RESUMEN
In this study, we focus on the analysis of a previously identified cancer-related gene signature (CGS) that underlies the cross talk between the p53 tumor suppressor and Ras oncogene. CGS consists of a large number of known Ras downstream target genes that were synergistically upregulated by wild-type p53 loss and oncogenic H-Ras(G12V) expression. Here we show that CGS expression strongly correlates with malignancy. In an attempt to elucidate the molecular mechanisms underling the cooperation between p53 loss and oncogenic H-Ras(G12V), we identified distinguished pathways that may account for the regulation of the expression of the CGS. By knocking-down p53 or by expressing mutant p53, we revealed that p53 exerts its negative effect by at least two mechanisms mediated by its targets B-cell translocation gene 2 (BTG2) and activating transcription factor 3 (ATF3). Whereas BTG2 binds H-Ras(G12V) and represses its activity by reducing its GTP loading state, which in turn causes a reduction in CGS expression, ATF3 binds directly to the CGS promoters following p53 stabilization and represses their expression. This study further elucidates the molecular loop between p53 and Ras in the transformation process.
Asunto(s)
Carcinoma de Pulmón de Células no Pequeñas/genética , Neoplasias Pulmonares/genética , Proteína p53 Supresora de Tumor/genética , Proteínas ras/genética , Factor de Transcripción Activador 3/genética , Factor de Transcripción Activador 3/metabolismo , Carcinoma de Pulmón de Células no Pequeñas/metabolismo , Transformación Celular Neoplásica/genética , Transformación Celular Neoplásica/metabolismo , Regulación Neoplásica de la Expresión Génica , Técnicas de Silenciamiento del Gen , Genes ras , Humanos , Proteínas Inmediatas-Precoces/genética , Proteínas Inmediatas-Precoces/metabolismo , Neoplasias Pulmonares/metabolismo , Sistema de Señalización de MAP Quinasas , Masculino , Fosfatidilinositol 3-Quinasas/metabolismo , Proteína p53 Supresora de Tumor/biosíntesis , Proteína p53 Supresora de Tumor/metabolismo , Proteínas Supresoras de Tumor/genética , Proteínas Supresoras de Tumor/metabolismo , Proteínas ras/biosíntesis , Proteínas ras/metabolismoRESUMEN
Ras transformation requires Ras membrane anchorage, which is promoted by a farnesylcysteine carboxymethyl ester and by additional sequences specific to each Ras isoform. We showed previously that S-trans,trans-farnesylthiosalicylic acid (FTS) disrupts Ras membrane anchorage and that this disturbance contributes to inhibition of cell transformation and tumor growth. Most tumor cells develop resistance to anticancer agents. Here we examined whether tumor cells develop resistance to FTS and evaluated the therapeutic potential of FTS combined with cytotoxic drugs, because oncogenic Ras promotes antiapoptotic signals in tumors of epithelial origin. We showed that Panc-1 pancreatic cancer cells, SW480 colon cancer cells, and H-ras (EJ)-transformed Rat-1 fibroblasts exposed to FTS for prolonged periods (>6 months) do not escape FTS-induced growth inhibition and do not develop drug resistance. These cells continued to express reduced amounts of Ras, exhibit a reversed phenotype, and show an altered response to the cytotoxic drugs doxorubicin and gemcitabine. FTS-treated Panc-1 or SW480 cells acquired sensitivity to the cytotoxic drugs, whereas FTS-treated EJ cells lost sensitivity to doxorubicin, reflecting the opposite effects of oncogenic Ras on the survival of epithelial cells and fibroblasts. Treatment with FTS led to a marked increase in sensitivity to gemcitabine of the formerly resistant SW480 cells and a 100-fold increase in sensitivity to gemcitabine of Panc-1 cells. Such treatment in mice with preexisting Panc-1 tumors provided a synergistic effect of FTS and gemcitabine, leading to enhanced inhibition of tumor growth and a 65% increase in survival rate.
