Effects of endogenous beta-amyloid overproduction on tau phosphorylation in cell culture.
Alzheimer's disease is characterized by beta-amyloid (Abeta) overproduction and tau hyperphosphorylation. Recent studies have shown that synthetic Abeta promotes tau phosphorylation in vitro. However, whether endogenously overproduced Abeta promotes tau phosphorylation and the underlying mechanisms remain unknown. Here, we used mouse neuroblastoma N2a stably expressing wild-type amyloid precursor protein (APPwt) or the Swedish mutant APP (APPswe) to determine the alterations of phosphorylated tau and the related protein kinases. We found that phosphorylation of tau at paired helical filament (PHF)-1, pSer396 and pThr231 epitopes was significantly increased in cells transfected with APPwt and APPswe, which produced higher levels of Abeta than cells transfected with vector or amyloid precursor-like protein 1. The activity of glycogen synthase kinase-3 (GSK-3) was up-regulated with a concomitant reduction in the inhibitory phosphorylation of GSK-3 at its N-terminal Ser9 residue. In contrast, the activity of cyclin-dependent kinase-5 (CDK-5) and protein kinase C (PKC) was down-regulated. Inhibition of GSK-3 by LiCl, but not inhibition of CDK-5 by roscovitine, arrested Abeta secretion and tau phosphorylation. Inhibition of PKC by GF-109203X activated GSK-3, whereas activation of PKC by phorbol-12,13-dibutyrate inhibited GSK-3. These results suggest that endogenously overproduced Abeta induces increased tau phosphorylation through activation of GSK-3, and that inactivation of PKC is at least one of the mechanisms involved in GSK-3 activation.
Wang
Ze-Fen
ZF
Pathophysiology Department, Hubei Provincial Key Laboratory of Neurological Diseases, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
Li
Hong-Lian
HL
Li
Xia-Chun
XC
Zhang
Qi
Q
Tian
Qing
Q
Wang
Qun
Q
Xu
Huaxi
H
Wang
Jian-Zhi
JZ
D016564:Amyloid beta-Protein Precursor / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000378:metabolism; D002470:Cell Survival / Q000502:physiology; D003470:Culture Media; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D009154:Mutation / Q000502:physiology; D009447:Neuroblastoma / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D016875:tau Proteins / Q000378:metabolism*
D016564:Amyloid beta-Protein Precursor; D003470:Culture Media; D004791:Enzyme Inhibitors; D016875:tau Proteins; D051360:Cyclin-Dependent Kinase 5; D011493:Protein Kinase C; D038362:Glycogen Synthase Kinase 3