title: Synaptic Drosophila UNC-13 is regulated by antagonistic G-protein pathways via a proteasome-dependent degradation mechanism.
abstract: UNC-13 is a highly conserved plasma membrane-associated synaptic protein implicated in the regulation of neurotransmitter release through the direct modulation of the SNARE exocytosis complex. Previously, we characterized the Drosophila homologue (DUNC-13) and showed it to be essential for neurotransmitter release immediately upstream of vesicular fusion ("priming") at the neuromuscular junction (NMJ). Here, we show that the abundance of DUNC-13 in NMJ synaptic boutons is regulated downstream of GalphaS and Galphaq pathways, which have inhibitory and facilitatory roles, respectively. Both cAMP modulation and PKA function are required for DUNC-13 synaptic up-regulation, suggesting that the cAMP pathway enhances synaptic efficacy via DUNC-13. Similarly, PLC function and DAG modulation also regulate the synaptic levels of DUNC-13, through a mechanism that appears independent of PKC. Our results suggest that proteasome-mediated protein degradation is the primary mechanism regulating DUNC-13 levels at the synapse. Both PLC- and PKA-mediated pathways appear to regulate synaptic levels of DUNC-13 through controlling the rate of proteasome-dependent DUNC-13 degradation. We conclude that the functional abundance of DUNC-13 at the synapse, a key determinant of synaptic vesicle priming and neurotransmitter release probability, is primarily regulated by the rate of protein degradation, rather than translocation or transport, convergently controlled via both cAMP and DAG signal transduction pathways.
authors.affiliation: Department of Biological Sciences, Vanderbilt University, VU Station B, Box 351634, Nashville, Tennessee 37235-1634, USA.
authors.forename: Bharathi
authors.initials: B
authors.lastname: Aravamudan
authors.forename: Kendal
authors.initials: K
authors.lastname: Broadie
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000906:Antibodies; D015153:Blotting, Western; D029742:Caenorhabditis elegans Proteins; D002227:Carbazoles; D002352:Carrier Proteins; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004330:Drosophila / Q000033:anatomy & histology / Q000378:metabolism*; D029721:Drosophila Proteins / Q000187:drug effects / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000145:classification / Q000378:metabolism*; D015801:Helminth Proteins / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism; D007150:Immunohistochemistry; D007211:Indoles / Q000494:pharmacology; D019476:Insect Proteins / Q000378:metabolism; D008301:Maleimides / Q000494:pharmacology; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods; D009097:Multienzyme Complexes / Q000378:metabolism*; D009154:Mutation; D009355:Neomycin / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D010742:Phospholipid Ethers / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000145:classification / Q000187:drug effects / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011758:Pyrroles / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D013569:Synapses / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D010738:Type C Phospholipases / Q000187:drug effects / Q000378:metabolism
chemical_list: D000906:Antibodies; D029742:Caenorhabditis elegans Proteins; D002227:Carbazoles; D002352:Carrier Proteins; C069672:Csp protein, Drosophila; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D004963:Estrenes; D015801:Helminth Proteins; D007211:Indoles; D019476:Insect Proteins; D008301:Maleimides; D009097:Multienzyme Complexes; D009842:Oligopeptides; D010703:Phorbol Esters; D010742:Phospholipid Ethers; D011758:Pyrroles; D011760:Pyrrolidinones; D025521:Tumor Suppressor Proteins; C444219:myristoylated-arginyl-arginyl-glycyl-alanyl-arginyl-arginyl-tryptophyl-arginyl-lysine; C083141:phorbol ester binding protein; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C067713:lactacystin; C070350:dlg1 protein, Drosophila; D005576:Colforsin; C026659:edelfosine; C057416:KT 5720; D006735:Horseradish Peroxidase; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D019204:GTP-Binding Proteins; D009355:Neomycin; C070515:bisindolylmaleimide I; D000111:Acetylcysteine