Triad3A Regulates Synaptic Strength by Ubiquitination of Arc

Homeostatic plasticity is a negative feedback mechanism that stabilizes neurons during periods of perturbed activity. The best-studied form of homeostatic plasticity in the central nervous system is the scaling of excitatory synapses. Postsynaptic AMPA-type glutamate receptors (AMPARs) can be inserted into synapses to compensate for neuronal inactivity or removed to compensate for hyperactivity. However, the molecular mechanisms underlying the homeostatic regulation of AMPARs remain elusive. Here, we show that the expression of GRIP1, a multi-PDZ (postsynaptic density 95/discs large/zona occludens) domain AMPAR-binding protein, is bidirectionally altered by neuronal activity. Furthermore, we observe a subcellular redistribution of GRIP1 and a change in the binding of GRIP1 to GluA2 during synaptic scaling. Using a combination of biochemical, genetic, and electrophysiological methods, we find that loss of GRIP1 blocks the accumulation of surface AMPARs and the scaling up of synaptic strength that occur in response to chronic activity blockade. Collectively, our data point to an essential role of GRIP1-mediated AMPAR trafficking during inactivity-induced synaptic scaling.synaptic scaling | postsynaptic density | glutamate receptor | PDZ domain

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“…S1). This protein degradation pathway is mainly mediated via the ubiquitin-proteasome system (41)(42)(43).…”

Section: Discussionmentioning

confidence: 99%

GRIP1 is required for homeostatic regulation of AMPAR trafficking

Tan

Queenan

Huganir

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…All constructs were verified by sequencing. HA-tagged ubiquitin, pGL3-BAR, TK-Renilla, pHAGE β-catenin WT, and pHAGE β-catenin mutant constructs were were previously described (39,66,67). G76V-Ubiquitin-GFP was obtained from Addgene (23969).…”

Section: Methodsmentioning

confidence: 99%

The autism-linked UBE3A T485A mutant E3 ubiquitin ligase activates the Wnt/β-catenin pathway by inhibiting the proteasome

Paranjape

Walker

et al. 2017

Journal of Biological Chemistry

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UBE3A is a HECT domain E3 ubiquitin ligase whose dysfunction is linked to autism, Angelman syndrome, and cancer. Recently, we characterized a de novo autism-linked UBE3A mutant (UBE3A T485A ) that disrupts phosphorylation control of UBE3A activity. Through quantitative proteomics and reporter assays, we found that the UBE3A T485A protein ubiquitinates multiple proteasome subunits, reduces proteasome subunit abundance and activity, stabilizes nuclear β-catenin, and stimulates canonical Wnt signaling more effectively than wild-type UBE3A. We also found that UBE3A T485A activates Wnt signaling to a greater extent in cells with low levels of ongoing Wnt signaling, suggesting that cells with low basal Wnt activity are particularly vulnerable to UBE3A T485A mutation. Ligase-dead UBE3A did not stimulate Wnt pathway activation. Overexpression of several proteasome subunits reversed the effect of UBE3A T485A on Wnt signaling. We also observed that subunits that interact with UBE3A and affect Wnt signaling are located along one side of the 19S regulatory particle, indicating a previously unrecognized spatial organization to the proteasome. Altogether, our findings indicate that UBE3A regulates Wnt signaling in a cell context-dependent manner and that an autism-linked mutation exacerbates these signaling effects. Our study has broad implications for human disorders associated with UBE3A gain or lossof-function, and suggest that dysfunctional UBE3A might affect additional proteins and pathways that are sensitive to proteasome activity.

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“…Indeed, numerous neuronal E3s have been identified that functionally regulate specific levels of postsynaptic proteins. These include γ-actin (79), GKAP, and Shank (80), which are regulated by TRIM3, PSD95 by Mdm2 (13) upon facilitation by CDK5 (81), AMPARs by RNF167 (82), and the postsynaptic cytoskeletal protein and immediate early gene Arc by both UBE3A (83) and RNF216/TRIAD3 (84). Targeted ubiquitination of presynaptic proteins is also prominent.…”

Section: Discussionmentioning

confidence: 99%

The ubiquitin-proteasome system functionally links neuronal Tomosyn-1 to dendritic morphology

Saldate¹,

Shiau

Cazares

et al. 2018

Journal of Biological Chemistry

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Altering the expression of Tomosyn-1 (Tomo-1), a soluble, R-SNARE domaincontaining protein, significantly affects behavior in mice, Drosophila, and Caenorhabditis elegans. Yet, the mechanisms that modulate Tomo-1 expression and its regulatory activity remain poorly defined. Here, we found that Tomo-1 expression levels influence postsynaptic spine density. Tomo-1 overexpression increased dendritic spine density, while Tomo-1 knockdown (KD) decreased spine density. These findings identified a novel action of Tomo-1 on dendritic spines, which is unique because it occurs independently of Tomo-1's C-terminal R-SNARE domain. We also demonstrate that the ubiquitinproteasome system (UPS), which is known to influence synaptic strength, dynamically regulates Tomo-1 protein levels. Immunoprecipitated and affinity-purified Tomo-1 from cultured rat hippocampal neurons was ubiquitinated, and the levels of ubiquitinated Tomo-1 dramatically increased upon pharmacological proteasome blockade. Moreover, Tomo-1 ubiquitination appeared to be mediated through an interaction with the E3 ubiquitin ligase HRD1, as immunoprecipitation of Tomo-1 from neurons coprecipitated HRD1, and this interaction increases upon proteasome inhibition. Further, in vitro reactions indicated direct, HRD1 concentrationdependent Tomo-1 ubiquitination. We also noted that the UPS regulates both Tomo-1 expression and functional output, as HRD1 KD in hippocampal neurons increased Tomo-1 protein level and dendritic spine density. Notably, the effect of HRD1 KD on spine density was mitigated by additional KD of Tomo-1, indicating a direct HRD1/Tomo-1 effector relationship. In summary, our results indicate that the UPS is likely to participate in tuning synaptic efficacy and spine dynamics by precise regulation of neuronal Tomo-1 levels.

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Triad3A Regulates Synaptic Strength by Ubiquitination of Arc

Cited by 107 publications

References 50 publications

GRIP1 is required for homeostatic regulation of AMPAR trafficking

GRIP1 is required for homeostatic regulation of AMPAR trafficking

The autism-linked UBE3A T485A mutant E3 ubiquitin ligase activates the Wnt/β-catenin pathway by inhibiting the proteasome

The ubiquitin-proteasome system functionally links neuronal Tomosyn-1 to dendritic morphology

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