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1. The individual and sequential influence of protein kinase C (PKC), protein kinase A (PKA) and mitogen-activated protein kinase (MAP kinase) on human brain tau was examined. 2. A range of PKC concentrations generated certain phosphoepitopes common with paired helical filaments. These epitopes were masked by higher PKC concentrations, suggesting the(More)
Limited proteolysis of protein kinase C (PKC) by calpain under cell free conditions cleaves the regulatory and catalytic PKC subunits, generating a free, co-factor independent catalytic subunit, termed PKM. In the present study, we demonstrate distinct differences in the rate, nature, and lipid-sensitivity of PKC and PKM proteolysis by microM and mM(More)
We examined the interdependence of calpain and protein kinase C (PKC) activities on neurite outgrowth in SH-SY-5Y human neuroblastoma cells. SH-SY-5Y cells elaborated neurites when deprived of serum or after a specific thrombin inhibitor, hirudin, was added to serum-containing medium. The extent of neurite outgrowth under these conditions was enhanced by(More)
Calcium influx into SH-SY5Y human neuroblastoma cells after ionophore treatment or transient permeabilization in calcium-containing medium increased ALZ-50 immunoreactivity markedly. This increase was prevented by inhibitors active against calpain or against protein kinase C (PKC), suggesting that both of these enzymes were required to mediate the effect of(More)
Limited proteolysis of protein kinase C (PKC) by calcium-activated proteolysis cleaves the regulatory and catalytic subunits of PKC, generating a free, constitutively activated kinase ("PKM") that, unlike the intact parent enzyme, is not calcium-dependent, and is not restricted to the plasma membrane. These latter properties leave open the possibility that(More)
Tau isoforms migrating at 46-68 and 97-115 kDa were prominent within heat-stable Triton-soluble material, and were present in lesser concentration with Triton-insoluble cytoskeletons, derived from undifferentiated SH-SY-5Y human neuroblastoma cells. Conversely, a 26-30 kDa tau isoform was enriched in the cytoskeleton and detected at relatively minor levels(More)
SH-SY-5Y human neuroblastoma cells were treated with combinations of the kinase inhibitors HA-1004, W-7 and H-7 and calcium ionophore A23187. Microdensitometric analyses revealed that, in the absence of ionophore-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(More)
The alpha isoform of protein kinase C (PKC alpha) is rapidly hydrolyzed by mM Ca(2+)-requiring calpain (calcium-activated neutral proteinase) under cell-free conditions (Shea et al, 1994, FEBS Lett. 350:223). In the present study, we demonstrate that this hydrolysis is inhibited by phosphatidyl serine, diacylglycerol, phosphatidyl choline, phosphatidyl(More)
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