Tumorigenicity of ten karyotypically distinct cell types present in the human melanoma cell line MeWo-A

The earliest passage of the human melanoma cell line, MeWo-A, consists of ten cell types that can be distinguished on the basis of chromosome markers. Two of these cell types have chromosomes with long homogeneously staining regions (HSR) containing sequences derived from the short arm of a chromosome #15. In one cell type the HSR is found on a chromosome #15 and in the other it is on a der(15;10)-HSR chromosome. Four other cell types were identifiable by morphologic differences of the short arm of chromosome #13, whereas, the four remaining cell types were identifiable by the presence of prominent satellites on other chromosomes. This study was directed at assessing the relative tumorigenic properties of the different cell types by injecting different numbers of cells intraperitoneally, subcutaneously, or intravenously into Balb/c nude mice. The primary tumors and nodules that developed in the peritoneal cavity and lungs were explanted into tissue culture. One hundred metaphase chromosome spreads from each established cell line were analyzed cytogenetically to detect changes in proportions of the different cell types. The cell type containing the der(15;10)-HSR chromosome was present in only 20% of the cells injected, but increased in proportion to between 28% and 98% after growth in nude mice. Although the degree of selection of the der(15;10)-HSR-containing cell type was influenced by the number of cells injected, the consistent selection of these cells strongly suggests that this cell type has a growth advantage. Because the 15-HSR-containing cell type rarely increased in proportion, it is likely that the HSR by itself can not confer the enhanced tumorigenic phenotype but requires the expression of other sequences present on other MeWo chromosomes to provide the selective growth advantage to the cells in which it is found.