Neuropeptides, biogenic amines, and neurotrophins affect synaptic transmission by regulating pre- and postsynaptic function. The regulated release of these neuromodulators is mediated by the Ca2+-dependent fusion of dense-core vesicles (DCVs) with the plasma membrane. Although regulated DCV exocytosis is similar to the Ca2+-dependent exocytosis of synaptic vesicles (SVs) that mediate synaptic transmitter release, these processes differ in speed, latency, Ca2+ regulation and location. A fuller understanding of molecular mechanisms underlying Ca2+-triggered DCV fusion will reveal similarities and differences in the two vesicle fusion pathways that could identify unique drug targets for the selective inhibition of modulator secretion without inhibiting synaptic transmission. The protein CAPS (Ca2+-dependent activator protein in secretion) appears to be required for DCV but not SV exocytosis. We will elucidate the molecular mechanism of CAPS function in regulated DCV fusion and determine the physiological role of this protein in the nervous system. CAPS is a PIP2-binding protein that exhibits high affinity interactions with syntaxin, a key component of the SNARE fusion machinery. These interactions may mediate the function of CAPS at a late pre-fusion step in DCV exocytosis. CAPS also binds rabphilin, which may in part mediate CAPS interactions with DCVs.
Our specific aims will be: 1. To determine the functional significance of CAPS-syntaxin interactions for DCV exocytosis;2. To determine if CAPS functions as a PIP2 effector in DCV exocytosis;3. To determine the basis for the selective role of CAPS in DCV exocytosis and whether this is mediated through rabphilin interactions;and 4. To determine the general role of CAPS in neural trafficking pathways that mediate neuropeptide, biogenic amine and neurotrophin secretion. The results from this work will contribute to understanding neural trafficking pathways and to the molecular basis for secretory vesicle fusion with the plasma membrane.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Synapses, Cytoskeleton and Trafficking Study Section (SYN)
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Malozowski, Saul N
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University of Wisconsin Madison
Schools of Earth Sciences/Natur
United States
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Zhang, Xingmin Aaron; Martin, Thomas F J (2018) High Throughput NPY-Venus and Serotonin Secretion Assays for Regulated Exocytosis in Neuroendocrine Cells. Bio Protoc 8:
Zhang, Xingmin; Jiang, Shan; Mitok, Kelly A et al. (2017) BAIAP3, a C2 domain-containing Munc13 protein, controls the fate of dense-core vesicles in neuroendocrine cells. J Cell Biol 216:2151-2166
Kabachinski, Greg; Kielar-Grevstad, D Michelle; Zhang, Xingmin et al. (2016) Resident CAPS on dense-core vesicles docks and primes vesicles for fusion. Mol Biol Cell 27:654-68
Petrie, Matt; Esquibel, Joseph; Kabachinski, Greg et al. (2016) The Vesicle Priming Factor CAPS Functions as a Homodimer via C2 Domain Interactions to Promote Regulated Vesicle Exocytosis. J Biol Chem 291:21257-21270
Martin, Thomas F J (2015) PI(4,5)P?-binding effector proteins for vesicle exocytosis. Biochim Biophys Acta 1851:785-93
Yamaga, Masaki; Kielar-Grevstad, D Michelle; Martin, Thomas F J (2015) Phospholipase C?2 Activation Redirects Vesicle Trafficking by Regulating F-actin. J Biol Chem 290:29010-21
Kabachinski, Greg; Yamaga, Masaki; Kielar-Grevstad, D Michelle et al. (2014) CAPS and Munc13 utilize distinct PIP2-linked mechanisms to promote vesicle exocytosis. Mol Biol Cell 25:508-21
Zhang, Zhao; Takeuchi, Hiroshi; Gao, Jing et al. (2013) PRIP (phospholipase C-related but catalytically inactive protein) inhibits exocytosis by direct interactions with syntaxin 1 and SNAP-25 through its C2 domain. J Biol Chem 288:7769-80
James, Declan J; Martin, Thomas F J (2013) CAPS and Munc13: CATCHRs that SNARE Vesicles. Front Endocrinol (Lausanne) 4:187
Martin, Thomas F J (2012) Role of PI(4,5)P(2) in Vesicle Exocytosis and Membrane Fusion. Subcell Biochem 59:111-30

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