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Basic fibroblast-like growth factor is present in the conditioned medium of simian sarcoma virus transformed NRK
K Hicks1, B Friedman, M R Rosner
1Massachusetts Institute of Technology, Cambridge 02139.
Abstract:
The conditioned medium of Simian sarcoma virus (SSV)-transformed NRK cells contains at least two activities that down regulate the epidermal growth factor receptor. To identify these activities, we analyzed the medium for the presence of factors both related to and distinct from the v-sis oncogene product. Fractionation of the conditioned medium from SSV-transformed NRK cells by chromatography on heparin-Sepharose yielded two active fractions capable of inhibiting EGF binding. The first component, which eluted at 0.8 M NaCl, is able to induce autophosphorylation of the platelet-derived growth factor (PDGF) receptor, is a mitogen for Swiss 3T3 cells and corresponds to the PDGF B chain product of the v-sis oncogene. The second component requires 2 M NaCl for elution, is mitogenic for Swiss 3T3 cells and inhibits high affinity EGF binding through a protein kinase C-independent pathway, all properties of basic FGF. These results suggest that the conditioned medium of v-sis-transformed cells contains at least two factors that can act in an autocrine capacity, one derived from v-sis and one corresponding to basic FGF.
Insights
Simian sarcoma virus-transformed cells release two factors that inhibit epidermal growth factor receptor binding. One factor is the PDGF B chain, and the other is basic FGF, acting in an autocrine manner.
Area of Science:
- Cell Biology
- Oncology
- Molecular Biology
Background:
- Simian sarcoma virus (SSV)-transformed NRK cells secrete factors affecting epidermal growth factor receptor (EGFR).
- Identifying these secreted factors is crucial for understanding autocrine signaling in cancer.
Purpose of the Study:
- To identify and characterize the factors in SSV-transformed NRK cell conditioned medium that downregulate EGFR.
- To determine if these factors are related to the v-sis oncogene product or distinct entities.
Main Methods:
- Fractionation of conditioned medium using heparin-Sepharose chromatography.
- Analysis of eluted fractions for biological activity, including induction of platelet-derived growth factor (PDGF) receptor autophosphorylation, mitogenicity for Swiss 3T3 cells, and inhibition of epidermal growth factor (EGF) binding.
Main Results:
- Two distinct active fractions were isolated.
- The first fraction (0.8 M NaCl eluate) contains the PDGF B chain, which induces PDGF receptor autophosphorylation and is mitogenic.
- The second fraction (2 M NaCl eluate) exhibits properties of basic FGF, is mitogenic, and inhibits high-affinity EGF binding via a protein kinase C-independent pathway.
Conclusions:
- SSV-transformed cell conditioned medium contains at least two autocrine factors.
- These factors include the v-sis oncogene product (PDGF B chain) and basic FGF.
- Both factors contribute to the observed downregulation of EGFR signaling.
