Publications by authors named "Peter Juo"

18 Publications

  • Page 1 of 1

The p97-UBXN1 complex regulates aggresome formation.

J Cell Sci 2021 Mar 12. Epub 2021 Mar 12.

Department of Developmental Molecular and Chemical Biology, Tufts University School of Medicine, Boston MA 02111, USA

The recognition and disposal of misfolded proteins is essential for the maintenance of cellular homeostasis. Perturbations in the pathways that promote degradation of aberrant proteins contribute to a variety of protein aggregation disorders broadly termed proteinopathies. The p97 AAA-ATPase in combination with adaptor proteins functions to identify ubiquitylated proteins and target them for degradation by the proteasome or autophagy. Mutations in p97 cause multi-system proteinopathies; however, the precise defects underlying these disorders are unclear. Here, we systematically investigate the role of p97 and its adaptors in the process of formation of aggresomes, membrane-less structures containing ubiquitylated proteins that arise upon proteasome inhibition. We demonstrate that p97 mediates aggresome formation and clearance and identify a novel role for the adaptor UBXN1 in the process of aggresome formation. UBXN1 is recruited to aggresomes and UBXN1 knockout cells are unable to form aggresomes. Loss of p97-UBXN1 results in increased Huntingtin polyQ inclusion bodies both in mammalian cells as well as in a model of Huntington's Disease. Together our work identifies evolutionarily conserved roles for p97-UBXN1 in the disposal of protein aggregates.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1242/jcs.254201DOI Listing
March 2021

The WD40-Repeat Protein WDR-20 and the Deubiquitinating Enzyme USP-46 Promote Cell Surface Levels of Glutamate Receptors.

J Neurosci 2021 Apr 23;41(14):3082-3093. Epub 2021 Feb 23.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts 02111

Reversible modification of AMPA receptors (AMPARs) with ubiquitin regulates receptor levels at synapses and controls synaptic strength. The conserved deubiquitinating enzyme (DUB) ubiquitin-specific protease-46 (USP-46) removes ubiquitin from AMPARs and protects them from degradation in both and mammals. Although DUBs are critical for diverse physiological processes, the mechanisms that regulate DUBs, especially in the nervous system, are not well understood. We and others previously showed that the WD40-repeat proteins WDR-48 and WDR-20 bind to and stimulate the catalytic activity of USP-46. Here, we identify an activity-dependent mechanism that regulates WDR-20 expression and show that WDR-20 works together with USP-46 and WDR-48 to promote surface levels of the AMPAR GLR-1. , , and loss-of-function mutants exhibit reduced levels of GLR-1 at the neuronal surface and corresponding defects in GLR-1-mediated behavior. Increased expression of WDR-20, but not WDR-48, is sufficient to increase GLR-1 surface levels in an -dependent manner. Loss of , , and function reduces the rate of local GLR-1 insertion in neurites, whereas overexpression of is sufficient to increase the rate of GLR-1 insertion. Genetic manipulations that chronically reduce or increase glutamate signaling result in reciprocal alterations in transcription and homeostatic compensatory changes in surface GLR-1 levels that are dependent on This study identifies as a novel activity-regulated gene that couples chronic changes in synaptic activity with increased local insertion and surface levels of GLR-1 via the DUB USP-46. Deubiquitinating enzymes (DUBs) are critical regulators of synapse development and function; however, the regulatory mechanisms that control their various physiological functions are not well understood. This study identifies a novel role for the DUB ubiquitin-specific protease-46 (USP-46) and its associated regulatory protein WD40-repeat protein-20 (WDR-20) in regulating local insertion of glutamate receptors into the neuronal cell surface. This work also identifies WDR-20 as an activity-regulated gene that couples chronic changes in synaptic activity with homeostatic compensatory increases in surface levels of GLR-1 via USP-46. Given that 35% of USP family DUBs associate with WDR proteins, understanding the mechanisms by which WDR proteins regulate USP-46 could have implications for a large number of DUBs in other cell types.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.1074-20.2021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8026351PMC
April 2021

VER/VEGF receptors regulate AMPA receptor surface levels and glutamatergic behavior.

