title: Scapinin-induced inhibition of axon elongation is attenuated by phosphorylation and translocation to the cytoplasm.
abstract: Scapinin is an actin- and PP1-binding protein that is exclusively expressed in the brain; however, its function in neurons has not been investigated. Here we show that expression of scapinin in primary rat cortical neurons inhibits axon elongation without affecting axon branching, dendritic outgrowth, or polarity. This inhibitory effect was dependent on its ability to bind actin because a mutant form that does not bind actin had no effect on axon elongation. Immunofluorescence analysis showed that scapinin is predominantly located in the distal axon shaft, cell body, and nucleus of neurons and displays a reciprocal staining pattern to phalloidin, consistent with previous reports that it binds actin monomers to inhibit polymerization. We show that scapinin is phosphorylated at a highly conserved site in the central region of the protein (Ser-277) by Cdk5 in vitro. Expression of a scapinin phospho-mimetic mutant (S277D) restored normal axon elongation without affecting actin binding. Instead, phosphorylated scapinin was sequestered in the cytoplasm of neurons and away from the axon. Because its expression is highest in relatively plastic regions of the adult brain (cortex, hippocampus), scapinin is a new regulator of neurite outgrowth and neuroplasticity in the brain.
authors.affiliation: Garvan Institute for Medical Research, Sydney, New South Wales 2010, Australia.
authors.forename: Hovik
authors.initials: H
authors.lastname: Farghaian
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.forename: Ada W Y
authors.initials: AW
authors.lastname: Fu
authors.forename: Amy K Y
authors.initials: AK
authors.lastname: Fu
authors.forename: Jacque P K
authors.initials: JP
authors.lastname: Ip
authors.forename: Nancy Y
authors.initials: NY
authors.lastname: Ip
authors.forename: Ann M
authors.initials: AM
authors.lastname: Turnley
authors.forename: Adam R
authors.initials: AR
authors.lastname: Cole
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D051360:Cyclin-Dependent Kinase 5 / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016501:Neurites / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000199:Actins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; C479826:PHACTR3 protein, human; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; C495907:Cdk5 protein, rat