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Identification of the HECT E3 ligase UBR5 as a regulator of MYC degradation using a CRISPR/Cas9 screen
Lina Schukur1,2, Tamara Zimmermann3, Ole Niewoehner4
1Novartis Institutes for Biomedical Research (NIBR) Oncology, Novartis, Basel, Switzerland. lina.schukur@roche.com.
Abstract:
MYC oncoprotein is a multifunctional transcription factor that regulates the expression of a large number of genes involved in cellular growth, proliferation and metabolism. Altered MYC protein level lead to cellular transformation and tumorigenesis. MYC is deregulated in > 50% of human cancers, rendering it an attractive drug target. However, direct inhibition of this class of proteins using conventional small molecules is challenging due to their intrinsically disordered state. To discover novel posttranslational regulators of MYC protein stability and turnover, we established a genetic screen in mammalian cells by combining a fluorescent protein-based MYC abundance sensor, CRISPR/Cas9-based gene knockouts and next-generation sequencing. Our screen identifies UBR5, an E3 ligase of the HECT-type family, as a novel regulator of MYC degradation. Even in the presence of the well-described and functional MYC ligase, FBXW7, UBR5 depletion leads to accumulation of MYC in cells. We demonstrate interaction of UBR5 with MYC and reduced K48-linked ubiquitination of MYC upon loss of UBR5 in cells. Interestingly, in cancer cell lines with amplified MYC expression, depletion of UBR5 resulted in reduced cell survival, as a consequence of MYC stabilization. Finally, we show that MYC and UBR5 are co-amplified in more than 40% of cancer cells and that MYC copy number amplification correlates with enhanced transcriptional output of UBR5. This suggests that UBR5 acts as a buffer in MYC amplified settings and protects these cells from apoptosis.
Insights
Researchers identified UBR5, a novel E3 ligase, as a key regulator of MYC oncoprotein degradation. UBR5 depletion stabilizes MYC, impacting cancer cell survival and suggesting a new therapeutic target for MYC-driven cancers.
Area of Science:
- Molecular Biology
- Cancer Biology
- Genetics
Background:
- MYC oncoprotein is crucial for cell growth and metabolism, but its dysregulation drives over 50% of human cancers.
- Targeting MYC is challenging due to its disordered structure, necessitating research into novel regulatory mechanisms.
- Understanding MYC protein stability and turnover is vital for developing effective cancer therapies.
Purpose of the Study:
- To identify novel posttranslational regulators of MYC protein stability and turnover.
- To investigate the role of E3 ligases in MYC degradation pathways.
- To explore the therapeutic potential of targeting MYC regulators in cancer.
Main Methods:
- A genetic screen using a fluorescent MYC sensor, CRISPR/Cas9 gene knockouts, and next-generation sequencing in mammalian cells.
- Assessing MYC protein levels and ubiquitination status upon UBR5 manipulation.
- Analyzing the impact of UBR5 depletion on cancer cell survival and gene expression.
Main Results:
- UBR5, a HECT-type E3 ligase, was identified as a novel regulator of MYC degradation.
- UBR5 depletion leads to MYC accumulation, reduced K48-linked ubiquitination, and interaction with MYC.
- In MYC-amplified cancers, UBR5 depletion reduces cell survival by stabilizing MYC.
- MYC and UBR5 are frequently co-amplified in cancers, with UBR5 expression correlating with MYC copy number.
Conclusions:
- UBR5 plays a significant role in regulating MYC protein stability and degradation.
- UBR5 functions as a buffer in MYC-amplified cancers, protecting cells from apoptosis.
- Targeting UBR5 may offer a novel therapeutic strategy for cancers with deregulated MYC.