PLoS Genet 2021 Feb 9;17(2):e1009375. Epub 2021 Feb 9.

Department of Developmental, Molecular, and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.

Several intracellular trafficking pathways contribute to the regulation of AMPA receptor (AMPAR) levels at synapses and the control of synaptic strength. While much has been learned about these intracellular trafficking pathways, a major challenge is to understand how extracellular factors, such as growth factors, neuropeptides and hormones, impinge on specific AMPAR trafficking pathways to alter synaptic function and behavior. Here, we identify the secreted ligand PVF-1 and its cognate VEGF receptor homologs, VER-1 and VER-4, as regulators of glutamate signaling in C. elegans. Loss of function mutations in ver-1, ver-4, or pvf-1, result in decreased cell surface levels of the AMPAR GLR-1 and defects in glutamatergic behavior. Rescue experiments indicate that PVF-1 is expressed and released from muscle, whereas the VERs function in GLR-1-expressing neurons to regulate surface levels of GLR-1 and glutamatergic behavior. Additionally, ver-4 is unable to rescue glutamatergic behavior in the absence of pvf-1, suggesting that VER function requires endogenous PVF-1. Inducible expression of a pvf-1 rescuing transgene suggests that PVF-1 can function in the mature nervous system to regulate GLR-1 signaling. Genetic double mutant analysis suggests that the VERs act together with the VPS-35/retromer recycling complex to promote cell surface levels of GLR-1. Our data support a genetic model whereby PVF-1/VER signaling acts with retromer to promote recycling and cell surface levels of GLR-1 to control behavior.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pgen.1009375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7899335PMC
February 2021

The Snail transcription factor CES-1 regulates glutamatergic behavior in C. elegans.

PLoS One 2021 2;16(2):e0245587. Epub 2021 Feb 2.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.

Regulation of AMPA-type glutamate receptor (AMPAR) expression and function alters synaptic strength and is a major mechanism underlying synaptic plasticity. Although transcription is required for some forms of synaptic plasticity, the transcription factors that regulate AMPA receptor expression and signaling are incompletely understood. Here, we identify the Snail family transcription factor ces-1 in an RNAi screen for conserved transcription factors that regulate glutamatergic behavior in C. elegans. ces-1 was originally discovered as a selective cell death regulator of neuro-secretory motor neuron (NSM) and I2 interneuron sister cells in C. elegans, and has almost exclusively been studied in the NSM cell lineage. We found that ces-1 loss-of-function mutants have defects in two glutamatergic behaviors dependent on the C. elegans AMPA receptor GLR-1, the mechanosensory nose-touch response and spontaneous locomotion reversals. In contrast, ces-1 gain-of-function mutants exhibit increased spontaneous reversals, and these are dependent on glr-1 consistent with these genes acting in the same pathway. ces-1 mutants have wild type cholinergic neuromuscular junction function, suggesting that they do not have a general defect in synaptic transmission or muscle function. The effect of ces-1 mutation on glutamatergic behaviors is not due to ectopic cell death of ASH sensory neurons or GLR-1-expressing neurons that mediate one or both of these behaviors, nor due to an indirect effect on NSM sister cell deaths. Rescue experiments suggest that ces-1 may act, in part, in GLR-1-expressing neurons to regulate glutamatergic behaviors. Interestingly, ces-1 mutants suppress the increased reversal frequencies stimulated by a constitutively-active form of GLR-1. However, expression of glr-1 mRNA or GFP-tagged GLR-1 was not decreased in ces-1 mutants suggesting that ces-1 likely promotes GLR-1 function. This study identifies a novel role for ces-1 in regulating glutamatergic behavior that appears to be independent of its canonical role in regulating cell death in the NSM cell lineage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0245587PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7853468PMC
February 2021

The WD40-repeat protein WDR-48 promotes the stability of the deubiquitinating enzyme USP-46 by inhibiting its ubiquitination and degradation.

