Targeting the specificity and function of fibroblast growth factor-1 (acidic FGF) by site-directed mutagenesis
Polypeptide growth factors are modulators of cellular proliferation, migration and differentiation. These functions are thought to be mediated primarily by extracellular binding to high-affinity cell surface receptors and subsequent alterations of cellular metabolism and gene expression. The complete cascades of signals initiated by growth factor occupancy of cell surface receptors is not known. The mechanisms of action associated with the functions of fibroblast growth factors (FGFs) clearly include binding to, and activation of cell surface receptor tyrosine kinases (RTKs). In addition, a significant amount of data has accumulated that supports the hypothesis that alternative or additional pathways that are parallel to, or independent of the RTKs also exist. The potential importance of the FGFs as regulators of cell growth and migration, angiogenesis, wound repair, neuronal survival and differentiation, and mesoderm induction has become more apparent over the last several years. Utility to the use of these factors in in vivo applications has been demonstrated. A better understanding of the structure-function relationships of these proteins and their mechanisms of signal transduction should aid in the use of these factors in the treatment of a variety of clinical situations. Recent work of our laboratory has focused on the design of specific mutants of FGF-1 or the construction of chimeric proteins that limit the functions or specificity of the growth factor for specific target cells. Data collected to date demonstrate that certain of the developmental activities of FGF-1 can be dissociated from its mitogenic activities. In addition, specific point mutations can alter the specificity of the mitogenic activity of the protein for target cells. Chimeric proteins that maintain mitogenic activity while targeting specific cell types have also been developed. The in vivo activities of most of these proteins have not been examined. However, the results obtained to date demonstrate a good correlation between in vitro assays and in vivu results. Together these results demonstrate that the utility of FGF-1 in a variety of in vivo applications may be improved by a rational approach to site-directed mutagenesis of the protein.