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Surface Morphology and Nucleoside Phosphatase Activity of Rat Liver Epithelial Cells during Oncogenic Transformation in Vitro¹

Institut du Cancer de Montréal, Centre Hospitalier Notre-Dame [S. K., A. S., G. de L.], and Départements d'Anatomie [S. K., A. S.] et de Biochimie [G. de L.], Université de Montréal, Montréal, Québec, Canada

Morphological and biochemical studies of surface membrane alterations associated with in vitro oncogenic transformation were performed with subcultures of seven liver epithelial cell lines, independently isolated from normal and carcinogen-treated Wistar rats. During the preoncogenic phase of passages in vitro, the cell populations exhibited a gradual increase of surface-located nucleoside triphosphatase activity. When the enzyme activity reached a high level, the cell lines revealed tumorigenicity upon implantation into newborn Wistar rats. Further biochemical analysis of oncogenic cultures indicated that the ectoenzyme was Mg²⁺- and Ca²⁺-dependent nucleoside triphosphatase similar to that found in association with contractile proteins. This enzyme was distributed on the entire external surface membranes of epithelial cells. Scanning electron microscopy of these cells showed reduction of cytoplasmic spreading and complexicity of surface membranes in the forms of microvilli, filopodia, blebs, and ruffles. Epithelial cells of the preoncogenic cultures were devoid of ectoenzyme activity and displayed smooth surfaces. Combined cytochemistry and scanning electron microscopy showed a correlation between the phosphatase reaction and the number of microvilli. Transmission electron microscopy of surface carbon replicas allowed visualization of the distribution of enzyme reaction products on ruffles and microvilli. It is proposed that nucleoside phosphatase activity provides an indirect measure of the dynamic surface morphology of oncogenic liver epithelial cells.

¹ This work was supported by grants from the National Cancer Institute of Canada, Le Ministère des Affaires Sociales du Québec, La Fondation J. H. Biermans, and Les Fondations J. Rhéaume.

² Research Associate of the National Cancer Institute of Canada. To whom requests for reprints should be addressed, at Institut du Cancer de Montréal, Centre Hospitalier Notre-Dame, Montréal, Canada H2L 4M1.

Received 3/16/77. Accepted 6/30/77.

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