J Biol Chem 2020 08 25;295(33):11776-11788. Epub 2020 Jun 25.

Graduate Program in Neuroscience, Graduate School of Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, USA

Ubiquitination is a reversible post-translational modification that has emerged as a critical regulator of synapse development and function. However, the mechanisms that regulate the deubiquitinating enzymes (DUBs) responsible for the removal of ubiquitin from target proteins are poorly understood. We have previously shown that the DUB ubiquitin-specific protease 46 (USP-46) removes ubiquitin from the glutamate receptor GLR-1 and regulates its trafficking and degradation in We found that the WD40-repeat proteins WDR-20 and WDR-48 bind and stimulate the catalytic activity of USP-46. Here, we identified another mechanism by which WDR-48 regulates USP-46. We found that increased expression of WDR-48, but not WDR-20, promotes USP-46 abundance in mammalian cells in culture and in neurons Inhibition of the proteasome increased USP-46 abundance, and this effect was nonadditive with increased WDR-48 expression. We found that USP-46 is ubiquitinated and that expression of WDR-48 reduces the levels of ubiquitin-USP-46 conjugates and increases the of USP-46. A point-mutated WDR-48 variant that disrupts binding to USP-46 was unable to promote USP-46 abundance Finally, siRNA-mediated knockdown of destabilizes USP46 in mammalian cells. Together, these results support a model in which WDR-48 binds and stabilizes USP-46 protein levels by preventing the ubiquitination and degradation of USP-46 in the proteasome. Given that a large number of USPs interact with WDR proteins, we propose that stabilization of DUBs by their interacting WDR proteins may be a conserved and widely used mechanism that controls DUB availability and function.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.RA120.014590DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7450142PMC
August 2020

Function of the Deubiquitinating Enzyme USP46 in the Nervous System and Its Regulation by WD40-Repeat Proteins.

Front Synaptic Neurosci 2017 14;9:16. Epub 2017 Dec 14.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Tufts University, Boston, MA, United States.

Posttranslational modification of proteins by ubiquitin regulates synapse development and synaptic transmission. Much progress has been made investigating the role of ubiquitin ligases at the synapse, however very little is known about the deubiquitinating enzymes (DUBs) which remove ubiquitin from target proteins. Although there are far fewer DUBs than ubiquitin ligases encoded by the human genome, it is becoming clear that DUBs have very specific physiological functions, suggesting that DUB activity is tightly regulated . Many DUBs function as part of larger protein complexes, and multiple regulatory mechanisms exist to control the expression, localization and catalytic activity of DUBs. In this review article, we focus on the role of the DUB USP46 in the nervous system, and illustrate potential mechanisms of regulating DUBs by describing how USP46 is regulated by two WD40-repeat (WDR) proteins, WDR48/UAF1 and WDR20, based on recent structural studies and genetic analyses .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnsyn.2017.00016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5735123PMC
December 2017

The CaM Kinase CMK-1 Mediates a Negative Feedback Mechanism Coupling the C. elegans Glutamate Receptor GLR-1 with Its Own Transcription.

PLoS Genet 2016 07 27;12(7):e1006180. Epub 2016 Jul 27.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.

