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Characterization of platelet-derived growth factor alpha receptor synthesis and metabolic turnover
S R Coats1, N E Olashaw, W J Pledger
1Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0615.
Abstract:
Cellular responses to the AA isoform of platelet-derived growth factor (PDGF-AA) are mediated via the PDGF alpha receptor. Several studies suggest this receptor may signal pathways distinct from those activated by the PDGF beta receptor. Because alpha receptors are less well characterized than are beta receptors, and because the quantity of cell surface PDGF receptors governs the extent and perhaps type of PDGF-stimulated response, we examined the synthesis and degradation of alpha receptors in BALB/c-3T3 cells. Our data show that the ligand-independent half-life of alpha receptors is 3 h and that optimal turnover of alpha receptors requires protein synthesis. In the presence of ligand, the half-life of alpha receptors markedly decreases and is independent of protein synthesis. Although PDGF-AA accelerated the rate of alpha receptor turnover, pretreatment of cells with PDGF-AA and essentially complete down-regulation of alpha receptors did not correspondingly increase the level of alpha receptor synthesis. These findings indicate that the number of cell surface PDGF alpha receptors is regulated by the rate of internalization of these receptors. Lastly, we report that the recovery of PDGF-AA binding following down-regulation of alpha receptors is not affected by inhibition of RNA synthesis. Thus, repopulation of cell surface PDGF alpha receptors may not necessitate an increase in the level of PDGF alpha receptor mRNA.
Insights
Platelet-derived growth factor alpha receptors (PDGF-AA) are regulated by internalization, not synthesis. Ligand binding accelerates PDGF-AA receptor turnover, independent of protein synthesis.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cellular responses to platelet-derived growth factor AA (PDGF-AA) involve the PDGF alpha receptor.
- PDGF alpha receptors may signal distinct pathways compared to PDGF beta receptors.
- Cell surface PDGF receptor quantity influences PDGF-stimulated cellular responses.
Purpose of the Study:
- To investigate the synthesis and degradation of PDGF alpha receptors in BALB/c-3T3 cells.
- To understand the regulation of cell surface PDGF alpha receptor numbers.
Main Methods:
- Measurement of ligand-independent and ligand-dependent half-life of PDGF alpha receptors.
- Assessment of the role of protein synthesis in PDGF alpha receptor turnover.
- Evaluation of PDGF-AA's effect on receptor synthesis and down-regulation.
- Investigation of RNA synthesis inhibition on receptor recovery.
Main Results:
- Ligand-independent half-life of PDGF alpha receptors is 3 hours, requiring protein synthesis for optimal turnover.
- Ligand binding significantly decreases PDGF alpha receptor half-life, independent of protein synthesis.
- PDGF-AA accelerates receptor turnover but does not increase synthesis levels after down-regulation.
- Inhibition of RNA synthesis does not affect the recovery of PDGF-AA binding after down-regulation.
Conclusions:
- Cell surface PDGF alpha receptor numbers are primarily regulated by the rate of receptor internalization.
- Repopulation of cell surface PDGF alpha receptors may not require increased PDGF alpha receptor mRNA levels.