DNA amplification and tumorigenicity of the human melanoma cell line MeWo

Homogeneously staining regions (HSRs) were found in hypodiploid cells (40%) of a subline of the human melanoma cell line, MeWo, (MeWo-C) but were absent from the hypotetraploid cells (60%). Another subline (MeWo-B) was also shown to contain two populations of cells, 70% hypodiploid and 30% hypotetraploid. None of the MeWo-B cells contained HSRs, but all four cell types from both sublines shared marker chromosomes indicating their common origin. The hypodiploid MeWo-B cells were karyotypically similar to the hypodiploid MeWo-C cells except for the presence of the HSRs in the latter. Both MeWo-C and MeWo-B sublines were injected into BALB/c nude mice. The MeWo-C cells were markedly more tumorigenic than MeWo-B cells as judged by tumor incidence, latency, average tumor size, and tumor take values. Cytogenetic and flow cytofluorometric analyses of the tumors induced by MeWo-C cells revealed a shift in the tumor cell population from 40% to greater than 90% HSR-containing hypodiploid cells during tumor growth. Hybridization of tumor DNA to a probe (D15Z1), the sequence of which is amplified in the HSRs, also indicated an increase in the proportion of HSR-bearing cells during tumor growth. No such selective advantage was found with the hypodiploid, HSR-lacking MeWo-B cells. The results suggest that HSRs found in the human melanoma line MeWo may confer enhanced tumorigenicity to the cells containing them.