Regulation of synaptic AMPA receptor levels is a major mechanism underlying homeostatic synaptic scaling. While in vitro studies have implicated several molecules in synaptic scaling, the in vivo mechanisms linking chronic changes in synaptic activity to alterations in AMPA receptor expression are not well understood. Here we use a genetic approach in C. elegans to dissect a negative feedback pathway coupling levels of the AMPA receptor GLR-1 with its own transcription. GLR-1 trafficking mutants with decreased synaptic receptors in the ventral nerve cord (VNC) exhibit compensatory increases in glr-1 mRNA, which can be attributed to increased glr-1 transcription. Glutamatergic transmission mutants lacking presynaptic eat-4/VGLUT or postsynaptic glr-1, exhibit compensatory increases in glr-1 transcription, suggesting that loss of GLR-1 activity is sufficient to trigger the feedback pathway. Direct and specific inhibition of GLR-1-expressing neurons using a chemical genetic silencing approach also results in increased glr-1 transcription. Conversely, expression of a constitutively active version of GLR-1 results in decreased glr-1 transcription, suggesting that bidirectional changes in GLR-1 signaling results in reciprocal alterations in glr-1 transcription. We identify the CMK-1/CaMK signaling axis as a mediator of the glr-1 transcriptional feedback mechanism. Loss-of-function mutations in the upstream kinase ckk-1/CaMKK, the CaM kinase cmk-1/CaMK, or a downstream transcription factor crh-1/CREB, result in increased glr-1 transcription, suggesting that the CMK-1 signaling pathway functions to repress glr-1 transcription. Genetic double mutant analyses suggest that CMK-1 signaling is required for the glr-1 transcriptional feedback pathway. Furthermore, alterations in GLR-1 signaling that trigger the feedback mechanism also regulate the nucleocytoplasmic distribution of CMK-1, and activated, nuclear-localized CMK-1 blocks the feedback pathway. We propose a model in which synaptic activity regulates the nuclear localization of CMK-1 to mediate a negative feedback mechanism coupling GLR-1 activity with its own transcription.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pgen.1006180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4963118PMC
July 2016

The DAF-7/TGF-β signaling pathway regulates abundance of the Caenorhabditis elegans glutamate receptor GLR-1.

Mol Cell Neurosci 2015 Jul 5;67:66-74. Epub 2015 Jun 5.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, MA 02111, USA. Electronic address:

Transforming growth factor-β (TGF-β) family signaling pathways have roles in both neuronal development and the regulation of synaptic function. Here we identify a novel role for the Caenorhabditis elegans DAF-7/TGF-β signaling pathway in the regulation of the AMPA-type glutamate receptor GLR-1. We found that the abundance of GLR-1 increases at synapses in the ventral nerve cord (VNC) of animals with loss-of-function mutations in multiple DAF-7/TGF-β pathway components including the TGF-β ligand DAF-7, the type I receptor DAF-1, and the Smads DAF-8 and DAF-14. The GLR-1 defect can be rescued by expression of daf-8 specifically in glr-1-expressing interneurons. The effect on GLR-1 was specific for the DAF-7 pathway because mutations in the DBL-1/TGF-β family pathway did not increase GLR-1 levels in the VNC. Immunoblot analysis indicates that total levels of GLR-1 protein are increased in neurons of DAF-7/TGF-β pathway mutants. The increased abundance of GLR-1 in the VNC of daf-7 pathway mutants is dependent on the transcriptional regulator DAF-3/Smad suggesting that DAF-3-dependent transcription controls GLR-1 levels. Furthermore, we found that glr-1 transcription is increased in daf-7 mutants based on a glr-1 transcriptional reporter. Together these results suggest that the DAF-7/TGF-β signaling pathway functions in neurons and negatively regulates the abundance of GLR-1, in part, by controlling transcription of the receptor itself. Finally, DAF-7/TGF-β pathway mutants exhibit changes in spontaneous locomotion that are dependent on endogenous GLR-1 and consistent with increased glutamatergic signaling. These results reveal a novel mechanism by which TGF-β signaling functions in the nervous system to regulate behavior.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.mcn.2015.06.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4540650PMC
July 2015

The AP2 clathrin adaptor protein complex regulates the abundance of GLR-1 glutamate receptors in the ventral nerve cord of Caenorhabditis elegans.

Mol Biol Cell 2015 May 18;26(10):1887-900. Epub 2015 Mar 18.

