PP18. DISCOVERY OF G PROTEIN-COUPLED RECEPTOR 158 AS A POTENTIAL GLIOMA BIOMARKER

INTRODUCTION: As reported previously, concomitant deletion of tumour suppressors p53 and Pten in mouse subventricular zone gives rise to glioma, while codeletion of p53 and Rb generates primitive neuroectodermal tumours (PNET). These experimental gliomas and PNETs exhibit significant differences in tumour proliferation and differentiation. Based on the two types of tumour, we aim to identify biomarkers for tumour malignance. In a later stage, biomarkers identified in mouse gliomas will be further analysed in human gliomas. METHODS: We performed gene exon and microRNA expression array of murine gliomas and PNETs. Differentially expressed candidates were further validated using quantitative PCR (qPCR). Direct binding of microRNA with its putative target RNAs was confirmed using a double pull-down assay, which hybrids Ago2 immunoprecipitation with biotin affinity pull-down. Human glioma RNA sequencing data (n=433) were downloaded from The Cancer Genome Atlas (TCGA), and human glioma tissue samples (n=78) were from our institution. RESULTS: The analysis of microRNA profiles identified a significant up-regulation of mir-449a in PNET. Among putative targets of mir-449a, G protein-coupled receptor 158 (GPR158) was identified as one of the key genes with a potential role in tumour malignance. Using double pull-down assay, we confirmed that GPR158 was a direct target of mir-449a. Subsequently, we analysed the expression of GPR158 in human gliomas, and found that patients with gliomas expressing higher levels of GPR158 survived longer. We then analysed GPR158 expression levels in glioma subtypes, which were stratified by a combination of molecular profile and histological features (integrated diagnosis). We found that GPR158 expression level was highest in central nervous system (CNS) and oligodendroglioma (IDH mutant and 1p/19q codeletion), followed by IDH mutant astrocytomas and it was lowest in primary glioblastomas in TCGA RNA-seq data and in glioma samples from our institution. Finally, as expected, the expression level of mir-449a and GPR158 was inversely correlated in human frozen glioma samples. CONCLUSION: In this study, we discovered the direct interaction between mir-449a and GPR158, and our data suggest that GPR158 is a potential diagnostic and prognostic marker in gliomas.