SWI/SNF-mutant cancers depend on catalytic and non-catalytic activity of EZH2

Area of Science:

• Oncology
• Molecular Biology
• Epigenetics

Background:

• SWI/SNF chromatin remodeling complexes are frequently mutated in human cancers, with some subunits acting as tumor suppressors.
• The functional consequences of SWI/SNF subunit mutations, particularly shared dependencies, remain largely unknown.
• Polycomb Repressive Complex 2 (PRC2) and its catalytic subunit EZH2 play critical roles in gene regulation and cancer development.

Purpose of the Study:

• To investigate whether mutations in SWI/SNF subunits lead to shared dependencies in cancer.
• To determine the role of EZH2 in cancers with mutations in SWI/SNF subunits.
• To explore the therapeutic implications of targeting EZH2 in SWI/SNF-mutant cancers.

Main Methods:

• Analysis of cancer cell lines and xenografts with specific SWI/SNF subunit mutations (ARID1A, PBRM1, SMARCA4).
• Assessment of EZH2 dependency in these cancer models, including the impact of co-occurring Ras pathway mutations.
• Investigation of EZH2's catalytic (histone methyltransferase) and non-catalytic roles in PRC2 complex stabilization.

Main Results:

• Cancer cell lines and xenografts with mutations in ARID1A, PBRM1, or SMARCA4 are dependent on EZH2.
• The presence of a Ras pathway mutation abrogates this EZH2 dependency.
• SWI/SNF-mutant cancers rely more on EZH2's non-catalytic function in stabilizing PRC2 than its enzymatic activity.

Conclusions:

• Genetic alterations in SWI/SNF subunits confer a shared dependency on EZH2.
• Ras pathway mutations can override the dependency on EZH2 in SWI/SNF-mutant cancers.
• Current EZH2 enzymatic inhibitors may not fully address the oncogenic activity of EZH2 in these contexts, necessitating alternative therapeutic strategies.