Department of Developmental, Molecular & Chemical Biology

Regulation of glutamate receptor (GluR) abundance at synapses by clathrin-mediated endocytosis can control synaptic strength and plasticity. We take advantage of viable, null mutations in subunits of the clathrin adaptor protein 2 (AP2) complex in Caenorhabditis elegans to characterize the in vivo role of AP2 in GluR trafficking. In contrast to our predictions for an endocytic adaptor, we found that levels of the GluR GLR-1 are decreased at synapses in the ventral nerve cord (VNC) of animals with mutations in the AP2 subunits APM-2/μ2, APA-2/α, or APS-2/σ2. Rescue experiments indicate that APM-2/μ2 functions in glr-1-expressing interneurons and the mature nervous system to promote GLR-1 levels in the VNC. Genetic analyses suggest that APM-2/μ2 acts upstream of GLR-1 endocytosis in the VNC. Consistent with this, GLR-1 accumulates in cell bodies of apm-2 mutants. However, GLR-1 does not appear to accumulate at the plasma membrane of the cell body as expected, but instead accumulates in intracellular compartments including Syntaxin-13- and RAB-14-labeled endosomes. This study reveals a novel role for the AP2 clathrin adaptor in promoting the abundance of GluRs at synapses in vivo, and implicates AP2 in the regulation of GluR trafficking at an early step in the secretory pathway.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1091/mbc.E14-06-1048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4436833PMC
May 2015

The WD40-repeat proteins WDR-20 and WDR-48 bind and activate the deubiquitinating enzyme USP-46 to promote the abundance of the glutamate receptor GLR-1 in the ventral nerve cord of Caenorhabditis elegans.

J Biol Chem 2014 Feb 19;289(6):3444-56. Epub 2013 Dec 19.

From the Department of Developmental, Molecular, and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts 02111.

Ubiquitin-mediated endocytosis and degradation of glutamate receptors controls their synaptic abundance and is implicated in modulating synaptic strength. The deubiquitinating enzymes (DUBs) that function in the nervous system are beginning to be defined, but the mechanisms that control DUB activity in vivo are understood poorly. We found previously that the DUB USP-46 deubiquitinates the Caenorhabditis elegans glutamate receptor GLR-1 and prevents its degradation in the lysosome. The WD40-repeat (WDR) proteins WDR20 and WDR48/UAF1 have been shown to bind to USP46 and stimulate its catalytic activity in other systems. Here we identify the C. elegans homologs of these WDR proteins and show that C. elegans WDR-20 and WDR-48 can bind and stimulate USP-46 catalytic activity in vitro. Overexpression of these activator proteins in vivo increases the abundance of GLR-1 in the ventral nerve cord, and this effect is further enhanced by coexpression of USP-46. Biochemical characterization indicates that this increase in GLR-1 abundance correlates with decreased levels of ubiquitin-GLR-1 conjugates, suggesting that WDR-20, WDR-48, and USP-46 function together to deubiquitinate and stabilize GLR-1 in neurons. Overexpression of WDR-20 and WDR-48 results in alterations in locomotion behavior consistent with increased glutamatergic signaling, and this effect is blocked in usp-46 loss-of-function mutants. Conversely, wdr-20 and wdr-48 loss-of-function mutants exhibit changes in locomotion behavior that are consistent with decreased glutamatergic signaling. We propose that WDR-20 and WDR-48 form a complex with USP-46 and stimulate the DUB to deubiquitinate and stabilize GLR-1 in vivo.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M113.507541DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916546PMC
February 2014

The Anaphase-Promoting Complex (APC) ubiquitin ligase regulates GABA transmission at the C. elegans neuromuscular junction.

Mol Cell Neurosci 2014 Jan 7;58:62-75. Epub 2013 Dec 7.

Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, MA 02111, USA. Electronic address:

