Ubiquitination precedes internalization and proteolytic cleavage of plasma membrane-bound glycine receptors.
The inhibitory glycine receptor (GlyR) in developing spinal neurones is internalized efficiently upon antagonist inhibition. Here we used surface labeling combined with affinity purification to show that homopentameric alpha1 GlyRs generated in Xenopus oocytes are proteolytically nicked into fragments of 35 and 13 kDa upon prolonged incubation. Nicked GlyRs do not exist at the cell surface, indicating that proteolysis occurs exclusively in the endocytotic pathway. Consistent with this interpretation, elevation of the lysosomal pH, but not the proteasome inhibitor lactacystin, prevents GlyR cleavage. Prior to internalization, alpha1 GlyRs are conjugated extensively with ubiquitin in the plasma membrane. Our results are consistent with ubiquitination regulating the endocytosis and subsequent proteolysis of GlyRs residing in the plasma membrane. Ubiquitin-conjugating enzymes thus may have a crucial role in synaptic plasticity by determining postsynaptic receptor numbers.
Büttner
C
C
Department of Pharmacology, Biocenter of the Johann Wolfgang Goethe University, Marie Curie Strasse 9, Frankfurt am Main 60439, Germany.
Sadtler
S
S
Leyendecker
A
A
Laube
B
B
Griffon
N
N
Betz
H
H
Schmalzing
G
G
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D003546:Cysteine Endopeptidases; D018076:DNA, Complementary / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005998:Glycine / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000737:chemistry; D008247:Lysosomes / Q000378:metabolism; D018942:Macrolides; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D018075:RNA, Complementary / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D014981:Xenopus
D000900:Anti-Bacterial Agents; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D018942:Macrolides; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D018075:RNA, Complementary; D025801:Ubiquitin; C067713:lactacystin; D006639:Histidine; D010664:Phenylmethylsulfonyl Fluoride; C036978:concanamycin A; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008239:Lysine; D005998:Glycine; D000111:Acetylcysteine