ABSTRACT
Although a growing body of evidence indicates that phenotypic plasticity exhibited by glioblastoma cells plays a central role in tumor development and post-therapy recurrence, the master drivers of their aggressiveness remain elusive. Here we mapped the changes in active (H3K4me3) and repressive (H3K27me3) histone modifications accompanying the repression of glioblastoma stem-like cells tumorigenicity. Genes with changing histone marks delineated a network of transcription factors related to cancerous behavior, stem state, and neural development, highlighting a previously unsuspected association between repression of ARNT2 and loss of cell tumorigenicity. Immunohistochemistry confirmed ARNT2 expression in cell sub-populations within proliferative zones of patients' glioblastoma. Decreased ARNT2 expression was consistently observed in non-tumorigenic glioblastoma cells, compared to tumorigenic cells. Moreover, ARNT2 expression correlated with a tumorigenic molecular signature at both the tissue level within the tumor core and at the single cell level in the patients' tumors. We found that ARNT2 knockdown decreased the expression of SOX9, POU3F2 and OLIG2, transcription factors implicated in glioblastoma cell tumorigenicity, and repressed glioblastoma stem-like cell tumorigenic properties in vivo. Our results reveal ARNT2 as a pivotal component of the glioblastoma cell tumorigenic signature, located at a node of a transcription factor network controlling glioblastoma cell aggressiveness.
Subject(s)
Aryl Hydrocarbon Receptor Nuclear Translocator/metabolism , Basic Helix-Loop-Helix Transcription Factors/metabolism , Brain Neoplasms/metabolism , Chromatin/metabolism , Glioblastoma/metabolism , Aged , Animals , Aryl Hydrocarbon Receptor Nuclear Translocator/genetics , Basic Helix-Loop-Helix Transcription Factors/genetics , Brain Neoplasms/genetics , Brain Neoplasms/pathology , Cells, Cultured , Epigenesis, Genetic , Gene Expression Regulation, Neoplastic , Gene Knockdown Techniques , Glioblastoma/genetics , Glioblastoma/pathology , Histone Code , Homeodomain Proteins/metabolism , Humans , Mice, Nude , Middle Aged , Neoplasm Invasiveness/genetics , Neoplasm Invasiveness/pathology , Neoplasm Invasiveness/physiopathology , Neoplasm Transplantation , Neoplastic Stem Cells/metabolism , Neoplastic Stem Cells/pathology , Oligodendrocyte Transcription Factor 2/metabolism , POU Domain Factors/metabolism , SOX9 Transcription Factor/metabolismABSTRACT
Cell populations with differing proliferative, stem-like and tumorigenic states co-exist in most tumors and especially malignant gliomas. Whether metabolic variations can drive this heterogeneity by controlling dynamic changes in cell states is unknown. Metabolite profiling of human adult glioblastoma stem-like cells upon loss of their tumorigenicity revealed a switch in the catabolism of the GABA neurotransmitter toward enhanced production and secretion of its by-product GHB (4-hydroxybutyrate). This switch was driven by succinic semialdehyde dehydrogenase (SSADH) downregulation. Enhancing GHB levels via SSADH downregulation or GHB supplementation triggered cell conversion into a less aggressive phenotypic state. GHB affected adult glioblastoma cells with varying molecular profiles, along with cells from pediatric pontine gliomas. In all cell types, GHB acted by inhibiting α-ketoglutarate-dependent Ten-eleven Translocations (TET) activity, resulting in decreased levels of the 5-hydroxymethylcytosine epigenetic mark. In patients, low SSADH expression was correlated with high GHB/α-ketoglutarate ratios, and distinguished weakly proliferative/differentiated glioblastoma territories from proliferative/non-differentiated territories. Our findings support an active participation of metabolic variations in the genesis of tumor heterogeneity.
