Phosphorylation of neurofilament heavy chain side-arms by stress activatedprotein kinase-1b/Jun N-terminal kinase-3

Neurofilaments comprise three subunit proteins; neurofilament light, middle and heavy chains (NF-L, NF-M and NF-H), The carboxy-terminal domains of NF -M and NF-H form side-arms that project from the filament and that of NF-H contains multiple repeats of the motif lys-ser-pro, the serines of which ar e targets for phosphorylation, The level of phosphorylation on the lys-ser- pro repeats varies topographically within the cell; in cell bodies and prox imal axons, the side-arms are largely nonphosphorylated whereas in more dis tal regions of axons, the side-arms are heavily phosphorylated. Here we sho w that stress activated protein kinase 1b (SAPK1b), a major SAPK in neurone s will phosphorylate NF-H side-arms both in vitro and in transfected cells. These studies suggest that SAPK1b targets multiple phosphorylation sites w ithin NF-H side-arms. Additionally, we show that glutamate treatment induce s activation of SAPK1b in primary cortical neurones and increased phosphory lation of NF-H in cell bodies. This suggests that glutamate causes increase d NF-H phosphorylation at least in part by activation of stress activated p rotein kinases.