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Phosphorylation of Protein Kinase C substrate proteins in rat hippocampal slices - effect of calpain inhibition

100%
Domanska-Janik K., Zablocka B., Zalewska T., Zajac H.
Acta Neurobiologiae Experimentalis
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1998
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vol. 58
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issue 4
247-252
EN
Incubation of the acutely dissected rat hippocampal slices in calcium-containing media resulted in spontaneous activation-translocation of classical PKC isoforms and their subsequent (especially g- type) proteolytic degradation. These changes were blocked by calpain inhibitor MDL 28 170 in 100 mM concentration. Rat hippocampal slices were metabolically prelabelled with 32Pi and stimulated with NMDA/glycine, depolarization or phorbol dibutyrate (PDBu) treatment. The basal phosphorylation of specific PKC substrates (MARCKS, neuromodulin and neurogranin) was significantly reduced in non-stimulated slices by MDL pretreatment. In contrast, only the slices where calpain activity was inhibited responded to further NMDA or phorbol dibutyrate stimulation by a substantial increase of PKC-dependent protein phosphorylation. It is concluded that the PKC phosphorylation system is severely affected by non-specific activation and a subsequent, calpain-dependent proteolysis in the acutely prepared hippocampal slices. Calpain inhibition by 100 mM MDL partially prevented these changes and increased stimulus-dependent phosphorylation of PKC-specific protein substrates.
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Molecular pathology of Alzheimer neurofibrillary degeneration

88%
Iqbal K., Alonso A., Gong C. X., Khatoon S., Kudo T., Singh T., Grundke-Iqbal I.
Acta Neurobiologiae Experimentalis
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1993
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vol. 53
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issue 1
325-335
EN
The most characteristic brain lesion of Alzheimer disease is the accumulation of paired helical filaments(PHF) in the affected neurons. Based on solubility in detergents there are two general populations of PHF, the readily soluble (PHF I) and the sparingly soluble (PHF II) types. The major polypeptides of PHF are the microtubule associated protein tau. Tau in PHF is present in abnormally phosphorylated forms. In addition to the PHF, the abnormal tau is also present in unpolymerized form in the AD brain. Small amounts of ubiquitin (%) are associated with PHF II but neither with PHF I nor with the unpolymerized abnormally phosphorylated tau in AD brain. Furthermore, the pretangle neurons can readily be immunolabeled for abnormally phosphorylated tau but not for ubiquitin. The level of tau in neocortex is several-fold higher than in AD aged control cases, but this increase is in the form of the abnormally phosphorylated protein. The microtubule associated proteins from AD brain do not promote the assembly of microtubules in vitro, whereas the in vitro dephosphorylated PHF polypeptides stimulate the binding of GTP to the exchangeable site of tubulin and the assembly of microtubules. In vitro the phosphate groups in PHF are less accessible than those of tau to alkaline phosphatase. It is suggested that a defect in the protein phosphorylation/dephosphorylation system leads to hyperphosphory-lation of tau. The altered tau contributes to a microtubule assembly defect and consequently compromises the axoplasmic flow and leads to neuronal degeneration.
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