N-myc regulation of type I insulin-like growth factor receptor in a human neuroblastoma cell

Insulin-like growth factors I and II(IGF-I and IGF-II) stimulate proliferat ion and differentiation in many cell types, including cell lines derived fr om human neuroblastomas. Their effects are mediated via the IGF-I receptor (IGF-IR) that is essential for growth in these cells. Amplification of the N-myc oncogene is a marker for poor prognosis in neuroblastoma development, and it therefore seemed of interest to analyze the relationships that may exist between IGF-IR and N-myc, N-myc-deficient SK-N-SH neuroblastoma cells were used as an experimental model. lifter stable transfection with N-myc cDNA, Northern blotting revealed a marked increased in IGF-IR, IGF-II, IGF- binding protein (IGFBP)-2, and IGFBP-4 mRNA levels, whereas IGFBP-6 mRNA le vels were clearly diminished. Western immunoblot analysis also demonstrated increased intact IGFBP-2 but decreased IGFBP-6 in the presence of N-myc on cogene. Parallel binding experiments using IGF-I missing the first 3 amino acids revealed a 47% increase in binding sites for IGF-I and an increase of at least 335% in DNA synthesis, as measured by labeled thymidine incorpora tion into DNA, s.c. injection of these cells into nude mice provoked xenogr aft development in 50-100% of eases (depending on the series of experiments ). Control cells, in contrast, were not tumorigenic, In cells transfected w ith bp -420/+60 of the human IGF-IR promoter controlling expression of the luciferase reporter gene, promoter activity was stimulated by a factor of 3 .8 +/- 0.6 (n = 6) in the presence of N-myc oncogene. This suggests transcr iptional regulation of IGF-IR expression by N-myc. IGF-IR activity and N-my c amplification are two events that to date have been identified as indepen dently instrumental in the etiology of human neuroblastoma, Our results pro vide the first evidence of a direct link between them and demonstrate the e ffects of the oncogene on components of the IGF system in neuroblastoma cel l growth in vitro and in vivo.