The Two Regulatory Subunits of Aplysia cAMP-Dependent Protein Kinase Mediate Distinct Functions in Producing Synaptic Plasticity (original) (raw)
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2013
Activation of the cAMP-dependent protein kinase (PKA) is critical for both short- and long-term facilitation in Aplysia sensory neurons. There are two types of the kinase, I and II, differing in their regulatory (R) subunits. We cloned Aplysia RII; RI was cloned previously. Type I PKA is mostly soluble in the cell body whereas type II is enriched at nerve endings where it is bound to two prominent A kinaseanchoring-proteins (AKAPs). Disruption of the binding of RII to AKAPs by Ht31, an inhibitory peptide derived from a human thyroid AKAP, prevents both the short- and the long-term facilitation produced by serotonin (5-HT). During long-term facilitation, RII is transcriptionally upregulated; in contrast, the amount of RI subunits decreases, and previous studies have indicated that the decrease is through ubiquitin–proteosome-mediated proteolysis. Experiments with antisense oligonucleotides injected into the sensory neuron cell body show that the increase in RII protein is essential f...
Modulation of a cAMP/protein kinase A cascade by protein kinase C in sensory neurons of Aplysia
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
The synaptic connections between the sensory neurons of Aplysia and their follower neurons have been used as a model system for examining the cellular mechanisms contributing to neuronal and synaptic plasticity. Recent studies suggest that at least two protein kinases, protein kinase A (PKA) and protein kinase C (PKC), contribute to serotonin (5-HT)-induced short-term facilitation. The interaction between these two kinase cascades has not been examined, however. Using electrophysiological and biochemical approaches, we examined possible interactions between PKA and PKC cascades. The results indicated that prolonged activation of PKC by preincubation with phorbol esters attenuated PKA-mediated actions of 5-HT, including increases in sensory neuron excitability and spike broadening in the presence of tetraethylammonium (TEA) and nifedipine. Although phorbol esters also attenuated increases in excitability by an analog of cAMP and small cardioactive peptide B (SCPB), the degree of atte...
Neuron, 1999
What are the downstream events produced by CREB? In addition to the activation of genes that regulate the synthesis of new proteins, such as the transcription factor ApC/EBP (Alberini et al., 1994), Hegde et al. (1997) found that the induction of the immediate-early gene (IEG) ubiquitin carboxy-terminal hydrolase (Ap-uch) is College of Physicians and Surgeons essential for LTF. This deubiquitinase, which is neuron-New York, New York 10032 specific, belongs to a diverse class of isopeptidases † Department of Cell Biology with several functions, among which is the enhancement Harvard Medical School of proteolysis by proteasomes (Eytan et al., 1993; Wilkin-Boston, Massachusetts 02115 son, 1997). The degradation of proteins by the ubiquitin-proteasome pathway has been implicated in regulating several Summary important cellular processes (Mykles, 1998), including transcriptional activation (Verma et al., 1995), progres-The formation of a persistently active cAMP-depension through the cell cycle (Pagano, 1997), apoptosis dent protein kinase (PKA) is critical for establishing (Hale et al., 1996), antigen presentation (Rock et al., long-term synaptic facilitation (LTF) in Aplysia. The 1994), differentiation and growth (Zhu et al., 1996), musinjection of bovine catalytic (C) subunits into sensory cle atrophy (Mitch and Goldberg, 1996), and synaptoneurons is sufficient to produce protein synthesisgenesis (Muralidhar and Thomas, 1993; Oh et al., 1994).
Neuron, 1992
Two second messenger pathways, one that uses the CAMP-dependent protein kinase A (PKA), the other that uses protein kinase C (PKC), have been found to contribute to the short-term presynaptic facilitation of the connections between the sensory neurons in Aplysia and their target cells, the interneurons and motor neurons of the gill-withdrawal reflex. To study their relative contributions as a function of the previous history of the neuron's activity, we have examined the effects of inhibiting PKA (using Rp-CAMPS) and PKC (using H7) on the shortterm facilitation of spontaneous release as well as of the evoked release induced by serotonin at nondepressed, partially depressed, and highly depressed synapses. Our results suggest that whereas activation of PKA is sufficient to trigger the facilitation of nondepressed synapses, activation of both PKA and PKC is required to facilitate depressed synapses, with the contribution of PKC becoming progressively more important as synaptic transmission becomes more depressed.
