CDB15:0000643 FGF9 — FGFR3

ABSTRACT: Tissue homeostasis in normal prostate and two-compartment nonmalignant prostate tumors depends on harmonious two-way communications between epithelial and stromal compartments. Within the fibroblast growth factor (FGF) family, signaling to an epithelial cell-specific FGF receptor (FGFR) 2IIIb-heparan sulfate complex from stromal-specific FGF7 and FGF10 delivers directionally specific instruction from stroma to epithelium without autocrine interference. Using a two-compartment transplantable prostate tumor model in which survival of stromal cells in vivo depends on epithelial cells, we show that signaling from epithelial FGF9 to stromal FGFR3 potentially mediates epithelial-to-stromal communication that also is directionally specific. FGF9 mRNA was expressed exclusively in the epithelial cells derived from well-differentiated, two-compartment Dunning R3327 rat prostate tumors. In contrast, FGFR3 was expressed at functionally significant levels only in the derived stromal cells. Competition binding and immunoprecipitation assays revealed that FGF9 only bound to an FGFR on the stromal cells. FGF9 also failed to covalently cross-link to clonal lines of stromal cells devoid of FGFR3 that expressed FGFR1 and FGFR2IIIc. Furthermore, FGF9 specifically stimulated DNA synthesis in stromal cells expressing FGFR3. These results demonstrate a directionally specific paracrine signaling from epithelial FGF9 and stromal FGFR3. Similar to the FGF7/FGF10 to FGFR2IIIb signaling from the stroma to the epithelium, the directional specificity from epithelium to stroma appears set by a combination of cell-specific expression of isoforms and cell-context specificity of FGFR isotypes for FGF.

ABSTRACT: In mammals, fibroblast growth factors (FGFs) are encoded by 22 genes. FGFs bind and activate alternatively spliced forms of four tyrosine kinase FGF receptors (FGFRs 1-4). The spatial and temporal expression patterns of FGFs and FGFRs and the ability of specific ligand-receptor pairs to actively signal are important factors regulating FGF activity in a variety of biological processes. FGF signaling activity is regulated by the binding specificity of ligands and receptors and is modulated by extrinsic cofactors such as heparan sulfate proteoglycans. In previous studies, we have engineered BaF3 cell lines to express the seven principal FGFRs and used these cell lines to determine the receptor binding specificity of FGFs 1-9 by using relative mitogenic activity as the readout. Here we have extended these semiquantitative studies to assess the receptor binding specificity of the remaining FGFs 10-23. This study completes the mitogenesis-based comparison of receptor specificity of the entire FGF family under standard conditions and should help in interpreting and predicting in vivo biological activity.

ABSTRACT: Receptor specificity is an essential mechanism governing the activity of fibroblast growth factors (FGF). To begin to understand the developmental role of FGF-9/glial activating factor, we have cloned and sequenced the murine FGF-9 cDNA and expressed the protein in mammalian cells and in Escherichia coli. We demonstrate that the FGF-9 protein is highly conserved between mouse and human. Receptor specificity was determined by direct binding to soluble and cell surface forms of FGF receptor (FGFR) splice variants and by the mitogenic activity on cells, which express unique FGF receptor splice variants. Our data demonstrate that FGF-9 efficiently activates the "c" splice forms of FGFR2 and FGFR3, receptors expressed in potential target cells for FGF-9. Significantly, FGF-9 also binds to and activates the "b" splice form of FGFR3, thus becoming the first FGF ligand besides FGF-1 to activate this highly specific member of the FGF receptor 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.