Nonredundant function of secretory carrier membrane protein isoforms in dense core vesicle exocytosis.
Five secretory carrier membrane proteins (SCAMP-1, -2, -3, -4, and -5) have been characterized in mammalian cells. Previously, SCAMP-1 and -2 have been implicated to function in exocytosis. RNA inhibitor-mediated deficiency of one or both of these SCAMPs interferes with dense core vesicle (DCV) exocytosis in neuroendocrine PC12 cells as detected by amperometry. Knockdowns of these SCAMPs each decreased the number and frequency of depolarization-induced exocytotic events. SCAMP-2 but not SCAMP-1 depletion also delayed the onset of exocytosis. Both knockdowns, however, altered fusion pore dynamics, increasing rapid pore closure and decreasing pore dilation. In contrast, knockdowns of SCAMP-3 and -5 only interfered with the frequency of fusion pore opening and did not affect the dynamics of newly opened pores. None of the knockdowns noticeably affected upstream events, including the distribution of DCVs near the plasma membrane and calcium signaling kinetics, although norepinephrine uptake/storage was moderately decreased by deficiency of SCAMP-1 and -5. Thus, SCAMP-1 and -2 are most closely linked to the final events of exocytosis. Other SCAMPs collaborate in regulating fusion sites, but the roles of individual isoforms appear at least partially distinct.
Liao
Haini
H
Dept. of Cell Biology and Cell and Developmental Biology Program , Univ. of Virginia, Charlottesville, VA 22908, USA.
Zhang
Jie
J
Shestopal
Svetlana
S
Szabo
Gabor
G
Castle
Anna
A
Castle
David
D
D000818:Animals; D020013:Calcium Signaling; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D005089:Exocytosis; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008561:Membrane Fusion; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008959:Models, Neurological; D009474:Neurons / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D016716:PC12 Cells; D020033:Protein Isoforms / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D014162:Transfection; D014316:Tritium
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; C083429:Scamp1 protein, rat; D014316:Tritium; D009638:Norepinephrine