Release of Hypoacetylated and Trimethylated Histone H4 Is an Epigenetic Marker of Early Apoptosis

Juan C. Cigudosa,Cristina Largo,J. Ignacio Casal,Rosalia Caballero,Juan Casado,Antonio Nuñez,Esteban Ballestar,Ana Villar-Garea,Jesus Espada,Manel Esteller,Mario F. Fraga,Manuel Boix-Chornet,Luis Franco

doi:10.1074/jbc.m601136200

Abstract

Nuclear events such as chromatin condensation, DNA cleavage at internucleosomal sites, and histone release from chromatin are recognized as hallmarks of apoptosis. However, there is no complete understanding of the molecular events underlying these changes. It is likely that epigenetic changes such as DNA methylation and histone modifications that are involved in chromatin dynamics and structure are also involved in the nuclear events described. In this report we have shown that apoptosis is associated with global DNA hypomethylation and histone deacetylation events in leukemia cells. Most importantly, we have observed a particular epigenetic signature for early apoptosis defined by a release of hypoacetylated and trimethylated histone H4 and internucleosomal fragmented DNA that is hypermethylated and originates from perinuclear heterochromatin. These findings provide one of the first links between apoptotic nuclear events and epigenetic markers.

Highlights

Histone modifications, the type of modification and the specific amino acid residue that is modified determine the functional effect
In the context of apoptosis, DNA fragmentation and chromatin condensation have been associated with changes in histone modifications [10, 11]
The breakdown of internal nuclear structures is a prerequisite for chromatin condensation and DNA fragmentation [27, 28], it has been proposed that the maintenance of high order chromatin structures is essential for proper chromatin condensation [29]

Summary

Introduction

Histone modifications, the type of modification (acetylation, methylation, phosphorylation, etc.) and the specific amino acid residue that is modified determine the functional effect. The analysis of H4 by HPCE showed that histones retained in the nuclear pellet did not exhibit significant differences between control and apoptotic samples (Fig. 3B), unlike the results obtained when total histone H4 had been analyzed where there were 5–10% decreases in acetylated histone H4 (Fig. 1B).

Results

Conclusion