Site-specific phosphorylation of neurofilament-L is mediated by calcium/calmodulin-dependent protein kinase II in the apical dendrites during long-term potentiation

Neurofilament-L (NF-L), one subunit of the neuronal intermediate filaments, is a major element of neuronal cytoskeletons. The dynamics of NF-L are reg ulated by phosphorylation of its head domain. The phosphorylation sites of the NF-L head domain by protein kinase A, protein kinase C, and Rho-associa ted kinase have been previously identified, and those by calcium/ calmoduli n-dependent protein kinase II (CaMKII) were identified in this study. A ser ies of site- and phosphorylation state-specific antibodies against NF-L was prepared to investigate NF-L phosphorylation in neuronal systems. Long-ter m potentiation (LTP) is a cellular model of neuronal plasticity that is tho ught to involve the phosphorylation of various proteins. NF-L is considered a possible substrate for phosphorylation. During LTP stimulation of mouse hippocampal slices, the series of antibodies demonstrated the increase in t he phosphorylation level of Ser(57) in NF-L and the visualization of the lo calized distribution of Ser(57) phosphorylation in a subpopulation of apica l dendrites of the pyramidal neurons. Furthermore, Ser(57) phosphorylation during LTP is suggested to be mediated by CaMKII. Here we show that NF-L is phosphorylated by CaMKII in a subpopulation of apical dendrites during LTP , indicating that Ser(57) is a novel phosphorylation site of NF-L in vivo r elated to the neuronal signal transduction.