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Processing, secretion, and biological properties of a novel growth factor of the fibroblast growth factor family with
P Delli-Bovi1, A M Curatola, K M Newman
1Department of Pathology, New York University School of Medicine, New York 10016.
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.
Insights
A novel Kaposi sarcoma growth factor, K-FGF, is secreted and glycosylated, unlike other FGFs. Overexpression of the K-fgf oncogene, not mutations, likely activates this potent cell growth factor.
Area of Science:
- Oncology
- Molecular Biology
- Cellular Biology
Background:
- A novel human oncogene from Kaposi sarcoma encodes a growth factor, K-FGF, homologous to fibroblast growth factors (FGFs).
- Understanding K-FGF's properties and its oncogene's transformation mechanism is crucial.
Purpose of the Study:
- To investigate the production, processing, and biological activity of K-FGF.
- To elucidate the mechanism of K-fgf oncogene-induced cell transformation.
Main Methods:
- Transfection of COS-1 cells with K-fgf cDNA to study protein production and processing.
- Assessing K-FGF secretion, glycosylation, and stability in cultured medium.
- Testing K-FGF mitogenic activity on fibroblasts, endothelial cells, and NIH 3T3 cells.
Main Results:
- K-FGF is cleaved after a signal peptide, glycosylated, and secreted as a mature protein, unlike basic/acidic FGFs.
- Glycosylation inhibition impaired secretion; heparin enhanced secreted K-FGF stability.
- K-FGF demonstrated mitogenic activity, inducing NIH 3T3 cell growth in serum-free medium, suggesting autocrine activation.
- K-fgf protooncogene product was identical to K-FGF, indicating overexpression as the activation mechanism.
Conclusions:
- K-FGF is a secreted, glycosylated growth factor with mitogenic properties.
- The K-fgf oncogene likely transforms cells through overexpression, leading to autocrine growth stimulation.
- These findings offer insights into Kaposi sarcoma pathogenesis and oncogene activation mechanisms.