Extracellular adenosine deprivation induces epithelial differentiation of HT29 cells: evidence for a concomitant adenosine A(1)/A(2) receptor balanceregulation

HT29 cells display an undifferentiated phenotype in culture. However. numer ous treatments are able to induce both epithelial differentiation and cell growth inhibition. We have previously demonstrated that adenosine and its a nalogues act through specific adenosine receptors to modulate cell prolifer ation in HT29 and other human colon adenocarcinoma cell lines. Among the tr eatments tested, the most potent inhibition of HT29 cell growth was induced by deprivation of extracellular adenosine using adenosine deaminase. Here, we investigated the capacity of adenosine deaminase to initiate epithelial differentiation. After 1 month of daily addition of 10 U/ml adenosine deam inase to the culture medium, HT29 cells were cloned by limited dilution. Am ong the clones obtained, we focused our attention on clone 13. Microscopic visualization and proliferation studies indicated that cells from this clon e grew very slowly and in a pseudo-monolayer, in marked contrast with the s ituation observed in the mother HT29 cell line. In addition, clone 13 cells displayed epithelial features that mimic the enterocytic differentiation o f Caco-2 cells. These modifications were accompanied by dramatic changes in the activity of adenosine receptors, as demonstrated by pharmacological st udies. In contrast to the original HT29 cells, clone 13 as well as Caco-2 c ells displayed (i) a very low number of adenosine A, receptors, and (ii) in creases in intracellular cAMP levels when challenged with adenosine analogu es, it is hypothesized that a loss of adenosine A, receptors, with no chang e or a concomitant increase in adenosine A(2) receptors, results in the eme rgence of adenosine Az receptor-mediated differentiation and inhibition of proliferation, through a cAMP-dependent pathway. (C) 2000 Elsevier Science B.V. All rights reserved.