title: Identification of SNAREs involved in regulated exocytosis in the pancreatic acinar cell.
abstract: The molecular basis of exocytotic membrane fusion in the pancreatic acinar cell was investigated using an in vitro assay that measures both zymogen granule-plasma membrane fusion and granule-granule fusion. These two fusion events were differentially sensitive to Ca(2+), suggesting that they are controlled by different Ca(2+)-sensing mechanisms. Botulinum neurotoxin C (BoNT/C) treatment of the plasma membranes caused cleavage of syntaxin 2, the apical isoform of this Q-SNARE, but did not affect syntaxin 4, the basolateral isoform. BoNT/C also cleaved syntaxin 3, the zymogen granule isoform. BoNT/C treatment of plasma membranes abolished granule-plasma membrane fusion, whereas toxin treatment of the granules reduced granule-plasma membrane fusion and abolished granule-granule fusion. Tetanus toxin cleaved granule-associated synaptobrevin 2 but caused only a small reduction in both granule-plasma membrane fusion and granule-granule fusion. Our results indicate that syntaxin 2 is the isoform that mediates fusion between zymogen granules and the apical plasma membrane of the acinar cell. Syntaxin 3 mediates granule-granule fusion, which might be involved in compound exocytosis. In contrast, the major R-SNARE on the zymogen granule remains to be identified.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, CB2 1QJ, United Kingdom.
authors.forename: N J
authors.initials: NJ
authors.lastname: Hansen
authors.forename: W
authors.initials: W
authors.lastname: Antonin
authors.forename: J M
authors.initials: JM
authors.lastname: Edwardson
mesh_terms: D000595:Amino Acid Sequence; D001905:Botulinum Toxins / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D002451:Cell Compartmentation; D002458:Cell Fractionation; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000502:physiology; D004792:Enzyme Precursors; D005089:Exocytosis / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000302:isolation & purification* / Q000378:metabolism; D008673:Metals, Alkaline Earth / Q000494:pharmacology; D008969:Molecular Sequence Data; D010179:Pancreas / Q000166:cytology / Q000502:physiology*; D020033:Protein Isoforms / Q000378:metabolism; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins
chemical_list: D002413:Cations, Divalent; D004792:Enzyme Precursors; D008565:Membrane Proteins; D008673:Metals, Alkaline Earth; D020033:Protein Isoforms; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D001905:Botulinum Toxins; C096324:botulinum toxin type C; D008274:Magnesium; D002118:Calcium