Prognostic relevance of global histone 3 lysine 9 acetylation in ependymal tumors

Object. Ependymal tumors are highly variable in clinical and molecular behavior and affect both children and adults. Regarding the paucity of appropriate experimental models, the underlying molecular mechanisms of their behavioral variability are poorly understood. Considering the increasing evidence of epigenetic changes in various tumors, in addition to the preclinical success of epigenetic-based therapeutics in tumors of the CNS, epigenetic study of ependymal tumors is warranted. Methods. Using immunohistochemistry, the authors investigated the patterns of global acetylation of lysine position 9 of histone 3 (H3K9Ac), an epigenetic marker of active gene transcription, in 85 ependymal tumors with various WHO grades and clinicopathological characteristics. Results. Most of the nuclei in all ependymal tumors were H3K9Ac negative (mean +/- SD 65.9% +/- 26.5 vs 34.1% +/- 26.5% positive, p <0.0001). Subependymomas had more H3K9Ac-positive nuclei (67.2% +/- 10.2%) than myxo-papillary ependymomas, ependymomas, and anaplastic ependymomas (p <0.05). Additionally, intracranial parenchymal tumors had significantly fewer H3K9Ac-positive nuclei (13.1% +/- 21.9%) than tumors of other CNS localizations (p <0.001), and supratentorial ventricular tumors had the highest number of H3K9Ac-positive nuclei (66.4% +/- 11.8%) among CNS ependymal tumors (p <0.0001). The H3K9Ac pattern in ependymal tumors also revealed prognostic significance such that tumors with less than 20% acetylated nuclei had a higher probability of recurrence than tumors with 20% or more acetylated nuclei (p = 0.0327), and recurrent tumors had significantly fewer H3K9Ac-positive nuclei than primary ones (16% +/- 22.5% vs. 38% +/- 25.8%; p <0.0001). However, the effect of tumor location on survival of patients was nonsignificant in a multivariate survival analysis, and H3K9 acetylation levels of tumors contributed independently to the survival of patients. In addition, ependymal tumors with more than or equal to 20% H3K9 acetylated cells had lower MIB-1 expression than those with less than 20% H3K9 acetylated cells (p <0.01). Conclusions. Global H3K9Ac contributes independently to the prognosis of patients with ependymal tumors such that tumors with lower H3K9Ac values have a higher probability of recurrence and are more proliferative. Additionally, subependymomas have a higher H3K9Ac profile than other ependymal tumor subclasses, underlining their benign clinical behavior.