Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Protein ubiquitination has been implicated in ATP-dependent protein turnover and in a number of biological processes in eukaryotic cells. The ubiquitination activating enzyme, E1, and ubiquitin carrier protein, E2, are two essential enzymes in the protein ubiquitination machinery. Using purified E1 and E2 from rabbit reticulocytes and various protein kinases, which include cAMP-dependent protein kinase, protein kinase C, and protein tyrosine kinase, we demonstrated that E1 is phosphorylated by protein kinase C, with a stoichiometry of 0.65 mol of phosphate/mol of E1, and one of the E2 isoforms, E2(32kDa), is phosphorylated by protein tyrosine kinase to 2 eq of phosphate/mol of protein. Phosphorylation of E1 causes a 2-fold enhancement of its activity as monitored by ubiquitin-dependent ATP in equilibrium PPi exchange. When 1 eq of phosphate was incorporated into E2(32kDa), a 2.4-fold activation was also observed for its activity to catalyze the ubiquitination of histone H2A. The regulatory significance of this finding is discussed.
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PMID:Protein ubiquitination is regulated by phosphorylation. An in vitro study. 132 Nov 38

In response to the facilitating neurotransmitter serotonin (5-HT), the cAMP-dependent protein kinase (PKA) acquires a special mnemonic characteristic in Aplysia sensory neurons. PKA becomes persistently activated at basal cAMP concentrations owing to a decreased regulatory (R) to catalytic (C) subunit ratio. We previously implicated ubiquitin-mediated proteolysis in this selective loss of R. Here we show that ubiquitin (Ub), Ub-conjugates and proteasomes are present in cell bodies, axon, neuropil and nerve terminals of Aplysia neurons. Because R subunits are not decreased in muscle exposed to 5-HT, comparison of the two tissues provides a tractable approach to determine how the Ub pathway is regulated. We compared the structure of M1, the muscle-specific R isoform, to that of N4, a major neuronal R isoform, to rule out the possibility that the differences in their stability result from differences in structure. We present evidence that N4 and M1 are encoded by identical transcripts; they also behave similarly as protein substrates for the Ub pathway in extracts of the two tissues. Nervous tissue contains 20-times more free Ub, but we present evidence that the susceptibility of R subunits to degradation in neurons relative to muscle results from the greater capacity of neurons to degrade ubiquitinated proteins through the proteasome. Thus, factors that regulate the activity of proteasomes could underlie the enhanced degradation of R subunits in long-term sensitization.
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PMID:Persistent activation of cAMP-dependent protein kinase by regulated proteolysis suggests a neuron-specific function of the ubiquitin system in Aplysia. 747 10

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 of ion-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 of PKA 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 of Aplysia 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 conjugates of R subunits and intermediates in the degradative pathway. We also show that vertebrate RI and RII subunits can be degraded through the ubiquitin pathway. We suggest that degradation is initiated by cAMP, which causes the holoenzyme to dissociate and, further, that the altered R-to-C ratio in Aplysia sensory neurons is maintained in long-term facilitation by newly synthesized proteins that help target R subunits for accelerated degradation.
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PMID:Regulatory subunits of cAMP-dependent protein kinases are degraded after conjugation to ubiquitin: a molecular mechanism underlying long-term synaptic plasticity. 839 48

The formation of a persistently active cAMP-dependent protein kinase (PKA) is critical for establishing long-term synaptic facilitation (LTF) in Aplysia. The injection of bovine catalytic (C) subunits into sensory neurons is sufficient to produce protein synthesis-dependent LTF. Early in the LTF induced by serotonin (5-HT), an autonomous PKA is generated through the ubiquitin-proteasome-mediated proteolysis of regulatory (R) subunits. The degradation of R occurs during an early time window and appears to be a key function of proteasomes in LTF. Lactacystin, a specific proteasome inhibitor, blocks the facilitation induced by 5-HT, and this block is rescued by injecting C subunits. R is degraded through an allosteric mechanism requiring an elevation of cAMP coincident with the induction of a ubiquitin carboxy-terminal hydrolase.
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PMID:Mechanisms for generating the autonomous cAMP-dependent protein kinase required for long-term facilitation in Aplysia. 1002 97

