Amplification units containing human N-myc and c-myc genes.

Abstract

The amplification units in human tumors containing amplified myc genes were examined. The amplifilcation unit in all cases consisted of a large genomic region coamplified with the coding region of the myc genes themselves. In eight independent neuroblastomas containing N-myc amplifications, the amplification unit was estimated to be 290 to 430 kilobases. This amplification unit was highly conserved among the different neuroblastomas, with some neuroblastomas containing almost identical units. In contrast, five tumor cell lines containing c-myc amplifications exhibited amplification units that were more variable in size (90 to 300 kilobases) and sequence content; at least three different patterns of c-myc amplification units could be discerned.It has been shown that increased levels of normal cellular oncogene products are capable of transforming cells (1, 2). Gene amplification provides a potent mechanism for increasing the amount of a normal cellular oncogene product (reviewed in refs. [3][4][5]. Amplification of various oncogenes has been reported in a variety of human tumors or cell lines derived from human tumors. These reports have included amplification of c-erbB in brain tumors and a squamous cell carcinoma (6-8), c-abl in leukemia (9, 10), c-myb in colon cancer and leukemia (11,12), N-myc in neuroblastomas and retinoblastomas (13)(14)(15)(16), and c-myc in several types of tumors (17-21). Despite the fact that amplified oncogenes have occurred in this wide variety of neoplasms, little is known about the mechanism of oncogene amplification or the structure of their amplification units.At the chromosomal level, the amplified oncogenes are contained within double minute chromosomes (DM) or homogeneously staining regions (HSR) (reviewed in refs. [3][4][5]. DM and HSR also occur in drug resistant cell lines. In such cases, it has been shown that the genes conferring drug resistance are amplified within a large domain of DNA that includes 100 to 1000 kilobases (kb) of sequences flanking the drug resistance genes themselves (22-26). The amplified gene and coamplified flanking sequences form the amplification unit. An understanding of the structure of the amplification unit is essential to delineating the mechanism of amplification.We have now partially characterized the amplification units in eight human neuroblastomas containing amplified N-myc genes and five human cell lines containing amplified c-myc genes. In both cases, large domains of coamplified sequences accompanied the amplification of the coding region of the oncogene. The N-myc amplification unit was approximately 290 to 430 kb in length and was highly conserved among neuroblastomas from eight different patients. The size of the c-myc amplification unit was much more variable, ranging from 90 to 300 kb. The patterns of amplified sequences indicated that at least three different c-myc amplification units were represented by the five cell lines studied. These results with oncogene amplification units are compared with the amplification units i...

Characterization of DNA rearrangements of N‐myc gene amplification in three neuroblastoma cell lines by pulsed‐field gel electrophoresis

“…Kinzler et al [24] reported that the amplification unit in eight neuroblastomas containing N-myc amplification was 290-430 kb long. They estimated the values from the sum of the sizes of bands detected using Roninson's technique [9].…”

Characterization of N-myc amplification units in human neuroblastoma cells.

“…In contrast to the large amount of information available on amplicon organization in drug-resistant cell lines of rodents, there have been relatively few studies on the structural organization of amplicons containing oncogenes (3,16,32,33). In the study reported here, we established numerous clones from the N-myc amplification unit of a neuroblastoma tumor to determine several basic structural features of the amplification units in these cells.…”

Neoplastic transformation by the human gene N-myc.

“…Amplification of the gene in fact appears to correlate with metastatic progression and poor clinical prognosis in patients with neuroblastoma (5,33). It nevertheless remains conceivable that N-myc is fortuitously amplified as part of a larger unit (estimated to be 300 to 3,000 kilobases in length [9,12]) that contains an as-yet-unidentified gene involved in tumorigenesis. In an effort to explore this issue, we and others have examined the biological activity of N-myc in cell culture.…”