RESUMO
A proportion of the microtubule-associated protein, tau, is in an elevated state of phosphorylation in foetal and adult brain whereas all of the tau in paired helical filaments, which are characteristic of Alzheimer's disease is hyperphosphorylated; it is important therefore to elucidate the mechanisms that regulate tau phosphorylation. Here we describe results that show that although MAP kinase can hyperphosphorylate tau in vitro, activation of MAP kinase in transformed fibroblasts does not result in hyperphosphorylation of transfected tau, whereas glycogen synthase kinase-3 beta (GSK-3 beta) when co-transfected with tau does result in tau hyperphosphorylation. The findings imply that GSK-3 beta may be a stronger candidate than MAP kinase for inducing tau hyperphosphorylation in vivo.
Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Proteínas Quinases Ativadas por Mitógeno , Proteínas Oncogênicas de Retroviridae/metabolismo , Proteínas tau/metabolismo , Células 3T3 , Animais , Western Blotting , Proteínas Quinases Dependentes de Cálcio-Calmodulina/genética , Ativação Enzimática , Quinase 3 da Glicogênio Sintase , Quinases da Glicogênio Sintase , Camundongos , Proteína Quinase 3 Ativada por Mitógeno , Proteínas Oncogênicas v-raf , Fosforilação , Proteínas Oncogênicas de Retroviridae/genética , Transformação Genética , Proteínas tau/genéticaRESUMO
Two cellular systems have been used to investigate the modulation of tau hyperphosphorylation. In the first system, the effects of the excitatory amino acid glutamate, the microtubule destabilising agent colchicine, and beta 25-35-amyloid peptide on tau phosphorylation were studied in rat cortical neurones in primary culture. Using immunocytochemistry and western blot analysis, we demonstrated that tau in these cultures is normally highly phosphorylated, but a proportion becomes rapidly dephosphorylated following treatment of the cultures with glutamate or colchicine. These changes in tau phosphorylation occurred prior to cell death. In the second system, the ability of p42 MAP and p44 MAP kinases, glycogen synthase kinases 3 alpha and 3 beta (GSK-3 alpha and GSK-3 beta) to phosphorylate tau in transfected COS cells was investigated. Both GSK-3 alpha and GSK-3 beta phosphorylated tau to produce a PHF-like state of phosphorylation but the MAP kinases failed to induce such a transformation in tau. These results suggest that aberrant regulation of GSK-3 alpha/beta may be a pathogenic mechanism in Alzheimer's disease.