The effect of Phaseolus vulgaris isolectin E4 on polyamine concentrations and ornithine decarboxylase activity of proliferating and differentiating Caco-2 cells was investigated. Values of putrescine, spermidine, and spermine in control cells were highest during the early phase of proliferative cell growth and lowest in the stationary phase. Phytohaemagglutinin E4 significantly increased cellular polyamine values during the late proliferative phase of cell growth. Ornithine decarboxylase activity was high during intensive proliferation and growth, but was lower when proliferation slowed down or ceased. Exposure of Caco-2 cells in the early proliferative phase of cell growth to increasing concentrations of the potent intestinal growth factor phytohaemagglutinin E4 greatly stimulated enzyme activity. In contrast, the activity of ornithine decarboxylase was not stimulated in Caco-2 cells of the late proliferative phase nor was there any increase in the enzyme activity in differentiating and fully differentiated cells of the stationary phase. Accordingly, when proliferating Caco-2 cells possessed the highest ornithine decarboxylase activity, the polyamine values were also at their highest. During differentiation, as the ornithine decarboxylase activity fell close to zero, polyamine values also decreased. In the early proliferative phase of cell growth ornithine decarboxylase activity coincided with DNA synthesis in cells exposed to Phaseolus vulgaris isolectin E4. These findings with Caco-2 cells were similar to those found in brush border cells of the rat small intestine.
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