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Inhibitory effects of alpha-interferon on epidermal growth factor-mediated receptor-dependent events
E N Fish1, J Ghislain, J Trogadis
1Department of Microbiology, University of Toronto, Ontario, Canada.
Abstract:
To examine the mechanisms by which alpha-interferon (IFN-alpha) inhibits growth factor-mediated proliferative responses, we examined specific ligand-activated, receptor-dependent events. In direct ligand binding studies, we showed that IFN-alpha treatment of cells leads to a reduction in epidermal growth factor (EGF) receptor recognition at the cell surface, coupled with an alteration in the binding characteristics of EGF for its specific receptors. Specifically, the heterogeneity of binding exhibited by EGF was affected, and there was loss of the high affinity binding component. EGF-induced autophosphorylation of the EGF receptor was unaffected by IFN treatment. The trafficking of EGF-receptor complexes was followed using three-dimensional confocal microscopy. Confocal imaging revealed that the rapid internalization of EGF-receptor complexes was significantly reduced when cells were exposed to IFN. Accompanying the IFN-induced changes in receptor binding characteristics, we identified an alteration in EGF receptor gene expression; when cells were treated with IFN-alpha, elevated RNA levels specific for the EGF receptor were detected. Overall, IFN-alpha treatment inhibited EGF-induced cell proliferation. Our results imply that EGF-bound receptors that are unable to internalize are not fully competent with respect to signal regulation of both gene expression and growth. The data suggest that the signaling potential of the bound growth factor-receptor complex is apparently increased by an unspecified, species-specific, high affinity binding component. We propose that IFN treatment of responsive cell prevents the interaction of EGF-bound receptor with this component.
Insights
Alpha-interferon (IFN-alpha) inhibits epidermal growth factor (EGF)-induced cell proliferation by altering EGF receptor binding and reducing receptor internalization. This suggests IFN-alpha disrupts key signaling pathways essential for cell growth.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Alpha-interferon (IFN-alpha) is known to modulate cellular responses.
- Growth factors, such as epidermal growth factor (EGF), regulate cell proliferation through receptor-mediated signaling.
- The precise mechanisms by which IFN-alpha influences EGF signaling remain incompletely understood.
Purpose of the Study:
- To investigate how IFN-alpha affects EGF receptor (EGFR) function and downstream signaling.
- To elucidate the role of EGFR binding, trafficking, and gene expression in IFN-alpha's inhibitory effects on cell proliferation.
Main Methods:
- Ligand binding assays to assess EGF-EGFR interactions.
- Three-dimensional confocal microscopy to track EGFR internalization.
- Analysis of EGFR gene expression via RNA levels.
- Cell proliferation assays to measure the impact of IFN-alpha on EGF-induced growth.
Main Results:
- IFN-alpha treatment reduced EGF binding affinity to EGFR, specifically diminishing high-affinity interactions.
- Internalization of EGF-EGFR complexes was significantly inhibited by IFN-alpha.
- IFN-alpha treatment led to elevated EGFR gene expression.
- IFN-alpha inhibited EGF-induced cell proliferation.
Conclusions:
- IFN-alpha interferes with EGF receptor-mediated signaling by altering ligand binding and receptor trafficking.
- Impaired internalization of EGF-bound receptors suggests a loss of signaling competence for gene expression and growth.
- IFN-alpha may prevent the interaction of EGF-bound receptors with a critical high-affinity binding component, thereby inhibiting proliferation.