ABSTRACT
Although the available evidence suggests that whereas the caspase family plays a major role in apoptosis, they are not the sole stimulators of death. A random yeast two-hybrid screen of a lymphocyte cDNA library (using caspase-3 as the bait) found an interaction between caspase-3 and the regulatory subunit Aalpha of protein phosphatase 2A. This protein was found to be a substrate for caspase-3, but not caspase-1, and could compete effectively against either a protein or synthetic peptide substrate. In Jurkat cells induced to undergo apoptosis with anti-Fas antibody, protein phosphatase 2A (PP2A) activity increased 4.5-fold after 6 h. By 12 h, the regulatory Aalpha subunit could no longer be detected in cell lysates. There was no change in the amount of the catalytic subunit. The effects on PP2A could be prevented by the caspase family inhibitors acetyl-Asp-Glu-Val-Asp (DEVD) aldehyde or Ac-DEVD fluoromethyl ketone. The mitogen-activated protein (MAP) kinase pathway is regulated by PP2A. At 12 h after the addition of anti-Fas antibody, a decrease in the amount of the phosphorylated forms of MAP kinase was observed. Again, this loss of activated MAP kinase could be prevented by the addition of DEVD-cho or DEVD-fmk. These data are consistent with a pathway whereby induction of apoptosis activates caspase-3. This enzyme then cleaves the regulatory Aalpha subunit of PP2A, increasing its activity. These data show that the activated PP2A will then effect a change in the phosphorylation state of the cell. These data provide a link between the caspases and signal transduction pathways.
Subject(s)
Apoptosis , Caspases , Cysteine Endopeptidases/metabolism , Phosphoprotein Phosphatases/metabolism , Caspase 3 , Cysteine Proteinase Inhibitors/pharmacology , Enzyme Activation , Humans , Hydrolysis , Jurkat Cells , Oligopeptides/pharmacology , Protein Phosphatase 2 , Saccharomyces cerevisiae/genetics , Substrate Specificity , Tumor Necrosis Factor-alpha/pharmacologyABSTRACT
O emprego da ventilacao mandatoria intermitente e avaliado na insuficiencia respiratoria aguda. Discutem-se os criterios para sua adocao, tecnicas de isntalacao do circuito, parametros de controle do siste= ma. Apresentam-se casuistica em que o metodo foi utilizado para desmame dos respiradores, bem como situacoes de indicacao precoce para manutencao da ventilacao mecanica. Analisam-se os fatores basicos para o sucesso do metodo, que, embora possuindo algumas limitacoes, e componente fundamental do arsenal terapeutico da insuficiencia respiratoria aguda.Concluem os autores que o metodo e valido para o desmame do paciente do ventilador e que permite a indicacao de ventilacao mecanica mais precocemente
