Synaptic activation of ribosomal protein S6 phosphorylation occurs locally in activated dendritic domains (original) (raw)
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Phosphorylation of rpt6 regulates synaptic strength in hippocampal neurons
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012
It has become increasingly evident that protein degradation via the ubiquitin proteasome system plays a fundamental role in the development, maintenance and remodeling of synaptic connections in the CNS. We and others have recently described the activitydependent regulation of proteasome activity (Djakovic et al., 2009) and recruitment of proteasomes into spine compartments (Bingol and Schuman, 2006) involving the phosphorylation of the 19S ATPase subunit, Rpt6, by the plasticity kinase Ca 2ϩ /calmodulin-dependent protein kinase II ␣ (CaMKII␣) (Bingol et al., 2010). Here, we investigated the role of Rpt6 phosphorylation on proteasome function and synaptic strength. Utilizing a phospho-specific antibody we verified that Rpt6 is phosphorylated at Serine 120 (S120) by CaMKII␣. In addition, we found that Rpt6 is phosphorylated by CaMKII␣ in an activity-dependent manner. In addition, we showed that a serine 120 to aspartic acid phospho-mimetic mutant of Rpt6 (S120D) increases its resistance to detergent extraction in rat hippocampal dendrites, indicating phosphorylated Rpt6 may promote the tethering of proteasomes to scaffolds and cytoskeletal components. Interestingly, expression of Rpt6 S120D decreased miniature EPSC (mEPSC) amplitude, while expression of a phospho-dead mutant (S120A) increased mEPSC amplitude. Surprisingly, homeostatic scaling of mEPSC amplitude produced by chronic application of bicuculline or tetrodotoxin is both mimicked and occluded by altered Rpt6 phosphorylation. Together, these data suggest that CaMKII-dependent phosphorylation of Rpt6 at S120 may be an important regulatory mechanism for proteasome-dependent control of synaptic remodeling in slow homeostatic plasticity.
Frontiers in Molecular Neuroscience, 2017
The phosphorylation of the ribosomal protein S6 (rpS6) is widely used to track neuronal activity. Although it is generally assumed that rpS6 phosphorylation has a stimulatory effect on global protein synthesis in neurons, its exact biological function remains unknown. By using a phospho-deficient rpS6 knockin mouse model, we directly tested the role of phospho-rpS6 in mRNA translation, plasticity and behavior. The analysis of multiple brain areas shows for the first time that, in neurons, phospho-rpS6 is dispensable for overall protein synthesis. Instead, we found that phospho-rpS6 controls the translation of a subset of mRNAs in a specific brain region, the nucleus accumbens (Acb), but not in the dorsal striatum. We further show that rpS6 phospho-mutant mice display altered long-term potentiation (LTP) in the Acb and enhanced novelty-induced locomotion. Collectively, our findings suggest a previously unappreciated role of phospho-rpS6 in the physiology of the Acb, through the translation of a selective subclass of mRNAs, rather than the regulation of general protein synthesis.
Long-term potentiation and synaptic protein phosphorylation
Behavioural Brain Research, 1995
Long-term potentiation (LTP) is a well known experimental model for studying the activity-dependent enhancement of synaptic plasticity, and because of its long duration and its associative properties, it has been proposed as a system to investigate the molecular mechanisms of memory formation. At present, there are several lines of evidence that indicate that pre-and postsynaptic kinases and their specific substrates are involved in molecular mechanisms underlying LTP. Many studies focus on the involvement of protein kinase C (PKC). One way to investigate the role of PKC in long-term potentiation is to determine the degree of phosphorylation of its substrates after in situ phosphorylation in hippocampal slices. Two possible targets are the presynaptic membrane-associated protein B-50 (a.k.a. GAP 43, neuromodulin and F1), which has been implicated in different forms of synaptical plasticity in the brain such as neurite outgrowth, hippocampal LTP and neurotransmitter release, and the postsynaptic protein neurogranin (a.k.a. RC3, BICKS and p17) which function remains to be determined. This review will focus on the protein kinase C activity in pre-and postsynaptic compartment during the early phase of LTP and the possible involvement of its substrates B-50 and neurogranin.
