The FGF family is comprised of at least nine polypeptides that show a variety of biological activities toward cells of mesenchymal, neuronal, and epithelial origin. All FGFs have two conserved cysteine residues and share 30-50% sequence identity at the amino acid level. FGF-9, also named glia-activating factor, was originally identified and purified from the supernatant of a human glioma cell line as a heparin-binding mitogenic growth factor for glial cells. FGF-9 has also been shown to stimulate the proliferation of oligodendrocyte type 2 astrocyte progenitor cells, Balb/c3T3 fibroblasts, and PC-12 cells. However, unlike FGF acidic and basic, FGF-9 is not a mitogen for human umbilical vein endothelial cells.
The human FGF-9 cDNA encodes a 208 amino acid residue protein that contains a potential N-linked glycosylation site. The native protein is glycosylated. FGF-9 exhibits approximately 30% sequence similarity to other members of the FGF family. Although FGF-9 lacks a typical secretion signal, the protein is secreted efficiently after synthesis. Rat FGF-9 cDNA has been cloned and shown to be highly homologous to human FGF-9. The two proteins differ only in one amino acid residue. The expression of the FGF-9 transcripts has been shown to be restricted to the brain and the kidney.
