Poster Presentation 36th Lorne Cancer Conference 2024

Characterization of the effects of H3K27M variants on the DNA-damage response in diffuse midline glioma (#109)

Nicolas Poux 1 2 3 , Adam F Kebede 2 3 , Jens Maile 2 3 , Olivia Blumenshine 2 3 , Rameen Beroukhim 2 4 , Pratiti Bandopadhayay 2 3
  1. Harvard Medical School, Boston, MA, USA
  2. Cancer Program, Broad Institute, Cambridge, MA, USA
  3. Pediatric Oncology, Dana Farber Cancer Institute, Boston, MA, USA
  4. Medical Oncology, Dana Farber Cancer Institute, Boston, MA, USA

Diffuse midline gliomas (DMGs) are universally fatal brain tumors affecting young children that are genetically driven by mutations in histone 3 N-terminal tail at lysine 27 (H3K27M)1–3. Histone 3 is encoded by several variants, including the canonical H3.1, that is deposited after DNA-replication, and H3.3, which is deposited in dynamically-regulated loci in a cell-cycle independent manner4. K27M mutations in H3.1 or H3.3 disrupt differentiation processes and lead to tumorigenesis5–7, though H3K27M mutations are not solely sufficient for transformation8.

Since radiotherapy is the only approved treatment shown to have any efficacy in prolonging survival in DMG9, understanding the mechanisms by which DMGs respond to DNA-damage is crucial to improving therapeutic approaches. Previous work by our group has shown that H3.3K27M DMGs show greater genomic instability than H3.1K27M tumors – with a greater number and higher complexity of structural variants (SV) – and that H3.1K27M tumors infrequently show direct p53 alterations relative to H3.3K27M tumors10. This raises the possibility that histone variants differentially influence the state of DNA-damage repair within in the tumor.

Here we present an early-stage project that aims to investigate whether H3K27M variants differentially affect tolerance to DNA-damage and p53 loss, and whether tumor evolution is directed by cell-tolerance to DNA-damage. We will also predict that H3.1K27M and H3.3K27M differentially affect chromatin organization, leading to separate patterns of SV formation in regions of open chromatin.

Using isogenic cell-line models expressing H3.1K27M or H3.3K27M, we aim to characterize the DNA-damage response pathways in each cell line, and measure the response to p53 inactivation to assess whether H3.1K27M mutations are sufficient to induce a differential dependency on DNA-damage repair pathways relative to H3.3K27M. Additionally, we aim to use multiomics techniques to create genomic maps of chromatin-accessibility of H3.1K27M vs H3.3K27M cells, and will correlate these maps with locations of known SVs to assess whether oncohistone variants bias the location and frequency of SV formation.

Together, these experiments represent a novel approach to understanding the role that H3 mutations contribute to tumor evolution, and provide a pathway to elucidating differences in DNA-damage response between H3.1K27M and H3.3K27M-driven DMGs.


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