title: UEV-1 is an ubiquitin-conjugating enzyme variant that regulates glutamate receptor trafficking in C. elegans neurons.
abstract: The regulation of AMPA-type glutamate receptor (AMPAR) membrane trafficking is a key mechanism by which neurons regulate synaptic strength and plasticity. AMPAR trafficking is modulated through a combination of receptor phosphorylation, ubiquitination, endocytosis, and recycling, yet the factors that mediate these processes are just beginning to be uncovered. Here we identify the ubiquitin-conjugating enzyme variant UEV-1 as a regulator of AMPAR trafficking in vivo. We identified mutations in uev-1 in a genetic screen for mutants with altered trafficking of the AMPAR subunit GLR-1 in C. elegans interneurons. Loss of uev-1 activity results in the accumulation of GLR-1 in elongated accretions in neuron cell bodies and along the ventral cord neurites. Mutants also have a corresponding behavioral defect--a decrease in spontaneous reversals in locomotion--consistent with diminished GLR-1 function. The localization of other synaptic proteins in uev-1-mutant interneurons appears normal, indicating that the GLR-1 trafficking defects are not due to gross deficiencies in synapse formation or overall protein trafficking. We provide evidence that GLR-1 accumulates at RAB-10-containing endosomes in uev-1 mutants, and that receptors arrive at these endosomes independent of clathrin-mediated endocytosis. UEV-1 homologs in other species bind to the ubiquitin-conjugating enzyme Ubc13 to create K63-linked polyubiquitin chains on substrate proteins. We find that whereas UEV-1 can interact with C. elegans UBC-13, global levels of K63-linked ubiquitination throughout nematodes appear to be unaffected in uev-1 mutants, even though UEV-1 is broadly expressed in most tissues. Nevertheless, ubc-13 mutants are similar in phenotype to uev-1 mutants, suggesting that the two proteins do work together to regulate GLR-1 trafficking. Our results suggest that UEV-1 could regulate a small subset of K63-linked ubiquitination events in nematodes, at least one of which is critical in regulating GLR-1 trafficking.
authors.affiliation: The Waksman Institute, Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States of America.
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Kramer
authors.forename: Jaegal
authors.initials: J
authors.lastname: Shim
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Previtera
authors.forename: Nora R
authors.initials: NR
authors.lastname: Isack
authors.forename: Ming-Chih
authors.initials: MC
authors.lastname: Lee
authors.forename: Bonnie L
authors.initials: BL
authors.lastname: Firestein
authors.forename: Christopher
authors.initials: C
authors.lastname: Rongo
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000502:physiology*; D002966:Clathrin / Q000737:chemistry; D004705:Endocytosis; D005786:Gene Expression Regulation; D014644:Genetic Variation; D007395:Interneurons / Q000378:metabolism; D008954:Models, Biological; D008957:Models, Genetic; D009154:Mutation; D018091:Receptors, AMPA / Q000378:metabolism; D017470:Receptors, Glutamate / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000502:physiology*
chemical_list: D029742:Caenorhabditis elegans Proteins; D002966:Clathrin; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D025801:Ubiquitin; C559057:Uev-1 protein, C elegans; D044763:Ubiquitin-Conjugating Enzymes