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Augmented desensitization to epidermal growth factor (EGF) immediate actions: a novel mechanism for altered EGF
A Karasik1, S S Reddy, R B Pepinsky
1Research Division, Joslin Diabetes Center, Boston, Massachusetts.
Abstract:
Epidermal growth factor (EGF) may either stimulate or inhibit cell growth. To elucidate the mechanism of these varied effects, we compared EGF action in parental A431 cells in which cell growth is inhibited, and clone 15, a mutant of these cells resistant to EGF growth inhibition. In both lines, EGF receptor was present in similar concentrations and underwent tyrosine phosphorylation to the same extent. Likewise, in both lines, acute exposure to EGF stimulated an increase in free cytoplasmic [Ca2+], as well as a similar increase in phosphorylation of lipocortin 1, a major substrate for the EGF receptor kinase whose phosphorylation is calcium-dependent. On the other hand, pretreatment of clone 15 cells with EGF for 72 h abolished EGF-induced phosphorylation of lipocortin 1 and led to a loss of the increase in cytoplasmic free [Ca2+], whereas no such desensitization was seen in the parental A431 cells. These data indicate a link between EGF-induced increase in cytoplasmic calcium, lipocortin phosphorylation, and cell growth and suggest that differences in mechanisms of desensitization to these immediate actions of EGF may lead to altered growth response to this hormone.
Insights
Epidermal growth factor (EGF) affects cell growth differently. Desensitization to EGF
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Epidermal growth factor (EGF) exhibits dual effects on cell growth, capable of both stimulation and inhibition.
- Understanding the mechanisms behind EGF's varied cellular responses is crucial for comprehending cell signaling pathways.
- A431 cells and their resistant mutant, clone 15, provide a model system to investigate differential EGF action.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the differential effects of EGF on cell growth.
- To compare the action of EGF in parental A431 cells (growth inhibited) and clone 15 cells (resistant to inhibition).
- To investigate the role of calcium signaling and lipocortin 1 phosphorylation in EGF-mediated growth regulation.
Main Methods:
- Comparative analysis of EGF receptor expression and phosphorylation in parental A431 cells and clone 15.
- Measurement of intracellular free calcium ([Ca2+]) levels following EGF stimulation.
- Assessment of lipocortin 1 phosphorylation, a calcium-dependent substrate of the EGF receptor kinase.
- Evaluation of EGF desensitization effects on calcium signaling and lipocortin 1 phosphorylation after prolonged EGF exposure.
Main Results:
- EGF receptor concentration and tyrosine phosphorylation were similar in both cell lines.
- Acute EGF exposure increased cytoplasmic free [Ca2+] and lipocortin 1 phosphorylation in both cell types.
- Clone 15 cells, upon 72-hour EGF pretreatment, showed abolished EGF-induced lipocortin 1 phosphorylation and loss of [Ca2+] increase, indicating desensitization.
- Parental A431 cells did not exhibit this desensitization to EGF's immediate actions.
Conclusions:
- A direct link exists between EGF-induced cytoplasmic calcium increase, lipocortin 1 phosphorylation, and cell growth modulation.
- Differential desensitization mechanisms to the immediate effects of EGF contribute to altered cellular growth responses.
- These findings highlight the complexity of EGF signaling and its impact on cell proliferation control.