[Changes in the actin cytoskeleton during transformation and tumor progression in liver epithelium in culture]

Two patterns of actin distribution were revealed by indirect immunofluorescence in non-tumorigenic cell lines of cultured liver epithelium. The first one was represented by large marginal cable, lining the active edge of epithelial sheet. The second one was represented by numerous inner bundles randomly distributed in all cells. The following changes in actin pattern were detected in cultures of transformed epithelium: A) The reduction of inner bundles in all cells and the appearance of the marginal actin cable in central cells of the sheet, and B) The reduction of marginal cable and the presence of inner bundles, preferentially oriented along the longer axis of cells which became more polarized. In tumor cells, arising from transformed epithelium with A-type of actin pattern alteration, a secondary redistribution of actin bundles towards B-type occurred. Histochemical staining of such cells revealed a high activity of gamma-glutamyltranspeptidase, a marker enzyme for transformed cultures. The complete loss of actin bundles was observed in soft agar clone originated from cells with B-type alteration of actin pattern.