RIM1alpha phosphorylation at Serine-413 by protein Kinase a is not required for presynaptic long-term plasticity or learning

Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2008; 105(38):14680-5. DOI: 10.1073/pnas.0806679105
Source: PubMed


Activation of presynaptic cAMP-dependent protein kinase A (PKA) triggers presynaptic long-term plasticity in synapses such as cerebellar parallel fiber and hippocampal mossy fiber synapses. RIM1alpha, a large multidomain protein that forms a scaffold at the presynaptic active zone, is essential for presynaptic long-term plasticity in these synapses and is phosphorylated by PKA at serine-413. Previous studies suggested that phosphorylation of RIM1alpha at serine-413 is required for presynaptic long-term potentiation in parallel fiber synapses formed in vitro by cultured cerebellar neurons and that this type of presynaptic long-term potentiation is mediated by binding of 14-3-3 proteins to phosphorylated serine-413. To test the role of serine-413 phosphorylation in vivo, we have now produced knockin mice in which serine-413 is mutated to alanine. Surprisingly, we find that in these mutant mice, three different forms of presynaptic PKA-dependent long-term plasticity are normal. Furthermore, we observed that in contrast to RIM1alpha KO mice, RIM1 knockin mice containing the serine-413 substitution exhibit normal learning capabilities. The lack of an effect of the serine-413 mutation of RIM1alpha is not due to compensation by RIM2alpha because mice carrying both the serine-413 substitution and a RIM2alpha deletion still exhibited normal long-term presynaptic plasticity. Thus, phosphorylation of serine-413 of RIM1alpha is not essential for PKA-dependent long-term presynaptic plasticity in vivo, suggesting that PKA operates by a different mechanism despite the dependence of long-term presynaptic plasticity on RIM1alpha.

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Available from: Pablo E Castillo, Dec 24, 2013
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    • "In addition, we found a minor role of PKA but a major relevance of Epac proteins as cAMP targets involved in preventing presynaptic silencing in cerebellar granule cells. In this context, in some presynaptic forms of long term plasticity dependent on cAMP and the active zone protein RIM1α [6], [49], the role of PKA remains controversial as presynaptic potentiation is unchanged in mice expressing a mutant form of RIM1 lacking the critical PKA phosphorylation site [50]. "
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    ABSTRACT: Cannabinoid receptors are the most abundant G protein-coupled receptors in the brain and they mediate retrograde short-term inhibition of neurotransmitter release, as well as long-term depression of synaptic transmission at many excitatory synapses. The induction of presynaptically silent synapses is a means of modulating synaptic strength, which is important for synaptic plasticity. Persistent activation of cannabinoid type 1 receptors (CB1Rs) mutes GABAergic terminals, although it is unclear if CB1Rs can also induce silencing at glutamatergic synapses. Cerebellar granule cells were transfected with VGLUT1-pHluorin to visualise the exo-endocytotic cycle. We found that prolonged stimulation (10 min) of cannabinoid receptors with the agonist HU-210 induces the silencing of previously active synapses. However, the presynaptic silencing induced by HU-210 is transient as it reverses after 20 min. cAMP with forskolin prevented CB1R-induced synaptic silencing, via activation of the Exchange Protein directly Activated by cAMP (Epac). Furthermore, Epac activation accelerated awakening of already silent boutons. Electron microscopy revealed that silencing was associated with synaptic vesicle (SV) redistribution within the nerve terminal, which diminished the number of vesicles close to the active zone of the plasma membrane. Finally, by combining functional and immunocytochemical approaches, we observed a strong correlation between the release capacity of the nerve terminals and RIM1α protein content, but not that of Munc13-1 protein. These results suggest that prolonged stimulation of cannabinoid receptors can transiently silence glutamatergic nerve terminals.
    PLoS ONE 02/2014; 9(2):e88594. DOI:10.1371/journal.pone.0088594 · 3.23 Impact Factor
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    • "Interestingly, Bassoon is not the only 14-3-3 interacting CAZ component. The interaction of 14-3-3 with RIM was suggested to be critical for the induction of presynaptic LTP [60], although this was controversially discussed later and the absence of a phosphorylation site in RIM did not cause an identifiable phenotype in vivo [61], [62] CAST and liprin-α were found to bind 14-3-3 in two independent proteomic screenings for 14-3-3 interaction partners [63], [64] but the function of these interactions was not investigated yet. We suggest, that phosphorylation of CAZ components and their binding by 14-3-3 might support their solubilization by interfering with the intermolecular interactions among them. "
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    ABSTRACT: The proper organization of the presynaptic cytomatrix at the active zone is essential for reliable neurotransmitter release from neurons. Despite of the virtual stability of this tightly interconnected proteinaceous network it becomes increasingly clear that regulated dynamic changes of its composition play an important role in the processes of synaptic plasticity. Bassoon, a core component of the presynaptic cytomatrix, is a key player in structural organization and functional regulation of presynaptic release sites. It is one of the most highly phosphorylated synaptic proteins. Nevertheless, to date our knowledge about functions mediated by any one of the identified phosphorylation sites of Bassoon is sparse. In this study, we have identified an interaction of Bassoon with the small adaptor protein 14-3-3, which depends on phosphorylation of the 14-3-3 binding motif of Bassoon. In vitro phosphorylation assays indicate that phosphorylation of the critical Ser-2845 residue of Bassoon can be mediated by a member of the 90-kDa ribosomal S6 protein kinase family. Elimination of Ser-2845 from the 14-3-3 binding motif results in a significant decrease of Bassoon's molecular exchange rates at synapses of living rat neurons. We propose that the phosphorylation-induced 14-3-3 binding to Bassoon modulates its anchoring to the presynaptic cytomatrix. This regulation mechanism might participate in molecular and structural presynaptic remodeling during synaptic plasticity.
    PLoS ONE 03/2013; 8(3):e58814. DOI:10.1371/journal.pone.0058814 · 3.23 Impact Factor
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    • "Some of the same forms of plasticity were also shown to be dependent on Rab3A (Castillo et al., 1997; Huang et al., 2005) or Rab3B (Tsetsenis et al., 2011), suggesting that RIM1a acts in long-term plasticity via binding to Rab3. It was initially thought that PKA-dependent phosphorylation of RIM1a at serine-413 controls long-term plasticity (Lonart et al., 2003), but knockin mice with a constitutive alanine substitution of serine-413 exhibited normal presynaptic LTP, ruling out this hypothesis (Kaeser et al., 2008b). "
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    ABSTRACT: Neurotransmitters are released by synaptic vesicle exocytosis at the active zone of a presynaptic nerve terminal. In this review, I discuss the molecular composition and function of the active zone. Active zones are composed of an evolutionarily conserved protein complex containing as core constituents RIM, Munc13, RIM-BP, α-liprin, and ELKS proteins. This complex docks and primes synaptic vesicles for exocytosis, recruits Ca(2+) channels to the site of exocytosis, and positions the active zone exactly opposite to postsynaptic specializations via transsynaptic cell-adhesion molecules. Moreover, this complex mediates short- and long-term plasticity in response to bursts of action potentials, thus critically contributing to the computational power of a synapse.
    Neuron 07/2012; 75(1):11-25. DOI:10.1016/j.neuron.2012.06.012 · 15.05 Impact Factor
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