8-Cl-cAMP, a cAMP analogue that antagonizes type I cAMP-dependent protein kinase, is a novel anti-tumor agent presently under investigation in clinical trials. Herein we report the effects of this agent on epidermal growth factor receptor expression and degradation in human KB cancer cells. Exposure to 10 microM 8-Cl-cAMP for 48 h induced a 65% increase in epidermal growth factor receptor surface expression while the receptor synthesis was 22-fold enhanced. Analysis of epidermal growth factor-dependent receptor internalization in 8-Cl-cAMP-treated cells showed a higher endocytosis rate as well as an accelerated degradation which occurred together with an increased receptor ubiquitination. The enhanced degradation of epidermal growth factor receptor correlated with the lack of epidermal growth factor-induced proliferation and mitogen-activated protein kinase stimulation. The disregulation of epidermal growth factor receptor internalization and ubiquitin-dependent degradation could underlay a new mechanism of the anti-tumor activity of 8-Cl-cAMP suggesting its combination with agents that disrupt epidermal growth factor receptor signalling.
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PMID:Up-regulated EGF receptors undergo to rapid internalization and ubiquitin-dependent degradation in human cancer cells exposed to 8-Cl-cAMP. 1021 46

Varied intensities of nitrotyrosine immunoreactivity were detected by Western blots after the reaction of proteins or enzymes with peroxynitrite (PN), a strong oxidant derived from nitric oxide. Intense immunoreactivity of cAMP-dependent protein kinase, calmodulin and most histones may depend on greater access to tyrosine residues in the reaction, whereas the absence of immunoreactivity of caspase-3, ubiquitin and S-100 proteins may reflect lack of accessibility. In addition, the changes in UV/visible absorbency were observed after PN-treatment of polynucleotides, polypeptides or proteins. Brief PN-treatment of invertase increased its enzymatic activity. Furthermore, PN-treatment of rabbit IgG decreased its recognition by anti-IgG. The results suggest that PN may chemically modify polypeptides, proteins and polynucleotides and may subsequently alter their biological activity.
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PMID:Modification of proteins and polynucleotides by peroxynitrite. 1053 71

Sensitization of defensive reflexes in Aplysia is a simple behavioral paradigm for studying both short- and long-term memory. In the marine mollusk, as in other animals, memory has at least two phases: a short-term phase lasting minutes and a long-term phase lasting several days or longer. Short-term memory is produced by covalent modification of pre-existing proteins. In contrast, long-term memory needs gene induction, synthesis of new protein, and the growth of new synapses. The switch from short-term (STF) to long-term facilitation (LTF) in Aplysia sensory neurons requires not only positive regulation through gene induction, but also the specific removal of several inhibitory proteins. One important inhibitory protein is the regulatory (R) subunit of the cAMP-dependent protein kinase (PKA). Degradation of R subunits, which is essential for initiating long-term stable memory, occurs through the ubiquitin-proteasome pathway.
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PMID:Ubiquitin-mediated proteolysis in learning and memory. 1096 18

