressively increased (highest value 499 ± 78 U/mg) along with sucrase activity. The high diamine oxidase activity recorded in the medium (highest value 1292 ± 310 U/ml) and the evidence of diamine oxidase secretion through the basolateral membrane of the cells cultured on porous filters support the hypothesis of an extracellular role of intestinal diamine oxidase. The CaCo-2 cell line, which shows several analogies with small bowel enterocytes, can be proposed as an interesting in vitro model for studying many aspects of cell replication and differentiation depending on polyamine metabolism.