title: Parkin promotes proteasomal degradation of synaptotagmin IV by accelerating polyubiquitination.
abstract: Parkin is an E3 ubiquitin ligase whose mutations cause autosomal recessive juvenile Parkinson's disease (PD). Unlike the human phenotype, parkin knockout (KO) mice show no apparent dopamine neuron degeneration, although they demonstrate reduced expression and activity of striatal mitochondrial proteins believed to be necessary for neuronal survival. Instead, parkin-KO mice show reduced striatal evoked dopamine release, abnormal synaptic plasticity, and non-motor symptoms, all of which appear to mimic the preclinical features of Parkinson's disease. Extensive studies have screened candidate synaptic proteins responsible for reduced evoked dopamine release, and synaptotagmin XI (Syt XI), an isoform of Syt family regulating membrane trafficking, has been identified as a substrate of parkin in humans. However, its expression level is unaltered in the striatum of parkin-KO mice. Thus, the target(s) of parkin and the molecular mechanisms underlying the impaired dopamine release in parkin-KO mice remain unknown. In this study, we focused on Syt IV because of its highly homology to Syt XI, and because they share an evolutionarily conserved lack of Ca2+-binding capacity; thus, Syt IV plays an inhibitory role in Ca2+-dependent neurotransmitter release in PC12 cells and neurons in various brain regions. We found that a proteasome inhibitor increased Syt IV protein, but not Syt XI protein, in neuron-like, differentiated PC12 cells, and that parkin interacted with and polyubiquitinated Syt IV, thereby accelerating its protein turnover. Parkin overexpression selectively degraded Syt IV protein, but not Syt I protein (indispensable for Ca2+-dependent exocytosis), thus enhancing depolarization-dependent exocytosis. Furthermore, in parkin-KO mice, the level of striatal Syt IV protein was increased. Our data indicate a crucial role for parkin in the proteasomal degradation of Syt IV, and provide a potential mechanism of parkin-regulated, evoked neurotransmitter release.
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. Electronic address: kabayama@brain.riken.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kabayama
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Tokushige
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Takeuchi
authors.affiliation: Division of Functional Morphology, Department of Basic Veterinary Medicine, School of Veterinary Medicine, Nippon Veterinary and Life Science University, 1-7-1 Kyonantyo, Musashino, Tokyo 180-8602, Japan.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Kabayama
authors.affiliation: Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: Laboratory for Developmental Neurobiology, Brain Science Institute, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. Electronic address: mikosiba@brain.riken.jp.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000494:pharmacology; D019556:COS Cells; D002522:Chlorocebus aethiops; D003342:Corpus Striatum / Q000166:cytology; D005089:Exocytosis / Q000235:genetics; D008565:Membrane Proteins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020932:Nerve Growth Factor / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D016716:PC12 Cells / Q000187:drug effects / Q000648:ultrastructure; D061988:Proteasome Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D059748:Proteolysis / Q000187:drug effects; D051381:Rats; D050857:Synaptotagmins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects / Q000502:physiology*; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
chemical_list: D001324:Autoantigens; C097741:Golgin subfamily A member 2; D008565:Membrane Proteins; D009842:Oligopeptides; D061988:Proteasome Inhibitors; D050988:Vesicle-Associated Membrane Protein 2; D050857:Synaptotagmins; D020932:Nerve Growth Factor; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; C078846:epoxomicin
keywords: Evoked exocytosis regulator; Parkinson's disease; Polyubiquitination; Proteasomal degradation; Syt IV