Histone-acetylation in DFMO-treated glioblastoma cells in vitro

Introduction - A good inverse correlation between progression-free survival and tumor levels of ornitine decarboxylase (ODC) was found in patients with anaplastic gliomas treated with the specific irreversible inhibitor of ODC difluoromethylornithine (DFMO) [Levin et al. 2007]. This observation fits well with a number of evidences that polyamine-mediated changes in gene expression may contribute to tumour development/progression. Moreover, it has recently shown that polyamines can exert both positive and negative influence on the function of chromatin modifying histone acetyltransferase (HAT) and deacetylase (HDAC) enzymes, suggesting that polyamines upregulate some genes while downregulating others via epigenetic modifications of the structure of chromatin [Hobbs et al. 2003, Wei et al. 2007]. Material and Methods - Here we investigated, by western blotting, how DFMO treatment (0.5 - 2 mM up to 24 h) affects (a) the acetylation status of histones H3 and H4 and (b) the concurrent level of expression of O6-methylguanine-DNA methyltransferase (MGMT) – a tumor suppressor gene whose transcription is known to be regulated via epigenetic modifications – in glioblastoma cells grown in vitro. Results and Discussion – Inhibiting ODC resulted in a dose- and time-dependent increase in the acetylation level of both H3 and H4 histones, with respect to untreated control. A concurrent upregulation of MGMT expression was also scored. These findings suggests that polyamines might contribute to tumour development/progression promoting chromatin condensation, thus transcriptional silencing, at the level of oncosuppressor gene sequences. In order to strengthen these results we are evaluating specific histone marks on MGMT promoter using chromatin immunoprecipitation.