Id2 mediates oligodendrocyte precursor cell maturation arrest and is tumorigenic in a PDGF-rich microenvironment

Maturation defects occurring in adult tissue progenitor cells have the potential to contribute to tumor development; however, there is little experimental evidence implicating this cellular mechanism in the pathogenesis of solid tumors. Inhibitor of DNA-binding 2 (Id2) is a transcription factor known to regulate the proliferation and differentiation of primitive stem and progenitor cells. Id2 is derepressed in adult tissue neural stem cells (NSC) lacking the tumor suppressor Tp53 and modulates their proliferation. Constitutive expression of Id2 in differentiating NSCs resulted in maturation-resistant oligodendroglial precursor cells (OPC), a cell population implicated in the initiation of glioma. Mechanistically, Id2 overexpression was associated with inhibition of the Notch effector Hey1, a bHLH transcription factor that we here characterize as a direct transcriptional repressor of the oligodendroglial lineage determinant Olig2. Orthotopic inoculation of NSCs with enhanced Id2 expression into brains of mice engineered to express platelet-derived growth factor in the central nervous system resulted in glioma. These data implicate a mechanism of altered NSC differentiation in glioma development and characterize a novel mouse model that reflects key characteristics of the recently described proneural subtype of glioblastoma multiforme. Such findings support the emerging concept that the cellular and molecular characteristics of tumor cells are linked to the transformation of distinct subsets of adult tissue progenitors.