Regulation of both excitatory and inhibitory synaptic transmission is critical for proper nervous system function. Aberrant synaptic signaling, including altered excitatory to inhibitory balance, is observed in numerous neurological diseases. The ubiquitin enzyme system controls the abundance of many synaptic proteins and thus plays a key role in regulating synaptic transmission. The Anaphase-Promoting Complex (APC) is a multi-subunit ubiquitin ligase that was originally discovered as a key regulator of protein turnover during the cell cycle. More recently, the APC has been shown to function in postmitotic neurons, where it regulates diverse processes such as synapse development and synaptic transmission at glutamatergic synapses. Here we report that the APC regulates synaptic GABA signaling by acting in motor neurons to control the balance of excitatory (acetylcholine) to inhibitory (GABA) transmission at the Caenorhabditis elegans neuromuscular junction (NMJ). Loss-of-function mutants in multiple APC subunits have increased muscle excitation at the NMJ; this phenotype is rescued by expression of the missing subunit in GABA neurons. Quantitative imaging and electrophysiological analyses indicate that APC mutants have decreased GABA release but normal cholinergic transmission. Consistent with this, APC mutants exhibit convulsions in a seizure assay sensitive to reductions in GABA signaling. Previous studies in other systems showed that the APC can negatively regulate the levels of the active zone protein SYD-2 Liprin-α. Similarly, we found that SYD-2 accumulates in APC mutants at GABAergic presynaptic sites. Finally, we found that the APC subunit EMB-27 CDC16 can localize to presynapses in GABA neurons. Together, our data suggest a model in which the APC acts at GABAergic presynapses to promote GABA release and inhibit muscle excitation. These findings are the first evidence that the APC regulates transmission at inhibitory synapses and have implications for understanding nervous system pathologies, such as epilepsy, that are characterized by misregulated GABA signaling.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.mcn.2013.12.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4036811PMC
January 2014

The scaffolding protein SYD-2/Liprin-α regulates the mobility and polarized distribution of dense-core vesicles in C. elegans motor neurons.

PLoS One 2013 24;8(1):e54763. Epub 2013 Jan 24.

Department of Molecular Physiology and Pharmacology, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, USA.

The polarized trafficking of axonal and dendritic components is essential for the development and maintenance of neuronal structure and function. Neuropeptide-containing dense-core (DCVs) vesicles are trafficked in a polarized manner from the cell body to their sites of release; however, the molecules involved in this process are not well defined. Here we show that the scaffolding protein SYD-2/Liprin-α is required for the normal polarized localization of Venus-tagged neuropeptides to axons of cholinergic motor neurons in C. elegans. In syd-2 loss of function mutants, the normal polarized localization of INS-22 neuropeptide-containing DCVs in motor neurons is disrupted, and DCVs accumulate in the cell body and dendrites. Time-lapse microscopy and kymograph analysis of mobile DCVs revealed that syd-2 mutants exhibit decreased numbers of DCVs moving in both anterograde and retrograde directions, and a corresponding increase in stationary DCVs in both axon commissures and dendrites. In addition, DCV run lengths and velocities were decreased in both axon commissures and dendrites of syd-2 mutants. This study shows that SYD-2 promotes bi-directional mobility of DCVs and identifies SYD-2 as a novel regulator of DCV trafficking and polarized distribution.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0054763PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3554613PMC
September 2013

The role of deubiquitinating enzymes in synaptic function and nervous system diseases.

Neural Plast 2012 18;2012:892749. Epub 2012 Dec 18.

Department of Biological Sciences, Butler University, Indianapolis, IN 46208, USA.

Posttranslational modification of proteins by ubiquitin has emerged as a critical regulator of synapse development and function. Ubiquitination is a reversible modification mediated by the concerted action of a large number of specific ubiquitin ligases and ubiquitin proteases, called deubiquitinating enzymes (DUBs). The balance of activity of these enzymes determines the localization, function, and stability of target proteins. While some DUBs counter the action of specific ubiquitin ligases by removing ubiquitin and editing ubiquitin chains, other DUBs function more generally to maintain the cellular pool of free ubiquitin monomers. The importance of DUB function at the synapse is underscored by the association of specific mutations in DUB genes with several neurological disorders. Over the last decade, although much research has led to the identification and characterization of many ubiquitin ligases at the synapse, our knowledge of the relevant DUBs that act at the synapse has lagged. This review is focused on highlighting our current understanding of DUBs that regulate synaptic function and the diseases that result from dysfunction of these DUBs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1155/2012/892749DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3536295PMC
April 2013

The kinesin-3 family motor KLP-4 regulates anterograde trafficking of GLR-1 glutamate receptors in the ventral nerve cord of Caenorhabditis elegans.

