BETA-AMYLOID AND IONOPHORE A23187 EVOKE TAU-HYPERPHOSPHORYLATION BY DISTINCT INTRACELLULAR PATHWAYS - DIFFERENTIAL INVOLVEMENT OF THE CALPAIN PROTEIN-KINASE-C SYSTEM

SH-SY-5Y human neuroblastoma cells were treated with 22 mu M of a synt hetic peptide corresponding to amino acid residues 25-35 of beta-amylo id (beta A) or 3 mu M calcium ionophore A23187 in culture medium conta ining 1.8 mM extracellular calcium, Both agents increased tau immunore activity towards antibodies (PHF-1, ALZ-50) that recognize epitopes co mmon with paired helical filaments (PHFs) and towards an antibody (5E2 ) that recognized a phosphate-independent tau epitope, However, only i onophore increased immunoreactivity with an additional phosphate-depen dent antibody (AT-8) that recognized an epitope of tau when phosphoryl ated, and induced a corresponding decrease in immunoreactivity towards an additional antibody (Tau-l) that recognizes the same site when tha t site is not phosphorylated, Moreover, the ionophore-mediated increas e in PHF-1 was blocked by EGTA, by the calpain inhibitor calpeptin and by the PKC inhibitor H7, while that evoked by beta A treatment was no t inhibited by any of these treatments, Since ionophore-mediated calpa in activation induces proteolytic PKC activation, we further examined the influence of PKC inhibition on beta A and ionophore-mediated PHF-1 induction, Antisense oligonucleotide-mediated downregulation of PKC e psilon in a stable transfectant SH-SY-5Y subclone diminished the ionop hore-mediated, but not the beta A-mediated, increase in PHF-1 immunore activity. These data indicate specific differences in the intracellula r cascade of events invoked by beta A and ionophore A23187, Moreover, although beta A invoked calcium influx in these cells, our findings fu rther suggest that the induction of tau hyperphosphorylation by beta A may not be due to calcium influx. (C) 1997 Wiley-Liss, Inc.