Correlation between tumor induction and the large external transformation sensitive protein on the cell surface.

The distribution on the cell surface of the large external LETS protein that is transformation sensitive of normal, transformed and tumorigenic cells was examined by immunofluorescent staining. A correlation was established between the expression of fibril-like LETS protein and the oncogenic capabilities of a series of adenovirus-transformed cell lines. In cells expressing a transformed phenotype in vitro, LETS protein is only detected in cell-cell contact areas, wheras in "untransformed" cells LETS protein is distributed over the cell surface. Transformed cells capable of inducing invasive tumors, and the cells of established tumor lines, have low or undetectable levels of LETS protein, as measured by this method. The results indicate that LETS protein has a role in cell-cell adhesion and that reduced expression of this protein at the cell surface is related to the oncogenic phenotype. This relationship has been established for experimentally induced and spontaneous tumors.