title: Regulation of protein phosphatase inhibitor-1 by cyclin-dependent kinase 5.
abstract: Inhibitor-1, the first identified endogenous inhibitor of protein phosphatase 1 (PP-1), was previously reported to be a substrate for cyclin-dependent kinase 5 (Cdk5) at Ser67. Further investigation has revealed the presence of an additional Cdk5 site identified by mass spectrometry and confirmed by site-directed mutagenesis as Ser6. Basal levels of phospho-Ser6 inhibitor-1, as detected by a phosphorylation state-specific antibody against the site, existed in specific regions of the brain and varied with age. In the striatum, basal in vivo phosphorylation and dephosphorylation of Ser6 were mediated by Cdk5, PP-2A, and PP-1, respectively. Additionally, calcineurin contributed to dephosphorylation under conditions of high Ca2+. In biochemical assays the function of Cdk5-dependent phosphorylation of inhibitor-1 at Ser6 and Ser67 was demonstrated to be an intramolecular impairment of the ability of inhibitor-1 to be dephosphorylated at Thr35; this effect was recapitulated in two systems in vivo. Dephosphorylation of inhibitor-1 at Thr35 is equivalent to inactivation of the protein, as inhibitor-1 only serves as an inhibitor of PP-1 when phosphorylated by cAMP-dependent kinase (PKA) at Thr35. Thus, inhibitor-1 serves as a critical junction between kinase- and phosphatase-signaling pathways, linking PP-1 to not only PKA and calcineurin but also Cdk5.
authors.affiliation: Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Chan
authors.initials: C
authors.lastname: Nguyen
authors.forename: Akinori
authors.initials: A
authors.lastname: Nishi
authors.forename: Janice W
authors.initials: JW
authors.lastname: Kansy
authors.forename: Joseph
authors.initials: J
authors.lastname: Fernandez
authors.forename: Kanehiro
authors.initials: K
authors.lastname: Hayashi
authors.forename: Frank
authors.initials: F
authors.lastname: Gillardon
authors.forename: Hugh C
authors.initials: HC
authors.lastname: Hemmings
authors.forename: Angus C
authors.initials: AC
authors.lastname: Nairn
authors.forename: James A
authors.initials: JA
authors.lastname: Bibb
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001921:Brain / Q000378:metabolism*; D019703:Calcineurin / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D051360:Cyclin-Dependent Kinase 5 / Q000235:genetics / Q000378:metabolism*; D008297:Male; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D016716:PC12 Cells; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D011506:Proteins; C073882:phosphoprotein phosphatase inhibitor 1; D051360:Cyclin-Dependent Kinase 5; D017868:Cyclic AMP-Dependent Protein Kinases; C495906:Cdk5 protein, mouse; C495907:Cdk5 protein, rat; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1