Molecular mechanisms of platelet exocytosis: role of SNAP-23 and syntaxin 2 and 4 in lysosome release.
On stimulation by strong agonists, platelets release the contents of 3 storage compartments in 2 apparent waves of exocytosis. The first wave is the release of alpha- and dense core granule contents and the second is the release of lysosomal contents. Using a streptolysin O-permeabilized platelet exocytosis assay, we show that hexosaminidase release is stimulated by either Ca(++) or by GTP-gamma-S. This release step retains the same temporal separation from serotonin release as seen in intact platelets. This assay system was also used to dissect the molecular mechanisms of lysosome exocytosis. Lysosome release requires adenosine triphosphate and the general membrane fusion protein, N-ethylmaleimide sensitive factor. Uniquely, 2 syntaxin t-SNAREs, syntaxin 2 and 4, which localize to granules and open canalicular membranes, together with the general target membrane SNAP receptor (t-SNARE) protein SNAP-23 appear to make up the heterodimeric t-SNAREs required for lysosome exocytosis. These studies further show that regardless of stimuli (Ca(++) or GTP-gamma-S) serotonin and hexosaminidase release requires the same membrane fusion machinery. (Blood. 2000;96:1782-1788)
Chen
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D
Department of Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, USA.
Lemons
P P
PP
Schraw
T
T
Whiteheart
S W
SW
D000954:Antigens, Surface / Q000502:physiology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000502:physiology; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000648:ultrastructure; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D016253:Microscopy, Immunoelectron; D009419:Nerve Tissue Proteins / Q000502:physiology; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050600:SNARE Proteins; D012701:Serotonin / Q000378:metabolism; D050827:Syntaxin 1; D014316:Tritium; D033921:Vesicular Transport Proteins; D001619:beta-N-Acetylhexosaminidases / Q000187:drug effects / Q000378:metabolism
D000954:Antigens, Surface; D002352:Carrier Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human; D050600:SNARE Proteins; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D014316:Tritium; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D001619:beta-N-Acetylhexosaminidases; D002118:Calcium