Seventy-five clonal populations of morphologically transformed 10T1/2 cells were established from independent Type II and Type III foci that were of spontaneous origin or were induced by the carcinogenic agents N-methyl-N′-nitrosoguanidine, benzo(a)pyrene diol epoxide-I, and 3-methylcholanthrene. Clonal populations were characterized for expression of selected transformation phenotypes, including growth to elevated saturation density before cessation of proliferation, anchorage independence, ability to reconstruct foci when plated in the presence of wild-type 10T1/2 cells, and tumorigenicity. Forty-one % of the clonal populations expressed only the phenotype of morphological transformation, while 20% expressed all of the transformation phenotypes, including tumorigenicity, in addition to morphological transformation. The remaining clonal populations expressed varying combinations of one or more of the four transformation phenotypes. Clonal populations expressing almost all of the 16 possible combinations of the transformation phenotypes were observed, suggesting that the individual phenotypes segregated independently. Morphological transformation alone was a poor indicator of tumorigenicity, correctly predicting the tumorigenic potential of only 37% of the clonal populations. Among morphologically transformed clonal populations, coexpression of anchorage independence correctly predicted the tumorigenicity of 81% and coexpression of reconstruction of foci on a confluent lawn of wild-type cells correctly predicted the tumorigenicity of 91%. The probability that a morphologically transformed clonal population was tumorigenic correlated with the total number of transformation phenotypes expressed. Expression of the transformation phenotypes differed between tumorigenic and nontumorigenic clonal populations but not between clonal populations established from Type II and Type III foci. Tumorigenicity varied among transformed clonal populations that were induced by the different carcinogenic agents or were of spontaneous origin but did not differ between clonal populations established from Type II and Type III foci.

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Supported by NIH Grants CA42765 and CA24144.

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