Metastatic phenotype in hybrid cells derived from B16 melanoma

To determine whether or not the metastatic phenotype of mouse melanoma B16 is dominant, two derivative cell lines of B16, high metastatic F10 and low metastatic F1 were hybridized by somatic cell fusion. Prior to fusion, F10 and F1 cells were transfected with plasmid pKOneo or pSV2hph, which confers resistance to G-418 or hygromycin B, respectively. Hybrid clones were isolated by dual resistance to G-418 and hygromycin B. The seven isolated near-tetraploid hybrid clones were examined for metastatic phenotypes. Hybrid cells were injected into the tail vein of syngeneic C57BL/6N mice and the number of metastatic nodules in the lung was counted 21 days later. Four hybrid clones had high metastatic phenotypes while one clone showed an intermediate metastatic phenotype and two low metastatic phenotypes. Most of the hybrid clones retained modally stable chromosome compositions, whereas one of the two low metastatic clones lost chromosomes during in vitro and in vivo proliferations. These results suggest that the high metastatic ability is genetically dominant in B16 melanoma cells and low metastatic hybrid cells may be the result of a loss of a gene(s) responsible for acquisition of the metastatic phenotype in the process of chromosomal rearrangement.