Caco-2 intestinal epithelial cells differentiate spontaneously after confluence when contact inhibition slows proliferation. We hypothesized that such reversible differentiation might be dependent on DNA synthesis and repair. We studied the effects of the topoisomerase II inhibitor etoposide on Caco-2 proliferation and on the differentiation markers alkaline phosphatase and dipeptidyl dipeptidase specific activity, as well as cell motility. Etoposide (0.3-10 microM) dose-dependently inhibited proliferation and alkaline phosphatase activity. However, etoposide (0.7-3 microM dose-dependently stimulated dipeptidyl dipeptidase activity. Above this concentration, dipeptidyl dipeptidase was also inhibited. Similar effects on enzyme activity were observed when proliferation was blocked with mitomycin C. Etoposide (1-10 microM) also dose-dependently inhibited cell motility. The selective stimulation of dipeptidyl dipeptidase activity by etoposide may offer a clue to the regulation of intestinal brush border enzyme expression at the molecular level.