Differences in Proliferation Properties Among Sublines of Rat 3y1 Fibroblasts Transformed by Various Agents in Vitro

Alterations in cellular characteristics associated with transformation were compared among various agents, including simian virus 40, mouse polyoma virus, adenovirus type 12, the E1A region of adenovirus type 12, Rous sarcoma virus, v-H-ras oncogene, and N-methyl-N’-nitro-N-nitrosoguanidine. To avoid the difficulty in interpretation due to differences in the original cellular characteristics, all transformed lines (three to four independent lines for each agent) were derived from the same parental line, i.e. rat clonal diploid fibroblasts 3Y1. Doubling time, saturation density, serum requirement, efficiency of colony formation, Ca dependency, anchorage dependency, cell volume, density-dependent inhibition of proliferation, and alteration of morphology were examined. In the lines transformed either by DNA virus, RNA virus, or transforming oncogene, the characteristics were similar among the lines induced by the same transforming agent but distinguishable between the lines induced by different agents. In such cases, a transformed line displayed phenotypes specific to each transforming agent. In contrast, nitrosoguanidine-transformed lines showed different properties. Only one characteristic was shared by all the transformed lines: the ability to attain a higher saturation density than that of the untransformed parent. The fact that (cellular) densitydependent inhibition of DNA synthesis became weak may be responsible for this characteristic.