RESUMEN
The Notch1 signaling pathway contributes to tumorigenesis by influencing differentiation, proliferation and apoptosis. Here, we demonstrate that inhibition of the Notch1 signaling pathway sensitizes glioblastoma cell lines and glioblastoma initiating cells to apoptosis induced by the death ligand TRAIL. This sensitization occurs through transcriptional upregulation of the death receptor 5 (DR5, TRAIL-R2). The increase in DR5 expression is abrogated by concomitant repression of the transcription factor Sp1, which directly binds to the DR5 promoter in the absence of Notch1 as revealed by chromatin immunoprecipitation. Consistent with these findings, Notch1 inhibition resulted in increased DR5 promoter activity, which was impaired by mutation of one out of two Sp1-binding sites within the proximal DR5 promoter. Moreover, we demonstrate that JNK signaling contributes to the regulation of DR5 expression by Notch1. Taken together, our results identify Notch1 as key driver for TRAIL resistance and suggest Notch1 as a promising target for anti-glioblastoma therapy.
Asunto(s)
Antineoplásicos/farmacología , Receptor Notch1/metabolismo , Receptores del Ligando Inductor de Apoptosis Relacionado con TNF/metabolismo , Factor de Transcripción Sp1/metabolismo , Ligando Inductor de Apoptosis Relacionado con TNF/farmacología , Apoptosis/efectos de los fármacos , Caspasa 8/metabolismo , Línea Celular Tumoral , Resistencia a Antineoplásicos , Expresión Génica/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Humanos , Receptor Notch1/genética , Receptores del Ligando Inductor de Apoptosis Relacionado con TNF/genética , Transducción de Señal , Regulación hacia ArribaRESUMEN
The Notch1-mediated signaling pathway has a central role in the maintenance of neural stem cells and contributes to growth and progression of glioblastomas, the most frequent malignant brain tumors in adults. Here, we demonstrate that the Notch1 receptor promotes survival of glioblastoma cells by regulation of the anti-apoptotic Mcl-1 protein. Notch1-dependent regulation of Mcl-1 occurs cell type dependent at a transcriptional or post-translational level and is mediated by the induction of epidermal growth factor receptor (EGFR). Inhibition of the Notch1 pathway overcomes apoptosis resistance and sensitizes glioblastoma cells to apoptosis induced by ionizing radiation, the death ligand TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) or the Bcl-2/Bcl-XL inhibitor ABT-737. In conclusion, targeting Notch1 might represent a promising novel strategy in the treatment of glioblastomas.
Asunto(s)
Receptores ErbB/metabolismo , Glioblastoma/genética , Glioblastoma/metabolismo , Proteínas Proto-Oncogénicas c-bcl-2/genética , Receptor Notch1/metabolismo , Transducción de Señal , Apoptosis/genética , Línea Celular Tumoral , Proliferación Celular , Supervivencia Celular/genética , Resistencia a Antineoplásicos/genética , Regulación Neoplásica de la Expresión Génica , Silenciador del Gen , Humanos , Proteína 1 de la Secuencia de Leucemia de Células Mieloides , Proteínas Proto-Oncogénicas c-raf/metabolismo , Procesamiento Postranscripcional del ARN , Receptor Notch1/genética , Transcripción GenéticaRESUMEN
Defects in the apoptotic signaling cascades contribute to the poor therapeutic response of malignant gliomas. As glioblastomas are characterized by high expression levels of anti-apoptotic Bcl-2 family proteins, we studied the effects of the novel Bcl-2 inhibitor, ABT-737, on malignant glioma cells. ABT-737 treatment released the pro-apoptotic Bax protein from its binding partner Bcl-2 and potently induced apoptotic cell death in glioblastoma cells in vitro and in vivo. The local administration of ABT-737 prolonged the survival in an intracranial glioma xenograft model. Downregulation of Mcl-1 and overexpression of Bcl-2 sensitized the cells to ABT-737-mediated apoptosis. Moreover, ABT-737 potentiated the cytotoxicity of the chemotherapeutic drugs vincristine and etoposide, and of the death ligand TRAIL. As glioma stem cells may play a crucial role for the tumor progression and the resistance to treatment in glioblastomas, we investigated the effects of ABT-737 on the subpopulation of glioma cells exhibiting stem cell characteristics. Inhibition of proliferation and induction of apoptosis by ABT-737 were less efficient in glioma stem cells than in non-stem cell-like glioma cells. As the resistance of glioma stem cells was associated with high Mcl-1 expression levels, ABT-737 treatment combined with downregulation of Mcl-1 could represent a promising novel approach in glioblastoma treatment.
Asunto(s)
Apoptosis/efectos de los fármacos , Compuestos de Bifenilo/farmacología , Glioblastoma/metabolismo , Glioblastoma/patología , Nitrofenoles/farmacología , Proteínas Proto-Oncogénicas c-bcl-2/antagonistas & inhibidores , Sulfonamidas/farmacología , Animales , Línea Celular Tumoral , Glioblastoma/genética , Humanos , Ratones , Células Madre Neoplásicas/citología , Células Madre Neoplásicas/efectos de los fármacos , Piperazinas/farmacología , Unión Proteica , Proteínas Proto-Oncogénicas c-bcl-2/clasificación , Proteínas Proto-Oncogénicas c-bcl-2/genética , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Tasa de Supervivencia , Ligando Inductor de Apoptosis Relacionado con TNF/metabolismo , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
A total of 38 isolates of Candida albicans were collected from clinical specimens and tested for minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) of amphotericin B, flucytosine and fluconazole. For amphotericin B and flucytosine all patients had isolates with MICs < or = 2 micrograms ml-1 and < or = 8 micrograms ml-1 respectively. For fluconazole all but two isolates had MICs < or = 16 micrograms ml-1. In vitro susceptibility testing remains problematic since standardized methods have not been established and the susceptibility and resistance ranges of MIC/MFC values still have to be defined in relation to in vivo data. Nevertheless, these results indicate that topical application of amphotericin B (more than 1 kg of amphotericin B per year at an intensive care unit performing selective digestive tract decontamination on certain trauma patients) had no major impact on the resistance patterns of C. albicans. In contrast, in this study both fluconazole-resistant isolates were from AIDS patients who were known to have received fluconazole therapy. Treatment with fluconazole--quite common in patients with AIDS--may produce resistant fungal isolates.
Asunto(s)
Antifúngicos/farmacología , Candida albicans/efectos de los fármacos , Anfotericina B/farmacología , Austria , Fluconazol/farmacología , Flucitosina/farmacología , Humanos , Pruebas de Sensibilidad MicrobianaRESUMEN
Fifty patients with moderate or severe bronchitis were randomly allocated into groups receiving orally either 1000 mg amoxycillin twice daily or 750 mg three times daily. Overall cure rates (both 92%) and the incidence of side-effects (4% and 8%, respectively) were similar in both groups. A twice daily regimen, therefore, seems to be as effective as conventional treatment and has the advantage of being more convenient for the patient.