Osteopontin Expression in Intratumoral Astrocytes Marks Tumor Progression in Gliomas Induced by Prenatal Exposure to N-Ethyl-N-Nitrosourea

Abstract

To better study early events in glioma genesis, markers that reliably denote landmarks in glioma development are needed. In the present study, we used microarray analysis to compare the gene expression patterns of magnetic resonance imaging (MRI)-localized N-ethyl-N-nitrosourea (ENU)-induced tumors in rat brains with those of uninvolved contralateral side and normal brains. Our analysis identified osteopontin (OPN) as the most up-regulated gene in glioma. Using immunohistochemistry we then confirmed OPN expression in every tumor examined (n = 17), including those with diameters as small as 300 mum. By contrast, no OPN immunostaining was seen in normal brain or in brains removed from ENU-exposed rats before the development of glioma. Further studies confirmed that OPN was co-localized exclusively in intratumoral glial fibrillary acidic protein-expressing cells and was notably absent from nestin-expressing ones. In conjunction with this, we confirmed that both normal neurosphere cells and ENU-im-mortalized subventricular zone/striatal cells produced negligible amounts of OPN compared to the established rat glioma cell line C6. Furthermore, inducing OPN expression in an immortalized cell line increased cell proliferation. Based on these findings, we conclude that OPN overexpression in ENU-induced gliomas occurs within a specific subset of intratumoral glial fibrillary acidic protein-positive cells and becomes evident at the stage of tumor progression.

Wnt/β-catenin/Tcf Signaling Pathway Activation in Malignant Progression of Rat Gliomas Induced by Transplacental N-Ethyl-N-Nitrosourea Exposure

“…Characterization of different phases may be significant in the identification of effective molecular targets. This ENUinduced glioma rat model is a suitable model to study stage specific alterations during the tumor progression [42]. In the present study, we studied the stage specific alterations of b-catenin/Tcf signaling at initiation (P90), promotion (P135) and progression stages (P180).…”

pERK, pAkt and pBad: A Possible Role in Cell Proliferation and Sustained Cellular Survival During Tumorigenesis and Tumor Progression in ENU Induced Transplacental Glioma Rat Model

“…Characterization of different phases may be significant in the identification of effective molecular targets. Recent study has indicated N-ethyl N-nitrosourea (ENU) induced rat model, as a suitable model to study stage specific alterations as evident by osteopontin expression during the tumor progression [4]. Heterogeneous or complex nature of gliomas is one of the limitations to understand the effective molecular targets.…”

Identification of Potential Serum Biomarkers of Glioblastoma: Serum Osteopontin Levels Correlate with Poor Prognosis

“…Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-β/BMPs/Smad/Hox, and Wnt/β-catenin/APC/GSK-3β/Tcf-4 (29). OPN expression has been found to correlate with tumor progression in astrocytoma with high levels in GBM (33)(34)(35). OPN levels detected by immunohistochemistry identified that high cytoplasmic OPN expression correlates with poor patient survival (36).…”