Nerve Growth Factor‐Induced Phosphorylation of SNAP‐25 in PC12 Cells

Abstract

Synaptosomal-associated protein of 25 kDa (SNAP-25), a t-SNARE protein essential for neurotransmitter release, is phosphorylated at Ser 187 following activation of cellular protein kinase C by treatment with phorbol 12-myristate 13-acetate. However, it remains unclear whether neuronal activity or an endogenous ligand induces the phosphorylation of SNAP-25. Here we studied the phosphorylation of SNAP-25 in PC12 cells using a specific antibody for SNAP-25 phosphorylated at Ser 187 . A small fraction of SNAP-25 was phosphorylated when cells were grown in the absence of nerve growth factor (NGF). A brief treatment with NGF that was enough to activate the mitogen-activated protein kinase signal transduction pathway did not increase the phosphorylation of SNAP-25; however, phosphorylation was up-regulated after a prolonged incubation with NGF. Up-regulation was transitory, and maximum phosphorylation (a fourfold increase over basal phosphorylation) was achieved between 36 and 48 h after the addition of NGF. Immunofluorescent microscopy showed that SNAP-25 was localized primarily in the plasma membrane, although a significant population was also present in the cytoplasm. Quantitative microfluorometry revealed that prolonged treatment with NGF resulted in a preferential localization of SNAP-25 in the plasma membrane. A mutational study using a fusion protein with green fluorescent protein as a tag indicated that the point mutation of Ser 187 to Ala abolished the NGF-dependent relocalization. A population of SNAP-25 in the plasma membrane was not increased by a point mutation at Ser 187 to Glu; however, it was increased by prolonged treatment with NGF, indicating that the SNAP-25 phosphorylation is essential, but not sufficient, for the NGF-induced relocation to the plasma membrane. Our results suggest a close temporal relationship between the up-regulation of SNAP-25 phosphorylation and its relocation, and NGF-induced differentiation of PC12 cells. Key Words: SNAP-25-Phosphorylation-Localization-Nerve growth factor-PC12. J. Neurochem. 74, 2058Neurochem. 74, -2066Neurochem. 74, (2000.Plasticity of neuronal networks in the brain is essential for learning and memory, and their cellular basis is believed to be the modulation of the strength and/or number of synaptic contacts (Bailey and Kandel, 1993).Numerous studies suggest that the regulation of synaptic strength can be controlled by protein phosphorylation through kinases and phosphatases; however, the precise mechanisms, including the identification of the relevant protein substrates of these enzymes, are still poorly understood. Many proteins participate in various synaptic functions and are substrates for several protein kinases Nielander et al., 1995;Hirling and Scheller, 1996;Risinger and Bennett, 1999). Synaptosomal-associated protein of 25 kDa (SNAP-25) is a membrane protein expressed in neurons and endocrine cells (Oyler et al., 1989). In neurons, SNAP-25 is localized primarily in axons and nerve terminals, and a large part of SNAP-25 is associated ...

SNAP-25 phosphorylation at Ser187 regulates synaptic facilitation and short-term plasticity in an age-dependent manner

“…Furthermore, the size of readily-releasable pool of synaptic vesicles was unchanged but the refilling rate of synaptic vesicles was faster in KI mice. All of these phenotypes indicate for the first time that the phosphorylation of SNAP-25 is closely related to the regulation of presynaptic functions in physiological conditions, although the role of the phosphorylation in exocytosis was examined in chromaffin and PC12 cells 20 , 21 . Interestingly, our data also indicate that developmental changes in release probability and presynaptic plasticity are regulated by the SNAP-25 phosphorylation.…”

SNAP25 expression in mammalian retinal horizontal cells

“…The two SNAP25 isoforms differ at exon 5, which introduces a palmitoylation site into SNAP25b (Bark, 1993; Bark and Wilson, 1994). Variability in immunolabeling patterns may arise also from the expression of both SNAP25 splice variants in the retina and subsequent post-translational modifications, such as palmitoylation (Veit et al, 1996; Veit, 2000) and phosphorylation (Genoud et al, 1999; Iwasaki et al, 2000; Kataoka et al, 2000, 2006; Pozzi et al, 2008), which has been implicated in increasing vesicle recruitment (Nagy et al, 2004) and regulation of the primed vesicle pool size (Nagy et al, 2004). …”

Activity-dependent phosphorylation of Ser187 is required for SNAP-25-negative modulation of neuronal voltage-gated calcium channels

“…However, SNAP-25 phosphorylation at ser187 might control the intracellular distribution of the protein, favoring its localization at the plasmamembrane, where SNARE proteins and calcium channels are clustered in lipid microdomains (46). In line with this possibility, ser187 phosphorylation of SNAP-25 in PC12 cells has been reported to result in the protein relocating to the plasma membrane (47). Interestingly, SNAP-25a, which fails to modulate calcium dynamics, differs from the b isoform by only nine residues, which include palmitoylated cysteines necessary for proper membrane localization, therefore raising the possibility that SNAP-25a may be less efficiently targeted to the plasma membrane (2,3,48).…”