Metastatic tumor cells adhere preferentially to the extracellular matrix underlying vascular endothelial cells

Two metastatic cell lines, mouse B16-Fl melanoma and human Hs939 melanoma, were examined for their abilities to adhere to confluent vascular endothelial cell monolayers and to the underlying endothelial extracellular matrix. Tumor cells attacked slowly to the endothelial cell monolayers while they adhered rapidly to isolated extracellular matrix. When analyzed by polyacrylamide gel electrophoresis in sodium dodecylsulfate solutions, the extracellular matrix was shown to be primarily composed of a protein of identical migration and molecular weight to fibronectin. Tumor-cell adhesion to fibronectin-coated polyvinyl surfaces mimicked the rapid rate of attachment of tumor cells to extracellular matrix, and tumor cells adherent to either extracellular matrix or fibronectin-coated polyvinyl dishes adopted an unusual, highly spread and flattened morphology with numerous small projections. These results suggest that fibronectin associated with the endothelial basement membrane may be, in part, responsible for establishing an adhesive gradient that could be important in malignant cell extravasation.