PO-336 Identification of SOX2 and SFRP2 as opposing regulators of glioblastoma heterogeneous subtypes

Abstract

IntroductionGlioblastomas display high levels of intra-tumour heterogeneity. It has recently been shown that individual glioblastomas may contain an intermixture of cells that display gene expression profiles representing the four gene expression based subtypes: proneural, neural, classical and mesenchymal. We have previously identified gene expression signatures that define two subtypes of glioblastoma cell cultures, where one represents a stem like, type A, and one a mesenchymal signature, type B, connected with a high or low capacity to grow as neurospheres and form intracranial tumours, respectively. Type A cultures are also defined by their expression of GFAP, and type B cultures by FN1. However, the relationship and regulation of these states is not well understood. In this study we aimed to identify genes that transition glioblastoma cells between a non-mesenchymal and mesenchymal cell state.Material and methodsTo identify transition genes we performed two overexpression screens of 27 candidate genes. Candidate genes, selected based on high differential expression between type A and type B cultures, were screened based on their capacity to alter FN1 or GFAP expression levels. Identified candidate genes where subsequently further tested for the capacity to alter gene expression, sphere forming capacity, anchorage independent growth, cell motility and cell growth.Results and discussionsWe identified SOX2 and SFRP2 as genes with opposite effects on GFAP and FN1 expression levels. SOX2 had the capacity to shift cell from a mesenchymal to a non-mesenchymal glioblastoma subtype profile. Global gene expression changes occurred where expression of progenitor related genes increased and mesenchymal related genes decreased. This was connected with increased tumour sphere formation, anchorage independent growth and reduced Matrigel invasion capacity. Conversely, SFRP2 increased FN1 expression, through an identified mechanism where it ablated SOX2 expression and thus reversed SOX2 induced phenotypes.ConclusionWe conclude that SOX2 and SFRP2 are opposing regulators of glioblastoma subtypes. Overall, these findings illustrate how the transition of glioblastoma cells from non-mesenchymal to a mesenchymal gene expression signature can be regulated during tumour cell evolution. Further understanding of the regulation of cell states in tumours with intratumoral heterogeneity and the interplay between cell populations is important for identifying targetable cancer driver pathways.