Different expression of cell surface fibronectin in spontaneously and X-ray transformed cells

The presence of cell surface fibronectin was examined by indirect immunofluorescence in 8 groups of related rat fibroblast lines expressing an in vitro transformed phenotype. The transformed cells were selected for anchorage independent growth either after X-ray treatment (X-ray transformed cells) or from control cultures (spontaneously transformed cells). All transformed fibroblasts of the latter class showed reduced expression of fibronectin at the cell surface, whereas most of the X-ray transformed derivatives exhibited a fibronectin-positive phenotype, like the untransformed parents. Moreover, from the fibronectin-negative spontaneously transformed cells, ouabain-resistant variants were isolated, the majority of which had regained the capacity to form an extracellular matrix of fibronectin. These results emphasize the variability in the properties of transformed cells and suggest that the properties of in vitro transformed cells may depend on the cause of transformation.