Coamplification of multiple regions of chromosome 2, including MYCN, in a single patchwork amplicon in cancer cell lines

Coamplification of multiple segments of chromosome 2, including an MYCN-bearing segment, was examined in 2 cancer cell lines, NCI-H69 (lung cancer) and IMR-32 (neuroblastoma). High-resolution array-CGH analysis revealed 13 and 6 highly amplified segments located at different sites in chromosome 2 in NCI-H69 and IMR-32, respectively. FISH analysis demonstrated that these segments were co-localized in double minutes in NCI-H69 and in homogeneously staining regions in IMR-32. Connectivity of the segments was determined by a PCR assay using designed primer sets. It was found that all the segments were connected to each other irrespective of their order and orientation against the genome sequence, and a single chain-like cluster was configured in both cell lines. Such patchwork structures of the amplicons suggest the possibility that massive genomic rearrangements, explained by the single catastrophic event model, are involved in the formation of the amplicons, enabling the coamplification of different chromosomal regions including the MYCN locus. The model comprises massive fragmentation of chromosomes and random rejoining of the fragments.