RESUMO
Bax translocation from cytosol to mitochondria is believed to be a crucial step for triggering cytochrome c release from mitochondria. However, it is unclear whether Bax translocation is associated with Bax induction by DNA damaging agents. The induction of Bax in response to DNA damaging agents has been considered to be linked with p53. In this study, we used the p53 negative human chronic myeloid leukaemia K562 cell line. Bax up-regulation occurred at the whole cell level after DNA damage induced by etoposide. However, after incubation with etoposide, Bax failed to translocate to mitochondria and as a result, the apoptotic process was blocked. A Bax stable transfectant, the K/Bax cell line, expressed more Bax protein in the cytosol, mitochondria and nuclei. This Bax overexpression induced cytochrome c release, a reduction of cytochrome c oxidase activity and mitochondrial membrane potential (Delta(Psi)m). However, Bax-induced apoptosis was blocked downstream of mitochondria in K562 cells. The increased levels of mitochondrial Bax sensitized cells to etoposide-induced activation of caspases-2, -3 and -9 and apoptosis. However, after transient transfection with the Apaf-1 gene, K/Bax cells were sensitized to etoposide-induced caspase activation and apoptosis to a larger extent compared with Bax or Apaf-1 transfection alone. We therefore conclude that two mechanisms contribute to the resistance of K562 cells to etoposide-induced apoptosis; firstly failure of Bax targeting to mitochondria and, secondly, deficiency of Apaf-1. Uncoupling of Bax translocation from Bax induction can occur in response to etoposide-induced DNA damage.
Assuntos
Antineoplásicos Fitogênicos/farmacologia , Apoptose/efeitos dos fármacos , Etoposídeo/farmacologia , Leucemia/tratamento farmacológico , Proteínas Proto-Oncogênicas c-bcl-2 , Proteínas Proto-Oncogênicas/metabolismo , Fator Apoptótico 1 Ativador de Proteases , Transporte Biológico , Caspases/fisiologia , Dano ao DNA , Humanos , Células K562 , Leucemia/patologia , Proteínas/fisiologia , Proteína X Associada a bcl-2RESUMO
We have previously shown that Bax translocation was crucial in TNFalpha or etoposide-induced apoptosis. Overexpression of Bax sensitized chronic myeloid leukemic K562 cells to etoposide-induced apoptosis. Treatment with TNF-related apoptosis-inducing ligand (TRAIL) induces a loss of mitochondrial membrane potential (DeltaPsim), cytochrome c release from mitochondria, activation of caspases-8, -9, and -3, and cleavage of Bid in the K562 cell line. Bax failed to sensitize K562 cells to TRAIL-induced apoptosis. TRAIL did not induce Bax expression and/or translocation from cytosol to mitochondria in the K562 cell line. However, 100 microM Z-VAD.fmk, a pan caspase inhibitor, completely blocked TRAIL-initiated mitochondrial alterations and cleavages of caspases and Bid. We propose that TRAIL-induced apoptosis in K562 cells is via Type I apoptotic signal pathway. Bax translocation is not essential for TRAIL-induced cytochrome c release and DeltaPsim collapse in the Type I cells.
Assuntos
Apoptose/fisiologia , Glicoproteínas de Membrana/farmacologia , Proteínas Proto-Oncogênicas c-bcl-2 , Fator de Necrose Tumoral alfa/farmacologia , Clorometilcetonas de Aminoácidos/farmacologia , Apoptose/efeitos dos fármacos , Proteínas Reguladoras de Apoptose , Proteína Agonista de Morte Celular de Domínio Interatuante com BH3 , Proteínas de Transporte/metabolismo , Caspase 3 , Caspase 8 , Caspase 9 , Caspases/metabolismo , Inibidores de Cisteína Proteinase/farmacologia , Grupo dos Citocromos c/metabolismo , Precursores Enzimáticos/metabolismo , Humanos , Membranas Intracelulares/fisiologia , Células K562 , Leucemia Mielogênica Crônica BCR-ABL Positiva , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Mitocôndrias/fisiologia , Proteínas Proto-Oncogênicas/genética , Proteínas Recombinantes/metabolismo , Ligante Indutor de Apoptose Relacionado a TNF , Transfecção , Proteína X Associada a bcl-2RESUMO
Attendance rates at a diarrhea clinic were monitored in a defined population in rural Bangladesh. Weekly home visits were also carried out to determine diarrheal attacks in communities within six miles of the clinic. Within the first one mile radius, 90 per cent of diarrheal cases came to the clinic for treatment. At two miles the attendance fell to 70 per cent for males and 40 per cent for females. On an average, the greater the distance to the clinic, the more severe was the degree of dehydration on presentation, requiring more frequent use of intravenous fluid. Mortality secondary to diarrhea was significantly reduced only within a two-mile radius of the clinic.
Assuntos
Centros Comunitários de Saúde/estatística & dados numéricos , Atenção à Saúde , Diarreia/mortalidade , Adolescente , Adulto , Fatores Etários , Bangladesh , Criança , Pré-Escolar , Diarreia/epidemiologia , Diarreia/terapia , Métodos Epidemiológicos , Feminino , Hidratação , Humanos , Lactente , Recém-Nascido , Masculino , Pessoa de Meia-Idade , Saúde da População Rural , Fatores SexuaisRESUMO
To combat dehydration from diarrhoea in Shamlapur, a village of 7021 people, multiple community-based points were set up by trained volunteers for the distribution of glucose-electrolyte oral rehydration salt (ORS) packets. The comparable adjoining village, Bordil, with a population of 3888, obtained its supply of ORS from Shamlapur. Surveilance for 2 years showed that although diarrhoeal attack-rates were equal, consumption of ORS after diarrhoea was 80% in Shamlapur and 38% in Bordil. There were 8 deaths in Shamlapur caused by diarrhoea and 23 in Bordil, showing an overall case fatality-rate of 0.5% and 2.4%, respectively, and a diarrhoeal mortality-rate per 1000 population of 0.6 and 2.9, respectively. The observation indicated that although it may not be possible to reduce diarrhoeal attack-rates, easy availability of rehydration solution and its early use after village-based training may save many lives, particularly those of children.
