Adhesion and spreading characterization of a rat tumor cell system exhibiting different metastatic behavior.

The rat tumor cell system BSp73AS/BSp73ASML was investigated for its structural aspects. The non-metastasizing line BSp73AS has less nuclear atypism than the metastasizing line BSp73ASML. Microvilli are scanty and variable in length and structure; in BSp73ASML they cover the cells densely, are short and homogeneous in size. In vitro adhesion and spreading tests show structurally flexible BSp73AS cells which flatten completely onto substrata. BSp73ASML cells remain spherical and develop only small attachment areas. In vitro aggregation of the BSp73AS cells leads to round, tightly packed aggregates, their outer cell layer is epitheloid BSp73ASML cells form clusters of mostly ball-shaped cells. Surprisingly, as judged from EM images, the intercellular junctions in BSp73ASML cell clusters are qualitatively the same as in BSp73AS cell aggregates. However, the extent of apposition between cells in BSp73AS aggregates is much higher than between cells in the BSp73ASML clusters. BSp73ASML cells lack the ability to vary their shape. This is the prominent difference revealed by these tests between the two cell lines. Hence, this fact could play an important role in their different metastatic behavior in vivo. We speculate that the ability to vary the cell shape is necessary for expansive growth in the host environment but not for the metastatic spread.