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Updated: Feb 6, 2026
Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates
Published on: May 10, 2022
Erioflorin stabilizes the tumor suppressor Pdcd4 by inhibiting its interaction with the E3-ligase β-TrCP1
Johanna S Blees1, Heidi R Bokesch, Daniela Rübsamen
1Institute of Biochemistry I, Faculty of Medicine, Goethe-University Frankfurt, Frankfurt, Germany.
Abstract:
Loss of the tumor suppressor Pdcd4 was reported for various tumor entities and proposed as a prognostic marker in tumorigenesis. We previously characterized decreased Pdcd4 protein stability in response to mitogenic stimuli, which resulted from p70(S6K1)-dependent protein phosphorylation, β-TrCP1-mediated ubiquitination, and proteasomal destruction. Following high-throughput screening of natural product extract libraries using a luciferase-based reporter assay to monitor phosphorylation-dependent proteasomal degradation of the tumor suppressor Pdcd4, we succeeded in showing that a crude extract from Eriophyllum lanatum stabilized Pdcd4 from TPA-induced degradation. Erioflorin was identified as the active component and inhibited not only degradation of the Pdcd4-luciferase-based reporter but also of endogenous Pdcd4 at low micromolar concentrations. Mechanistically, erioflorin interfered with the interaction between the E3-ubiquitin ligase β-TrCP1 and Pdcd4 in cell culture and in in vitro binding assays, consequently decreasing ubiquitination and degradation of Pdcd4. Interestingly, while erioflorin stabilized additional β-TrCP-targets (such as IκBα and β-catenin), it did not prevent the degradation of targets of other E3-ubiquitin ligases such as p21 (a Skp2-target) and HIF-1α (a pVHL-target), implying selectivity for β-TrCP. Moreover, erioflorin inhibited the tumor-associated activity of known Pdcd4- and IκBα-regulated αtranscription factors, that is, AP-1 and NF-κB, altered cell cycle progression and suppressed proliferation of various cancer cell lines. Our studies succeeded in identifying erioflorin as a novel Pdcd4 stabilizer that inhibits the interaction of Pdcd4 with the E3-ubiquitin ligase β-TrCP1. Inhibition of E3-ligase/target-protein interactions may offer the possibility to target degradation of specific proteins only as compared to general proteasome inhibition.
Insights
Erioflorin, a natural compound, stabilizes the tumor suppressor Pdcd4 by blocking its interaction with the E3-ubiquitin ligase β-TrCP1. This novel mechanism inhibits cancer cell proliferation and offers a targeted approach to protein degradation therapy.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Loss of the tumor suppressor Pdcd4 is linked to various cancers and serves as a prognostic marker.
- Pdcd4 protein stability is regulated by phosphorylation, ubiquitination, and proteasomal degradation, particularly in response to mitogenic stimuli via p70(S6K1) and β-TrCP1.
Purpose of the Study:
- To identify natural compounds that stabilize Pdcd4 protein.
- To elucidate the mechanism of action of identified compounds on Pdcd4 degradation pathways.
- To evaluate the anti-cancer effects of the identified compound.
Main Methods:
- High-throughput screening of natural product extracts using a luciferase reporter assay for Pdcd4 degradation.
- Identification of active compounds via biochemical assays.
- Western blotting and co-immunoprecipitation to assess protein levels, ubiquitination, and protein interactions.
- Cell culture experiments to evaluate effects on cell cycle and proliferation.
- In vitro binding assays to confirm target interactions.
Main Results:
- A crude extract from Eriophyllum lanatum stabilized Pdcd4 against TPA-induced degradation.
- Erioflorin was identified as the active component, stabilizing both reporter and endogenous Pdcd4 at low micromolar concentrations.
- Erioflorin specifically inhibited the interaction between Pdcd4 and the E3-ubiquitin ligase β-TrCP1, reducing Pdcd4 ubiquitination and degradation.
- Erioflorin demonstrated selectivity for β-TrCP targets, stabilizing IκBα and β-catenin but not Skp2 or pVHL targets.
- Erioflorin inhibited AP-1 and NF-κB transcription factors, altered cell cycle, and suppressed proliferation in cancer cell lines.
Conclusions:
- Erioflorin is a novel Pdcd4 stabilizer that selectively inhibits the β-TrCP1 E3-ubiquitin ligase interaction.
- Targeting E3-ligase/target-protein interactions offers a precise strategy for protein degradation modulation, distinct from general proteasome inhibition.
- Erioflorin exhibits anti-cancer properties by stabilizing Pdcd4 and inhibiting key oncogenic pathways.
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