Receptor Specificity of the Fibroblast Growth Factor Family

Abstract

Fibroblast growth factors (FGFs) are essential molecules for mammalian development. The nine known FGF ligands and the four signaling FGF receptors (and their alternatively spliced variants) are expressed in specific spatial and temporal patterns. The activity of this signaling pathway is regulated by ligand binding specificity, heparan sulfate proteoglycans, and the differential signaling capacity of individual FGF receptors. To determine potentially relevant ligand-receptor pairs we have engineered mitogenically responsive cell lines expressing the major splice variants of all the known FGF receptors. We have assayed the mitogenic activity of the nine known FGF ligands on these cell lines. These studies demonstrate that FGF 1 is the only FGF that can activate all FGF receptor splice variants. Using FGF 1 as an internal standard we have determined the relative activity of all the other members of the FGF family. These data should serve as a biochemical foundation for determining developmental, physiological, and pathophysiological processes that involve FGF signaling pathways. Fibroblast growth factor (FGF)1 was identified as an activity that stimulates the proliferation of NIH3T3 cells (1). Currently, FGFs comprise a family of nine structurally related proteins (FGF 1-9). FGFs are expressed in specific spatial and temporal patterns and are involved in developmental processes, angiogenesis, wound healing, and tumorigenesis (2-5).FGFs bind and activate high-affinity receptor tyrosine kinases. The cloning of FGF receptors (FGFRs) has identified four distinct genes (6 -13). These receptors bind members of the FGF family with varying affinity (13-16), and alternative mRNA splicing leads to isoforms of these receptors which have unique ligand binding properties (15,17,18). An additional mechanism regulating FGF activity involves heparin or heparan sulfate proteoglycans, molecules which facilitate ligandreceptor interactions (12,19,20). FGFRs contain an extracellular ligand binding domain, a single transmembrane domain, and an intracellular tyrosine kinase domain. The extracellular domain determines ligand binding specificity and mediates ligand-induced receptor dimerization. Dimerization in turn results in one or more trans-phosphorylation events and the subsequent activation of the receptor (21).The extracellular region of the FGFR contains three immunoglobulin-like (Ig-like) domains (6). Alternative mRNA splicing creates several forms of the FGF receptor which differ in their extracellular sequence and have unique ligand binding properties. One splicing event results in the skipping of exons encoding the amino-terminal Ig-like domain (domain I) resulting in a "short" two Ig-like domain form of the receptor (22). The ligand binding properties of the short (two Ig-like domain) and long (three Ig-like domain) FGFRs are similar.2 However, the short form of the receptor may have a higher affinity for some FGFs than the long form (23). Changes in this alternative splicing pattern may correlate with the progression of se...

Studies of genes in the FGF signaling pathway and oral clefts with or without dental anomalies

“…In addition, the diversity in the binding specificity of FGF receptors for FGFs clearly can lead to a large combinatorial set of possible interactions. It has been demonstrated that FGF3 activates the b splice forms of FGFRs 1 and 2 [Ornitz et al, 1996] and that FGFR2b binds to FGF10 [Yeh et al, 2003]. It is interesting to observe that increased risks of CL/P in our study were found for alleles in FGF3, FGF10, and FGFR2.…”

FGF8 isoform b expression in human prostate cancer

“…Four receptors have been detailed (designated FGFR 1 -4) and multiple splice variants of these receptors have been described (Ornitz et al, 1996). FGF8 is known to activate FGFR2, 3 and 4, as well as FGFR1 if applied in high concentrations (Ornitz et al, 1996;Blunt et al, 1997).…”

“…Four receptors have been detailed (designated FGFR 1 -4) and multiple splice variants of these receptors have been described (Ornitz et al, 1996). FGF8 is known to activate FGFR2, 3 and 4, as well as FGFR1 if applied in high concentrations (Ornitz et al, 1996;Blunt et al, 1997). In addition, developmental studies have shown that it is the c splice forms of FGFRs that are the preferred targets of FGF8 and these are expressed predominantly in the mesenchymal tissue (MacArthur et al, 1995b).…”

FGF-3 and FGF-4 elicit distinct oncogenic properties in mouse mammary myoepithelial cells

“…As it stands now, the FGF family comprises 10 characterized growth regulatory proteins that share 35 ± 50% overall homology (reviews in Basilico and Moscatelli, 1992;Goldfarb, 1996, and for FGF-10: Yamasaki et al, 1996). FGF-3 to 8 and FGF-10 are each synthesized with a signal peptide which transports them to the secretory pathway, whereas FGF-1, -2 and -9 which lack a signal peptide, are released from the cells by unknown mechanisms.…”

“…Four genes encode the high a nity receptors, FGFR-1 to -4, but alternative splicing generates at least 60 isoforms of the proteins. Thus, FGF-3 binds mainly to the IIIb isoforms of FGFR-1 and FGFR-2 (Mathieu et al, 1995) whereas FGF-4 binds to the IIIc isoforms of FGFR-1, -2 and -3 (Kanai et al, 1997) and to FGFR-4 (Ornitz et al, 1996;review in Goldfarb, 1996).…”