title: Protein phosphatase 2A dephosphorylates SNAP-25 through two distinct mechanisms in mouse brain synaptosomes.
abstract: Synaptosomal-associated protein 25 (SNAP-25) plays an essential role in exocytotic neurotransmitter release as a t-SNARE protein. SNAP-25 is phosphorylated at Ser(187) in a protein kinase C (PKC)-dependent manner, but the mechanism for dephosphorylation has yet to be clarified. We investigated SNAP-25 dephosphorylation by comparing it to growth associated protein 43 (GAP-43), another PKC-dependent presynaptic phosphoprotein, in crude mouse brain synaptosome preparations. Phosphorylation levels for both SNAP-25 and GAP-43 increased significantly after treatment with PKC activator phorbol 12, 13-dibutyrate (PDB), and ionomycin treatment induced a striking reduction in a time-dependent manner. This dephosphorylation occurred only in the presence of extracellular Ca(2+), indicating involvement of a Ca(2+)-dependent phosphatase. Ca(2+)-dependent dephosphorylation was not suppressed by calcineurin/PP2B inhibitors such as FK506 and cyclosporine A. SNAP-25 dephosphorylation, however, was suppressed by calyculin A, a non-selective inhibitor of PP1 and PP2A, and okadaic acid selective for PP2A, but not by tautomycin selective for PP1. In contrast, none of these inhibitors suppressed GAP-43 dephosphorylation. PDB-induced SNAP-25 phosphorylation was enhanced by okadaic acid in a concentration-dependent manner. These results suggest that PP2A participates in SNAP-25 dephosphorylation through Ca(2+)-dependent and Ca(2+)-independent mechanisms but is not involved in GAP-43 dephosphorylation.
authors: Kitasato University Graduate School of Medical Sciences, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0374, Japan.
authors: Yuuki
authors: Y
authors: Iida
authors: Saori
authors: S
authors: Yamamori
authors: Makoto
authors: M
authors: Itakura
authors: Hitoshi
authors: H
authors: Miyaoka
authors: Masami
authors: M
authors: Takahashi
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D019922:GAP-43 Protein / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000378:metabolism* / Q000502:physiology; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism* / Q000502:physiology
chemical_list: D019922:GAP-43 Protein; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; C578496:PPP2CA protein, mouse; D054648:Protein Phosphatase 2