Abstract 4027: Regulation of p16INK4A and TGF-beta by DNA hydroxymethylation in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most prevalent form of primary brain cancer in adults. Cancer stem cells (CSCs) are thought to drive the growth and metastasis of tumors, and are readily isolated from GBM patient tumors. These GBM CSCs are maintained under serum-free conditions in neurosphere media, and form tumors upon orthotopic injection in mice. However, when grown in the presence of serum, GBM CSCs undergo morphological changes, have reduced proliferation, exhibit loss of stem cell markers, and have reduced tumorigenicity following orthotopic implantation into the brains of immune compromised mice. Upon return to serum-free neurosphere media, these GBM CSCs revert to neurospheres. We set out to define the transcriptional incongruities between these culture condition-dependent states, and the underlying epigenetic changes which regulate these differences in gene expression. Although genetic alterations in cancer are irreversible, epigenetic changes are inherently reversible, and we hypothesize that the plasticity between culture condition-dependent states is mediated by epigenetic regulation of genes relevant to the ability of these cells to form tumors. Recently, a novel epigenetic mark, 5-hydroxymethylcytosine (5hmC), has been shown to be enriched at regulatory elements within polycomb target genes in embryonic stem cells, and is frequently found at genes that are involved in the maintenance of stem cells. We found that 5hmC levels of several polycomb target genes, including p16INK4A and several components of the TGF-beta pathway involved in epithelial to mesenchymal transition (EMT), are altered in neurospheres compared to CSCs cultured in serum. Loss of p16INK4A expression has recently been associated with increased CSC abundance in breast cancer, and our results suggest that a similar trend exists in GBM. Furthermore, our results suggest that 5hmC is involved in the regulation of polycomb target genes in CSCs, including p16INK4A and components of the TGF-beta pathway. These findings implicate 5hmC in the maintenance of CSCs and regulation of EMT. 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 4027. doi:1538-7445.AM2012-4027