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Characterization of a growth factor that binds exclusively to the erbB-2 receptor and induces cellular responses
1Vincent T. Lombardi Cancer Research Center, Georgetown University Medical Center, Washington, DC 20007.
Abstract:
The erbB-2 oncogene encodes a 185-kDa transmembrane protein that has been suggested to be a growth factor receptor. We have previously identified and purified a 30-kDa growth factor (gp30) that is a ligand for the p185erbB-2 protein that at high concentrations induces growth inhibition of cells with erbB-2 amplification. We now report the purification and characterization of a protein from SKBr-3 human breast cancer cells with a molecular mass of 75 kDa (p75) that is a p185erbB-2 ligand. An affinity column coupled to the extracellular domain of p185erbB-2 was used for the purification. We found that p75 induced tyrosine phosphorylation of the erbB-2 oncoprotein, as determined by in vivo and in vitro phosphorylation and phosphoamino acid analysis. p75, as well as gp30, stimulated cell proliferation and colony formation of cells overexpressing erbB-2. The specificity of this effect was confirmed by showing that the antiproliferative effects of soluble erbB-2 extracellular domain were reversed by either p75 or gp30. p75 did not show binding to the epidermal growth factor receptor and had no growth effects on cells overexpressing epidermal growth factor receptor. These data show that SKBR-3 cells, which exhibit erbB-2 amplification and overexpression, secrete a growth factor that binds and activates p185erbB-2 specifically.
Insights
Researchers identified a 75 kDa protein (p75) from breast cancer cells that acts as a ligand for the erbB-2 receptor. This protein specifically binds and activates erbB-2, promoting cell proliferation in overexpressing cells.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- The erbB-2 oncogene encodes the p185erbB-2 receptor tyrosine kinase.
- Aberrant erbB-2 signaling is implicated in various cancers, particularly breast cancer.
- Previous work identified a 30 kDa growth factor (gp30) as a p185erbB-2 ligand inducing growth inhibition at high concentrations.
Purpose of the Study:
- To purify and characterize a novel ligand for the p185erbB-2 protein from SKBr-3 human breast cancer cells.
- To investigate the functional effects of this novel ligand on erbB-2 signaling and cell proliferation.
Main Methods:
- Affinity chromatography using the extracellular domain of p185erbB-2 for protein purification.
- In vivo and in vitro phosphorylation assays to assess p75's effect on erbB-2.
- Cell proliferation and colony formation assays to evaluate functional responses.
- Binding assays to determine specificity against epidermal growth factor receptor (EGFR).
Main Results:
- Purification and characterization of a 75 kDa protein (p75) from SKBr-3 cells, identified as a p185erbB-2 ligand.
- p75 induced tyrosine phosphorylation of the p185erbB-2 oncoprotein.
- Both p75 and gp30 stimulated cell proliferation and colony formation in cells overexpressing erbB-2.
- p75 did not bind to EGFR and had no effect on EGFR-overexpressing cells, confirming specificity.
Conclusions:
- SKBR-3 cells secrete a novel growth factor, p75, that specifically binds and activates the p185erbB-2 receptor.
- This interaction promotes cell proliferation, highlighting a potential autocrine signaling loop in erbB-2 amplified cancers.
- The findings provide insights into erbB-2 mediated growth regulation and potential therapeutic targets.