Malignant gliomas are the most common type of primary brain tumors affecting 16,000 new patients every year in the United States. In this study, we undertook a large-scale transcriptomics mining study of Affymetrix data from 9,783 samples from the genesapiens database (www.genesapiens.org) focusing on glioma biomarkers. We searched for genes that were specifically expressed in Glioblastoma Multiforme (GBM) and anaplastic astrocytoma using gene expression data from 475 different types of glioma samples (including 322 GBM, 66 anaplastic astrocytomas) and 425 samples from different normal anatomical locations of central nervous system. One of the prominent biomarkers arising from this bioinformatic search was the transcription cofactor HES6 (Hairy and enhancer of split 6), which was highly expressed in gliomas compared to normal brain. Since the role of HES6 in glioma pathogenesis is poorly understood, we chose to validate its expression by immunostaining and functional role by siRNA knockdown studies in glioma cell lines.

HES6 protein levels were studied in a glioma tissue microarray material that consisted of 414 samples as well as in normal brain tissue controls. Positive HES6 immunoreactivity was present in 99 % of available gliomas. Recurrent tumors of grade 2 astrocytomas and grade 2-3 oligodenrogliomas showed higher levels of HES6 immunoreactivity than the primary tumors of these classes. Endothelial cells that aligned the blood vessels within the tumors were also stained in 75 % of gliomas. HES6 immunoreactivity was also present in glial and endothelial cell nuclei in non-neoplastic cerebral white matter and cortex.

Cell viability was reduced by 60 % after HES6 silencing in A172 and LN405 cells and by ∼20-25 % in the U87MG and SVG p12 cell lines. HES6 silencing also increased apoptosis 2-3 fold in two cell lines as measured by Apo-ONE Homogeneous Caspase-3/7 Assay. We then studied the biological consequences of HES6 silencing by genome-wide gene expression studies. Gene ontology analysis implicated genes involved in cellular movement, development and RNA post-transcriptional modification. Also, aberrant expression around key regulator genes, such as p53, c-myc and SP1 was seen.

In conclusion, these results suggest that HES6 is a possible glioma marker that also has critical functional role in glioma growth.

This work was supported by funding under the 6th FP of the European Union, Project RIGHT (LSHB-CT-2004-005276), and the Academy of Finland.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4708.