Abstract 3343: Upregulation of SOX5 perturbs human glioma cell proliferation and is associated with proneural glioblastoma
Authors: Boije Maria , Krajisnik Tijana , Jiang Yiwen , Kastemar Marianne , Uhrbom Lene 
Published: August 2012

Abstract
Background: The proneural subtype of glioblastoma (GBM) is characterized by PDGFRα alterations. In a retroviral insertional mutagenesis screen (Johansson et al., PNAS, 2004) the transcription factor Sox5 was identified as a candidate brain tumor locus and the mode of insertions indicated an overexpression of the short version of Sox5 (s-Sox5). This led to an investigation of the role of s-Sox5 in glioma development, and we subsequently found that opposite to our hypothesis, s-Sox5 could inhibit glioma development in mice, reduce cell proliferation and clone formation ability of human glioma cell lines, and induce acute cellular senescence in primary mouse glial cells through regulation of AKT and p27Kip1 (Tchougounova et al., Oncogene, 2009). Aims: To investigate if s-SOX5 alterations are associated with a certain subtype of human GBM, and to identify the mechanism behind the anti-tumoral properties of s-SOX5 in newly established human glioma cell cultures (HGCCs). Methods: The TCGA dataset for GBM was analyzed via the cBio Cancer Genomics Portal (http://cbioportal.org) for alterations in SOX5 + other SOX genes and glioma genes. Endogenous SOX5 + expression of other SOX proteins were analyzed with immunostainings in six newly established HGCCs maintained under stem cell conditions. These HGCCs were also transfected with pcDNA-V5-s-Sox5, and analyzed by flow cytometry for EdU incorporation, cleaved Caspase-3 and V5. Results: We found that the majority of SOX5 alterations were confined to the proneural subtype (10/56 cases) with 90% of the alterations being upregulations. In fact, all upregulations of SOX5 were found in the proneural group. Only a few alterations (3/56; all downregulations) were found in the mesenchymal subtype, and none in the classical or neural subgroups. The upregulated SOX5 expression in the proneural subtype could be connected to a slight increase in patient survival. Co-occurring alterations in s-SOX5, PDGFRα, SOX6 and SOX10 were found in the proneural subtype. These findings are only suggestive and need to be validated in larger set of tumor samples. Immunostainings showed that all HGCCs expressed SOX2, SOX6, SOX9 and SOX10. For SOX5, two were completely negative while the remaining four showed varying expression. The transfection efficiency was very low (10%), but when specifically analyzing the V5-s-SOX5 positive cells, we found in all HGCCs a reduced number of EdU positive cells compared to the uninfected cell population of the same sample (statistically significant in three HGCCs). Conclusion: Our preliminary data suggest that upregulation of s-SOX5 could be a defining alteration in the proneural subgroup of GBM, and that s-SOX5 suppresses proliferation of human glioma cell cultures. Further studies are underway to solidify our findings and clarify the mechanism behind s-SOX5/Sox5 inhibition of glioma cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3343. doi:1538-7445.AM2012-3343