Synaptotagmin VII regulates Ca(2+)-dependent exocytosis of lysosomes in fibroblasts

Synaptotagmins (Syts) are transmembrane proteins with two Ca(2+)-binding C(2) domains in their cytosolic region. Syt I, the most widely studied isoform, has been proposed to function as a Ca(2+) sensor in synaptic vesicle exocytosis. Several of the twelve known Syts are expressed primarily in brain,...

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Bibliographic Details
Published in:The Journal of cell biology 2000-03, Vol.148 (6), p.1141-1149
Main Authors: Martinez, I, Chakrabarti, S, Hellevik, T, Morehead, J, Fowler, K, Andrews, N W
Format: Article
Language:English
Subjects:
Animals
beta-N-Acetylhexosaminidases - metabolism
Binding Sites
Brain - physiology
Calcium - physiology
Calcium-Binding Proteins - metabolism
Cell Line
Cell Membrane Permeability
Cloning, Molecular
Exocytosis - physiology
Fibroblasts - physiology
Fibroblasts - ultrastructure
Kidney
Kinetics
Lysosomes - physiology
Lysosomes - ultrastructure
Membrane Glycoproteins - genetics
Membrane Glycoproteins - metabolism
Nerve Tissue Proteins - genetics
Nerve Tissue Proteins - metabolism
Protein Isoforms - metabolism
Rats
Recombinant Proteins - metabolism
Synaptotagmins
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Summary:Synaptotagmins (Syts) are transmembrane proteins with two Ca(2+)-binding C(2) domains in their cytosolic region. Syt I, the most widely studied isoform, has been proposed to function as a Ca(2+) sensor in synaptic vesicle exocytosis. Several of the twelve known Syts are expressed primarily in brain, while a few are ubiquitous (Sudhof, T.C., and J. Rizo. 1996. Neuron. 17: 379-388; Butz, S., R. Fernandez-Chacon, F. Schmitz, R. Jahn, and T.C. Sudhof. 1999. J. Biol. Chem. 274:18290-18296). The ubiquitously expressed Syt VII binds syntaxin at free Ca(2+) concentrations ([Ca(2+)]) below 10 microM, whereas other isoforms require 200-500 microM [Ca(2+)] or show no Ca(2+)-dependent syntaxin binding (Li, C., B. Ullrich, Z. Zhang, R.G.W. Anderson, N. Brose, and T.C. Sudhof. 1995. Nature. 375:594-599). We investigated the involvement of Syt VII in the exocytosis of lysosomes, which is triggered in several cell types at 1-5 microM [Ca(2+)] (Rodríguez, A., P. Webster, J. Ortego, and N.W. Andrews. 1997. J. Cell Biol. 137:93-104). Here, we show that Syt VII is localized on dense lysosomes in normal rat kidney (NRK) fibroblasts, and that GFP-tagged Syt VII is targeted to lysosomes after transfection. Recombinant fragments containing the C(2)A domain of Syt VII inhibit Ca(2+)-triggered secretion of beta-hexosaminidase and surface translocation of Lgp120, whereas the C(2)A domain of the neuronal- specific isoform, Syt I, has no effect. Antibodies against the Syt VII C(2)A domain are also inhibitory in both assays, indicating that Syt VII plays a key role in the regulation of Ca(2+)-dependent lysosome exocytosis.
ISSN:0021-9525
DOI:10.1083/jcb.148.6.1141