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A more recent version of this article appeared on December 1, 2002
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Submitted on March 7, 2002
Revised on August 14, 2002
Accepted on August 23, 2002
1 Department of Cell Biology, University of Virginia Health Sciences Center
* Corresponding author. E-mail address: jdc4r{at}virginia.edu.
In Secretory Carrier Membrane Proteins (SCAMPs), the most conserved structural segment is between transmembrane spans 2 and 3, facing the cytosol. A synthetic peptide CWYRPIYKAFR (E peptide) from this segment of SCAMP2 potently inhibits exocytosis in permeabilized neuroendocrine (PC12) cells. E peptide blocked discharge of [35S]secretogranin with the same structural selectivity and potency as observed for hexosaminidase secretion in mast cells (Guo et al, 2002). SCAMPs 1 and 2 are mainly concentrated on intracellular membranes in PC12 cells. Both, however, are found on plasma membranes but neither is present on large dense core vesicles. Yet, large dense core vesicles marked by secretogranin attach to plasma membranes at foci containing SCAMP2 along with syntaxin1 and complexin at putative cell surface docking/fusion sites. Regulated overexpression of SCAMP2 with point mutations in its E peptide but not of normal SCAMP2 caused dose-dependent inhibition of depolarization-induced secretion. The SCAMP2 mutants also inhibited secretion stimulated by elevated calcium. Inhibition was largely overcome by adding lysophosphatidylcholine to the medium at concentrations that do not otherwise affect secretion. Although overexpression of normal or mutant SCAMP2 slightly inhibits endocytosis, this effect does not appear to be related to the specific effect of the mutant SCAMP on stimulated exocytosis. Thus SCAMP2 not only colocalizes with fusion sites but also appears to have an essential function in granule exocytosis through actions mediated by its E peptide-containing domain.
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