Osteopontin expression in intratumoral astrocytes marks tumor progression in gliomas induced by prenatal exposure to N-ethyl-N-nitrosourea

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)-toduced tumors to rat brains with those of untovolved 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 to every tumor examined (n = 17), including those with, diameters as small as 300 μm. By contrast, no OPN immunostaining was seen in normal brain or to brains removed from ENU-exposed rats before the development of glioma. Further studies confirmed that OPN was co-localized exclusively in totratemoral glial fibrillary acidic protein-expressing cells and was notably absent from nesn-expressing ones. In conjunction with this, we confirmed that both normal neurosphere cells and ENU-immortalized suliventricular zone/striatal cells produced negligible amounts of OPN compared to the established rat glioma eel line C6. Furthermore, inducing OPN expression to an immortalized cell line increased cell proliferation. Based on these findings, we conclude that OPN overexpression to 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.