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  • Title: Expression and localisation of synaptotagmin isoforms in endocrine beta-cells: their function in insulin exocytosis.
    Author: Gut A, Kiraly CE, Fukuda M, Mikoshiba K, Wollheim CB, Lang J.
    Journal: J Cell Sci; 2001 May; 114(Pt 9):1709-16. PubMed ID: 11309201.
    Abstract:
    Exocytosis of insulin containing Large Dense Core Vesicles (LDCVs) from pancreatic beta-cells and derived cell lines is mainly controlled by Ca(2+). Several lines of evidence have demonstrated a role of the Ca(2+)- and phospholipid-binding protein synaptotagmin (syt) in this event. Synaptotagmins form a large protein family with distinct affinities for Ca(2+) determined by their two C(2) domains (C(2)A/B). Except for the well-characterized isoforms I and II, their role is still unclear. We have used here insulin-secreting cells as a model system for LDCV exocytosis to gain insight into the function of synaptotagmins. Immunocytochemical analysis revealed that of the candidate Ca(2+) sensors in LDCV exocytosis, syt III was not expressed in primary beta-cells, whereas syt IV was only found adjacent to the TGN. However, syt V-VIII isoforms were expressed at different levels in various insulin-secreting cells and in pancreatic islet preparations. In streptolysin-O permeabilized primary beta-cells the introduction of recombinant peptides (100 nM) corresponding to the C(2) domains of syt V, VII and VIII, but not of syt III, IV or VI, inhibited Ca(2+)-evoked insulin exocytosis by 30% without altering GTP gamma S-induced release. Our observations demonstrate that syt III and IV are not involved in the exocytosis of LDCVs from primary beta-cells whereas V, VII and VIII may mediate Ca(2+)-regulation of exocytosis.
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