Expression of transformation in cell hybrids. I. Isolation and application of density-inhibited Balb/3T3 cells deficient in hypoxanthine phosphoribosyltransferase and resistant to ouabain.

A cell line, THO2, was isolated from Balb/3T3 clone A31 after sequential nitrosoguanidine treatments and selection for resistance to 6-thioguanine and ouabain. THO2 retains the properties of density-dependent inhibition of growth and serum dependence of DNA synthesis characteristic of 3T3. The codominant expression of ouabain resistance and inability of THO2 to utilize exogenous hypoxanthine in the presence of aminopterin allows isolation of somatic cell hybrids involving THO2 and any ouabain-sensitive, hypoxanthine phosphoribosyltransferase-positive cell line. Hybrid clones derived from THO2 and SV40-transformed cells show dominant expression of the transformed phenotype with respect to multilayered arrangement of cells and ability to synthesize DNA in 1% calf-serum medium.