Comparison of intracellular and extracellular mitogenic activity

Endothelial cell‐derived growth factor (ECDGF) is a soluble mitogen secreted in vitro by bovine aortic endothelium. ECDGF is a mixture of at least two distinct heat‐stable and trypsin‐sensitive mitogens. Large amounts of mitogenic activity were found in lysates prepared from cultured endothelial cells. Other nonmitogen‐secreting cells in culture, including bovine dermal fibroblasts and vascular smooth muscle cells, also contained a similar activity. In contrast to ECDGF, the lysate mitogenic activities were sensitive to heat (56°C) and were not inactivated by trypsin. Similar to platelet‐derived growth factor (PDGF), ECDGF and cell lysate mitogens promoted cell proliferation in the absence of other defined mitogens when added to culture medium and after exposure to plastic. The cytoplasmic mitogens, however, were distinct from PDGF by receptor competition assays and other criteria.