Acute rise in the concentration of free cytoplasmic calcium leads to dephosphorylation of the microtubule-associated protein tau.
The objective of this study was to asses the response of the microtubule-associated protein tau to acute rise in the concentration of free cytoplasmic calcium ([Ca2+]i) in rat cortical neurons and mouse cerebellar granule cells in culture. One-hour exposure to glutamate (100 microM), N-methyl-D-aspartate (100 microM), KCl (50 mM), and ionomycin (5 microM) led to tau protein dephosphorylation as indicated by an appearance of additional faster moving bands on Western immunoblots with a phosphorylation-independent antibody and an increase in the tau-1 immunoreactivity associated with the appearance of an additional faster moving band. Lowering the extracellular concentration of Ca2+ to less than 1 microM fully prevented the drug-induced tau protein dephosphorylation indicating a dependence on Ca2+ influx from the extracellular environment. Administration of okadaic acid (inhibitor of phosphatase 1/2A) simultaneously with the above mentioned drugs decreased the drug-mediated dephosphorylation. Pre-incubation with okadaic acid fully prevented the dephosphorylation. Treatment with cypermethrin (inhibitor of phosphatase 2B) was without effect when administered either alone, simultaneously with the drugs, or pre-incubated. These findings indicate that, independently of the influx pathway, [Ca2+]i elevation leads to dephosphorylation of the microtubule-associated protein tau and implicate phosphatase 1 and/or 2A in the process.
Adamec
E
E
Laboratories for Molecular Neuroscience, Mailman Research Center, McLean Hospital, Belmont, MA 02178, USA. edamec@crcii.mclean.org
Mercken
M
M
Beermann
M L
ML
Didier
M
M
Nixon
R A
RA
D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004622:Embryo, Mammalian; D018698:Glutamic Acid / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011189:Potassium Chloride / Q000494:pharmacology; D054645:Protein Phosphatase 1; D011722:Pyrethrins / Q000494:pharmacology; D051381:Rats; D016875:tau Proteins / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*
D011722:Pyrethrins; D016875:tau Proteins; C017160:cypermethrin; D019319:Okadaic Acid; D018698:Glutamic Acid; D015759:Ionomycin; D016202:N-Methylaspartate; D011189:Potassium Chloride; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D002118:Calcium