(1) Fractalkine is a CX(3)C chemokine for mononuclear leukocytes that is expressed mainly by vascular cells, and regulated by pro-inflammatory cytokines. This study investigated signal transduction mechanisms by which tumor necrosis factor (TNF)-alpha stimulated fractalkine expression in cultured rat vascular smooth muscle cells (VSMCs), and the modulatory effect of a haemorrheologic agent, pentoxifylline, on its production. (2) TNF-alpha (1-50 ng ml(-1)) stimulated fractalkine mRNA and protein expression in concentration- and time-dependent manners. Pretreatment with calphostin C (0.4 micro M, a selective inhibitor of protein kinase C (PKC), and PD98059 (40 micro M), a specific inhibitor of p42/44 mitogen-activated protein kinase (MAPK) kinase, attenuated TNF-alpha-stimulated fractalkine mRNA and protein expression. In contrast, H-89 (2 micro M), a selective inhibitor of cAMP-dependent protein kinase, wortmannin (0.5 micro M), a selective inhibitor of phosphatidylinositol 3-kinase, and SB203580 (40 micro M), a specific inhibitor of p38 MAPK, had no discernible effect. (3) The ubiquitin/proteosome inhibitors, MG132 (10 micro M) and pyrrolidine dithiocarbamate (200 micro M), suppressed activation of NF-kappaB as well as stimulation of fractalkine mRNA and protein expression by TNF-alpha. (4) TNF-alpha-activated phosphorylation of PKC was blocked by calphostin C, whereas TNF-alpha-augmented phospho-p42/44 MAPK and phospho-c-Jun levels were reduced by PD98059. Neither calphostin C nor PD98059 affected TNF-alpha-induced degradation of I-kappaBalpha or p65 nuclear translocation. (5) Pretreatment with pentoxifylline (0.1-1 mg ml(-1)) decreased TNF-alpha-stimulated fractalkine mRNA and protein expression, which was preceded by a reduction in TNF-alpha-activated phosphorylation of PKC, p42/44 MAPK and c-Jun as well as degradation of I-kappaBalpha and p65/NF-kappaB nuclear translocation. (6) These data indicate that activation of PKC, p42/44 MAPK kinase, and NF-kappaB are involved in TNF-alpha-stimulated fractalkine production in VSMCs. Down-regulation of the PKC, p42/44 MAPK, and p65/NF-kappaB signals by PTX may be therapeutically relevant and provide an explanation for the anti-fractalkine effect of this drug.
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PMID:Inhibition by pentoxifylline of TNF-alpha-stimulated fractalkine production in vascular smooth muscle cells: evidence for mediation by NF-kappa B down-regulation. 1264 97

Ran1/Pat1 kinase and cAMP-dependent protein kinase (PKA) regulate sexual differentiation in Schizosaccharomyces pombe. A reduction in the activity of both enzymes is a prerequisite for meiosis. Together, PKA and Pat1 control the level of expression of the Mei2 RNA-binding protein. Pat1 further regulates the activity of Mei2 by phosphorylation. Phosphorylation inactivates Mei2 by interfering with its cellular localization and by causing degradation of the protein via the ubiquitin-proteasome pathway. The inhibitor of Pat1, Mei3, is found only in diploid cells undergoing meiosis. Expression of mei3 is sufficient to induce meiosis. Here, we examine the relationship between Pat1, PKA and Mei3. We demonstrate that Mei3 is an in vitro substrate for PKA. Using site-specific mutagenesis, the major PKA phosphorylation site is identified. In vivo assays indicate that phosphorylation of Mei3 by PKA does not significantly alter the ability of the inhibitor to regulate Pat1. Although it does not function as an inhibitor for PKA, ectopic expression of Mei3 causes cells containing high PKA levels to undergo meiosis. Expression of various mei3 alleles in cells containing unregulated PKA activity shows that the ability to undergo meiosis correlates with Pat1 activity. Notably, induced levels of mei2 are not a prerequisite for meiotic differentiation, as previously thought. The implications of this result to developmental regulation are discussed.
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PMID:Inactivation of Ran1/Pat1 kinase bypasses the requirement for high-level expression of mei2 during fission yeast meiosis. 1266 34

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 kinase-anchoring-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 for the production of long-term facilitation. Using synaptosomes, we found that 5-HT treatment causes RII protein to increase at nerve endings. In addition, using reverse transcription-PCR, we found that RII mRNA is transported from the cell body to nerve terminals. Our results suggest that type I operates in the nucleus to maintain cAMP response element-binding protein-dependent gene expression, and type II PKA acts at sensory neuron synapses phosphorylating proteins to enhance release of neurotransmitter. Thus, the two types of the kinase have distinct but complementary functions in the production of facilitation at synapses of an identified neuron.
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PMID:The two regulatory subunits of aplysia cAMP-dependent protein kinase mediate distinct functions in producing synaptic plasticity. 1501 22


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