title: Differential regulation of the Cdk5-dependent phosphorylation sites of inhibitor-1 and DARPP-32 by depolarization.
abstract: While cyclin-dependent kinase 5 (Cdk5) is of growing importance to neuronal signaling, its regulation remains relatively unexplored. Examination of the mechanism by which NMDA modulates the phosphorylation of protein phosphatase inhibitor-1 at Ser6 and Ser67 and dopamine- and cAMP-regulated phosphoprotein M(r) 32 000 at Thr75 revealed that generalized depolarization, rather than specific activation of NMDA receptors, was sufficient to induce decreases in these Cdk5 sites. Although no evidence for the involvement of the Cdk5 cofactors p35 or p39, or for L- and T-type voltage-gated Ca(2+) channels, was found, evaluation of the role of phosphatases and extracellular cations revealed differential regulation of the three sites. NMDA-induced decreases in the phosphorylation of Thr75 of dopamine- and cAMP-regulated phosphoprotein M(r) 32 000 required protein phosphatase 1/2A activity and extracellular Ca(2+). In contrast, the effects on Ser6 and Ser67 of inhibitor-1 were not cation specific; either Na(+) or Ca(2+) sufficed. Furthermore, while the decrease in phosphorylation of Ser6 was partially dependent on protein phosphatase 2B, that of Ser67 was independent of the major protein serine/threonine phosphatases, likely indicating the presence of a pathway by which NMDA inhibits Cdk5 activity. Thus, in the striatum the regulation of phosphorylation of Cdk5-dependent sites by NMDA occurs through multiple distinct pathways.
authors.affiliation: Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Chan
authors.initials: C
authors.lastname: Nguyen
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hosokawa
authors.forename: Mahomi
authors.initials: M
authors.lastname: Kuroiwa
authors.forename: Nancy Y
authors.initials: NY
authors.lastname: Ip
authors.forename: Akinori
authors.initials: A
authors.lastname: Nishi
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Hisanaga
authors.forename: James A
authors.initials: JA
authors.lastname: Bibb
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism* / Q000502:physiology; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016202:N-Methylaspartate / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
chemical_list: D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D004791:Enzyme Inhibitors; C497929:Ppp1r1b protein, mouse; D011506:Proteins; C073882:phosphoprotein phosphatase inhibitor 1; D016202:N-Methylaspartate; D051360:Cyclin-Dependent Kinase 5; D010749:Phosphoprotein Phosphatases