Concomitant down-regulation of expression of integrin subunits by N-myc in human neuroblastoma cells: Differential regulation of alpha 2, alpha 3 and beta 1

Amplification and over-expression of the N-myc oncogene is associated with the progression of neuroblastoma in children and in a nude mouse model system. Neuroblastoma cell lines with widely different levels of N-myc illustrate an inverse relationship between N-myc over-expression and reduced expression of several integrin extracellular matrix receptors. Transfection and over-expression of N-myc in a neuroblastoma cell line not normally expressing the protein resulted in cells that grew loosely associated with tissue culture plates; this correlated with reduced levels of beta 1 integrin subunit. Evidence is now presented that alpha 2 and alpha 3 integrin subunit levels are also reduced in cells that over-express N-myc, with virtually no association of alpha 2 or alpha 3 subunits with beta 1. Consequently, maturation of the beta 1 subunit and cell surface expression of the integrins are greatly reduced in N-myc-transfected cells. A small amount of beta 1 protein does get to the cell surface, however, suggesting that an as yet unidentified alpha subunit is produced by the N-myc-expressing cells. Finally, the observed reductions in integrin protein levels are reflections of greatly reduced levels of integrin alpha 2 and alpha 3 mRNAs, as well as a smaller reduction in beta 1 mRNA (80%, 94% and 52%, respectively). Post-transcriptional mechanisms modulating beta 1 integrin levels are also operative. These results indicate that over-expression of N-myc from a transfected gene in a neuroblastoma cell line that does not normally produce the protein generates cell lines with many of the characteristics of naturally metastatic cells with amplified N-myc genes. Modulation of N-myc and integrin expressions may play a significant role in progression of human neuroblastoma.