title: Synaptotagmin IV overexpression inhibits depolarization-induced exocytosis in PC12 cells.
abstract: Depolarization-induced vesicle exocytosis is a complex mechanism involving a number of proteins. In this process, synaptotagmins work as members of the Ca(2+)-sensing system that triggers the fusion of the synaptic vesicle with the plasma membrane. Synaptotagmin IV (SytIV), an immediate-early gene induced by depolarization in PC12 pheochromocytoma cells and in the hippocampus, has been suggested to work as a negative regulator of neurotransmitter release. Unlike other synaptotagmins, SytIV has an evolutionarily conserved substitution of an aspartate to a serine in the Ca(2+) coordination site of its C2A domain, preventing SytIV from binding anionic lipids in a Ca(2+)-dependent fashion. We used the secretion of human growth hormone (hGH) as a reporter system with which to examine the effects of overexpressing SytIV and other depolarization-induced immediate-early genes (the protein kinases KID-1, SIK, and PIM-1 and the transcription factors rTLE3 and Nurr1) on depolarization-induced vesicle exocytosis in PC12 cells. SytIV overexpression resulted in decreased depolarization-induced hGH release. However, conversion of the unique serine in SytIV to an aspartate eliminated this inhibitory activity. In addition, rTLE3 overexpression produced only a modest increase in spontaneous vesicle exocytosis, whereas KID-1, SIK, PIM-1, and Nurr1 overexpression had no effect on depolarization-induced exocytosis.
authors.affiliation: Department of Biological Chemistry, UCLA Center for the Health Sciences, Los Angeles, California, USA.
authors.forename: Hidevaldo B
authors.initials: HB
authors.lastname: Machado
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Vician
authors.forename: Harvey R
authors.initials: HR
authors.lastname: Herschman
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D017781:Genes, Immediate-Early / Q000502:physiology; D019382:Human Growth Hormone / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D041681:NIH 3T3 Cells; D009419:Nerve Tissue Proteins / Q000502:physiology*; D016716:PC12 Cells / Q000378:metabolism*; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D050857:Synaptotagmins
chemical_list: D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C494293:Syt4 protein, mouse; C494294:Syt4 protein, rat; D019382:Human Growth Hormone; D050857:Synaptotagmins