Proceedings of the …, 1993
In Aplysia, behavioral sensitization of defensive reflexes and the underlying presynaptic facilitation of sensory-to-motor neuron synapses lasts for several minutes (short term) or days to weeks (long term). Short-term sensitization has been explained by modulation ofion-channel function through cAMP-dependent protein phosphorylation. Long-term facilitation requires additional molecular changes including protein synthesis. A key event is the persistent activation of the cAMP-dependent protein kinase at baseline concentrations of cAMP. This activation is due to selective loss of regulatory (R) subunits ofPKA without any change in catalytic (C) subunits. To understand the molecular mechanisms that produce the loss of R subunits in long-term facilitation, we investigated how R subunits are degraded in extracts of Aplysia nervous tissue and in rabbit reticulocyte lysates. Degradation ofAplysia R subunits requires ATP, ubiquitin, and a particulate component that appears to be the proteasome complex. Degradation is blocked by hemin, which causes the accumulation of high molecular weight derivatives of R subunits that are likely to be ubiquitin
Neuroscience, 2003
Activation of the extracellular signal-related kinase is important for long-term increases in synaptic strength in the Aplysia nervous system. However, there is little known about the mechanism for the activation of the kinase in this system. We examined the activation of Aplysia extracellular signal-related kinase using a phosphopeptide antibody specific to the sites required for activation of the kinase. We found that phorbol esters led to a prolonged activation of extracellular signal-related kinase in sensory cells of the Aplysia nervous system. Surprisingly, inhibitors of protein kinase C did not block this activation. Serotonin, the physiological transmitter involved in long-term synaptic facilitation, also led to prolonged activation of extracellular signal-related kinase, but inhibitors of protein kinase A or protein kinase C did not block this activation. We examined whether the protein synthesis-dependent increase in excitability stimulated by phorbol esters was dependent on phorbol ester activation of extracellular signal-related kinase, but increases in excitability were still seen in the presence of inhibitors of extracellular signal-related kinase activation. Our results suggest that prolonged phosphorylation of extracellular signal-related kinase in the Aplysia system is not mediated by either of the classic second messenger activated kinases in this system, protein kinase A or protein kinase C and that extracellular signal-related kinase is not important for phorbol ester induced long-term effects on excitability.
Neuron, 1997
program of cAMP-inducible gene expression and the and Eric R. Kandel* † synthesis of new proteins (Bailey et al., 1996). Both the *Howard Hughes Medical Institute and short-and long-term processes are represented on an † Center for Neurobiology and Behavior elementary, cellular level in the connections between College of Physicians and Surgeons of identified sensory neurons and motor neurons. The Columbia University monosynaptic pathway can be reconstituted in dissoci-New York State Psychiatric Institute ated cell culture, where 5-hydroxytryptamine (5-HT; se-New York, New York 10032 rotonin), a modulatory neurotransmitter normally re-‡ Molecular Neurobiology Laboratory leased by sensitizing stimuli, can substitute for the tail Institute for Molecular Biology and Genetics shock used during behavioral training in the intact ani-Department of Biology mal (Montarolo et al., 1986). In parallel to behavioral Program in Cognitive Sciences sensitization (Frost et al., 1985), a single application of Seoul National University 5-HT produces short-term changes in synaptic effec-San 56-1, Silim-dong, Kwanak-gu tiveness, whereas five spaced applications, or continu-Seoul 151-742 ous exposure for 1.5 hr, produce long-term changes Korea lasting 1 day or more. About 20 proteins have now been identified that are modified by repeated pulses of 5-HT (Barzilai et al., 1989; Summary Noel et al., 1993). Whereas the majority of these increase in their level of expression, five proteins are down-regu-The synaptic growth that accompanies 5-HT-induced lated by 5-HT. Four of these are immunoglobulin cell long-term facilitation of the sensory to motor neuron adhesion molecules related to the vertebrate neural cell connection in Aplysia is associated with the internaladhesion molecule (NCAM) and to Fasciclin II in Droization of apCAM at the surface membrane of the sensophila (Mayford et al., 1992). Using gold-conjugated sory neuron. We have now used epitope tags to exammonoclonal antibodies to apCAM, Bailey et al. (1992) ine the fate of each of the two apCAM isoforms found that within 1 hr of the application of 5-HT or cAMP, (membrane bound and GPI-linked) and find that only a second messenger activated by 5-HT, there is also a the transmembrane form is internalized. This internaldecrease in the density of apCAM at the surface memization can be blocked by overexpression of transbrane of the sensory neuron. There is no comparable membrane constructs with a single point mutation in change in the postsynaptic cell. This presynaptic downthe two MAPK consensus sites, as well as by injection regulation of preexisting cell adhesion molecules is of a specific MAPK antagonist into sensory neurons. achieved by a rapid and transient activation of the These data suggest MAPK phosphorylation at the endocytic pathway, leading to a protein synthesismembrane is important for the internalization of apdependent internalization of apCAM and its rerouting CAMs and, thus, may represent an early regulatory from a pathway of apparent recycling to a pathway that step in the growth of new synaptic connections that seems destined for degradation. Concomitant with the accompanies long-term facilitation. down-regulation of apCAM, 5-HT and cAMP also induce in the sensory neurons an increase in the expression of
Proceedings of the National Academy of Sciences, 1998
Long-term facilitation of the connections between the sensory and motor neurons of the gill-withdrawal ref lex in Aplysia requires five repeated pulses of serotonin (5-HT). The repeated pulses of 5-HT initiate a cascade of gene activation that leads ultimately to the growth of new synaptic connections. Several genes in this process have been identified, including the transcriptional regulators apCREB-1, apCREB-2, apC͞EBP, and the cell adhesion molecule ap-CAM, which is thought to be involved in the formation of new synaptic connections. Here we report that the transcriptional regulators apCREB-2 and apC͞EBP, as well as a peptide derived from the cytoplasmic domain of apCAM, are phosphorylated in vitro by Aplysia mitogen-activated protein kinase (apMAPK). We have cloned the cDNA encoding apMAPK and show that apMAPK activity is increased in sensory neurons treated with repeated pulses of 5-HT and by the cAMP pathway. These results suggest that apMAPK may participate with cAMP-dependent protein kinase during long-term facilitation in sensory cells by modifying some of the key elements involved in the consolidation of short-to long-lasting changes in synaptic strength.