Transfer of methotrexate resistance by somatic cell hybridization

SEWATC13 mouse cells, resistant to 10 fig methotrexate (MTX)/ml, were fused to sensitive V79 Chinese hamster cells. Several resistant cell hybrids were isolated. In the mouse parental line MTX resistance is due to amplification of the dihydrofolate reductase gene, which cytologically is expressed in about 40 % of the cells as an HSR marker and in about 60 % as numerous DM. No DM were seen in 6 hybrids studied. Two hybrids analyzed in detail exhibited presence of the HSR marker in a majority of the cells. When subjected to 2-dimensional gel electrophoresis, both hybrids displayed a protein spot at the location of mouse DHFR. The results indicate (1) the MTX resistance due to amplification of the DHFR gene can be transferred with cell fusion, and (2) that the transfer of an HSR marker appears to be preferred to transfer of DM in the cell system employed.