Emerging role of linker histone variant H1x as a biomarker with prognostic value in astrocytic gliomas. A multivariate analysis including trimethylation of H3K9 and H4K20.

Athanasia Sepsa,Efstathios Boviatsis,Irene Thymara,Athanassios Zisakis,Christos Adamopoulos,Marios S Themistocleous,Efstratios Patsouris,Georgia Dalagiorgou,Vassilis Samaras,Kalliopi Petraki,Penelope Korkolopoulou,George Vrettakos,Anastasia Spyropoulou,Antonis Gargalionis,Georgia Levidou,Christina Piperi,Wei-Guo Zhu

doi:10.1371/journal.pone.0115101

Abstract

Although epigenetic alterations play an essential role in gliomagenesis, the relevance of aberrant histone modifications and the respective enzymes has not been clarified. Experimental data implicates histone H3 lysine (K) methyltransferases SETDB1 and SUV39H1 into glioma pathobiology, whereas linker histone variant H1.0 and H4K20me3 reportedly affect prognosis. We investigated the expression of H3K9me3 and its methyltransferases along with H4K20me3 and H1x in 101 astrocytic tumors with regard to clinicopathological characteristics and survival. The effect of SUV39H1 inhibition by chaetocin on the proliferation, colony formation and migration of T98G cells was also examined. SETDB1 and cytoplasmic SUV39H1 levels increased from normal brain through low-grade to high-grade tumors, nuclear SUV39H1 correlating inversely with grade. H3K9me3 immunoreactivity was higher in normal brain showing no association with grade, whereas H1x and H4K20me3 expression was higher in grade 2 than in normal brain or high grades. These expression patterns of H1x, H4K20me3 and H3K9me3 were verified by Western immunoblotting. Chaetocin treatment significantly reduced proliferation, clonogenic potential and migratory ability of T98G cells. H1x was an independent favorable prognosticator in glioblastomas, this effect being validated in an independent set of 66 patients. Diminished nuclear SUV39H1 expression adversely affected survival in univariate analysis. In conclusion, H4K20me3 and H3K9 methyltransferases are differentially implicated in astroglial tumor progression. Deregulation of H1x emerges as a prognostic biomarker.

Highlights

Gliomas are highly invasive and vascularised neoplasms accounting for more than 70% of all brain tumors
Endothelial cells were always positive for H3K9me3 and H4K20me3, whereas cells in mitosis were consistently negative
The present investigation was undertaken mainly in an attempt to shed light upon the clinical relevance of the two H3K9 methyltransferases-SETDB1 and SUV39H1 for which experimental data imply their involvement into gliomagenesis [19]

Summary

Introduction

Gliomas are highly invasive and vascularised neoplasms accounting for more than 70% of all brain tumors. Epigenetic modifications, in contrast to genetic alterations, are defined as heritable changes in gene expression that do not result in any alteration of DNA sequence. Their mechanisms include DNA methylation, covalent histone modification, dynamic shuffling of histone variants and microRNAs [3]. The H1 family represents the linker histones which bind to the linker DNA between the nucleosome cores [6, 7] This family includes 11 subtypes of lysine-rich proteins functioning to ensure genomic integrity and regulating the transcription of genes involved in aging, DNA repair, DNA methylation, imprinting and apoptosis [8, 9]. HKMTs catalyzing the H3K9me (trimethylation of H3K9) include the SET domain family of HKMTs, SETDB1 and SUV39H1, as well as G9A

Methods

Results

Conclusion