The emerging role of NG2 in pediatric diffuse intrinsic pontine glioma.

Sridevi Yadavilli,Amanda M Saratsis,Tobey J Macdonald,Roger J Packer,Javad Nazarian,Madhuri Kambhampati,Kari-Elise Codispoti,Joseph Scafidi,Rebecca L Hiner,Oren J Becher,Santi Mariarita,Suresh N Magge,Jyoti K Jaiswal

doi:10.18632/oncotarget.3716

Abstract

Diffuse intrinsic pontine gliomas (DIPGs) have a dismal prognosis and are poorly understood brain cancers. Receptor tyrosine kinases stabilized by neuron-glial antigen 2 (NG2) protein are known to induce gliomagenesis. Here, we investigated NG2 expression in a cohort of DIPG specimens (n= 50). We demonstrate NG2 expression in the majority of DIPG specimens tested and determine that tumors harboring histone 3.3 mutation express the highest NG2 levels. We further demonstrate that microRNA 129-2 (miR129-2) is downregulated and hypermethylated in human DIPGs, resulting in the increased expression of NG2. Treatment with 5-Azacytidine, a methyltransferase inhibitor, results in NG2 downregulation in DIPG primary tumor cells in vitro. NG2 expression is altered (symmetric segregation) in mitotic human DIPG and mouse tumor cells. These mitotic cells co-express oligodendrocyte (Olig2) and astrocyte (glial fibrillary acidic protein, GFAP) markers, indicating lack of terminal differentiation. NG2 knockdown retards cellular migration in vitro, while NG2 expressing neurospheres are highly tumorigenic in vivo, resulting in rapid growth of pontine tumors. NG2 expression is targetable in vivo using miR129-2 indicating a potential avenue for therapeutic interventions. This data implicates NG2 as a molecule of interest in DIPGs especially those with H3.3 mutation.

Highlights

Pediatric brainstem gliomas (BSGs) account for 15% of all brain tumors in children [1]
To investigate neuron-glial antigen 2 (NG2) expression in Diffuse intrinsic pontine gliomas (DIPGs), we performed immunohistochemical (IHC) staining on formalin fixed paraffin embedded (FFPE) specimens from DIPG children obtained at postmortem
Our study shows NG2 expression to be associated with 78% of our DIPG cohort

Summary

Introduction

Pediatric brainstem gliomas (BSGs) account for 15% of all brain tumors in children [1]. Other genomic aberrations of DIPGs include p53 mutations and amplification of tyrosine receptor kinase/ Ras/phosphatidylinositol 3-kinase signaling pathways including platelet derived growth factor receptor alpha (PDGFRα) [6]. Receptor tyrosine kinases including PDGFRα are stabilized by the transmembrane protein NG2, known as chondroitin sulfate proteoglycan 4 (CSPG4) [9]. In malignant gliomas, NG2 is symmetrically expressed in both daughter cells resulting in active expression of other growth factor receptors including epidermal growth factor receptor (EGFR) [13]. Despite the potential role of NG2 in EGFR-mediated neoplasm, NG2 expression has not been previously established in pediatric gliomas. We have recently reported elevated mRNA expression of NG2 in a large percentage of pediatric DIPGs [8]

Methods

Results

Conclusion