CALCIUM INFLUX RECRUITS AN ADDITIONAL CLASS OF KINASES TO HYPERPHOSPHORYLATE-TAU

SH-SY-5Y human neuroblastoma cells were treated with combinations of t he kinase inhibitors HA-1004, W-7 and H-7 and calcium ionophore A23187 . Microdensitometric analyses revealed that, in the absence of ionopho re-mediated calcium influx, PHF-1 levels were reduced by approximately half in cultures treated with HA-1004 or W-7, but were not reduced by H-7. By contrast, the doubling in PHF-1 immunoreactivity that resulte d following ionophore treatment was prevented by all three inhibitors. These analyses demonstrate the recruitment of an additional kinase or kinases in tau phosphorylation following calcium influx, and undersco re the possibility that de novo hyperactivation of calcium-dependent k inases may be involved in the early events that propagate PHF formatio n.