RESUMEN
c-Myc drives uncontrolled cell proliferation in various human cancers. However, in mouse embryo fibroblasts (MEFs), c-Myc also induces apoptosis by activating the p19Arf tumor suppressor pathway. Tbx2, a transcriptional repressor of p19Arf, can collaborate with c-Myc by suppressing apoptosis. MEFs overexpressing c-Myc and Tbx2 are immortal but not transformed. We have performed an unbiased genetic screen, which identified 12 oncogenes that collaborate with c-Myc and Tbx2 to transform MEFs in vitro. One of them encodes the LPA2 receptor for the lipid growth factor lysophosphatidic acid (LPA). We find that LPA1 and LPA4, but not LPA3, can reproduce the transforming effect of LPA2. Using pharmacological inhibitors, we show that the in vitro cell transformation induced by LPA receptors is dependent on the Gi-linked ERK and PI3K signaling pathways. The transforming ability of LPA1, LPA2 and LPA4 was confirmed by tumor formation assays in vivo and correlated with prolonged ERK1/2 activation in response to LPA. Our results reveal a direct role for LPA receptor signaling in cell transformation and tumorigenesis in conjunction with c-Myc and reduced p19Arf expression.
Asunto(s)
Transformación Celular Neoplásica , Genes myc , Lisofosfolípidos/fisiología , Receptores del Ácido Lisofosfatídico/fisiología , Animales , División Celular/fisiología , Supervivencia Celular/fisiología , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Embrión de Mamíferos/fisiología , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Fibroblastos/fisiología , Regulación Neoplásica de la Expresión Génica , Pruebas Genéticas/métodos , Humanos , Ratones , Neoplasias/patologíaAsunto(s)
Compensación de Dosificación (Genética) , Proteínas de Drosophila/genética , Silenciador del Gen , Células Madre/metabolismo , Animales , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/metabolismo , Epigénesis Genética , Femenino , N-Metiltransferasa de Histona-Lisina , Histonas/química , Histonas/metabolismo , Humanos , Masculino , Modelos Genéticos , Proteína de la Leucemia Mieloide-Linfoide , Neoplasias/etiología , Nucleosomas/metabolismo , Complejo Represivo Polycomb 1 , Proteínas del Grupo Polycomb , Proto-Oncogenes/genética , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Ubiquitina/metabolismoRESUMEN
Otto Warburg's classic treatise on the reprogramming of tumour metabolism from oxidative to glycolytic metabolism was published in London in 1930. Although the Warburg effect is one of the most universal characteristics of solid tumours, the molecular basis for this phenomenon has only recently been elucidated by studies indicating that increased expression of genes encoding glucose transporters and glycolytic enzymes in tumour cells is mediated by the transcription factors c-MYC and HIF-1. Whereas c-myc is a direct target for oncogenic mutations, expression of hypoxia-inducible factor 1 (HIF-1) is indirectly up-regulated via gain-of-function mutations in oncogenes and loss-of-function mutations in tumour suppressor genes that result increased HIF-1alpha protein expression and/or increased HIF-1 transcriptional activity in a cell-type-specific manner. As a result of genetic alterations and intratumoral hypoxia, HIF-1alpha is overexpressed in the majority of common human cancers relative to the surrounding normal tissue. In human breast cancer and brain tumours, HIF-1alpha overexpression is strongly correlated with tumour grade and vascularity.
Asunto(s)
Neoplasias/metabolismo , Factores de Transcripción , Hipoxia de la Célula/fisiología , Proteínas de Unión al ADN/genética , Genes myc , Glucólisis , Humanos , Factor 1 Inducible por Hipoxia , Subunidad alfa del Factor 1 Inducible por Hipoxia , Mutación , Proteínas Nucleares/genéticaRESUMEN
Hypoxia-inducible factor 1 (HIF-1) is a transcriptional activator composed of HIF-1alpha and HIF-1beta subunits. Several dozen HIF-1 targets are known, including the gene encoding vascular endothelial growth factor (VEGF). Under hypoxic conditions, HIF-1alpha expression increases as a result of decreased ubiquitination and degradation. The tumor suppressors VHL (von Hippel-Lindau protein) and p53 target HIF-1alpha for ubiquitination such that their inactivation in tumor cells increases the half-life of HIF-1alpha. Increased phosphatidylinositol 3-kinase (PI3K) and AKT or decreased PTEN activity in prostate cancer cells also increases HIF-1alpha expression by an undefined mechanism. In breast cancer, increased activity of the HER2 (also known as neu) receptor tyrosine kinase is associated with increased tumor grade, chemotherapy resistance, and decreased patient survival. HER2 has also been implicated as an inducer of VEGF expression. Here we demonstrate that HER2 signaling induced by overexpression in mouse 3T3 cells or heregulin stimulation of human MCF-7 breast cancer cells results in increased HIF-1alpha protein and VEGF mRNA expression that is dependent upon activity of PI3K, AKT (also known as protein kinase B), and the downstream kinase FRAP (FKBP-rapamycin-associated protein). In contrast to other inducers of HIF-1 expression, heregulin stimulation does not affect the half-life of HIF-1alpha but instead stimulates HIF-1alpha synthesis in a rapamycin-dependent manner. The 5'-untranslated region of HIF-1alpha mRNA directs heregulin-inducible expression of a heterologous protein. These data provide a molecular basis for VEGF induction and tumor angiogenesis by heregulin-HER2 signaling and establish a novel mechanism for the regulation of HIF-1alpha expression.
