Ubiquitin-Dependent Regulation of the Synapse (original) (raw)

The Ubiquitin Proteasome System Acutely Regulates Presynaptic Protein Turnover and Synaptic Efficacy

Current Biology, 2003

East ubiquitin ligase (E3) to attach ubiquitin to an internal University of Utah lysine residue of the substrate protein ( ). Sub-Salt Lake City, Utah 84112-0840 strate specificity is typically attributed to the ubiquitin 2 Department of Biological Sciences ligase, which can recognize various signals including Vanderbilt University primary sequence and posttranslational modifications VU Station B to regulate ubiquitylation of the substrate. Attachment Box 351634 of ubiquitin to cellular proteins can serve as a signal for Nashville, Tennessee 37235-1634 a growing number of biological processes, including degradation by the proteasome or endocytosis and trafficking to the lysosomal pathway. The tightly regulated Summary cascade controlling protein degradation via the proteasome has pivotal regulatory roles in a wide spectrum of Background: The ubiquitin proteasome system (UPS) cellular processes, ranging from cell cycle control to mediates regulated protein degradation and provides a modulation of the immune response. Therefore, it is surmechanism for closely controling protein abundance in prising that little work has been done to investigate putaspatially restricted domains within cells. We hypothetive functional roles of the (UPS) in the mature nervous sized that the UPS may acutely determine the local consystem, particularly in the regulation of the complex centration of key regulatory proteins at neuronal synprotein cycles that acutely modulate the efficacy of synapses as a means for locally modulating synaptic aptic transmission. efficacy and the strength of neurotransmission commu-Recent work has begun to reveal roles for ubiquitinnication. dependent processes in neuronal development, espe-Results: We investigated this hypothesis at the Drocially during synapse formation and modulation. In Drosophila neuromuscular synapse by using an array of sophila, ubiquitin conjugation triggers the endocytosis genetic and pharmacological tools. This study demonof signaling proteins with key guidance functions in axostrates that UPS components are present in presynaptic nal pathfinding [1]. At the Drosophila neuromuscular boutons and that the UPS functions locally in the presynjunction (NMJ), both functional and anatomical synaptic aptic compartment to rapidly eliminate a conditional development is regulated by a balance between ubiquitransgenic reporter of proteasome activity. We assayed tylation and de-ubiquitylation [2]. Recent studies of C. a panel of synaptic proteins to determine whether the elegans central synapses have shown that ubiquitin is UPS acutely regulates the local abundance of native also involved in the endocytosis and possible degradasynaptic targets. Both acute pharmacological inhibition tion of the glutamate receptor subunit GLR-1 at postsynof the proteasome (Ͻ1 hr) and targeted genetic perturaptic sites [3].The authors propose that this mechanism bation of proteasome function in the presynaptic neuron may regulate the strength of synaptic transmission; mucause the specific accumulation of the essential synaptations that decrease GLR-1 ubiquitylation also increase tic vesicle-priming protein DUNC-13. Most importantly, locomotory activity. These Drosophila and C. elegans acute pharmacological inhibition of the proteasome (Ͻ1 studies clearly demonstrate that ubiquitin-dependent hr) causes a rapid strengthening of neurotransmission mechanisms play vital roles in synapses, most particu-(an approximately 50% increase in evoked amplitude) larly in regulating endocytosis to control protein traffickbecause of increased presynaptic efficacy. The proing to and from the plasma membrane. However, the teasome-dependent regulation of presynaptic protein direct involvement of proteasomal protein degradation abundance, both of the exogenous reporter and native in regulating these synaptic mechanisms is unclear. DUNC-13, and the modulation of presynaptic neuro-In addition to developmental functions, the UPS has transmitter release occur on an intermediate, rapid tens also been implicated in the manifestation of long-term of minutes) timescale. synaptic plasticity. Recent studies in Aplysia synapses Conclusions: Taken together, these studies demonhave demonstrated that transition from short-term facilistrate that the UPS functions locally within synaptic boutation (STF) to long-term facilitation (LTF) depends on tons to acutely control levels of presynaptic protein and proteasome-mediated protein degradation [4]. Similarly, that the rate of UPS-dependent protein degradation is in rat synapses the transition from short-term potentiaa primary determinant of neurotransmission strength. tion (STP) to long-term potentiation (LTP) requires UPS function in the hippocampus [5]. Null mutations in the Introduction E3 ubiquitin ligase E6-AP prevent this synaptic plasticity transition in mouse hippocampal neurons [6]. To date, The attachment of ubiquitin to substrate proteins is aconly a few synaptic proteins have been identified as complished via a regulated cascade of enzymes beginsubstrates of ubiquitin attachment; ␣-synuclein [7], synphilin [8], and CDCrel-1 [9] are ubiquitylated by the ubi-Correspondence: kendal.broadie@vanderbilt.edu Current Biology 900

Rapid Ca2+-dependent decrease of protein ubiquitination at synapses

Proceedings of the National Academy of Sciences, 2003

Protein ubiquitination has been implicated in the regulation of axonal growth and synaptic plasticity as well as in the pathogenesis of neurodegenerative diseases. Here we show that depolarization-dependent Ca 2؉ influx into synaptosomes produces a global, rapid (range of seconds), and reversible decrease of the ubiquitinated state of proteins, which correlates with the Ca 2؉dependent dephosphorylation of several synaptic proteins. A similar general decrease in protein ubiquitination was observed in nonneuronal cells on Ca 2؉ entry induced by ionomycin. Both in synaptosomes and in nonneuronal cells, this decrease was blocked by FK506 (a calcineurin antagonist). Proteins whose ubiquitinated state was decreased include epsin 1, a substrate for the deubiquitinating enzyme fat facets͞FAM, which we show here to be concentrated at synapses. These results reveal a fast regulated turnover of protein ubiquitination. In nerve terminals, protein ubiquitination may play a role both in the regulation of synaptic function, including vesicle traffic, and in the coordination of protein turnover with synaptic use.

