EVIDENCE FOR A DUAL CONTROL OF MACROAUTOPHAGIC SEQUESTRATION AND INTRACELLULAR TRAFFICKING OF N-LINKED GLYCOPROTEINS BY THE TRIMERIC G(I3) PROTEIN IN HT-29 CELLS

The trimeric G(i3) protein-dependent lysosomal-autophagic pathway is r esponsible for the degradation of a pool of N-linked glycoproteins in the human colon cancer HT-29 cell line. Here we have followed the fate of N-glycans using HT-29 cells either overexpressing the wild-type G alpha(i3) protein or transfected with different mutants of the G alpha (i3) protein. The stabilization of N-glycans was dependent upon the in hibition of autophagic sequestration by either 3-methyladenine (3-MA) or pertussis toxin (PTX). However, PTX allowed the processing of high- mannose glycans whereas 3-MA did not. The destabilization of the Golgi apparatus by brefeldin A, which interrupts the intracellular traffick ing of N-linked glycoproteins along the secretory pathway, did not int erfere with the macroautophagic pathway. These results suggest that th e lysosomal-autophagic pathway is not dependent upon the integrity of the Golgi apparatus and points to differences between the molecular pr operties of two membrane how processes (macroautophagy, exocytic pathw ay) controlled by the trimeric G(i3) protein. (C) 1997 Academic Press.