The Y641C mutation of EZH2 alters substrate specificity for histone H3 lysine 27 methylation states

Area of Science:

• Biochemistry
• Molecular Biology
• Oncology

Background:

• Mutations at tyrosine 641 (Y641) in the enhancer of zeste homolog 2 (EZH2) gene are recurrent in certain non-Hodgkin lymphomas (NHL).
• These EZH2 Y641 mutations affect substrate specificity for histone H3 lysine 27 (H3K27) methylation states.
• The Y641C mutation, identified in NHL and myelodysplastic syndrome (MDS) contexts, was previously reported to reduce EZH2 enzymatic activity.

Purpose of the Study:

• To investigate the enzymatic activity of the EZH2 Y641C mutation.
• To characterize the substrate specificity of EZH2 Y641C in comparison to wild-type EZH2.
• To understand the impact of the Y641C mutation on H3K27 methylation dynamics.

Main Methods:

• Enzymatic assays using wild-type and mutant EZH2 proteins.
• Analysis of H3K27 methylation states (un-, mono-, di-, and trimethylated) as substrates and products.
• Comparison of catalytic efficiency for different methylation states.

Main Results:

• The EZH2 Y641C mutation significantly reduces enzymatic activity towards unmethylated and monomethylated H3K27.
• Conversely, the Y641C mutation demonstrates enhanced activity in catalyzing the formation of trimethylated H3K27 from its dimethylated precursor.
• This indicates a specific alteration in substrate preference rather than a complete loss of function.

Conclusions:

• The EZH2 Y641C mutation exhibits differential effects on H3K27 methylation, ablating activity on lower methylation states while enhancing trimethylation from dimethylation.
• These findings provide novel insights into the mechanistic consequences of EZH2 mutations in hematological malignancies.
• Understanding these specific enzymatic alterations is crucial for developing targeted therapies for EZH2-mutated cancers.