Transforming potential is detectable in arteriosclerotic plaques of young animals

The carcinogen-treated cockerel is a model for studying the early stages of arteriosclerotic plaque development. Carcinogen administration accelerates arteriosclerotic plaque development in cockerels, and transforming elements are present in DNA from advanced human plaques. In this study, we asked whether transforming elements could also be detected at early stages of plaque development in cockerels. NIH3T3 cells were transfected with DNA from plaques isolated from carcinogen-treated cockerels and from the healthy arterial wall underlying the plaques. Approximately 5 x 10(6) cells from each group were injected into nude mice. Tumors appeared in five of five mice in the plaque DNA group; no tumors appeared in mice from the healthy arterial wall group. All five plaque DNA-associated tumors hybridized to a cockerel genomic probe. Eight cockerel-specific bands were identified in EcoRI digests of first-round (primary) tumors. DNA from a primary tumor was tested in a second round of transfection. Five of five mice developed tumors after injection with these secondary transformants. All second-round tumors contained cockerel DNA, and a prominent cockerel-specific band (greater than 28 kb) was seen in EcoRI digests of all second-round tumors. In addition, a 5.2-kb band appeared prominently in one of five second-round tumors. No evidence was found for activation of the oncogenes Ha-ras, Ki-ras, src, or myc in the plaque-associated tumors. Similarly, DNA from plaque-associated tumors did not hybridize to probes for Marek disease virus, herpes simplex virus 1, or reverse transcriptase, suggesting that neither herpesviruses nor retroviruses are involved in the transforming activity of plaque DNA. These results indicate that transforming elements are a general property of arteriosclerotic plaques and are detectable in plaques of young animals.