Oncogenic Y641 mutations in EZH2 prevent Jak2/β-TrCP-mediated degradation

Area of Science:

• Epigenetics and Gene Regulation
• Cancer Biology
• Ubiquitin Ligase Function

Background:

• Enhancer of zeste homolog 2 (EZH2) is a key component of Polycomb Repressive Complex 2 (PRC2), responsible for H3K27 trimethylation and gene silencing.
• EZH2 dysregulation, including mutations and overexpression, is implicated in various cancers, particularly lymphomas.
• The precise post-translational mechanisms regulating EZH2 activity remain incompletely understood.

Purpose of the Study:

• To investigate novel regulatory mechanisms of EZH2, focusing on its post-translational modifications.
• To elucidate the role of the SCF E3 ubiquitin ligase complex, specifically β-TrCP, in EZH2 degradation.
• To determine the impact of EZH2 Y641 mutations on EZH2 stability and its contribution to lymphoma pathogenesis.

Main Methods:

• Co-immunoprecipitation assays to identify EZH2 interactors.
• Western blotting to assess protein levels and ubiquitination.
• RNA interference (RNAi) to silence β-TrCP.
• Jak2 inhibition studies.
• Analysis of endogenous EZH2 Y641 mutants in lymphoma cell lines.

Main Results:

• EZH2 was identified as a novel substrate for the SCF E3 ubiquitin ligase β-TrCP.
• Phosphorylation of EZH2 at Y641 by Jak2 promotes β-TrCP-mediated degradation.
• Silencing of β-TrCP or inhibition of Jak2 led to EZH2 stabilization and increased H3K27 trimethylation.
• Recurrent lymphoma-associated EZH2 Y641 mutants failed to bind β-TrCP, resulting in enhanced stability and H3K27me3 hyperactivity.

Conclusions:

• β-TrCP acts as a crucial regulator of EZH2 stability and H3K27 trimethylation activity.
• The inability of EZH2 Y641 mutants to interact with β-TrCP contributes to their hyperactivity and lymphoma pathogenesis.
• Targeting the β-TrCP-EZH2 axis offers a potential therapeutic strategy for EZH2-driven lymphomas.