Related Experiment Video
Updated: Nov 18, 2025
Identification of Transcription Factor Regulators using Medium-Throughput Screening of Arrayed Libraries and a Dual-Luciferase-Based Reporter
Published on: March 27, 2020
Ubash3b promotes TPA-mediated suppression of leukemogenesis through accelerated downregulation of PKCδ protein
Yao Yao1, Wuling Liu1, Babu Gajendran1
1State Key Laboratory for Functions and Applications of Medicinal Plants, Guizhou Medical University, Guiyang, 550014, PR China; The Key Laboratory of Chemistry for Natural Products of Guizhou Province and Chinese Academic of Sciences, Guiyang, Guizhou, 550014, PR China.
Abstract:
Acquired drug-resistance, often involving downregulation or mutations in the target protein, is a major caveat in precision medicine. Understanding mechanisms of resistance to therapeutic drugs may unravel strategies to overcome or prevent them. We previously identified phorbol ester (PE) compounds such as TPA that induce Protein Kinase δ (PKCδ), thereby suppressing leukemogenesis. Here we identified erythroleukemia cell lines that resist PEs and showed that reduced PKCδ protein expression underlies drug resistance. Reduced level of PKCδ in resistant cell lines was due to its phosphorylation followed by protein degradation. Indeed, proteasome inhibition prevented PE-induced loss of PKCδ. Accordingly, a combination of TPA and the proteasome inhibitor ALLN significantly suppressed leukemia in a mouse model of leukemia. PKCδ downregulation by TPA was independent of the downstream MAPK/ERK/P38/JNK pathway. Instead, expression of ubiquitin-associated and SH3 domain-containing protein b (Ubash3b) was induced by TPA, which leads to PKCδ protein dephosphorylation and degradation. This specific degradation was blocked by RNAi-mediated depletion of Ubash3b. In drug-sensitive leukemic cells, TPA did not induce Ubash3b, and consequently, PKCδ levels remained high. A PE-resistant cell line derived from PE-treated sensitive cells exhibited very low PKCδ expression. In these drug resistance cells, a Ubash3b independent mechanism led to PKCδ degradation. Thus, PE compounds in combination with proteasome or specific inhibitors for Ubash3b, or other factors can overcome resistance to TPA, leading to durable suppression of leukemic growth. These results identify Ubash3b as a potential target for drug development.
Insights
Phorbol ester (PE) compounds suppress leukemia by inducing Protein Kinase δ (PKCδ). Drug resistance involves reduced PKCδ due to degradation mediated by Ubash3b, offering new therapeutic targets for overcoming leukemia.
Area of Science:
- Oncology
- Molecular Biology
- Drug Discovery
Background:
- Acquired drug resistance is a significant challenge in precision medicine.
- Understanding resistance mechanisms is crucial for developing effective cancer therapies.
- Phorbol ester (PE) compounds, like TPA, suppress leukemogenesis by inducing Protein Kinase δ (PKCδ).
Purpose of the Study:
- To investigate the mechanisms underlying resistance to PE compounds in erythroleukemia.
- To identify novel therapeutic strategies to overcome drug resistance in leukemia.
Main Methods:
- Utilized erythroleukemia cell lines with varying sensitivity to PE compounds.
- Analyzed Protein Kinase δ (PKCδ) protein expression and degradation pathways.
- Investigated the role of ubiquitin-associated and SH3 domain-containing protein b (Ubash3b) in PKCδ regulation.
- Employed proteasome inhibitors and RNA interference (RNAi) for mechanistic studies.
- Evaluated therapeutic efficacy in a mouse model of leukemia.
Main Results:
- PE-resistant erythroleukemia cell lines exhibit reduced PKCδ protein levels due to enhanced phosphorylation and subsequent degradation.
- TPA induces Ubash3b expression, leading to PKCδ dephosphorylation and proteasomal degradation in sensitive cells.
- Proteasome inhibition and Ubash3b depletion counteract PE-induced PKCδ loss.
- Combination therapy with TPA and a proteasome inhibitor suppressed leukemia in a mouse model.
- PE-resistant cells displayed Ubash3b-independent PKCδ degradation mechanisms.
Conclusions:
- Reduced PKCδ expression, often mediated by Ubash3b-induced degradation, is a key mechanism of PE resistance in leukemia.
- Targeting Ubash3b or utilizing proteasome inhibitors in combination with PE compounds can overcome drug resistance.
- These findings highlight Ubash3b as a potential therapeutic target for durable leukemia suppression.
More Related Videos
08:49Identification of Mediators of T-cell Receptor Signaling via the Screening of Chemical Inhibitor Libraries
Published on: January 22, 2019
10:59Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment
Published on: November 23, 2017
Related Concept Videos
01:20The JAK-STAT Signaling Pathway
02:23Abnormal Proliferation
01:31The Intrinsic Apoptotic Pathway
01:19Interactions Between Signaling Pathways
Convergence and divergence, and cross-talk between signaling pathways
Two distinct signaling pathways can converge on a single functional unit, which may either be a single protein or a complex of proteins. The response is either functionally distinct or synergistic between the two pathways but different from the response...
01:07MAPK Signaling Cascades
01:22PI3K/mTOR/AKT Signaling Pathway