THE IMPORTANCE OF CELL-DENSITY IN THE INTERPRETATION OF GROWTH-FACTOREFFECTS ON COLLAGENASE-IV ACTIVITY RELEASE AND EXTRACELLULAR-MATRIX PRODUCTION FROM C6 ASTROCYTOMA-CELLS

We have examined the influence of basic fibroblast growth factor (FGF- 2) and vascular endothelial growth factor (VEGF) on the release of col lagenase type IV activity and the production of extracellular matrix ( ECM) molecules using C6 astrocytoma cells in monolayer culture. Collag enase type IV activity was significantly increased in a dose dependent manner in the low cell, density group by treatment with FGF-2 and VEG F but significantly decreased in a dose dependent fashion in the high cell density group. These results were corroborated using Western blot technique with an antibody to gelatinase A. Addition of exogenous lam inin and fibronectin to the media decreased collagenase type IV activi ty in a dose dependent fashion with the minimum concentration of 0.1 m u g/ml. Laminin and fibronectin reached a concentration of 0.1 mu g/ml in only the high cell density group after treatment with the growth f actors tested. These findings indicate that C6 astrocytoma cells appea r to have two regulatory mechanisms for collagenase type IV activity w hich are dependent on cell density. In a low cell density, C6 astrocyt oma cells respond to the dominant effect of FGF-2 and VEGF by increasi ng the release of collagenase IV activity. In a high cell density coll agenase type TV activity is decreased due to it's down regulation by r eleased ECM molecules in response to FGF-2 and VEGF. These regulatory mechanisms may be crucial to the understanding of the coordination of tumor-associated angiogenesis by malignant glial cells.