Perturbazioni chimiche e genetiche rivelano il ruolo di HMGB2 nei programmi trascrizionali del glioma pontino intrinseco diffuso (DIPG) H3.3K27M

Diffuse Intrinsic Pontine Glioma (DIPG) is a fatal pediatric brainstem tumor driven by H3.3K27M oncohistone mutations, which reprogram Polycomb repressive complex 2 (PRC2). By acting as a “molecular poison” for PRC2 catalytic activity, K27M induces global depletion of H3K27me3 marks, consequently deregulating epigenetic states and developmental gene expression programs. At the cellular level, DIPG exhibits marked intratumoral transcriptional heterogeneity, comprising transcriptional programs matching astrocyte-like (AC), oligodendrocyte-like (OC), oligodendrocyte progenitor-like (OPC), and mesenchymal-like (MES) cells, reflecting intrinsic aberrant neurodevelopmental states. Such plasticity confers consistent proliferative capacity and intrinsic aggressiveness in DIPG tumors, which highly depend on proper chromatin organization. While epigenetic regulators have been extensively studied in recent years, chromatin architectural proteins (CAPs) remain unexplored in the DIPG context. Among molecular targets identified by an unbiased chromatin proteomics screening, HMGB2 emerged as a selectively enriched protein in chromatin fractions of DIPG tumors compared to glioblastoma. As a DNA-bending CAP known to play a role in DNA replication and DNA damage responses (DDR), HMGB2 represented a promising therapeutic target for investigation in the context of DIPG tumors. Using complementary genetic models (Tet-ON shRNA knockdown and CRISPR-Cas9 knockout) in patient-derived DIPG7 cells, we demonstrated that HMGB2 is essential for cell proliferation and viability. Its loss causes cells to arrest in G1 phase, transcriptional downregulation of replication factors (ORC complex), and compromised DNA damage responses, as shown by flow cytometry analysis of cell cycle and immunofluorescence assays of γH2AX. Complementary, bulk transcriptomics revealed that HMGB2 depletion constrains cells toward an oligodendrocyte progenitor-like (OPC) transcriptional state, characterized by reduced proliferative output and altered differentiation dynamics. This state is associated with attenuation of oncogenic stemness programs, suggesting that HMGB2 is required to sustain the coupling between progenitor identity and active cell cycle progression. Our data support a model in which HMGB2 functions as a chromatin scaffolder, linking DNA damage responses, replication competence, and lineage plasticity in H3.K27M DIPG tumors.