Signal Transduction in Diffuse Intrinsic Pontine Glioma

Abstract

Diffuse intrinsic pontine glioma (DIPG) is an untreatable, heterogeneous high-grade glioma (HGG) of the brainstem. This highly aggressive cancer affects mostly young children and is uniformly fatal. Genomic studies show that DIPG is driven by somatic mutations to histone H3, either H3.1 or H3.3 variants (HIST1H3B/C and H3F3A), altering the epigenetic landscape of primitive oligodendrocyte or astrocyte precursor cells of the pontine region of the brainstem. Lysine-to-methionine point mutations at amino acid 27 (H3K27M) co-occur with alterations in signaling genes, including the receptor tyrosine kinases (PDGFR/KIT/VEGFR/MET/EGFR), activin A receptor (ACVR1), intracellular kinases (PI3K/AKT/mTOR), cyclin-dependent kinases (CDKs1/4/6), transcriptional regulators (MYCN), and tumor suppressors (PTEN/TP53). This cooperation drives gene expression signatures that inhibit cellular differentiation (ID1/2, Hedgehog) and promotes malignant transformation. Unique to DIPG, is the frequency of co-occurring sets of genomic insults. However, mapping of the oncogenic signaling pathways activated in response to recurring mutations is unresolved. Herein, known oncogenic signal pathways activated in response to recurring somatic mutations and gene amplifications in DIPG are reviewed. Additionally, an important role for high-resolution quantitative proteomics/phosphoproteomics in the characterization of signaling cascades are highlighted. These regulate the cell cycle, epigenetics and anti-apoptotic processes, information critical for the development of improved treatment strategies for DIPG.

Keywords: diffuse intrinsic pontine glioma (DIPG); epigenetics; pediatric high grade glioma (pHGG); phosphoproteomics; proteomics; signal transduction.