Mol Biol Cell 2012 Sep 1;23(18):3647-62. Epub 2012 Aug 1.

Department of Molecular Physiology and Pharmacology, Tufts University School of Medicine, Boston, MA 02111, USA.

The transport of glutamate receptors from the cell body to synapses is essential during neuronal development and may contribute to the regulation of synaptic strength in the mature nervous system. We previously showed that cyclin-dependent kinase-5 (CDK-5) positively regulates the abundance of GLR-1 glutamate receptors at synapses in the ventral nerve cord (VNC) of Caenorhabditis elegans. Here we identify a kinesin-3 family motor klp-4/KIF13 in a cdk-5 suppressor screen for genes that regulate GLR-1 trafficking. klp-4 mutants have decreased abundance of GLR-1 in the VNC. Genetic analysis of klp-4 and the clathrin adaptin unc-11/AP180 suggests that klp-4 functions before endocytosis in the ventral cord. Time-lapse microscopy indicates that klp-4 mutants exhibit decreased anterograde flux of GLR-1. Genetic analysis of cdk-5 and klp-4 suggests that they function in the same pathway to regulate GLR-1 in the VNC. Interestingly, GLR-1 accumulates in cell bodies of cdk-5 but not klp-4 mutants. However, GLR-1 does accumulate in klp-4-mutant cell bodies if receptor degradation in the multivesicular body/lysosome pathway is blocked. This study identifies kinesin KLP-4 as a novel regulator of anterograde glutamate receptor trafficking and reveals a cellular control mechanism by which receptor cargo is targeted for degradation in the absence of its motor.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1091/mbc.E12-04-0334DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3442412PMC
September 2012

Cyclin-dependent kinase 5 regulates the polarized trafficking of neuropeptide-containing dense-core vesicles in Caenorhabditis elegans motor neurons.

J Neurosci 2012 Jun;32(24):8158-72

Department of Molecular Physiology and Pharmacology, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.

The polarized trafficking of axonal and dendritic proteins is essential for the structure and function of neurons. Cyclin-dependent kinase 5 (CDK-5) and its activator CDKA-1/p35 regulate diverse aspects of nervous system development and function. Here, we show that CDK-5 and CDKA-1/p35 are required for the polarized distribution of neuropeptide-containing dense-core vesicles (DCVs) in Caenorhabditis elegans cholinergic motor neurons. In cdk-5 or cdka-1/p35 mutants, the predominantly axonal localization of DCVs containing INS-22 neuropeptides was disrupted and DCVs accumulated in dendrites. Time-lapse microscopy in DB class motor neurons revealed decreased trafficking of DCVs in axons and increased trafficking and accumulation of DCVs in cdk-5 mutant dendrites. The polarized distribution of several axonal and dendritic markers, including synaptic vesicles, was unaltered in cdk-5 mutant DB neurons. We found that microtubule polarity is plus-end out in axons and predominantly minus-end out in dendrites of DB neurons. Surprisingly, cdk-5 mutants had increased amounts of plus-end-out microtubules in dendrites, suggesting that CDK-5 regulates microtubule orientation. However, these changes in microtubule polarity are not responsible for the increased trafficking of DCVs into dendrites. Genetic analysis of cdk-5 and the plus-end-directed axonal DCV motor unc-104/KIF1A suggest that increased trafficking of UNC-104 into dendrites cannot explain the dendritic DCV accumulation. Instead, we found that mutations in the minus-end-directed motor cytoplasmic dynein, completely block the increased DCVs observed in cdk-5 mutant dendrites without affecting microtubule polarity. We propose a model in which CDK-5 regulates DCV polarity by both promoting DCV trafficking in axons and preventing dynein-dependent DCV trafficking into dendrites.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.0251-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3392131PMC
June 2012

The deubiquitinating enzyme USP-46 negatively regulates the degradation of glutamate receptors to control their abundance in the ventral nerve cord of Caenorhabditis elegans.

J Neurosci 2011 Jan;31(4):1341-54

Department of Molecular Physiology and Pharmacology, Tufts University School of Medicine, Boston, MA 02111, USA.

