RESUMO
In Alzheimer's Disease brain, the microtubule-associated protein tau is hyperphosphorylated at specific epitopes and abnormally aggregates into filamentous structures. In addition, there is significant neurodegeneration in Alzheimer's disease brain, and there is data to suggest that apoptotic-like processes may contribute to the neurodegeneration. It has been demonstrated that in PC12 cells undergoing apoptosis due trophic factor removal, tau is hyperphosphorylated prior to chromatin condensation. To establish that increased tau phosphorylation is a generalized outcome of the apoptotic process, and to examine the involvement of the protein kinase in these events, apoptosis was induced in retinoic-acid differentiated human SH-SY5Y neuroblastoma cells using the topoisomerase-1 inhibitor camptothecin. Treatment of the differentiated SH-SY5Y cells with camptothecin resulted in a time and concentration dependent activation of caspase-3 with a concomitant increase in the presence of apoptotic nuclei. Immunoblotting revealed that camptothecin treatment resulted in a significant increase in tau phosphorylation. Addition of a cyclin-dependent kinase inhibitor reduced camptothecin-induced cell death in the differentiated SH-SY5Y cells and decreased the effects of camptothecin on tau phosphorylation. In contrast, a general caspase inhibitor decreased camptothecin-induced cell death, but did not significantly decrease the increases in tau phosphorylation. These results suggest that increased tau phosphorylation is likely a generalized outcome of apoptotic processes in neuron-related cells, and that cyclin-dependent kinases probably play a role in this process.
Assuntos
Doença de Alzheimer/metabolismo , Apoptose/fisiologia , Encéfalo/metabolismo , Neurônios/metabolismo , Proteínas Quinases/metabolismo , Proteínas tau/metabolismo , Doença de Alzheimer/fisiopatologia , Anticorpos/farmacologia , Apoptose/efeitos dos fármacos , Encéfalo/fisiopatologia , Camptotecina/farmacologia , Caspase 3 , Inibidores de Caspase , Caspases/efeitos dos fármacos , Caspases/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/fisiologia , Células Cultivadas , Quinases Ciclina-Dependentes/antagonistas & inibidores , Quinases Ciclina-Dependentes/metabolismo , DNA Topoisomerases Tipo I/efeitos dos fármacos , DNA Topoisomerases Tipo I/metabolismo , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Humanos , L-Lactato Desidrogenase/efeitos dos fármacos , L-Lactato Desidrogenase/metabolismo , Microtúbulos/efeitos dos fármacos , Microtúbulos/metabolismo , Neuroblastoma , Neurônios/efeitos dos fármacos , Fosforilação/efeitos dos fármacos , Proteína Supressora de Tumor p53/efeitos dos fármacos , Proteína Supressora de Tumor p53/metabolismoRESUMO
RNA encoding the B subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptor (GluR-B) undergoes a posttranscriptional modification in which a genomically encoded adenosine is represented as a guanosine in the GluR-B complementary DNA. In vitro editing of GluR-B RNA transcripts with HeLa cell nuclear extracts was found to result from an activity that converts adenosine to inosine in regions of double-stranded RNA by enzymatic base modification. This activity is consistent with that of a double-stranded RNA-specific adenosine deaminase previously described in Xenopus oocytes and widely distributed in mammalian tissues.
