Abstract
Our radiogenomic screen identified Periostin (POSTN) to be highly expressed in glioblastoma (GBM) with high edema/FLAIR. Subsequently, POSTN is implicated in glioblastoma invasion and recruitment of tumor associated macrophages. However, its impact on glioblastoma stem cells (GSC) biology/properties is largely unknown. Here GSC lines with high endogenous POSTN expression levels were used to generate inducible shRNA mediated loss of function (LOF) clones. GSCs with low/undetectable levels of POSTN expression were used to generate Gain of function (GOF) clones. In vitro tests were performed to assess the impact of POSTN LOF and GOF on GSC properties such as self-renewal, BrdU label retention, differentiation potential etc. We show that GSCs with POSTN LOF acquired an increased stem like state with unaltered proliferation rate. When these clones were implanted at orthotopic locations in mouse, POSTN LOF was associated with increased survival of mice. Cells of human origin were isolated from tumors using human specific HLA Class I ABC antibody by FACS. Total RNA from these sorted cells (without cell-culture) were used for expression profile analysis by HTA 2.0 array from affymetrix. Transcriptome analyses of POSTN LOF cells show inhibition of multiple mesenchymal associated networks such as CEBPB (a master regulator of mesenchymal program in GBM), PRDM1, TGFB1, FGF2, WNT3A, HIF1A etc. with concomitant activation of MYCN network, indicating a mesenchymal to proneural switch. We have generated POSTN and CEBPB dual knockdown clones and are currently investigating the molecular link between these two key mesenchymal genes in GSC context. Our results show that POSTN maintains a mesenchymal program in GSC by coopting with intracellular factors such as CEBPB. Therefore, neutralizing extracellular POSTN will have far reaching impact in terms of therapeutics where while blocking GBM invasion and it may simultaneously block a mesenchymal program in stem cell niche in GBM.
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