Endothelial Growth Factors and Extracellular Matrix Regulate DNA Synthesis Through Modulation of Cell and Nuclear Expansion

Studies were carried out to analyze the mechanism by which extracellular matrix (ECM) molecules and soluble growth factors interplay to control capillary endothelial cell growth. Bovine adrenal capillary endothelial cells attached to purified matrix components but spread poorly and exhibited low levels of DNA synthesis in the absence of exogenous growth factors or serum. Addition of cationic, heparin-binding growth factor purified from either human hepatoma cells or normal bovine pituitary (fibroblast growth factor) induced extensive cell spreading and up to eight fold increases in DNA synthetic rates relative to levels observed in cells on similar substrata in the absence of mitogen. However, the extent of this response differed depending upon the type of ECM molecule used for cell attachment (fold increase on type III collagen greater than gelatin greater than type IV collagen greater than fibronectin greater than type V collagen much greater than laminin). Computerized morphometry demonstrated that endothelial cell DNA synthetic rates increased in an exponential fashion in direct relation to linear increases in cell and nuclear size (projected areas). Similarly sized cells always displayed the same level of DNA synthesis independent of the type of ECM molecule used for cell attachment or the presence of saturating amounts of growth factor. In all cases, DNA metabolism appeared to be coupled to physical expansion of the cell and nucleus rather than to a specific cell morphology (e.g. polygonal versus bipolar). These findings suggest that ECM may act locally as a "solid state" regulator of angiogenesis through its ability to selectively support or prohibit cell and nuclear extension in response to stimulation by soluble mitogens.