Journal of Neurochemistry, 2004
The acute hippocampal slice preparation has been widely used to study the cellular mechanisms underlying activitydependent forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD). Although protein phosphorylation has a key role in LTP and LTD, little is known about how protein phosphorylation might be altered in hippocampal slices maintained in vitro. To begin to address this issue, we examined the effects of slicing and in vitro maintenance on phosphorylation of six proteins involved in LTP and/or LTD. We found that AMPA receptor (AMPAR) glutamate receptor 1 (GluR1) subunits are persistently dephosphorylated in slices maintained in vitro for up to 8 h. a calcium/calmodulin-dependent kinase II (aCamKII) was also strongly dephosphorylated during the first 3 h in vitro but thereafter recovered to near control levels. In contrast, phosphorylation of the extracellular signal-regulated kinase ERK2, the ERK kinase MEK, proline-rich tyrosine kinase 2 (Pyk2), and Src family kinases was significantly, but transiently, increased. Electrophysiological experiments revealed that the induction of LTD by low-frequency synaptic stimulation was sensitive to time in vitro. These findings indicate that phosphorylation of proteins involved in N-methyl-D-aspartate (NMDA) receptor-dependent forms of synaptic plasticity is altered in hippocampal slices and suggest that some of these changes can significantly influence the induction of LTD.
Regulation of Synaptic Strength by Protein Phosphatase 1
Neuron, 2001
synapses is modified to influence synaptic strength has 1 Nancy Pritzker Laboratory only recently begun to be analyzed, often in the context Department of Psychiatry and Behavioral Sciences of elucidating the mechanisms of synaptic plasticity. Stanford University School of Medicine Experiments using pharmacological inhibitors or ge-Palo Alto, California 94304 netic disruptions have implicated a myriad of signaling 2 Department of Pharmacology and Cancer Biology proteins. In particular, numerous protein kinases have Duke University Medical Center been implicated in the triggering of long-term potentia-Durham, North Carolina 27710 tion (LTP) (Malenka and Nicoll, 1999; Sanes and Licht-3 Department of Biology, Neurobiology, man, 1999). These include PKA, PKC, and CaMKII, all and Cognitive Sciences of which can modulate glutamate receptor function by University of Maryland phosphorylation of specific AMPA receptor (AMPAR) College Park, Maryland 20742 subunits (Soderling and Derkach, 2000). PKA appears to be anchored adjacent to AMPARs via AKAP79 (A-kinase anchoring protein) (Colledge et al., 2000), while its Summary ability to modulate NMDA receptor (NMDAR) function may be due to its binding to the scaffolding protein We investigated the role of postsynaptic protein phosyotiao (Fraser and Scott, 1999). CaMKII can bind directly phatase 1 (PP1) in regulating synaptic strength by to the intracellular tail of NMDAR subunits (Bayer et al., loading CA1 pyramidal cells either with peptides that 2001; Leonard et al., 1999; Strack and Colbran, 1998), disrupt PP1 binding to synaptic targeting proteins or
Molecular Brain, 2015
Background: Sustained changes in network activity cause homeostatic synaptic plasticity in part by altering the postsynaptic accumulation of N-methyl-D-aspartate receptors (NMDAR) and α-amino-3-hydroxyle-5-methyl-4isoxazolepropionic acid receptors (AMPAR), which are primary mediators of excitatory synaptic transmission. A key trafficking modulator of NMDAR and AMPAR is STriatal-Enriched protein tyrosine Phosphatase (STEP 61) that opposes synaptic strengthening through dephosphorylation of NMDAR subunit GluN2B and AMPAR subunit GluA2. However, the role of STEP 61 in homeostatic synaptic plasticity is unknown. Findings: We demonstrate here that prolonged activity blockade leads to synaptic scaling, and a concurrent decrease in STEP 61 level and activity in rat dissociated hippocampal cultured neurons. Consistent with STEP 61 reduction, prolonged activity blockade enhances the tyrosine phosphorylation of GluN2B and GluA2 whereas increasing STEP 61 activity blocks this regulation and synaptic scaling. Conversely, prolonged activity enhancement increases STEP 61 level and activity, and reduces the tyrosine phosphorylation and level of GluN2B as well as GluA2 expression in a STEP 61-dependent manner. Conclusions: Given that STEP 61-mediated dephosphorylation of GluN2B and GluA2 leads to their internalization, our results collectively suggest that activity-dependent regulation of STEP 61 and its substrates GluN2B and GluA2 may contribute to homeostatic stabilization of excitatory synapses.
