Induction of Proteases and Protease Inhibitors by Growth Factors

Most polypeptide growth factors have been identified and assayed on the basis of their ability to stimulate DNA synthesis and cell division. The binding of growth factors to specific cell surface receptors initiates a cascade of biochemical reactions which alter many aspects of cellular physiology, change the pattern of gene expression, and, ultimately, trigger DNA synthesis and cell division. In addition to changes in those processes associated with the initiation of cell division, other effects of growth factors on cells include alterations in the cytoskeleton associated with modifications in cell shape, alterations in ion transport, phosphorylation of specific cellular proteins, and activation of certain genes, including, in some cases, those coding for proteases and protease inhibitors. At this time it is not clear whether all of these growth factor-induced changes are necessary for cell division or whether they indicate that growth factors affect cellular physiology in ways which are independent of their growth-promoting effects.