GENE-51. ROLE OF TUMOR ENDOTHELIAL MARKER 8 (TEM8) IN PRIMARY AND RECURRENT GLIOBLASTOMA.

Abstract

Abstract Glioblastoma (GBM) is the most common primary malignant tumor of the adult central nervous system. It is highly invasive and almost inevitably recurs; leading to a median survival of 15 months. The recurrent tumor in most cases is radiotherapy and chemotherapy-resistant, making them quite challenging to treat. Several studies have elucidated key driver genes and molecular pathways involved in Gliomagenesis, but genes/pathways that might be involved in aiding relapse are not well elucidated. Interestingly, chemotherapy with Temozolomide and γ-irradiation have been documented to alter the DNA methylome of cells in vitro. A probable hypothesis could be that following surgical resection, therapy alters the epigenome of residual cancer cells giving rise to aggressively resistant recurrent tumors. To examine this possibility, 24 GBM biopsies (11 primary and 13 recurrent GBMs) were subjected to Methylation Bead Array to assess differential methylation of genes in recurrent GBM compared to primary tumors. This was correlated with RNA-seq data for recurrent tumors in TCGA database. A total of 1751 differentially methylated regions (DMRs) were identified, among which 205 differentially methylated genes (74 hypomethylated and 131 hypermethylated) were found to correlate with methylation and RNA-sequencing data of recurrent tumors in TCGA. Among these genes, ANTXR1/TEM8 (Tumor Endothelial Marker 8) was found to be overexpressed in recurrent tumors compared to primary tumors at both transcript and protein levels using RT-PCR and immunohistochemistry, respectively. When overexpressed in Glioma cell lines, TEM8 was found to upregulate phospho-GSK3β, phospho-AKT and lead to β-catenin translocation to the nucleus resulting in activation of Wnt signaling pathway. TEM8 overexpressing cells showed mild enhancement in proliferation and resistance to Temozolomide, Cisplatin and 5-fluoroUracil. Stem cells markers like Oct4 and Nanog are also upregulated. In conclusion, TEM8 may be involved in GBM recurrence and may have a role in conferring chemo- and radioresistance.