The HERC1 ubiquitin ligase regulates presynaptic membrane dynamics of central synapses

Scientific Reports, 2020

HERC1 is a ubiquitin ligase protein, which, when mutated, induces several malformations and intellectual disability in humans. The animal model of HERC1 mutation is the mouse tambaleante characterized by: (1) overproduction of the protein; (2) cerebellar Purkinje cells death by autophagy; (3) dysregulation of autophagy in spinal cord motor neurons, and CA3 and neocortical pyramidal neurons; (4) impairment of associative learning, linked to altered spinogenesis and absence of LTP in the lateral amygdala; and, (5) motor impairment due to delayed action potential transmission, decrease synaptic transmission efficiency and altered myelination in the peripheral nervous system. To investigate the putative role of HERC1 in the presynaptic dynamics we have performed a series of experiments in cultured tambaleante hippocampal neurons by using transmission electron microscopy, FM1-43 destaining and immunocytochemistry. Our results show: (1) a decrease in the number of synaptic vesicles; (2) r...

The Role of Deubiquitinating Enzymes in Synaptic Function and Nervous System Diseases

Neural Plasticity, 2012

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 l...

Multiple ubiquitin conjugates are present in rat brain synaptic membranes and postsynaptic densities

Neuroscience Letters, 1994

The pattern of ubiquitin-protein conjugates present in a range of adult rat forebrain subcellular fractions has been investigated by immunoblotting with a monoclonal antibody specific for ubiquitin and its conjugates. Each fraction contains a complex and characteristic pattern of ubiquitin conjugates. Many integral synaptic membrane proteins are ubiquitinated, including a subset of high M r (> 120 kD) concanavalin A-binding glycoproteins. Postsynaptic densities are also enriched in ubiquitin conjugates, the profile being distinct from that of synaptic membranes. These results suggest that many plasma membrane and synaptic proteins are ubiquitinated.

Think locally: control of ubiquitin-dependent protein degradation in neurons

EMBO reports, 2009

The nervous system coordinates many aspects of body function such as learning, memory, behaviour and locomotion. Therefore, it must develop and maintain an intricate network of differentiated neuronal cells, which communicate efficiently with each other and with non-neuronal target cells. Unlike most somatic cells, differentiated neurons are post-mitotic and characterized by a highly polarized morphology that determines the flow of information. Among other post-translational modifications, the ubiquitination of specific protein substrates was recently shown to have a crucial role in the regulation of neuronal development and differentiation. Here, we review recent findings that illustrate the mechanisms that mediate the temporal and spatial control of neuronal protein turnover by the ubiquitin-proteasome system (UPS), which is crucial for the development and function of the nervous system.

Ubiquitination of Neurotransmitter Receptors and Postsynaptic Scaffolding Proteins

Neural Plasticity, 2013

The human brain is made up of an extensive network of neurons that communicate by forming specialized connections called synapses. The amount, location, and dynamic turnover of synaptic proteins, including neurotransmitter receptors and synaptic scaffolding molecules, are under complex regulation and play a crucial role in synaptic connectivity and plasticity, as well as in higher brain functions. An increasing number of studies have established ubiquitination and proteasome-mediated degradation as universal mechanisms in the control of synaptic protein homeostasis. In this paper, we focus on the role of the ubiquitin-proteasome system (UPS) in the turnover of major neurotransmitter receptors, including glutamatergic and nonglutamatergic receptors, as well as postsynaptic receptor-interacting proteins.

The ubiquitin proteasome system functions as an inhibitory constraint on synaptic strengthening

Current biology : CB, 2003

Long-lasting forms of synaptic plasticity have been shown to depend on changes in gene expression. Although many studies have focused on the regulation of transcription and translation during learning-related synaptic plasticity, regulated protein degradation provides another common means of altering the macromolecular composition of cells. We have investigated the role of the ubiquitin proteasome system in long-lasting forms of learning-related plasticity in Aplysia sensory-motor synapses. We find that inhibition of the proteasome produces a long-lasting (24 hr) increase in synaptic strength between sensory and motor neurons and that it dramatically enhances serotonin-induced long-term facilitation. The increase in synaptic strength produced by proteasome inhibitors is dependent on translation but not transcription. In addition to the increase in synaptic strength, proteasome inhibition leads to an increase in the number of synaptic contacts formed between the sensory and motor neu...

Ubiquitination Acutely Regulates Presynaptic Neurotransmitter Release in Mammalian Neurons

Journal of Neuroscience, 2010

The ubiquitin proteasome system (UPS) plays a crucial role in modulating synaptic physiology both presynaptically and postsynaptically, but the regulatory mechanisms remain obscure. To determine acute effects of proteasome inhibition on neurotransmission, we performed whole-cell voltage-clamp recordings from cultured rodent hippocampal neurons. We find that proteasome inhibitors induce a strikingly fast, severalfold increase in the frequency of both miniature (mini) and spontaneous synaptic currents at excitatory and inhibitory synapses. The lack of change in mini amplitude and kinetics indicates a presynaptic site of action. This effect does not depend on increased levels of presynaptic proteins, previously suggested as proteasomal targets. Furthermore, blockade of the UPS using E1-activating enzyme inhibitors also increases mini frequency, demonstrating that accumulation of ubiquitinated proteins is not required. Overall, these data suggest that the UPS not only orchestrates protein turnover, but also dynamically regulates the activity state of presynaptic proteins, thus crucially shaping synaptic transmission.