Aberrant mesenchymal differentiation of glioma stem-like cells: implications for therapeutic targeting.

Veerakumar Balasubramaniyan,Erik P Sulman,Shuzhen Wang,H.W.G.M Boddeke,Joy Gumin,Kenneth Aldape,Krishna P Bhat,Howard Colman,Se Hoon Kim,Brian Vaillant,Farah Mukheef,Ke Sai,M Elena Butalid,Frederick Lang

doi:10.18632/oncotarget.5219

Abstract

Differentiation has been proposed as a therapeutic strategy for glioblastoma (GBM) in part due to observations of stem-like cells in GBM that have been shown to undergo terminal differentiation in response to growth factor withdrawal and BMP activation. However, the effects of long term exposure to serum culture conditions on glioma sphere cultures/glioma stem-like cells (GSCs) have not been examined. Here we show that GSCs retained both neurosphere formation and tumor initiation abilities after short or long term serum exposure. Under these conditions, GSCs expressed both neural lineage and stem cell markers, highlighting the aberrant pseudo-differentiation state. GSCs maintained under adherent serum cultured conditions continued to proliferate and initiate tumor formation with efficiencies similar to GSCs maintained under proliferating (neurosphere) conditions. Proneural (PN) GSCs under serum exposure showed an induction of mesenchymal (MES) gene expression signatures. Our data indicate that exposure to serum containing media result in aberrant differentiation (e.g. toward MES lineage) and activation of alternative oncogenic pathways in GSCs.

Highlights

Glioblastoma (GBM) is the most common malignant primary central nervous system tumor in adults
To extend our recent molecular characterization on glioma stem-like cells (GSCs), we compared the global gene expression signatures of these cell types against published human neural stem cells (NSCs) and MES stem cell (MSC) datasets. The classification of these GSCs based on a metagene successfully clustered PN GSCs alongside human NSCs, whereas MES GSCs clustered with the human MSCs (Figure 1A) [20]
Consistent with a NSC-like signature, the PN GSCs (GSC11 and 23) grew as compact neurospheres whereas the MES GSCs (GSC2 and 20) grew as loose clusters (Figure 1B). In spite of these morphological differences, immunocytochemical analysis of neural stem cell marker nestin showed no variable expression amongst GSCs (Figure 1C)

Summary

Introduction

Glioblastoma (GBM) is the most common malignant primary central nervous system tumor in adults. The cancer stem cell hypothesis postulates that tumor initiation and recurrence is dependent on a small subset of cells with stem cell like properties including multi-lineage differentiation potential and indefinite self-renewal [5,6,7]. Consistent with this hypothesis, glioma sphere cultures/ glioma stem-like cells (GSCs) have been successfully isolated and expanded from human tumors using serumfree “neurosphere” culture methods pioneered in studies of neural stem cell biology [8,9,10,11]. The observed molecular heterogeneity of human GBMs has, at least in part, been attributed to the multi-lineage differentiation property of GSCs

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Results

Conclusion