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Decreased epidermal growth factor binding in cells growth arrested in G1 by nutrient deficiency
Abstract:
Previous studies have shown that the nontransformed AKR-2B mouse embryo derived cell line may growth arrest by two separate mechanisms in the G1 phase of the cell cycle--growth factor deficiency arrest (G0) and low molecular weight nutrient deficiency arrest. An examination of epidermal growth factor (EGF) receptors under the different resting or growth conditions has shown that rapidly growing cells or cells arrested due to growth factor deficiency have the expected amount of 125I-EGF binding with approximately 10(5) receptors per cell being present in G0 arrested cells. In contrast, cells arrested due to nutrient deficiency show a reduction in 125I-EGF binding to 10-20% of that observed under the other conditions. This effect appears to be due to decreased receptor number and not to a change in the affinity of the receptor. Stimulation of DNA synthesis by nutrient replenishment causes a tenfold increase in EGF binding 20 hours later, with some increase in binding being detectable as early as six hours. The increase in binding is inhibited by cycloheximide and actinomycin D. This suggests that new mRNA synthesis as well as increased protein synthesis is required for the increase in EGF binding.
Insights
Nutrient deficiency reduces epidermal growth factor (EGF) receptors in AKR-2B cells, impacting cell cycle regulation. Replenishing nutrients restores EGF receptor levels, requiring new protein and mRNA synthesis.
Area of Science:
- Cell Biology
- Molecular Biology
Background:
- AKR-2B mouse embryo cells exhibit G1 phase arrest via growth factor or nutrient deficiency.
- Epidermal growth factor (EGF) signaling is crucial for cell growth and proliferation.
Purpose of the Study:
- To investigate the role of epidermal growth factor (EGF) receptors in nutrient-deficient cell cycle arrest.
- To understand the mechanism of EGF receptor regulation in response to nutrient availability.
Main Methods:
- Quantification of 125I-EGF binding to AKR-2B cells under various growth and arrest conditions.
- Analysis of EGF receptor number and affinity.
- Assessment of the effects of nutrient replenishment on EGF binding.
- Inhibition studies using cycloheximide and actinomycin D.
Main Results:
- Nutrient-deficient cells show a 80-90% reduction in 125I-EGF binding compared to growth factor-deficient or growing cells.
- This reduction is attributed to decreased EGF receptor number, not altered receptor affinity.
- Nutrient replenishment leads to a tenfold increase in EGF binding within 20 hours.
- This increase is dependent on new mRNA and protein synthesis.
Conclusions:
- Nutrient deficiency significantly downregulates EGF receptor expression in AKR-2B cells.
- Restoration of nutrient levels upregulates EGF receptors through de novo protein and mRNA synthesis.
- EGF receptor regulation is a key factor in nutrient-mediated cell cycle control.