Isolation of variants resistant to methylglyoxal bis(guanylhydrazone) from adenovirus-transformed rat cells.

It is presumed that proteins encoded by viral oncogenes interact with proteins encoded by cellular genes to bring about the transformed phenotype. To demonstrate the existence of such cellular genes we attempted to isolate mutants with a nontransformed phenotype from an adenovirus-transformed rat cell line (F4) which contains multiple copies of the transforming E1 region. F4 cells were mutagenized with ethyl methanesulfonate and variants resistant to the anticancer drug methylglyoxal bis(guanylhydrazone) were selected. The proportion of such variants was about one in 10(6) and increased 5-fold after mutagenesis. Two variant clones (G1 and G2) were isolated and characterized: they were 5-fold more resistant to methylglyoxal bis(guanylhydrazone); they had a stable phenotype; they showed decreased drug uptake; they had a reduced ability to grow in soft agar, low serum, and nude mice; there was no detectable change in the restriction pattern of integrated viral genes or in the expression of the E1a and E1b proteins. These properties suggest that selection for methylglyoxal bis(guanylhydrazone) resistance may result in the isolation of variants with phenotypic characteristics of nontransformed cells. It was likely that these variants were altered in a cellular function required for the maintenance of the transformed phenotype.