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Down-regulation of epidermal growth factor receptors by nerve growth factor in PC12 cells is p140(trk)-, Ras-, and
P Lazarovici1, M Oshima, D Shavit
1Section on Growth Factors, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
Abstract:
Nerve growth factor (NGF) treatment causes a profound down-regulation of epidermal growth factor receptors during the differentiation of PC12 cells. This process is characterized by a progressive decrease in epidermal growth factor (EGF) receptor level measured by 125I-EGF binding, tyrosine phosphorylation, and Western blotting. Treatment of the cells with NGF for 5 days produces a 95% reduction in the amount of [35S]methionine-labeled EGF receptors. This down-regulation does not occur in PC12nnr5 cells, which lack the p140(trk) NGF receptor. However, in PC12nnr5 cells stably transfected with p140(trk), the NGF-induced heterologous down-regulation of EGF receptors is reconstituted in part. NGF-induced heterologous down-regulation, but not EGF-induced homologous down-regulation of EGF receptors, is blocked in Ras- and Src-dominant-negative PC12 cells. Treatment with either pituitary adenylate cyclase-activating peptide (PACAP) or staurosporine stimulates neurite outgrowth in PC12 cell variants, but neither induces down-regulation of EGF receptors. NGF treatment of PC12 cells in suspension induces down-regulation of EGF receptors in the absence of neurite outgrowth. These results strongly suggest a p140(trk)-, Ras- and Src-dependent mechanism of NGF-induced down-regulation of EGF receptors and separate this process from NGF-induced neurite outgrowth in PC12 cells.
Insights
Nerve growth factor (NGF) profoundly reduces epidermal growth factor (EGF) receptors in PC12 cells via a p140(trk), Ras, and Src-dependent pathway. This receptor down-regulation is distinct from NGF-induced neurite outgrowth.
Area of Science:
- Cell biology
- Neuroscience
- Molecular signaling
Background:
- PC12 cells are a model for neuronal differentiation.
- Epidermal growth factor (EGF) receptors are crucial for cell growth and differentiation.
- Nerve growth factor (NGF) plays a key role in neuronal development.
Purpose of the Study:
- To investigate the mechanism of NGF-induced down-regulation of EGF receptors in PC12 cells.
- To determine the role of specific signaling pathways (p140(trk), Ras, Src) in this process.
- To differentiate the EGF receptor down-regulation from NGF-induced neurite outgrowth.
Main Methods:
- Utilized 125I-EGF binding assays to quantify EGF receptor levels.
- Employed Western blotting and tyrosine phosphorylation assays to assess receptor status.
- Investigated NGF effects in wild-type PC12 cells, PC12nnr5 variants, and cells with dominant-negative Ras/Src.
Main Results:
- NGF treatment caused a 95% reduction in EGF receptors in PC12 cells.
- Down-regulation was dependent on the p140(trk) NGF receptor and signaling through Ras and Src.
- Neither PACAP nor staurosporine induced EGF receptor down-regulation, and NGF-induced down-regulation occurred independently of neurite outgrowth.
Conclusions:
- NGF-induced EGF receptor down-regulation in PC12 cells is mediated by a p140(trk)-, Ras-, and Src-dependent pathway.
- This mechanism is distinct from the process of NGF-induced neurite outgrowth.
- Highlights the complexity of signaling crosstalk between growth factor pathways in neuronal differentiation.