In neuroblastoma lines in which the N-myc gene is present as a single copy, the expression of N-myc as messenger RNA is increased relative to that in nonneuroblastoma cell lines and tumors.
We have analyzed a 3.8 kb Eco RI fragment of genomic DNA obtained from the amplified N-myc gene of human neuroblastoma cell line BE(2)-C. This fragment contains an exon with an open reading frame encoding approximately 170 amino acids of the carboxy-terminal end of the putative N-myc protein.
The N-myc gene, first detected by its homology to the second exon of the c-myc gene, is amplified and/or expressed in tumours or cell lines derived from neuroblastoma, retinoblastoma and SCLC.
We have demonstrated that the entire murine N-myc gene and the sequences necessary for its expression in human neuroblastoma cells are contained within a 7.4-kilobase murine genomic clone.
Moreover, extra-copies of cellular oncogenes have been located in tumor cells in vivo; particularly N-myc gene amplification was discovered in advanced stage of neuroblastoma (NB).
Gene amplification and rearrangements are discussed through review of recent work on the N-myc gene in neuroblastoma and the epidermal growth factor receptor (EGFR) gene in glioblastoma.
It is concluded that in situ hybridization of tissue sections is as effective as Southern blot analysis of tumor cell DNA in identifying human neuroblastoma tumors in which the N-myc gene is of prognostic significance.
According to this criterion, 14 cases (12 cases of neuroblastoma and 2 cases of ganglioneuroblastoma) were positive for N-myc gene amplification of 27 cases (18 cases of neuroblastoma, 5 cases of ganglioneuroblastoma, and 4 cases of composite ganglioneuroblastoma).
In the human neuroblastoma cell line IMR32 the N-myc gene happens to be amplified and actively expressed, whereas no stable c-myc RNA can be detected in the same cells.
Thus, flow cytometric analysis of DNA content together with N-myc gene dosage allowed us to distinguish two different subsets of neuroblastoma tumors: the first one aneuploid, with single-copy N-myc, usually observed in patients younger than 24 months with localized or IV-S clinical stages; the second one near-diploid, with frequent N-myc amplification, usually observed in patients older than 24 months with advanced clinical stages.
N-myc gene amplification of the gynecological malignant tumor cell lines and a neuroblastoma cell line was studied by the Southern hybridization method along with the production of neuron-specific enolase (NSE) by these cell lines.
To determine directly whether NMYC might modulate class I MHC expression in NB, we transfected a plasmid containing a recombinant NMYC gene into two tumor cell lines derived from a NB and a related neuroepithelioma tumor.
It is concluded that immunohistochemical staining for the N-myc gene product will facilitate prediction of the prognosis of patients with neuroblastoma.
With the identification of amplified MYCN and the demonstration of a consensus deletion spanning the chromosome 1p36.1-2 region it appears now likely that both amplification of a cellular oncogene and loss of a tumour-suppressor gene play an important role in neuroblastoma.
Because N-myc protein is thought to have a regulatory role, prolongation of the half-life of this protein may be an important factor in the regulation of growth in NBs which lack N-myc amplification and rapidly progress.
To investigate the interrelationships between these two parameters, tumor samples from 18 patients with neuroblastoma were analyzed for both total DNA and N-myc gene content.