Degradation of the subendothelial matrix by tumor cells
Laug, W.E.; DeClerck, Y.A.; Jones, P.A.
Cancer Research 43(4): 1827-1834
1983
ISSN/ISBN: 0008-5472 PMID: 6572556 Document Number: 203287
Cloned bovine endothelial cells produced a subendothelial matrix in vitro which resembled a vascular basement membrane. Analysis of this structure by polyacrylamide gel electrophoresis, sequential enzymatic digestion and immunofluorescence revealed the presence of a glycoprotein component containing laminin, fibronectin and a collagen component consisting of the collagen isotypes I, III, IV and V. Plasmin (or trypsin) digested the glycoprotein component of this matrix, whereas the matrix collagens were sensitive to clostridial collagenase. Complete degradation of the matrices was obtained by either sequential or combined exposure to plasmin (or trypsin) and collagenase. The human fibrosarcoma HT1080 cells, which produce large quantities of plasminogen activator (PA), degraded labeled matrix glycoproteins at maximal rates in the presence of a plasminogen source. However, plasminogen-independent glycoprotein digestion was also observed. In addition, the cells were also able to digest subendothelial collagens indicating the presence of a collagenolytic enzyme(s). Human rhabdomyosarcoma, neuroblastoma and osteogenic sarcoma cells digested mainly the glycoprotein components of the subendothelium, and only little collagenolytic activity was displayed by these cells, whereas normal human fibroblasts degraded only small amounts of either component. Clones which secreted small or large amounts of PA but displayed similar cellular PA activity were obtained from the parental fibrosarcoma cell line. Both kinds of clones digested the glycoprotein components of the complete matrix at similar rates, suggesting either that the cell-associated PA was mainly responsible for glycoprotein degradation or that an additional plasminogen-independent enzyme was involved. When grown on the glycoprotein-depleted matrix, the clones secreting high levels of PA elaborated low collagenolytic activity than did the clones secreting low levels of PA and vice versa, indicating a clonal variation of collagenolytic activity in these cells. Both the PA-plasmin and the collagenolytic system apparently play important roles in the degradation of the subendothelial matrix.