Effects of epidermal growth factor on diamine oxidase expression and cell growth in Caco-2 cells

To investigate the role of diamine oxidase (DAO) in the intestinal mucosa, we compared its expression with cell proliferation and differentiation in the human colon carcinoma cell line Caco-2. DAO synthesis was evaluated in subconfluent and confluent cultures and in the presence of epidermal growth factor (EGF), a polypeptide hormone known to have specific trophic effects on the small intestinal mucosa. EGF stimulated DNA synthesis, significantly increased cellular DAO activity and the amount of enzyme secreted into the culture medium, but decreased expression of dipeptidyl peptidase IV, a marker of cell differentiation in confluent Caco-2 cells. Immunoprecipitation of DAO from cells labeled metabolically with [35S]methionine failed to demonstrate an increased enzyme synthesis in EGF-treated cells, suggesting that this hormone acted primarily at a posttranslational level by reducing DAO degradation before intracellular storage or secretion. A possible relationship between changes in cellular DAO activity and cell proliferation was also investigated by using aminoguanidine, a specific and potent DAO inhibitor. Although DAO activity was markedly suppressed, aminoguanidine had no significant effects on the rate of DNA synthesis. These results demonstrated that in Caco-2 cells EGF stimulated DNA synthesis and DAO expression; however, cell proliferation and differentiation were not correlated with the levels of cellular DAO, suggesting that this enzyme does not play a major role in the regulation of intestinal epithelial cell turnover.