Development- and activity-dependent regulation of SNAP-25 phosphorylation in rat brain

Synaptosomal-associated protein of 25 kDa (SNAP-25), a member of the SNARE proteins essential for neurotransmitter release, is phosphorylated at Ser¹⁸⁷ in PC12 cells and in the rat brain in a protein kinase C-dependent manner. It remains unclear how the phosphorylation of SNAP-25 is regulated during development and by neuronal activity. We studied the mode of SNAP-25 phosphorylation at Ser¹⁸⁷ in the rat brain using an anti-phosphorylated SNAP-25 antibody. Both the expression and phosphorylation of SNAP-25 increased remarkably during the early postnatal period, but their onsets were quite different. SNAP-25 expression was detected as early as embryonic Day 18, whereas the phosphorylation of SNAP-25 could not be detected until postnatal Day 4. A delay in the onset of phosphorylation was also observed in cultured rat hippocampal neurons. The phosphorylation of SNAP-25 was regulated in a neuronal activity-dependent manner and, in the rat hippocampus, decreased by introducing seizures with kainic acid. These results clearly indicated that the phosphorylation of SNAP-25 at Ser¹⁸⁷ is regulated in development- and neuronal activity-dependent manners, and is likely to play important roles in higher brain functions.