Intracellular transport, sorting, and turnover of acetylcholinesterase. Evidence for an endoglycosidase H-sensitive form in Golgi apparatus, sarcoplasmic reticulum, and clathrin-coated vesicles and its rapid degradation by a non-lysosomal mechanism.
Tissue-cultured muscle cells synthesize several oligomeric forms of acetylcholinesterase (AChE) destined for the cell surface or secretion. Previous studies on the biogenesis of AChE polypeptide chains have shown that only a small fraction become assembled into catalytically active oligomers which transit the Golgi apparatus and acquire endoglycosidase H (endo H) resistance. Most of the AChE polypeptides remain endo H-sensitive and are rapidly degraded intracellularly. We now show that all newly synthesized AChE polypeptides are transported from the rough endoplasmic reticulum to the Golgi apparatus where they acquire N-acetylglucosamine. However, approximately 80% of these AChE polypeptides remain endo H-sensitive and are degraded intracellularly with a half-life of about 1.5 h by a mechanism which is insensitive to lysosomotropic agents. These endo H-sensitive AChE molecules can be chased into clathrin-coated vesicles and/or the sarcoplasmic reticulum prior to degradation. Pulse-chase studies of isotopically labeled or catalytically active AChE molecules suggest that there are at least two discreet populations of clathrin-coated vesicles which leave the Golgi, one whose origin is cis/medial and one whose origin is trans. These studies indicate the existence of a post-rough endoplasmic reticulum, non-lysosomal degradative pathway for intra-luminal proteins and suggest that post-translational events at the levels of protein sorting and degradation may play a role in regulating the abundance of exportable proteins.
Rotundo
R L
RL
Department of Anatomy and Cell Biology, University of Miami School of Medicine, Florida 33101.
Thomas
K
K
Porter-Jordan
K
K
Benson
R J
RJ
Fernandez-Valle
C
C
Fine
R E
RE
D000110:Acetylcholinesterase / Q000378:metabolism*; D000117:Acetylglucosamine / Q000378:metabolism; D000118:Acetylglucosaminidase / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D002642:Chick Embryo; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000201:enzymology*; D003208:Concanavalin A / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000201:enzymology; D011992:Endosomes / Q000201:enzymology*; D006056:Golgi Apparatus / Q000201:enzymology*; D006596:Hexosaminidases / Q000378:metabolism*; D007163:Immunosorbent Techniques; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D009132:Muscles / Q000196:embryology / Q000201:enzymology / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014909:Wheat Germ Agglutinins / Q000378:metabolism
D002966:Clathrin; D014909:Wheat Germ Agglutinins; D003208:Concanavalin A; D000110:Acetylcholinesterase; D006596:Hexosaminidases; D000118:Acetylglucosaminidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D000117:Acetylglucosamine