Down-regulation of endothelial cell growth inhibitors by enhanced MYCN oncogene expression in human neuroblastoma cells

Recent evidence indicates that the genetic alterations of the multistage process of malignant transformation appear to activate tumor neovascularization by altering the balance between stimulators and inhibitors of angiogenesis. In the present study, we have attempted to define the effect of enhanced MYCN oncogene expression on the profile of endothelial cell growth modulators in neuroblastoma cells. We report here that conditioned medium of human neuroblastoma cells with normal MYCN expression contains three inhibitors of endothelial cell proliferation, which appear to;be novel proteins as judged by their physicochemical, immunological and biological properties. All three inhibitors are diminished or become undetectable upon experimental increase of MYCN expression. Our results suggest that enhanced MYCN expression in human neuroblastoma cells alters the angiogenic balance by down-regulating endothelial cell growth inhibitors but leaving the expression of the stimulators unaffected. These data shed light on the molecular mechanisms linking the genetic changes of malignant transformation with initiation of tumor angiogenesis. Moreover, our observations might explain the poor prognosis of human neuroblastomas following MYCN oncogene amplification through initiation of angiogenesis and subsequent tumor growth and spread.