β-amyloid and ionophore A23187 evoke tau hyperphosphorylation by distinct intracellular pathways: Differential involvement of the calpain/protein kinase C system
✍ Scribed by Thomas B. Shea; Sathya Prabhakar; Fatma J. Ekinci
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 211 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
SH-SY-5Y human neuroblastoma cells were treated with 22 M of a synthetic peptide corresponding to amino acid residues 25-35 of -amyloid (A) or 3 M calcium ionophore A23187 in culture medium containing 1.8 mM extracellular calcium. Both agents increased tau immunoreactivity towards antibodies (PHF-1, ALZ-50) that recognize epitopes common with paired helical filaments (PHFs) and towards an antibody (5E2) that recognized a phosphate-independent tau epitope. However, only ionophore increased immunoreactivity with an additional phosphatedependent antibody (AT-8) that recognized an epitope of tau when phosphorylated, and induced a corresponding decrease in immunoreactivity towards an additional antibody (Tau-1) that recognizes the same site when that site is not phosphorylated. Moreover, the ionophore-mediated increase in PHF-1 was blocked by EGTA, by the calpain inhibitor calpeptin and by the PKC inhibitor H7, while that evoked by A treatment was not inhibited by any of these treatments. Since ionophore-mediated calpain activation induces proteolytic PKC activation, we further examined the influence of PKC inhibition on A and ionophoremediated PHF-1 induction. Antisense oligonucleotidemediated downregulation of PKC⑀ in a stable transfectant SH-SY-5Y subclone diminished the ionophoremediated, but not the A-mediated, increase in PHF-1 immunoreactivity. These data indicate specific differences in the intracellular cascade of events invoked by A and ionophore A23187. Moreover, although A invoked calcium influx in these cells, our findings further suggest that the induction of tau hyperphosphorylation by A may not be due to calcium influx. J.