DIFFERENTIATION-DEPENDENT AUTOPHAGY CONTROLS THE FATE OF NEWLY SYNTHESIZED N-LINKED GLYCOPROTEINS IN THE COLON ADENOCARCINOMA HT-29 CELL-LINE

Our previous results have demonstrated that, in undifferentiated human colon cancer HT-29 cells, a pool of glycoproteins bearing high-mannos e oligosaccharides rapidly escapes the exocytic pathway to be degraded in the lysosomal compartment [Trugnan, Ogier-Denis, Sapin, Darmoul, B auvy, Aubery and Codogno (1991) J. Biol. Chem. 266, 20849-20855], We r eport here on the mechanism that governs this degradative pathway. Usi ng pulse-chase experiments in combination with subcellular fractionati on, we have observed that the sequestration of high-mannose glycoprote ins in lysosomes was impaired by drugs which interfere with the autoph agic-lysosomal pathway. The accumulation of high-mannose glycoproteins in the lysosomal fraction was shown to be part of the general autopha gic pathway constitutively expressed in undifferentiated cells, as ind ependently measured by the sequestration of the cytosolic enzyme lacta te dehydrogenase and electroloaded raffinose. Furthermore, when HT-29 cells were cultured under differentiation-permissive conditions, the d ecreased accumulation of high-mannose glycoproteins in the lysosomal c ompartment was correlated with the decrease in autophagy.