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The TERT Promoter is Polycomb-Repressed in Neuroblastoma Cells with Long Telomeres
Mindy K Graham1,2, Beisi Xu3, Christine Davis4
1Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Cancer Research Communications
|June 5, 2024
Summary
Epigenetic regulation of telomerase (TERT) differs in neuroblastoma based on telomere maintenance. H3K27 methylation represses TERT in long-telomere neuroblastoma, while MYCN drives TERT in short-telomere cases.
Area of Science:
- Oncology
- Epigenetics
- Cancer Biology
Background:
- Neuroblastoma, a high-risk cancer, often maintains telomeres via telomerase (TERT) or alternative lengthening of telomeres (ALT).
- A subset of neuroblastoma exhibits long telomeres without a clear telomere maintenance mechanism, suggesting alternative regulatory pathways.
- The epigenetic regulation of the TERT locus in neuroblastoma remains incompletely understood, particularly in cases with distinct telomere lengths and maintenance statuses.
Purpose of the Study:
- To investigate the epigenetic mechanisms governing telomerase (TERT) expression in neuroblastoma with varying telomere lengths and maintenance statuses.
- To elucidate the role of DNA methylation and histone modifications, specifically H3K27 trimethylation (H3K27me3), in regulating TERT expression.
- To determine the influence of MYCN oncogene binding and Polycomb Repressive Complex 2 (PRC2) activity on TERT locus regulation.
Main Methods:
- Analysis of TERT promoter and locus DNA methylation patterns across neuroblastoma subtypes.
- Chromatin immunoprecipitation (ChIP) to assess active and repressive histone marks (e.g., H3K27me3) at the TERT locus.
- Investigation of MYCN binding to the TERT promoter using ChIP assays.
- Pharmacological inhibition of EZH2, a key component of PRC2, to assess its impact on TERT expression and MYCN binding.
Main Results:
- Neuroblastoma exhibits broad TERT promoter hypomethylation, distinct from most cancers.
- Telomerase-positive neuroblastoma shows active chromatin at TERT with MYCN-driven expression.
- Neuroblastoma with long telomeres displays widespread H3K27me3 enrichment across the TERT locus and nearby genes, alongside subtelomeric repressive marks.
- EZH2 inhibition reactivates TERT expression in long-telomere neuroblastoma cells and facilitates MYCN binding to the TERT promoter.
Conclusions:
- Epigenetic regulation of TERT expression is heterogeneous in neuroblastoma, correlating with telomere length and maintenance mechanisms.
- H3K27 methylation by PRC2 plays a critical role in repressing TERT expression in neuroblastoma with long telomeres.
- Targeting EZH2 may offer a therapeutic strategy to reactivate TERT in specific neuroblastoma subtypes.
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