RESUMO
Neurofibromatosis type 1 (NF1) is characterized by a high incidence of benign and malignant tumors attributed to loss of function of Nf1, which encodes neurofibromin, a tumor suppressor with Ras-GAP activity. Neurofibromin deficiency typically causes chronic activation of Ras, considered the major contributor to manifestation of NF1. Resistance to radio- and chemotherapy are typical of NF1-associated tumors, but the underlying mechanism is unknown. Here, we investigated interrelationships between neurofibromin expression, Ras activity, and sensitivity to apoptosis. Neurofibromin-deficient mouse embryonic fibroblasts (MEFs) and human NF1 tumor cells were more resistant than neurofibromin-expressing cells to apoptosis. Moreover, Nf1(-/-), Nf1(+/-), and Nf1(+/+) MEFs exhibited gene-dosage-related resistance to apoptosis. Resistance of the Nf1-deficient cells was mediated by two survival pathways: a Ras-dependent pathway, and a Ras-independent pathway promoted by the lack of an NF1-GRD-independent proapoptotic action of neurofibromin. Therefore, besides its Ras-dependent growth inhibition, neurofibromin can exert tumor suppression via a proapoptotic effect.
Assuntos
Apoptose , Neurofibromina 1/metabolismo , Proteínas ras/metabolismo , Animais , Apoptose/efeitos dos fármacos , Linhagem Celular Transformada , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , AMP Cíclico/metabolismo , Embrião de Mamíferos/citologia , Embrião de Mamíferos/efeitos dos fármacos , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Farneseno Álcool/análogos & derivados , Farneseno Álcool/farmacologia , Fibroblastos/citologia , Fibroblastos/efeitos dos fármacos , Dosagem de Genes/efeitos dos fármacos , Genótipo , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/deficiência , Camundongos , Neurofibromina 1/deficiência , Fosforilação/efeitos dos fármacos , Proteínas Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Salicilatos/farmacologia , Vírus 40 dos Símios , Serina-Treonina Quinases TOR , Proteínas ras/antagonistas & inibidoresRESUMO
A method for obtaining left ventricular (LV) volume curves, synchronized with average LV pressure (LVP) curves for calculation of LV contractility, is described. Multiple gated blood pool imaging was performed to calculate average LV volume curves. Simultaneously with this acquisition, LVPs and aortic pressures were measured by indwelling catheters and recorded on an FM tape recorder. These signals were fed to the computer as image information and averaged and processed by the software developed for this purpose. Pressure resolution of the calibrated images was 4 mmHg/pixel when provision was made for a maximum pressure of 200 mmHg. A good correlation (r = 0.99) was obtained between the calculated peak LVPs and mean peak LVPs read from the chart recorder. The regression equation was: digitized peak LVP = 1.04 x chart recording--5.11 mmHg and the standard error of the estimate was 2.9 mmHg. Similar results were obtained with the aortic pressure (AP) measurements (digitized AP = 0.94 x chart recording + 6.37 mmHg, the standard error of the estimate was 3.8 mmHg). The digitized data also allowed the construction of pressure-volume loops for interpretation of ventricular contractility.