RESUMO
Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates cellular and systemic homeostatic responses to reduced O(2) availability in mammals, including angiogenesis, erythropoiesis, and glycolysis. HIF-1 activity is controlled by the O(2)-regulated expression of the HIF-1alpha subunit. Under nonhypoxic conditions, HIF-1alpha protein is subject to ubiquitination and proteasomal degradation. Here we report that missense mutations and/or deletions involving several different regions of HIF-1alpha result in constitutive expression and transcriptional activity in nonhypoxic cells. We demonstrate that hypoxia results in decreased ubiquitination of HIF-1alpha and that missense mutations increase HIF-1alpha expression under nonhypoxic conditions by blocking ubiquitination.
Assuntos
Proteínas de Ligação a DNA/genética , Regulação da Expressão Gênica , Mutação de Sentido Incorreto , Proteínas Nucleares/genética , Oxigênio/fisiologia , Deleção de Sequência , Ubiquitinas/metabolismo , Linhagem Celular , Núcleo Celular/metabolismo , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/metabolismo , Sequências Hélice-Alça-Hélice , Humanos , Fator 1 Induzível por Hipóxia , Subunidade alfa do Fator 1 Induzível por Hipóxia , Substâncias Macromoleculares , Mutagênese Sítio-Dirigida , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Mutação Puntual , Processamento de Proteína Pós-Traducional , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Fatores de Transcrição/genética , TransfecçãoRESUMO
The switch to an angiogenic phenotype is a fundamental determinant of neoplastic growth and tumor progression. We demonstrate that homozygous deletion of the p53 tumor suppressor gene via homologous recombination in a human cancer cell line promotes the neovascularization and growth of tumor xenografts in nude mice. We find that p53 promotes Mdm2-mediated ubiquitination and proteasomal degradation of the HIF-1alpha subunit of hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor that regulates cellular energy metabolism and angiogenesis in response to oxygen deprivation. Loss of p53 in tumor cells enhances HIF-1alpha levels and augments HIF-1-dependent transcriptional activation of the vascular endothelial growth factor (VEGF) gene in response to hypoxia. Forced expression of HIF-1alpha in p53-expressing tumor cells increases hypoxia-induced VEGF expression and augments neovascularization and growth of tumor xenografts. These results indicate that amplification of normal HIF-1-dependent responses to hypoxia via loss of p53 function contributes to the angiogenic switch during tumorigenesis.
