title: Divergent and convergent roles for kinases and phosphatases in neurofilament dynamics.
abstract: C-terminal neurofilament phosphorylation mediates cation-dependent self-association leading to neurofilament incorporation into the stationary axonal cytoskeleton. Multiple kinases phosphorylate the C-terminal domains of the heavy neurofilament subunit (NF-H), including cyclin-dependent protein kinase 5 (CDK5), mitogen-activated protein kinases (MAPKs), casein kinase 1 and 2 (CK1 and CK2) and glycogen synthase kinase 3β (GSK3β). The respective contributions of these kinases have been confounded because they phosphorylate multiple substrates in addition to neurofilaments and display extensive interaction. Herein, differentiated NB2a/d1 cells were transfected with constructs expressing GFP-tagged NF-H, isolated NF-H sidearms and NF-H lacking the distal-most 187 amino acids. Cultures were treated with roscovitine, PD98059, Li(+), D4476, tetrabromobenzotriazole and calyculin, which are active against CDK5, MKK1 (also known as MAP2K1), GSK3β, CK1, CK2 and protein phosphatase 1 (PP1), respectively. Sequential phosphorylation by CDK5 and GSK3β mediated the neurofilament-neurofilament associations. The MAPK pathway (i.e. MKK1 to ERK1/2) was found to downregulate GSK3β, and CK1 activated PP1, both of which promoted axonal transport and restricted neurofilament-neurofilament associations to axonal neurites. The MAPK pathway and CDK5, but not CK1 and GSK3β, inhibited neurofilament proteolysis. These findings indicate that phosphorylation of neurofilaments by the proline-directed MAPK pathway and CDK5 counterbalance the impact of phosphorylation of neurofilaments by the non-proline-directed CK1 and GSK3β.
authors.affiliation: Center for Cellular Neurobiology and Neurodegeneration Research, Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA 01854, USA sangmook_lee@uml.edu PantH@ninds.nih.gov thomas_shea@uml.edu.
authors.forename: Sangmook
authors.initials: S
authors.lastname: Lee
authors.affiliation: Cytoskeletal Protein Regulation Section, NIH, NINDS, Bethesda, MD 20892, USA sangmook_lee@uml.edu PantH@ninds.nih.gov thomas_shea@uml.edu.
authors.forename: Harish C
authors.initials: HC
authors.lastname: Pant
authors.affiliation: Center for Cellular Neurobiology and Neurodegeneration Research, Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA 01854, USA sangmook_lee@uml.edu PantH@ninds.nih.gov thomas_shea@uml.edu.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Shea
mesh_terms: D000818:Animals; D001370:Axonal Transport; D001369:Axons / Q000201:enzymology; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism; D047390:Casein Kinase II / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007382:Intermediate Filaments / Q000201:enzymology* / Q000235:genetics; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D011494:Protein Kinases; D047389:Casein Kinase I; D047390:Casein Kinase II; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D048052:Mitogen-Activated Protein Kinase 3; D038362:Glycogen Synthase Kinase 3; D010749:Phosphoprotein Phosphatases
keywords: Axonal stability; Cytoskeleton; Kinase; Neurofilament; Phosphatase