Ubiquitin-mediated endocytosis and post-endocytic trafficking of glutamate receptors control their synaptic abundance and are implicated in modulating synaptic strength. Ubiquitination is a reversible modification, but the identities and specific functions of deubiquitinating enzymes in the nervous system are lacking. Here, we show that the deubiquitinating enzyme ubiquitin-specific protease-46 (USP-46) regulates the abundance of the glutamate receptor GLR-1 in the ventral nerve cord of Caenorhabditis elegans. Mutants lacking usp-46 have decreased GLR-1 in the ventral nerve cord and corresponding defects in GLR-1-dependent behaviors. The amount of ubiquitinated GLR-1 is increased in usp-46 mutants. Mutations that block GLR-1 ubiquitination or receptor degradation in the multi-vesicular body/lysosome prevent the decrease in GLR-1 observed in usp-46 mutants. These data support a model in which USP-46 promotes GLR-1 abundance at synapses by deubiquitinating GLR-1 and preventing its degradation in the lysosome. This work suggests that the balance between the addition and removal of ubiquitin is important for glutamate receptor trafficking.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.4765-10.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3084541PMC
January 2011

CDK-5 regulates the abundance of GLR-1 glutamate receptors in the ventral cord of Caenorhabditis elegans.

Mol Biol Cell 2007 Oct 1;18(10):3883-93. Epub 2007 Aug 1.

Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02114, USA.

The proline-directed kinase Cdk5 plays a role in several aspects of neuronal development. Here, we show that CDK-5 activity regulates the abundance of the glutamate receptor GLR-1 in the ventral cord of Caenorhabditis elegans and that it produces corresponding changes in GLR-1-dependent behaviors. Loss of CDK-5 activity results in decreased abundance of GLR-1 in the ventral cord, accompanied by accumulation of GLR-1 in neuronal cell bodies. Genetic analysis of cdk-5 and the clathrin adaptin unc-11 AP180 suggests that CDK-5 functions prior to endocytosis at the synapse. The scaffolding protein LIN-10/Mint-1 also regulates GLR-1 abundance in the nerve cord. CDK-5 phosphorylates LIN-10/Mint-1 in vitro and bidirectionally regulates the abundance of LIN-10/Mint-1 in the ventral cord. We propose that CDK-5 promotes the anterograde trafficking of GLR-1 and that phosphorylation of LIN-10 may play a role in this process.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1091/mbc.e06-09-0818DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1995742PMC
October 2007

The anaphase-promoting complex regulates the abundance of GLR-1 glutamate receptors in the ventral nerve cord of C. elegans.

Curr Biol 2004 Nov;14(22):2057-62

Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, MA 02114, USA.

The anaphase-promoting complex (APC) is a multisubunit E3 ubiquitin ligase that targets key cell cycle regulatory proteins for degradation. Blockade of APC activity causes mitotic arrest. Recent evidence suggests that the APC may have roles outside the cell cycle. Several studies indicate that ubiquitin plays an important role in regulating synaptic strength. We previously showed that ubiquitin is directly conjugated to GLR-1, a C. elegans non-NMDA (N-methyl-D-aspartate) class glutamate receptor (GluR), resulting in its removal from synapses. By contrast, endocytosis of rodent AMPA GluRs is apparently regulated by ubiquitination of associated scaffolding proteins. Relatively little is known about the E3 ligases that mediate these effects. We examined the effects of perturbing APC function on postmitotic neurons in the nematode C. elegans. Temperature-sensitive mutations in APC subunits increased the abundance of GLR-1 in the ventral nerve cord. Mutations that block clathrin-mediated endocytosis blocked the effects of the APC mutations, suggesting that the APC regulates some aspect of GLR-1 recycling. Overexpression of ubiquitin decreased the density of GLR-1-containing synapses, and APC mutations blunted this effect. APC mutants had locomotion defects consistent with increased synaptic strength. This study defines a novel function for the APC in postmitotic neurons.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cub.2004.11.010DOI Listing
November 2004