RESUMO
Amplification of N-myc oncogene is a frequent event in advanced stages of human neuroblastoma and correlates with poor prognosis and enhanced neovascularization. Angiogenesis is an indispensable prerequisite for the progression and metastasis of solid malignancies, which is modulated by tumor suppressors and oncogenes. We have addressed the possibility that N-myc oncogene might regulate angiogenesis in neuroblastoma. Here, we report that experimental N-Myc overexpression results in down-regulation of leukemia inhibitory factor (LIF), a modulator of endothelial cell proliferation. Reporter assays using the LIF promoter and a series of N-Myc mutants clearly demonstrated that down-regulation of the LIF promoter was independent of Myc/Max interaction and required a contiguous N-terminal N-Myc domain. STAT3, a downstream signal transducer, was essential for LIF activity as infection with adenoviruses expressing a phosphorylation-deficient STAT3 mutant rendered endothelial cells insensitive to the antiproliferative action of LIF. LIF did not influence neuroblastoma cell proliferation suggesting that, at least in the context of neuroblastoma, LIF is involved in paracrine rather than autocrine interactions. Our data shed light on the mechanisms by which N-myc oncogene amplification enhances the malignant phenotype in neuroblastoma.
Assuntos
Inibidores do Crescimento/metabolismo , Interleucina-6 , Linfocinas/metabolismo , Neuroblastoma/genética , Proteínas Proto-Oncogênicas c-myc/genética , Divisão Celular/efeitos dos fármacos , Meios de Cultivo Condicionados , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação para Baixo , Endotélio/citologia , Endotélio/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Inibidores do Crescimento/genética , Inibidores do Crescimento/farmacologia , Humanos , Fator Inibidor de Leucemia , Linfocinas/genética , Linfocinas/farmacologia , Mutação , Neuroblastoma/tratamento farmacológico , Neuroblastoma/patologia , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas c-myc/metabolismo , Fator de Transcrição STAT3 , Transativadores/genética , Transativadores/metabolismo , Transfecção , Células Tumorais CultivadasRESUMO
Angiogenesis is an indispensable prerequisite for the progression and metastasis of solid malignancies. Tumor angiogenesis appears to be governed by alterations of tumor suppressor or oncogenes operant in a broad range of tumors. We have addressed this issue in neuroblastoma, a malignancy characterized by the near-exclusive amplification and overexpression of the N-Myc oncogene. Here, we report that N-Myc overexpression results in down-regulation of interleukin-6 (IL-6) and that IL-6 is an inhibitor of endothelial cell proliferation and VEGF-induced rabbit corneal angiogenesis. STAT3 is instrumental for IL-6 activity as infection with adenoviruses expressing a phosphorylation deficient STAT3 mutant renders endothelial cells insensitive to the antiproliferative action of IL-6. Finally, though IL-6 does not influence neuroblastoma cell growth, IL-6-expressing xenograft tumors in mice exhibit reduced neovascularization and suppressed growth. Our data shed new light on the mechanisms by which N-myc oncogene amplification enhances the malignant phenotype in neuroblastomas.
