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Inhibition of epidermal growth factor binding system by ionizing radiation in A431 human squamous carcinoma cells
Abstract:
To elucidate the effect of ionizing radiation on the membrane anchored signal transduction, the binding of 125I epidermal growth factor (EGF) to its receptor (EGF-R) and the EGF-dependent EGF-R tyrosine phosphorylation were examined in a human squamous cell carcinoma cell line, A431. The significant suppression of 125I EGF binding to A431 cells was observed from 3-5 h after 10 Gy irradiation, whereas this inhibition was not observed both in non-irradiated and in 5 Gy-irradiated cells. This phenomenon was mediated by the protein kinase C pathway, because the inhibition was not observed in cells which had been pretreated with phorbol ester and treated with an inhibitor of the enzyme, H7. Scatchard analysis showed that the receptor affinity was decreased. In contrast, the level of EGF-dependent EGF-R-tyrosine phosphorylation was not decreased, compared with non-irradiated cells. These results suggest that ionizing radiation may modulate the function of EGF/EGF-R interaction through the direct activation of protein kinase C.
Insights
Ionizing radiation (10 Gy) suppresses epidermal growth factor (EGF) binding to its receptor (EGF-R) in A431 cancer cells, mediated by protein kinase C. This radiation effect on EGF/EGF-R signaling suggests altered cell communication.
Area of Science:
- Oncology
- Cell Biology
- Radiation Biology
Background:
- Membrane-anchored signal transduction pathways are crucial for cell communication and cancer progression.
- The epidermal growth factor receptor (EGF-R) pathway plays a significant role in cell growth and is often dysregulated in cancer.
- Understanding the impact of ionizing radiation on these pathways is vital for cancer treatment strategies.
Purpose of the Study:
- To investigate the effects of ionizing radiation on epidermal growth factor (EGF) binding to its receptor (EGF-R) in human squamous cell carcinoma cells.
- To examine the influence of ionizing radiation on EGF-dependent EGF-R tyrosine phosphorylation.
- To elucidate the specific molecular mechanisms, particularly the role of protein kinase C, involved in radiation-induced modulation of EGF/EGF-R signaling.
Main Methods:
- Utilized A431 human squamous cell carcinoma cell line.
- Quantified 125I epidermal growth factor (EGF) binding to EGF receptors (EGF-R) after varying doses of ionizing radiation (5 Gy and 10 Gy).
- Assessed EGF-dependent EGF-R tyrosine phosphorylation levels.
- Investigated the involvement of the protein kinase C pathway using phorbol ester pretreatment and H7 inhibitor.
Main Results:
- Significant suppression of 125I EGF binding to A431 cells was observed 3-5 hours after 10 Gy irradiation.
- This inhibition of EGF binding was dose-dependent and not observed with 5 Gy irradiation or in non-irradiated cells.
- Scatchard analysis indicated a decrease in EGF receptor affinity post-irradiation.
- EGF-dependent EGF-R tyrosine phosphorylation levels remained unchanged compared to non-irradiated controls.
- The observed inhibition of EGF binding was mediated by the protein kinase C pathway.
Conclusions:
- Ionizing radiation, specifically at 10 Gy, can suppress the binding of EGF to its receptor in A431 cells.
- The protein kinase C pathway is implicated in mediating this radiation-induced suppression of EGF binding.
- While EGF binding is affected, EGF-R tyrosine phosphorylation remains intact, suggesting a complex modulation of EGF/EGF-R signaling by ionizing radiation.