The emergence of a basolateral 1-deoxymannojirimycin-sensitive mannose carrier is a function of intestinal epithelial cell differentiation. Evidence for a new inhibitory effect of 1-deoxymannojirimycin on facilitative mannose transport.

Abstract

We have previously reported that 1-deoxymannojirimycin (dMM), a specific alpha-mannosidase I inhibitor interfered with the uptake of D-[2-3H]mannose in differentiated HT-29 cells (a cell line derived from a human colon adenocarcinoma) (Ogier-Denis, E., Trugnan, G., Sapin, C., Aubery, M., and Codogno, P. (1990) J. Biol. Chem. 265, 5366-5369). In the present work, we have used another cell line derived from a human colon adenocarcinoma, Caco-2 cells, which has the capacity to grow and to differentiate on porous filters. We have determined that mannose could enter the cells by two distinct transporters. One sensitive to dMM, present at the basolateral membrane of differentiated Caco-2 cells, and one insensitive to the drug localized at the brush border membrane of these cells. The basolateral mannose uptake is mediated by a Na(+)-independent transporter whereas the apical entry of mannose is under the dependence of Na+. We have focused our studies on the basolateral dMM-sensitive mannose carrier. Kinetic studies indicated that this facilitative mannose transporter has a Km and a Vmax of 55 +/- 8 microM and 0.144 +/- 0.005 mumol/mg of protein/min, respectively. This basolateral transporter is clearly distinct from facilitative glucose transporters. Moreover, this dMM-sensitive mannose transport accurately follows the differentiation process of intestinal epithelial cells as well in vitro as shown using Caco-2 cells as in vivo when experiments were done on crypt cells and villus cells isolated from rat jejunum.