Intestinal Epithelial Cell Surface Membrane Glycoprotein Synthesis

The cell surface membranes of mitotically active crypt cells from rat intestinal epithelium were found to have glycosyltransferase activities and endogenous acceptors not found on the differentiating villus cells. Rat intestinal epithelial cells were isolated as intact cells from different levels of the villus and crypt areas representing sequential stages of cellular differentiation. Incubation of these cells with UDP-N-acetyl[l-14C]glucosamine, UDP-[UJ4C]glucose, UDP[l-3H]galactose, GDP-[UJ4C]mannose, and GDP-[U-Wlfucose demonstrated up to a lo-fold greater incorporation into crypt cells as compared to villus cells. In marked contrast, incubation with CMP-[4,5,6,7,8, 9-14C]sialic acid showed that radioactive sialic acid was preferably transferred to villus cell rather than to crypt cell surface. Effective transfer of sugars to exogenous acceptors gave further indication for the presence of galactosyltransferase enzyme activity on crypt cells rather than villus cells, and of sialyltransferase enzyme activity as being predominantly on villus cells. Neither glycosyltransferase activities nor endogenous acceptors were released into the incubation medium. Analysis of labeled endogenous product by dialysis, acid precipitation, differential solvent extraction, graded acid hydrolysis, high voltage electrophoresis, and descending chromatography suggested that most of the label was present as the original monosaccharide derived from the nucleotide sugar, and that it had been incorporated into a membrane-associated glycoprotein. Incubation of human fetal intestinal epithelial cells with UDP-[l-3H]galactose also showed galactosyltransferase enzyme activity to an exogenous as well as an endogenous acceptor. These results suggest that the plasma membrane of the mitotically active undifferentiated crypt cell and the fetal cell both contain (a) active glycosyltransferase enzymes and (b) acceptor sites which are glycoproteins with incomplete polysaccharide chains.