Expression of transformation-associated phenotypic markers in rat tracheal epithelial cell lines

The detection of neoplastic transformation in epithelial cells in vitro is made difficult by the lack of consistent markers for carcinogen-altered cells. In an attempt to identify such markers in rat tracheal epithelial cells, the expression of several growth-associated alterations reported to reflect the transformed state in other cell culture systems was examined. When tumorigenic and non-tumorigenic tracheal epithelial cell lines were compared using a colony formation assay, decreased dependence on calcium or serum for proliferation was demonstrated in the transformed cells. The coordinate control of nuclear and cytoplasmic division was also relaxed in the tumorigenic cell lines, resulting in greater multinucleation when cytokinesis was disrupted by cytochalasin B. In addition, differences in cell population dynamics were seen as decreased exfoliation in tumorigenic cell lines. In the presence of vitamin A, exfoliation was markedly increased in the tumorigenic cells along with increased proliferation and an inhibition of keratinization.

The value of certain of these changes as markers for the emergence of neoplastic transformation was tested in a non-tumorigenic tracheal epithelial cell line following exposure to N-methyl-N'-nitro-N-nitrosoguanidine or (+)anti benzo[a]pyrene diol-epoxide. Cells were tested during serial passage in vitro for the emergence of these markers and for the ability to form tumors in vivo. Several of the markers showed increased expression in carcinogen-exposed cells prior to the emergence of neoplastic potential, suggesting their usefulness as early markers for the transformed state. Some unexposed populations also expressed these markers after prolonged in vitro culture, suggesting that neoplastic progression may occur in these cells following tissue culture passage alone. Altered cell population dynamics correlated best with exposure to carcinogens in vitro. Changes in the exfoliation of cells from the cultures suggest that the kinetics of cell turnover in carcinogen-exposed cell populations may play an important role in the stable acquisition of altered phenotypic properties in rat tracheal epithelial cells. Culture conditions which affected the exfoliative behavior of the cells (low density seeding or increased serum) demonstrated a powerful influence on the stability of the expression of transformation-associated phenotypic markers in the carcinogen-exposed and unexposed populations.