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-mannose oligosaccharides rapidly escapes the exocytic pathway to be degraded in the lysosomal compartment [Trugnan, Ogier-Denis, Sapin, Darmoul, Bauvy, Aubery and Codogno (1991) J. Biol. Chem. 266, 20849-20855], We report here on the mechanism that governs this degradative pathway. Using pulse-chase experiments in combination with subcellular fractionation, we have observed that the sequestration of high-mannose glycoproteins in lysosomes was impaired by drugs which interfere with the autophagic-lysosomal pathway. The accumulation of high-mannose glycoproteins in the lysosomal fraction was shown to be part of the general autophagic pathway constitutively expressed in undifferentiated cells, as independently measured by the sequestration of the cytosolic enzyme lactate dehydrogenase and electroloaded raffinose. Furthermore, when HT-29 cells were cultured under differentiation-permissive conditions, the decreased accumulation of high-mannose glycoproteins in the lysosomal compartment was correlated with the decrease in autophagy.