PREDOMINANCE OF THE METASTATIC PHENOTYPE IN HYBRIDS FORMED BY FUSION OF MOUSE AND HUMAN-MELANOMA CLONES

The fusion of mouse and human melanoma cells that were tumorigenic but had different metastatic capabilities resulted in hybrids that were m etastatic when injected intravenously or subcutaneously into nude mice , regardless of whether it was the mouse or the human melanoma clone t hat was metastatic. The H7 hybrid line, formed by fusing murine nonmet astatic K1735 C19 cells with human metastatic A375 C15 cells retained high metastatic potential over more than 50 sub-culture passages, sugg esting that the dominant metastatic phenotype in these hybrid cells wa s stable, Using fluorescent in situ hybridization (FISH), human chromo some 17 was consistently identified as the predominant human chromosom e in the majority of H7 cells tested between passages 20 and 60, Weste rn blot analysis showed that the hybrid cells expressed human nm23 pro tein, indicating that at least one gene on the human chromosome 17 was functional, Immunocytochemistry and immunoprecipitation showed that t he metastatic A375 C15 and H7 cells expresed mutated p53 protein, but that the nonmetastatic K1735 C19 melanoma cells did not, Sequencing th e human p53 gene in A375 C15N and H7 showed mutations in exon 7, Using a bioassay technique, we showed that K1735 C19 cells can spread from subcutaneous tumors to the lungs of nude mice yet fail to form metasta ses. With the addition of human chromosome 17 from A375 C15 cells, whi ch carries a mutant p53 gene, the cells readily formed lung metastases , In this melanoma hybrid, a mutant p53 gene appears to confer a survi val advantage on cells arrested in the lungs of nude mice and thus con tributes to the growth of metastatic cells.