Acid modulation of HT29 cell growth and differentiation. An in vitro model for Barrett's esophagus.

Cell proliferation and differentiation are influenced by environmental factors, including the extracellular pH. We recently showed, using an ex vivo organ culture system of human mucosal Barrett's esophageal biopsies, that acid has a highly variable effect on cell proliferation and differentiation depending on the pattern of acid exposure. Study of the mechanisms underlying these dynamic effects of acid on this premalignant intestinal-like epithelium is hampered by lack of an immortalized cell line. We therefore investigated the effect of acid exposure on the human colonic carcinoma cell line HT29, chosen because of its intestinal cell derivation and its ability to differentiate in vitro. HT29 cells exposed to pH 5 medium either continuously (up to 3 weeks), or as a short (1 hour) pulse, were compared with cells cultured at pH 7.4. Villin expression was induced only by long term acid exposure, and correlated with the development of differentiated polarized cells that contain a brush border and microvillus inclusions. Chronic acid exposure arrested cell proliferation, whereas a 1 hour acid-pulse enhanced cell proliferation, as determined by [3H]thymidine incorporation assays and proliferating cell nuclear antigen expression. Serum starvation attenuated the hyperproliferative effect of an acid-pulse. In addition, the doubling time of at least the first cell cycle after an acid-pulse was shortened. The Na/H exchanger is likely to play a role since the hyperproliferative acid-induced response was blocked by amiloride; and the activity of the exchanger was increased at acidic pH as determined by 22Na uptake. These results support a role for extracellular pH on cell proliferation and differentiation of HT29 cells. Furthermore, these findings parallel the dynamic effects of acid on Barrett's esophagus, and suggest that HT29 cells could serve as an in vitro model for studying the mechanism of acid modulation in Barrett's esophagus.