INVASION OF SELECTIVELY PERMEABLE SEA-URCHIN EMBRYO BASEMENT-MEMBRANES BY METASTATIC TUMOR-CELLS, BUT NOT BY THEIR NORMAL COUNTERPARTS

The selectively permeable basement membranes and the associated extrac ellular matrix of sea urchin embryos can be obtained intact. Their ext erior surfaces have been used as invasion substrates for metastatic me lanoma, squamous cell carcinoma, and fibrosarcoma cells,for primary sq uamous cell carcinoma cells, and for neonatal melanocytes, fibroblasts , and keratinocytes. About 18% of all metastatic tumor cells placed in contact with sea urchin embryo basement membranes and their associate d extracellular matrix invaded them. About 4% of the cells of a primar y squamous cell carcinoma, which Later metastasized, invaded these sub strates. As expected, neonatal melanocytes, keratinocytes, and fibrobl asts faded to invade; however, melanocytes treated with scatter factor (hepatocyte growth factor) invaded as efficiently as metastatic tumor cells. This suggests that the lack of invasion by epidermal melanocyt es is not due to irreversible differentiation to a noninvasive phenoty pe. Invasion time courses showed that the metastatic cells tested reac hed their maximal invasion frequencies in 4 h; thus, invasion of these substrates is rapid and efficient. This suggests that molecules parti cipating in basement membrane recognition and invasion have been funct ionally conserved during the time separating vertebrates from inverteb rates and that their constitutive activity may allow metastatic cells to escape their tissues of origin.