Solubilization and degradation of subendothelial matrix glycoproteins and proteoglycans by metastatic tumor cells.

Abstract

Successful blood-borne tumor metastasis depends on the abilities of the arrested tumor cell to invade both the endothelium and associated basement membrane, permitting subsequent tumor cell migration to an extravascular compartment.In an in vitro model system, we have examined the capacity of metastatic murine B16 melanoma cells to invade, solubilize, and degrade the subendothelial matrix produced by vascular endothelial cell monolayer cultures.B16 melanoma cells were found to invade subendothelial matrix with the concurrent solubilization of matrix polypeptides and sulfated proteoglycans in a process which required tumor cell-matrix contact but was not dependent on serum plasmin production.Fibronectin, a major polypeptide constituent of the matrix, was solubilized from matrix by melanoma cells and appeared in the supernatant medium in a partially degraded form.Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions revealed a decrease in the M, of the solubilized fibronectin from M, -230,000 to -225,000.Sulfated proteoglycans in the matrix were found to be rich in heparan sulfate with minor amounts of chondroitin 6-sulfate and chondroitin 4-sulfate.The relative molecular mass of sulfated proteoglycans as determined on Sepharose columns in the presence of 4 M guanidine-HC1 was estimated to be approximately 1 X lo6.After incubation of the matrix with tumor cells, a new low molecular weight heparan sulfate-containing fragment was released.The fact that sulfated glycosaminoglycan chains produced from matrix proteoglycans by treatment with alkaline borohydride were approximately three times larger than this fragment suggested that the tumor cells elaborated a glycosidase capable of cleaving specifically glycosaminoglycans and releasing heparan sulfate-rich fragments.The pattern of degradation of matrix fibronectin and sulfated proteoglycans appeared to be unique to the tumor cells, since no such products were detected in the medium from endothelial cells.