Processing, secretion, and biological properties of a novel growth factor of the fibroblast growth factor family with oncogenic potential.

Abstract

We recently reported that the protein encoded in a novel human oncogene isolated from Kaposi sarcoma DNA was a growth factor with significant homology to basic and acidic fibroblast growth factors (FGFs). To study the properties of this growth factor (referred to as K-FGF) and the mechanism by which the K-fgf oncogene transforms cells, we have studied the production and processing of K-FGF in COS-1 cells transfected with a plasmid encoding the K-fgf cDNA. The results show that, unlike basic and acidic FGFs, the K-FGF protein is cleaved after a signal peptide, glycosylated, and efficiently secreted as a mature protein of 176 or 175 amino acids. Inhibition of glycosylation impaired secretion, and the stability of the secreted K-FGF was greatly enhanced by the presence of heparin in the cultured medium. We have used the conditioned medium from transfected COS-1 cells to test K-FGF biological activity. Similar to basic FGF, the K-FGF protein was mitogenic for fibroblasts and endothelial cells and induced the growth of NIH 3T3 mouse cells in serum-free medium. Accordingly, K-fgf-transformed NIH 3T3 cells grew in serum-free medium, consistent with an autocrine mechanism of growth. We have also expressed the protein encoded in the K-fgf protooncogene in COS-1 cells, and it was indistinguishable in its molecular weight, glycosylation, secretion, and biological activity from K-FGF. Taken together, these results suggest that the mechanism of activation of this oncogene is due to overexpression rather than to mutations in the coding sequences.

Paracrine and autocrine effects of fibroblast growth factor-4 in endothelial cells

“…Hst activation results in the overexpression of the growth factor that is e ciently secreted and binds to cell surface tyrosine kinase FGF receptors (FGFRs), thus creating an autocrine loop of stimulation (Moscatelli and Quarto, 1989). Also, FGF4 stimulates endothelial cell proliferation, migration, and protease production in vitro and neovascularization in vivo (Delli Bovi et al, 1988;Yoshida et al, 1994). FGF2 shares with FGF4 a potent angiogenic activity .…”

Isolation and characterization of a macrophage-derived heparin-binding growth factor.

“…Acidic FGF (aFGF) and bFGF bind to immobilized heparin columns and are eluted with 1-1.2 and 1.5-1.8 M NaCI, respectively. Several growth factors structurally homologous to aFGF and bFGF, including hst/Kfgf and KGF have an affinity for heparin as well (Delli-Bovi et al, 1988;Finch et al, 1989). PDGF also binds to immobilized heparin but with relatively low affinity and is eluted with 0.5 M NaCI, typical of cationic proteins in general (Shing et al, 1984).…”

“…It is also unlikely that MD-HBGF is another member of the FGF family, e.g., int-2, hstlKfgf, FGF 5, and KGF. int-2 has not been shown to be mitogenic for any cell type, hst/Kfgfand FGF 5 are mitogenic for endothelial cells, and KGF is specific for epithelial cells (Delli-Bovi et al, 1988;Finch et al, 1989;Zhan et al, 1988). Other known macrophage-derived growth factors differ from MD-HBGF in that either they do not bind to heparin, e.g., TGF-f, TGF-a, TNF-a ( Figure 5); they are endothelial cell mitogens, e.g., TGF-a (Schreiber et al, 1986); or they are endothelial cell inhibitors (TGF-3, TNF-a) (Baird and Durkin, 1986;Heimark et al, 1986;Frater-Schroder et aL., 1987;Muller et aL, 1987;Schweigerer et aL, 1987).…”

Growth factors as transforming proteins

“…The product of hstlKS3 has also been shown to have growth-promoting activity for NIH3T3 cells [116] as well as for endothelial cells [117]; the int-2 protein may also be a growth factor. Thus, the mechanisms for the transforming activities of these oncogenes are most likely analogous to that of the sis oncogene.…”