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Degradation process of ligand-stimulated platelet-derived growth factor beta-receptor involves ubiquitin-proteasome
1Second Department of Internal Medicine, Chiba University School of Medicine, Japan.
Abstract:
The platelet-derived growth factor beta-receptor undergoes polyubiquitination as a consequence of ligand binding. We have previously reported that ligand-induced ubiquitination of the receptor plays a negative regulatory role in its mitogenic signaling possibly by promoting the efficient degradation of the ligand-activated receptor (Mori, S., Heldin, C.-H., and Claesson-Welsh, L. (1993) J. Biol. Chem. 268, 577-583). In the present study, we have examined effects of different kinds of cell-penetrating proteasome inhibitors, including substrate-related peptidyl aldehydes, Cbz-Ile-Glu(O-t-Bu)-Ala-leucinal (where Bu is butyl and Cbz is benzyloxycarbonyl) (PSI) and Cbz-Leu-Leu-norvalinal (MG115), and a Streptomyces metabolite lactacystin, on degradation of the receptor in intact cells with the aim of evaluating the role of the receptor ubiquitination in the proteasome-dependent proteolytic process. These proteasome inhibitors were found to considerably inhibit ligand-stimulated degradation of the wild-type beta-receptor; however, their inhibitory effect was not observed when the cells expressing the ubiquitination-deficient mutant beta-receptor were analyzed. These data suggest that the degradation process of the ligand-stimulated beta-receptor involves the ubiquitin-proteasome proteolytic pathway.
Insights
Ligand binding triggers platelet-derived growth factor beta-receptor ubiquitination, leading to its proteasome-dependent degradation. Proteasome inhibitors block this process, confirming the ubiquitin-proteasome pathway
Area of Science:
- Cellular signaling
- Molecular biology
- Protein degradation
Background:
- Platelet-derived growth factor beta-receptor (PDGFR-beta) signaling is regulated by ligand-induced ubiquitination.
- Previous work suggests ubiquitination negatively impacts mitogenic signaling by promoting receptor degradation.
Purpose of the Study:
- To investigate the role of receptor ubiquitination in proteasome-dependent degradation.
- To evaluate the involvement of the ubiquitin-proteasome pathway in ligand-stimulated PDGFR-beta degradation.
Main Methods:
- Utilized cell-penetrating proteasome inhibitors: PSI, MG115, and lactacystin.
- Compared effects on wild-type PDGFR-beta and a ubiquitination-deficient mutant.
- Analyzed receptor degradation in intact cells.
Main Results:
- Proteasome inhibitors significantly inhibited ligand-stimulated degradation of wild-type PDGFR-beta.
- Inhibitory effects were absent in cells expressing the ubiquitination-deficient PDGFR-beta mutant.
- These findings highlight the necessity of ubiquitination for proteasome-mediated degradation.
Conclusions:
- Ligand-stimulated degradation of PDGFR-beta is mediated by the ubiquitin-proteasome proteolytic pathway.
- Ubiquitination is a critical step for the proteasomal degradation of the activated receptor.