Unusual distribution of chromosome 12 in a testicular germ-cell tumor cell line (833K) and its cisplatin-resistant derivative (64CP9).

The distribution of chromosome 12 in a cisplatin-sensitive testicular germ-cell tumor (TGCT) cell line (833K), and its cisplatin-resistant derivative (64CP9), was studied by fluorescent in situ hybridization (FISH) using DNA alpha satellite and whole chromosome painting probes for chromosome 12. Chromosomes 12 and i(12p) in these cell lines were readily identified. However, chromosome 12-derived chromatin was also observed in acrocentric- and nonacrocentric-derived chromosomes. Several of the chromosome 12 painted regions resembled satellites and were separated from the chromosome by nonstaining stalk-like regions. In each cell line, different chromosomes were involved. In the 833K TGCT cell line these were a der(8), a der(14) with a 12-labeled "satellite" on the q arm and a der(14) with a 12-labeled "satellite" on the p arm. In the 64CP9 TGCT cell line, these were a der(5), a der(17), and a der(8). The der(8) observed in 64CP9 was different from the der(8) seen in 833K. These derived chromosomes were characterized using sequential FISH, Wright staining, and silver staining for nucleolar organizing regions (AgNORs). The non-staining stalk-like regions were AgNOR positive, indicating "ectopic" NORs. Chromosome 22 distribution in these cell lines was also studied. FISH, using a chromosome 22-specific painting probe, identified a small metacentric marker and a der(12)t(12;22) in each cell line. It is not known whether the differences in distribution of chromosome 12-derived chromatin between the two cell lines are related to cisplatin resistance. Our study shows that the distribution of chromosome 12 in the two TGCT cell lines is much more extensive than could be identified in GTG-banded karyotypes. FISH allows characterization of unidentified chromatin and thus is a valuable adjunct to traditional cytogenetic techniques.