Phosphorylation of synapsin domain A is required for post-tetanic potentiation
Journal of Cell Science, 2007
Post-tetanic potentiation (PTP) is a form of homosynaptic plasticity important for information processing and short-term memory in the nervous system. The synapsins, a family of synaptic vesicle (SV)-associated phosphoproteins, have been implicated in PTP. Although several synapsin functions are known to be regulated by phosphorylation by multiple protein kinases, the role of individual phosphorylation sites in synaptic plasticity is poorly understood. All the synapsins share a phosphorylation site in the N-terminal domain A (site 1) that regulates neurite elongation and SV mobilization. Here, we have examined the role of phosphorylation of synapsin domain A in PTP and other forms of short-term synaptic enhancement (STE) at synapses between cultured Helix pomatia neurons. To this aim, we cloned H. pomatia synapsin (helSyn) and overexpressed GFPtagged wild-type helSyn or site-1-mutant helSyn mutated in the presynaptic compartment of C1-B2 synapses. We found that PTP at these synapses depends both on Ca 2+ /calmodulin-dependent and cAMP-dependent protein kinases, and that overexpression of the non-phosphorylatable helSyn mutant, but not wild-type helSyn, specifically impairs PTP, while not altering facilitation and augmentation. Our findings show that phosphorylation of site 1 has a prominent role in the expression of PTP, thus defining a novel role for phosphorylation of synapsin domain A in shortterm homosynaptic plasticity.
Tyrosine Phosphatase STEP Is a Tonic Brake on Induction of Long-Term Potentiation
Neuron, 2002
Huang et al., 2001; Lu et al., 1998). Thus, tyrosine phosphorylation has emerged as a key regulator of NMDAR function and thereby of excitatory synaptic transated with the receptor (Wang et al., 1996) but the identity of this PTP has remained elusive. PTPs are a large, Canada 4 The Child Study Center structurally diverse superfamily of enzymes which may have exquisite specificity of their effects in cells (Tonks Yale University School of Medicine New Haven, Connecticut 06520 and Neel, 2001). A number of PTPs have been shown to be expressed in the CNS, the majority of which are receptor-type PTPs, which have been implicated in neuronal morphogenesis, neural development, and axon Summary guidance (Arregui et al., 2000; Naegele and Lombroso, 1994; Stoker and Dutta, 1998; Stoker, 2001). The level The functional roles of protein tyrosine phosphatases (PTPs) in the developed CNS have been enigmatic.
Nucleolar integrity is required for the maintenance of long-term synaptic plasticity
PloS one, 2014
Long-term memory (LTM) formation requires new protein synthesis and new gene expression. Based on our work in Aplysia, we hypothesized that the rRNA genes, stimulation-dependent targets of the enzyme Poly(ADP-ribose) polymerase-1 (PARP-1), are primary effectors of the activity-dependent changes in synaptic function that maintain synaptic plasticity and memory. Using electrophysiology, immunohistochemistry, pharmacology and molecular biology techniques, we show here, for the first time, that the maintenance of forskolin-induced late-phase long-term potentiation (L-LTP) in mouse hippocampal slices requires nucleolar integrity and the expression of new rRNAs. The activity-dependent upregulation of rRNA, as well as L-LTP expression, are poly(ADP-ribosyl)ation (PAR) dependent and accompanied by an increase in nuclear PARP-1 and Poly(ADP) ribose molecules (pADPr) after forskolin stimulation. The upregulation of PARP-1 and pADPr is regulated by Protein kinase A (PKA) and extracellular signal-regulated kinase (ERK)-two kinases strongly associated with long-term plasticity and learning and memory. Selective inhibition of RNA Polymerase I (Pol I), responsible for the synthesis of precursor rRNA, results in the segmentation of nucleoli, the exclusion of PARP-1 from functional nucleolar compartments and disrupted L-LTP maintenance. Taken as a whole, these results suggest that new rRNAs (28S, 18S, and 5.8S ribosomal components)-hence, new ribosomes and nucleoli integrity-are required for the maintenance of long-term synaptic plasticity. This provides a mechanistic link between stimulation-dependent gene expression and the new protein synthesis known to be required for memory consolidation.
2019
Dynamic control of protein degradation via the ubiquitin proteasome system is thought to play a crucial role in neuronal function and synaptic plasticity. The proteasome subunit Rpt6, an AAA ATPase subunit of the 19S regulatory particle, has emerged as an important site for regulation of 26S proteasome function in neurons. Phosphorylation of Rpt6 on serine 120 (S120) can stimulate the catalytic rate of substrate degradation by the 26S proteasome and this site is targeted by the plasticity-related kinase calcium/calmodulin-dependent kinase II (CaMKII), making it an attractive candidate for regulation of proteasome function in neurons. Several in vitro studies have shown that altered Rpt6 S120 phosphorylation can affect the structure and function of synapses. To evaluate the importance of Rpt6 S120 phosphorylation in vivo, we created two mouse models which feature mutations at S120 that block or mimic phosphorylation at this site. We find that peptidase and ATPase activities are upreg...