Role of secretory carrier membrane protein SCAMP2 in granule exocytosis.
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 (35)S-labeled secretogranin with the same structural selectivity and potency as observed for hexosaminidase secretion in mast cells. SCAMPs 1 and 2 are concentrated primarily 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.
Liu
Lixia
L
Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908-0001, USA.
Guo
Zhenheng
Z
Tieu
Quyen
Q
Castle
Anna
A
Castle
David
D
D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005089:Exocytosis; D007476:Ionophores / Q000494:pharmacology; D008565:Membrane Proteins / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D016716:PC12 Cells; D010455:Peptides / Q000737:chemistry; D010703:Phorbol Esters / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D050827:Syntaxin 1; D013752:Tetracycline / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014168:Transferrin / Q000378:metabolism
D033942:Adaptor Proteins, Vesicular Transport; D000954:Antigens, Surface; D002352:Carrier Proteins; D018076:DNA, Complementary; D007476:Ionophores; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010455:Peptides; D010703:Phorbol Esters; C466776:SCAMP2 protein, human; D050827:Syntaxin 1; D014168:Transferrin; C095992:complexin I; D013752:Tetracycline; D002118:Calcium