title: Tau becomes a more favorable substrate for GSK-3 when it is prephosphorylated by PKA in rat brain.
abstract: Microtubule-associated protein tau is abnormally hyperphosphorylated in Alzheimer's disease (AD) and other tauopathies and is believed to lead to neurodegeneration in this family of diseases. Here we show that infusion of forskolin, a specific cAMP-dependent protein kinase A (PKA) activator, into the lateral ventricle of brain in adult rats induced activation of PKA by severalfold and concurrently enhanced the phosphorylation of tau at Ser-214, Ser-198, Ser-199, and or Ser-202 (Tau-1 site) and Ser-396 and or Ser-404 (PHF-1 site), which are among the major abnormally hyperphosphorylated sites seen in AD. PKA activation positively correlated to the extent of tau phosphorylation at these sites. Infusion of forskolin together with PKA inhibitor or glycogen synthase kinase-3 (GSK-3) inhibitor revealed that the phosphorylation of tau at Ser-214 was catalyzed by PKA and that the phosphorylation at both the Tau-1 and the PHF-1 sites is induced by basal level of GSK-3, because forskolin activated PKA and not GSK-3 and inhibition of the latter inhibited the phosphorylation at Tau-1 and PHF-1 sites. Inhibition of cdc2, cdk5, or MAPK had no significant effect on the forskolin-induced hyperphosphorylation of tau. Forskolin inhibited spatial memory in a dose-dependent manner in the absence but not in the presence of R(p)-adenosine 3',5'-cyclic monophosphorothioate triethyl ammonium salt, a PKA inhibitor. These results demonstrate for the first time that phosphorylation of tau by PKA primes it for phosphorylation by GSK-3 at the Tau-1 and the PHF-1 sites and that an associated loss in spatial memory is inhibited by inhibition of the hyperphosphorylation of tau. These data provide a novel mechanism of the hyperphosphorylation of tau and identify both PKA and GSK-3 as promising therapeutic targets for AD and other tauopathies.
authors.affiliation: Pathophysiology Department, Neuroscience Institute, Tongji Medical College, Hua-Zhong University of Science and Technology, Wuhan 430030, People's Republic of China.
authors.forename: Shi Jie
authors.initials: SJ
authors.lastname: Liu
authors.forename: Jia Yu
authors.initials: JY
authors.lastname: Zhang
authors.forename: Hong Lian
authors.initials: HL
authors.lastname: Li
authors.forename: Zheng Yu
authors.initials: ZY
authors.lastname: Fang
authors.forename: Qun
authors.initials: Q
authors.lastname: Wang
authors.forename: Heng Mei
authors.initials: HM
authors.lastname: Deng
authors.forename: Cheng Xin
authors.initials: CX
authors.lastname: Gong
authors.forename: Inge
authors.initials: I
authors.lastname: Grundke-Iqbal
authors.forename: Khalid
authors.initials: K
authors.lastname: Iqbal
authors.forename: Jian Zhi
authors.initials: JZ
authors.lastname: Wang
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D016203:CDC2 Protein Kinase / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D006624:Hippocampus / Q000201:enzymology / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects; D010766:Phosphorylation; D051381:Rats; D016875:tau Proteins / Q000378:metabolism*
chemical_list: D020536:Enzyme Activators; D016875:tau Proteins; D005576:Colforsin; D051360:Cyclin-Dependent Kinase 5; D017868:Cyclic AMP-Dependent Protein Kinases; D016203:CDC2 Protein Kinase; C495907:Cdk5 protein, rat; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3