RESUMEN
Oncogenic types of human papillomaviruses (HPVs) cause cervical cancer in humans. The antiapoptotic viral E6 gene has been identified as a key factor for maintaining the viability of HPV-positive cancer cells. Although E6 has the potential to modulate many apoptosis regulators, the crucial apoptotic pathway blocked by endogenous E6 in cervical cancer cells remained unknown. Using RNA interference (RNAi), here, we show that targeted inhibition of E6 expression in cervical cancer cells leads to the transcriptional stimulation of the PUMA promoter, in a p53-dependent manner. This is linked to the activation and translocation of Bax to the mitochondrial membrane, cytochrome c release into the cytosol, and activation of caspase-3, in a PUMA-dependent manner. Moreover, inhibition of Bax expression by RNAi efficiently reverts the apoptotic phenotype, which results from inhibition of E6 expression. Thus, interference with the p53/PUMA/Bax cascade is crucial for the antiapoptotic function of the viral E6 oncogene in HPV-positive cancer cells.
Asunto(s)
Apoptosis , Proteínas de Unión al ADN/metabolismo , Regulación Neoplásica de la Expresión Génica , Proteínas Oncogénicas Virales/metabolismo , Proteínas Represoras/metabolismo , Proteína X Asociada a bcl-2/metabolismo , Apoptosis/efectos de los fármacos , Apoptosis/genética , Proteínas Reguladoras de la Apoptosis/genética , Proteínas Reguladoras de la Apoptosis/metabolismo , Caspasa 3 , Caspasas/metabolismo , Citocromos c/genética , Citocromos c/metabolismo , Proteínas de Unión al ADN/genética , Activación Enzimática/genética , Femenino , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Regulación Neoplásica de la Expresión Génica/genética , Células HeLa , Humanos , Mitocondrias/genética , Mitocondrias/metabolismo , Proteínas Oncogénicas Virales/genética , Transporte de Proteínas/genética , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Interferencia de ARN/efectos de los fármacos , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/farmacología , Proteínas Represoras/genética , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismo , Neoplasias del Cuello Uterino/genética , Neoplasias del Cuello Uterino/metabolismo , Neoplasias del Cuello Uterino/virología , Proteína X Asociada a bcl-2/antagonistas & inhibidores , Proteína X Asociada a bcl-2/genéticaRESUMEN
Cancer cells are typically characterized by apoptosis deficiency. In order to investigate a possible role for the anti-apoptotic livin gene in renal cell cancer (RCC), we analyzed its expression in tumor tissue samples and in RCC-derived cell lines. In addition, we studied the contribution of livin to the apoptotic resistance of RCC cells by RNA interference (RNAi). Livin gene expression was detected in a significant portion of RCC tumor tissue specimens (13/14, 92.9%) and tumor-derived cell lines (12/15, 80.0%). Moreover, targeted inhibition of livin by RNAi markedly sensitized RCC cells towards proapoptotic stimuli, such as UV irradiation or the chemotherapeutic drugs etoposide, 5-fluorouracil, and vinblastine. These effects were specific for livin expressing tumor cells. We conclude that livin can contribute significantly to the apoptosis resistance of RCC cells. Targeted inhibition of livin could represent a novel therapeutic strategy to increase the sensitivity of renal cancers towards pro-apoptotic agents.