Postsynthetic Trimethylation of Histone H4 at Lysine 20 in Mammalian Tissues Is Associated with Aging

Abstract

Methylation of the N-terminal region of histones was first described more than 35 years ago, but its biological significance has remained unclear. Proposed functions range from transcriptional regulation to the higher order packing of chromatin in progress of mitotic condensation. Primarily because of the recent discovery of the SET domain-depending H3-specific histone methyltransferases SUV39H1 and Suv39h1, which selectively methylate lysine 9 of the H3 N terminus, this posttranslational modification has regained scientific interest. In the past, investigations concerning the biological significance of histone methylation were largely limited because of a lack of simple and sensitive analytical procedures for detecting this modification. The present work investigated the methylation pattern of histone H4 both in different mammalian organs of various ages and in cell lines by applying mass spectrometric analysis and a newly developed hydrophilic-interaction liquid chromatographic method enabling the simultaneous separation of methylated and acetylated forms, which obviates the need to work with radioactive materials. In rat kidney and liver the dimethylated lysine 20 was found to be the main methylation product, whereas the monomethyl derivative was present in much smaller amounts. In addition, for the first time a trimethylated form of lysine 20 of H4 was found in mammalian tissue. A significant increase in this trimethylated histone H4 was detected in organs of animals older than 30 days, whereas the amounts of mono-and dimethylated forms did not essentially change in organs from young (10 days old) or old animals (30 and 450 days old). Trimethylated H4 was also detected in transformed cells; although it was present in only trace amounts in logarithmically growing cells, we found an increase in trimethylated lysine 20 in cells in the stationary phase.In vivo methylation of the side chains of specific lysines, histidines, and arginines in proteins is a very common phenomenon in nature involving numerous classes of proteins in both prokaryotic and eukaryotic cells (1, 2). During the last several years, studies on the methylation of proteins have yielded many important observations. While these studies were under way, it was generally realized that protein methylation is far more complex and has more ramifications than originally assumed.Methylation is also a well known posttranslational modification reaction of histone proteins on lysine and/or arginine residues with a site selectivity for lysine methylation at specific positions in the N termini of histones H3 and H4. In combination with other posttranslational modifications, i.e. acetylation and phosphorylation, methylation seems to play a significant role in regulating nuclear functions. Thus, it has been suggested that distinct combinations of covalent histone modifications, also referred to as "histone code," provide a specific mark on the hydrophilic histone tails, which, when read by other proteins, cause specific downstream events finally inducing transi...

Aging by epigenetics—A consequence of chromatin damage?

“…CpG islands are CG rich sequences that are typically unmethylated, but can become methylated. In addition, the total abundance of histone H4 methylated on lysine 20 (H4K20Me) has also been reported to increase with age in rat liver and kidney [38]. Like DNA methylation, H4K20Me is linked to transcriptional repression [6], supporting the notion that heterochromatin accumulates with tissue aging, at least at some sites.…”

Testis-specific Linker Histone H1t Is Multiply Phosphorylated during Spermatogenesis

“…This technique is particularly suitable for separating posttranslationally modified proteins (e.g. acetylated core (45) and H1 histones (46), methylated and deamidated histones (35,(47)(48)(49), and phosphorylated H1 proteins (34, 50)). As shown in Fig.…”

Deficiency of H3K79 Histone Methyltransferase Dot1-like Protein (DOT1L) Inhibits Cell Proliferation

“…DOT1L depletion enhanced the level of H3K4me3, in which demethylase JHDM1B has been shown to inhibit senescence (35). H4K20me3, a substantially increased mark in aged rat liver and Hutchinson-Gilford progeria syndrome (36,37), was increased by DOT1L deficiency. H4K16ac, which increases with age in yeast and is enhanced upon oncogene-induced senescence (38,39), was also significantly induced.…”