Studies on the regulation of the enterocytic differentiation of the human
colon cancer cell line HT-29, which is differentiated in the absence (Glc-) but not in the presence of
glucose (Glc+), have recently shown that the post-translational processing of
sucrase-
isomaltase and particularly its glycosylation vary as a function of cell differentiation (Trugnan G., Rousset, M., Chantret, I., Barbat, A., and Zweibaum, A. (1987) J. Cell Biol. 104, 1199-1205). Other studies indicate that in undifferentiated HT-29 Glc+ cells there is an accumulation of
UDP-N-acetylhexosamine, which is involved in the glycosylation process (Wice, B. M., Trugnan, G., Pinto, M., Rousset, M., Chevalier, G., Dussaulx, E., Lacroix, B., and Zweibaum, A. (1985) J. Biol. Chem. 260, 139-146). The purpose of the present work is to investigate whether an overall alteration of protein glycosylation is associated with the inability of HT-29 cells to differentiate. At least three alterations are detected: (i) after a 10-min pulse, the incorporation of D-[2-3H]
mannose in undifferentiated cells is severely reduced, compared to differentiated cells. (ii) After a 24-h period of labeling with D-[2-3H]
mannose, undifferentiated cells accumulate more than 60% of the radioactivity in the high
mannose glycopeptides, whereas differentiated HT-29 Glc- cells accumulate only 38%. (iii) The analysis of the high
mannose oligosaccharides transferred "en bloc" from the
lipid precursor shows that Man9,8-GlcNAc2 species accumulate in undifferentiated cells, whereas no such accumulation can be detected in differentiated cells. This glycosylation pattern is consistent with an impairment of the trimming of high
mannose into complex
glycans. It is concluded that N-
glycan processing is correlated with the state of enterocytic differentiation of HT-29 cells.